Recent Progress in Hormone Research 58:131-153 (2003)
© 2003 The Endocrine Society
Role of Defective Apoptosis in Type 1 Diabetes and Other Autoimmune Diseases
Takuma Hayashi and
Denise L. Faustman
Immunobiology Laboratory, Massachusetts General Hospital, and Harvard Medical School, Charlestown, Massachusetts 02129
 |
ABSTRACT
|
|---|
Lymphocyte development, selection, and education are strictly controlled to prevent autoimmunity, with potentially autoreactive cells being removed by apoptosis. Dysregulation of apoptosis is a central defect in diverse murine autoimmune diseases. In murine models of autoimmune lupus, for example, mutations in the death receptor Fas (CD95) or in its ligand, FasL (CD95L), have been identified and shown to render lymphoid cells resistant to apoptosis. In contrast, select lymphoid subpopulations of mice with autoimmune diabetes manifest an increased susceptibility to apoptosis as a result of impaired activation of the transcription factor nuclear factor-kappa B (NF-
B), which normally protects cells against tumor necrosis factor-alpha (TNF-
)-induced apoptosis. The genetic basis of this defect in NF-B activation is a mutation in the promoter-enhancer region of a gene that encodes an essential subunit (LMP2) of the proteasome. Although no specific genetic defects have been identified in most common forms of human autoimmune disease, functional assays consistently demonstrate heightened apoptosis attributable to multiple death signaling pathways.
|
I. Introduction
|
|---|
Autoimmunity encompasses a diverse group of diseases that are defined clinically by the target organ or tissue destroyed. Rheumatoid arthritis and type 1 diabetes mellitus (also known as insulin-dependent or juvenile-onset diabetes), for example, result from a presumed T-cell attack on the joints and insulin-secreting beta (ß) cells of the pancreas, respectively. Although the clinical manifestations of each autoimmune disease are distinct, the underlying genetics of these conditions are similar, with most showing an association with the human leukocyte antigen (HLA; also known as the human major histocompatibility complex, or MHC) region of the genome or with nearby non-HLA loci (Becker et al., 1998).
Apoptosis may play a role in two different aspects of autoimmune disease. First, controlled apoptotic cell death contributes to normal T-cell selection and education. Thus, interruption of this process might result in the generation of autoreactive cells. Second, apoptosis might represent a lymphocyte-independent mechanism of organ or tissue destruction. To date, most experimental data as well as identified genetic defects that promote or impair apoptosis have implicated abnormal T-cell selection and development in autoimmunity. Although a target cell apoptotic defect, possibly involving the Fas death receptor, has been proposed to affect the pancreatic islets of individuals with type 1 diabetes (Chervonsky et al., 1997; Itoh et al., 1997; Amrani et al., 1999; Suarez-Pinzon et al., 1999), other studies have suggested that apoptosis is not a major mechanism of ß-cell destruction (Kang et al., 1997,1998; Kim et al., 1999; Pakala et al., 1999; Thomas et al., 1999; Kim et al., 2000; Restifo, 2000). This chapter will focus on the role of apoptotic defects that affect education of the lymphoid system in autoimmunity.
A prominent feature of autoimmunity is the failure of autoreactive cells, either during development or subsequently, to undergo negative selection and die. Such apoptotic defects in humans and mice result in autoreactivity and may lead to marked lymphoproliferation. In certain instances, these defects have been attributed to mutations in the genes for proteins that function in apoptotic signaling pathways. One such example is the lpr/lprmouse, a model of human systemic lupus erythematosus (SLE), in which defective apoptosis results in lymphoproliferation and generalized autoimmunity. These animals harbor a spontaneous mutation in the gene for Fas (Watanabe-Fukunaga et al., 1992; Watson et al., 1992; Mountz et al., 1996), a cell-surface molecule also known as CD95 that belongs to the tumor necrosis factor receptor (TNF-R) superfamily. Similarly, the gld/gldmouse, which also manifests a lupus-like autoimmune disease, harbors a point mutation in the intracellular domain of the Fas ligand (FasL) (Allen et al., 1990; Lynch et al., 1994; Ramsdell et al., 1994; Takahashi et al., 1994). The identification of these autoimmunity-associated defects in the Fas signaling pathway stimulated a search for similar mutations in humans with lupus. However, only individuals with a rare form of lupus associated with diffuse lymphoproliferation have been shown to possess a mutation in the FasL gene (Wu et al., 1996a). Only patients with the rare Canale-Smith syndrome or autoimmune lymphoproliferative syndrome have been found to harbor a Fas mutation (Rieux-Laucat et al., 1995; Drappa et al., 1996). Not unexpectedly, the lymphoproliferation apparent in these patients resembles that in lpr/lprand gld/gldmice and is thought to result from the failure of select lymphocyte populations to undergo apoptosis. Most individuals with lupus do not appear to harbor mutations in the Fas or FasL genes. Indeed, lymphocytes from such individuals manifest an increased susceptibility to apoptosis in vitro as well as increased FasL expression (Emlen et al., 1994; Mysler et al., 1994; Desai-Mehta et al., 1996; Koshy et al., 1996; Wu et al., 1996a; Kovacs et al., 1997; Lorenz et al., 1997; Wong et al., 1999).
In most spontaneous forms of human or murine autoimmunity, severe lymphoproliferation is not a prominent feature of the disease. Indeed, we have shown that the pathogenic cells may manifest an increased susceptibility to apoptosis. In the nonobese diabetic (NOD) mouse, for example, a spontaneous model of human type 1 diabetes, lymphocytes are more susceptible to TNF--induced apoptosis than are lymphocytes from control animals. This results from a defect in the activation of nuclear factor-kappa B (NF-B) (Hayashi and Faustman, 1999), a transcription factor that protects against TNF--induced cell death. In addition to the accelerated apoptosis, there is increased FasL expression exhibited by peripheral blood lymphocytes from humans with lupus in vitro (Wong et al., 1999). The genetic basis of these human defects remains unknown.
Members of the TNF-R superfamily appear to play an important role in autoimmune disease. These proteins comprise an extracellular domain consisting of cysteine-rich motifs, a transmembrane domain, and a cytoplasmic tail (Liang and Fesik, 1997; Wallach et al., 1999).
Activation of NF-B protects cells against TNF--induced apoptosis but this transcription factor also contributes to cell death mediated by Fas (Quaaz et al., 1999), another TNF-R family member. In addition, NF-B activation in response to TNF- may contribute to FasL expression (Hsu et al., 1999). The interplay between these various overlapping apoptotic pathways may explain why the apoptotic defects associated with autoimmune disease confer phenotypes of enhanced or diminished T-cell selection.
|
II. Genetic Risk Factors for Type 1 Diabetes Located in the MHC Region of the Genome
|
|---|
Genetic risk factors for type 1 diabetes map to the MHC region of the genome. In both human type 1 diabetes and two rodent models of this disease (the NOD mouse and BB rat), pancreatic ß cells are selectively destroyed as a result of a chronic autoimmune reaction (Figure 1A and B) (Crisa et al., 1992; Rabinovitch and Skyler, 1998). The MHC region of the genome contains immune response genes that are important for T-cell education and for antigen presentation by both MHC class I and class II molecules. Studies of both humans and rodents have suggested that the centrally located MHC class II genes confer the greatest statistical risk for autoimmune disease. However, functional derangement of MHC class II genes has not been demonstrated in humans with autoimmune disease. In contrast, cellular abnormalities in expression of maturation markers or in antigen presentation have been detected in both NOD mice and diabetic humans. These defects include reduced expression of the maturation antigen CD45 and a reduced abundance of conformationally correct complexes of MHC class I molecules and self-peptides on the cell surface (Faustman et al., 1989,1991; Smerdon et al., 1993; Jansen et al., 1995).
View larger version (82K):
[in this window]
[in a new window]
|
FIG. 1. Insulitis and diabetes prevalence in the NOD mouse. Sections of a normal pancreas from a 4-month-old BALB/c female mouse (A) and of a pancreas with marked leukocyte infiltration (insulitis) from a 4-month-old NOD female mouse (B). Sections were stained with hematoxylin and eosin (H&E). Arrowheads indicate sites of extensive leukocyte infiltration. (C) Age dependence of diabetes prevalence in male and female NOD mice.
|
|
Evidence based on functional assays suggests that human autoimmune diseases are associated with impairment of antigen processing controlled by the MHC. Thus, cytosolic extracts of lymphocytes from either humans with type 1 diabetes or NOD mice exhibit altered patterns of cleavage of test substrates by the proteasome. This results in the generation of peptides that are poorly suited for assembly with MHC class I molecules (Faustman et al., 1989,1991; Smerdon et al., 1993; Jansen et al., 1995). In addition, lymphocytes of individuals with diverse autoimmune diseases — including type 1 diabetes, multiple sclerosis, and rheumatoid arthritis — manifest a reduced expression of peptide-loaded MHC class I molecules on their surface (Faustman et al., 1991; Fu et al., 1993; Li et al., 1995). Moreover, clinical studies have shown that the antigen presentation defect correlates with disease expression in identical twins with type 1 diabetes (Faustman et al., 1991). The genes responsible for antigen processing map to the MHC region of the genome, suggesting that abnormalities in this region might underlie these various conditions.
Candidate genes in the MHC region of the genome in humans and rodents that might be responsible for the antigen presentation defects associated with autoimmune disease include those for the TAP peptide transporters and the LMP proteasome subunits. Thus, for example, both LMP2 and LMP7 are encoded by genes located in the MHC region of the genome (Figure 2). These proteins are expressed constitutively in most cell types but their expression is markedly increased in antigen-presenting cells (APCs) or lymphoid cells in response to exposure to interferon-gamma (
) (Fruh et al., 1992; Van Kaer et al., 1994; Hisamatsu et al., 1996; Griffin et al., 1998). Knockout (KO) mice that lack specific TAP or LMP genes exhibit abnormal T-cell selection and autoreactivity against transplants of syngeneic normal tissue (Aldrich et al., 1994; Glas et al., 1994; Van Kaer et al., 1994; Wakatsuki et al., 1994).
View larger version (38K):
[in this window]
[in a new window]
|
FIG. 2. Identification of a point mutation in the shared promotor-enhancer region of the LMP2 and TAP1 genes in the NOD mouse. The mutation creates a CAAT box in the shared promoter-enhancer region. CAAT box-binding proteins likely act as negative regulators of gene transcription. Northern blot analysis reveals that the abundance of both LMP2 and TAP1 mRNAs is reduced markedly in splenocytes derived from adult NOD female and male mice with type 1 diabetes, compared with those in splenocytes from control BALB/c mice.
|
|
Ubiquitin-dependent proteolysis mediated by the proteasome, a multisubunit adenosine triphosphate (ATP)-dependent protease, plays important roles in various cellular processes, including cell-cycle progression, gene transcription, and signal transduction (Goldberg, 1995; Coux et al., 1996). In many instances, the target protein is marked for degradation or processing by both phosphorylation and ubiquitination. Cleavage of endogenous proteins by the proteasome also generates small peptide fragments that contribute to T-cell education as a result of their presentation by MHC class I molecules. Although, in general, the proteasome exhibits minimal variability in substrate selectivity and subunit composition, incorporation of the LMP2 and LMP7 subunits during assembly of the proteasome changes its specificity for self-proteins in such a manner that the suitability of the generated peptides for presentation in the peptide-binding groove of MHC class I molecules is increased (Belich et al., 1994; Gaczynska et al., 1996). The abundance of LMP2 mRNA in lymphocytes derived from NOD mice is reduced, compared with that in lymphocytes from control animals (Figure 2) (Yan et al., 1997), which likely explains, at least in part, the altered T-cell education toward self apparent in these mice.
|
III. The NOD Mouse: A Spontaneous Model of Type 1 Diabetes
|
|---|
Type 1 diabetes usually is caused by T-cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic ß cells, including insulin. In general, the autoantibodies recognize intracellular proteins and likely are generated in response to islet death. The NOD mouse frequently is studied as a rodent model of human type 1 diabetes. The etiology of diabetes in the NOD mouse is complex and multifactorial (Delovitch and Singh, 1997; Rabinovitch, 1998; Atkinson and Leiter, 1999). Both CD4+ and CD8+ T cells mediate the autoimmune response, with underlying functional defects being present in bone marrow-derived APCs. Many CD4+ and CD8+ T-cell lines and clones with diabetogenic potential that are targeted to a variety of identified and unidentified antigens have been established from both the islets and spleen of NOD mice. Destruction of pancreatic ß cells appears to be mediated by both necrotic and apoptotic death triggered by invasion of islets by leukocytes, a process referred to as insulitis (Rabinovitch, 1998). Although insulitis is not apparent in NOD mice up to 3 weeks of age, its prevalence increases in both female and male animals after 5 weeks of age. A clear sex difference is observed with respect to the onset of diabetes, however (Figure 1C). In NOD females, the onset of diabetes occurs as early as 10 weeks, with the number of affected animals increasing with age (Makino et al., 1980). The cumulative prevalence of diabetes in NOD females by 50 weeks of age is 
70–80%. In contrast, only about 20% of NOD males are affected by diabetes at this age. The large numbers of leukocytes apparent in the islet infiltrates of NOD mice are suggestive of lymph node formation around islets (Figure 1A and B). A strain-specific characteristic of NOD mice is the accumulation of many T lymphocytes in peripheral lymphoid organs, the pancreas, and submandibular salivary glands. This T-cell accumulation may reflect low interleukin (IL)-2 concentrations and the resistance of thymocytes and peripheral T cells to the induction of apoptosis. Such apoptotic resistance may be an early phenotype of lymphoid lineages prior to disease initiation (Lamhamedi-Cherradi et al., 1998).
Type 1 diabetes in the NOD mouse, like that in humans, exhibits a marked genetic component that maps to the MHC region of the genome. We have identified a specific proteasome defect in NOD mouse lymphocytes that results from downregulation of expression of the LMP2 proteasome subunit (Figures 2 and 3) (Hayashi and Faustman, 1999), which is encoded by a gene located in the MHC genomic region. This defect both prevents the proteolytic processing required for the production and activation of NF-B, which plays an important role in immune and inflammatory responses, and increases the susceptibility of the affected cells to apoptosis induced by TNF- (Figure 4). The proteasome dysfunction in NOD mice is both tissue and developmental stage specific; it is not apparent in islet cells.
|
IV. Defects in Proteasome-mediated NF-B Activation and T-cell Education in NOD Mice
|
|---|
The proteasome mediates the processing and activation of the transcription factor NF-B (Figure 5). NF-B is activated in response to various extracellular stimuli, including IL-1, lipopolysaccharide, and TNF- (Thanos and Maniatis, 1995; Verma et al., 1995; Baeuerle and Baltimore, 1996; Baldwin, 1996). It contributes to regulation of the gene expression for cytokine production, cell adhesion, lymphocyte maturation, and protection from TNF--induced apoptosis, as well as antigen processing and presentation by MHC class I molecules (Bohnline et al., 1988; Cross et al., 1989; Tan et al., 1992; Beg and Baltimore, 1996; Van Antwerp et al., 1996). Insights into the various biological functions of NF-B have been provided by the generation and characterization of KO mice lacking either subunits of this protein or associated regulatory factors (Burkly et al., 1995; Kontgen et al., 1995; Weih et al., 1995; Franzoso et al., 1997; Bushdid et al., 1998; Caamano et al., 1998; Kanegae et al., 1998; Hu et al., 1999; Li et al., 1999a,b; Takeda et al., 1999).
View larger version (98K):
[in this window]
[in a new window]
|
FIG. 5. Impaired expression of LMP2 in NOD mouse splenocytes. (A) Schematic representations of 26S and 20S proteasomes. (B) Lysates of spleen cells from adult male (M) or female (F) BALB/c or NOD mice were subjected to immunoblot analysis with antibodies specific for the indicated 20S proteasome subunits or, as controls, with antibodies to various cyclin-dependent kinases (CDKs) or to the transcriptional factor TAFII250.
|
|
Active NF-B exists predominantly as a heterodimer composed of p65 (RelA) and either p50 or p52 subunits. The p50 and p52 subunits are generated constitutively but their abundance is increased markedly by various extracellular stimuli, including IL-l and TNF-. These proteins are generated as a result of the proteasome-mediated removal of the carboxyl termini of p105 and p100 precursors, respectively (Fan and Maniatis, 1991; Schmid et al., 1991; Palombella et al., 1994; Coux and Goldberg, 1998; Lin et al., 1998; Sears et al., 1998). In resting cells, NF-B is sequestered in the cytoplasm as a result of its association with IB or other members of the IB family of inhibitory proteins (Ghosh and Baltimore, 1990; Hayashi et al., 1993a,b). Cell stimulation results in the phosphorylation of IB by the IB kinase (IKK) complex and its degradation by the ubiquitin-proteasome pathway, thereby allowing the p50–p65 or p52–p65 heterodimer to translocate to the nucleus and initiate transcription of target genes (Figure 3) (Ghosh and Baltimore 1990; Oeri et al., 1991; Palombella et al., 1994; MacKichan et al., 1996; Belich et al., 1999). Complexes of p65 and p105 also have been detected but these do not appear to translocate rapidly to the nucleus in response to cell stimulation (Sun et al., 1994; Lin et al., 1998).
Our laboratory has sought to understand why, in type 1 diabetes, T cells treat pancreatic ß cells as foreign. We therefore have attempted to understand the process of T-cell education to self-antigens and how this process is altered in individuals with type 1 diabetes. T-cell education requires the presentation of self-antigens, a task that is undertaken by "professional" APCs such as macrophages, dendritic cells, and B cells. Until recently, it was thought that autoimmunity results from the inappropriate activation of T cells by foreign antigens (e.g., viral proteins) that generate cross-reactivity with self-antigens, which was considered an MHC class II defect. However, we proposed, and presented evidence for the notion, in both NOD mice and humans with type 1 diabetes, that interruption of the presentation of self-antigens by MHC class I molecules underlies the development of autoimmune disease (Faustman et al., 1991). This proposal was based on the contention that such MHC class I-mediated presentation of self-peptides is essential for the development of normal tolerance. Previously, MHC class I proteins were thought to function primarily in the presentation of peptides derived from foreign intracellular proteins, especially viral proteins, for the generation of cytotoxic T cells. Subsequent studies in transgenic mice deficient in chaperone proteins required for the intracellular assembly of MHC class I complexes confirmed the importance of self-peptide presentation by MHC class I molecules in T-cell education to self (Aldrich et al., 1994; Glas et al., 1994; Van Kaer et al., 1994).
In our attempt to discover the basis for the impairment in presentation of self-peptides by MHC class I molecules in the NOD mouse, we found that the abundance of LMP2 mRNA in lymphoid cells from these animals was markedly reduced, compared with that in control animals. This defect in LMP2 expression in the NOD mouse was shown to be attributable, at least in part, to a specific mutation in the shared bidirectional promoter-enhancer region of the LMP2 and TAP1 genes in the MHC class II region of the genome (Figure 2). The reduced abundance of LMP2 interrupts the proteasome-mediated generation of self-peptides for presentation by MHC class I molecules and the consequent development of T-cell tolerance to self-antigens (Yan et al., 1997). It also prevents the processing of NF-B precursor proteins and the degradation of IB required for activation of NF-B (Hayashi and Faustman, 1999), events important for T-cell maturation and normal immune and inflammatory responses. The LMP2 expression defect in NOD mice is specific for lymphoid lineage cells and becomes apparent after 10 weeks of age (Hayashi and Faustman, 1999).
The interruption by the LMP2 defect in NOD mice of both self-peptide presentation by APCs as well as normal T-cell development — two phenotypes we had established as important in both murine and human autoimmune diabetes — suggests that the onset of LMP2 downregulation is an essential trigger for disease initiation. The expression of MHC class I molecules in islets is upregulated early during islet invasion by T cells in both humans and NOD mice with type 1 diabetes. This phenomenon probably defines target selection by augmenting self-antigen presentation, thereby promoting cytotoxic T-cell attack mediated by poorly educated, LMP2-deficient T cells.
|
V. Increased Sensitivity of NOD Mouse Lymphocytes to TNF--induced Apoptosis
|
|---|
Recent reports indicate that NF-B is an important protector of cells from TNF--induced apoptosis (Beg et al., 1995). Embryos of mice lacking the NF-B p65 subunit, IKKß or IKK, manifest marked hepatic apoptosis that appears to result from the associated defects in NF-B activation (Beg and Baltimore, 1996; Li et al., 1999b, Rudolph et al., 2000). The activation of NFB by the ubiquitin-proteasome pathway also is thought to protect cells from TNF--induced cell death (Figure 3) (Beg and Baltimore, 1996; Van Antwerp et al., 1996; Wang et al., 1996; Wu et al., 1996b). The antiapoptotic effect of NF-B is likely mediated by the activation of genes that encode cell survival-promoting factors.
We investigated the effect of TNF- on the viability of adult NOD mouse lymphocytes, in which TNF--induced activation of NF-B is impaired. Whereas incubation of BALB/c mouse splenocytes with various concentrations (2–20 ng/ml) of TNF- for 24 hours had virtually no effect on cell survival, TNF- induced a dose- and time-dependent decrease in the survival of splenocytes derived from male or female NOD mice (Hayashi and Faustman, 1999; Hayashi et al., 2000). Similarly, whereas incubation of BALB/c mouse splenocytes with TNF- (10 ng/ml) for up to 48 hours had no effect on cell viability, the survival of NOD splenocytes already was reduced markedly after incubation with the same concentration of TNF- for only 12 hours (Hayashi and Faustman, 1999; Hayashi et al., 2000). The toxic effect of TNF- on NOD mouse lymphocytes appeared more pronounced for female than for male animals. Exposure of lymphocytes from LMP2 KO mice to TNF- also resulted in marked cell death (Hayashi and Faustman, 1999; Hayashi et al., 2000). Agarose gel electrophoresis confirmed that TNF- induced a pattern of internucleosomal DNA fragmentation characteristic of apoptosis in lymphocytes from NOD mice and LMP2 KO, whereas it did not induce DNA fragmentation in those from BALB/c mice (Hayashi and Faustman, 1999). It is thus likely that the toxicity of TNF- for NOD mouse lymphocytes is attributable to the NF-B inactivation due to defective proteasome function.
TNF- also reduced the viability of spleen cells derived from 7-day-old NOD mice but to a lesser extent than it did in cells derived from adult animals. It had no effect on the viability of spleen cells derived from 7-day-old BALB/c mice. Whereas TNF- had no effect on the viability of cultured macrophages derived from 13.5-day BALB/c or NOD mouse fetal liver, it induced a dose- and time-dependent decrease in the viability of such cells derived from LMP2 KO mouse fetal liver at the same stage of development (Hayashi and Faustman, 1999). Similarly, TNF- had no effect on the viability of cultured BALB/c or NOD mouse embryonic fibroblasts, whereas TNF- treatment of such cells derived from LMP2 KO mice resulted in prominent cell death (Hayashi and Faustman, 1999,2000). Although disruption of the NF-B p65, IKKß, or IKK genes is associated with marked abnormalities in liver development (Beg et al., 1995; Beg and Baltimore, 1996; Li et al., 1999b; Rudolph et al., 2000), hematoxylin-eosin staining of liver sections from 6-week-old NOD mice did not reveal any apparent defects (Hayashi and Faustman, 1999).
|
VI. Impaired Granulocyte-Macrophage Colony Formation by NOD Mouse Spleen Cells
|
|---|
NF-B also plays an important role in the maturation of lymphocytes and monocytes. We therefore examined the development of the granulocyte-macrophage (GM) cell lineage with splenocytes isolated from 6-week-old NOD and BALB/c mice. Colony-formation assays revealed that, whereas GM-colony-stimulating factor (CSF) induced the formation of clusters of mature GMs in BALB/c mouse splenocytes, the formation of such clusters was impaired in splenocytes from NOD mice (Figure 4, A-D). Furthermore, whereas exposure of GM-CSF-treated spleen cell cultures from BALB/c mice to TNF- had no effect on cell viability or colony development, TNF- induced the death of all cells in NOD mouse cultures (Figure 4, E-H).
The specificity of the developmental defect and cytotoxic effect of TNF- in the GM lineage of NOD mice was investigated by examining colony-forming units (CFUs) of erythrocytes in cultures of spleen cells derived from 6-week-old BALB/c and NOD animals. Erythrocyte colony formation appeared normal in erythropoietin-supplemented cultures of NOD mouse spleen cells, compared to that observed in spleen cells from BALB/c mice (Hayashi and Faustman, 1999). Moreover, TNF- had no effect on erythrocyte colony formation, which is known to require NF-B, in spleen cells from either BALB/c or NOD mice. These results suggest that a lack of NF-B activation in GM precursors derived from NOD mice at 6 weeks of age impairs the maturation of these cells and renders them susceptible to the cytotoxic effect of TNF-. In contrast, NF-B appears to be functional in the erythrocyte lineage of these mice, which seem to develop normally and be resistant to TNF--induced apoptosis. Given that TNF- had no effect on the viability of cultured macrophages derived from 13.5-day BALB/c or NOD mouse fetal liver, the proteasome defect in NOD mice appears to be specific for both cell type and developmental stage.
|
VII. Gender, Age, and Tissue Specificity of Proteasome Dysfunction and Disease Expression in NOD Mice
|
|---|
The prevalence of diabetes is markedly greater in NOD females than in NOD males. Most human autoimmune diseases also are expressed preferentially in females. Consistent with a role for defective proteasome activity and consequent impaired NF-B function in NOD mouse diabetes, cytosolic extracts of splenocytes from male NOD mice were able to convert a small proportion of recombinant NF-B p105 to p50. However, the product of this reaction appeared to differ in size slightly from that of the p50 subunit produced by extracts of BALB/c mice (Hayashi and Faustman, 1999). Splenocyte extracts from NOD females did not generate any detectable p50 protein in this assay. Furthermore, as mentioned previously, both the time course and dose-response relation for the effect of TNF- on cell viability revealed that the sensitivity of splenocytes from NOD females to this cytokine was greater than that of cells from NOD males (Hayashi and Faustman, 1999; Hayashi et al., 2000).
The characteristics of KO mice that lack NF-B subunits or LMP2 overlap partially with those of NOD mice (Van Kaer et al., 1994; Burkly et al., 1995; Kontgen et al., 1995; Weih et al., 1995; Horwitz et al., 1997). However, LMP2-deficient mice do not develop diabetes by 32 weeks of age (D.L. Faustman, unpublished observation), consistent with the contribution of multiple chromosomal regions to disease penetrance in both NOD mice and humans. The homogeneous nature of the gene defect in all tissues of LMP2 KO mice differs from the apparent developmental stage and tissue specificity of the proteasome defect in NOD mice, which might underlie target selection in disease expression. LMP2-deficient and other KO mice with defects in the assembly of MHC class I molecules with self-peptides destroy transplanted syngeneic tissues from control animals (Li and Faustman, 1993; Vidal-Puig and Faustman, 1994; Freland et al., 1998). Target cell loss thus might result from preferential direct attack by cytotoxic T lymphocytes in the early stages of autoimmune disease.
The marked proapoptotic effect of TNF- in NOD mouse lymphocytes also suggested a possible role for this cytokine in early ß-cell destruction in these animals. Such a mechanism of ß-cell death would require that ß cells exhibit the same proteasome defect as that apparent in NOD mouse lymphocytes. This defect is characterized by loss of LMP2 expression, aberrant NF-B activation, increased sensitivity to the cytotoxic effect of TNF-, and reduced expression of peptide-filled MHC class I molecules on the cell surface. However, one of the early pathological features of autoimmune diabetes in both humans and rodent models is hyperexpression of correctly assembled MHC class I molecules on the surface of ß cells (Foulis, 1987; Ono et al., 1988; Weringer and Like, 1988; Hanafusa et al., 1990; Kay et al., 1991; Vivés-Pi et al., 1996; Stephens et al., 1997), a phenomenon that requires intact proteasome function. Studies of both humans and animals with diabetes or other autoimmune diseases suggest that discordance in the regulation of MHC-linked genes between tissues might confer target specificity for attack by cytotoxic T lymphocytes (Hayashi and Faustman, 1999).
Macrophages and fibroblasts derived from 13.5-day NOD mouse embryos exhibited normal cell growth and resistance to TNF- cytotoxicity. In contrast, TNF- exhibited a marked proapoptotic effect in the corresponding cell types derived from LMP2 KO mice (Hayashi and Faustman, 1999,2000; Hayashi et al., 2000). TNF- also induced a relatively small decrease in the viability of spleen cells derived from 7-day-old NOD mice but had no such effect on the corresponding cells from BALB/c mice. In contrast, lymphoid cells of splenic origin, lung macrophages (Kupffer cells), and GMs from 6- to 8-week-old NOD mice exhibit reduced LMP2 expression, impaired NF-B activation, and increased sensitivity to the cytotoxic effect of TNF- (Hayashi and Faustman, 1999). Furthermore, consistent with a role for the proteasome and NF-B in normal cell growth, culture of spleen cells from 6-week-old NOD mice with GM-CSF failed to induce normal expansion of the GM cell lineage. The islets of Langerhans, liver, and erythrocytes of 6- to 8-week-old NOD mice appear normal. The ability of NOD mouse macrophages to activate regulatory T cells in an autologous mixed lymphocyte reaction also has been shown to be impaired (Atkinson and Leiter, 1999).
The age-dependent proteasome defect in the macrophages of NOD mice likely explains some of the important features of disease development in these animals. Thus, female NOD mice show no signs of autoimmunity up to 3 weeks of age. At 5 weeks and older, insulitis begins to appear. By 8 weeks of age, autoantibodies are detectable. The insulitis gradually increases in intensity, with complete destruction of islets usually apparent by 30 weeks of age (Makino et al., 1980). Furthermore, the outcomes of various interventions and treatments in NOD mice are age dependent. For instance, the administration of TNF- to animals older than 6 weeks sometimes prevents the development of diabetes, whereas the same treatment in animals younger than 4 weeks has no effect or a detrimental effect (Yang et al., 1994). Therefore, both the time course of the histopathology of autoreactivity and the paradoxical responses to TNF- treatment parallel the altered developmental regulation of LMP2 expression and NF-B activity in these animals.
|
VIII. Defective Proteasome Function and Autoimmunity
|
|---|
The ubiquitin-proteasome pathway plays an essential role in many important biological processes (Maniatis, 1999). Protein degradation by this pathway thus generates peptides for presentation by MHC class I molecules and either activates or inactivates transcription factors. In general, proteasome subunit composition varies minimally among eukaryotic cells. However, the interferon--induced expression of the MHC-encoded proteasome subunits LMP2 and LMP7 is thought to promote the generation of endogenous peptides compatible with the peptide-binding cleft of MHC class I molecules (Akiyama et al., 1994; Belich et al., 1994). The MHC-encoded proteasome subunits also play a role in general proteasome function, including the processing and activation of NF-B.
The defect in proteasome function in NOD mouse splenocytes is attributable to a loss of expression of the LMP2 subunit and was evident from the impaired proteolytic processing of the p105 precursor of the NF-B subunit p50 in vitro as well as from the lack of degradation of phosphorylated IB in these cells in response to TNF-. This defect confers sensitivity on the affected cells to the apoptotic action of TNF- (Figure 6). The role of LMP2 in NF-B activation was confirmed by observations that 1) cytosolic extracts of lymphocytes from LMP2 KO mice also failed to convert p105 to p50 and 2) only NOD mouse tissues that lack LMP2 subunit showed impaired activation of NF-B and sensitivity to TNF--induced apoptosis (Hayashi and Faustman, 1999,2000). The defect in LMP2 protein production in NOD mice is both developmental stage (age) and tissue specific. Dysfunction of a gene in the MHC region of the genome thus virtually abolishes the activity of a transcription factor that plays important roles in both immune and nonimmune cellular functions. The NOD mouse therefore represents a newly defined mosaic model of discordant MHC gene expression that exhibits marked proteasome dysfunction in an age- and tissue-specific manner.
The delayed maturation of lymphocytes and cytokine abnormalities apparent in NOD mice that spontaneously develop type 1 diabetes are mirrored, in part, by the phenotypes of KO mice lacking NK-B subunits or LMP2 (Van Kaer et al., 1994; Sha et al., 1995; Beg and Baltimore, 1996; Snapper et al., 1996; Franzoso et al., 1997; Horwitz et al., 1997; Iotsova et al., 1997; Caamano et al., 1998; Tanaka et al., 1999). The clinical relevance of the phenotypes of the NOD mouse and of these various KO animals to human disease is supported by the existence of nearly identical cytokine and lymphocyte maturation defects in humans with type 1 diabetes.
In conclusion, we have demonstrated the existence of a marked defect in proteasome function in lymphocytes from autoimmune diabetes-prone NOD mice. This defect results from a deficiency of the LMP2 subunit, which is encoded by a gene located in the MHC region of the genome. It results in both impaired processing of self-peptides for presentation by MHC class I molecules as well as the inability to activate NF-B. A similar age-related defect in GMs is proposed to confer target specificity in autoimmunity toward tissues with intact LMP2 expression. Abnormal processing of intracellular proteins thus may contribute to the pathogenesis of type 1 diabetes.
Akiyama K, Yokota K, Kagawa S, Shimbara N, Tamura T, Akioka H, Nothwang HG, Noda C, Tanaka K, Ichihara A 1994
cDNA cloning and interferon down-regulation of proteasomal subunits X and Y. Science 265
: 1231
–1234
Aldrich CJ, Ljunggren HG, Van Kaer L, Ashton-Rickardt PG, Tonegawa S, Forman J 1994
Positive selection of self- and alloreactive CD8+ T cells in TAP-1 mutant mice. Proc Natl Acad Sci USA
91
: 6525
–6528[Abstract/Free Full Text]
Allen RD, Marshall JD, Roths JB, Sidman CL 1990
Differences defined by bone marrow transplantation suggest that lprand gldare mutations of genes encoding an interacting pair of molecules. J Exp Med
172
: 1367
–1375[Abstract/Free Full Text]
Amrani A, Verdaguer J, Anderson B, Utsugi T, Bou S, Santamaria P 1999
Perforin-independent beta-cell destruction by diabetogenic CD8+ T lymphocytes in transgenic nonobese diabetic mice. J Clin Invest
103
: 1201
–1209[Medline]
Atkinson MA, Leiter EH 1999
The NOD mouse model of type 1 diabetes: as good as it gets? Nat Med
5
: 601
–604[CrossRef][Medline]
Baeuerle PA, Baltimore D 1996
NF-B: ten years after. Cell
87
: 13
–20[CrossRef][Medline]
Baldwin AS 1996
The NF-B and IB proteins: new discoveries and insights. Annu Rev Immunol
12
: 141
–179[Medline]
Becker KG, Simon RM, Bailey-Wilson JE, Freidlin B, Biddison WE, McFarland HF, Trent JM 1998
Clustering of non-major histocompatibility complex susceptibility candidate loci in human autoimmune diseases. Proc Natl Acad Sci USA
95
: 9979
–9984[Abstract/Free Full Text]
Beg AA, Baltimore D 1996
An essential role for NF-B in preventing TNF--induced cell death. Science
274
: 782
–784[Abstract/Free Full Text]
Beg AA, Sha WC, Bronson RT, Ghosh S, Baltimore D 1995
Embryonic lethality and liver degeneration in mice lacking the relA component of NF-B. Nature
376
: 167
–170[CrossRef][Medline]
Belich MP, Glynne RJ, Senger G, Sheer D, Trowsdale J 1994
Proteasome components with reciprocal expression to that of the MHC-encoded LMP proteins. Curr Biol
4
: 769
–776[CrossRef][Medline]
Belich MP, Salmeron A, Johnston LH, Ley SC 1999
TPL-2 kinase regulates the proteolysis of the NF-B-inhibitory protein NF-B1 p105. Nature
397
: 363
–368[CrossRef][Medline]
Bohnline E, Lowenthal JW, Siekevitz M, Franza BR, Greene WC 1988
The same inducible nuclear protein regulates mitogen activation of both the interleukin-2 receptor- gene and type 1 HIV. Cell
53
: 827
–836[CrossRef][Medline]
Burkly L, Hession C, Ogata L, Reilly C, Marconi LA, Olson D, Tizard R, Cate R, Lo D 1995
Expression of relB is required for the development of thymic medulla and dendritic cells. Nature
373
: 531
–536[CrossRef][Medline]
Bushdid PB, Brantley DM, Yull FE, Blaeuer GL, Hoffman LH, Niswander L, Kerr LD 1998
Inhibition of NF-B activity results in disruption of the apical ectodermal ridge and aberrant limb morphogenesis. Nature
392
: 615
–618[CrossRef][Medline]
Caamano JH, Rizzo CA, Durham SK, Barton DS, Raventos-Suarez C, Snapper CM, Bravo R 1998
Nuclear factor (NF)-B2 (p100/p52) is required for normal splenic microarchitecture and B cell-mediated immune responses. J Exp Med
187
: 185
–196[Abstract/Free Full Text]
Chervonsky AV, Wang Y, Wong FS, Visintin I, Flavell RA, Janeway CA Jr, Matis LA 1997
The role of Fas in autoimmune diabetes. Cell
89
: 17
–24[CrossRef][Medline]
Coux O, Goldberg AL 1998
Enzymes catalyzing ubiquitination and proteolytic processing of the p105 precursor of nuclear factor B1. J Biol Chem
273
: 8820
–8828[Abstract/Free Full Text]
Coux O, Tanaka K, Goldberg AL 1996
Structure and functions of the 20S and 26S proteasomes. Annu Rev Biochem
65
: 801
–847[CrossRef][Medline]
Crisa L, Mordes JP, Rossini AA 1992
Autoimmune diabetes mellitus in the BB rat. Diabetes Metab Rev
8
: 9
–37
Cross SL, Halden NF, Lenardo M, Leonard WJ 1989
Functionally distinct NF-B binding sites in the immunoglobulin and IL-2 receptor chain genes. Science
244
: 466
–468[Abstract/Free Full Text]
Delovitch TL, Singh B 1997
The nonobese diabetic mouse as a model of autoimmune diabetes: immune dysregulation gets the NOD [published erratum appears in Immunity 1998;8:53l]. Immunity
7
: 727
–738[CrossRef][Medline]
Desai-Mehta A, Lu L, Ramsey-Goldman R, Datta SK 1996
Hyperexpression of CD40 ligand by B and T cells in human lupus and its role in pathogenic autoantibody production. J Clin Invest
97
: 2063
–2073[Medline]
Drappa J, Vaishnaw AK, Sullivan KE, Chu JL, Elkon KB 1996
Fas gene mutations in the Canale-Smith syndrome, an inherited lymphoproliferative disorder associated with autoimmunity [see comments]. N Engl J Med
335
: 1643
–1649[Abstract/Free Full Text]
Emlen W, Niebur J, Kadera R 1994
Accelerated in vitro apoptosis of lymphocytes from patients with systemic lupus erythematosus. J Immunol
152
: 3685
–3692.[Abstract]
Fan CM, Maniatis T 1991
Generation of p50 subunit of NF-B by processing of p105 through an ATP-dependent pathway. Nature
354
: 395
–398[CrossRef][Medline]
Faustman D, Eisenbarth G, Daley J, Breitmeyer J 1989
Abnormal T lymphocyte subsets in type I diabetes mellitus: analysis with anti-2H4 and anti-4B4 antibodies. Diabetes
38
: 1462
–1468[Abstract]
Faustman D, Li X, Lin HY, Fu Y, Eisenbarth G, Avruch J, Guo J 1991
Linkage of faulty major histocompatibility complex class I to autoimmune diabetes. Science
254
: 1756
–1761[Abstract/Free Full Text]
Foulis AK 1987
The pathogenesis of beta cell destruction in type I (insulin-dependent) diabetes mellitus. J Pathol
152
: 141
–148[CrossRef][Medline]
Franzoso G, Carlson L, Xing L, Poljak L, Shores EW, Brown KD, Leonardi A, Tran T, Boyce BF, Siebenlist U 1997
Requirement for NF-B in osteoclast and B-cell development. Genes Dev
11
: 3482
–3496[Abstract/Free Full Text]
Freland S, Chambers BJ, Andersson M, Van Kaer L, Ljunggren HG 1998
Rejection of allogeneic and syngeneic but not MHC class I-deficient tumor grafts by MHC class I-deficient mice. J Immunol
160
: 572
–579[Abstract/Free Full Text]
Fruh K, Yang Y, Arnold D, Chambers J, Wu L, Waters JB, Spies T, Peterson PA 1992
Alternative exon usage and processing of the major histocompatibility complex-encoded proteasome subunits. J Biol Chem
267
: 22131
–22140[Abstract/Free Full Text]
Fu Y, Nathan DM, Li F, Li X, Faustman DL 1993
Defective major histocompatibility complex class I expression on lymphoid cells in autoimmunity. J Clin Invest 9
1
: 2301
–2307
Gaczynska M, Goldberg AL, Tanaka K, Hendil KB, Rock KL 1996
Proteasome subunits X and Y alter peptidase activities in opposite ways to the interferon--induced subunits LMP2 and LMP7. J Biol Chem 27
1
: 17275
–17280
Ghosh S, Baltimore D 1990
Activation in vitro of NF-B by phosphorylation of its inhibitor IB. Nature
344
: 678
–682[CrossRef][Medline]
Glas R, Ohlen C, Hoglund P, Karre K 1994
The CD8+ T cell repertoire in ß2-microglobulin-deficient mice is biased towards reactivity against self-major histocompatibility class I. J Exp Med
179
: 661
–672[Abstract/Free Full Text]
Goldberg AL 1995
Functions of the proteasome: the lysis at the end of the tunnel [see comment]. Science
268
: 522
–523[Free Full Text]
Griffin TA, Nandi D, Cruz M, Fehling HJ, Kaer LV, Monaco JJ, Colbert RA 1998
Immunoproteasome assembly: cooperative incorporation of interferon (IFN-)-inducible subunits. J Exp Med
187
: 97
–104[Abstract/Free Full Text]
Hanafusa T, Miyazaki A, Miyagawa J, Tamura S, Inada M, Yamada K, Shinji Y, Katsura H, Yamagata K, Itoh N 1990
Examination of islets in the pancreas biopsy specimens from newly diagnosed type 1 (insulin-dependent) diabetic patients. Diabetologia
33
: 105
–111[CrossRef][Medline]
Hayashi T, Faustman D 1999
NOD mice are defective in proteasome production and activation of NF-B. Mol Cell Biol
19
: 8646
–8659[Abstract/Free Full Text]
Hayashi T, Faustman D 2000 Essential role of HLA-encoded proteasome subunits in NF-B activation and prevention of TNF--induced apoptosis. J Biol Chem
275
: 5238
–5247
Hayashi T, Sekine T, Okamoto T 1993a
Identification of a new serine kinase that activates NFB by direct phosphorylation. J Biol Chem
268
: 26790
–26795[Abstract/Free Full Text]
Hayashi T, Ueno Y, Okamoto T 1993b
Oxireductive regulation of nuclear factor B, involvement of a cellular reducing catalyst thioredoxin. J Biol Chem
268
: 11380
–11388[Abstract/Free Full Text]
Hayashi T, Kodama S, Faustman D 2000 LMP2 expression and proteasome activity in NOD mice. Nat Med
6
: 1064
–1066
Hisamatsu H, Shimbara N, Saito Y, Kristensen P, Hendil KB, Fujiwara T, Takahashi E, Tanahashi N, Tamura T, Ichihara A, Tanaka K 1996
Newly identified pair of proteasomal subunits regulated reciprocally by interferon-. J Exp Med
183
: 1807
–1816[Abstract/Free Full Text]
Horwitz BH, Scott ML, Cherry SR, Bronson RT, Baltimore D 1997
Failure of lymphopoiesis after adoptive transfer of NF-B-deficient fetal liver cells. Immunity
6
: 765
–772[CrossRef][Medline]
Hsu SC, Gavrilin MA, Lee HH, Wu CC, Han SH, Lai MZ 1999
NF-B-dependent Fas ligand expression. Eur J Immunol
29
: 2948
–2956[CrossRef][Medline]
Hu Y, Baud V, Delhase M, Zhang P, Deerinck T, Ellisman M, Johnson R, Karin M 1999
Abnormal morphogenesis but intact IKK activation in mice lacking the IKK subunit of IB kinase [see comments]. Science
284
: 316
–320[Abstract/Free Full Text]
Iotsova V, Caamano J, Loy J, Yang Y, Lewin A, Bravo R 1997
Osteopetrosis in mice lacking NF-B1 and NF-B2. Nat Med
3
: 1285
–1289[CrossRef][Medline]
Itoh N, Imagawa A, Hanafusa T, Waguri M, Yamamoto K, Iwahashi H, Moriwaki M, Nakajima H, Miyagawa J, Namba M, Makino S, Nagata S, Kono N, Matsuzawa Y 1997
Requirement of Fas for the development of autoimmune diabetes in nonobese diabetic mice. J Exp Med
186
: 613
–618[Abstract/Free Full Text]
Jansen A, Van Hagen M, Drexhage HA 1995
Defective maturation and function of antigen-presenting cells in type I diabetes. Lancet
345
: 491
–492[CrossRef][Medline]
Kanegae Y, Tavares AT, Izpisua Belmonte JC, Verma IM 1998
Role of Rel/NF-B transcription factors during the outgrowth of the vertebrate limb. Nature
392
: 611
–614[CrossRef][Medline]
Kang SM, Schneider DB, Lin Z, Hanahan D, Dichek DA, Stock PG, Baekkeskov S 1997
Fas ligand expression in islets of Langerhans does not confer immune privilege and instead targets them for rapid destruction [see comments]. Nat Med
3
: 738
–743[CrossRef][Medline]
Kang SM, Lin Z, Ascher NL, Stock PG 1998
Fas ligand expression on islets as well as multiple cell lines results in accelerated neutrophilic rejection. Transplant Proc
30
: 538[CrossRef][Medline]
Kay TWH, Campbell IL, Oxbrow L, Harrison LC 1991
Overexpression of class I major histocompatibiity complex accompanies insulitis in the nonobese diabetic mouse and is prevented by anti-interferon- antibody. Diabetologia
34
: 779
–785[CrossRef][Medline]
Kim S, Kim KA, Hwang DY, Lee TH, Kayagaki N, Yagita H, Lee MS2000 Inhibition of autoimmune diabetes by Fas ligand: the paradox is solved. J Immunol
164
: 2931
–2936
Kim YH, Kim S, Kim KA, Yagita H, Kayagaki N, Kim KW, Lee MS 1999
Apoptosis of pancreatic beta-cells detected in accelerated diabetes of NOD mice: no role of Fas-Fas ligand interaction in autoimmune diabetes. Eur J Immunol
29
: 455
–465[CrossRef][Medline]
Kontgen F, Grumont RJ, Strasser A, Metcalf D, Li R, Tarlinton D, Gerondakis S 1995
Mice lacking the c-rel proto-oncogene exhibit defects in lymphocyte proliferation, humoral immunity, and interleukin-2 expression. Genes Dev
9
: 1965
–1977[Abstract/Free Full Text]
Koshy M, Berger D, Crow MK 1996
Increased expression of CD40 ligand on systemic lupus erythematosus lymphocytes. J Clin Invest
98
: 826
–837[Medline]
Kovacs B, Liossis SN, Dennis GJ, Tsokos GC 1997
Increased expression of functional Fas-ligand in activated T cells from patients with systemic lupus erythematosus. Autoimmunity
25
: 213
–221[Medline]
Lamhamedi-Cherradi SE,Luan JJ, Eloy L, Fluteau G, Bach JF, Garchon HJ 1998
Resistance of T-cells to apoptosis in autoimmune diabetic (NOD) mice is increased early in life and is associated with dysregulated expression of Bcl-x. Diabetologia
41
: 178
–184[CrossRef][Medline]
Li F, Hauser SL, Linan MJ, Stein MC, Faustman DL 1995
Reduced expression of peptideloaded HLA class I molecules on multiple sclerosis lymphocytes. Ann Neurol
38
: 147
–154[CrossRef][Medline]
Li Q, Lu Q, Hwang JY, Buscher D, Lee KF, Izpisua-Belmonte JC, Verma IM 1999a
IKK1deficient mice exhibit abnormal development of skin and skeleton. Genes Dev
13
: 1322
–1328[Abstract/Free Full Text]
Li Q, Van Antwerp D, Mercurio F, Lee KF, Verma IM 1999b
Severe liver degeneration in mice lacking the IB kinase 2 gene [see comments]. Science
284
: 321
–325[Abstract/Free Full Text]
Li X, Faustman D 1993
Use of donor ß2-microglobulin-deficient transgenic mouse liver cells for isografts, allografts, and xenografts. Transplantation
55
: 940
–946[Medline]
Liang H, Fesik SW 1997
Three-dimensional structures of proteins involved in programmed cell death. J Mol Biol
274
: 291
–302[CrossRef][Medline]
Lin J, Tserng K, Chen C, Lin L, Tung T 1970
Abrin and ricin: new anti-tumor substances. Nature
227
: 562
–563
Lin L, DeMartino GN, Greene WC 1998
Co-translational biogenesis of NF-B p50 by the 26S proteasome. Cell
92
: 819
–828[CrossRef][Medline]
Lorenz HM, Grunke M, Hieronymus T, Herrmann M, Kuhnel A, Manger B, Kalden JR 1997
In vitro apoptosis and expression of apoptosis-related molecules in lymphocytes from patients with systemic lupus erythematosus and other autoimmune diseases [see comments]. Arthritis Rheum
40
: 306
–317[Medline]
Lynch DH, Watson ML, Alderson MR, Baum PR, Miller RE, Tough T, Gibson M, Davis-Smith T, Smith CA, Hunter K 1994
The mouse Fas-ligand gene is mutated in gldmice and is part of a TNF family gene cluster. Immunity
1
: 131
–136[CrossRef][Medline]
MacKichan ML, Logeat F, Israel A 1996
Phosphorylation of p105 PEST sequences via a redox-insensitive pathway up-regulates processing of p50 NF-B. J Biol Chem
271
: 6084
–6091[Abstract/Free Full Text]
Makino S, Kunimoto K, Muraoka Y, Mizushima Y, Katagiri K, Tochino Y 1980
Breeding of a non-obese, diabetic strain of mice. Jikken Dobutsu Exp Animals
29
: 1
–13
Maniatis T 1999
A ubiquitin ligase complex essential for the NF-B, Wnt/Wingless, and Hedgehog signaling pathways. Genes Dev
13
: 505
–510[Free Full Text]
Mountz JD, Zhou T, Su X, Cheng J, Pierson M, Bluethmann H, Edwards CK III 1996
Autoimmune disease results from multiple interactive defects in apoptosis induction molecules and signaling pathways. Behring Inst Mitteilungen
6
: 200
–219
Mysler E, Bini P, Drappa J, Ramos P, Friedman SM, Krammer PH, Elkon KB 1994
The apoptosis-1/Fas protein in human systemic lupus erythematosus. J Clin Invest
93
: 1029
–1034
Oeri A, Chang CC, Lombardi L, Salina M, Corradini P, Maiolo AT, Chaganti RS, Dalla-Favera R 1991
B cell lymphoma-associated chromosomal translocation involves candidate oncogene lyt-10, homologous to NF-B p50. Cell
67
: 1075
–1087[CrossRef][Medline]
Ono SJ, Issa-Chergui B, Colle E, Guttmann RD, Seemayer TA, Fuks A 1988
IDDM in BB rats. Enhanced MHC class I heavy-chain gene expression in pancreatic islets. Diabetes
37
: 1411
–1418[Abstract]
Pakala SV, Chivetta M, Kelly CB, Katz JD 1999
In autoimmune diabetes the transition from benign to pernicious insulitis requires an islet cell response to tumor necrosis factor . J Exp Med
189
: 1053
–1062[Abstract/Free Full Text]
Palombella V, Rando OJ, Goldberg AL, Maniatis T 1994
The ubiquitin-proteasome pathway is required for processing the NF-B1 precursor protein and the activation of NF-B. Cell
78
: 773
–785[CrossRef][Medline]
Quaaz F, Li M, Beg AA 1999
A critical role for the RelA subunit of nuclear factor B in regulation of multiple immune-response genes and in Fas-induced cell death. J Exp Med
189
: 999
–1004[Abstract/Free Full Text]
Rabinovitch A 1998
An update on cytokines in the pathogenesis of insulin-dependent diabetes mellitus. Diabetes Metab Rev
14
: 129
–151[CrossRef][Medline]
Rabinovitch A, Skyler JS 1998
Prevention of type 1 diabetes. Med Clin N Am
82
: 739
–755[CrossRef][Medline]
Ramsdell F, Seaman MS, Miller RE, Tough TW, Alderson MR, Lynch DH 1994
gld/gldmice are unable to express a functional ligand for Fas. Eur J Immunol
24
: 928
–933[Medline]
Restifo NP 2000 Not so Fas: re-evaluating the mechanisms of immune privilege and tumor escape. Nat Med
6
: 493
–495
Rieux-Laucat F, Le Deist F, Hivroz C, Roberts IA, Debatin KM, Fischer A, de Villartay JP 1995
Mutations in Fas associated with human lymphoproliferative syndrome and autoimmunity. Science
268
: 1347
–1349[Abstract/Free Full Text]
Rudolph D, Yeh WC, Wakeham A, Rudolph B, Nallainathan D, Potter J, Elia AJ, Mak TW2000 Severe liver degeneration and lack of NF-B actvation in NEMO/IKK-deficient mice. Genes Dev
14
: 854
–862
Schmid RM, Perkins ND, Duckett CS, Andrews PC, Nabel GJ 1991
Cloning of an NF-B subunit which stimulates HIV transcription in synergy with p65. Nature
352
: 733
–736[CrossRef][Medline]
Sears C, Olesen J, Rubin D, Finley D, Maniatis T 1998
NF-B p105 processing via the ubiquitin-proteasome pathway. J Biol Chem
273
: 1409
–1419[Abstract/Free Full Text]
Sha WC, Liou HC, Tuomanen El, Baltimore D 1995
Targeted disruption of the p50 subunit of NF-B leads to multifocal defects in immune responses. Cell
80
: 321
–330[CrossRef][Medline]
Smerdon RA, Peakman M, Hussain MJ, Alviggi L, Watkins PJ, Leslie RD, Vergani D 1993
Increase in simultaneous coexpression of naive and memory lymphocyte markers at diagnosis of IDDM. Diabetes
42
: 127
–133[Abstract]
Snapper CM, Zelazowski P, Rosas FR, Kehry MR, Tian M, Baltimore D, Sha WC 1996
B cells from p50/NF-B knockout mice have selective defects in proliferation, differentiation, germ-line CH transcription, and Ig class switching. J Immunol
156
: 183
–191[Abstract]
Stephens LA, Thomas HE, Kay TW 1997
Protection of NIT-l pancreatic beta-cells from immune attack by inhibition of NF-B. J Autoimmunity
10
: 293
–298[CrossRef]
TOP
ABSTRACT
I. Introduction
