TCR zeta chain lacking exon 7 in two patients with systemic lupus erythematosus

Naturally Occurring Genetic Alterations in Proximal TCR Signaling and Implications for Cancer Immunotherapy

T cell-based immunotherapies including genetically engineered T cells, adoptive transfer of tumor-infiltrating lymphocytes, and immune checkpoint blockade highlight the impressive anti-tumor effects of T cells. These successes have provided new hope to many cancer patients with otherwise poor prognoses. However, only a fraction of patients demonstrates durable responses to these forms of therapies and many develop significant immune-mediated toxicity. These heterogeneous clinical responses suggest that underlying nuances in T cell genetics, phenotypes, and activation states likely modulate the therapeutic impact of these approaches. To better characterize known genetic variations that may impact T cell function, we 1) review the function of early T cell receptor-specific signaling mediators, 2) offer a synopsis of known mutations and genetic alterations within the associated molecules, 3) discuss the link between these mutations and human disease and 4) review therapeutic strategies under development or in clinical testing that target each of these molecules for enhancing anti-tumor T cell activity. Finally, we discuss novel engineering approaches that could be designed based on our understanding of the function of these molecules in health and disease.

Emerging targets for the treatment of lupus erythematosus: There is no royal road to treating lupus

Systemic lupus erythematosus (SLE) is a highly heterogeneous autoimmune disease that preferentially affects women of child-bearing age. Most current treatments for SLE with the exception of belimumab are not target-specific. Nontargeted therapy such as corticosteroids, cyclophosphamide, and other immunosuppressive drugs results in unwanted adverse effects. Although progress in treatment, including supportive therapy, has dramatically improved the prognosis of patients with SLE, better treatment drugs and protocols with fewer adverse effects and higher efficacy for the most severe form of SLE are needed. Advancements in genomics, immunology, and pathophysiology in the field of systemic autoimmunity have provided physicians with increasing knowledge, but the most appropriate treatment for each patient with SLE remains to be established. Therefore, the search for novel treatment targets in patients with SLE is ongoing. This review focuses on recent findings in the genetics of lupus and the abnormalities in cellular interactions, cytokine profiles, and intracellular signaling in patients with SLE. Novel molecular targets for lupus, mostly introduced through clinical trials, are then discussed based on these findings.

Decreased Expression of Serine/Arginine-Rich Splicing Factor 1 in T Cells From Patients With Active Systemic Lupus Erythematosus Accounts for Reduced Expression of RasGRP1 and DNA Methyltransferase 1

OBJECTIVE

T cells from systemic lupus erythematosus (SLE) patients have reduced protein levels of RasGRP1, a guanine nucleotide exchange factor for Ras, and increased transcript of alternatively spliced (AS) forms lacking exon 11. Serine/arginine-rich splicing factor 1 (SRSF1) binds pre-messenger RNA (pre-mRNA) to regulate AS forms of several genes, including CD3ζ in SLE T cells. This study was undertaken to assess whether SRSF1 controls the expression of RasGRP1 in T cells from patients with SLE.

METHODS

We studied T cells from 45 SLE patients and 18 healthy subjects. Expression levels of SRSF1, wild-type (WT) RasGRP1, and DNA methyltransferase 1 (DNMT1) were assessed by quantitative polymerase chain reaction. Direct binding of SRSF1 to exon 11 of RasGRP1 mRNA was evaluated with an oligonucleotide-protein pulldown assay. Healthy T cells and SLE T cells were treated with SRSF1-specific small interfering RNA or SRSF1 expression vector, respectively, and then evaluated for mRNA/protein expression.

RESULTS

SRSF1 expression levels were significantly lower in T cells from SLE patients compared to those from healthy subjects, and correlated inversely with disease activity and positively with levels of RasGRP1-WT and DNMT1. SRSF1 bound directly to exon 11 of RasGRP1 mRNA. Silencing of SRSF1 in human T cells led to increased ratios of RasGRP1-AS to RasGRP1-WT and decreased levels of RasGRP1 protein, whereas overexpression of SRSF1 in SLE T cells caused recovery of RasGRP1, which in turn induced DNMT1/interleukin-2 expression.

CONCLUSION

SRSF1 controls the alternative splicing of RasGRP1 and subsequent protein expression. Our findings extend evidence that alternative splicing plays a central role in the aberrant T cell function in patients with SLE by controlling the expression of multiple genes.

CD3Z hypermethylation is associated with severe clinical manifestations in systemic lupus erythematosus and reduces CD3ζ-chain expression in T cells

Objective

The importance of hypomethylation in SLE is well recognized; however, the significance of hypermethylation has not been well characterized. We screened hypermethylated marks in SLE and investigated their possible implications.

Methods

DNA methylation marks were screened in SLE whole-blood DNA by microarray, and two marks ( CD3Z and VHL hypermethylations) were confirmed by a methylation single-base extension method in two independent ethnic cohorts consisting of 207 SLE patients and 151 controls. The correlation with clinical manifestations and the genetic influence on those epigenetic marks were analysed.

Results

Two epigenetic marks, CD3Z and VHL hypermethylation, were significantly correlated with SLE: CD3Z hypermethylation (odds ratio = 7.76; P = 1.71 × 10 -13 ) and VHL hypermethylation (odds ratio = 3.77; P = 3.20 × 10 -8 ), and the increased CD3Z methylation was correlated with downregulation of the CD3ζ-chain in SLE T cells. In addition, less genetic influence on CD3Z methylation relative to VHL methylation was found in analyses of longitudinal and twin samples. Furthermore, a higher CD3Z methylation level was significantly correlated with a higher SLE disease activity index and more severe clinical manifestations, such as proteinuria, haemolytic anaemia and thrombocytopenia, whereas VHL hypermethylation was not.

Conclusion

CD3Z hypermethylation is an SLE risk factor that can be modified by environmental factors and is associated with more severe SLE clinical manifestations, which are related to deranged T cell function by downregulating the CD3ζ-chain.

T-cell receptor ζ mRNA with an alternatively spliced 3' untranslated region is generated predominantly in the peripheral blood T cells of systemic lupus erythematosus patients

Abstract  To investigate the mechanism of the downregulation of T-cell receptor ζ chain (TCRζ) expression in the peripheral blood T cells (PBTs) of systemic lupus erythematosus (SLE) patients, we analyzed the 3' untranslated region (3'UTR) of TCRζ mRNA, because the 3'UTR in mRNA is responsible for posttranscriptional regulation. Use of the reverse transcriptase polymerase chain reaction (RT-PCR) to amplify the 917 bp TCRζ 3'UTR cDNA demonstrated that the short variant cDNA (355 bp), expressed as an alternatively spliced 3'UTR with 562-bp deletion, was predominated in the PBTs of 11 of 14 SLE patients, whereas mainly the wild-form cDNA (917 bp) was detected in the PBTs of seven negative controls (two systemic sclerosis patients, five normal controls) and in two T-cell line hybridomas. Semiquantitative PCR also revealed the predominant expression of the TCRζ mRNA with alternatively spliced 3'UTR (TCRζ mRNA/as-3'UTR), and a decreased expression of TCRζ mRNA with the wild form 3'UTR (TCRζ mRNA/w-3'UTR) in SLE T cells. However, there was no difference in the expression of the open reading frame (ORF) TCRζ mRNA between the negative controls and SLE patients. The TCRζ protein expression level according to Western blot analysis correlated well with that of TCRζ mRNA/w-3'UTR (r= 0.931) and reversibly with TCRζ mRNA/as-3'UTR (r=-0.614), but not with ORF TCRζ mRNA (r=-0.296). It can be concluded that the reduced expression of TCRζ mRNA/w-3'UTR and the predominant expression of TCRζ mRNA/as-3'UTR lead to downregulation of the TCRζ protein in SLE T cells.

Alternative expression of TCRζ related genes in patients with chronic myeloid leukemia

A previous study has demonstrated a significant decrease in the TCRζ gene expression level in chronic myeloid leukemia (CML); thus, we further investigated the expression of TCRζ-regulating factors, the distribution of the TCRζ 3' untranslated region (3'-UTR) splice variants, and the expression level and correlation of the alternative splicing factor/splicing factor 2 (ASF/SF-2), FcεRIγ and ZAP-70 genes. TCRζ 3'-UTR splice variants were identified in peripheral blood mononuclear cells (PBMCs) from 14 healthy individuals, 40 patients with CML and 22 patients with CML in complete remission (CML-CR) by RT-PCR. The expression level of the TCRζ, FcεRIγ, ASF/SF-2 and ZAP-70 genes was analyzed by real-time quantitative PCR. While the expression of TCRζ gene in the CML group was significantly lower than that in the healthy individual and CML-CR groups, a significantly higher expression of the FceRIγ and ASF/SF-2 genes was found in the CML group. Two types of splicing forms were detected in all of the healthy individual CML-CR cases: wild type (WT) TCRζ 3'-UTR and alternatively splieced (AS) TCRζ 3'-UTR which have been alternatively splieced in the WT TCRζ 3'-UTR . However, 35% of the CML cases contained only the wild type TCRζ 3'-UTR isoform. Based on the TCRζ 3'-UTR isoform expression characteristic, we divided the patients with CML into two subgroups: the WT+AS- CML group, containing patients that express only the wild type TCRζ 3'-UTR, and the WT+AS+ CML group, which contained patients that expressed two TCRζ 3'-UTR isoforms. A significantly different ASF/SF-2 and FcεRIγ gene expression pattern was found between the WT+AS- and WT+AS+CML groups. We concluded that defective TCRζ expression may be characterized in the WT+AS-and WT+AS+CML subgroups by the different gene expression pattern. The overexpression of ASF/SF2, which alternatively splices the TCRζ 3'-UTR, is thought to participate in feedback regulation. The characteristics of TCRζ 3'-UTR alternative splicing may be a novel immunological marker for the evaluation of the CML immune status.

CD3 ζ defects in systemic lupus erythematosus

The prototype autoimmune disease, systemic lupus erythematosus (SLE), has been known to be associated with deficiency of ζ chain, a component of the T-cell receptor-CD3 complex. Comprehensive analysis has shown that expression of the CD3 ζ chain is attenuated or absent in over half of SLE patients. Furthermore, aberrant transcripts of the CD3 ζ chain, including spliced variants lacking exon 7 or having a short 3'-untranslated region, have been detected in SLE T cells. Although attenuated expression of the CD3 ζ chain is also observed in cancer patients, infections and other autoimmune diseases, sustained attenuation of the CD3 ζ expression accompanied with aberrant transcripts are only observed in SLE. In this study, the authors review the unique features of CD3 ζ defects observed in SLE and discuss the molecular basis of the defects by recent findings in animal models, single-nucleotide polymorphisms and genome-wide association studies.

The role of endocytic recycling in autoimmunity

Abnormalities in T cell signal transduction underlie pathology in systemic lupus erythematosus. Lupus T cells are more sensitive to stimulation, yet have reduced expression of T cell antigen receptor (TCR) at the surface. The amount of TCR expressed at the surface of a T cell directly determines the ability of a T cell to become activated. The endocytic recycling machinery regulates transport of T cell receptors to the plasma membrane, internalization of surface receptors, and recycling to the cell surface, which determines the ability of a T cell to become activated. Increased recycling of CD3 and CD4 receptors occurs in lupus T cells, and could represent a mechanism by which T cells are sensitized to stimulation. This chapter explains methods used to investigate endocytic recycling of the TCR, CD4, and CD8 co-receptors in peripheral blood lymphocytes, T cells, and in splenocytes from lupus-prone murine models. The assays described will allow the study of surface receptor turnover in live untouched lymphocytes by flow cytometry.

Methods and protocols to study T cell signaling abnormalities in human systemic lupus erythematosus

Abnormal expression of key signaling molecules and defective functions of T lymphocytes play a significant role in the pathogenesis of systemic lupus erythematosus (SLE). T cell receptor (TCR/CD3)-mediated stimulation of SLE T cells show increased protein tyrosine phosphorylation of cellular proteins with faster kinetics, heightened calcium flux response, and decreased IL-2 production. The molecular mechanisms of T cell signaling abnormalities in SLE T cells are complex. Current research has been directed towards investigating various factors that contribute to abnormal tyrosine phosphorylation, intracellular calcium response, and cytokine production. Central to this dysfunction is the aberrant expression and function of the TCR/CD3ζ chain. Latest developments suggest multiple explanations are involved, including altered receptor structure, supramolecular assembly, modulation of membrane clustering, aberrant cellular distribution, and pre-compartmentalization with lipid-rafts. The methods and protocols described here pertaining to T cell signaling abnormalities in SLE T cells are optimized in many ways and are derived by the combined task and continuous efforts of many researchers in the lab over a long period of time. These simplified protocols can be readily applied to study T cell signaling abnormalities in SLE to identify the genetic, molecular, and biochemical factors contributing to aberrant immune cell function and unravel the pathophysiology of SLE.

NKG2D initiates caspase-mediated CD3zeta degradation and lymphocyte receptor impairments associated with human cancer and autoimmune disease

Deficiencies of the T cell and NK cell CD3ζ signaling adapter protein in patients with cancer and autoimmune diseases are well documented, but mechanistic explanations are fragmentary. The stimulatory NKG2D receptor on T and NK cells mediates tumor immunity but can also promote local and systemic immune suppression in conditions of persistent NKG2D ligand induction that include cancer and certain autoimmune diseases. In this paper, we provide evidence that establishes a causative link between CD3ζ impairment and chronic NKG2D stimulation due to pathological ligand expression. We describe a mechanism whereby NKG2D signaling in human T and NK cells initiates Fas ligand/Fas-mediated caspase-3/-7 activation and resultant CD3ζ degradation. As a consequence, the functional capacities of the TCR, the low-affinity Fc receptor for IgG, and the NKp30 and NKp46 natural cytotoxicity receptors, which all signal through CD3ζ, are impaired. These findings are extended to ex vivo phenotypes of T and NK cells among tumor-infiltrating lymphocytes and in peripheral blood from patients with juvenile-onset lupus. Collectively, these results indicate that pathological NKG2D ligand expression leads to simultaneous impairment of multiple CD3ζ-dependent receptor functions, thus offering an explanation that may be applicable to CD3ζ deficiencies associated with diverse disease conditions.

Reduced expression of TCR zeta is involved in the abnormal production of cytokines by peripheral T cells of patients with systemic lupus erythematosus

Accumulating evidence suggests that dysfunction of T cells underlies the pathogenesis of systemic lupus erythematosus (SLE). We revealed that SLE T cells produced an abnormally excessive amount of IFN-γin vitro upon stimulation through TCR, and the expression level of TCR zeta was significantly reduced. The production of IFN-γ by SLE T cells was negatively correlated with the expression level of TCR zeta. This correlation was abolished when the cells were stimulated with TPA and ionomycin, which bypass TCR and introduce signals directly into the cells, but the production of IFN-γ by SLE T cells remained abnormally elevated. Taken together, these data suggest that regulatory mechanisms not only for the expression of TCR zeta but also for the production of IFN-γ were impaired in SLE T cells. These impairments may be responsible for the aberrant responses of SLE T cells and partly involved in the development of SLE.

T cell abnormalities in systemic lupus erythematosus

Because of the consensus that T cells play a central role in the pathogenesis of systemic lupus erythematosus (SLE), we explored the molecular basis of the defective function of SLE T cells for expression of signal transduction molecules, as well as surface structures such as adhesion molecules, by extensively testing peripheral blood T cells from SLE patients. Upregulated expression and function of adhesion molecules was observed in T cells from patients with active SLE who had specific clinical manifestations such as vasculitis, epithelitis and arthritis, but proximal signal transduction was defective. Comprehensive analysis to identify the molecules responsible for the defects showed the expression of the TCR zeta chain was attenuated, or absent in more than half of SLE patients. Moreover, the aberrant transcripts of the TCR zeta chain, including spliced variants lacking exon 7 and with a short 3' UTR, were detected in SLE T cells. Although attenuated expression of the TCR zeta chain is also observed in patients with cancers, infections and other autoimmune diseases, sustained attenuation of TCR zeta expression and aberrant transcripts are only observed in SLE. In this review we discuss the unique features of the TCR zeta defects in SLE.

The CD3Z 844 T>A polymorphism within the 3'-UTR of CD3Z confers increased risk of incidence of systemic lupus erythematosus

Recently, a family-based association analysis showed that the haplotype carrying a low expression of the variant CD3Z 844 T>A (rs1052231) polymorphism located in the 3'-untranslated region of CD3Z predisposes to systemic lupus erythematosus (SLE) incidence. We analyzed the prevalence of the CD3Z 844 T>A polymorphism in SLE patients (n = 152) and controls (n = 304) in Poland. We observed that women with the CD3Z AA and CD3Z AT genotypes exhibited a 1.845-fold increased risk of SLE [95% confidence intervals (95% CI) = 1.222-2.787, P = 0.0038]. However, we did not find an increased risk for the homozygous CD3Z AA genotype (odds ratio = 1.204, 95% CI = 0.2838-5.108, P = 1.0000). This observation confers that genetic factors causing a decreased level of CD3-zeta in T cells may predispose to SLE incidence.

Alterations in the expression pattern of TCR zeta chain in T cells from patients with hematological diseases

The TCR zeta chain, a component of the T cell receptor (TCR)/CD3 complex, plays a significant role in the assembly of the receptor complex and in connecting antigen recognition to the intracellular signal transduction apparatus. Recently, studies have demonstrated altered expression and function of this signal transduction molecule in T cells from patients with hematological diseases. In this review, current knowledge concerning the biological feature and function of TCR zeta protein, splice variant and mutation of TCR zeta chain gene and alteration of expression pattern in hematological diseases and the related mechanism are summarized.

Scalable signaling mediated by T cell antigen receptor-CD3 ITAMs ensures effective negative selection and prevents autoimmunity

The T cell antigen receptor (TCR)-CD3 complex is unique in having ten cytoplasmic immunoreceptor tyrosine-based activation motifs (ITAMs). The physiological importance of this high TCR ITAM number is unclear. Here we generated 25 groups of mice expressing various combinations of wild-type and mutant ITAMs in TCR-CD3 complexes. Mice with fewer than seven wild-type CD3 ITAMs developed a lethal, multiorgan autoimmune disease caused by a breakdown in central rather than peripheral tolerance. Although there was a linear correlation between the number of wild-type CD3 ITAMs and T cell proliferation, cytokine production was unaffected by ITAM number. Thus, high ITAM number provides scalable signaling that can modulate proliferation yet ensure effective negative selection and prevention of autoimmunity.

Polymorphisms in the CD3Z gene influence TCRzeta expression in systemic lupus erythematosus patients and healthy controls

TCRzeta (CD247) functions as an amplification module in the TCR signaling cascade and is essential for assembly and surface expression of the TCR/CD3 complex. The TCRzeta-chain is down-regulated in many chronic infectious and inflammatory diseases, including systemic lupus erythematosus (SLE). It is unclear whether reduced TCRzeta expression is a cause or a consequence of chronic inflammatory responses. We have addressed this question by adopting a combined genetic and functional approach. We analyzed TCRzeta protein expression using a FACS-based expression index and documented considerable, but longitudinally stable, variation in TCRzeta expression in healthy individuals. The variation in TCRzeta expression was associated with polymorphisms in the CD3Z 3'-untranslated region (UTR) in SLE patients and healthy controls. Detailed mapping of the 3'-UTR revealed that the minor alleles of two single nucleotide polymorphisms (SNPs) in strong disequilibrium (rs1052230 and rs1052231) were the causal variants associated with low TCRzeta expression (p=0.015). Using allelic imbalance analysis, the minor alleles of these 3'-UTR SNPs were associated with one-third of the level of mRNA compared with the major allele. A family-based association analysis showed that the haplotype carrying the low-expression variants predisposes to SLE (p=0.033). This suggests that a genetically determined reduction in TCRzeta expression has functional consequences manifested by systemic autoimmunity.

Conservative sequences in 3'UTR of TCRzeta mRNA regulate TCRzeta in SLE T cells

We have demonstrated that T-cell receptor zeta (zeta) mRNA with a 562-bp deleted alternatively spliced 3'-untranslated region (3'UTR) observed in T cells of patients with systemic lupus erythematosus (SLE) can lead to a reduction in zeta and TCR/CD3 (J. Immunol., 2003 & 2005). To determine the region in zeta mRNA 3'UTR for the regulation of zeta, zeta mRNA with 3'UTR truncations ligated into pDON-AI was used to infect murine T-cell hybridoma MA5.8 cells, which do not contain zeta. As a Western blot analysis demonstrated the importance of the regions from +871 to +950, containing conservative sequence 1 (CS1), and +1070 to +1136, containing CS2, for the production of zeta, we constructed MA5.8 mutants carrying zeta mRNA 3'UTR with deletions of these regions (DeltaCS1 and DeltaCS2 mutants). Western blot and FACS analyses showed significant reduction in the cell surface zeta and TCR/CD3 in both these mutants, and IL-2 production was decreased, compared with MA5.8 cells transfected with wild-type zeta mRNA. Furthermore, real-time PCR demonstrated the instability of zeta mRNA with 3'UTR deletions in these MA5.8 mutants. In conclusion, CS1 and CS2 may be responsible for the regulation of zeta and TCR/CD3 through the stability of zeta mRNA in SLE T cells.

Allelic variant in CTLA4 alters T cell phosphorylation patterns

Little is known regarding the functional effects of common autoimmune susceptibility variants on human immune cells. The SNP CT60 (rs3087243; A/G) located in the 3' UTR of the CTLA4 gene has been associated with autoimmune diseases. We examined a cohort of healthy individuals stratified by genotypes at CTLA4 to gain insight into the functional effects of allelic variation on T cell signaling. Using phospho-site-specific mAbs, we tested the hypothesis that the CT60 genotype at CTLA4 is associated with altered T cell antigen receptor (TCR) signaling in naive and/or memory T cells. By normalizing for the extent of the initial TCR signaling event at CD3zeta, we observed that the relative responsiveness to TCR stimulation as assessed by phosphorylation levels of downstream signaling molecules was altered in naive (CD4(+)CD45RA(high)) and memory (CD4(+)CD45RA(low)) T cells obtained from individuals with the disease-susceptibility allele at CTLA4. Thus, allelic variation associated with autoimmune disease can alter the signaling threshold of CD4(+) T cells. These experiments provide a rational approach for the dissection of T cell-susceptibility genes in autoimmune diseases.

Stability and translation of TCR zeta mRNA are regulated by the adenosine-uridine-rich elements in splice-deleted 3' untranslated region of zeta-chain

Systemic lupus erythematosus (SLE) T cells display reduced expression of TCR zeta protein. Recently, we reported that in SLE T cells, the residual TCR zeta protein is predominantly derived from an alternatively spliced form that undergoes splice deletion of 562 nt (from 672 to 1233 bases) within the 3' untranslated region (UTR) of TCR zeta mRNA. The stability and translation of the alternatively spliced form of TCR zeta mRNA are low compared with that of the wild-type TCR zeta mRNA. We report that two adenosine-uridine-rich sequence elements (AREs), defined by the splice-deleted 3' UTR region, but not an ARE located upstream are responsible for securing TCR zeta mRNA stability and translation. The stabilizing effect of the splice-deleted region-defined AREs extended to the luciferase mRNA and was not cell type-specific. The findings demonstrate distinct sequences within the splice-deleted region 672 to 1233 of the 3' UTR, which regulate the transcription, mRNA stability, and translation of TCR zeta mRNA. The absence of these sequences represents a molecular mechanism that contributes to altered TCR zeta-chain expression in lupus.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

TCRzeta mRNA splice variant forms observed in the peripheral blood T cells from systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease of unknown etiology. Tyrosine phosphorylation and protein expression of the T-cell receptor zeta chain (zeta) have been reported to be significantly decreased in SLE T cells. In addition, zeta mRNA with alternatively spliced 3' untranslated region (zetamRNA/as-3'UTR) is detected predominantly in SLE T cells, and aberrant zeta mRNA accompanied by the mutations in the open reading frame including zeta mRNA lacking exon7 (zetamRNA/exon7-) is observed in SLE T cells. These zeta mRNA splice variant forms exhibit a reduction in the expression of TCR/CD3 complex and zeta protein on their cell surface due to the instability of zeta mRNA splice variant forms as well as the reduction in interleukin (IL)-2 production after stimulating with anti-CD3 antibody. Data from cDNA microarray showed that 36 genes encoding cytokines and chemokines, including IL-2, IL-15, IL-18, and TGF-beta2, were down-regulated in the MA5.8 cells transfected with the zeta mRNA splice variant forms. Another 16 genes were up-regulated and included genes associated with membranous proteins and cell damage granules, including the genes encoding poliovirus-receptor-related 2, syndecan-1, and granzyme A.

DNA microarray gene expression profile of T cells with the splice variants of TCRzeta mRNA observed in systemic lupus erythematosus

We have reported that the TCRzeta mRNA with alternatively spliced 3' UTR (zeta mRNA/as-3'-untranslated region (UTR)) and zeta mRNA lacking exon 7 (zeta mRNA/exon 7-) observed in systemic lupus erythematosus patient T cells can lead to down-regulation of both zeta and TCR/CD3 complexes. To determine whether these T cells expressing decreased zeta exhibit differential transcription patterns, we transfected retrovirus vectors containing wild-type zeta cDNA, zeta cDNA/as-3' UTR, and zeta cDNA/exon 7- into murine T cell hybridoma MA5.8 cells which lack zeta expression to construct the MA5.8 mutants WT, AS3' UTR, and EX7-, respectively. FACS analyses demonstrated reduced cell surface expression of zeta and TCR/CD3 complexes on the AS3' UTR mutant and the EX7- mutant in comparison to that on the WT mutant. Total RNA was collected after stimulating the MA5.8 mutants with anti-CD3 Ab. Reverse-transcribed cDNA was applied to the mouse cDNA microarray containing 8691 genes, and the results were confirmed by real-time PCR. The results showed that 36 genes encoding cytokines and chemokines, including IL-2, IL-15, IL-18, and TGF-beta2, were down-regulated in both the AS3' UTR mutant and the EX7- mutant. Another 16 genes were up-regulated in both, and included genes associated with membranous proteins and cell damage granules, including the genes encoding poliovirus receptor-related 2, syndecan-1, and granzyme A. Increased protein expression of these genes was confirmed by Western blot and FACS analyses. Identification of these responsive genes in T cells in which the zeta and TCR/CD3 complexes were down-regulated may help to better understand the pathogenesis of systemic lupus erythematosus.

Altered regulation of IL-2 production in systemic lupus erythematosus: an evolving paradigm

In systemic lupus erythematosus (SLE), IL-2 production by T lymphocytes in vitro is impaired. Deficient IL-2 production may be an outcome of a primary SLE T cell disorder that is due to impaired signal transduction. In this issue of the JCI, evidence is presented that an anti-TCR/CD3 complex autoantibody present in SLE sera can bind to T cells and activate the Ca(2+)-calmodulin kinase IV (CaMKIV) signaling cascade, resulting in downregulation of IL-2 transcription and IL-2 production. Because IL-2 may contribute to the maintenance of T cell tolerance, deficient IL-2 production could promote a breach of T cell tolerance that results in autoantibody production in SLE.

A splice variant of the TCR zeta mRNA lacking exon 7 leads to the down-regulation of TCR zeta, the TCR/CD3 complex, and IL-2 production in systemic lupus erythematosus T cells

The reduction or absence of TCR zeta-chain (zeta) expression in patients with systemic lupus erythematosus (SLE) is thought to be a factor in the pathogenesis of SLE. We previously reported a splice variant of zeta mRNA that lacks the 36-bp exon 7 (zeta mRNA/exon 7(-)) and is accompanied by the down-regulation of zeta protein in T cells from SLE patients. In this study, we show that EX7- mutants (MA5.8 cells deficient in zeta protein that have been transfected with zeta mRNA/exon 7(-)) exhibit a reduction in the expression of TCR/CD3 complex and zeta protein on their cell surface as well as a reduction in the production of IL-2 after stimulation with anti-CD3 Ab, compared with that in wild-type (WT) mutants (MA5.8 cells transfected with the WT zeta mRNA). Furthermore, real-time PCR analyses demonstrated that zeta mRNA/exon 7(-) in EX7- mutants was easily degraded compared with zeta mRNA by the WT mutants. Pulse-chase experiment showed zeta protein produced by this EX7- mutants was more rapidly decreased compared with the WT mutants. Thus, the lower stability of zeta mRNA/exon 7(-) might also be responsible for the reduced expression of the TCR/CD3 complex, including zeta protein, in SLE T cells.

Decreased stability and translation of T cell receptor zeta mRNA with an alternatively spliced 3'-untranslated region contribute to zeta chain down-regulation in patients with systemic lupus erythematosus

The molecular mechanisms involved in the aberrant expression of T cell receptor (TCR) zeta chain of patients with systemic lupus erythematosus are not known. Previously we demonstrated that although normal T cells express high levels of TCR zeta mRNA with wild-type (WT) 3' untranslated region (3' UTR), systemic lupus erythematosus T cells display significantly high levels of TCR zeta mRNA with the alternatively spliced (AS) 3' UTR form, which is derived by splice deletion of nucleotides 672-1233 of the TCR zeta transcript. Here we report that the stability of TCR zeta mRNA with an AS 3' UTR is low compared with TCR zeta mRNA with WT 3' UTR. AS 3' UTR, but not WT 3' UTR, conferred similar instability to the luciferase gene. Immunoblotting of cell lysates derived from transfected COS-7 cells demonstrated that TCR zeta with AS 3' UTR produced low amounts of 16-kDa protein. In vitro transcription and translation also produced low amounts of protein from TCR zeta with AS 3' UTR. Taken together our findings suggest that nucleotides 672-1233 bp of TCR zeta 3' UTR play a critical role in its stability and also have elements required for the translational regulation of TCR zeta chain expression in human T cells.

Altered expression of the T cell receptor-CD3 complex in systemic lupus erythematosus

SLE T cells may play a key role in autoantibody production in SLE B cells. In addition, accumulating evidence has shown that SLE T cells participate in the attack on target cells or tissues through the overproduction of pro-inflammatory cytokines or an increase in cell-to-cell adhesion. Thus, the functional abnormality of SLE T cells appears to be pivotal to an understanding of SLE pathogenesis. Accumulating evidence suggests that potential defects may reside in the proximal signal transduction around the TCR-CD3 complex. We have demonstrated that the expression of TCR zeta chain is significantly decreased in peripheral blood T cells from SLE patients. To explore the mechanism of defective expression of TCR zeta chain, we examined mRNA of TCR zeta, and found that two alternatively spliced variants such as exon 7 (-) and short 3'-UTR are detected in SLE. We review the possible role of the TCR zeta defects in autoimmunity and discuss how the splicing variants lead to downregulated protein expression of TCR zeta chain.

Dissecting the molecular mechanisms of TCR zeta chain downregulation and T cell signaling abnormalities in human systemic lupus erythematosus

Abnormal expression of key signaling molecules and defective function of T lymphocytes play a significant role in the pathogenesis of systemic lupus erythematosus (SLE). Probing on altered expression of genes that may predispose to SLE revealed that the expression of TCR zeta chain is defective in the majority of SLE patients. Current research has been directed towards understanding the molecular basis of TCR zeta chain deficiency and dissecting the T cell signalling abnormalities in SLE T cells. Latest developments suggest that interplay of abnormal transcriptional factor expression, aberrant mRNA processing/editing, unbiquitination, proteolysis, and the effects of oxidative stress as well as changes in chromatin structure invariably contribute to TCR zeta chain deficiency in SLE T cells. On the other hand, multiple factors, including altered receptor structure, modulation of membrane clustering, lipid-raft distribution of signaling molecules, and defective signal silencing mechanisms, play a key role in delivering the increased TCR/CD3-mediated intracellular calcium response in SLE T cells.

Association of a four-amino acid residue insertion polymorphism of the HS1 gene with systemic lupus erythematosus: Molecular and functional analysis

OBJECTIVE

To investigate whether polymorphism(s) or mutation(s) in the hematopoietic cell-specific Lyn substrate 1 (HS1) gene are involved in the pathogenesis of systemic lupus erythematosus (SLE).

METHODS

The entire coding region of the HS1 gene was analyzed by reverse transcriptase-polymerase chain reaction/single-strand conformational polymorphism analysis. HS1-transfected WEHI-231 cells or B lymphocytes from patients with SLE were studied for apoptosis, activation, and proliferation by flow cytometric analysis and MTT assay.

RESULTS

We identified a glutamic acid-proline-glutamic acid-proline insertion between codons 366 and 367 (EPEP366-367ins) and 2 amino acid substitutions (A235T and E361K). The genotype frequency among individuals homozygous for the EPEP+ allele was 0.184 in 201 patients with SLE but only 0.098 in 184 healthy individuals (P = 0.016). The allele frequency of EPEP366-367ins was 0.408 in patients with SLE; this frequency was significantly higher than that in healthy controls (0.312) (P = 0.006). WEHI-231 cells transfected with EPEP+ HS1 were 100-fold more sensitive to B cell receptor (BCR)-mediated apoptosis than were those transfected with HS1 without EPEP. B lymphocytes from SLE patients with the EPEP+ allele were significantly more apoptotic without BCR stimulation and less activated after BCR stimulation than were those from SLE patients without the EPEP allele.

CONCLUSION

These results suggest that HS1 with the EPEP insertion polymorphism transmits accelerated signals from BCR and is involved in the pathogenesis of SLE.

Altered thymic T-cell selection due to a mutation of the ZAP-70 gene causes autoimmune arthritis in mice

Rheumatoid arthritis (RA), which afflicts about 1% of the world population, is a chronic systemic inflammatory disease of unknown aetiology that primarily affects the synovial membranes of multiple joints. Although CD4(+) T cells seem to be the prime mediators of RA, it remains unclear how arthritogenic CD4(+) T cells are generated and activated. Given that highly self-reactive T-cell clones are deleted during normal T-cell development in the thymus, abnormality in T-cell selection has been suspected as one cause of autoimmune disease. Here we show that a spontaneous point mutation of the gene encoding an SH2 domain of ZAP-70, a key signal transduction molecule in T cells, causes chronic autoimmune arthritis in mice that resembles human RA in many aspects. Altered signal transduction from T-cell antigen receptor through the aberrant ZAP-70 changes the thresholds of T cells to thymic selection, leading to the positive selection of otherwise negatively selected autoimmune T cells. Thymic production of arthritogenic T cells due to a genetically determined selection shift of the T-cell repertoire towards high self-reactivity might also be crucial to the development of disease in a subset of patients with RA.

TCR zeta mRNA with an alternatively spliced 3'-untranslated region detected in systemic lupus erythematosus patients leads to the down-regulation of TCR zeta and TCR/CD3 complex

The reduction or absence of TCR zeta-chain (zeta) expression in systemic lupus erythematosus (SLE) patients is thought to be related to the pathogenesis of SLE. Recently, we reported the predominant expression of zeta mRNA containing an alternatively spliced 3'-untranslated region (3'UTR; zetamRNA/as-3'UTR) and a reduction in the expression of zeta mRNA containing the wild-type 3'UTR (zetamRNA/w-3'UTR) in T cells from SLE patients. Here we show that AS3'UTR mutants (MA5.8 cells deficient in zeta protein that have been transfected with zetamRNA/as-3'UTR) exhibit a reduction in the expression of TCR/CD3 complex and zeta protein on their cell surface as well as a reduction in the production of IL-2 after stimulation with anti-CD3 Ab compared with that in wild-type 3'UTR mutants (MA5.8 cells transfected with zetamRNA/w-3'UTR). Furthermore, the real-time PCR analyses demonstrated that the half-life of zetamRNA/as-3'UTR in AS3'UTR mutants (3 h) was much shorter than that of zetamRNA/w-3'UTR in wild-type 3'UTR mutants (15 h). Thus, the lower stability of zetamRNA/as-3'UTR, which is predominant in SLE T cells, may be responsible for the reduced expression of the TCR/CD3 complex, including zeta protein, in SLE T cells.

Prevalence of T cell receptor zeta chain deficiency in systemic lupus erythematosus

T cells from patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain expression. We determined the prevalence of TCR zeta chain deficiency in SLE from a large cohort of unselected racially diverse patients with different levels of clinical disease activity as determined by SLE Disease Activity Index (SLEDAI). Our data show that the occurrence of TCR zeta chain deficiency is 78% in SLE patients. There was no relationship between the deficiency of TCR zeta chain and the SLEDAI scores or theapy. TCR zeta chain deficiency was also not associated with age, race or gender and persisted over a 3 year follow-up period. Thus, there is a high prevalence of TCR zeta chain deficiency in SLE patients that is independent of disease activity, and persists over time indicating an important role for TCR zeta chain deficiency in SLE pathogenesis.

Defective activity of ERK-1 and ERK-2 mitogen-activated protein kinases in peripheral blood T lymphocytes from patients with systemic lupus erythematosus: potential role of altered coupling of Ras guanine nucleotide exchange factor hSos to adapter protein Grb2 in lupus T cells

The integrity of the Ras/Raf/mitogen-activated protein kinase (MAPK) cascade is critical for maintenance of T cell tolerance, a process that fails in patients with systemic lupus erythematosus (SLE). In this study we have examined the activity of mitogen-activated protein kinases ERK-1 and ERK-2 in resting and TCR-activated peripheral blood T lymphocytes from patients with SLE. We also examined the binding of Ras guanine nucleotide exchange factor, human Son of Sevenless (hSos), to cytosolic adapter protein growth factor receptor-bound protein 2. T cells from lupus patients showed diminished catalytic activity and TCR-driven dual phosphorylation of ERK-1 and ERK-2 upon stimulation through the TCR/CD3 receptor, a defect that may be related to altered translocation of hSos to the Ras/Raf membrane complex and diminished nuclear translocation of trans-acting factor AP-1. Defective MAPK activity triggered by TCR/ CD3 activation may alter the coordination of signals needed for normal interleukin-2 production and maintenance of tolerance in lupus T cells.

Effect of trichostatin A on human T cells resembles signaling abnormalities in T cells of patients with systemic lupus erythematosus: a new mechanism for TCR zeta chain deficiency and abnormal signaling

Trichostatin A (TSA) is a potent reversible inhibitor of histone deacetylase, and it has been reported to have variable effects on the expression of a number of genes. In this report, we show that TSA suppresses the expression of the T cell receptor zeta chain gene, whereas, it upregulates the expression if its homologous gene Fc(epsilon) receptor I gamma chain. These effects are associated with decreased intracytoplasmic-free calcium responses and altered tyrosine phosphorylation pattern of cytosolic proteins. Along with these effects, we report that TSA suppresses the expression of the interleukin-2 gene. The effects of TSA on human T cells are predominantly immunosuppressive and reminiscent of the signaling aberrations that have been described in patients with systemic lupus erythematosus.

An update on genetic studies of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex, multifactorial autoimmune disease. Genetic factors are thought to contribute to its pathogenesis. There have been numerous recent advances in the study of murine and human lupus genetics. In well-defined experimental transgenic or gene-knockout mouse models, the development of lupus-like disease has implicated specific genes and pathways in the disease pathogenesis. Linkage analyses have mapped multiple susceptibility loci and disease suppressive loci using inbred strains of mice that spontaneously develop lupus-like disease. Elegant genetic dissection and function studies have led to the recent identification of two murine candidate susceptibility genes, Ifi202 (encoding an interferon-inducible protein) and Cr2 (encoding complement receptors 1 and 2). In human lupus, case- control studies have established associations of SLE with certain major histocompatibility class II alleles, complement deficiencies, and polymorphisms of Fc gamma receptor genes, a complement-related gene, and cytokine genes. During the past several years, linkage analyses using SLE multiplex families have provided many chromosomal regions for further exploration of susceptibility genes. Six regions exhibiting significant linkage to SLE are promising. Studies are underway to fine map these linked regions and to identify the genes in the susceptibility regions. An understanding of the genes involved in the development of lupus should provide targets for more focused therapy in lupus.

Defective expression and tyrosine phosphorylation of the T cell receptor zeta chain in peripheral blood T cells from systemic lupus erythematosus patients

We have reported that tyrosine phosphorylation and expression of the T cell receptor zeta chain (TCR zeta) was decreased in two systemic lupus erythematosus (SLE) patients with an abnormal TCR zeta lacking exon-7. To examine further the TCR zeta defect and any possible relationship with specific clinical features, we studied the expression of TCR zeta in peripheral blood T cells from 44 patients with SLE, 53 with other rheumatic diseases (30 rheumatoid arthritis (RA), 11 systemic sclerosis (SSc) and 12 primary Sjögren's syndrome(SjS)) and 39 healthy individuals. Flow cytometric analysis demonstrated a significant decrease in the expression of TCR zeta in SLE (P < 0.001), but not in the other rheumatic diseases. Immunoprecipitation experiments confirmed that the expression of TCR zeta in SLE T cells was decreased dramatically (normal: 111.4 +/- 22.6%, SLE: 51.6 +/- 37.4%, P < 0.0001). The decrease in TCR zeta did not correlate with disease activity, or with the dose of prednisolone (PSL). There were, however, three SLE patients in whom the level of TCR zeta expression normalized after treatment, suggesting that mechanisms responsible for the TCR zeta defect appear to be heterogeneous. These results confirm the defective expression and altered tyrosine phosphorylation of TCR zeta in a large proportion of SLE patients, suggesting that it may play an important role in T cell dysfunction in SLE.

Abnormal expression of various molecular forms and distribution of T cell receptor zeta chain in patients with systemic lupus erythematosus

OBJECTIVE

T cells from the majority of patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain expression. The TCR zeta chain, a critical signaling molecule, exists in multiple molecular forms and membrane fractions with distinct functions in antigen-mediated signaling processes. This study was undertaken to investigate the complete spectrum of expression of the different forms and distribution of the TCR zeta chain in SLE T cells.

METHODS

T cells were isolated from 48 SLE patients and 21 healthy subjects. The expression of various forms of the TCR zeta chain was investigated by immunoblotting with specific antibodies. The lipid raft-associated form of the zeta chain was determined by quantitating the solubilized zeta chain after disruption of the lipid rafts by cholesterol depletion using methyl-betacyclodextrin. The distribution of the zeta chain was investigated by fluorescence microscopy.

RESULTS

The phosphorylated 21- and 23-kd forms and the detergent-insoluble membrane-associated form of the TCR zeta chain and alternatively spliced zeta chain were significantly decreased in SLE T cells. In contrast, major ubiquitinated forms of the zeta chain were increased in these cells. We also identified up-regulation of a novel 14-kd form of the zeta chain in SLE T cells. Resting SLE T cell membranes had an increased percentage of the residual membrane-bound zeta chain in the lipid rafts. Fluorescence microscopy findings indicated that the residual zeta chain is more clustered on the cell membranes of SLE T cells.

CONCLUSION

These results suggest that, in addition to the 16-kd form, expression of other molecular forms and fractions of the TCR zeta chain as well as its membrane distribution are abnormal in SLE T cells. Increased lipid raft association and surface clustering of the zeta chain may explain the molecular mechanisms underlying the signaling abnormalities in these cells.

Comparative study on the effect of phosphorylated TCR zeta chain ITAM sequences on early activation events in Jurkat T cells

One of the main dilemma in T cell receptor (TCR) signal transduction is whether the presence of multiple Immunoreceptor Tyrosine-based Activation Motifs (ITAMs) within the TCR signaling module serves for signal amplification or signal distribution. To contribute to answer this question, we analyzed the effect of synthetic oligopeptides representing the three bi-phosphorylated zeta chain-ITAMs on the early signaling events in permeabilized leukemia T cells. Our main observations were as follows: 1/Stimulation of the cells with the bi-phosphorylated membrane proximal and central ITAMs (zeta (1)y(p)y(p) and zeta (2)y(p)y(p), respectively) resulted in a strong phosphorylation of proteins with a similar pattern. In contrast, the membrane distal ITAM, zeta (3)y(p)y(p) had a reduced ability to promote tyrosine phosphorylation and failed to induce the phosphorylation of a number of proteins. 2/ The phospho-peptide induced tyrosine phosphorylation events were at least partially mediated by p56(lck) and Syk/ZAP70 protein tyrosine kinases as it was shown in p56(lck) and Syk/ZAP70 deficient Jurkat variants. 3/The patterns of the association of the adaptor protein, Grb2 with tyrosine phosphorylated proteins following cell stimulation with the bi-phosphorylated membrane proximal or the central ITAMs were similar, while the membrane distal ITAM was unable to induce any of these associations. Our data provide additional evidence that the three zetaITAMs differ in their capacity to induce tyrosine phosphorylation of intracellular proteins in permeabilized T cells, depending to their primary sequence. The first and second ITAM sequences of the zeta chain may have similar but not totally overlapping functions. This conclusion results from their similar but not identical abilities to induce tyrosine phosphorylation and association of Grb-2 with intracellular phosphoproteins. In contrast, the third ITAM (zeta3) may have distinct functions since this peptide fails to induce tyrosine phosphorylation of a number of proteins compared to the other two ITAMs, and it is unable to induce either new association or the increase in the amount of Grb-2 associated phosphoproteins.

B cell receptor signaling and autoimmunity

The immune receptors of lymphocytes are able to sense the nature of bound ligands. Through coupled signaling pathways the generated signals are appropriately delivered to the intracellular machinery, allowing specific functional responses. A central issue in contemporary immunology is how the fate of B lymphocytes is determined at the successive developmental stages and how the B cell receptor distinguishes between signals that induce immune response or tolerance. Experiments with mice expressing transgenes or lacking signal transduction molecules that lead to abnormal lymphocyte development and/or response are providing important clues to the mechanisms that regulate signaling thresholds at different developmental stages. The studies are also revealing novel potential mechanisms of induction of autoimmunity, which may have a bearing on the understanding of human diseases.

Fc epsilon receptor type I gamma chain replaces the deficient T cell receptor zeta chain in T cells of patients with systemic lupus erythematosus

OBJECTIVE

T cells from the majority of patients with systemic lupus erythematosus (SLE) express significantly lower levels of T cell receptor zeta chain, a critical signaling molecule. However, TCR/CD3 triggering of SLE T cells shows increased phosphorylation of downstream signaling intermediates and increased [Ca2+]i response, suggesting the presence of alternative signaling mechanisms. We investigated whether Fcepsilon receptor type I gamma chain (FcepsilonRIgamma) could substitute for TCR zeta chain and contribute to T cell signaling in SLE.

METHODS

T cells were purified from the peripheral blood of 21 patients with SLE and 5 healthy volunteers. The expression of FcepsilonRIgamma was investigated using immunoblotting, reverse transcriptase-polymerase chain reaction, and flow cytometry methods. Involvement of the FcepsilonRIgamma in T cell signaling was studied by immunoprecipitation and/or immunoblotting after TCR/CD3 stimulation.

RESULTS

Western blotting and densitometric analysis showed that the expression of FcepsilonRIgamma in SLE T cells was 4.3-fold higher than in normal T cells (P < 0.001). Flow cytometric analyses of T lymphocyte subsets revealed that the proportions of FcepsilonRIgamma+,CD3+, FcepsilonRIgamma+,CD4+, and FcepsilonRIgamma+, CD8+ cells were significantly greater in SLE patients than in healthy controls (P < 0.001). Immunoprecipitation of SLE T cell lysates with an anti-FcepsilonRIgamma antibody showed that FcepsilonRIgamma associates with the tyrosine kinase Syk and the CD3epsilon chain, suggesting that FcepsilonRIgamma is functionally involved in TCR signaling.

CONCLUSION

These results demonstrate that the FcepsilonRIgamma chain is expressed at high levels in a large proportion of SLE T cells. The increased expression of FcepsilonRIgamma chain in SLE T cells may account in part for the aberrant antigen receptor-initiated signaling and contribute to the diverse cellular abnormalities found in this disease.

Genetics and systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex, multifactorial autoimmune disease. Genetic factors are believed to contribute to its pathogenesis. There have been numerous recent advances in the study of murine and human lupus genetics. In well-defined, experimental, transgenic or gene-knockout mouse models, the development of lupus-like disease has implicated specific genes and pathways in the disease pathogenesis. Linkage analyses have mapped multiple susceptibility loci and disease suppressive loci using inbred strains of mice that spontaneously develop lupus-like disease. Elegant genetic dissection has demonstrated that a component phenotype of SLE is displayed by each congenic strain carrying a single susceptibility locus on a resistant genetic background, whereas polycongenic strains exhibit fatal lupus nephritis. These studies suggest that genes in separate pathways can interact to augment or suppress the initiation and progression of systemic autoimmunity. In association studies of human lupus, the contributions of the MHC loci, Fcg receptors, various cytokines, components of the complement cascade, and proteins involved in apoptosis have been explored. Most recently, linkage analyses have been performed and provide many chromosomal regions for further exploration for susceptibility genes. Studies to identify the genes in the susceptibility regions are underway. An understanding of the genes involved in the development of lupus should provide targets for more focused therapy in lupus.

T cell signaling abnormalities in systemic lupus erythematosus are associated with increased mutations/polymorphisms and splice variants of T cell receptor zeta chain messenger RNA

OBJECTIVE

T cells from patients with systemic lupus erythematosus (SLE) display antigen receptor-mediated signaling aberrations associated with defective T cell receptor (TCR) zeta chain protein and messenger RNA (mRNA) expression. This study was undertaken to explore the possibility that coding-region mutations/polymorphisms of the TCR zeta chain could account for its decreased expression and altered signaling in SLE T cells.

METHODS

TCR zeta chain mRNA from 48 SLE patients, 18 disease controls, and 21 healthy volunteers was reverse transcribed, amplified by polymerase chain reaction, and cloned, and complementary DNA (cDNA) was sequenced. DNA sequences from multiple clones were analyzed for silent single-nucleotide polymorphisms, mutations, and splice variations, to promote the identification of heterozygosity.

RESULTS

DNA sequence analysis revealed several widely distributed missense mutations and silent polymorphisms in the coding region of the TCR zeta chain, which were more frequent in SLE patients than in patients with other rheumatic diseases or healthy controls (P < 0.0001). Several of the missense mutations were located in the 3 immunoreceptor tyrosine activation motifs or the GTP binding domain, and this could lead to functional alterations in the TCR zeta chain. A splice variant of the TCR zeta chain with a codon CAG (glutamine) insertion between exons IV and V was found in half of the SLE and control samples. Two larger spliced isoforms of the TCR zeta chain, with an insertion of 145 bases and 93 bases between exons I and II, were found only in SLE T cells. We also identified various alternatively spliced forms of the TCR zeta chain resulting from the deletion of individual exons II, VI, or VII, or a combined deletion of exons V and VI; VI and VII; II, III, and IV; or V, VI, and VII in SLE T cells. The frequency of the deletion splice variants was significantly higher in SLE than in control samples (P = 0.004). These variations were observed in cDNA and may not reflect the status of the genomic DNA.

CONCLUSION

These findings demonstrate that heterogeneous mutations/polymorphisms and alternative splicing of TCR zeta chain cDNA are more frequent in SLE T cells than in T cells from non-SLE subjects and may underlie the molecular basis of known T cell signaling abnormalities in this disease.

A possible pathogenic role of CD8+ T cells and their derived cytokine, IL-16, in SLE

Current investigations into the role of CD8+ T cells and their derived cytokine, interleukin (IL)-16, in the induction of CD4+ T cell abnormalities in systemic lupus erythematosus (SLE) were reviewed and discussed on the basis of results mainly obtained in our laboratory.

Expression of B cell receptor-associated signaling molecules in human lupus

B cell receptor (BcR) signaling requires a tight regulation of several protein tyrosine kinases and phosphatases, and associated co-receptors. Mounting evidence indicates that abnormal BcR signaling, such as occurs in SHP-1 and Lyn-deficient mice, results in production of pathogenic autoantibodies and lupus-like glomerulonephritis, suggesting that altered signaling thresholds could underlie the development of systemic autoimmunity. To test this hypothesis, we investigated expression of BcR-associated signaling molecules in lymphocytes from patients with systemic lupus erythematosus (SLE) during inactive phases of the disease. We found that the transmembrane regulatory protein tyrosine phosphatase CD45 is expressed at abnormal levels. Strikingly, this reduction persisted during four months of follow-up. By contrast, despite its potent role as a regulator of thymus-independent immune responses and of B cell life span, the CD22 co-receptor is expressed at normal levels in B lymphocytes isolated ex vivo from SLE patients. We also noted unusual levels of the cytosolic protein tyrosine kinase Lyn and the protein tyrosine phosphatase SHP-1 in the lymphocytes of the patients. Since in normal B cells Lyn and SHP-1 act in concert within a common negative pathway in which CD45 counteracts SHP-I regulatory role, we propose that this feedback regulatory pathway is crippled to different degrees in human SLE B cells. Break of the balance between positive and negative signaling molecules likely modifies the BcR signaling thresholds. Such alterations, together with other factors, may contribute to the disruption of self-tolerance in this disease.