Correction of accelerated autoimmune disease by early replacement of the mutated lpr gene with the normal Fas apoptosis gene in the T cells of transgenic MRL-lpr/lpr mice

Wild-type human p53 and a temperature-sensitive mutant induce Fas/APO-1 expression

Fas/APO-1 is a cell surface protein known to trigger apoptosis upon specific antibody engagement. Because wild-type p53 can activate transcription as well as induce apoptosis, we queried whether p53 might upregulate Fas/APO-1. To explore this possibility, we examined human p53-null (H358 non-small-cell lung adenocarcinoma and K562 erythroleukemia) and wild-type p53-containing (H460 non-small-cell lung adenocarcinoma) cell lines. When H358 or H460 cells were transduced with a replication-deficient adenovirus expression construct containing the human wild-type p53 gene but not with vector alone, a marked upregulation (approximately a three-to fourfold increase) of cell surface Fas/APO-1 was observed by flow cytometry. Similarly, K562, cells stably transfected with a plasmid vector containing the temperature-sensitive human p53 mutant Ala-143 demonstrated a four- to sixfold upregulation of Fas/APO-1 by flow-cytometric analysis at the permissive temperature of 32.5 degrees C. Temperature-sensitive upregulation of Fas/APO-1 in K562 Ala-143 cells was verified by immunoprecipitation and demonstrated to result from enhanced mRNA production by nuclear run-on and Northern (RNA) analyses. Stably transfected K562 cells expressing temperature-insensitive, transcriptionally inactive p53 mutants (His-175, Trp-248, His-273, or Gly-281) failed to upregulate Fas/APO-1 at either 32.5 degrees or 37.5 degrees C. The temperature-sensitive transcription of Fas/APO-1 occurred in the presence of cycloheximide, indicating that de novo protein synthesis was not required and suggested a direct involvement of p53. Collectively, these observations argue that Fas/APO-1 is a target gene for transcriptional activation by p53.

The Fas death factor

Fas ligand (FasL), a cell surface molecule belonging to the tumor necrosis factor family, binds to its receptor Fas, thus inducing apoptosis of Fas-bearing cells. Various cells express Fas, whereas FasL is expressed predominantly in activated T cells. In the immune system, Fas and FasL are involved in down-regulation of immune reactions as well as in T cell-mediated cytotoxicity. Malfunction of the Fas system causes lymphoproliferative disorders and accelerates autoimmune diseases, whereas its exacerbation may cause tissue destruction.

The basis of autoimmunity: Part II. Genetic predisposition

In Part II of his review of the basis of autoimmunity, Argyrios N. Theofilopoulos summarizes current knowledge on the genetic factors that contribute to autoimmune disease predisposition. The findings indicate that multiple genes contribute to the induction of pathogenic autoimmunity, and that no single genetic abnormality is sufficient in itself to induce disease. The definition of these genetically complex diseases is about to be revolutionized by the development of genome scanning approaches, such as dense chromosomal maps based on polymorphic microsatellite DNA and other informative markers. These will allow the loci and genes that predispose to these diseases to be identified broadly.

Autoimmunity, apoptosis defects and retroviruses

Autoimmunity and AIDS both share the common feature of increased expression of retroviral protein products and abnormal apoptosis of immune cells (81). This leads to a more global immunomodulatory defect (82-84). The challenge in the future will be to devise compounds that can either regulate the effect of the retroviral products on apoptosis, or that can inhibit apoptosis pathways in order to restore normal immune system function.

Curing lupus--views from the foothills

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Autoimmune disease. A problem of defective apoptosis

Human autoimmune diseases share the common feature of an imbalance between the production and destruction of various cell types including lymphocytes (SLE), synovial cells (RA), and fibroblasts (scleroderma). Patients with SLE have increased levels of soluble Fas that inhibit proper apoptosis of lymphocytes. In animal models of autoimmune diseases, mutations of genes involved in apoptosis including Fas, Fas ligand, and the hematopoietic cell phosphatase gene have been identified. Oncogenes, including bcl-2, p53, and myc, that regulate apoptosis are also expressed abnormally. Potent inducers of apoptosis including steroids, azathioprine, cyclophosphamide, and methotrexate are the most efficacious therapies for autoimmune disease currently known. Specific therapies that induce apoptosis without incurring side effects should improve treatment of autoimmune disease.

Apoptosis defects analyzed in TcR transgenic and fas transgenic lpr mice

Although autoreactive T cells are thought to play a prominent role in autoimmune disease in MRL-lpr/lpr mice, it has been difficult to directly determine if autoreactive T cells escape from the thymus and react with self-antigens in the periphery. Defective expression of the Fas apoptosis antigen in MRL-lpr/lpr mice results from the insertion of the ETn retrotransposon. The fas defect can be partially corrected in CD2-fas transgenic mice in which the expression of fas is corrected in T cells. To identify a possible defect in clonal deletion or clonal anergy induction of auto-specific T cells, we have studied C57BL/6-lpr/lpr transgenic mice that express TcR genes that recognize a known self-antigen, the male H-Y antigen. In addition, we have analyzed clonal deletion and tolerance induction after neonatal tolerance induction and superantigen-induced arthritis with the class II MHC reactive superantigen staphylococcal enterotoxin B (SEB) in V beta 8 TcR transgenic and non-transgenic MRL-lpr/lpr mice. Neonatal tolerance induction to SEB was normal in lpr/lpr mice. However, over time a loss of tolerance (thymic or peripheral) was observed in lpr/lpr mice but not in +/+ TcR transgenic mice. This defect in lpr/lpr mice was thymic-dependent and was due to increased CD28/CTLA4 signaling. These results suggest that an apoptosis defect involving both thymocytes and peripheral lymphoid cells leads to autoimmune disease in lpr/lpr mice. The challenge in the future will be to determine the role of defective apoptosis in other autoimmune diseases.