title: c-Maf increases apoptosis in peripheral CD8 cells by transactivating Caspase 6.
abstract: In addition to transactivation of interleukin-4 (IL-4), cellular muscular aponeurotic fibrosarcoma (c-Maf) enhances CD4 cell apoptosis by limiting Bcl-2 expression. The CD8 cells also express c-Maf and peripheral CD8 cell numbers are reduced in c-Maf transgenic mice, suggesting that c-Maf may influence CD8 cell survival in a manner similar to CD4 cells. Here we confirm that, similar to CD4 cells, c-Maf enhances CD8 cell susceptibility to apoptosis induced by multiple stimuli, independent of IL-4. However, unlike CD4 cells, c-Maf enhancement of apoptosis is independent of Bcl-2, suggesting that c-Maf uses other mechanisms to regulate CD8 cell apoptosis. Real-time reverse transcription-polymerase chain reaction reveals that the pro-apoptotic gene Caspase 6 is upregulated in c-Maf transgenic CD8 cells, suggesting that Caspase 6 is a novel c-Maf target gene. Luciferase reporter assays and site-directed mutagenesis reveal a functional c-Maf recognition element (MARE) within the first intron of Caspase 6. Binding of c-Maf to the MARE site is detectable by chromatin immunoprecipitation using non-transgenic T-cell lysates, so c-Maf can interact with the Caspase 6 MARE site in normal T cells. Furthermore, caspase 6 activity is increased among CD8 cells from c-Maf transgenic mice following T-cell receptor engagement. As expected, activity of the downstream caspases 3 and 7 is also increased. Consistent with the ability of caspase 6 to participate in positive feedback loops, cytochrome c release and caspase 8 activation are also increased. Together these results indicated that c-Maf increases CD8 cell sensitivity to apoptotic stimuli, at least in part, by direct transactivation of Caspase 6, providing increased substrate for Caspase 6-dependent apoptosis pathways.
authors.affiliation: Department of Medical Microbiology, Southern Illinois University School of Medicine, Springfield, 62794, USA.
authors.forename: Siying
authors.initials: S
authors.lastname: Peng
authors.forename: Hailong
authors.initials: H
authors.lastname: Wu
authors.forename: Yin-Yuan
authors.initials: YY
authors.lastname: Mo
authors.forename: Kounosuke
authors.initials: K
authors.lastname: Watabe
authors.forename: Mary E
authors.initials: ME
authors.lastname: Pauza
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D053178:Caspase 6 / Q000235:genetics / Q000276:immunology*; D002478:Cells, Cultured; D015536:Down-Regulation / Q000276:immunology; D004789:Enzyme Activation / Q000276:immunology; D025461:Feedback, Physiological / Q000276:immunology; D015847:Interleukin-4 / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051257:Proto-Oncogene Proteins c-maf / Q000276:immunology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015533:Transcriptional Activation / Q000276:immunology
chemical_list: C495608:Maf protein, mouse; D019253:Proto-Oncogene Proteins c-bcl-2; D051257:Proto-Oncogene Proteins c-maf; D015847:Interleukin-4; D053178:Caspase 6