title: CIITA is silenced by epigenetic mechanisms that prevent the recruitment of transactivating factors in rhabdomyosarcoma cells.
abstract: Rhabdomyosarcomas (RMS) are highly malignant pediatric sarcomas. We have discovered that the gene encoding the major histocompatibilty complex class II transactivator, CIITA, is silenced in cells representing both major subtypes of RMS. Silencing of CIITA prevents the IFN-γ inducible expression of MHC class II genes in these cells. Overexpression of CIITA in these cells can restore MHC expression. We have found that IFN-γ signaling is intact in these cells, but pSTAT1 and IRF1 do not bind to the CIITA PIV promoter. The CIITA promoter is not hypermethylated in RD (ERMS) cells but does show a modestly enhanced methylation status in SJRH30 (ARMS) cells. We have found that histone acetylation, which normally increases on the CIITA PIV promoter following IFN-γ treatment, is blocked in both types of RMS cells. In RD cells, treatment with a histone deacetylase inhibitor (TSA) reverses the silencing of CIITA. In SJRH30 cells, treatment with DNA methyltransferase inhibitors and TSA cooperatively restores CIITA expression. Surprisingly, we have also shown that the expression of two components of the immunoproteasome, which are embedded in the class II locus, is stimulated by IFN-γ in certain RMS cells in the absence of stimulation by CIITA. CIITA overexpression can also activate the expression of these genes, indicating that the immunoproteasome genes LMP2 and LMP7 can be activated by both CIITA dependent and CIITA independent pathways.
authors: Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, Carbondale, IL, USA.
authors: Priya
authors: P
authors: Londhe
authors: Bo
authors: B
authors: Zhu
authors: Jinu
authors: J
authors: Abraham
authors: Charles
authors: C
authors: Keller
authors: Judith
authors: J
authors: Davie
mesh_terms: D000107:Acetylation; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D000077209:Decitabine; D044127:Epigenesis, Genetic; D005434:Flow Cytometry; D020869:Gene Expression Profiling; D020868:Gene Silencing; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007371:Interferon-gamma / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012208:Rhabdomyosarcoma / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
chemical_list: D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D015534:Trans-Activators; C012589:trichostatin A; D000077209:Decitabine; D007371:Interferon-gamma; D001374:Azacitidine