title: Varying functions of specific major histocompatibility class II transactivator promoter III and IV elements in melanoma cell lines.
abstract: Melanoma cells commonly express MHC class II molecules constitutively. This is a rare, or possibly unique, phenotype for a nonprofessional antigen-presenting cell, where MHC class II expression ordinarily occurs only after IFN-gamma treatment. Despite the fact that constitutive expression of MHC class II on melanoma cells has been observed for decades and that the regulation of the MHC class II genes is well understood for many different cell types, there is no data regarding the basis for constitutive MHC class II expression in melanoma cells. Here we report that MHC class II expression in melanoma cells can be traced to constitutive expression of the class II transactivator protein (CIITA), which mediates both IFN-gamma-inducible and -constitutive MHC class II expression in all other cell types. In addition, we determined that constitutive CIITA expression is the result of the activation of both the B cell-specific CIITA promoter III and the IFN-gamma-inducible CIITA promoter IV, the latter of which previously has never been known to function as a constitutive promoter in any cell type. The recently described B cell-related ARE-1 activity is important for promoter III activation in the melanoma cells. Constitutive promoter IV activation involves the IFN regulatory factor element (IRF-E), which binds members of the IRF family of proteins, although the major, IFN-gamma inducible member of this family, IRF-1, is not constitutively expressed in these cells. In cells with constitutively active promoter IV, the promoter IV IRF-E is most likely activated by IRF-2. The relevance of these results to the pathway of melanoma development is discussed.
authors: Department of Biochemistry and Molecular Biology, College of Medicine and Immunology Program, H. Lee Moffitt Cancer Center and Research Institute, University of South Florida, Tampa, Florida 33612, USA.
authors: B L
authors: BL
authors: Goodwin
authors: H
authors: H
authors: Xi
authors: R
authors: R
authors: Tejiram
authors: D D
authors: DD
authors: Eason
authors: N
authors: N
authors: Ghosh
authors: K L
authors: KL
authors: Wright
authors: U
authors: U
authors: Nagarajan
authors: J M
authors: JM
authors: Boss
authors: G
authors: G
authors: Blanck
mesh_terms: D004268:DNA-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D000949:Histocompatibility Antigens Class II; D051863:Host Cell Factor C1; D006801:Humans; D007371:Interferon-gamma / Q000378:metabolism / Q000494:pharmacology; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism; D008545:Melanoma; D009687:Nuclear Proteins; D050811:Octamer Transcription Factor-1; D011401:Promoter Regions, Genetic / Q000502:physiology*; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; D000949:Histocompatibility Antigens Class II; D051863:Host Cell Factor C1; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D007371:Interferon-gamma