Identification of distinct regions of 5' flanking DNA that mediate constitutive, IFN-gamma, STAT1, and TGF-beta-regulated expression of the class II transactivator gene.
Class II transactivator (CIITA) is a master regulator required for constitutive and IFN-gamma-inducible expression of class II MHC genes. Although the role of CIITA is greatly appreciated, the mechanisms underlying constitutive and IFN-gamma-induced expression of CIITA are not understood. The study of CIITA induction is extremely important, but has been fraught with difficulty. This study describes for the first time a large (7-kb) fragment of 5' flanking sequences that mediates the B cell-specific, IFN-gamma-induced, and TGF-beta-suppressed expression of CIITA. This pattern of expression matches the authentic expression of the endogenous gene. Within the 7-kb fragment, sequences that lie between nucleotides -545 and -113 relative to the transcriptional start site are critical for constitutive promoter expression in B cells. In contrast, inducible activation of CIITA by IFN-gamma requires sequences contained in an additional 4 kb of upstream DNA. This region mediates an IFN-gamma response when linked to either the endogenous CIITA promoter or a heterologous promoter. A role for STAT1 in regulation of the CIITA promoter is shown by the rescue of IFN-gamma induction by expression of STAT1 in STAT1-defective U3A cells. TGF-beta significantly inhibits IFN-gamma-mediated induction of the CIITA promoter in 2fTGH fibroblasts, which indicates that the promoter is a target for TGF-beta. This inhibition is achieved by suppression of the basal promoter. This study provides a focal point for understanding the mechanism of B cell-specific, IFN-gamma-induced, and TGF-beta-suppressed expression of CIITA.
Piskurich
J F
JF
University of North Carolina Lineberger Comprehensive Cancer Center, Department of Microbiology-Immunology, University of North Carolina at Chapel Hill, 27599, USA.
Wang
Y
Y
Linhoff
M W
MW
White
L C
LC
Ting
J P
JP
D001402:B-Lymphocytes / Q000502:physiology; D001483:Base Sequence; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D007371:Interferon-gamma / Q000502:physiology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000235:genetics* / Q000502:physiology*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000502:physiology*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D012333:RNA, Messenger; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D007371:Interferon-gamma