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pubmed:abstractText |
The human major histocompatibility complex (MHC) class Ib gene, HLA-E, codes for the major ligand of the inhibitory receptor NK-G-2A, which is present on most natural killer (NK) cells and some CD8(+) cytotoxic T lymphocytes. We have previously shown that gamma interferon (IFN-gamma) induction of HLA-E gene transcription is mediated through a distinct IFN-gamma-responsive element, the IFN response region (IRR), in all cell types studied. We have now identified and characterized a cell type-restricted enhancer of IFN-gamma-mediated induction of HLA-E gene transcription, designated the upstream interferon response region (UIRR), which is located immediately upstream of the IRR. The UIRR mediates a three- to eightfold enhancement of IFN-gamma induction of HLA-E transcription in some cell lines but not in others, and it functions only in the presence of an adjacent IRR. The UIRR contains a variant GATA binding site (AGATAC) that is critical to both IFN-gamma responsiveness and to the formation of a specific binding complex containing GATA-1 in K562 cell nuclear extracts. The binding of GATA-1 to this site in response to IFN-gamma was confirmed in vivo in a chromatin immunoprecipitation assay. Forced expression of GATA-1 in nonexpressing U937 cells resulted in a four- to fivefold enhancement of the IFN-gamma response from HLA-E promoter constructs containing a wild-type but not a GATA-1 mutant UIRR sequence and increased the IFN-gamma response of the endogenous HLA-E gene. Knockdown of GATA-1 expression in K562 cells resulted in a approximately 4-fold decrease in the IFN-gamma response of the endogenous HLA-E gene, consistent with loss of the increase in IFN-gamma response of HLA-E promoter-driven constructs containing the UIRR in wild-type K562 cells. Coexpression of wild-type and mutant adenovirus E1a proteins that sequester p300/CBP eliminated IFN-gamma-mediated enhancement through the UIRR, but only partially reduced induction through the IRR, implicating p300/CBP binding to Stat-1alpha at the IRR in the recruitment of GATA-1 to mediate the cooperation between the UIRR and IRR. We propose that the GATA-1 transcription factor represents a cell type-restricted mediator of IFN-gamma induction of the HLA-E gene.
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