Role of Chromatin Structure in Regulating MHC Class I Expression

Division Of Basic Sciences - Nci

Investigators

Abstract

To examine the role of chromatin in transcriptional regulation of the MHC class I gene, we determined nucleosome occupancy and positioning, histone modifications and H2A.Z occupancy across its regulatory region in murine tissues that have widely different expression levels. Surprisingly, nucleosome occupancy and positioning were indistinguishable between spleen, kidney and brain. In all three tissues, the 200 bp upstream of the transcription start site had low nucleosome occupancy. In contrast, nuclease hypersensitivity, histone modifications and H2A.Z occupancy, showed tissue-specific differences. Thus, tissue-specific differences in MHC class I transcription correlate with histone modifications, not nucleosomal organization. Further, activation of class I transcription by -Interferon or its inhibition by alpha-amanitin did not alter nucleosome occupancy, positioning, nuclease hypersensitivity, histone modifications or H2A.Z occupancy in any of the tissues examined. Thus, chromatin remodeling was not required to dynamically modulate transcriptional levels. These findings suggest that the MHC class I promoter remains poised and accessible to rapidly respond to infection and environmental cues.