Autorepression of the Human Cytomegalovirus Major Immediate-Early Promoter/Enhancer at Late Times of Infection Is Mediated by the Recruitment of Chromatin Remodeling Enzymes by IE86

Abstract

The human cytomegalovirus major immediate-early protein IE86 is pivotal for coordinated regulation of viral gene expression throughout infection. A relatively promiscuous transactivator of viral early and late gene transcription, IE86 also acts during infection to negatively regulate its own promoter via direct binding to a 14-bp palindromic IE86-binding site, the cis repression sequence (crs), located between the major immediate-early promoter (MIEP) TATA box and the start of transcription. Although such autoregulation does not involve changes in the binding of basal transcription factors to the MIEP in vitro, it does appear to involve selective inhibition of RNA polymerase II recruitment. However, how this occurs is unclear. We show that autorepression by IE86 at late times of infection correlates with changes in chromatin structure around the MIEP during the course of infection and that this is likely to result from physical and functional interactions between IE86 and chromatin remodeling enzymes normally associated with transcriptional repression of cellular promoters. Firstly, we show that IE86-mediated autorepression is inhibited by histone deacetylase inhibitors. We also show that IE86 interacts, in vitro and in vivo, with the histone deacetylase HDAC1 and histone methyltransferases G9a and Suvar(3-9)H1 and that coexpression of these chromatin remodeling enzymes with IE86 increases autorepression of the MIEP. Finally, we show that mutation of the crs in the context of the virus abrogates the transcriptionally repressive chromatin phenotype normally found around the MIEP at late times of infection, suggesting that negative autoregulation by IE86 results, at least in part, from IE86-mediated changes in chromatin structure of the viral MIEP.