Viral Retasking of hBre1/RNF20 to Recruit hPaf1 for Transcriptional Activation

Abstract

Upon infection, human adenovirus (HAdV) must activate the expression of its early genes to reprogram the cellular environment to support virus replication. This activation is orchestrated in large part by the first HAdV gene expressed during infection, early region 1A (E1A). E1A binds and appropriates components of the cellular transcriptional machinery to modulate cellular gene transcription and activate viral early genes transcription. Previously, we identified hBre1/RNF20 as a target for E1A. The interaction between E1A and hBre1 antagonizes the innate antiviral response by blocking H2B monoubiquitination, a chromatin modification necessary for the interferon (IFN) response. Here, we describe a second distinct role for the interaction of E1A with hBre1 in transcriptional activation of HAdV early genes. Furthermore, we show that E1A changes the function of hBre1 from a ubiquitin ligase involved in substrate selection to a scaffold which recruits hPaf1 as a means to stimulate transcription and transcription-coupled histone modifications. By using hBre1 to recruit hPaf1, E1A is able to optimally activate viral early transcription and begin the cycle of viral replication. The ability of E1A to target hBre1 to simultaneously repress cellular IFN dependent transcription while activating viral transcription, represents an elegant example of the incredible economy of action accomplished by a viral regulatory protein through a single protein interaction.

Adenovirus E1A Recruits the Human Paf1 Complex To Enhance Transcriptional Elongation

“…and E4 genes. This agrees with our previous work showing that transcription of E2e, E3, and E4 was substantially reduced by hPaf1 knockdown (6). hPaf1 knockdown reduces RNA pol II occupancy at the 3= ends of the HAdV E2e, E3, and E4 genes.…”

“…Previously, hPaf1 was shown to be recruited to HAdV early genes by hBre1 and E1A (6). We first confirmed the ability of E1A to interact physically with hPaf1 via coimmunoprecipitation.…”

“…Our previous work showed that recruitment of the hPaf1 complex to HAdV genes required hBre1 (6). The hPaf1 complex comprises 6 subunits: Cdc73, Ctr9, Leo1, hPaf1, Rtf1, and Ski8 (17)(18)(19)(20).…”

“…The N terminus of E1A adapts the cellular ubiquitin ligase hBre1 to recruit hPaf1 to the viral genome, and this is required for efficient transcription of the viral E2, E3, and E4 genes but not for that of the E1A or E1B gene (6). However, the role that the hPaf1 complex plays in enhancing viral transcription has not been established.…”

“…Through these interactions, E1A is able to bind to more than 17,000 human genomic promoters, resulting in cell cycle progression, dedifferentiation, and inhibition of the interferon response (3)(4)(5). As well as modulating cellular transcription, E1A is required for the transcription of the HAdV early genes (6)(7)(8)(9). HAdV early genes are activated through two regions of the E1A protein: CR3 and the N-terminal region, which includes CR1.…”