Adenovirus 5 E1A Interacts with E4orf3 To Regulate Viral Chromatin Organization

Abstract

Human adenovirus expresses several early proteins that control various aspects of the viral replication program, including an orchestrated expression of viral genes. Two of the earliest viral transcriptional units activated after viral genome entry into the host cell nucleus are the E1 and E4 units, which each express a variety of proteins. Chief among these are the E1A proteins that function to reprogram the host cell and activate transcription of all other viral genes. The E4 gene encodes multiple proteins, including E4orf3, which functions to disrupt cellular antiviral defenses, including the DNA damage response pathway and activation of antiviral genes. Here we report that E1A directly interacts with E4orf3 via the conserved N terminus of E1A to regulate the expression of viral genes. We show that E4orf3 indiscriminately drives high nucleosomal density of viral genomes, which is restrictive to viral gene expression and which E1A overcomes via a direct interaction with E4orf3. We also show that during infection E1A colocalizes with E4orf3 to nuclear tracks that are associated with heterochromatin formation. The inability of E1A to interact with E4orf3 has a significant negative impact on overall viral replication, the ability of the virus to reprogram the host cell, and the levels of viral gene expression. Together these results show that E1A and E4orf3 work together to fine-tune the viral replication program during the course of infection and highlight a novel mechanism that regulates viral gene expression.IMPORTANCE To successfully replicate, human adenovirus needs to carry out a rapid yet ordered transcriptional program that executes and drives viral replication. Early in infection, the viral E1A proteins are the key activators and regulators of viral transcription. Here we report, for the first time, that E1A works together with E4orf3 to perfect the viral transcriptional program and identify a novel mechanism by which the virus can adjust viral gene expression by modifying its genome's nucleosomal organization via cooperation between E1A and E4orf3.

Keywords: E1A; E4orf3; adenovirus; chromatin; histone.