HPV replication regulation by acetylation of a conserved lysine in the E2 protein

Abstract

Papillomaviruses (PVs) are non-enveloped DNA viruses that are the primary etiological agents of cervical and oropharyngeal cancers. Vaccines for H(human)PV have proven to be effective prophylactic treatments; however, there is no treatment available for those currently infected. To develop new therapies, we require a clear understanding of viral pathogenesis and regulation. The Papillomavirus E2 protein is a sequence specific DNA binding protein that recruits cellular factors to its genome in infected epithelial cells. E2 also binds to and loads the viral E1 DNA helicase at the origin of replication. Post-translational modifications of PV E2 have been identified as potential regulators of E2 functions. We recently reported lysine (K) 111 as a target of p300 acetylation in B(bovine)PV that is involved in the regulation of viral transcription. K111 is conserved in most papillomaviruses, so we pursued a mutational approach to query the functional significance of lysine in HPV E2. Amino acid substitutions that prevent acetylation, including arginine, were unable to stimulate transcription and E1 mediated DNA replication. The arginine K111 mutant retained E2 transcriptional repression, nuclear localization, DNA and chromatin binding, and association with E2 binding partners involved in PV transcription and replication. When directly investigating origin unwinding, the replication defective E2 K111R mutant recruited E1 to the viral replication origin, but surprisingly, unwinding of the duplex DNA did not occur. In contrast, the glutamine K111 mutant increased origin melting and stimulated replication compared to wild type E2. We have identified Topoisomerase I as a key host factor involved in viral replication whose recruitment is dependent on K111 acetylation, and propose a new model for viral origin dynamics during replication initiation. This work reveals a novel activity of E2 necessary for denaturing the viral origin that likely depends on acetylation of highly conserved lysine 111.