Abstract
The life cycle of HPV is tied to the differentiation status of its host cell, with productive replication, late gene expression and virion production restricted to the uppermost layers of the stratified epithelium. HPV DNA is histone-associated, exhibiting a chromatin structure similar to that of the host chromosome. Although HPV chromatin is subject to histone post-translational modifications, how the viral life cycle is epigenetically regulated is not well understood. SETD2 is a histone methyltransferase that places the trimethyl mark on H3K36 (H3K36me3), a mark of active transcription. Here, we define a role for SETD2 and H3K36me3 in the viral life cycle. We have found that HPV positive cells exhibit increased levels of SETD2, with SETD2 depletion leading to defects in productive viral replication and splicing of late viral RNAs. Reducing H3K36me3 by overexpression of KDM4A, an H3K36me3 demethylase, or an H3.3K36M transgene also blocks productive viral replication, indicating a significant role for this histone modification in facilitating viral processes. H3K36me3 is enriched on the 3’ end of the early region of the high-risk HPV31 genome in a SETD2-dependent manner, suggesting that SETD2 may regulate the viral life cycle through the recruitment of H3K36me3 readers to viral DNA. Intriguingly, we have found that activation of the ATM DNA damage kinase, which is required for productive viral replication, is necessary for the maintenance of H3K36me3 on viral chromatin and for processing of late viral RNAs. Additionally, we have found that the HPV31 E7 protein maintains the increased SETD2 levels in infected cells through an extension of protein half-life. Collectively, our findings highlight the importance of epigenetic modifications in driving the viral life cycle and identify a novel role for E7 as well as the DNA damage response in the regulation of viral processes through epigenetic modifications.
Highlights
Human papillomaviruses (HPVs) are small, circular, double-stranded DNA viruses that have a genome of approximately 8 kilobases
SETD2 places the trimethyl mark on H3K36 (H3K36me3) and we have found that SETD2 as well as H3K36me3 are necessary for productive viral replication and splicing of late viral RNAs upon epithelial differentiation
H3K36me3 is present on the HPV31 genome suggesting that SETD2 regulates viral processes through the recruitment of effector proteins to H3K36me3 on viral DNA
Summary
Human papillomaviruses (HPVs) are small, circular, double-stranded DNA viruses that have a genome of approximately 8 kilobases. More than 200 types of HPV have been identified and are categorized based on their dominant site of infection; either the cutaneous or mucosal epithelium [1]. Mucosal HPVs are further divided into high and low-risk types based on their potential to induce transformation [2]. The high-risk types, of which there are ~15, are the causative agents of cervical cancer [3]. High-risk HPV types are associated with other anogenital cancers, as well as an increasing number of head and neck cancers [4]. HPV-associated cancers are driven by the two main oncoproteins E6 and E7, which do not exhibit enzymatic function, but work primarily through protein-protein interactions, affecting cellular signaling pathways to provide a replication-competent environment [5, 6]
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