The SMC5/6 Complex Represses the Replicative Program of High-Risk Human Papillomavirus Type 31.

Ryan T Gibson,Elliot J Androphy

doi:10.3390/pathogens9100786

Ryan T Gibson, Elliot J Androphy

Open Access

https://doi.org/10.3390/pathogens9100786

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Abstract

The multi-subunit structural maintenance of chromosomes (SMC) 5/6 complex includes SMC6 and non-SMC element (NSE)3. SMC5/6 is essential for homologous recombination DNA repair and functions as an antiviral factor during hepatitis B (HBV) and herpes simplex-1 (HSV-1) viral infections. Intriguingly, SMC5/6 has been found to associate with high-risk human papillomavirus (HPV) E2 regulatory proteins, but the functions of this interaction and its role during HPV infection remain unclear. Here, we further characterize SMC5/6 interactions with HPV-31 E2 and its role in the HPV life cycle. Co-immunoprecipitation (co-IP) revealed that SMC6 interactions with HPV-31 E2 require the E2 transactivation domain, implying that SMC5/6 interacts with full-length E2. Using chromatin immunoprecipitation, we found that SMC6 is present on HPV-31 episomes at E2 binding sites. The depletion of SMC6 and NSE3 increased viral replication and transcription in keratinocytes maintaining episomal HPV-31, indicating that SMC5/6 restricts the viral replicative program. SMC6 interactions with E2 were reduced in the presence of HPV-31 E1, suggesting that SMC6 and E1 compete for E2 binding. Our findings demonstrate SMC5/6 functions as a repressor of the viral replicative program and this may involve inhibiting the initiation of viral replication.

Highlights

Human papillomaviruses (HPVs) are non-enveloped, circular double-stranded DNA viruses that infect basal keratinocytes of stratified squamous epithelia
We found that the depletion of SMC6 and NSE3 resulted in increased HPV-31 replication and transcription, suggesting that the SMC5/6 complex represses the replicative program of HPV-31
The SMC5/6 complex (Figure 1A) subunit SMC6 reportedly co-precipitates with several HPV E2 proteins [12,13,14], so we began our investigation by attempting to confirm this interaction with HPV-31 E2

Summary

Introduction

Human papillomaviruses (HPVs) are non-enveloped, circular double-stranded DNA viruses that infect basal keratinocytes of stratified squamous epithelia. The HPV genome is roughly eight kilobases in length, encoding for eight proteins essential for the viral life cycle that are classified as early (E1–E7) or late (L1 and L2), based upon their temporal expression during HPV infection. The HPV replicative program can be divided into three hypothetical phases: Establishment, maintenance, and amplification. During the initial establishment of infection, HPV E1 and E2 proteins, together with the host replicative machinery, replicate HPV genomes to low copy numbers in host cells. The HPV genome enters the maintenance phase, whereby viral genome copy numbers are maintained and replication occurs in synchrony with host cells. In the outer layers of the epithelium, the viral replicative program transitions from maintenance to amplification, whereupon viral genomes are replicated to thousands of copies per Pathogens 2020, 9, 786; doi:10.3390/pathogens9100786 www.mdpi.com/journal/pathogens

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