Browsing by Subject "SMC5/6"

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    The Eukaryotic SMC5/6 Complex Represses the Replicative Program of High-Risk Human Papillomavirus
    (2020-10) Gibson, Ryan Taylor; Androphy, Elliot; Guo, Haitao; Yu, Andy; Mayo, Lindsey
    Human papillomaviruses (HPVs) are non-enveloped, circular double-stranded DNA viruses that infect basal keratinocytes of stratified squamous epithelia. High-risk HPV (HR-HPV) infection causes nearly all cervical cancers and an increasing number of head and neck cancers. While prophylactic vaccinations have reduced the incidence of HPV infection and attributable cancers, currently there is no cure for pre-existing HPV infection. As such, HPV remains a global health threat and a better understanding of HPV biology remains of significant medical importance for identification of novel therapeutic targets. The multi-subunit structural maintenance of chromosomes 5/6 complex (SMC5/6) is comprised of SMC5, SMC6 and NSE1-4. SMC5/6 is essential for homologous recombination DNA repair and reportedly functions as an antiviral factor during hepatitis B and herpes simplex-1 viral infections. Intriguingly, SMC5/6 has been found to associate with HR-HPV E2 proteins, which are multifunctional transcription factors essential to regulation of viral replication and transcription. The function of SMC5/6 associations with E2, as well as its role during HR-HPV infection remain unclear and we explored this question in the context of HR-HPV- 31. SMC6 interacted with HPV-31 E2 and co-immunoprecipitation of SMC6/E2 complexes required the E2 transactivation domain, inferring SMC6 association is limited to the full-length E2 isoform. Depletion of SMC6 and NSE3 increased HPV replication and transcription in keratinocytes stably maintaining episomal HPV-31, suggesting that the SMC5/6 complex represses these processes. Neither SMC6 nor NSE3 co-IP the viral E1 DNA helicase alone or E1/E2 complexes but the association of SMC6 with E2 was reduced in the presence of E1, indicating that SMC6 competes with E1 for E2 binding. This infers that SMC6 repression of the viral replicative program may involve inhibiting initiation of viral replication by disrupting E2 interactions with E1. Chromatin immunoprecipitation determined that SMC6 is present on episomal HPV-31 genomes, alluding to a possible role for SMC5/6 in modifying the chromatin state of viral DNA. Taken together, these findings describe a novel function for SMC5/6 as a repressor of the HPV-31 replicative program.
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    The SMC5/6 Complex Represses the Replicative Program of High-Risk Human Papillomavirus Type 31
    (MDPI, 2020-09) Gibson, Ryan T.; Androphy, Elliot J.; Microbiology and Immunology, School of Medicine
    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.