Beta HPV8 E6 Induces Micronuclei Formation and Promotes Chromothripsis

Abstract

Cutaneous beta genus human papillomaviruses ({beta}-HPV) are suspected to promote the development of non-melanoma skin cancer (NMSC) by destabilizing the host genome. Multiple studies have established the genome destabilizing capacities of {beta}-HPV proteins E6 and E7 as a co-factor with UV. However, the E6 protein from {beta}-HPV8 (HPV8 E6) induces tumors in mice without UV exposure. Here, we examined a UV-independent mechanism of HPV8 E6-induced genome destabilization. We showed that HPV8 E6 reduced the abundance of anaphase bridge resolving helicase, Bloom syndrome protein (BLM). The diminished BLM was associated with increased segregation errors and micronuclei. These HPV8 E6-induced micronuclei had disordered micronuclear envelopes yet retained replication and transcription competence. HPV8 E6 decreased antiproliferative responses to micronuclei and time-lapse imaging revealed HPV8 E6 promoted cells with micronuclei to complete mitosis. Finally, whole genome sequencing revealed that HPV8 E6 induced chromothripsis in 9 chromosomes. These data provide insight into mechanisms by which HPV8 E6-induces genome instability independent of UV exposure. ImportanceSome beta genus human papillomaviruses ({beta}-HPVs) may promote skin carcinogenesis by inducing mutations in the host genome. Supporting this, the E6 protein from {beta}-HPV8 (8E6) promotes skin cancer in mice with or without UV exposure. Many mechanisms by which 8E6 increases mutations caused by UV have been elucidated, but less is known about how 8E6 induces mutations without UV. We address that knowledge gap by showing 8E6 causes mutations stemming from mitotic errors. Specifically, 8E6 reduces the abundance of BLM, a helicase that resolves and prevents anaphase bridges. This hinders anaphase bridge resolution and increases their frequency. 8E6 makes the micronuclei that can result from anaphase bridges more common. These micronuclei often have disrupted envelopes yet retain localization of nuclear-trafficked proteins. 8E6 promotes the growth of cells with micronuclei and causes chromothripsis, a mutagenic process where hundreds to thousands of mutations occur in a chromosome.