Regulation and Deregulation of Viral Gene Expression During High-Risk HPV Infection

Cervical cancer remains a global health burden, with persistent infection by high-risk human papillomaviruses (HR-HPVs) being the primary etiological factor. HR-HPVs target stem-like cells of the cervical epithelium to establish chronic infections. Upon infection of the cervical transformation zone (TZ)-a region adjacent to the squamocolumnar junction (SCJ)-these viruses drive neoplastic transformation, which is due in part to the unique cellular composition and hormonal responsiveness of the TZ. Reserve cells, which can accumulate at the cervical crypt entrances of the TZ, are thought to be highly susceptible to HR-HPV infection because of their location beneath a single layer of columnar cells. Infection of the stratified ectocervical epithelium, in contrast, requires a wound to allow basal cell infection, replication, and the expression of early genes to adjust epithelial homeostasis while facilitating immune evasion. Persistent infection by HR-HPV types, particularly HPV16 and HPV18, can result in the deregulated expression of viral genes E6 and E7, driving cell cycle disruption, genomic instability, and subsequent viral genome integration. Differences in the microenvironment and transcriptional environment of the ectocervix compared with the TZ could explain the frequent deregulation of E6 and E7 at the latter site, which can drive disease progression towards cancer.