Persistent infection with oncogenic genotypes of human papillomavirus (HPV) can cause oropharyngeal and anogenital cancers. The HPV E7 oncoprotein is both a central driver of HPV-mediated oncogenesis and an important accessory protein for sustaining HPV infection. This proposal focuses on a highly conserved activity of HPV E7: degradation of the host protein tyrosine phosphatase, PTPN14. It was recently discovered that PTPN14 degradation by HPV E7 repress epithelial differentiation. PTPN14 was previously not characterized as a regulator of differentiation, and repression of differentiation through PTPN14 is significant because HPV+ cancers are often poorly differentiated. In an HPV infected stratified epithelium, HPV establishes the stable maintenance phase of its life cycle undifferentiated basal keratinocytes, and HPV exits this phase of its life cycle and commits to productive replication when an infected cell differentiates. Therefore, repression of differentiation through PTPN14 degradation by HPV E7 is also significant because it could play a role in regulating the transition between these phases of the HPV life cycle. However, the mechanism by which PTPN14 degradation by HPV E7 represses differentiation is not defined, and the impact of repressing differentiation on the HPV life cycle has yet to be identified. PTPN14 is a tumor suppressor that can inhibit the transcriptional regulators Yes-associated protein (YAP) and TAZ. PTPN14 can also bind to the scaffolding protein, KIBRA, to inhibit YAP/TAZ. YAP/TAZ are oncogenes that promote epithelial basal cell identity and repress differentiation. Therefore, PTPN14 degradation by HPV E7 may repress differentiation by disrupting PTPN14- and KIBRA-containing signaling complexes and activating YAP/TAZ. Preliminary data gathered for this proposal implicate YAP/TAZ and KIBRA in mechanisms surrounding PTPN14 in keratinocytes. The objectives of this proposal are to determine the mechanism by which PTPN14 degradation by E7 represses differentiation and to determine how this mechanism impacts the HPV life cycle.
The specific aims of this proposal are 1) to determine if PTPN14 degradation by HPV E7 activates YAP/TAZ and regulates the HPV life cycle, and 2) to determine if PTPN14 degradation by HPV E7 disrupts KIBRA- mediated signaling.
Aim 1 will test if PTPN14 degradation by HPV E7 activates YAP/TAZ and promotes the transcription of YAP/TAZ transcriptional targets in oral epithelial keratinocytes. Furthermore, it will test how constitutively active YAP/TAZ impact the HPV life cycle.
Aim 2 will test if PTPN14 requires KIBRA to induce differentiation in oral keratinocytes, and test whether PTPN14 degradation by HPV E7 disrupts KIBRA-containing signaling complexes. Defining this mechanism will augment our understanding of the HPV E7 oncoprotein, which has implications for both its carcinogenic activities and its role in HPV infection. Completing the proposed aims will provide training in several key skills, preparing me to pursue post-doctoral research following this award.
The life cycle of human papillomavirus depends upon the cellular differentiation program in the stratified epithelium. In this proposal, I aim to elucidate how one activity of the viral E7 oncoprotein manipulates this differentiation program and facilitates the viral life cycle. Studies such as this are vital to understand how the activities of human papillomaviruses proteins manipulate fundamental cellular processes, how these activities facilitate the viral life cycle, and how they can be targeted to prevent persistent infections from progressing to cancer.
