Windle, B. | Search bioRxiv

bioRxiv2018

PTPN14 Degradation by High-Risk Human Papillomavirus E7 Limits Keratinocyte Differentiation and Contributes to HPV-Mediated Oncogenesis

High-risk human papillomavirus (HPV) E7 proteins enable oncogenic transformation of HPV-infected cells by inactivating host cellular proteins. High-risk but not low-risk HPV E7 target PTPN14 for proteolytic degradation, suggesting that PTPN14 degradation may be related to their oncogenic activity. HPV infects human keratinocytes but the role of PTPN14 in keratinocytes and the consequences of PTPN14 degradation are unknown. Using an HPV16 E7 variant that can inactivate RB1 but cannot degrade PTPN14 we found that high-risk HPV E7-mediated PTPN14 degradation impairs keratinocyte differentiation. Deletion of PTPN14 from primary human keratinocytes decreased keratinocyte differentiation gene expression. Related to oncogenic transformation, both HPV16 E7-mediated PTPN14 degradation and PTPN14 deletion promoted keratinocyte survival following detachment from a substrate. PTPN14 degradation contributed to high-risk HPV E6/E7-mediated immortalization of primary keratinocytes and HPV-positive but not HPV-negative cancers exhibit a gene expression signature consistent with PTPN14 inactivation. We find that PTPN14 degradation impairs keratinocyte differentiation and propose that this contributes to high-risk HPV E7-mediated oncogenic activity independent of RB1 inactivation.\n\nSignificance StatementHuman papillomaviruses uncouple proliferation from differentiation in order to enable virus replication in epithelial cells. HPV E7 proteins are well established to promote proliferation by binding to and inactivating retinoblastoma family proteins and other cell cycle inhibitors. However, mechanisms by which high-risk HPV oncoproteins inhibit differentiation have not been defined. This paper identifies the first mechanism by which high-risk HPV E7 inhibit keratinocyte differentiation. The inhibition of differentiation requires degradation of the cellular protein PTPN14 by high-risk HPV E7 and this degradation is related to the ability of high-risk HPV oncoproteins to immortalize keratinocytes and to cause cancer.

microbiology↗

bioRxiv2018

Human papillomavirus 16 E2 regulates keratinocyte gene expression relevant to cancer and the viral life cycle

Human papillomaviruses (HPV) are causative agents in ano-genital and oropharyngeal cancers. The virus must reprogram host gene expression to promote infection, and E6 and E7 contribute to this via targeting of cellular transcription factors including p53 and pRb, respectively. The HPV16 E2 protein regulates host gene expression in U2OS cells and in this study we extend these observations into TERT immortalized oral keratinocytes (NOKs) that are capable of supporting late stages of the HPV16 life cycle. We observed repression of innate immune genes by E2 that are also repressed by the intact HPV16 genome in NOKs. RNA-seq data identified 167 up and 395 downregulated genes by E2; there was a highly significant overlap of the E2 regulated genes with those regulated by the intact HPV16 genome in the same cell type. siRNA targeting of E2 reversed repression of E2 targeted genes. The ability of E2 to repress innate immune genes was confirmed in an ano-genital immortalized keratinocyte cell line, N/Tert-1. We present analysis of data from The Cancer Genome Atlas (TCGA) for HPV16 positive and negative head and neck cancers (HNC) suggesting that E2 plays a role in regulation of the host genome in cancers. Patients with HPV16 positive HNC with a loss of E2 expression exhibit a worse clinical outcome and we discuss how this could, at least partially, be related to the loss of E2 host gene regulation.\n\nImportanceHPV16 positive tumors that retain expression of E2 have a better clinical outcome than those that have lost E2 expression. It has been suggested that this is due to a loss of E2 repression of E6 and E7 expression but this is not supported by data from tumors where there is not more E6 and E7 expression in the absence of E2. Here we report that E2 regulates host gene expression and place this regulation in context of the HPV16 life cycle and HPV16 positive head and neck cancers (the majority of which retain E2 expression). We propose that this E2 function may play an important part in the increased response of HPV16 positive cancers to radiation therapy. Therefore, host gene regulation by E2 may be important for promotion of the HPV16 life cycle, and also for the response of HPV16 positive tumors to radiation therapy.

molecular biology↗