Hyaluronan-CD44 interaction promotes HPV 16 E6 oncogene-mediated oropharyngeal cell carcinoma survival and chemoresistance

Head and neck squamous cell carcinoma (HNSCC) is a malignancy that often involves the oral cavity, pharynx, larynx, or paranasal sinuses. There is a compelling evidence of the human papilloma virus including HPV16 E6 oncogene drives cell transformation and oncogenic processes of HPV positive (HVP+) HNSCC [in particular, Oropharyngeal Squamous Cell Carcinoma (OPSCC)]. In this study, we determined that human OPSCC-derived, HPV16 E6+ cells (UMSCC-104 and UMSCC-47 cell lines) express CD44 and a regulatory transcription factor, c-Jun. Importantly, interaction between matrix hyaluronan (HA) and CD44 (an HA receptor) promotes c-Jun phosphorylation followed by phospho-c-Jun nuclear translocation and co-localization with HPV16 E6 in the nucleus of both UMSCC-104 and UMSCC-47 cells. Further analyses revealed that HPV16 E6 expression is regulated by an upstream promoter containing AP1/c-Jun binding site(s), and chromatin immunoprecipitation (ChIP) assays demonstrated that stimulation of HPV16 E6 expression by HA-CD44 interaction is phospho-c-Jun dependent in these HPV16+ UMSCC-104 and UMSCC-47 cells. This process results in an upregulation of survival proteins, inhibitors of the apoptosis family of proteins (IAPs) and chemoresistance in these HPV16+ cells. Treatment of UMSCC-104 or UMSCC-47 cells with c-Jun-specific or HPV16 E6-specific small interfering RNAs effectively blocks HA/CD44-mediated c-Jun signaling and abrogates HPV16 E6 expression as well as causes downregulation of survival proteins (cIAP-1 and cIAP-2) expression and enhancement of chemosensitivity. Together, these findings suggest that the HA/CD44-induced c-Jun signaling plays a pivotal role in HPV16 E6 upregulation leading to survival protein (cIAP-1/cIAP-2) production and chemoresistance in HPV16+ UMSCC-104 and UMSCC-47 cells. Most importantly, using a mouse xenograft model, we have observed that Cisplatin chemotherapy combined with the suppression of CD44, c-Jun and HPV16 E6 (by treating both UMSCC-104 cells and UMSCC-47 cells with CD44shRNA or c-Jun shRNA or HPV16 E6 shRNA) appears to be more effective in tumor size reduction than chemotherapy alone. Thus, these newly-discovered HA/CD44-c-Jun/HPV16E6 signaling pathways may provide new drug targets for overcoming cisplatin chemoresistance in HPV16E6-positive OPSCC cells.