HPV E5 Mediates Resistance to Chemotherapy and Radiation by Promoting a Stem Cell–Like Phenotype in Head and Neck Squamous Cell Carcinoma

Human papillomavirus (HPV)-associated head and neck squamous cell carcinoma (HPV+ HNSCC) is one of the most rapidly increasing cancers in the United States. Although patients with HPV+ HNSCC exhibit better responses to chemoradiation compared with patients with HPV- HNSCC, a subset still develops recurrent/refractory disease. In this study, we investigated the role and mechanisms by which the HPV E5 oncogene promotes resistance to conventional chemotherapy and radiation. After treatment with chemotherapy and radiation, HNSCC cells expressing HPV E5 had decreased apoptosis, improved cell viability, enhanced DNA damage response, and increased tumor growth in murine xenograft models when compared with empty vector controls. Transcriptomic analysis showed an enrichment of signaling pathways associated with epithelial development and increased expression of stem cell markers, including SOX9 and SOX4, in HPV E5 cells compared with empty vector cells. Knockdown of SOX9 restored sensitivity to chemo- and/or radiotherapy in HPV E5-expressing cells. In patients with HNSCC, RNA sequencing analysis showed that high expression of HPV E5 was associated with enrichment of pathways involved in cellular senescence and stem cell pluripotency. Furthermore, an HPV E5-associated gene set was identified that correlates with poor patient prognosis and is significantly overexpressed in recurrent HPV+ HNSCC tumors. Taken together, these data identify HPV E5 as a viral mediator of resistance to standard-of-care therapies for HPV+ HNSCC by promoting a stem cell-like phenotype that enhances DNA damage responses and tumor cell survival. Thus, HPV E5 may contribute to chemotherapy resistance, tumor recurrence after radiation, and poor prognosis of patients with refractory or metastatic disease. SIGNIFICANCE: HPV E5 upregulates SOX9 to induce stem cell-like characteristics in head and neck cancer that drive resistance to chemotherapy and radiation, providing rationale for developing therapeutic agents targeting HPV E5.