Subjugation of TGFb signaling by human papilloma virus in head and neck squamous cell carcinoma shifts DNA repair from homologous recombination to alternative end joining

Abstract

Purpose: Following cytotoxic therapy, 70% of patients with human papillomavirus (HPV)-positive oropharyngeal head and neck squamous cell carcinoma (HNSCC) are alive at 5 years compared with 30% of those with similar HPV-negative cancer. Loss of TGFb signaling is a poorly studied consequence of HPV that could contribute to patient outcome by compromising DNA repair. Experimental Design: Human HNSCC cell lines (n ¼ 9), patient-derived xenografts (n ¼ 9), tissue microarray (n ¼ 194), TCGA expression data (n ¼ 279), and primary tumor specimens (n ¼ 10) were used to define the relationship between TGFb competency, response to DNA damage, and type of DNA repair. Results: Analysis of HNSCC specimens in situ and in vitro showed that HPV associated with loss of TGFb signaling that increased response to radiation or cisplatin. TGFb suppressed miR-182, which inhibited both BRCA1, necessary for homologous recombination repair (HRR), and FOXO3, required for ATM kinase activity. TGFb signaling blockade by either HPV or inhibitors released miR182 control, compromised HRR and increased response to PARP inhibition. Antagonizing miR-182 rescued the HRR deficit in HPV-positive cells. Loss of TGFb signaling unexpectedly increased repair by error prone, alternative end-joining (alt-EJ). Conclusions: HPV-positive HNSCC cells are unresponsive to TGFb. Abrogated TGFb signaling compromises repair by HRR and increases reliance on alt-EJ, which provides a mechanistic basis for sensitivity to PARP inhibitors. The effect of HPV in HNSCC provides critical validation of TGFb's role in DNA repair proficiency and further raises the translational potential of TGFb inhibitors in cancer therapy.