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 to 30% of those with similar HPV-negative cancer, which is thought to be due to dysregulation of DNA repair. Loss of transforming growth factor β (TGFβ) signaling is a poorly studied consequence of HPV that could contribute to this phenotype.
Experimental Design: Human HNSCC cell lines (n=9), patient-derived xenografts (n=9), tissue microarray (n=194), TCGA expression data and primary tumor specimens (n=10) were used to define the relationship between TGFβ competency, response to DNA damage, and type of DNA repair.
Results: Analysis of HNSCC specimens in situ and in vitro showed that HPV associates with loss of TGFβ signaling that increases the response to radiation or cisplatin. TGFβ suppressed miR-182 that inhibited both BRCA1, necessary for homologous recombination repair, and FOXO3, which is required for ATM kinase activity. TGFβ signaling blockade by either HPV or inhibitors released this control, compromised HRR and increased response to PARP inhibition. Antagonizing miR-182 rescued the homologous recombination deficit in HPV+ cells. Loss of TGFβ signaling unexpectedly increased error-prone, alternative end-joining repair.
Conclusions: HPV-positive HNSCC cells are unresponsive to TGFβ. Abrogated TGFβ signaling compromises homologous recombination and shifts reliance on alt-EJ repair that provides a mechanistic basis for sensitivity to PARP inhibitors. The effect of HPV in HNSCC provides critical validation of TGFβ’s role in DNA repair proficiency and further raises the translational potential of TGFβ inhibitors in cancer therapy.
Footnotes
For Subsection: Biology of Human Tumors
Financial Support: This study was funded by the UCSF Department of Radiation Oncology to MHBH.
Conflict of Interests: MHBH has received funds for speaker bureau or advisory boards from Genzyme, Inc., Varian, Inc., and Genentech on topics related to this project. The other authors have declared that no conflict of interest exists.
Translational Relevance The prognosis for oropharyngeal HNSCC patients suggests that human papilloma virus (HPV) confers vulnerability to standard-of-care radiation and chemotherapy. Although HPV impairs p53 and retinoblastoma proteins, it can also compromise TGFβ signaling. We show that loss of TGFβ signaling leads to homologous recombination deficiency that increases sensitivity to radiation and chemotherapy, but the penultimate basis for poor DNA damage repair is the shift to error-prone, alternative end-joining repair (Alt-EJ) requiring both PARP1 and POLQ. The loss of TGFβ signaling in HPV-positive HNSCC is an experiment of nature that underscores a novel route by which TGFβ inhibitors can be exploited clinically in poor prognosis HPV-negative HNSCC.
