p16 Expression Represses DNA Damage Repair via a Novel Ubiquitin-Dependent Signaling Cascade.

Squamous cell carcinoma driven by human papillomavirus (HPV) is more sensitive to DNA-damaging therapies, such as radiation, than its HPV-negative counterpart. Here we show that p16, the clinically utilized surrogate for HPV positivity, renders cells more sensitive to radiation via a ubiquitin-dependent signaling pathway, linking high levels of this protein to increased activity of the transcription factor SP1, increased HUWE1 transcription and degradation of ubiquitin-specific protease 7 (USP7). Activation of this pathway in HPV-positive disease leads to an absence of TRIP12, decreased DNA damage repair as well as improved clinical outcomes. Conversely, repression of this pathway in HPV-negative disease is druggable via USP7 inhibitors under clinical development, resulting in potentiation of radiation response. Our findings may lead to improved outcomes for patients with HPV-negative radioresistant tumors, while allowing decreased intensity of therapy for patients with HPV-positive tumors.