USP14 Regulates DNA Damage Response and Is a Target for Radiosensitization in Non-Small Cell Lung Cancer.

Non-small cell lung cancer (NSCLC) represents ~85% of the lung cancer cases. Despite recent advances in NSCLC treatment, the five-year survival rate is still around 23%. Radiotherapy is indicated in the treatment of both early and advanced stage NSCLC; however, treatment response in patients is heterogeneous. Thus, identification of new and more effective treatment combinations is warranted. We have identified Ubiquitin-specific protease 14 (USP14) s a regulator of major double-strand break (DSB) repair pathways in response to ionizing radiation (IR) by its impact on both non-homologous end joining (NHEJ) and homologous recombination (HR) in NSCLC. USP14 is a proteasomal deubiquitinase. IR treatment increases levels and DSB recruitment of USP14 in NSCLC cell lines. Genetic knockdown, using shUSP14 expression or pharmacological inhibition of USP14, using IU1, increases radiosensitization in NSCLC cell lines, as determined by a clonogenic survival assay. Moreover, shUSP14-expressing NSCLC cells show increased NHEJ efficiency, as indicated by chromatin recruitment of key NHEJ proteins, NHEJ reporter assay, and increased IR-induced foci formation by 53BP1 and pS2056-DNA-PKcs. Conversely, shUSP14-expressing NSCLC cells show decreased RPA32 and BRCA1 foci formation, suggesting HR-deficiency. These findings identify USP14 as an important determinant of DSB repair in response to radiotherapy and a promising target for NSCLC radiosensitization.