NEDD9 Restrains dsDNA Damage Response during Non-Small Cell Lung Cancer (NSCLC) Progression

SIMPLE SUMMARY: Altered DNA damage response (DDR) contributes to numerous processes during the progression of tumors, such as genomic instability, the emergence of neoantigens, aberrations in cell-cell signaling, and acquired tumor resistance to DNA damaging agents, such as platinating agents and irradiation. This study describes a novel role for the scaffolding protein NEDD9 in regulating DDR signaling and characterizes its effects on sensitivity to DNA damaging therapies in a non-small cell lung cancer (NSCLC) setting. Our data demonstrate that NEDD9 depletion is capable of upregulating ATM-CHK2 signaling, shifting NEDD9 depleted cells towards a more mesenchymal phenotype and elevated sensitivity to UV irradiation. Immunohistochemical analysis of the cohort of human NSCLC samples revealed an association between reduced NEDD9 protein expression and a decrease in overall (OS) survival of NSCLC patients. ABSTRACT: DNA damaging modalities are the backbone of treatments for non-small cell lung cancer (NSCLC). Alterations in DNA damage response (DDR) in tumor cells commonly contribute to emerging resistance to platinating agents, other targeted therapies, and radiation. The goal of this study is to identify the previously unreported role of NEDD9 scaffolding protein in controlling DDR processes and sensitivity to DNA damaging therapies. Using a siRNA-mediated approach to deplete NEDD9 in a group of human and murine KRAS/TP53-mutant NSCLC cell lines, coupled with a set of cell viability and clonogenic assays, flow cytometry analysis, and Western blotting, we evaluated the effects of NEDD9 silencing on cellular proliferation, DDR and epithelial-to-mesenchymal transition (EMT) signaling, cell cycle, and sensitivity to cisplatin and UV irradiation. Using publicly available NSCLC datasets (TCGA) and an independent cohort of primary NSCLC tumors, subsequent in silico and immunohistochemical (IHC) analyses were performed to assess relevant changes in NEDD9 RNA and protein expression across different stages of NSCLC. The results of our study demonstrate that NEDD9 depletion is associated with the increased tumorigenic capacity of NSCLC cells. These phenotypes were accompanied by significantly upregulated ATM-CHK2 signaling, shifting towards a more mesenchymal phenotype in NEDD9 depleted cells and elevated sensitivity to UV-irradiation. IHC analyses revealed an association between reduced NEDD9 protein expression and a decrease in overall (OS) and progression-free survival (PFS) of the NSCLC patients. These data, for the first time, identified NEDD9 as a negative regulator of ATM kinase activity and related DDR signaling in numerous KRAS/TP53 mutated NSCLC, with its effects on the regulation of DDR-dependent EMT signaling, sensitivity to DNA damaging modalities in tumor cells, and the survival of the patients.