Caspase-3 Silencing Attenuates Tumor Repopulation Via Impairing Radiation-Induced DNA Damage Response and Downstream Pathway in Non-Small-Cell Lung Cancer

Abstract

Background: Radiotherapy is an effective treatment on non-small-cell lung cancer (NSCLC). However, radiation-induced dying tumor cells are postulated to generate potent growth signals to stimulate the repopulation of adjacent surviving tumor cells, which may promote tumor recurrence. We investigated the role of caspase-3-centered molecular mechanism in NSCLC repopulation after radiotherapy.Methods: The stable caspase-3 knockout (Casp3 KO) NSCLC cells were compared with wild-type cells for growth-promoting effect after radiotherapy using in vitro repopulation model. Western blotting, quantitative real-time PCR, enzyme-linked immunosorbent assay and luciferase reporter assay were used to identify the possible molecules and pathway. To elucidate the function of caspase-3 in tumor repopulation, a series of in vitro assays were performed with Casp3 KO NSCLC cells. Finally, tumor cell growth rate of Casp3 KO and wild-type tumor cells in vivo was tested using xenograft tumor assay and key proteins were further confirmed in tumor tissues with or without radiotherapy.Results: We found that radiation induced DNA damage response (DDR) and caspase-3 activation, as well as promoted tumor repopulation in NSCLC cells. Unexpectedly, depleting caspase-3 significantly attenuated ataxia-telangiectasia mutated kinase (ATM)/p53-mediated DDR via attenuating endonuclease G (EndoG) nuclear migration, thus decreasing the growth-promoting effect of irradiated dying cells. Moreover, we identified p53 as a regulator of the Cox-2/PGE2 axis, which was probably involved in caspase-3-centered tumor repopulation after radiotherapy. Additionally, depleting caspase-3 in NSCLC cells showed impaired tumor growth in nude mice model.Conclusions: Our findings demonstrated that caspase-3 was implicated in tumor repopulation and that was accompanied by promoting DDR and downstream Cox-2/PGE2 axis activation in NSCLC cells. This hitherto undescribed signaling pathway mediated by caspase-3 may deepen insight into the radiobiology and provide therapeutic targets to reduce NSCLC recurrence after radiotherapy.