Molecular Basis of Autophagy-Mediated Resistance to Radiation and Apo2L/TRAIL Therapy in Prostate Cancer Cells

摘要

Cell death and survival signaling pathways are important for the cellular response against ionizing radiation (IR) and chemotherapy in prostate cancer (PCa). IR and Apo2L/TRAIL, are widely used as therapeutics for PCa, however cellular resistance developed over the time may hinder their effectiveness. In this study we have investigated the response of Apo2L/TRAIL and IR in PCa cell lines. PC3 cells were more sensitive to Apo2L/TRAIL-mediated cell death as compared to LNCaP-derived C4-2. The cell death observed showed both apoptotic and non-apoptotic characteristics, suggesting that autophagy might also contribute to cytotoxicity. We therefore further investigated the role of autophagy in the IR and Apo2/TRAIL response in PCa. Following Apo2L/TRAIL treatment of PC3 cells, microtubule-associated protein 1 light chain LC3, a classical marker for autophagy showed enhanced autophagosomal staining. In contrast, LC3 failed to associate with autophagosomes in C4-2 cells. Moreover, ATG7 levels were lower in C4-2 in comparison to PC3 cells. Furthermore, the ATG5-12 complex protein levels were decreased in PC3 cells while remaining unchanged in C4-2 cells. Sub-cellular fractionation revealed decreased ATG5 levels in the membrane fraction upon Apo2L/TRAIL and IR in PC3 cells. In C4-2 cells ATG5 was enriched in the soluble fraction upon IR while it decreased in both fractions upon Apo2L/TRAIL treatment. Real time PCR data showed differential expression of various autophagy related genes in PC3 and C4- 2 cells. More cell death was observed in PC3 cells upon Apo2L/TRAIL treatment and was inhibited by inhibiting autophagy by 3-MA and/or by using pan-caspase inhibitor z-VAD, suggesting that autophagy induced by Apo2L/TRAIL results in caspase dependent cell death in PC3 cells. On the other hand, C4-2 cells did not show any cell death following Apo2L/TRAIL treatment, and inhibiting autophagy increased Apo2L/TRAIL-induced cell death in C4-2 cells.