Resveratrol-induced apoptosis depends on the lipid kinase activity of Vps34 and on the formation of autophagolysosomes

In human colorectal DLD1 cancer cells, the dietary bioflavonoid resveratrol (RV) rapidly induced autophagy. This effect was reversible (on removal of the drug) and was associated with increased expression and cytosolic redistribution of the proteins Beclin1 and LC3 II. Supplementing the cells with asparagine (Asn) abrogated the Beclin-dependent autophagy. When applied acutely (2 h), RV was not toxic; however, reiterate chronic (48 h) exposure to RV eventually led to annexin V- and terminal deoxinucleotidyl transferase-mediated dUTP-biotin nick end labelingpositive cell death. This toxic effect was autophagy dependent, as it was prevented either by Asn, by expressing a dominant-negative lipid kinase-deficient class III phosphoinositide 3-phosphate kinase, or by RNA interference knockdown of Beclin1. Lamp2b silencing abolished the fusion of autophagosomes with lysosomes and preserved cell viability despite the ongoing formation of autophagosomes in cells chronically exposed to RV. The pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone inhibited RV-induced cell death, but not autophagy. These results uncover a novel pathway of RV cytotoxicity in which autophagy plays a dual role: (i) at first, it acts as a prosurvival stress response and (ii) at a later time, it switches to a caspase-dependent apoptosis pathway. The present data also indicate that genetic or epigenetic inactivation of autophagy proteins in cancer cells may confer resistance to RV-mediated killing.