Prostate cancer chemoprevention by sulforaphane (SFN), which is a metabolic by-product of glucoraphanin found in broccoli, in preclinical models is associated with induction of both apoptosis and autophagy. However, the molecular mechanism underlying SFN-mediated autophagy, which is protective against apoptotic cell death by this phytochemical, is still poorly understood. The present study demonstrates a role for lysosome-associated membrane protein 2 (LAMP2) in SFN-mediated autophagy and apoptosis. Western blotting revealed dose-dependent induction of LAMP2 protein after treatment with SFN as well as its naturally-occurring analogs in PC-3 and 22Rv1 human prostate cancer cell lines that was confirmed by microscopy (SFN). The mRNA level of LAMP2 was also increased upon treatment with SFN in both cell lines. SFN-mediated increase in the level of autophagy marker microtubule-associated protein light-chain 3B (LC3BII) was augmented by RNA interference of LAMP2 in PC-3 and 22Rv1 cells. Apoptosis induction by SFN treatment was also increased significantly by knockdown of the LAMP2 protein in PC-3 and 22Rv1 cells. Augmentation of SFN-mediated apoptosis by RNA interference of LAMP2 was accompanied by induction and activation of pro-apoptotic protein Bak. Oral administration of SFN to TRAMP mice also resulted in induction of LAMP2 protein expression. Targeted microarray in SFN-treated PC-3 cells revealed induction of many autophagy-related genes (e.g., HSP90AA1, NRF2, etc.) and their expression positively correlated with that of LAMP2 in prostate cancer TCGA. In conclusion, the present study reveals that induction of LAMP2 by SFN inhibits its ability to induce apoptotic cell death at least in human prostate cancer cells.
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