Galectin-3 regulates mitochondrial stability and antiapoptotic function in response to anticancer drug in prostate cancer.

Prostate cancer is one of the malignant tumors which exhibit resistance to anticancer drugs, at least in part due to enhanced antiapoptotic mechanisms. Therefore, the understanding of such mechanisms should improve the design of chemotherapy against prostate cancer. Galectin-3 (Gal-3), a multifunctional oncogenic protein involved in the regulation of tumor proliferation, angiogenesis, and apoptosis has shown antiapoptotic effects in certain cell types. Here, we show that the expression of exogenous Gal-3 in human prostate cancer LNCaP cells, which do not express Gal-3 constitutively, inhibits anticancer drug-induced apoptosis by stabilizing the mitochondria. Thus, Gal-3-negative cells showed 66.31% apoptosis after treatment with 50 micromol/L cis-diammine-dichloroplatinum for 48 hours, whereas two clones of Gal-3-expressing cells show only 2.92% and 1.42% apoptotic cells. Similarly, Gal-3-negative cells showed 43.8% apoptosis after treatment with 300 micromol/L etoposide for 48 hours, whereas only 15.38% and 14.51% of Gal-3-expressing LNCaP cells were apoptotic. The expression of Gal-3 stimulated the phosphorylation of Ser(112) of Bcl-2-associated death (Bad) protein and down-regulated Bad expression after treatment with cis-diammine-dichloroplatinum. Gal-3 also inhibited mitochondrial depolarization and damage after translocation from the nuclei to the cytoplasm, resulting in inhibition of cytochrome c release and caspase-3 activation. These findings indicate that Gal-3 inhibits anticancer drug-induced apoptosis through regulation of Bad protein and suppression of the mitochondrial apoptosis pathway. Therefore, targeting Gal-3 could improve the efficacy of anticancer drug chemotherapy in prostate cancer.