Lithocholic acid induces endoplasmic reticulum stress, autophagy and mitochondrial dysfunction in human prostate cancer cells

Lithocholic acid (LCA) is a secondary bile acid that is selectively toxic to human neuroblastoma, breast and prostate cancer cells, whilst sparing normal cells.. We previously reported that LCA inhibited cell viability and proliferation and induced apoptosis and necrosis of androgen-dependent LNCaP and androgen-independent PC-3 human prostate cancer cells. In the present study, we investigated the roles. the toxicity reticulum (ER) stress, autophagy and mitochondrial dysfunctioin45incetile.. of LCA in PC-3 and autophagy. deficient, androgen independent DU-145 cells. LCA induced ER stress-related proteins, such as CCAAT-enhancer-binding protein homologous protein (CHOP), and the phosphorylation of eukaryotic initiation factor 2-alpha (p-eIF2 alpha) c-and-Jon N terminal kinases (p-JNK) in both cancer cell-types. The p53 upregulatedmodulator ofapoptosis (PUMA) and B cell lymphoma-like protein 11 (BIM) levels were decreased at overtly toxic LCA concentrations, although PUMA levels increased at lower LCA concentrations in both cell lines LCA induced autophagyrelated conversion of microtuhuie-associated proteins light chain 3B (LC3I3I - LC3BII), and autophagy-related protein ATG5 in PC-3 cells, but not in autophagydeficient DU-145 cells. LCA (>10 mu M) increased levels of reactive oxygen species (ROS) e concentration-depend ntly in PC-3 cells, whereas ROS levels were not affected in DU 145 cells. Solubrinal, an inhibitor of eIF2 alpha dephosphorylation and ER stress, reduced LCA-induced CHOP levels slightly in PC-3, but not DU-145 cells. Salubrinal pretreatment increased the cyt toxicity ofLCA in PC-3 and DU-145 cells and resulted in a statistically significant loss of viability at normally non-toxic concentrations of LCA. The late-stage autophagy inhibitor bafilomyciu Al exacerbated LCA toxicity at subtoxic LCA concentrations in PC-3 cells. The antioxidant alpha-tocotrienol strongly inhibited the toxicity of LCA in PC-3 cells, but not in DU-145 cells. Collectively, although LCA induces autophagy and ER stress in PC-3 cells, these processes app ear to beinitially of protective nature and subsequently consequential to, but not critical for the ROSmediated mitochondrial dysfunction and cytotoxicity of LCA. The full mechanism of LCA-induced mitochondrial dysfunction DU-145 cells remains to be elucidated.