bafilomycin-a and Carcinoma--Hepatocellular

Hepatocellular carcinoma has extremely poor prognosis. In cancerous liver tissues, aberrant proliferation of cancer cells leads to the creation of an area where an immature vascular network is formed. Since oxygen is supplied to cancer tissues through the bloodstream, a part of the tumor is exposed to hypoxic conditions. As hypoxia is known to severely reduce the effectiveness of existing anticancer agents, novel valid therapeutic targets must be identified for the treatment of hepatocellular carcinoma. Generally, autophagy has been reported to play an important role in the adaptation of cancer cells to hypoxia. However, the exact role and significance of this process vary depending on the cancer type, requiring detailed analysis in individual primary tumors and cell lines. In the present study, we examined autophagy induced by cobalt chloride, a hypoxia‑mimicking agent, in hepatocellular carcinoma cells with the aim to evaluate the validity of this process as a potential therapeutic target. We observed that treatment with cobalt chloride induced autophagy, including the intracellular quality control mechanism, in an AMPK‑dependent manner. Furthermore, treatment with autophagy inhibitors (bafilomycin and LY294002) resulted in significant, highly‑selective cytotoxicity and apoptosis activation under hypoxia‑mimicking conditions. The knockdown of AMPK also revealed significant cytotoxicity in hypoxia‑mimicking conditions. These results clearly demonstrated that autophagy, especially mitophagy, was induced by the AMPK pathway when hepatocellular carcinoma cells were subjected to hypoxic conditions and played an important role in the adaptation of these cells to such conditions. Thus, autophagy may constitute an attractive therapeutic target for the treatment of hepatocellular carcinoma.

Topics: AMP-Activated Protein Kinases; Apoptosis; Autophagy; Carcinoma, Hepatocellular; Cell Hypoxia; Cell Line, Tumor; Cell Proliferation; Chromones; Cobalt; Gene Knockdown Techniques; Humans; Liver Neoplasms; Macrolides; Morpholines; Oxygen; Signal Transduction

We studied the effects of bafilomycin A1, a potent and specific inhibitor of vacuolar H+ ATPase (V-ATPase), on the process of autophagy in rat hepatoma cell line, H-4-II-E cells. To induce autophagy, cells were transferred from Dulbecco's modified Eagle medium containing 12% fetal calf serum into Hanks' balanced salt solution. When bafilomycin A1 was added to Hanks' balanced salt solution, endogenous protein degradation was strongly inhibited and numerous autophagosomes accumulated in H-4-II-E cells, whereas autolysosomes decreased in number. Acid phosphatase activity was not detected in the autophagosomes which accumulated in the presence of bafilomycin A1, suggesting that fusion between autophagosomes and lysosomes was disturbed by this drug. Inhibition of the fusion was reversible, and the autophagosomes changed into autolysosomes after the removal of the inhibitor. Bafilomycin A1 also prevented the appearance of endocytosed HRP in autophagic vacuoles. These results suggested that acidification of the lumenal space of autophagosomes or lysosomes by V-ATPase is important for the fusion between autophagosomes and lysosomes.

Topics: Amino Acids; Animals; Anti-Bacterial Agents; Autophagy; Carcinoma, Hepatocellular; Cell Differentiation; Culture Media, Conditioned; Culture Media, Serum-Free; Growth Inhibitors; Histocytochemistry; Hydrogen-Ion Concentration; Kinetics; Lysosomes; Macrolides; Neoplasm Proteins; Phagosomes; Rats; Tumor Cells, Cultured; Vacuoles