Effects of the Mortalin Inhibitor MKT-077 on the Tumor Suppressor p53 in Neuroblastoma IMR-32 Cells

The tumor suppressor protein, p53, is an important cell cycle regulator in humans. Over half of all human cancers involve disruption of p53 function. One way this is achieved is by tethering p53 to the mitochondrial 70 kilodalton heat shock protein (Hsp70), mortalin, in the cytoplasm, and preventing p53 from entering the nucleus. The mortalin inhibitor, MKT-077, binds competitively to the p53 binding site in mortalin, and disrupts the p53-mortalin complex in cancer cell lines, allowing p53 to enter the nucleus and promote apoptotic cell death. Previous research reported that cytoplasmic tethering of p53 occurs in certain human neuroblastomas. Thus, we have studied the effects of MKT-077 on the human neuroblastoma cell line, IMR-32, using viability assays to determine cell death following treatment with MKT-077 (0 µM to 10 µM), and using immunocytochemistry to localize p53 within the cell. There was a positive correlation between cell death and concentration of MKT-077. Treatment with MKT-077 increased cell death from 21% to 78% as the concentration increased from 2 µM to 10 µM. Immunocytochemistry showed that p53 was located in the cytoplasm in untreated cells, and that treatment with MKT-077 caused it to enter the nucleus, and to become more concentrated there at higher concentrations of MKT-077. Overall, the results suggested that the p53-mortalin complex is likely to be present in IMR-32 cells, and that mortalin inhibitors could be a group of agents that are effective in selectively targeting cells characterized by this complex