Significance of the way to dissociate Bax from Bcl-2 after the treatment of human lung cancer cells in the decision of the fate of cancer cells

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Apoptosis is induced by many kinds of apoptotic stimuli. As apoptotic pathways are very complicated, it is very important to analyze these apoptotic pathways to map out the strategy of cancer treatment. Therefore, we mainly focused on post-translational and transcriptional modifications of Bcl-2 and Bax induced by apoptotic stimuli in human lung cancer cells. Although Bax induces apoptosis, so-called immortalized lung cancer cell lines entirely expressed quite large amounts of Bax. BcI-2 was localized in the cytoplasm in all of cell lines tested. However, Bax was localized in the nucleus and/or the cytoplasm. Paclitaxel (PTX) treatment induced typical apoptosis, in which phosphorylated Bcl-2 dissociated hetero-dimerized Bax and Bax remained at mitochondria to induce apoptosis. On the other hands, lung cancer cells escaped from apoptosis after hyperthermia at 42.5 °C by translocating Bax from the cytoplasm to the nucleus. This translocation was initiated within 30 min and accomplished within 3 h after the beginning of hyperthermia. Bcl-2 was not phosphorylated. Therefore, Bcl-2 phosphorylation seemed to have very important role in apoptosis induced by Bax. Accordingly, as Bax has no nucleus localization signal, we checked candidate partner proteins by cDNA microarray analysis after PTX treatment or hyperthermia and failed to find any specific mRNA elevation. Confocal laser scanning microscopy and coimmunoprecipitation showed that HSP 70 and proteasome 32 translocated into the nucleus separately from Bax. However, Ku70 bound Bax and translocated it into the nucleus with time after hyperthermia. Thus, an association of Bax with mitochondria and Ku70 may have key role in deciding the fate of cancer cells to induce apoptosis and to escape from apoptosis, respectively. However, a true key to decide the fate of treated cells may consist in the way to dissociate Bax from Bcl-2. Our results indicate that it is necessary to clarify exact mechanisms to dissociate Bax from Bcl-2 for mapping up cancer treatment strategy.