TNFalpha induces apoptosis through JNK/Bax-dependent pathway in differentiated, but not naïve PC12 cells.

Differentiated PC12 cells have been used widely as a model for the analysis of neuronal degeneration. Some evidences showed that differentiated PC12 cells were more sensitive than naïve PC12 against apoptosis stimuli. However, the apoptosis mechanism of both types of PC12 cells was not fully known. In this study, the signaling pathways involved in tumor necrosis factor-alpha (TNFalpha)-induced apoptosis in living differentiated and naïve PC12 cells were investigated using confocal microscope for the first time. Our results showed that during TNFalpha-induced apoptosis, Bax translocation to mitochondria and cytochrome C (Cyt c) release from mitochondria were observed in differentiated PC12 cells, but not in naïve PC12 cells. Furthermore, the mRNA levels of bim, c-Jun N-terminal protein kinase 1 and 2 (JNK1 and JNK2) increased noticeably in differentiated PC12 cells. The apoptosis induced by TNFalpha was inhibited by Z-IETD-fmk (specific inhibitor of caspase-8) but not SP600125 (specific inhibitor of JNK) in naïve PC12 cells. While in differentiated PC12 cells, the process of apoptosis could only be inhibited effectively by Z-IETD-fmk and SP600125 cotreatment, and SP600125 inhibited the Bax translocation to mitochondria implying that JNK mediated activation of Bax. The experimental data strongly demonstrated that TNFalpha induced apoptosis through JNK/Bax-dependent pathway in differentiated, but not naïve PC12 cells.