Role of mitogen-activated protein kinases in crambene-induced pancreatic acinar cell apoptosis

Crambene (CHB), a plant nitrile, induces pancreatic acinar cell apoptosis, mainly through the mitochondrial pathway. However, a role for mitogen-activated protein kinases (MAPKs) in this process remains unknown. The present study examined the role of MAPKs and their relation to the NF-κB and AP-1 pathways in CHB-induced pancreatic acinar cell apoptosis. CHB induced activation of the MAPKs, ERK1/2, JNK1/2 and p38 in pancreatic acini. Moreover, this activation was blocked by pretreatment with the corresponding inhibitor of each MAPK in a dose-dependent manner. CHB led to an increase in caspase 3 activities and this activity was attenuated when caspase 3 inhibitor were used. Also, the cleavage of caspase 3 correlated with that of poly-(ADP)-ribose-polymerase (PARP) cleavage. CHB induced the release of cytochrome c, smac to the cytoplasm, bax translocation to the mitochondria and decreased the protein level of Bcl-2. The MEK inhibitor, PD98059, caused further enhancement of apoptosis, while the JNK 1/2 inhibitor, SP600125, and the p38 inhibitor, SB203580, abrogated apoptosis. Furthermore, whereas activation of NF-κB and AP-1 was observed in crambene only treated pancreatic acinar cells, treatment with crambene plus SP600125 or SB203580 did not induce any significant change in NF-κB activity. Furthermore, inhibition of SP600125 and SB203580 correlated with the attenuation of apoptosis. PD98059, on the other hand inhibited NF-κB activation by CHB but this attenuation did not inhibit apoptosis. These data suggests that CHB-induced apoptosis may be dependent on AP-1 acting via activation of JNK and p38 in a manner independent of NF-κB activation.