Activation of mitogen-activated protein kinases in different models of pancreatic acinar cell damage

Mitogen-activated protein kinase (MAPK) family members, namely MAPK, c-Jun NH2-terminal protein kinase (JNK), and p38MAPK, have been recently reported to have opposing effects on apoptosis. Aim: To determine the activity of MAPKs and the level of Bar, Bcl-2 and p53 - proteins known to be involved in the regulation of apoptosis - in pancre atic acini subjected to stressful stimuli leading to cell death. Methods and Results: Isolated pancreatic acini were irradiated for 30 min w ith ultraviolet B (UV-B) or stimulated with supraphysiological concentratio ns of cholecystokinin (CCK). As it was assessed by means of acridine orange /ethidium bromide staining, irradiation with UV-B induced predominantly apo ptosis while necrosis predominated in CCK-stimulated acini. The activity of MAPK, JNK and p38MAPK was determined by means of Western-blotting, with th e use of antibodies which recognize active, dually phosphorylated enzymes. Irradiation with UV-B induced a rapid, 3-fold increase in MAPK activity. It had a maximum at 30 min and then gradually declined to reach the normal le vel at 120 min. Concomitantly, early activation of p38-MAPK was found at 30 min. However, unlike MAPK, p38-MAPK activity was then gradually rising to reach a maximum (5-fold increase) at 180 min. UV-B-induced activation of bo th kinases was not affected by the pretreatment with antioxidant - N-acetyl o-L-cysteine or protein kinase C inhibitor - GF-109203X. In UV-B-irradiated cells, we did not detect any significant JNK activation as well as any sig nificant changes in Bar, Bcl-2 and p53 levels assessed by means of Western- blotting. Conclusion: It seems likely that a specific interaction between MAPK and p3 8MAPK signaling pathway may be involved in the determination of the cell de ath mechanism in pancreatic acini subjected to stressful stimuli.