Induction of apoptosis via mitogen-activated protein kinase pathway by a K vitamin analog in rat hepatocytes

Background/Aims: Compound 5 (Cpd 5), a vitamin K analog, inhibits rat hepatocyte DNA synthesis and hepatoma cell growth. The aim of this study was to determine if the inhibitory effect of Cpd 5 on cell growth was related to apoptosis. Methods: Isolated rat hepatocytes were cultured with Cpd 5, and mitogen-activated signaling pathway and apoptosis pathway were investigated using Western blot analysis. Results: When rat hepatocytes were cultured with Cpd 5 for 48 h, apoptosis was evident, which included characteristic morphological changes, DNA fragmentation, and the activation of caspase 3 (CPP 32)-like protease. Examination of upstream events of apoptosis pathway showed that the expression of Bax was induced and bcl-2 was inhibited by Cpd 5 treatment. Concomitant with the induction of apoptosis, Cpd 5 activated the extracellular signal-regulated kinase (ERK) signaling pathway. PD 98059, a mitogen-activated protein kinase kinase inhibitor, and glutathione, an anti-thiolo oxidant, not only blocked Cpd 5-induced ERK phosphorylation, but also antagonized the activation of CPP-32, the altered Bcl-2/Bax expression, and DNA fragmentation. Conclusions: The data suggest that the ERK signaling pathway may be involved in the regulation of rat hepatocyte apoptosis induced by Cpd 5. (C) 2002 European Association for the Study of the Liver. Published by Elsevier Science B.V. All rights reserved.