The role of PKC isoforms in the inhibition of NF- kappaB activation by vitamin K2 in human hepatocellular carcinoma cells.

摘要

Vitamin K (VK) has diverse protective effects against osteoporosis, atherosclerosis and carcinogenesis. We recently reported that menatetrenone, a VK2 analogue, suppressed nuclear factor (NF)- kappaB activation in human hepatoma cells. Although NF- kappaB is regulated by isoforms of protein kinase C (PKC), the involvement of PKCs in VK2-mediated NF- kappaB inhibition remains unknown. Therefore, the effects of VK2 on the activation and the kinase activity of each PKC isoform were investigated. The human hepatoma Huh7 cells were treated with PKC isoform-specific inhibitors and/or siRNAs against each PKC isoform with or without 12-O-tetradecanoylphorbol-13-acetate (TPA). VK2 inhibited the TPA-induced NF- kappaB activation in Huh7 cells. NF- kappaB activity was inhibited by the pan-PKC inhibitor Ro-31-8425, but not by the PKC alpha-specific inhibitor Go6976. The knockdown of individual PKC isoforms including PKC alpha, delta and epsilon showed only marginal effects on the NF- kappaB activity. However, the knockdown of both PKC delta and PKC epsilon, together with treatment with a PKC alpha-specific inhibitor, depressed the NF- kappaB activity. VK2 suppressed the PKC alpha kinase activity and the phosphorylation of PKC epsilon after TPA treatment, but neither the activation nor the enzyme activity of PKC delta was affected. The knockdown of PKC epsilon abolished the TPA-induced phosphorylation of PKD1, and the effects of PKD1 knockdown on NF- kappaB activation were similar to those of PKC epsilon knockdown. Collectively, all of the PKCs, including alpha, delta and epsilon, and PKD1 are involved in the TPA-mediated activation of NF- kappaB. VK2 inhibited the NF- kappaB activation through the inhibition of PKC alpha and epsilon kinase activities, as well as subsequent inhibition of PKD1 activation