Mechanisms of PKC-Mediated Enhancement of HIF-1 Activity and its Inhibition by Vitamin K2 in Hepatocellular Carcinoma Cells

Hypoxia-inducible factor 1 (HIF-1) plays important roles in cancer cell biology. HIF-1 is reportedly activated by several factors, including protein kinase C (PKC), in addition to hypoxia. We investigated the role of PKC isoforms and the effects of vitamin K2 (VK2) in the activation process of HIF-1. Human hepatocellular carcinoma (HCC)-derived Huh7 cells were cultured under normoxic and hypoxic (1% O-2) conditions with or without the PKC stimulator TPA. The expression, transcriptional activity and nuclear translocation of HIF-1 were examined under treatment with PKC inhibitors, siRNAs against each PKC isoform and VK2. Hypoxia increased the expression and activity of HIF-1. TPA increased the HIF-1 activity several times under both normoxic and hypoxic conditions. PKC- siRNA-mediated knockdown, PKC- inhibitor (rottlerin) and pan-PKC inhibitor (Ro-31-8425) suppressed the expression and transcriptional activity of HIF-1. VK2 significantly inhibited the TPA-induced HIF-1 transcriptional activity and suppressed the expression and nuclear translocation of HIF-1 induced by TPA without altering the HIF-1 mRNA levels. These data indicate that PKC- enhances the HIF-1 transcriptional activity by increasing the nuclear translocation, and that VK2 might suppress the HIF-1 activation through the inhibition of PKC in HCC cells.