PROTEIN-KINASE-C IS INVOLVED IN 24-HYDROXYLASE GENE-EXPRESSION INDUCED BY 1,25(OH)(2)D-3 IN RAT INTESTINAL EPITHELIAL-CELLS

Effects of protein kinase C (PKC) inhibitor and activator on 1,25(OH)(2)D-3-induced gene expression were examined in rat intestinal epithelial cells, IEC-6 cells. A potent PKC inhibitor, H-7 (20 mu M), completely abated 1,25(OH)(2)D-3-induced 24-hydroxylase gene expression at 3 and 6 h. The effect of H-7 was dose dependent with IC50 around 5 mu M. Other protein kinase inhibitors, HA-1004 and H-89 (20 mu M), had no effects. Furthermore, the activation of PKC by 12-O-tetradecanoylphorbol-13-acetate (TPA) potentiated the effect of 1,25(OH)(2)D-3 by 1 h. TPA appeared to exert its effect at a transcriptional step, since mRNA stability was not affected by TPA treatment. At 3 h after the treatment of the cells with H-7 and TPA, vitamin D receptor (VDR) contents estimated by H-3-1,25(OH)(2)D-3 binding capacity were 72.4 and 63.2% of vehicle-treated cells without significant changes of binding affinities, suggesting that the effect of H-7 and TPA was not the result of changes in VDR content or its binding affinity. In conclusion, PKC is involved in 1,25(OH)(2)D-3-induced 24-hydroxylase gene expression in IEC-6 cells between 1,25(OH)(2)D-3-VDR binding and VDR-induced gene transactivation. (C) 1994 Wiley-Liss, Inc.