Protein kinase C signaling modulates 1alpha,25(OH)2D3‐regulated CYP24 gene expression in differentiated Caco‐2 cells

Abstract

A number of kinase pathways have been found to modulate the genomic action of 1α, 25 dihydroxyvitamin D3 (1,25 D) but this has not been well studied in enterocytes, a primary 1,25 D target cell. We examined the role of protein kinase C (PKC) on 1,25 D action in differentiated Caco-2 cells, an established model for 1,25 D-mediated intestinal calcium (Ca) absorption. Activation of PKC with phorbol ester (PMA 100 nM, 5 min pre-treatment) significantly enhanced 1,25 D (10 nM, 2 h)-induced accumulation of 24-hydroxylase (CYP24) mRNA by 160% but had no impact on induction of the mRNA for the apical Ca channel TRPV6. Inhibition of Ca-dependent PKC isoforms (2 and 10 μM Go6976) reduced basal (by 40 and 70%) and PMA-enhanced effects of 1,25 D on CYP24 mRNA accumulation. MAPK family members ERK1/2 and p38 kinase were activated by PMA treatment (100 nM, 5min). However, while MEK (10 μM U0126) and p38 kinase (8.75 μM SB202190) inhibition reduce 1,25 D-mediated CYP24 mRNA accumulation by 50–60%, only the p38 inhibitor reduced the PMA effect on 1,25 D action (by 40%). Thus, our data show that PMA enhances 1,25 D-induced CYP24 mRNA accumulation through activation of Ca-dependent PKC isoforms and p38 kinase. In addition, the induction of CYP24 mRNA by 1,25 D in enterocytes is dependent upon PKC, p38 kinase and ERK 1/2. However, the molecular targets for these interactions remain to be determined. Supported by NIDDK Award DK54111 to JCF.