Phorbol ester markedly increases the sensitivity of intestinal epithelial cells to 1,25‐dihydroxyvitamin D3

Abstract
We have used a clonal intestinal epithelial cell line (IEC-18) to study the mechanism of action of 1,25-dihydroxyvitamin D3 (1,25(OH)2D) in vitro. 1,25(OH)2D(10(-7) M) elevated by over 10-fold the mRNA levels for the cytochrome P450 component (P450cc24) of the 1,25(OH)2D-24-hydroxylase. Increased P450cc24 mRNA levels were detectable at 6 h and peaked at 36 h. Below a concentration of 10(-7) M, 1,25(OH)2D had almost no effect. However, addition of phorbol ester for 2 h made the intestine responsive to 1,25(OH)2D concentrations as low as 10(-9) M.

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