Ke. Thummel et al., Transcriptional control of intestinal cytochrome P-4503A by 1 alpha,25-dihydroxy vitamin D-3, MOLEC PHARM, 60(6), 2001, pp. 1399-1406
It was previously shown that CYP3A4 is induced in the human intestinal Caco
-2 cell model by treatment with 1 alpha ,25-dihydroxy vitamin D-3 (1,25-D-3
). We demonstrate the vitamin D analog, 19-nor-1 alpha ,25-dihydroxy vitami
n D-2, is also an effective inducer of CYP3A4 in Caco-2 cells, but with hal
f the potency of 1,25-D-3. We report that treatment of LS180 cells, a human
intestinal cell line, with 1 to 10 nM 1,25-D-3 dose dependently increased
CYP3A4 protein and CYP3A4 mRNA expression. CYP3A4- and CYP3A23-promoter-Luc
iferase reporter constructs transiently transfected into LS180 cells were t
ranscriptionally activated in a dose-dependent manner by 1,25-D-3, whereas
mutation of the nuclear hormone receptor binding motif (ER6) in the CYP3A4
promoter abrogated 1,25-D-3 activation of CYP3A4. Although the CYP3A4 ER6 p
romoter element has been shown to bind the pregnane X receptor (PXR), this
receptor does not mediate 1,25-D-3 induction of CYP3A4 because a) PXR is no
t expressed in Caco-2 cells; b) PXR mRNA expression is not induced by 1,25-
D-3 treatment of LS180 cells; and c) the ligand binding domain of human PXR
was not activated by 1,25-D-3. 1,25-D-3 uses the vitamin D receptor to ind
uce CYP3A4 because a) the vitamin D receptor (VDR)-retinoid X receptor (RXR
) heterodimer binds specifically to the CYP3A4 ER6; b) selective mutation o
f the CYP3A4 ER6 disrupted the binding of VDR-RXR; and c) reporter construc
ts containing only three copies of the CYP3A4 ER6 linked to a TK-CAT report
er were activated by 1,25-D-3 only in cells cotransfected with a human VDR
expression plasmid. These data support the hypothesis that 1,25-D-3 and VDR
induce expression of intestinal CYP3A by binding of the activated VDR-RXR
heterodimer to the CYP3A PXR response element and promoting gene transcript
ion.