Regulation of Human Vitamin D 3 25-Hydroxylases in Dermal Fibroblasts and Prostate Cancer LNCaP Cells

ABSTRACT In this study, we examined whether 1␣,25-dihydroxyvitamin D 3 (calcitriol), phenobarbital, and the antiretroviral drug efavirenz, drugs used by patient groups with high incidence of low bone mineral density, could affect the 25-hydroxylase activity or expression of human 25-hydroxylases in dermal fibroblasts and prostate cancer LNCaP cells. Fibroblasts express the 25-hydroxylating enzymes CYP2R1 and CYP27A1. LNCaP cells were found to express two potential vitamin D 25-hydroxylases-CYP2R1 and CYP2J2. The presence in different cells of nuclear receptors vitamin D receptor (VDR), pregnane X receptor (PXR), and constitutive androstane receptor (CAR) was also determined. Phenobarbital suppressed the expression of CYP2R1 in fibroblasts and CYP2J2 in LNCaP cells. Efavirenz suppressed the expression of CYP2R1 in fibroblasts but not in LNCaP cells. CYP2J2 was slightly suppressed by efavirenz, whereas CYP27A1 was not affected by any of the two drugs. Calcitriol suppressed the expression of CYP2R1 in both fibroblasts and LNCaP cells but had no clear effect on the expression of either CYP2J2 or CYP27A1. The vitamin D 3 25-hydroxylase activity in fibroblasts was suppressed by both calcitriol and efavirenz. In LNCaP cells, consumption of substrate (1␣-hydroxyvitamin D 3 ) was used as indicator of metabolism because no 1␣,25-dihydroxyvitamin D 3 product could be determined. The amount of 1␣-hydroxyvitamin D 3 remaining in cells treated with calcitriol was significantly increased. Taken together, 25-hydroxylation of vitamin D 3 was suppressed by calcitriol and drugs. The present study provides new information indicating that 25-hydroxylation of vitamin D 3 may be regulated. In addition, the current results may offer a possible explanation for the impaired bone health after treatment with certain drugs. The metabolic activation of vitamin D is initiated by 25-hydroxylation of the side chain followed by a 1␣-hydroxylation. 1␣,25-Dihydroxyvitamin D 3 (calcitriol), the biologically most active form of vitamin D 3 , is known as a calciumregulating hormone but is involved also in other processes such as modulation of the immune system and cell proliferation and differentiation. At the moment, at least four enzymes capable of 25-hydroxylation of vitamin D 3 and/or vitamin D 2 have been described in humans, including the mitochondrial CYP27A1 and the microsomal CYP2R1, CYP2J2, and CYP3A4 In previous studies, both vitamin D metabolites and drugs affecting bone health have been shown to affect the promoter of the porcine vitamin D 25-hydroxylase, CYP2D25, in liverderived HepG2 cell