Estrogen enhances vitamin D3-mediated expression of osteocalcin mRNA by increasing vitamin D3 receptor expression in osteoblasts

Abstract

Regulation of osteocalcin (OC) gene expression in osteoblasts by estrogen has been controversial. Thus investigated was the effect of 17beta-estradiol (E(sub 2)) on 1-alpha,25-dihydroxyvitamin D(sub 3) (VD(sub 3))-mediated increase in the transcription of OC gene in rat osteoblastic ROS 17/2.8 cells. Treatment of the cells with E(sub 2) or VD(sub 3) alone did not increase OC mRNA. However, combined treatment with E(sub 2) and VD(sub 3) significantly increased the OC mRNA levels, suggesting that VD(sub 3)-dependent up-regulation of OC expression requires E(sub 2) action. Since it was demonstrated that treatment with E(sub 2) alone increased the expression of VD(sub 3) receptor mRNA, it was suggested that E(sub 2)-mediated increase in the receptor number is contributing to VD(sub 3)-mediated increase in OC gene transcription.