Competition between c‐fos and 1,25(OH)₂ vitamin D₃ in the transcriptional control of type I collagen synthesis in MC3T3‐E1 osteoblastic cells

Interaction between c‐fos and 1,25(OH) 2 vitamin D 3 (VD) on the type I collagen synthesis was studied. VD inhibited collagen synthesis and type I collagen mRNA expression in MC3T3‐E1 osteoblastic cells. In contrast, VD reversed the inhibition of collagen synthesis and mRNA expression of the c‐fos transfectants that overexpressed c‐fos gene to a comparable level as those of the control transfectants. The gel shift assay showed that vitamin D receptor (VDR) complex binding to vitamin D responsive element (VDRE) was inhibited under constitutively expressed c‐fos gene, suggesting that c‐fos gene product, c‐Fos, may inhibit the binding of VDR complex to VDRE by making a c‐Fos‐VDR complex. The result suggests the existence of a fine tuning between c‐fos and VD in the bone metabolism which may be relevant to the pathogenesis of rheumatoid bone lesion.