Differential regulation of matrix Gla protein (MGP) gene expression by retinoic acid and estrogen in human breast carcinoma cells

Expression of matrix Gla protein (MGP) gene and its regulation by retinoic acid (RA) and estrogen was investigated in eight human breast cancer cell lines. The promoter region of the MGP gene contains a consensus retinoic acid response element (RARE) and the MGP gene expression has been shown to be strongly induced by RA in other systems. Our results suggest that RA negatively regulates MGP mRNA expression in human breast cancer cells that have high levels of estrogen receptors (ER), i.e. MCF-7, ZR-75 and BT474 and positively regulates its expression in cells with either no ERs, i.e. MDA-MB-468 or very low levels of ERs, i.e. T47D. This indicates that ER levels may affect RA modulation of MGP gene expression in human breast cancer cells. The inhibitory effect of RA on MGP gene expression was abolished in RRO-I, the RA-resistant MCF-7 subline. We also demonstrate for the first time that estrogen strongly induces MGP gene expression in ER-positive cells and that estrogen-mediated induction of MGP is blocked by RA even in otherwise RA-resistant cells.