Identification of a novel negative retinoic acid responsive element in the promoter of the human matrix Gla protein gene

The vitamin K-dependent matrix Gla protein (MGP) is synthesized in a wide variety of tissues such as lung, heart, kidney, cartilage, and bone. Expression of the MGP gene is regulated by various growth factors, steroid hormones, and the vitamin A metabolite retinoic acid (RA). In this report, we present evidence that RA down-regulates MGP gene expression in different rat and human cell lines via endogenous retinoid receptors [RA receptor (RAR) and retinoid X receptor (RXR)]. Repression of the human MGP (hMGP) gene is specifically mediated by ligand-activated RAR and RXR. Deletion analysis led to the identification of a novel negative response element (NRE) within the hMGP promoter. DNA binding studies performed with bacterially expressed RAR/RXR reveal the formation of a specific heterodimer/NRE complex. Furthermore, electrophoretic mobility-shift assays performed with proteins from RA-treated cells show that endogenous RAR/RXR binds to the NRE. We demonstrate that the NRE contains a CCAAT box and that both RAR/RXR and CCAAT-binding proteins such as c/EBPβ recognize this common regulatory sequence in the hMGP promoter. Our results indicate that RA-mediated repression of the hMGP gene is due to binding of liganded RAR/RXR to a novel negative RA response element.