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 w ide variety of tissues such as lung, heart, kidney, cartilage, and bon e, 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 expre ssion in different rat and human cell lines via endogenous retinoid re ceptors [RA receptor (RAR) and retinoid X receptor (RXR)], Repression of the human MGP (hMGP) gene is specifically mediated by ligand-activa ted RAR and RXR, Deletion analysis led to the identification of a nove l negative response element (NRE) within the hMGP promoter, DNA bindin g studies performed with bacterially expressed RAR/RXR reveal the form ation of a specific heterodimer/ NRE complex, Furthermore, electrophor etic mobility-shift assays performed with proteins from RA-treated cel ls 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 p roteins such as c/EBP beta recognize this common regulatory sequence i n 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 nega tive RA response element.