REGULATION OF THE MOUSE CARTILAGE-DERIVED RETINOIC ACID-SENSITIVE PROTEIN GENE BY THE TRANSCRIPTION FACTOR AP-2

The expression of cartilage-derived retinoic acid-sensitive protein (C D-RAP) is initiated at the beginning of chondrogenesis and continues t hroughout the cartilage development, In chondrocytes, CD-RAP is down-r egulated by retinoic acid, To understand the molecular mechanism under lying this regulation and the cell-specific expression, the deletion c onstructs of the mouse CD-RAP promoter were transfected into chondrocy tes and a melanoma cell line, The results revealed a domain that demon strated high levels of expression specifically in chondrocytes. In thi s functional domain, we show that a cis-acting element, 5'-GCCTGAGGC-3 ', binds to the trans-acting factor protein AP-2, Mutation of the AP-2 site on the CD-RAP promoter led to decreased transcription in C5.18 c hondrocytes, indicating that this site may act as an activator of tran scription, In contrast, increased concentration of AP-2, stimulated by retinoic acid, led to decreased transcription of the CD RAP promoter, an effect that was abolished by mutation of the AP-2 binding site, Th e effect of AP-2 was further examined by co-transfection of C5.18 and HepG2 cells with the CD-RAP promoter constructs and an AP-2 expression plasmid, In a dose-dependent manner, cotransfection with AP-2 elevate d and then decreased CD-RAP promoter activity, Taken together, these r esults suggest that AP-2 is involved in the biphasic regulation of CD- RAP transcription.