A promoter element of the CD-RAP gene is required for repression of gene expression in non-cartilage tissues in vitro and in vivo

The cartilage-derived retinoic acid-sensitive protein (CD-RAP) gene is expressed predominately in cartilage. Previous studies in transgenic mice have shown that the DNA promoter segment from -2,251 bp to -2,068 bp of the CD-RAP gene contains elements critical for gene expression. Subsequent studies revealed both positive and negative regulatory motifs in this 183 bp element. Here we show that this element demonstrates activation or repression of gene expression in vitro and in vivo based on cell type and content of transcription factors. The distribution of Sox (positive) and C/EBP (negative) transcription factors in cell lines and in mouse tissues is consistent with their positive and negative roles. In transgenic mice, when the 183-bp element was removed from a 3,345-bp cartilage-specific CD-RAP promoter, expression of the reporter gene became widespread, being observed in muscle, bone, lung, and liver in addition to cartilage. In vitro, mutation of the C/EBP site activated the inactive 3,345-bp CD-RAP gene promoter in myoblastic cells, suggesting that this site is responsible for (-2,079 bp) repression. These results indicate that the 183-bp element plays an important role in cartilage-specific gene expression by acting as a chondrocyte-regulatory module repressing transcription in non-chondrocytes and contributing to activation in chondrocytes. This is the first report of a functional DNA element necessary for repression in non-cartilage tissues in vivo.