Cell-type specific promoters of the chick alpha 2(I) collagen gene in chondrocytes and fibroblasts.

Two different promoter regions responsible for the cell-type specific transcripts of the collagen alpha 2(I) gene in chick embryonic fibroblasts and chondrocytes are described. A region including part of intron 1 of the fibroblast alpha 2(I) gene is able to promote transcription in chondrocytes. This promoter region is located 5' to the chondrocyte-specific transcript, from -2205 to +42, relative to the chondrocyte transcription start site. When it is placed upstream of a luciferase reporter gene in transiently transfected chondrocytes, luciferase activity is stimulated 78-fold. The region between -2205 and -1298 is most important for the activity of the chondrocyte promoter, since a truncated promoter from -1298 through +42 gives only 15% as much activity. A similar low level of activity is given by the sequence -96 through +42. In transfected fibroblasts, a region from -1600 through +46, relative to the fibroblast transcription start site, stimulates transcription of a luciferase reporter gene by more than 1,000-fold. Deletions from -1185 through -807 and from -707 through -90 reduce promoter activity to 22% and 32%, respectively, of that given by the intact promoter. The chondrocyte and fibroblast promoters are each cell-type specific and are relatively inactive in the other cell type. Subregions within the fibroblast promoter, from -1154 through -1055, from -712 through -85, and the sequence containing the inverted CCAAT motif from -93 through -67, differentially bind factors in fibroblast but not chondrocyte nuclear extracts.