PROXIMAL DNA ELEMENTS MEDIATE REPRESSOR ACTIVITY CONFERRED BY THE DISTAL PORTION OF THE CHICKEN COLLAGEN-X PROMOTER

Collagen X is expressed specifically in hypertrophic chondrocytes with in cartilage that is undergoing endochondral ossification. The chicken collagen X gene is transcriptionally regulated, and under the control of multiple cis elements within the distal promoter region (-4,442 to -558 base pairs from the transcription start) as well as the proximal region (- 558 to + 1). Our previous data (LuValle et at., [1993] J.. Cell Biol. 121.1173-1179) demonstrated that the proximal sequence dire cted high reporter gene activity in the three cell types tested (hyper trophic chondrocytes, immature chondrocytes, and fibroblasts), while d istal elements acted in an additive manner to repress the effects of t he proximal sequence on reporter gene activity in non-collagen X expre ssing cells only (immature chondrocytes and fibroblasts). We show here that elements within the proximal sequence (nucleotides -557 to -513) are necessary for the cell-specific expression of type X collagen by hypertrophic chondrocytes. These elements bind to proteins of 100 kDa in all three cell types, and 47 kDa in non-collagen X expressing cells . Reporter gene activity in hypertrophic chondrocyles is reduced to th e levels seen in non-collagen X-expressing cells in the absence of the se elements. J. Cell. Biochem. 70:507-516, 1998. (C) 1998 Wiley-Liss, Inc.