The transcription factor delta EF1 is inversely expressed with type II collagen mRNA and can repress Col2a1 promoter activity in transfected chondrocytes

The regulation of Col2a1, which encodes type II collagen, likely results fr om a balance of both positive and negative proteins. Here we present eviden ce that the transcription factor delta EF1 participates in the negative reg ulation of Col2a1 transcription. A deletion analysis suggested that a regio n between -100 and -307 of the rat Col2a1 gene was required for activity in differentiating chick limb bud mesenchymal cells; however, mutation of a c onserved E2 box site in this region actually increased promoter activity. S upershift analysis demonstrated that delta EF1, a known transcriptional rep ressor, bound to the E2 box in a sequence-dependent manner. Chick limb bud mesenchymal cells, which do not express type II collagen, expressed abundan t delta EF1 mRNA, but, following differentiation in micromass culture, delt a EF1 mRNA expression was lost. Primary embryonic chick sternal chondrocyte s, which express abundant type II collagen, displayed minimal levels of del ta EF1 mRNA The inhibition of Col2a1 transcription following treatment of c hick sternal chondrocytes with growth factors was accompanied by increased delta EF1 expression. Overexpression of delta EF1 in differentiated chondro cytes resulted in decreased expression of a reporter construct containing a collagen II promoter/enhancer insert; however, this negative regulation wa s not dependent on the proximal E2 box. This is the first report of a speci fic transcription factor involved in the negative regulation of Col2a1.