Structural and functional analysis of the chick chondroitin sulfate proteoglycan (aggrecan) promoter and enhancer region.

Aggrecan is a large chondroitin sulfate proteoglycan, the expression of which is both tissue-specific and developmentally regulated. Here we report the cloning and sequencing of the 1.8-kilobase genomic 5' flanking sequence of the chick aggrecan gene and provide a functional and structural characterization of its promoter and enhancer region. Sequence analysis reveals potential Sp1, AP2, and NF-I related sites, as well as several putative transcription factor binding sites, including the cartilage-associated silencers CIIS1 and CIIS2. A number of these transcription factor binding motifs are embedded in a sequence flanked by prominent inverted repeats. Although lacking a classic TATA box, there are two instances in the 1.8-kb genomic fragment of TATA-like TCTAA sequences, as have been defined previously in other promoter regions. Primer extension and S1 protection analyses reveal three major transcription start sites, also located between the inverted repeats. Transient transfections of chick sternal chondrocytes and fibroblasts with reporter plasmids bearing progressively reduced portions of the aggrecan promoter region allowed mapping of chondrocyte-specific transcription enhancer and silencer elements that are consistent with the sequence analysis. These findings suggest the importance of this regulatory region in the tissue-specific expression of the chick aggrecan gene.