Identification and characterization of the human SOX6 promoter.

The present study attempted to identify and characterize the embryonic promoter of Sox6, a determinant regulator of chondrogenic differentiation. A common transcription start region for human and mouse Sox6 was initially identified, which contained a highly conserved sequence, A-box. Tandem repeats of A-box had a strong transcriptional activity both at the basal level and in response to Sox9. Cells carrying the 4xA-box-DsRed2 reporter fluoresced only upon chondrogenic differentiation. The 46-bp core enhancer region (CES6) was then identified in the 3' half of A-box, within which a C/EBP-binding motif was identified. Overexpressed C/EBPbeta activated the Sox6 promoter, and mutant 4xCES6 constructs lacking the C/EBP motif lost their basal activity. CES6 and nuclear extracts formed a specific complex, which was supershifted by anti-C/EBPbeta antibody, and in vitro translated C/EBPbeta specifically bound to CES6. Thus, we successfully identified the Sox6 promoter and its core enhancer and characterized the interactions with regulatory transcription factors.