Abstract
The transcription factor SOX9 is essential for multiple steps during skeletal development, including mesenchymal cell chondrogenesis and endochondral bone formation. We recently reported that the human SOX9 proximal promoter region is regulated by the CCAAT-binding factor through two CCAAT boxes located within 100 bp of the transcriptional start site. Here we report that the human SOX9 proximal promoter is also regulated by the cyclic-AMP response element binding protein (CREB) and Sp1. We show by DNaseI protection and EMSA analysis that CREB and Sp1 interact with specific sites within the SOX9 proximal promoter region. By transient transfection analysis we also demonstrate that mutations of the CREB and Sp1 binding sites result in a profound reduction of SOX9 promoter activity. Chromatin immunoprecipitation (ChIP) assay demonstrated that both Sp1 and CREB interact with the SOX9 promoter in vivo. Finally, we demonstrate that IL-1beta treatment of chondrocytes isolated from human normal and osteoarthritic (OA) cartilage down-regulates SOX9 promoter activity, an effect accompanied by a reduction of Sp1 binding to the SOX9 proximal promoter.