Sp1 upregulates the proximal promoter activity of the mouse collagen α1(XI) gene () in chondrocytes

Type XI collagen is a cartilage-specific extracellular matrix, and is important for collagen fibril formation and skeletal morphogenesis. We have previously reported that NF-Y regulated the proximal promoter activity of the mouse collagen α1(XI) gene () in chondrocytes (Hida In Vitro ). However, the mechanism of the gene regulation in chondrocytes has not been fully elucidated. In this study, we further characterized the proximal promoter activity of the mouse gene in chondrocytes. Cell transfection experiments with deletion and mutation constructs indicated that the downstream region of the NF-Y binding site (-116 to +1) is also necessary to regulate the proximal promoter activity of the mouse gene. This minimal promoter region has no TATA box and GC-rich sequence; we therefore examined whether the GC-rich sequence (-96 to -67) is necessary for the transcription regulation of the gene. Luciferase assays using a series of mutation constructs exhibited that the GC-rich sequence is a critical element of promoter activity in chondrocytes. Moreover, in silico analysis of this region suggested that one of the most effective candidates was transcription factor Sp1. Consistent with the prediction, overexpression of Sp1 significantly increased the promoter activity. Furthermore, knockdown of Sp1 expression by siRNA transfection suppressed the proximal promoter activity and the expression of endogenous transcript of the mouse gene. Taken together, these results indicate that the transcription factor Sp1 upregulates the proximal promoter activity of the mouse gene in chondrocytes.