[Expression of SOX9 in pulmonary fibrosis and its effects on caveolin-1 gene expression]

Objective To investigate the expression of the transcription factor sex-determining region Y-box protein 9 (SOX9) in pulmonary fibrosis (PF), its regulatory effects on the expression of the PF-related gene caveolin 1 (Cav-1), and the underlying molecular mechanisms. Methods The expression levels and correlation of SOX9 and Cav-1 in PF patients were analyzed using the GEO database (GSE2052 dataset). Chromatin immunoprecipitation (ChIP) assays were conducted to verify the binding of SOX9 to the Cav-1 promoter. The Cav-1 promoter fragment (-1000 to +60 nt) was cloned into the luciferase reporter vector pGL3-basic to generate pCav-1-1060, and potential SOX9 binding sites within this fragment were predicted using bioinformatics tools. The activity of the Cav-1 promoter fragment in MRC-5 cells was evaluated using a dual-luciferase reporter system. To assess SOX9-mediated regulation of Cav-1, pCav-1-1060 was co-transfected with either SOX9-targeting small interfering RNA (siRNA) or SOX9 overexpression plasmids into MRC-5 cells, followed by dual-luciferase reporter assays. Quantitative real-time PCR (qPCR) and Western blotting were employed to examine the effects of SOX9 knockdown and overexpression on Cav-1 expression at mRNA and protein levels. Results In PF patients (GSE2052 dataset), Cav-1 expression was downregulated, while SOX9 expression was upregulated, showing a significant negative correlation between them. SOX9 directly bound to the Cav-1 promoter. The Cav-1 promoter fragment (-1000 to +60 nt) displayed transcriptional activity in MRC-5 cells and contained predicted SOX9 binding motifs. SOX9 negatively regulated Cav-1 expression at the promoter, transcriptional, and translational levels. Conclusion The transcription factor SOX9 is upregulated in PF and exerts a negative transcriptional regulatory effect on the promoter activity, mRNA, and protein expression of the PF-associated gene Cav-1.