PAX9 and Col1A1 may regulate the progression of colon cancer through interactions with the TGF-β1/Smad pathway.

Transforming growth factor-β1 (TGF-β1) is widely involved in the progression of advanced cancer through the downstream Smad pathway, but the underlying mechanisms are still not fully understood. This project aimed to explore the relationship between key molecules of the TGF-β1/Smad pathway and the progression of colon cancer, as well as its upstream and downstream regulatory mechanisms. Clinical data and related gene expression data of patients with colon cancer were retrieved from clinical databases and genomic libraries such as TCGA-COAD, GEO, and ENCODE. The expression levels of key molecules of the TGF-β1/Smad pathway (TGF-β1, TGF-β1 receptor, and SMAD2/3/4) in colon cancer/paracancerous tissue samples and their relationships with prognosis were analyzed. R packages and RStudio were used to analyze genes that were differentially expressed between colon cancer and normal tissues and the promoter regions bound by Smad2/3. JASPAR and GO/KEGG enrichment were used to predict upstream transcription factors and downstream regulatory genes of the TGF-β1/Smad pathway. A total of 459 patients with colon cancer were included in this study. Different TGF-β1 expression levels significantly affected the overall survival (OS) and disease-free survival (DFS) of patients with colon cancer (P < 0.05). The expression of TGF-β1/Smad pathway molecules was significantly associated with the specific stage of cancer. A total of 954 genes had Smad2/3 binding sites in their promoter regions. The expression of the main transcription factor, paired box 9 (PAX9), that regulates the Smad2/3 pathway was generally higher in colon cancer tissues than in normal tissues. The expression of the transcription factor vitamin D (1,25- dihydroxyvitamin D3) receptor (VDR) was significantly different among different cancer types, especially in colon cancer, where its expression was significantly higher than that in normal tissues. Col1A1 expression was strongly correlated with that of TGF-β1 (R = 0.79, P < 0.001). High expression of COL1A1 tended to reduce overall survival (P = 0.072), and the high-expression group had a 1.6 times lower risk of DFS than the low-expression group did (P < 0.05). The TGF-β1/Smad pathway may regulate the progression and prognosis of colon cancer in conjunction with multiple upstream and downstream target genes (including PAX9, VDR, and Col1A1) and is related to cancer stage.