Knockdown of peroxisome proliferator-activated receptor-b induces less differentiation and enhances cell-fibronectin adhesion of colon cancer cells

The role of peroxisome proliferator-activated receptor-b/d (PPAR-b/d) in the pathogenesis of colon cancer remains highly controversial. This study specifically silenced the PPAR-b expression in three colon cancer cell lines with different metastatic potentials. Although PPAR-b knockdown resulted in more malignant morphological changes, bigger colony sizes and lower carcinoembryonic antigen (CEA) secretion, and enhanced the cell-fibronectin adhesion, cell invasion and migration were unaffected. These effects were stronger in poorly metastatic cell lines compared with highly metastatic ones. Simultaneously, PPAR-b knockdown decreased the mRNAs encoding adipocyte differentiation-related protein and liver fatty acid binding protein, and increased the mRNA of ILK, whereas the mRNAs encoding integrin-b1 and angiopoietin-like 4 were unchanged. Using immunohistochemistry, we determined that the intensity of PPAR-b expression was stronger in rectal cancers with better differentiation than in those with poor differentiation, and was stronger in early-stage tumors than in advanced ones. Together, these findings consistently indicate that PPAR-b may facilitate differentiation and inhibit the cell-fibronectin adhesion of colon cancer, having a role as an inhibitor in the carcinogenesis and progression of colorectal cancer. Interestingly, PPAR-b seems to have a more important role in poorly metastatic cells than in highly metastatic ones.