Introduction: To verify whether human colon carcinoma cells can express Toll-like receptor 4 (TLR4) and investigate the biological function of TLR4 on human colon carcinoma cells.
Methods: Human colon carcinoma cells SW480 was cultured with RPMI 1640 medium. The expression of TLR4 was analyzed by reverse transcription polymerase chain reaction and quantified by flow cytometry. Cell proliferation was evaluated by 3-[4, 5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide assay. The production of transforming growth factor-beta, vascular endothelial growth factor, and interleukin-8 induced by lipopolysaccharide (LPS)-the TLR4 ligand was tested by enzyme-linked immunosorbent assay. Whether mitogen-associated protein kinases and nuclear factor-kappaB (NF-kappaB) proteins were activated was analyzed by Western blot. Apoptosis was analyzed by Annenxin V/PI staining.
Results: TLR4 is expressed on SW480 cells. LPS could not affect TLR4 expression and the proliferation of SW480 cells. LPS increased the phosphorylation of ERK1/2 and P38 and activated NF-kappaB. LPS promoted the production of vascular endothelial growth factor, transforming growth factor-beta, and interleukin-8. In addition, LPS induced resistance of SW480 cells to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. Furthermore, NF-kappaB activation was necessary for apoptosis resistance of SW480 cells induced by LPS.
Conclusion: TLR4 is expressed on human colon carcinoma cells and functionally active. It may play important roles in promoting immune escape of human colon carcinoma cells by inducing immunosuppressive factors and apoptosis resistance.