A TLR4-interacting peptide inhibits lipopolysaccharide-stimulated inflammatory responses, migration and invasion of colon cancer SW480 cells

Inflammation is a major risk factor for carcinogenesis in patients affected by chronic colitis, yet the molecular mechanisms underlying the progression from chronic inflammation to cancer are not completely understood. Activation of the Toll-like receptor 4 (TLR4)-NF kappa B signaling axis is associated with inflammation. Thus, we hypothesized that inhibition of TLR4-NF kappa B signaling might help in limiting inflammatory responses and inflammation-induced oncogenesis. In this work, we studied the effects of a TLR4-interacting surfactant protein A-derived (SPA4) peptide on lipopolysaccharide (LPS)-induced TLR4-NF kappa B signaling and cancer progression. We first characterized this peptide for its ability to bind the TLR4 ligand-LPS and for physico-chemical characteristics. Inflammation was induced by challenging the colon cancer SW480 cells with Escherichia coli LPS. Cells were then treated with varying amounts of the SPA4 peptide. Changes in the expression of TLR4, interleukin (IL)-1 beta and IL-6, in intracellular NF kappa B-related signal transducers (IKB alpha, p65, phosphorylated IKB alpha, phosphorylated p65, RelB, COX-2) as well as in the transcriptional activity of NF kappa B were studied by immunocytochemistry, immunoblotting and NF kappa B reporter assay, respectively. Simultaneously, the effects on LPS-induced cell migration and invasion were determined. We found that the SPA4 peptide does not bind to LPS. Rather, its binding to TLR4 inhibits the LPS-induced phosphorylation of p65, production of IL-1 beta and IL-6, activity of NF kappa B, migration and invasion of SW480 cells. In conclusion, our results suggest that the inhibition of TLR4-NF kappa B signaling by a TLR4-binding peptide may help for the treatment of chronic inflammation and prevention of inflammation-induced cancer in patients with colitis.