Metastatic Cancerous Intestinal Epithelial Cells express Toll-like receptor 3 and release RANTES/CCL5 and IP-10/CXCL10 in response to Double-stranded RNA
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Toll-like receptors (TLR)s are important for mounting an inflammatory response against invading microorganisms by recognizing pathogen-associated molecular patterns (PAMP)s, which are rare or absent in vertebrates. TLRs can also recognize a number of endogenous ligands collectively termed danger-associated molecular patterns (DAMP)s, such as degradation products of hyaluronan, nucleic acids and uric acid. Versican is an extracellular protoglycan which is reported to be an endogenous ligand for TLR2. Upregulation of Versican is associated with several types of cancers, including melanomas, lung and breast cancer. Versican secreted by Lewis lung carcinoma cells activate TLR2 on macrophages to secrete TNF-αand create an inflammatory environment which promotes tumor metastasis. The aim of this study was to determine if similar mechanisms are involved in the progression of colon cancer. The four IEC cancer cell lines, SW480, SW620, CaCO-2 and HT-29, are reported to display differences with respect to metastatic ability, and were therefore screened in this study with respect to versican expression and for their ability to release immune-stimulating components. The cell lines were found to differentially express versican mRNA. Notably, the highest expression of versican was, however, found in healthy IEC cells, while cancerous IEC cells had lower, or no, versican mRNA expression. Conditioned medium from IEC cancer cell lines further failed to stimulate TNF production in peripheral blood mononuclear cells (PBMC). Combined, these results imply that versican expression in IEC cells does not correlate with metastatic ability. Conditioned medium from both healthy and cancerous IEC induced varying levels of the chemokines interleukin (IL) 8 and RANTES/CCL5 in PBMC. Both healthy and cancerous IEC cell lines were also found to constitutively express IL-8, suggesting that this is not a feature of cancerous cells. Constitutive release of the anti-inflammatory cytokine IL-10 was found to be a unique feature of SW480 cells, and appeared to be down-regulated in the more metastatic cell line SW620. We further compared the responsiveness of the different IEC cells to TLR ligands and found that a number of TLR ligands induced inflammatory responses in cancerous IEC cells, but not in healthy IEC cells. The TLR3 ligand poly-IC strongly induced several chemokines, including interferon inducible protein-10 (IP-10), IL-8, and RANTES in all tested cell lines, except CaCO-2. Interestingly, the most metastatic cell lines highly expressed TLR3, induced the highest levels of IP-10, and displayed the broadest range of responses to Poly-IC. Combined, these results suggest an unexpected, and a potentially detrimental role, for TLR3 activation and IP-10 induction in the progression of colon cancer. Taken together, these findings provide further insight into the TLR biology of IEC cells, the roles these receptors play in modulating inflammation and the consequences this may have for colon cancer development.