Interleukin-6, CCL2 production in Oral Cancer Cells, Keratinocytes and Fibroblasts

Bacteria colonize oral squamous cell carcinoma (OSCC), but their role in carcinoma progression is not known. Important soluble factors associated with OSCC progression are present in the inflammatory tumor microenvironment: interleukin (IL)-6 that can contribute to cancer cell survival and the chemokine CCL2 that recruits monocytes, which produce IL-6 in response to bacterial products. Carcinoma cells vary markedly in the ability to produce these factors, and little is known about how IL-6 and CCL2 are regulated in the OSCC microenvironment. Objectives: To examine the regulation of CCL2 production in OSCC cells, keratinocytes and fibroblasts in vitro. Methods: We investigated the relationship between IL-6 and CCL-2 production in three OSCC, one oral keratinocyte and one fibroblast cell lines and the impact of Gram (G)-negative (E. coli lipopolysaccharide, LPS) and G-positive (P3CSK4) bacterial products. Results: All three OSCC cell lines produced little to none IL-6 and CCL2. Combined LPS+P3CSK4 stimulated an increase in IL-6 production in OSCC, without any impact on CCL2. In contrast to the keratinocytes, accumulation of IL-6 in cultures over 72 hrs, or addition of recombinant IL-6 to OSCC cells failed to induce CCL2 production in any of the OSCC cells. On the other hand, unstimulated fibroblasts produced CCL2, which significantly increased in response to LPS and LPS+P3CSK4, but not to P3CSK4 only or to recombinant IL-6. Conclusion: Results of this study suggest that OSCC cells may not be a significant source of CCL2 or IL-6. Rather, stromal cells, such as fibroblasts, especially when stimulated with certain bacterial products, could be more important for monocyte recruitment leading to IL-6 production in the tumor microenvironment. Supported by the NYU College of Dentistry.