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Carcinoma-produced factors activate myeloid cells through TLR2 to stimulate metastasis


Metastatic progression depends on genetic alterations intrinsic to cancer cells as well as the inflammatory microenvironment of advanced tumours1,2. To understand how cancer cells affect the inflammatory microenvironment, we conducted a biochemical screen for macrophage-activating factors secreted by metastatic carcinomas. Here we show that, among the cell lines screened, Lewis lung carcinoma (LLC)3 were the most potent macrophage activators leading to production of interleukin-6 (IL-6) and tumour-necrosis factor-α (TNF-α) through activation of the Toll-like receptor (TLR) family members4 TLR2 and TLR6. Both TNF-α and TLR2 were found to be required for LLC metastasis. Biochemical purification of LLC-conditioned medium (LCM) led to identification of the extracellular matrix proteoglycan versican, which is upregulated in many human tumours including lung cancer5,6, as a macrophage activator that acts through TLR2 and its co-receptors TLR6 and CD14. By activating TLR2:TLR6 complexes and inducing TNF-α secretion by myeloid cells, versican strongly enhances LLC metastatic growth. These results explain how advanced cancer cells usurp components of the host innate immune system, including bone-marrow-derived myeloid progenitors7, to generate an inflammatory microenvironment hospitable for metastatic growth.

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Figure 1: Metastatic carcinomas secrete factors that induce macrophage production of TNF-α, needed for lung metastasis.
Figure 2: LLC-secreted factor activates TLR2 to induce lung inflammation.
Figure 3: TLR2 is required for metastatic growth.
Figure 4: Versican is a TLR2 agonist and metastasis-enhancing factor.


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S.K. was supported by the International Human Frontier Science Program Organization (IHFSPO), the National Cancer Institute-sponsored Cancer Therapeutic Training Program and a Ruth L. Kirschstein National Research Service Award. Y.K., H.T., J.-L.L., P.D. and S.G. were supported by the California Institute of Regenerative Medicine, the Japanese Respiratory Society, the Life Science Research Foundation, IHFSPO and the Crohn’s and Colitis Foundation of America, respectively. Work in the M.K. laboratory was supported by grants from the National Institutes of Health and a Littlefield-AACR grant in Metastatic Colon Cancer Research. M.K. is an American Cancer Society Research Professor. We thank S. Akira and B. Beutler for TLR and adaptor protein deficient mice, D. Zimmermann for human versican construct, R. Hoffman for DsRed-LLC cells and K. Takenaga for LLC-P29 cells. We also thank R. Gallo and K. Yamasaki for the hyaluronan-inhibiting peptides and advice, J. Varner for analysing cell migration and Santa Cruz Biotechnology for gifts of antibodies.

Author Contributions S.K., H.T., W.-W.L. and M.K. conceived the project and planned experiments and analyses, which were performed by S.K., H.T. and W.-W.L. Y.K. and J.-L.L. helped with protein purification and tail-vein injection of cancer cells and tumour analysis, respectively. P.D. and S.G. analysed M2 macrophages and tissue versican content, and effect of TNF-α neutralization on lung metastasis. M.K. oversaw the entire project and wrote the manuscript with S.K.

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Correspondence to Michael Karin.

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Kim, S., Takahashi, H., Lin, WW. et al. Carcinoma-produced factors activate myeloid cells through TLR2 to stimulate metastasis. Nature 457, 102–106 (2009).

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