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

Abstract

Metastatic progression depends on genetic alterations intrinsic to cancer cells as well as the inflammatory microenvironment of advanced tumors 1,2 . To understand how cancer cells affect the inflammatory microenvironment, we conducted a biochemical screen for macrophage activating factors secreted by metastatic carcinomas. Amongst the cell lines screened, Lewis lung carcinoma (LLC) 3 were the most potent macrophage activators leading to production of IL-6 and TNF-α through activation of the Toll-like receptor family members 4 TLR2 and TLR6. Both TNF-α and TLR2 were found to be required for LLC metastasis. Biochemical purification of LLC conditional medium (LCM) led to identification of the extracellular matrix proteoglycan versican, which is upregulated in many human tumors including lung cancer 5,6 , as a macrophage activator that acts via 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 progenitors 7 , to generate an inflammatory microenvironment hospitable for metastatic growth.Distant site metastases are the leading cause of cancer-associated mortality and depend on genetic and/or epigenetic alterations that are intrinsic to cancer cells or extrinsic factors provided by the tumor microenvironment 1 . For instance, cytokines produced by inflammatory cells can enhance metastatogenesis by repressing the metastasis suppressor maspin within primary prostate carcinoma cells 8 . Furthermore, tumor progression and metastasis positively correlate with presence of infiltrates containing myeloid and lymphoid cells 2,9 . It was shown that certain carcinomas secrete factors that upregulate fibronectin and recruit vascular endothelial growth factor receptor 1 (VEGFR1)-positive hematopoetic progenitors to sites of Correspondence and requests for materials should be addressed to M.K. future metastatic growth, termed the pre-metastatic niche 7 . To examine whether cancer cells secrete factors that directly activate myeloid cells to produce tumor promoting cytokines 10 , we collected serum free conditioned medium (CM) from different cancer cell lines, derived mainly from C57BL6 mice, and applied it to bone marrow (BM)-derived macrophages (BMDM), which were assayed for production of IL-1β, IL-6 and TNF-α. The screen included 1C1C7 and TrampC1, which are liver and prostate cancer cell lines, respectively, with little or no metastatic activity, and two metastatic breast and lung carcinomas, 4T1 and LLC, respectively. CM from metastatic cells, especially LLC, induced higher amounts of IL-6 and TNF-α secretion than CM from non-metastatic cells (Fig. 1A). IL-1β secretion was undetectable and the CM did not contain IL-6 or TNF-α (data not shown). LLC-CM (LCM) also induced expression of Il1β, Il6 and Tnfα mRNAs, whereas serum free medium (SFM) and NIH3T3 CM were inacti...

The ADAMTS1 Protease Gene Is Required for Mammary Tumor Growth and Metastasis

“…Accumulation of cleaved versican in Adamts1 ϩ/ϩ tumors may help to polarize a tumor-promoting immune response, as reported in Lewis lung carcinoma, in which tumor-derived versican interacting with Toll-like receptor 2 (TLR2) on immune cells is required for establishment of tumor foci in lungs. 59 The present study provides in vivo evidence that ADAMTS1 plays a nonredundant role in growth and metastasis of mammary cancers. Lung metastasis in the PyMT mouse model is associated with spontaneously increased levels of ADAMTS1.…”

Versican expression is associated with tumor-infiltrating CD8-positive T cells and infiltration depth in cervical cancer

“…Recently, in a rat experimental model, fragments of versican were shown to activate TLR2-positive macrophages. 41 We could demonstrate TLR2-positive macrophages in both the stroma and within the epithelial compartment (data not shown); however, no statistically significant association between versican expression and the presence of TLR2-positive macrophages was observed. In addition, we did not find an association between TLR2-positive macrophages and TNFa expression (data not shown).…”

Premetastatic milieu explained by TLR4 agonist-mediated homeostatic inflammation

“…2 In metastasis induced by tumor-derived versican, TLR2 plays an essential role in driving the production of bone marrow-derived myeloid cells. 32 In both cases, cross-talk between TLR and the TNF receptor exists. SAA3 is capable of inducing TNF-a expression in the lungs, 33 and versican-induced metastasis is abrogated by knocking out TNF-a.…”

“…SAA3 is capable of inducing TNF-a expression in the lungs, 33 and versican-induced metastasis is abrogated by knocking out TNF-a. 32 TLR4 is expressed in granulocyte-macrophage progenitors through differentiated myeloid cells. This differentiation usually occurs upon the action of cytokines, such as G-CSF, but LPS-stimulated granulocytemacrophage progenitors do not require cytokine action.…”