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Evidence suggests that interplay of malignant and stromal cells is essential in tumorigenesis. Our earlier results indicated that human colon cancer cells enhance mouse stromal cell-derived CSF-1, matrix metalloprotease (MMP) and VEGF-A production. This study sought to characterize the mechanisms by which colon cancer cells upregulate host CSF-1 and MMPs. A cDNA expression array was used to profile cytokine expression in human SW620 colon cancer cells in vitro and in lysates from SW620 tumors grown in immune-deficient mice. mRNA expression analyses were performed by real time RT-PCR. SW620 cells were co-cultured with CSF-1-dependent mouse macrophages or with fibroblasts. These co-cultures were treated with small interfering (si)RNAs directed against human or mouse TNF-α, mouse CSF-1, human EMMPRIN, or mouse basigin, or with recombinant TNF-α. The effect of soluble cancer cell-derived factors on stromal cells was investigated by treating mouse macrophages and fibroblasts with conditioned medium of SW620 cells. Human TNF-α and EMMPRIN mRNA increased significantly with tumor growth. Mouse CSF-1 blockade by antisense oligonucleotides in mice bearing human SW620 xenografts reduced host tissue CSF-1, MMP-2, and VEGF-A and upregulated tumor cell-derived TNF-α expression. Inhibiting mouse basigin expression by siRNAs downregulated MMP-2 but did not reduce tumor growth in mice. Treatment of mouse macrophages and fibroblasts with conditioned medium of SW620 cells or recombinant TNF-α upregulated TNF-α, CSF-1, MMP-2, and VEGF-A expression in macrophages, but only CSF-1 in fibroblasts. In macrophage co-cultures, human TNF-α gene silencing decreased mouse TNF-α, CSF-1, MMP-2, and VEGF-A but did not affect human EMMPRIN and mouse basigin expression. In fibroblast co-cultures mouse basigin and human EMMPRIN gene silencing suppressed mouse MMP-2, while no MMP-2 inhibition was observed in macrophage co-cultures following basigin and EMMPRIN inhibition. These results indicate that human colon cancer cell-derived TNF-α stimulates CSF-1 and TNF-α production by mouse macrophages and CSF-1 production by fibroblasts. The CSF-1 in turn, induces VEGF-A and MMP-2 over-expression in macrophages in an autocrine and paracrine manner. Finally, while CSF-1 regulates MMP-2 production in macrophages directly, MMP-2 production in fibroblasts seems to be indirectly regulated via basigin and EMMPRIN. This work provides evidence for a synergistic interaction between tumor cells and stromal cells; and indicates different mechanisms by which macrophages and fibroblasts can contribute to colon cancer progression.Supported by Austrian Research Foundation (FWF) grant #P15819 to S. Aharinejad.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]