Human Cancer Biology Reciprocal Interactions between Tumor-Associated Macrophages and CD44-Positive Cancer Cells via Osteopontin/CD44 Promote Tumorigenicity in Colorectal Cancer

Purpose:CD44 is of functional importance for tumor initiation and progression in colorectal cancer, but how this molecule benefits cancer cells from the tumor microenvironment, especially tumor-associated macrophages (TAM), remains poorly defined. ExperimentalDesign: In vivo tumorigenic assayswere conducted to assess the role ofmurine TAMs in the tumorigenesis of human colorectal cancer cells. Both in vitro and in vivoosteopontin (OPN) expression levels in TAMs were examined by immunohistochemistry, quantitative PCR, and Western blotting. Soft agar colony formation assays were used to estimate the clonogenicity of colorectal cancer cells that had received different treatments. The relationships between the expression levels of OPN, CD44v6, and CD68 and clinical prognosis were evaluated by tissue microarray analysis. Results: We found that macrophages, when coinjected or cocultured with CD44-positive colorectal cancer cells, were able to produce higher levels of OPN, which in turn facilitated the tumorigenicity and clonogenicity of the colorectal cancer cells. The knockdown of CD44 or treatment with blocking antibodies toCD44 attenuatedOPN secretion.OPN, through binding to its receptor CD44, activated c-jun-NH2-kinase signaling and promoted the clonogenicity of colorectal cancer cells. Moreover, tissue microarray data have shown thatOPNexpression, in combinationwith CD44v6, has a negative correlationwith colorectal cancer