We sought to understand the mechanisms behind the potent effect of stromal TGF-beta program on the capacity of colorectal cancer (CRC) cells to initiate metastasis. We discovered that mice subcutaneous tumors and metastases generated in the context of a TGF-beta activated microenvironment displayed prominent accumulation of p-STAT3 in CRC cells compared with those derived from control cells. STAT3 signaling depended on GP130 as shown by strong reduction of epithelial p STAT3 levels upon GP130 shRNA-mediated knockdown in CRC cells.

Metastasis depends on a gene program expressed by the tumor microenvironment upon TGF-beta stimulation. CRC (Colorectal cancer) cell lines did not induce robust stromal TGF-beta responses when injected into nude mice as shown by lack of p-SMAD2 accumulation in tumor-associated stromal cells. To enforce high TGF-beta signaling in xenografts, we engineered CRC cell lines to secrete active TGF-beta. Subcutaneous tumors obtained from HT29-M6TGF-β, KM12L4aTGF-β cells and SW48TGF-β cells contained abundant p-SMAD2⁺ stromal cells.