Loss of TGFß signaling promotes colon cancer progression and tumor-associated inflammation.

TGFß has both tumor suppressive and tumor promoting effects in colon cancer. Also, TGFß can affect the extent and composition of inflammatory cells present in tumors, contextually promoting and inhibiting inflammation. While colon tumors display intratumoral inflammation, the contributions of TGFß to this process are poorly understood. In human patients, we found that epithelial loss of TGFß signaling was associated with increased inflammatory burden; yet overexpression of TGFß was also associated with increased inflammation. These findings were recapitulated in mutant APC models of murine tumorigenesis, where epithelial truncation of TGFBR2 led to lethal inflammatory disease and invasive colon cancer, mediated by IL8 and TGFß1. Interestingly, mutant APC mice with global suppression of TGFß signals displayed an intermediate phenotype, presenting with an overall increase in IL8-mediated inflammation and accelerated tumor formation, yet with a longer latency to the onset of disease observed in mice with epithelial TGFBR-deficiency. These results suggest that the loss of TGFß signaling, particularly in colon epithelial cells, elicits a strong inflammatory response and promotes tumor progression. This implies that treating colon cancer patients with TGFß inhibitors may result in a worse outcome by enhancing inflammatory responses.

TGFß Signaling in the Pancreatic Tumor Microenvironment Promotes Fibrosis and Immune Evasion to Facilitate Tumorigenesis.

In early pancreatic carcinogenesis, TGFß acts as a tumor suppressor due to its growth-inhibitory effects in epithelial cells. However, in advanced disease, TGFß appears to promote tumor progression. Therefore, to better understand the contributions of TGFß signaling to pancreatic carcinogenesis, we generated mouse models of pancreatic cancer with either epithelial or systemic TGFBR deficiency. We found that epithelial suppression of TGFß signals facilitated pancreatic tumorigenesis, whereas global loss of TGFß signaling protected against tumor development via inhibition of tumor-associated fibrosis, stromal TGFß1 production, and the resultant restoration of antitumor immune function. Similarly, TGFBR-deficient T cells resisted TGFß-induced inactivation ex vivo, and adoptive transfer of TGFBR-deficient CD8(+) T cells led to enhanced infiltration and granzyme B-mediated destruction of developing tumors. These findings paralleled our observations in human patients, where TGFß expression correlated with increased fibrosis and associated negatively with expression of granzyme B. Collectively, our findings suggest that, despite opposing the proliferation of some epithelial cells, TGFß may promote pancreatic cancer development by affecting stromal and hematopoietic cell function. Therefore, the use of TGFBR inhibition to target components of the tumor microenvironment warrants consideration as a potential therapy for pancreatic cancer, particularly in patients who have already lost tumor-suppressive TGFß signals in the epithelium. Cancer Res; 76(9); 2525-39. ©2016 AACR.