TGF-β plays a critical dual role in the progression of cancer. During the early phase of tumor progression, TGF-β acts as a tumor suppressor. Later, however, TGF-β promotes SRT1720 processes that support tumor progression, including tumor cell invasion, dissemination and immune evasion [19]. In this study we also demonstrated that overexpressed TGF-β1 inhibits DC migration from tumors to TDLNs. Because DCs play a key role in cell-mediated immunity by acting as an antigen-presenting

cell, a TGF-β1-induced reduction in DC migration into TDLNs would be expected have an immunosuppressive effect within TDLNs, thereby promoting tumor metastasis into TDLNs. Following injection of CFSE-labeled DCs into SCCVII tumors, the numbers of labeled DCs that migrated into TDLNs from tumors expressing TGF-β1 was lower than the numbers that migrated from tumors not expressing TGF-β1. TGFβ1 can immobilize DCs, interfering with their migration and thus the transport of antigen to draining lymph nodes for presentation to adaptive immune cells. Although we do not provide direct evidence of the mechanism by which TGF-β1

inhibits DC migration toward TDLNs in this study, Weber et al. reported that TGFβ1 inhibits DC migration from skin tumors to draining lymph nodes, based on the disappearance Ion Channel Ligand Library of E-cadherin+ DCs from draining lymph nodes consistent with our results [20]. Moreover, Ogata et al. demonstrated that

TGF-β1 not only inhibits expression of CCR7 on DCs, it also inhibits chemokine-mediated DC migration in vitro [17]. We therefore conclude that tumor-derived TGF-β1 inhibits Fossariinae DC migration from tumors to TDLNs. In further investigating the role of TGF-β in metastasis, mice models of metastasis have revealed that systemic inhibition of the TGF-β signaling pathway negatively affects metastasis formation. Consistent with our hypothesis, several independent groups by Padua D et al. and reference therein [21] have found that small-molecule inhibitor of the TGF-β receptors (TGFBR) type I with a human breast cancer cell line, and TGF-β antagonist of the soluble TGFBR2 in a transgenic model decrease the cancer’s metastatic capacity. These results illustrate the capacity to target the TGF-β pathway in order to effectively inhibit metastatic events [21]. However, given the clinical and experimental evidence that TGF-β acts as a tumor suppressor, other groups have argued that TGF-β functions as an inhibitor of epithelial tumor growth and metastasis. In the example, loss of TGFBR2 in mammary epithelial cells or fibroblasts increased tumor formation and enhanced many markers of tumor progression [22]. TGFBR2 knockout animals developed significantly more pulmonary metastases [23]. Interestingly, TGFBR2 knockout tumors have high levels of TGF-β1 most likely secreted by myeloid suppressor cells [24].