Smad4 acts as tumor suppressor by antagonizing lymphangiogenesis in colorectal cancer.

Vascular endothelial growth factor-C (VEGF-C) is considered a vital promoter to tumor lymphangiogenesis. Smad4 is an important downstream mediator of transforming growth factor beta (TGF-β) signaling pathway. Smad4 is regarded as a tumor suppressor in colon cancer, but its role in lymphangiogenesis in colorectal cancer is still unclear. In the present study, we investigated the potential inhibiting effect of Smad4 in lymphangiogenesis, and its correlation with VEGF-C secretion in colon cancer. We investigated endogenous Smad4 expression in 7 human colorectal cancer cell lines, and found that six of colon cancer cell lines existed with loss of Smad4. Expression of Smad4 in SW480 cell line is extremely low. SW480 cells were used to establish a Smad4 over-expression model. We investigated the relationship between Smad4 and VEGF-C expression in SW480 cells and found that Smad4 can inhibit the expression of VEGF-C. In an in vitro assay, we found that overexpression of Smad4 can reduce migration and invasion ability in SW480 cells, but had no effect on cell proliferation. Interestingly, Smad4 definitely inhibited the growth in an in vivo assay, and the volumes of transplanted tumors which originated from Smad4 overexpressing SW480 cells in nude mice were smaller than those of normal SW480 cells. In addition, we also demonstrated that Smad4 can inhibit lymphangiogenesis in vivo by immunohistochemistry. In summary, our findings provide molecular evidence that Smad4 may reduce lymphangiogenesis of colon cancer cell by attenuating VEGF-C secretion and act as tumor suppressor by inhibiting migration, invasion and tumorigenicity.