Abstract
Type 1 transforming growth factor β receptor (TGFBR1)*6A, a common hypomorphic variant of TGFBR1, may act as a susceptibility allele in colorectal cancer. However, the contribution of TGFBR1*6A to colorectal cancer development is largely unknown. To test the hypothesis that TGFBR1*6A promotes colorectal cancer invasion and metastasis via Smad-independent transforming growth factor-β (TGF-β) signaling, the effect of TGFBR1*6A on the invasion of colorectal cancer cells was assessed. pCMV5-TGFBR1*6A-HA plasmids were transfected into SW48 and DLD-1 cells by Lipofectamine-mediated DNA transfection. The effect of TGF-β1 on the proliferation of SW48 and DLD-1 cells transfected with TGFBR1*6A was determined by MTT assay. The effects of the TGF-β1 on the invasion of the transfected SW48 and DLD-1 cells were determined using Matrigel-coated plates. Transforming migrating chambers were used to determine the effects of TGF-β1 on the migration of the transfected SW48 and DLD-1 cells. Western blot analysis was used to determine the expression of phosphorylated (p-) extracellular-signal-regulated kinase (ERK), p-P38 and p-SMAD family member 2 in SW48 cells. Using transfected TGFBR1*6A SW48 and DLD-1 cell lines our group demonstrated that, in comparison with TGFBR1*9A, TGFBR1*6A is capable of switching TGF-β1 growth-inhibitory signals into growth-stimulatory signals which significantly increased the invasion of SW48 and DLD-1 cells. Functional assays indicated that TGFBR1*6A weakened Smad-signaling but increased ERK and p38 signaling, which are crucial mediators of cell migration and invasion. From this, it was possible to conclude that TGFBR1*6A enhanced SW48 cell migration and invasion through the mitogen-activated protein kinase pathway and that it may contribute to colorectal cancer progression in a TGF-β1/Smad signaling-independent manner. This suggests that TGFBR1*6A may possess oncogenic properties and that it may affect the migration and invasion of colorectal cancer cells.