Reversing hypomethylation of TIAM1 promoter inhibits TIAM1 gene expression and cell proliferation and migration in colorectal cancer

Objective: To investigate the reversing effect of hypomethylation status of T lymphoma invasion and metastasis 1 (TIAM1) gene promoter on TIAM1 expression and evaluate the biological behavior of colorectal cancer cells in vivo and in vitro. Methods: DNA methyltransferase was used to hypermethylate the predicted TIAM1 promotor. Then the luciferase activity of the unmethylated TIAM1 promoter (UP-T) and hypermethylated TIAM1 promoter (MP-T) was examined by Dual Luciferase Reporter assay. We constructed plasmids with the PGL3.0-Basic-hypermethylated-promoter-TIAM1-cDNA vector and PGL3.0-Basic-unmethylated-promoter-TIAM1-cDNA vector and then transfected them into cell lines HT29, LS174T and SW480. Expression of TIAM1 protein were examined by Western blot. Subsequently, the biological behavior of the transfected cells were assessed by MTT, plate colony formation and in-vitro invasion analysis. SW480 cells labeled with green fluorescent protein (SW480/GFP) were treated with S-adenosylmethionine (SAM, methyl donor), S-adenosylhomocysteine (SAH, non-methyl donor), respectively. A visualized orthotopic animal model was built by injecting the above three group cells into nude mice subcutaneously and intravenously. Then the effects of aberrant DNA methylation on the biological behavior of colorectal cancer cells were detected in vivo. Results: The hypermethylated TIAM1 promoter showed lower luciferase activity than that of the unmethylated promoter. Expression of TIAM1 protein was statistically decreased in MP-T transfectant. Furthermore, a significant suppressed proliferation, migration and invasion ability were observed in MP-T transfectant cells as compared with those in the UP-T transfectant cells (P<0.05). Hypermethylation of SW480/GFP cells resulted in decreased proliferation, migration and invasion abilities in vivo. Conclusion: Aberrant methylation of TIAM1 promoter was closely related to aberrant TIAM1 expression in colorectal cancer. Reversing hypomethylation status of TIAM1 promoter can lead to inhibition of cell growth, migration and decreased invasion capacity of colorectal cancer in vivo and in vitro, which implied a potential therapy pathway for colorectal cancer clinically.