Effects of FoxO6 on proliferation and invasion of colorectal cancer cells

Abstract

Objective: To investigate the effects and the mechanism of FoxO6 on the proliferation and invasion of colorectal cancer cells. Methods: FoxO6 siRNA was transfected into colorectal cancer cell HCT116 and SW480. The overexpression vector pcDNA.3.1-c-Myc was constructed and co-transfected into HCT116 and SW480 cells with FoxO6 siRNA. Real-time fluorescent quantitative PCR (RT-qPCR) and western blot were used to detect the mRNA and protein expressions of FoxO6, c-Myc, and p21 in HCT116 and SW480 cells. Bromodeoxyuridine (BrdU) was used to detect cell proliferation and Transwell assay was performed to detect the invasion ability of these cells. SW480 cells transfected with FoxO6 shRNA lentivirus (LV-FoxO6) and were injected into the right armpit of BAL b/c nude mice to construct a tumor-bearing mode and the tumor volumes were measured on the days of 10, 13, 16, 19, 22, and 25 after injection. Results: The FoxO6 mRNA were 0.91±0.04, 1.72±0.07, and 2.03±0.06, and protein expression were 0.70±0.04, 1.35±0.08, and 1.56±0.07 in normal colon cell FHC, colorectal cancer cells HT116 and SW480, respectively. The protein and mRNA levels of FoxO6 in HCT116 and SW480 were significantly higher than those in FHC (both P<0.05). Knockdown of FoxO6 in HCT116 and SW480 cells decreased the mRNA and protein expressions of FoxO6 (both P<0.05), the cell proliferation ability (absorbances were 0.26±0.07 and 0.27±0.06, both P<0.05), cell invasion ability (the invaded cell numbers were 42.3±3.3 and 45.7±4.1, both P<0.05), and the mRNA and protein expressions of c-Myc, while increased the mRNA and protein expressions of p21 (both P<0.01). Overexpression of Myc in FoxO6 silenced HCT116 and SW480 cells decreased the expression of p21, while increased the cell proliferation ability (absorbances were 0.54±0.09 and 0.58±0.07, both P<0.01) and invasion ability (the invaded cell numbers were 79.2±5.9 and 80.5±6.4, both P<0.01). On the 25th day after cell inoculation in nude mice, the tumor volume of LV-FoxO6 group was (190.6±36.2) mm(3), significantly lower than (437.8.6±69.2) mm(3) of LV-NC group (P<0.05). Conclusion: FoxO6 promotes the proliferation and invasion of colorectal cancer cells through facilitating c-Myc mediated p21 expression inhibition.