Expression of mammalian target of rapamycin in colon cancer and its effect on proliferation and apoptosis of human colon cancer HT-29 cells

Abstract

To explore the expression of mammalian target of rapamycin (mTOR) in colon cancer and the inhibitory effect of mTOR siRNA on the proliferation and apoptosis of human colon cancer HT-29 cells. Immunohistochemistry was employed to detect the expression of phosphorylated mTOR (p-mTOR) in colon cancer tissues (n = 50) and normal colon tissues (n = 50) from First Affiliated Hospital of Zhengzhou University (October 2009 to June 2010). The correlations were examined between the expression of p-mTOR and such clinical pathological data as colon cancer staging and lymph node metastasis. The oligonucleotide templates of mTOR siRNA were designed and employed to transfect HT-29. The nonsense control groups were established accordingly by siRNA with an insignificant order. And the blank group had no transfection. The protein level of mTOR was measured by Western blotting. The method of MTT was used to detect the cell proliferation. And the method of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was employed to detect the apoptosis. The expression of p-mTOR was higher in the colon cancer group than the control group [60% (30 cases) vs 14% (7 cases), P < 0.05]. And the expression level was correlated with the degree of lymph node metastasis and tumor differentiation (r = 0.311, 0.427, both P < 0.05). The expression of mTOR protein in the transfection group was lower than the blank and the nonsense control groups (0.39 ± 0.25 vs 1.18 ± 0.05, 1.46 ± 0.09, both P < 0.05). The proliferation was lower than those of the blank and the nonsense control groups (0.275 ± 0.033 vs 0.460 ± 0.028, 0.450 ± 0.037, both P < 0.05). The apoptotic indices were higher than those of the blank and control groups (12.33 ± 1.53 vs 0.33 ± 0.31, 1.67 ± 0.58, both P < 0.05). The expression of mTOR was higher in colon cancer tissues than that in normal colon tissues. The RNA interference of mTOR in HT-29 cell line can effectively knock down the expression of mTOR so as to significantly inhibit cell proliferation and promote cell apoptosis.