[Serine hydroxymethyl transferase 2 regulates the AMPK/mTOR pathway and induces autophagy to promote chemotherapy resistance in colon cancer cells].

ABSTRACT

Objective To investigate the mechanism of serine hydroxymethyl transferase 2 (SHMT2) inducing autophagy and promoting chemotherapy resistance in colon cancer cells. Methods TCGA database and real-time quantitative PCR were used to analyze the level of SHMT2 mRNA in colon cancer tissues. Western blot analysis and immunohistochemistry were used to detect the expression and distribution of SHMT2 in colon cancer tissues. Western blot analysis was performed to detect the SHMT2 protein levels of SW480, SW620, HCT116, CACO2, RKO, HCT8, HT15 and HT29 cells. After over-expression of SHMT2 in CACO2 colon cancer cells, MTT assay was used to detect cell viability, and annexin V-FITC/PI double labeling was used to detect the apoptosis of colon cancer cells induced by 5-fluorouracil (5-Fu). The autophagosomes of colon cancer cells were observed by transmission electron microscopy. The protein levels of LC3 II/I, P62, cleaved PARP (c-PARP), and cleaved caspase-3 (c-caspase-3) were examined by Western blot analysis. Signaling Phospho-Antibody Array and Western blot analysis were applied to analyze the phosphorylation level of AMPK/mTOR. Results SHMT2 was highly expressed in colon cancer tissues and cells. Over-expression of SHMT2 significantly increased cell viability and the ratio of LC3 II/ LC3 I. It was found that the phosphorylation level of AMPK was raised and the phosphorylation level of mTOR was reduced after the over-expression of SHMT2. Conclusion SHMT2 may induce autophagy by promoting AMPK phosphorylation and directly or indirectly inhibiting mTOR activity, thus leading to chemotherapy-induced apoptosis tolerance and resistance to chemotherapeutics.