Malic enzyme 1 induces epithelial-mesenchymal transition and indicates poor prognosis in hepatocellular carcinoma

Malic enzyme 1 (ME1) links the glycolytic and citric acid cycles and is important for NADPH production, glutamine metabolism, and lipogenesis. Recently, its deregulation has been implicated in the progression of various cancers. However, the role of ME1 in the progression of hepatocellular carcinoma (HCC) remains unclear. In this study, we utilized short hairpin RNA-mediated gene silencing to investigate the biological effects of ME1 depletion in HCC and determined its prognostic significance in HCC. ME1 expression was examined by real-time (RT)-PCR and Western blot using five HCC cell lines and one normal liver cell line. We used polyethylenimine nanoparticles to deliver a short hairpin RNA to induce cessation of ME1 expression in HCC cells. Changes in NADPH production and reactive oxygen species (ROS) production were studied. Metastatic potentials of HCC cells were evaluated in vitro. Furthermore, we evaluated the protein level of ME1 in para-tumor and cancerous tissues of 65 HCC patients with detailed clinical, pathological, and clinical follow-up data. Patients' survivals were further assessed as well. Upregulated ME1 expression was observed in HCC cell lines. Downregulation of ME1 attenuated NADPH production and stimulated ROS production. Silencing ME1 was noted to inhibit migratory and invasive properties of HCC cells by inducing the E-cadherin expression and decreasing of N-cadherin and vimentin expression in a ROS-dependent pathway. Overexpression of ME1 was observed in a major fraction of HCC samples. Higher level of ME1 in tumors was significantly associated with reduced overall survival (Kaplan-Meier analysis, P = 0.024) and reduced progression-free survival (Kaplan-Meier analysis, P = 0.011). Inhibition of ME1 expression decreases HCC metastasis via suppression of epithelial-mesenchymal transition (EMT) processes in ROS-induced pathways. ME1 overexpression associates with unfavorable prognoses in patients with HCC, suggesting that ME1 is a poor prognostic predictor of hepatocellular carcinoma.