The mTOR Pathway Regulates PKM2 to Affect Glycolysis in Esophageal Squamous Cell Carcinoma.

OBJECTIVES: Esophageal squamous cell carcinoma is a highly prevalent cancer withpoor survival rate and prognosis. Increasing evidence suggests an important role for metabolic regulation in treating esophageal squamous cell carcinoma, but the underlying mechanism remains unclear. The pyruvate kinase M2 isoform is a key enzyme in the energy production process, and the upregulation of pyruvate kinase M2 isoform also plays a crucial role in gene transcription and tumorigenesis. The mammalian target of rapamycin pathway regulates an array of cellular functions, including protein synthesis, metabolism, and cell proliferation. The pyruvate kinase M2 isoform and mammalian target of rapamycin pathways both affect metabolism in cancers, and evidence also suggests that the mammalian target of rapamycin downstream transcription factor hypoxia-inducible factor-1α regulates pyruvate kinase M2 isoform. We therefore investigated the regulatory mechanism among pyruvate kinase M2 isoform, mammalian target of rapamycin, and aerobic glycolysis in esophageal squamous cell carcinoma, hoping to prove that mammalian target of rapamycin pathway regulates pyruvate kinase M2 isoform to affect glycolysis in esophageal squamous cell carcinoma.

METHODS: Immunohistochemical staining was used to compare pyruvate kinase M2 isoform and phospho-mammalian target of rapamycin expression in 30 human pathological esophageal squamous cell carcinoma sections and 30 nontumoral esophageal tissues. Short hairpin RNA was used to inhibit pyruvate kinase M2 isoform and activate mammalian target of rapamycin, after which we monitored changes in glucose consumption and lactate production. Finally, we determined the expression of pyruvate kinase M2 isoform and the mammalian target of rapamycin downstream transcription factor hypoxia-inducible factor-1α, as well as glucose consumption and lactate production, following the modification of mammalian target of rapamycin expression.

RESULTS: Immunohistochemical staining showed that both phospho-mammalian target of rapamycin and pyruvate kinase M2 isoform expression were higher in esophageal squamous cell carcinoma than in nontumor tissues. Glucose consumption and lactate production measurements demonstrated that altering mammalian target of rapamycin and pyruvate kinase M2 isoform levels caused corresponding changes in glycolysis in esophageal squamous cell carcinoma cells. When mammalian target of rapamycin was activated or inhibited, expression of pyruvate kinase M2 isoform and hypoxia-inducible factor-1α as well as glycolysis were altered, indicating that mammalian target of rapamycin regulates pyruvate kinase M2 isoform via the downstream transcription factor hypoxia-inducible factor-1α, thereby affecting glycolysis in esophageal squamous cell carcinoma.

CONCLUSION: Mammalian target of rapamycin pathway promotes aerobic glycolysis in esophageal squamous cell carcinoma by upregulating pyruvate kinase M2 isoform. Both proteins can serve as molecular targets for novel therapeutic strategies.