Expression and role of GLUT-1, MCT-1, and MCT-4 in malignant pleural mesothelioma

Malignant cells supply their energy needs through increased glucose consumption, producing large quantities of lactic acid via glycolysis. Glucose transporters (GLUTs) and monocarboxylate transporters (MCTs) are therefore commonly up-regulated in human malignancies to mediate glucose influx and lactic acid efflux, respectively. However, their roles in malignant pleural mesothelioma (MPM) have not been fully elucidated. Here, we evaluated GLUT-1, MCT-1, and MCT-4 expression in human MPM and reactive mesothelial hyperplasia (RMH) and elucidated their biological role in vitro. GLUT-1, MCT-1, and MCT-4 expression was determined in human MPM (n = 35) and RMH (n = 20) specimens by immunohistochemistry and in frozen tissue, and MPM cell lines, by real-time reverse transcription-polymerase chain reaction and western blot analysis. GLUT-1, MCT-1, and MCT-4 functions in MPM were evaluated by transfection with small interfering RNA. Immunohistochemical analysis revealed higher levels of GLUT-1, MCT-1, and MCT-4 in MPM than in RMH. Additionally, GLUT-1, MCT-1, and MCT-4 mRNA levels were higher in MPM than in non-neoplastic mesothelial cell lines. The siRNA-mediated knockdown of GLUT-1 or MCT-1 significantly suppressed tumor cell proliferation, and MCT-1 silencing inhibited invasion and induced apoptosis. Taken together, these results indicate that combined application of GLUT-1, MCT-1, and MCT-4 immunohistochemistry might be useful in differentiating MPM from RMH and suggest that MCT-1plays an important biological role.