Upregulation Of Pyruvate Kinase Type M2Induces Aerobic Glycolysis And Promotes Tumor Growth And Invasion In Colorectal Cancer

OBJECTIVE:To determine the expression pattern of the two isotypes PKM1and PKM2in colorectal cancer(CRC) tissues and evaluate the correlation between PKM2level and tumor type and tumor stage. And to investigated the effects of PKM2on glucose metabolism, tumorigenesis and metastasis in CRC.METHODS:A total of60CRC patients underwent colorectomy during December2009and April2010were adopted. Then levels of PKM1and PKM2proteins in the tumor tissues were determined by western blot(Wb) using PKM1-and PKM2-specific antibodies, and the normal colorectal tissues were adopted as negative control. Then cell specificity of the two isotypes were detemiined by immunohistochemistry (IH). PKM2-RNA levels were exmined by real-time PCR and the correlation between PKM2-RNA level and tumor type and tumor stage were analysed. PKM2expression was examined by immunoblotting and knocked down using short hairpin RNA (shRNA) in RKO cells, then glucose metabolism, cell proliferation as well as cell migration was measured. In vivo tumor growth was analyzed in nu/nu mice.RESULTS:The expression of PKM1is decreased(0.77±0.21vs0.91+0.28, P=0.010) and PKM2increased(1.32+0.49vs0.98±0.34, P=0.006) in colorectal cancer tissues compared with normal colorectal tissues. Levels of PKM2-mRNA were also increased in tumor tissues(ACt:4.65±2.09vs6.91±2.27, P=0.000). Normal colorectal tissues and stromal cells mainly express PKM1but cancer cells express PKM2. Increased expression of PKM2is associated with later stage and more lympho metastasis of CRC. Proliferating cell lines including several CRC cell lines, RKO, HCT116, SW480, HT29, transformed human embryonic kidney cell lines, HEK293and293and CCD841a cell line derived from fetus tissue all exclusively express PKM2. Knockdown of PKM2inhibited glycolysis(49.57vs32.77, p<0.01) and lactate production(8.71vs3.49, p<0.01) in RKO cells, but cell oxygen consumption was not affected(3.36vs3.70, p=0.266). Knockdown of PKM2inhibited cell proliferation and migration and tumorigenesis in vivo. Knockdown of PKM2induced a decreased5-day proliferation doubling(6.34vs4.81, p<0.01) and penetrated cells(136.3±8.5vs85.3±8.7, p<0.01). Knockdown of PKM2induced delayed tumor formulation and decreased tumor mass(3.0±0.4vs1.3±0.2, p=0.002) in vivo. Exclusive expression of PKM2is necessary for cell aerobic glycolysis and provides a metabolic and selective growth advantage for tumor cells.CONCLUSIONS:The expression of PKM2is increased in colorectal cancer tissues. Normal colorectal tissues and stromal cells mainly express PKM1but cancer cells express PKM2. Increased expression of PKM2is associated with later stage and more lympho metastasis of CRC. PKM2serves as an oxygen sensor and is necessary for aerobic glycolysis, which promotes cell growth and invision, and provides a selective growth advantage for tumor cells in vivo. High expression of PKM2may faciliate tumor growth and metastasis in CRC. PKM2could aid targeted therapy for patients with colorectal tumors.