Leukemogenic Tyrosine Kinases Inhibit PKM2 to Promote the Warburg Effect and Tumor Growth

Abstract 3142

The Warburg effect describes a pro-oncogenic metabolic switch in which cancer cells, including leukemia cells, take up more glucose than normal tissue, yet use less glucose for oxidative phosphorylation and favor glycolysis even in the presence of oxygen (aerobic glycolysis). However, the molecular mechanisms underlying the Warburg effect remain unclear. Growth factor (GF) receptors are believed to play a key role in programming cancer cell metabolism. These GF receptors are expressed in many hematopoietic malignancies as constitutively activated tyrosine kinase mutants. Thus, we examinined whether tyrosine kinase signaling — commonly upregulated in hematopoietic malignancies — regulates the Warburg effect to contribute to leukemogenesis and disease progression. We performed phospho-proteomics studies and found that pyruvate kinase M2 isoform (PKM2), which is a rate-limiting enzyme of glycolysis, is tyrosine phosphorylated in leukemia cells expressing FGFR1 fusion tyrosine kinases, which are associated with 8p11 leukemia/lymphoma syndrome. We also found that 8p11 leukemogenic FGFR1 directly phosphorylates and inhibits PKM2. Recent seminal studies from Dr. Lew Cantley's group demonstrated that the enzymatic activity of PKM2 is inhibited by phosphotyrosine binding; PKM2 expression is important for aerobic glycolysis and provides a growth advantage to tumors. However, it remains unclear which dedicated tyrosine kinase pathways are physiologically responsible for this regulation and whether PKM2 itself is tyrosine phosphorylated to achieve inhibition of PKM2 in cancer cells. Here we report that FGFR1 inhibits PKM2 by direct phosphorylation at Y105. This consequently inhibits the formation of tetrameric, active PKM2 by disrupting cofactor fructose-1,6-bisphosphate (FBP) binding in a putative “inter-molecule manner”, where one molecule in an active PKM2 tetramer, when phosphorylated, may function as an inhibitory binding partner to the other sister molecules. In addition, phosphorylation of PKM2 at Y105 is common in many human leukemia cell lines expressing oncogenic tyrosine kinases such as BCR-ABL, FLT3-ITD, and JAK2V617F. Furthermore, expression of the PKM2 Y105F mutant in cancer cells following RNAi-mediated knockdown of endogenous PKM2 leads to decreased cell proliferation under hypoxia, increased oxidative phosphorylation with reduced lactate production, and reduced tumor growth in xenograft nude mice. Our findings suggest that tyrosine phosphorylation regulates PKM2 to program cancer cell metabolism and promote tumor growth. This may represent a common, acute molecular mechanism to regulate the Warburg effect, in addition to the chronic changes that are believed to be regulated by hypoxia inducible factor 1 and Myc.