Search

Aerobic glycolysis supports proliferation through unresolved mechanisms. We have previously shown that aerobic glycolysis is required for the regulated proliferation of cerebellar granule neuron progenitors (CGNP) and for the growth of CGNP-derived medulloblastoma. Blocking the initiation of glycolysis via deletion of hexokinase-2 (Hk2) disrupts CGNP proliferation and restricts medulloblastoma growth. Here, we assessed whether disrupting pyruvate kinase-M (Pkm), an enzyme that acts in the terminal steps of glycolysis, would alter CGNP metabolism, proliferation, and tumorigenesis. We observed a dichotomous pattern of PKM expression, in which postmitotic neurons throughout the brain expressed the constitutively active PKM1 isoform, while neural progenitors and medulloblastomas exclusively expressed the less active PKM2. Isoform-specific Pkm2 deletion in CGNPs blocked all Pkm expression. Pkm2-deleted CGNPs showed reduced lactate production and increased SHH-driven proliferation. 13C-flux analysis showed that Pkm2 deletion reduced the flow of glucose carbons into lactate and glutamate without markedly increasing glucose-to-ribose flux. Pkm2 deletion accelerated tumor formation in medulloblastoma-prone ND2:SmoA1 mice, indicating the disrupting PKM releases CGNPs from a tumor-suppressive effect. These findings show that distal and proximal disruptions of glycolysis have opposite effects on proliferation, and that efforts to block the oncogenic effect of aerobic glycolysis must target reactions upstream of PKM. Cancer Res; 77(12); 3217–30. ©2017 AACR.

Immunofluorescence for PKM1 and PCNA demonstrates that PKM1+ cells within medulloblastomas are PCNA-.

Rates of change of select media metabolites in 24 hour cultures of CGNPs, with and without Pkm2 deletion

Schematic diagram showing the patterns of incorporation of 13C atoms from [1,6-13C] glucose into the products of the Krebs Cycle.

Documentation of germline Pkm2 deletion, showing A) change in the size of products genotyping PCR, B) genomic sequence showing absence of exon 10, and C) complete absence of PKM2 expression in all tissues within the brain, and intact PKM1 expression.

Supplementary Materials and Methods, including NMR, LC-MS and RNA-seq methods

Western blot showing explanted CGNP expresssion of pAKT, PKM1, PKM2 and cleaved caspse-3, comparing Pkm2-deleted and control genotypes.