Editors' ChoiceBiochemistry

PKM2 Moonlights as a Protein Kinase

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Science Signaling  20 Mar 2012:
Vol. 5, Issue 216, pp. ec81
DOI: 10.1126/scisignal.2003059

In its tetrameric form, pyruvate kinase M2 (PKM2) functions in glycolysis by transferring a phosphate from phosphenolpyruvate (PEP) to ADP to form pyruvate. In cancer cells, dimeric PKM2 becomes abundant, and this form lacks pyruvate kinase activity, leading to altered metabolism that may provide cancer cells a metabolic advantage. PKM2 has also been reported to function in the nucleus to promote cellular proliferation by regulating the activity of transcription factors (see Semenova and Chernoff). Gao et al. examined PKM2 localization and activity in several related cancer cell lines matched for fast proliferation or slow proliferation. PKM2 was more abundant in the nucleus of the faster-proliferating cells. Gene expression analysis showed that the gene encoding mitogen-activated protein kinase kinase 5 (MEK5) was one of several hundred induced in cells overexpressing HA-tagged PKM2. Chromatin immunoprecipitation (ChIP) and gel electrophoretic mobility shift assays confirmed the interaction between PKM2 and the promoter of mek5. Knockdown of MEK5 prevented the enhancement in proliferation in response to overexpression of HA-PKM2, and the abundance of MEK5 correlated with proliferation rate in the cancer cell lines. The transcription factor STAT3 promotes mek5 expression, and coimmunoprecipitation of endogenous proteins showed that STAT3 interacted with PKM2. ChIP showed that knockdown of PKM2 reduced the interaction of STAT3 with the mek5 promoter and that overexpression of PKM2 enhanced this interaction. Knockdown of STAT3 or expression of a dominant-negative mutant prevented the induction of mek5 in response to HA-PKM2. In vitro kinase assays with either recombinant PKM2 (rPKM2) or HA-PKM2 isolated from nuclear extracts showed that only HA-PKM2 exhibited kinase activity toward glutathione S-transferase (GST)–conjugated STAT3 and only in the presence of PEP, not in the presence of ATP. Size-exclusion chromatography revealed that rPKM2 and PKM2 isolated from cytoplasmic extracts were tetrameric, whereas nuclear-isolated PKM2 was dimeric. Introduction of a mutation into rPKM2 that disrupted the formation of the tetramer, allowing the protein to exist only as a dimer, resulted in protein kinase activity of this mutant toward STAT3 in vitro. Overexpression of the dimer-forcing mutant in cells promoted cell proliferation and stimulated STAT3 phosphorylation. Thus, dimeric PKM2 appears to localize preferentially to the nucleus, where it can function as a protein kinase to promote the expression of genes involved in cell proliferation.

X. Gao, H. Wang, J. J. Yang, X. Liu, Z.-R. Liu, Pyruvate kinase M2 regulates gene transcription by acting as a protein kinase. Mol. Cell 45, 598–609 (2012). [PubMed]

G. Semenova, J. Chernoff, PKM2 enters the morpheein academy. Mol. Cell 45, 583–584 (2012). [PubMed]

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