Sumoylation of Pyruvate Kinase M2 Inhibits Myeloid Differentiation in Hematopoietic Cells

The pyruvate kinase (PK) is a rate-limiting glycolytic enzyme catalyzing the dephosphorylation of phosphoenolpyruvate to pyruvate. M2 form of PK (PKM2) is expressed during embryogenesis and is the predominant form in tumors of different types. In contrast to the essential role of PKM2 in solid tumors, much less is known about the effects of PKM2 in hematopoietic cells and the development of leukemia. Here we found that PKM2 is modified by small ubiquitin-like modifier 1(SUMO1), which can be reduced by a SUMO1-specific protease SENP1 in hematopoietic cells. SUMOylation induced nuclear localization and conformation change from tetramer to dimer of PKM2. Importantly, SUMOylation of PKM2 is prevalent in a variety of leukemic cell lines as well as primary samples from patients with hematologic malignancies. In consistency, predominant nuclear localization and dimeric forms of PKM2 in leukemic cells were observed. Using in vitro SUMOylation reaction-coupled liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS), we identified K270 lysine residue of PKM2 as the SUMOylation target. Replacement of endogenous PKM2 with mutant PKM2^K270 showed a significant shift of PKM2 from tetramer to dimer. To investigate the potential leukemogenic effect of PKM2 SUMOylation, murine hematopoietic progenitor 32D clone 3 (32Dcl3) transfectants expressing wild type(WT) or mutant PKM2^K270 were generated and G-CSF-induced differentiation was evaluated by morphology appearance and expression of myeloid associated surface markers CD11b and Gr-1. The results showed that expression of WT PKM2 but not mutant PKM2^K270 significantly blocked myeloid differentiation. Further investigations revealed that SUMO1 modification of PKM2 at K270 is essential in mediating the interaction between PKM2 and Runt-related transcription factor 1(RUNX1), a master transcriptional factor implicated in the differentiation of hematopoietic cells. This interaction led to a downregulation of RUNX1 during G-CSF-induced myeloid differentiation of 32D cells, which could be abrogated by expression of mutant PKM2^K270. Collectively, these data indicated that SUMOylated PKM2 blocks myeloid differentiation through suppressing RUNX1. These findings reveal a novel nonmetabolic function of PKM2 in modulating myeloid differentiation and highlight the critical role of SUMOylation in leukemogenesis.