A Novel Role for Pyruvate Kinase M2 as a Corepressor for P53 during the DNA Damage Response in Human Tumor Cells

Abstract

Edited by Patrick SungThe pyruvate kinase (PK) is a rate-limiting glycolytic enzyme catalyzing the dephosphorylation of phosphoenolpyruvate to pyruvate, yielding one molecule of ATP. The M2 isoform of PK (PKM2) is predominantly expressed in normal proliferating cells and tumors, and both metabolic and non-metabolic activities for the enzyme in promoting tumor cell proliferation have been identified. However, the exact roles of PKM2 in tumor initiation, growth and maintenance are not yet fully understood. Using immunoprecipitation-coupled LC-MS/MS in MCF7 cells exposed to DNA-damaging agent, we report that the nuclear PKM2 interacts directly with P53 protein, a critical safeguard for genome stability. Specifically, PKM2 inhibits P53-dependent transactivation of the P21 gene by preventing P53 binding to the P21 promoter, leading to a nonstop G 1 phase. As a result, PKM2 expression provides a growth advantage for tumor cells in the presence of a DNA damage stimulus. In addition, PKM2 interferes with phosphorylation of P53 at serine 15, known to stimulate P53 activity by the ATM serine/threonine kinase. These findings reveal a new role for PKM2 in modulating the DNA damage response and illustrate a novel mechanism of PKM2 participating in tumorigenesis.Pyruvate kinase (PK), 4 a rate-limiting enzyme of glycolysis, catalyzes the transfer of phosphate from phosphoenolpyruvate (PEP) to ADP, yielding one molecule of ATP and pyruvate. The PK consists of four isoforms, the PKLR gene-encoded PKL and PKR isoforms and the PKM gene-encoded M1 (PKM1) and M2 (PKM2) isoforms, which express in different types of mammalian cells and tissues. PKM1 constitutively forms stable tetramers (the active form of PK) and is expressed in normal adult tissues that require high levels of energy, such as the heart, brain, and skeletal muscle. In contrast, PKM2 exists in either tetramers or dimers with less activity and metabolic intermediate fructose-1,6-bisphosphate (FBP) can allosterically activate PKM2 by promoting the formation of tetramer from dimer (1, 2). PKM2 is selectively expressed in normal proliferating cells as well as tumor cells, indicating an indispensable role in cancer development.There are two known mechanisms by which PKM2 favors tumor cell growth, one dependent on and one independent of glycolysis. As a glycolytic enzyme, PKM2 in tumor cells shifts glucose metabolism from oxidative phosphorylation to glycolysis under normoxic conditions, a phenomenon termed the Warburg effect or aerobic glycolysis (3). On the other hand, non-metabolic function of PKM2, which is mainly associated with the nuclear PKM2, has been identified as a major contributor during tumorigenesis. For example, nuclear PKM2 displays kinase activity in phosphorylating a number of protein substrates, including histone H3 (4, 5), signal transducer and activator of transcription 3 (stat3) (6, 7), Bub3 (8), and myosin light chain 2 (MLC2) (9), for which PKM2 uses the high-energy phosphate from PEP but not ATP as a phosphate donor. The PKM2-induced phosphorylation...

Endothelial pyruvate kinase M2 maintains vascular integrity

“…The reliance on p53 explains the observation that siPKM2 cells arrest in multiple points of the cell cycle, as observed by others (10), because p53 is known to block cell cycle progression in G1/S, S, and G2/M (20). There have been reports in cancer cells of PK-independent PKM2 functions, including a report of interaction with p53 upon DNA damage in human tumor cells that include MCF7 breast cancer, HCT116 colon cancer, and U2OS osteosarcoma cells (27). However, the report indicated that PKM2 binds to and inhibits p53-dependent transactivation of p21, whereas we found that PKM2 regulates p53 gene expression.…”

PKM2: A Potential Regulator of Rheumatoid Arthritis via Glycolytic and Non-Glycolytic Pathways

“…Recent studies have found that PKM2 may be involved in the regulation of p53 in tumor cells. In MCF7 cells exposed to DNA-damaging agent, PKM2 inhibited transactivation of the p21 gene by preventing p53 binding to the p21 promoter, leading to a nonstop G1 phase (58). Dimeric PKM2 has been found to bind directly with both p53 and MDM2 and to promote MDM2-mediated p53 ubiquitination (59).…”

Pyruvate kinase M2 represses thermogenic gene expression in brown adipocytes

“…As the effect of PKM2 knockdown was not mediated via secreted FGF21, we examined possible nuclear mediation of the effect. PKM2 contains an inducible nuclear localization signal, and in the nucleus, PKM2 can act as a cofactor for several transcription factors . We therefore measured the expression of five known target genes of the three established transcriptional pathways downstream of PKM2.…”

“…PKM2 interacts with the tumor suppressor p53 and negatively modulates its transcriptional activity . Therefore, by knocking down PKM2 we would expect a higher activity of p53, but as p53‐deficient mice and adipocytes displayed increased expression of Ucp1 , and as WT‐1 cells have compromised p53 function due to expression of simian virus 40 large T antigen , we do not consider p53 a potential mediator of PKM2 function in our studies.…”

“…PKM2 is considered important for aerobic glycolysis, that is, conversion of glucose to lactate under normoxic conditions, in cancer cells, a phenomenon known as the Warburg effect . Even though PKM2 is a cytosolic enzyme involved in glycolysis, it also contains an inducible nuclear localization signal . In the nucleus, PKM2 can act as a cofactor for several transcription factors and as a dual‐specificity protein kinase .…”