Pyruvate kinase M2 phosphorylates H2AX and promotes genomic instability in human tumor cells

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• Pyruvate kinase (PK) is a key glycolytic enzyme, with the M2 isoform (PKM2) prevalent in tumors.
• PKM2 exhibits nuclear localization and nonmetabolic roles in tumorigenesis beyond its cytosolic enzymatic function.
• Genomic instability is a hallmark of cancer, driven by DNA damage accumulation.

Purpose of the Study:

• To investigate the nonmetabolic functions of nuclear PKM2 in response to DNA damage.
• To determine if PKM2 interacts with and modifies histones, specifically H2AX, under DNA damage conditions.
• To elucidate the role of PKM2-mediated H2AX phosphorylation in promoting genomic instability in cancer cells.

Main Methods:

• Studied nuclear PKM2 interaction with histone H2AX under DNA damage.
• Assessed the effect of PKM2 depletion on serine 139-phosphorylated H2AX (γ-H2AX) levels.
• Performed *in vitro* kinase assays to confirm PKM2's direct phosphorylation of H2AX at serine 139.
• Utilized a kinase-dead PKM2 mutant (PKM2-Del515-520) to evaluate its impact on cell proliferation and chromosomal aberrations.

Main Results:

• Nuclear PKM2 was found to interact with histone H2AX following DNA damage.
• PKM2 depletion reduced γ-H2AX levels in response to DNA damage.
• PKM2 directly phosphorylates H2AX at serine 139, a function dependent on its FBP-binding pocket.
• Replacing wild-type PKM2 with a kinase-dead mutant decreased cell proliferation and chromosomal aberrations under DNA damage.

Conclusions:

• PKM2 directly phosphorylates H2AX at serine 139, contributing to DNA damage response.
• PKM2 promotes genomic instability in tumor cells through the direct phosphorylation of H2AX.
• PKM2 emerges as a novel regulator of genomic instability in cancer, highlighting its nonmetabolic roles.