Death-associated protein kinase (DAPk), a multi-domain
serine/threonine kinase, regulates numerous cell death mechanisms and harbors
tumor suppressor functions. In this study, we report that DAPk directly binds and functionally activates
pyruvate kinase M2 (PKM2), a key glycolytic
enzyme, which contributes to the regulation of
cancer cell metabolism. PKM2 was identified as a novel binding partner of DAPk by a yeast two-hybrid screen. This interaction was validated in vitro by
enzyme-linked
immunosorbent assay using purified
proteins and in vivo by co-immunoprecipitation of the two endogenous
proteins from cells. In vitro interaction with full-length DAPk resulted in a significant increase in the activity of PKM2. Conversely, a fragment of DAPk harboring only the functional
kinase domain (KD) could neither bind PKM2 in cells nor activate it in vitro. Indeed, DAPk failed to phosphorylate PKM2. Notably, transfection of cells, with a truncated DAPk lacking the KD, elevated endogenous PKM2 activity, suggesting that PKM2 activation by DAPk occurs independently of its
kinase activity. DAPk-transfected cells displayed changes in glycolytic activity, as reflected by elevated
lactate production, whereas
glucose uptake remained unaltered. A mild reduction in cell proliferation was detected as well in these transfected cells. Altogether, this work identifies a new role for DAPk as a metabolic regulator, suggesting the concept of direct interactions between a
tumor suppressor and a key glycolytic
enzyme to limit cell growth. Moreover, the work documents a unique function of DAPk that is independent of its catalytic activity and a novel mechanism to activate PKM2 by
protein-
protein interaction.