Pyruvate kinase isoform M2 (PKM2) plays an important role in the growth and metabolic reprogramming of cancer cells in stress conditions. Here, we report that SAICAR (succinylaminoimidazolecarboxamide ribose-5′-phosphate, an intermediate of the de novo purine nucleotide synthesis pathway) specifically stimulates PKM2. Upon glucose starvation, cellular SAICAR concentration increases in an oscillatory manner and stimulates PKM2 activity in cancer cells. Changes in SAICAR levels in cancer cells alter cellular energy level, glucose uptake, and lactate production. The SAICAR-PKM2 interaction also promotes cancer cell survival in glucose-limited conditions. SAICAR accumulation is not observed in normal adult epithelial cells or lung fibroblasts regardless of glucose conditions. This allosteric regulation may explain how cancer cells coordinate different metabolic pathways to optimize their growth in the nutrient-limited conditions commonly observed in the tumor microenvironment.

Abnormal metabolism and sustained proliferation are hallmarks of cancer. Pyruvate kinase M2 (PKM2) is a metabolic enzyme that plays important roles in both processes. Recently, PKM2 was shown to have protein kinase activity phosphorylating histone H3 and promoting cancer cell proliferation. However, the mechanism and extent of this novel protein kinase in cancer cells remain unclear. Here, we report that binding of SAICAR, a metabolite abundant in proliferating cells, induces PKM2’s protein kinase activity in vitro and in cells. Protein microarray experiments revealed that more than 100 human proteins– mostly protein kinases– are phosphorylated by PKM2-SAICAR. In particular, PKM2-SAICAR phosphorylates and activates Erk1/2, which in turn sensitizes PKM2 for SAICAR-binding through phosphorylation. Additionally, PKM2-SAICAR was necessary to induce sustained Erk1/2 activation and mitogen-induced cell proliferation. Thus, the ligand-induced protein kinase activity from PKM2 is a mechanism that directly couples cell proliferation with intracellular metabolic status.