Pyruvate kinase M2 (PKM2) is a glycolytic enzyme that has also been shown to function in the nucleus as a transcriptional co-activator. Yang et al. found that PKM2, but not PKM1, is phosphorylated by ERK2 following epidermal growth factor receptor (EGFR) activation in glioblastoma cells. This allows cis–trans isomerization of PKM2 by the peptidyl-prolyl isomerase PIN1, which exposes a nuclear localization sequence on PKM2 that is then bound by importin α5, leading to nuclear translocation of PKM2 and the expression of glycolytic genes. Furthermore, expression of a mutant PKM2 that is unable to translocate to the nucleus prevents the growth of glioblastoma xenografts in mice.