To investigate whether ERK1-mediated phosphorylation of GLYCTK2 at serine 220 under glucose deprivation regulates glioblastoma cell survival, we established GLYCTK2-knockdown U87 cells stably overexpressing shRNA-resistant Flag-tagged wild-type GLYCTK2 (rWT) or the non-phosphorylatable S220A mutant (rS220A) (Fig. 8A). Here, MAPK3 is linked to glioblastoma.