NFE2L2 and glioblastoma: Indeed, Nrf2 may be a key factor that increases the cobalamin content of glioblastoma cells in response to activation of the phosphoinositide 3-kinase (PI3K) or extracellular signal-regulated kinase (ERK) pathway induced by growth factor receptor signaling, irrespective of whether these pathways are stimulated by their respective ligands or transactivated by D4 receptors (34).