HK2 and neoplasm: Interestingly, hexokinase 2 (HK2), the enzyme that catalyzes the first step of glucose metabolism (the phosphorylation of glucose to glucose-6-phosphate), is a transcriptional target of hypoxia-inducible factor 1 (HIF1), the pleiotropic factor that regulates tumor hypoxia [28,31,32] and plays critical roles in tumors shifting from OXPHOS to glycolysis [36].