HIF1A and neoplasm: Tumor hypoxia activates and stabilizes transcriptionfactors, such as hypoxia-inducible factor 1 (HIF-1), a heterodimerictranscription factor that comprises an oxygen-regulated α-subunit(HIF-1α) and a constitutively expressed β-subunit (HIF-1β).This is followed by transcriptional regulation of a series of hypoxia-induciblegenes, including the principal proangiogenic factor VEGF.