Hypoxia-associated factor, a novel E3-ubiquitin ligase, binds and ubiquitinates hypoxia-inducible factor 1alpha, leading to its oxygen-independent degradation.
The hypoxia-inducible factor 1alpha (HIF-1alpha) is the master regulator of the cellular response to hypoxia. A key regulator of HIF-1alpha is von Hippel-Lindau protein (pVHL), which mediates the oxygen-dependent, proteasomal degradation of HIF-1alpha in normoxia. Here, we describe a new regulator of HIF-1alpha, the hypoxia-associated factor (HAF), a novel E3-ubiquitin ligase that binds HIF-1alpha leading to its proteasome-dependent degradation irrespective of cellular oxygen tension. HAF, a protein expressed in proliferating cells, binds and ubiquitinates HIF-1alpha in vitro, and both binding and E3 ligase activity are mediated by HAF amino acids 654 to 800. Furthermore, HAF overexpression decreases HIF-1alpha levels in normoxia and hypoxia in both pVHL-competent and -deficient cells, whereas HAF knockdown increases HIF-1alpha levels in normoxia, hypoxia, and under epidermal growth factor stimulation. In contrast, HIF-2alpha is not regulated by HAF. In vivo, tumor xenografts from cells overexpressing HAF show decreased levels of HIF-1alpha accompanied by decreased tumor growth and angiogenesis. Therefore, HAF is the key mediator of a new HIF-1alpha-specific degradation pathway that degrades HIF-1alpha through a new, oxygen-independent mechanism.
Koh
Mei Yee
MY
Department of Experimental Therapeutics, MD Anderson Cancer Center, Houston, Texas 77030, USA. mykoh@mdanderson.org
Darnay
Bryant G
BG
Powis
Garth
G
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000378:metabolism*; D049109:Cell Proliferation; D004815:Epidermal Growth Factor / Q000502:physiology; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins; D009374:Neoplasms, Experimental / Q000737:chemistry / Q000473:pathology; D009389:Neovascularization, Pathologic; D010100:Oxygen; D011485:Protein Binding; D017411:Ribonucleoproteins, Small Nuclear; D014183:Transplantation, Heterologous; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
D002352:Carrier Proteins; D051793:Hypoxia-Inducible Factor 1; D047908:Intracellular Signaling Peptides and Proteins; D009363:Neoplasm Proteins; D017411:Ribonucleoproteins, Small Nuclear; C431323:SART1 protein, human; D004815:Epidermal Growth Factor; D044767:Ubiquitin-Protein Ligases; D010100:Oxygen