title: The LIMD1 protein bridges an association between the prolyl hydroxylases and VHL to repress HIF-1 activity.
abstract: There are three prolyl hydroxylases (PHD1, 2 and 3) that regulate the hypoxia-inducible factors (HIFs), the master transcriptional regulators that respond to changes in intracellular O(2) tension. In high O(2) tension (normoxia) the PHDs hydroxylate two conserved proline residues on HIF-1α, which leads to binding of the von Hippel-Lindau (VHL) tumour suppressor, the recognition component of a ubiquitin-ligase complex, initiating HIF-1α ubiquitylation and degradation. However, it is not known whether PHDs and VHL act separately to exert their enzymatic activities on HIF-1α or as a multiprotein complex. Here we show that the tumour suppressor protein LIMD1 (LIM domain-containing protein) acts as a molecular scaffold, simultaneously binding the PHDs and VHL, thereby assembling a PHD-LIMD1-VHL protein complex and creating an enzymatic niche that enables efficient degradation of HIF-1α. Depletion of endogenous LIMD1 increases HIF-1α levels and transcriptional activity in both normoxia and hypoxia. Conversely, LIMD1 expression downregulates HIF-1 transcriptional activity in a manner depending on PHD and 26S proteasome activities. LIMD1 family member proteins Ajuba and WTIP also bind to VHL and PHDs 1 and 3, indicating that these LIM domain-containing proteins represent a previously unrecognized group of hypoxic regulators.
authors.affiliation: School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, NG7 2UH, UK.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Foxler
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Bridge
authors.forename: Victoria
authors.initials: V
authors.lastname: James
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Webb
authors.forename: Maureen
authors.initials: M
authors.lastname: Mee
authors.forename: Sybil C K
authors.initials: SC
authors.lastname: Wong
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Feng
authors.forename: Dumitru
authors.initials: D
authors.lastname: Constantin-Teodosiu
authors.forename: Thorgunnur Eyfjord
authors.initials: TE
authors.lastname: Petursdottir
authors.forename: Johannes
authors.initials: J
authors.lastname: Bjornsson
authors.forename: Sigurdur
authors.initials: S
authors.lastname: Ingvarsson
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Ratcliffe
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Longmore
authors.forename: Tyson V
authors.initials: TV
authors.lastname: Sharp
mesh_terms: D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D006900:Hydroxylation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D015151:Immunoblotting; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D060588:LIM Domain Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D025821:Polyubiquitin / Q000378:metabolism; D011393:Procollagen-Proline Dioxygenase / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D034622:RNA Interference; D014162:Transfection; D020798:Two-Hybrid System Techniques; D054875:Ubiquitination; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; C403807:LIMD1 protein, human; D025821:Polyubiquitin; C490190:EGLN1 protein, human; D011393:Procollagen-Proline Dioxygenase; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease