The LIMD1 protein bridges an association between the prolyl hydroxylases and VHL to repress HIF-1 activity

School of Biomedical Sciences, University of Nottingham, Queen's Medical Centre, NG7 2UH, UK.
Nature Cell Biology (Impact Factor: 20.06). 02/2012; 14(2):201-8. DOI: 10.1038/ncb2424
Source: PubMed

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.

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    • "Othercontrolsovereffectivehydroxylaseactivityare likelytobeexertedbyintracellularprocessesthat affectthesubcellularlocationoftheenzymeand/or itsaccesstoHIFsubstrate.Forinstance,bindingof theprincipalHIFprolylhydroxylaseenzymePHD2 tothepeptidyl-prolylcis-transisomeraseFKBP38is proposedtolimitPHD2activitybyaprocessthatinvolves membraneanchoringandproteasomaldegradationbut isindependentoftheisomeraseactivity(Barthetal. 2009).IthasalsobeenproposedthatPHDenzymes operateinaspatiallyrestrictedcontextthroughassociation withscaffoldproteins(Foxleretal.2012).Cellular compartmentalizationmayprovideanothercontrol.For instance,ithasbeenshownthatPHD2undergoes nuclear–cytoplasmicshuttlingandthatthedeletionof PHD2sequencesrequiredfornuclearentryisassociated withagreatlyimpairedcapacitytodownregulateHIF (Pientkaetal.2012).Whetherandhowsuchprocesses areusedtotunethePHD/pVHL/HIFsystemphysiologicallyisunclear ,butbiologicalcontrolatthislevel issupportedbytheobservationofassociationsbetween nuclearlocalizationofPHD2andaggressivecancer phenotypes(Jokilehtoetal.2010). Yetanotherpossiblemeansofregulatingenzyme activityhasbeenraisedbyrecentstudiesoftheHIF asparaginylhydroxylase,FIH.Thisenzymecatalysesthe hydroxylationofmanyothersubstrates,inparticular asparaginylresiduesthatformpartoftheconsensus 'ankyrinrepeat'inthefamilyof'ankyrinrepeatdomain' containingproteins(Cockmanetal.2006).Theseproteins showahighaffinityforFIHandareabundantincells,so thattheymightbepredictedtocompetewithHIFfor hydroxylation(Colemanetal.2007;Wilkinsetal.2009). "
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