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.
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Article: The LIMD1 protein bridges an association between the prolyl hydroxylases and VHL to repress HIF-1 activity
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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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ABSTRACT: Hypoxia inducible factor (HIF) is an oxygen-sensitive transcription factor that enables aerobic organisms to adapt to hypoxia. This is achieved through the transcriptional activation of up to 200 genes, many of which are critical to cell survival. Under conditions of normoxia, the hydroxylation of HIF by prolyl hydroxylase domain-containing (PHD) enzymes targets it for polyubiquitination and proteosomal degradation by the von Hippel-Lindau protein (VHL). However, under hypoxic conditions, PHD activity is inhibited, thereby allowing HIF to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Experimental studies suggest that HIF may act as a mediator of ischemic preconditioning, and that the genetic or pharmacological stabilization of HIF under normoxic conditions, may protect the heart against the detrimental effects of acute ischemia-reperfusion injury. The mechanisms underlying the cardioprotective effect of HIF are unclear, but it may be attributed to the transcriptional activation of genes associated with cardioprotection such as erythropoietin, heme oxygenase-1, and inducible nitric oxide synthase or it may be due to reprogramming of cell metabolism. In this review article, we highlight the role of HIF in mediating both adaptive and pathological processes in the heart, as well as focusing on the therapeutic potential of the HIF-signaling pathway as a target for cardioprotection.Pharmacology [?] Therapeutics 07/2012; 136(1):69-81. DOI:10.1016/j.pharmthera.2012.07.005 · 7.75 Impact Factor