title: MgcRacGAP, a cytoskeleton regulator, inhibits HIF-1 transcriptional activity by blocking its dimerization.
abstract: Hypoxia inducible factor-1 (HIF-1), a dimeric transcription factor of the bHLH-PAS family, is comprised of HIF-1α, which is inducible by hypoxia and ARNT or HIF-1β, which is constitutively expressed. HIF-1 is involved in cellular homeostasis under hypoxia, in development and in several diseases affected by oxygen availability, particularly cancer. Since its expression is positively correlated with poor outcome prognosis for cancer patients, HIF-1 is a target for pharmaceutical therapy. We have previously shown that male germ cell Rac GTPase activating protein (MgcRacGAP), a regulator of Rho proteins which are principally involved in cytoskeletal organization, binds to HIF-1α and inhibits its transcriptional activity. In this work, we have explored the mechanism of the MgcRacGAP-mediated HIF-1 inactivation. We show that the Myo domain of MgcRacGAP, which is both necessary and sufficient for HIF-1 repression, binds to the PAS-B domain of HIF-1α. Furthermore MgcRacGAP competes with ARNT for binding to the HIF-1α PAS-B domain, as shown by in vitro binding pull down assays. In mammalian cells, ARNT overexpression can overcome the MgcRacGAP-mediated inhibition and MgcRacGAP binding to HIF-1α in vivo inhibits its dimerization with ARNT. We additionally present results indicating that MgcRacGAP binding to HIF-1α is specific, since it does not affect the transcriptional activity of HIF-2, a close evolutionary relative of HIF-1 also involved in hypoxia regulation and cancer. Our results reveal a new mechanism for HIF-1 transcriptional activity regulation, suggest a novel hypoxia-cytoskeleton link and provide new tools for selective HIF-1 inhibition.
authors: School of Medicine, University of Thessaly, Larissa, Greece.
authors: Aggeliki
authors: A
authors: Lyberopoulou
authors: Ilias
authors: I
authors: Mylonis
authors: George
authors: G
authors: Papachristos
authors: Dimitrios
authors: D
authors: Sagris
authors: Alkmini
authors: A
authors: Kalousi
authors: Christina
authors: C
authors: Befani
authors: Panagiotis
authors: P
authors: Liakos
authors: George
authors: G
authors: Simos
authors: Eleni
authors: E
authors: Georgatsou
mesh_terms: D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002478:Cells, Cultured; D003599:Cytoskeleton; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics*; D047468:Immunoprecipitation; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: C497396:ARNT protein, human; D020690:GTPase-Activating Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; C115995:mgcRacGAP; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator