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Functional interference between hypoxia and dioxin signal transduction pathways: competition for recruitment of the Arnt transcription factor


Gradin, K; McGuire, J; Wenger, R H; Kvietikova, I; Whitelaw, M L; Toftgård, R; Tora, L; Gassmann, M; Poellinger, L (1996). Functional interference between hypoxia and dioxin signal transduction pathways: competition for recruitment of the Arnt transcription factor. Molecular and Cellular Biology, 16(10):5221-5231.

Abstract

Hypoxia-inducible factor 1 alpha (HIF-1 alpha) and the intracellular dioxin receptor mediate hypoxia and dioxin signalling, respectively. Both proteins are conditionally regulated basic helix-loop-helix (bHLH) transcription factors that, in addition to the bHLH motif, share a Per-Arnt-Sim (PAS) region of homology and form heterodimeric complexes with the common bHLH/PAS partner factor Arnt. Here we demonstrate that HIF-1 alpha required Arnt for DNA binding in vitro and functional activity in vivo. Both the bHLH and PAS motifs of Arnt were critical for dimerization with HIF-1 alpha. Strikingly, HIF-1 alpha exhibited very high affinity for Arnt in coimmunoprecipitation assays in vitro, resulting in competition with the ligand-activated dioxin receptor for recruitment of Arnt. Consistent with these observations, activation of HIF-1 alpha function in vivo or overexpression of HIF-1 alpha inhibited ligand-dependent induction of DNA binding activity by the dioxin receptor and dioxin receptor function on minimal reporter gene constructs. However, HIF-1 alpha- and dioxin receptor-mediated signalling pathways were not mutually exclusive, since activation of dioxin receptor function did not impair HIF-1 alpha-dependent induction of target gene expression. Both HIF-1 alpha and Arnt mRNAs were expressed constitutively in a large number of human tissues and cell lines, and these steady-state expression levels were not affected by exposure to hypoxia. Thus, HIF-1 alpha may be conditionally regulated by a mechanism that is distinct from induced expression levels, the prevalent model of activation of HIF-1 alpha function. Interestingly, we observed that HIF-1 alpha was associated with the molecular chaperone hsp90. Given the critical role of hsp90 for ligand binding activity and activation of the dioxin receptor, it is therefore possible that HIF-1 alpha is regulated by a similar mechanism, possibly by binding an as yet unknown class of ligands.

Abstract

Hypoxia-inducible factor 1 alpha (HIF-1 alpha) and the intracellular dioxin receptor mediate hypoxia and dioxin signalling, respectively. Both proteins are conditionally regulated basic helix-loop-helix (bHLH) transcription factors that, in addition to the bHLH motif, share a Per-Arnt-Sim (PAS) region of homology and form heterodimeric complexes with the common bHLH/PAS partner factor Arnt. Here we demonstrate that HIF-1 alpha required Arnt for DNA binding in vitro and functional activity in vivo. Both the bHLH and PAS motifs of Arnt were critical for dimerization with HIF-1 alpha. Strikingly, HIF-1 alpha exhibited very high affinity for Arnt in coimmunoprecipitation assays in vitro, resulting in competition with the ligand-activated dioxin receptor for recruitment of Arnt. Consistent with these observations, activation of HIF-1 alpha function in vivo or overexpression of HIF-1 alpha inhibited ligand-dependent induction of DNA binding activity by the dioxin receptor and dioxin receptor function on minimal reporter gene constructs. However, HIF-1 alpha- and dioxin receptor-mediated signalling pathways were not mutually exclusive, since activation of dioxin receptor function did not impair HIF-1 alpha-dependent induction of target gene expression. Both HIF-1 alpha and Arnt mRNAs were expressed constitutively in a large number of human tissues and cell lines, and these steady-state expression levels were not affected by exposure to hypoxia. Thus, HIF-1 alpha may be conditionally regulated by a mechanism that is distinct from induced expression levels, the prevalent model of activation of HIF-1 alpha function. Interestingly, we observed that HIF-1 alpha was associated with the molecular chaperone hsp90. Given the critical role of hsp90 for ligand binding activity and activation of the dioxin receptor, it is therefore possible that HIF-1 alpha is regulated by a similar mechanism, possibly by binding an as yet unknown class of ligands.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:04 Faculty of Medicine > Institute of Physiology
07 Faculty of Science > Institute of Physiology
Dewey Decimal Classification:570 Life sciences; biology
Language:English
Date:1996
Deposited On:11 Feb 2008 12:21
Last Modified:03 Aug 2017 14:46
Publisher:American Society for Microbiology
ISSN:0270-7306
Additional Information:Copyright: American Society for Microbiology
Free access at:PubMed ID. An embargo period may apply.
Related URLs:http://mcb.asm.org/cgi/content/abstract/16/10/5221 (Publisher)
PubMed ID:8816435

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