Molecular cloning and characterization of the Xenopus hypoxia-inducible factor 1α (xHIF1α)

We report the molecular cloning and the characterization of the Xenopus homolog of mammalian hypoxia-inducible factor I a (H IF 1 alpha), a member of the bHLH/PAS transcription factor family. Searches in Xenopus genome sequences and phylogenetic analysis reveal the existence of HIF1 alpha and HIF2 alpha paralogs in the Xenopus laevis species. Sequence data analyses indicate that the organization of protein domains in Xenopus HIF1 alpha]a (xHIF1 alpha is strongly conserved. We also show that xHIF1 alpha a heterodimerizes with the Xenopus Arnt1 protein (xArnt1) with the proteic complex being mediated by the HLH and PAS domains. Subcellular analysis in a Xenopus XTC cell line using chimeric GFP constructs show that over-expression of xHIF1 alpha and xArnt1 allows us to detect the xHIF1 alpha /xArnt1 complex in the nucleus, but only in the presence of both partners. Further analyses in XTC cell line show that over-producing xHIF1 alpha and xArnt1 mediates trans-activation of the hypoxia response element (HRE) reporter. The trans-activation level can be increased in hypoxia conditions. Interestingly such trans-activation properties can be also observed when human Arnt1 is used together with the xHIF1 alpha . J. Cell. Biochem. 102: 1542-1552, 2007. (c) 2007 Wiley-Liss, Inc.