KAJIMURA, S.*; AIDA, K.; DUAN, C.; University of Michigan, Ann Arbor; University of Tokyo, Tokyo; University of Michigan, Ann Arbor: Understanding hypoxia-induced gene expression in early development: In vitro and in vivo analysis of HIF-1-regulated zebrafish IGFBP-1 gene expression

Insulin-like growth factor binding protein-1 (IGFBP-1) is a hypoxia-inducible gene. Previous studies have shown that the induction of IGFBP-1 expression by hypoxia is a conserved physiological mechanism acting to restrict IGF-stimulated growth and developmental process under hypoxic stress (Kajimura et al., PNAS, 2005). The molecular mechanisms underlying hypoxia-induced IGFBP-1 gene expression in the embryonic tissues, however, are not well understood. Here we show that the hypoxia-inducible factor (HIF)-1 pathway is established in early embryogenesis and mediates hypoxia-induced IGFBP-1 expression in zebrafish embryos. Hypoxia exposure or HIF-1a overexpression significantly increased the zebrafish IGFBP-1 gene transcription in cultured cells in vitro and in developing embryos in vivo. Although the zebrafish IGFBP-1 promoter contains 13 consensus hypoxia response elements (HREs), deletion and point mutation analysis revealed that only the HRE positioned at -1090/-1086 is required during hypoxia and HIF-1-induced IGFBP-1 expression in vitro and in vivo. Further experiments revealed the presence of a putative HRE ancillary sequence (HAS) adjacent to the -1090/-1086 HRE but not the other HREs. Mutation of the HAS greatly reduced the responsiveness of the IGFBP-1 promoter to hypoxia and to HIF-1. These results suggest that HIF-1 mediates hypoxia-induced IGFBP-1 gene expression in early development by selectively interacting with the -1090/-1086 HRE in a context/location-dependent manner.