Inhibitory PAS domain protein is a negative regulator of hypoxia-inducible gene expression

Abstract

Alteration of gene expression is a crucial component of adaptive responses to hypoxia. These responses are mediated by hypoxia-inducible transcription factors (HIFs). Here we describe an inhibitory PAS (Per/Arnt/Sim) domain protein, IPAS, which is a basic helix-loop-helix (bHLH)/PAS protein structurally related to HIFs. IPAS contains no endogenous transactivation function but demonstrates dominant negative regulation of HIF-mediated control of gene expression. Ectopic expression of IPAS in hepatoma cells selectively impairs induction of genes involved in adaptation to a hypoxic environment, notably the vascular endothelial growth factor (VEGF) gene, and results in retarded tumour growth and tumour vascular density in vivo. In mice, IPAS was predominantly expressed in Purkinje cells of the cerebellum and in corneal epithelium of the eye. Expression of IPAS in the cornea correlates with low levels of expression of the VEGF gene under hypoxic conditions. Application of an IPAS antisense oligonucleotide to the mouse cornea induced angiogenesis under normal oxygen conditions, and demonstrated hypoxia-dependent induction of VEGF gene expression in hypoxic corneal cells. These results indicate a previously unknown mechanism for negative regulation of angiogenesis and maintenance of an avascular phenotype.

Hypoxia upregulates hypoxia inducible factor (HIF)-3α expression in lung epithelial cells: characterization and comparison with HIF-1α

“…The trans-regulation between HIF-3α and HIF-1α was suggested by Makino et al [41], who demonstrated that an alternatively spliced variant of mHIF-3α was a dominantnegative regulator of mouse HIF-1α. Recently, Marynard et al [33] found hIPAS, which they named hHIF-3α2.…”

The role of oxygen availability in embryonic development and stem cell function

“…HIF-1α is ubiquitously expressed, whereas HIF-2α (also called EPAS (endothelial PAS protein), HLF (HIF-1α-like factor), and HRF (HIF-related factor)) and HIF-3α exhibit more restricted tissue distributions. HIF-2α is expressed primarily in the vasculature of the early developing embryo and subsequently in the lung, kidney interstitial cells, liver parenchyma, and neural crest cells 116-118HIF-3α mRNA and protein are primarily detected in the thymus, kidney, cerebellar Purkinje cells, and corneal epithelium of the eye 119,120 . HIF-1β/ARNT is constitutively expressed and is largely insensitive to changes in O 2 levels, whereas all three HIF-α subunits are acutely regulated by hypoxia (see Box 2).…”

Understanding complexity in the HIF signaling pathway using systems biology and mathematical modeling

“…IPAS is an alternative splicing product of the HIF-3 locus that lacks the C-terminal transactivation domains of the HIF-1 and -2 [39]. As such, it competes with HIF-1 for binding the  subunits acting as a dominant negative regulator of HIFs [40]. The IPAS-specific splicing product of the HIF-3 locus is hypoxia-inducible and 8 HIF-1 binds to the hypoxia-responsive cis-element of the IPAS promoter representing a classic negative feedback that restricts HIF-mediated gene expression in hypoxia (Figure 2A) [39,41].…”