The Ternary Complex Factor Net Is Downregulated by Hypoxia and Regulates Hypoxia-Responsive Genes

Abstract

Hypoxia and the Net ternary complex factor (TCF) regulate similar processes (angiogenesis, wound healing, and cellular migration) and genes (PAI-1, c-fos, erg-1, NOS-2, HO-1, and vascular endothelial growth factor genes), suggesting that they are involved in related pathways. We show here that hypoxia regulates Net differently from the other TCFs and that Net plays a role in the hypoxic response in vivo in mice and in cells. Hypoxia induces Net depletion from target promoters, nuclear export, ubiquitylation, and proteasomal degradation. Key mediators of the hypoxic response, the prolyl-4-hydroxylases containing domain proteins (PHDs), regulate Net. PHD downregulation in normoxia leads to Net degradation, and PHD overexpression delays Net downregulation by hypoxia. Net inhibition by RNA interference or mutation leads to altered regulation by hypoxia of the Net targets PAI-1, c-fos, and egr-1. We propose that hypoxia stimulates transcription of target promoters through removal of the repressor function of Net. Interestingly, the hematocrit response to a chemical inducer of hypoxia-like responses (cobalt chloride) is strongly altered in Net mutant mice. Our results show that the Net TCF is part of the biological response to hypoxia, adding a new component to an important pathological and physiological process.

The ternary complex factor Net/Elk-3 participates in the transcriptional response to hypoxia and regulates HIF-1α

“…Thus, Net appears to be an indirect modulator of HIF-1a protein expression. We have previously shown that Net is downregulated in hypoxia, and that Net contributes to the hypoxic induction of several genes, egr-1, c-fos and PAI-1 (Gross et al, 2007). Our current study shows that the role of Net is not limited to a small number of genes.…”

“…We have previously shown that Net mutant mice subjected to chemically induced hypoxia have altered haematocrit levels (Gross et al, 2007). This study identifies various pathways that could be explored to understand this phenotype.…”

“…We have previously shown that the ternary complex factor Net is specifically downregulated in hypoxia in endothelial cells (Gross et al, 2007), a cell type that has important functions in the response to hypoxia. In order to study in detail the role of Net compared to HIF-1a in the transcriptional response to hypoxia, we inhibited Net and HIF-1a by RNAi, before submitting the cells to hypoxia and microarray analysis (Figure 1).…”

“…We have recently identified a new component of the hypoxic response, the Net (Elk-3) TCF (Gross et al, 2007). Net, together with Elk-1 and Sap-1, forms the ternary complex TCFs subfamily, and are notably known for their participation in the early response of quiescent cells to growth factor stimulation.…”

“…Mice that express mutant Net lacking its DNA binding domain exhibit respiratory distress (Ayadi et al, 2001), and delayed wound healing due to impaired angiogenesis (Zheng et al, 2003). We have recently shown that Net is downregulated in hypoxia and is required for the regulation of several genes in response to hypoxia (Gross et al, 2007). In order to identify more globally the genes and functions regulated by Net in hypoxia, we performed a large-scale analysis using microarrays.…”