Hypoxia-inducible Factor1 Stabilization in Nonhypoxic Conditions: Role of Oxidation and Intracellular Ascorbate Depletion

Centre de recherche de L'Hôtel-Dieu de Québec, Department of Medicine, Université Laval, Québec, QC, G1R 2J6, Canada.
Molecular biology of the cell (Impact Factor: 5.98). 02/2008; 19(1):86-94. DOI: 10.1091/mbc.E07-06-0612
Source: PubMed

ABSTRACT Hypoxia-inducible factor-1 (HIF-1) is a decisive element for the transcriptional regulation of many genes induced under low oxygen conditions. Under normal oxygen conditions, HIF-1alpha, the active subunit of HIF-1, is hydroxylated on proline residues by specific HIF prolyl-hydroxylases, leading to ubiquitination and degradation by the proteasome. In hypoxia, hydroxylation and ubiquitination are blocked and HIF-1alpha accumulates in cells. Recent studies have shown that in normal oxygen conditions G-protein-coupled receptor agonists, including angiotensin (Ang) II and thrombin, potently induce and activate HIF-1 in vascular smooth muscle cells. The current study identifies HIF-1alpha protein stabilization as a key mechanism for HIF-1 induction by Ang II. We show that hydroxylation on proline 402 is altered by Ang II, decreasing pVHL binding to HIF-1alpha and allowing HIF-1alpha protein to escape subsequent ubiquitination and degradation mechanisms. We show that HIF-1alpha stability is mediated through the Ang II-mediated generation of hydrogen peroxide and a subsequent decrease in ascorbate levels, leading to decreased HIF prolyl-hydroxylase activity and HIF-1alpha stabilization. These findings identify novel and intricate signaling mechanisms involved in HIF-1 complex activation and will lead to the elucidation of the importance of HIF-1 in different Ang II-related cell responses.

Download full-text


Available from: Darren E. Richard, Jan 24, 2014
  • Source
    • "In the nucleus, it dimerizes with HIF-1β, becomes transcriptionally active and upregulates genes, including pro-angiogenic, cell proliferation and survival factors, including enzymes of the glycolytic pathway and glucose transporters (Kietzmann et al. 2001; Rossant et al. 2002; Lee et al. 2004; Ke et al. 2006). A number of studies have described an oxygen-independent stabilization of HIF-1α induced by growth factors and cytokines (Lee et al. 2004), association with HSP-90 protein (Liu et al. 2007), mTOR (mammalian target of rapamycin) signaling (Land et al. 2007) or Ang IImediated oxidation (Page et al. 2008). These aspects of HIF regulation likely account for different levels of HIF-1α that are detected in different mouse organs under normoxic conditions (Stroka et al. 2001). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Hypoxia-inducible factor-1 alpha subunit (HIF-1α) is a transcriptional activator mediating adaptive cellular response to hypoxia. Normally degraded in most cell types and tissues, HIF-1α becomes stable and transcriptionally active under conditions of hypoxia. In contrast, we found that HIF-1α is continuously expressed in adult brain neurogenic zones, as well as in neural stem/progenitor cells (NSPCs) from the embryonic and post-natal mouse brain. Our in vitro studies suggest that HIF-1α does not undergo typical hydroxylation, ubiquitination, and degradation within NSPCs under normoxic conditions. Based on immunofluorescence and cell fractionation, HIF-1α is primarily sequestered in membranous cytoplasmic structures, identified by immuno-electron microscopy as HIF-1α-bearing vesicles (HBV), which may prevent HIF-1α from degradation within the cytoplasm. HIF-1α shRNAi-mediated knockdown reduced the resistance of NSPCs to hypoxia, and markedly altered the expression levels of Notch-1 and β-catenin, which influence NSPC differentiation. These findings indicate a unique regulation of HIF-1α protein stability in NSPCs, which may have importance in NSPCs properties and function.
    Cellular and Molecular Neurobiology 01/2011; 31(1):119-33. DOI:10.1007/s10571-010-9561-5 · 2.20 Impact Factor
  • Source
    • "Taken together, these results indicate that Ang II– generated mtROS are essential for HIF-1␣ prolyl-hydroxylase inactivation in VSMCs. Our previous studies showed that HIF-1␣ prolyl hydroxylase activity is inactivated during Ang II stimulation by a ROS-induced depletion of intracellular ascorbate (Page et al., 2008 "
    [Show abstract] [Hide abstract]
    ABSTRACT: Hypoxia-inducible factor-1 (HIF-1) is a key transcription factor for responses to low oxygen. Different nonhypoxic stimuli, including hormones and growth factors, are also important HIF-1 activators in the vasculature. Angiotensin II (Ang II), the main effecter hormone in the renin-angiotensin system, is a potent HIF-1 activator in vascular smooth muscle cells (VSMCs). HIF-1 activation by Ang II involves intricate mechanisms of HIF-1α transcription, translation, and protein stabilization. Additionally, the generation of reactive oxygen species (ROS) is essential for HIF-1 activation during Ang II treatment. However, the role of the different VSMC ROS generators in HIF-1 activation by Ang II remains unclear. This work aims at elucidating this question. Surprisingly, repression of NADPH oxidase-generated ROS, using Vas2870, a specific inhibitor or a p22(phox) siRNA had no significant effect on HIF-1 accumulation by Ang II. In contrast, repression of mitochondrial-generated ROS, by complex III inhibition, by Rieske Fe-S protein siRNA, or by the mitochondrial-targeted antioxidant SkQ1, strikingly blocked HIF-1 accumulation. Furthermore, inhibition of mitochondrial-generated ROS abolished HIF-1α protein stability, HIF-1-dependent transcription and VSMC migration by Ang II. A large number of studies implicate NADPH oxidase-generated ROS in Ang II-mediated signaling pathways in VSMCs. However, our work points to mitochondrial-generated ROS as essential intermediates for HIF-1 activation in nonhypoxic conditions.
    Molecular biology of the cell 09/2010; 21(18):3247-57. DOI:10.1091/mbc.E10-01-0025 · 5.98 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In recent years the interference of heart and kidney disease has increasingly found attention in basic science and clinical research. A new classification of cardiorenal syndromes has now been proposed to address acute and chronic heart or kidney disease with its consequences on the respective other organ. However, it also becomes clear that the different clinical cardiorenal syndromes share common pathways. These basically include activation of the renin angiotensin system and of the sympathetic nervous system, but also inflammation, fibrosis, and accelerated atherosclerosis. These factors eventually support generation of oxidative stress and tissue hypoxia in the kidney and heart, culminating in irreversible tissue damage and aggravation of organ ischemia. This chapter summarizes aspects of the cardiorenal connection and oxygenation imbalances.
Show more