Accumulation of HIF-1α under the influence of nitric oxide

Abstract

The key player for adaptation to reduced oxygen availability is the transcription factor hypoxia-inducible factor 1 (HIF-1), composed of the redox-sensitive HIF-1alpha and the constitutively expressed HIF-1beta subunits. Under normoxic conditions, HIF-1alpha is rapidly degraded, whereas hypoxia, CoCl(2), or desferroxamine promote protein stabilization, thus evoking its transcriptional activity. Because HIF-1 is regulated by reactive oxygen species, investigation of the impact of reactive nitrogen species was intended. By using different nitric oxide (NO) donors, dose- and time-dependent HIF-1alpha accumulation in close correlation with the release of NO from chemically distinct NO donors was established. Intriguingly, small NO concentrations induced a faster but transient HIF-1alpha accumulation than higher doses of the same NO donor. In contrast, NO attenuated up-regulation of HIF-1alpha evoked by CoCl(2) in a concentration- and time-dependent manner, whereas the desferroxamine-elicited HIF-1alpha signal remained unaltered. To demonstrate an autocrine or paracrine signaling function of NO, we overexpressed the inducible NO synthase and used a coculture system of activated macrophages and tubular cells. Expression of the NO synthase induced HIF-1alpha accumulation, which underscored the role of NO as an intracellular activator for HIF-1. In addition, macrophage-derived NO triggered HIF-1alpha up-regulation in LLC-PK(1) target cells, which points to intercellular signaling properties of NO in achieving HIF-1 accumulation. Our results show that NO does not only modulate the HIF-1 response under hypoxic conditions, but it also functions as a HIF-1 inducer. We conclude that accumulation of HIF-1 occurs during hypoxia but also under inflammatory conditions that are characterized by sustained NO formation.

Nitric Oxide Impairs Normoxic Degradation of HIF-1α by Inhibition of Prolyl Hydroxylases

“…Initial observations suggested that NO inhibits hypoxia-induced HIF-1␣ stabilization and HIF-1 transcriptional activation (Liu et al, 1998;Sogawa et al, 1998;Huang et al, 1999). More recent studies indicated that chemically diverse NO donors or enhanced endogenous NO formation by inducible NO-synthase or NO formation in a coculture system under normoxic conditions provoked HIF-1␣ stabilization, HIF-1 DNA-binding, and activation of downstream target gene expression (Kimura et al, 2001;Sandau et al, 2001aSandau et al, , 2001bZhou et al, 2003). Studies performed in several cell systems such as tubular LLC-PK 1 , human glioblastoma, human hepatoma, or bovine pulmonary artery endothelial cells imply that this is neither species specific nor restricted to certain cell types.…”

“…Studies performed in several cell systems such as tubular LLC-PK 1 , human glioblastoma, human hepatoma, or bovine pulmonary artery endothelial cells imply that this is neither species specific nor restricted to certain cell types. Guanylyl cyclase antagonists and lipophilic cGMP analogues did not attenuate/mimic HIF-1␣ accumulation and thus excluded a role of the soluble guanylyl cyclase-cGMP pathway (Kimura et al, 2000;Palmer et al, 2000;Sandau et al, 2001a), thus leaving molecular mechanisms of NO action unresolved.Herein, we demonstrate the inhibitory effect of NO on HIF-1␣ ubiquitination and interaction with pVHL. We present evidence that PHDs are targeted by NO, which suggests attenuation of prolyl hydroxylation as the underlying mechanism of NO-induced HIF-1␣ accumulation in normoxia.…”

“…Recent evidence suggests that HIF-1␣ can be accumulated and activated by certain growth factors, cytokines (Hellwig-Bü rgel et al, 1999), and hormones during normoxia. In addition, a modulatory role of nitric oxide (NO) emerged (Kimura et al, 2000;Palmer et al, 2000;Sandau et al, 2000Sandau et al, , 2001a. Regulation of HIF-1 activity by NO is likely to be of (patho)-physiological relevance but molecular mechanisms have not been defined yet.…”

Guanylyl cyclase is an ATP sensor coupling nitric oxide signaling to cell metabolism

“…Moreover, in some models of severe hypoxic stress, NO induces complete and reversible metabolic stasis required to survive the insult (19). The importance of NO in defending against ischemia is underscored by its regulation of the transcription factor hypoxia inducible factor 1, a master regulator of cellular homeostasis in the context of oxygen insufficiency (20).Coordination of energy supply and demand is mediated, in part, by NO activation of soluble guanylyl cyclase (sGC) and the associated accumulation of intracellular cGMP concentration ([cGMP] i ) (9,10,12,15,16,18), yet the mechanisms coordinating cGMP-dependent and metabolic signaling, beyond the production of NO, remain undefined. Recently, a novel mechanism was identified by which adenine nucleotides inhibit GCs (21,22) that is analogous to P site inhibition of adenylyl cyclases (23).…”

Gestation linked radical oxygen species fluxes and vitamins and trace mineral deficiencies in the ruminant

“…Suppression of ROS fluxes can suppress the expression of both Mn-and Cu/Zn-SOD [78]. Moreover, the coordination of the whole set of regulatory events and its relation to oxygen partial pressure can be altered by variation of the cellular contents of the • NO radical, because this compound inhibits HIF-1α stabilization under hypoxia [52] or its oxidation under normal oxygenation [91], or, again, triggers GSH synthesis to change the redox environment and the control of gene expression [15].…”