Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:4.6.1.2 (guanylate cyclase)
8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heme oxygenase (HO)-mediated heme degradation is the primary mechanism for production of cellular carbon monoxide (CO). Analogous to nitric oxide (NO), CO mediates physiological and cellular functions such as vasodilation, stimulation of guanylate cyclase, and neuronal transmission. In view of accumulating data demonstrating a correlation between the activity of these two gaseous molecules and that the predominant source of CO is via HO catalysis, we hypothesized that NO regulates HO expression. We demonstrate that the NO donor spermine NONOate (SNN) increases steady-state levels of HO-1 mRNA in aortic vascular smooth muscle cells (aSMC) in both a time- and dose-dependent manner. The accumulation of HO-1 mRNA that correlated with increased HO-1 protein synthesis resulted from both an increased rate of gene transcription and a decreased rate of mRNA turnover. Inhibition of the NO-induced HO-1 mRNA expression by cycloheximide suggests that new protein synthesis is required for increased HO-1 gene expression. Induction of HO-1 expression by SNN occurs in a guanosine 3',5'-cyclic monophosphate (cGMP)-independent manner because exposure of cells to 8-bromoguanosine 3',5'-cyclic monophosphate, a cGMP analog, did not increase HO-1 mRNA levels, and pretreatment of cells with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, a selective guanylate cyclase inhibitor, did not prevent SNN-induced HO-1 mRNA accumulation. The antioxidant N-acetyl-L-cysteine markedly inhibited SNN-induced HO-1 mRNA expression, whereas peroxynitrite did not induce HO-1 expression in aSMC. Interestingly, CO did not attenuate NO-induced HO-1 expression through an autocrine negative feedback mechanism as had been observed for hypoxia-induced HO-1 expression. These data provide evidence for an important regulatory network between NO and CO via HO-1.
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PMID:Regulation of heme oxygenase-1 gene expression in vascular smooth muscle cells by nitric oxide. 937 24

Heme oxygenase (HO) proteins are members of the HSP30 family and consist of 2 isozymes identified to date, termed HO-1 and HO-2. Separate genes encode the isozymes and protein products which are immunochemically distinct, share less than 50% similarity at the amino acid sequence level. Each form, however, shows greater than 90% similarity among species, including human and the rat (reviewed in ref.). Furthermore, these isozymes function in a well-defined role to carry out oxidation of the heme molecule (Fe-protoporphyrin IX) in concert with NADPH-cytochrome P450 reductase. The oxidation of heme is isomer specific and results in the formation of bile pigments, carbon monoxide, and iron. The heme molecule constitutes the prosthetic moiety of hemoproteins, such as hemoglobin, myoglobin, catalase, soluble guanylate cyclase, cytochrome b5, cytochromes P450 and NO synthase. HO-1 also known as heat shock protein (HSP) 32 is encoded by a gene which is exquisitely stress-responsive and a host of stimuli that mediate oxidative stress cause induction of the protein both in vivo and in vitro. The HO-2 form shows a unique pattern of regulation from that of HO-1. HO-2 is a constitutive protein and its expression is not affected by the inducers of HO-1 tested to date; rather, the only known regulator of HO-2 yet identified is adrenal glucocorticoids. The two isozymes display vast differences in tissue distribution and under normal conditions HO-1 is present in the whole brain at the limit of immunodetection and is discreetly localized in select neuronal populations. HO-1 protein (approximately 32 kDa) and its approximately 1.8 kb transcript are increased, however, in response to stressful stimuli primarily in non-neuronal cell populations. The heme oxygenase system serves in both a catabolic and anabolic capacity in the cell. In the former capacity, it down-regulates cellular heme and hemoprotein levels. And, as such it inactivates the most effective catalyst for formation of free radicals, the heme molecule. In its anabolic role, as noted above, heme oxygenase produces bile pigments, carbon monoxide, and iron, all of which are biologically active: bile pigments function as antioxidants; the carbon monoxide generated by HO activity has been correlated with the generation of cGMP; and iron regulates expression of various genes, including that of HO-1 itself, as well as transferrin receptors, ferritin, and NO synthase. We used rabbit anti-rat HO-2 polyclonal antibody and HO-2 cDNA to localize HO-2 immunoreactive protein and the 1.3- and 1.9 kb homologous transcripts, respectively, in rodent brain as visualized by histochemical staining procedures. These protocols provide the first detailed description of methodologies successfully used to define the pattern of HO-2 expression at the transcriptional and translational levels in the adult rat brain and glucocorticoid-treated newborn rats. The procedures described herein have the virtue of being non-radioactive, as well as applicability to the systemic organs, such as the cardiovascular system and the male reproductive organs. Visualization of cellular HO-2 expression aids in assessment of potential sites of carbon monoxide, iron, and bilirubin production within the nervous system.
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PMID:Histochemical localization of heme oxygenase-2 protein and mRNA expression in rat brain. 938 81

The past several years have been witness to a staggering rate of advancement in the understanding of how organisms respond to changes in the availability of diatomic molecules that are toxic and/or crucial to survival. Heme-based sensors presently constitute the majority of the proteins known to sense NO, O2 and CO and to initiate the chemistry required to adapt to changes in their availabilities. Knowledge of the three characterized members of this class, soluble guanylate cyclase, FixL and CooA, has grown substantially during the past year. The major advances have resulted from a broad range of approaches to elucidation of both function and mechanism. They include growth in the understanding of the interplay between the heme and protein in soluble guanylate cyclase, as well as alternate means for its stimulation. Insight into the O2-induced structural changes in FixL has been supplied by the single crystal structure of the heme domain of Bradyrhizobium japonicum. Finally, the ligation environment and ligand interchange that facilitates CO sensing by CooA has been established by spectroscopic and mutagenesis techniques.
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PMID:Heme-based sensors in biological systems. 1022 51

Heme is a complex of iron with protoporphyrin IX that is essential for the function of all aerobic cells. Heme serves as the prosthetic group of numerous hemoproteins (eg, hemoglobin, myoglobin, cytochromes, guanylate cyclase, and nitric oxide synthase) and plays an important role in controlling protein synthesis and cell differentiation. Cellular heme levels are tightly controlled; this is achieved by a fine balance between heme biosynthesis and catabolism by the enzyme heme oxygenase. On a per-cell basis, the rate of heme synthesis in the developing erythroid cells is at least 1 order of magnitude higher than in the liver, which is in turn the second most active heme producer in the organism. Differences in iron metabolism and in genes for 5-aminolevulinic acid synthase (ALA-S, the first enzyme in heme biosynthesis) are responsible for the differences in regulation and rates of heme synthesis in erythroid and nonerythroid cells. There are 2 different genes for ALA-S, one of which is expressed ubiquitously (ALA-S1), whereas the expression of the other (ALA-S2) is specific to erythroid cells. Because the 5'-untranslated region of the erythroid-specific ALA-S2 mRNA contains the iron-responsive element, a cis-acting sequence responsible for translational induction of erythroid ALA-S2 by iron, the availability of iron controls protoporphyrin IX levels in hemoglobin-synthesizing cells. In nonerythroid cells, the rate-limiting step of heme production is catalyzed by ALA-S1, whose synthesis is feedback-inhibited by heme. On the other hand, in erythroid cells, heme does not inhibit either the activity or the synthesis of ALA-S but does inhibit cellular iron acquisition from transferrin without affecting its utilization for heme synthesis. This negative feedback is likely to explain the mechanism by which the availability of transferrin iron limits heme synthesis rate. Moreover, in erythroid cells heme seems to enhance globin gene transcription, is essential for globin translation, and supplies the prosthetic group for hemoglobin assembly. Heme may also be involved in the expression of other erythroid-specific proteins. Furthermore, heme seems to play a role in regulating either transcription, translation, processing, assembly, or stability of hemoproteins in nonerythroid cells. Heme oxygenase, which catalyzes heme degradation, seems to be an important enzymatic antioxidant system, probably by providing biliverdin, which is an antioxidant agent.
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PMID:Cell biology of heme. 1052 52

Heme oxygenase (HO)-1 catalyzes the oxidative cleavage of heme to yield equimolar amounts of biliverdin, iron, and carbon monoxide. HO-1 is a stress response protein, the induction of which is associated with protection against oxidative stress. The mechanism(s) of protection is not completely elucidated, although it is suggested that one or more of the catalytic by-products provide antioxidant functions either directly or indirectly. The involvement of reactive oxygen species in apoptosis raised the question of a possible role for HO-1 in programmed cell death. Using the tetracycline-regulated expression system, we show here that conditional overexpression of HO-1 prevents tumor necrosis factor-alpha-induced apoptosis in murine L929 fibroblasts. Inhibition of apoptosis was not observed in the presence of tin protoporphyrin, a specific inhibitor of HO activity, and in cells overexpressing antisense HO-1. Interestingly, exogenous administration of a low concentration of carbon monoxide also prevented tumor necrosis factor-alpha-induced apoptosis in L929 fibroblasts. Inhibition of tumor necrosis factor-alpha-induced apoptosis by HO-1 overexpression was reversed by 1H-(1,2, 4)oxadiazolo(4,3-a)quinoxalin-1-one, an inhibitor of guanylate cyclase, which is a target enzyme for carbon monoxide. Taken together, our data suggest that the antiapoptotic effect of HO-1 may be mediated via carbon monoxide.
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PMID:Heme oxygenase-1 inhibits TNF-alpha-induced apoptosis in cultured fibroblasts. 1066 15

Heme oxygenase-2 (HO-2) synthesizes carbon monoxide (CO), a modulator of soluble guanylate cyclase (sGC). To examine this signal transduction pathway in the retina, we immunocytochemically localized HO-2, and investigated the effects of CO on cGMP levels. In turtle, HO-2-like immunoreactivity (-LI) was in all photoreceptors, some amacrine cells, and in numerous bipolar and ganglion cells. HO-2-LI colocalized with sGC activity in many cells. In rat, HO-LI was found only in the inner retina, in ganglion and amacrine cells. In turtle, stimulation with CO alone primarily increased cGMP-LI in bipolar cells in the visual streak. Stimulation with a combination of CO and nitric oxide (NO) dramatically increased cGMP-LI throughout the retina, in comparison to the smaller increases seen with NO or CO alone. These data suggest that CO is an endogenous modulator of the sGC/cGMP signaling pathway in many retinal neurons, and can dramatically amplify NO-stimulated increases in cGMP.
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PMID:Localization of heme oxygenase-2 and modulation of cGMP levels by carbon monoxide and/or nitric oxide in the retina. 1091 Jan 1

Heme is not only a very important prosthetic group that modulates the structure and activity of heme proteins but also a regulatory molecule that controls metabolic pathways and the biosynthesis of various proteins. However, investigation into heme regulatory effects in higher vertebrates has been hampered by the lack of a suitable animal model. A knockout mouse with targeted disruption of porphobilinogen deaminase, the third enzyme of the heme pathway, has been generated in our laboratory and used in the present study as an in vivo model of heme deficiency to explore diverse heme regulatory properties. In this model with a defined heme disturbance, we observed a superinductive response of delta-aminolevulinate synthase, the first enzyme in heme synthesis, after phenobarbital treatment. We also found that limited heme is associated with decreased induction of cytochrome P450 by phenobarbital as a consequence of impaired gene transcription. This inhibitory effect is isoenzyme-specific, being significant for cyp2a5. The activity and mRNA level of this particular cytochrome P450 are significantly lower in the phenobarbital-induced porphobilinogen deaminase-deficient mice (55% and 43%, respectively), but its expression can be restored to normal values when exogenous heme is administered. Other heme proteins, namely neuronal nitric oxide synthase and soluble guanylate cyclase, function normally in mice with limited heme. Our results demonstrate that the expression of various heme proteins is differentially regulated in conditions of reduced heme availability. Moreover, our findings emphasize the importance of heme protein function in the genesis of pathophysiological manifestations in acute intermittent porphyria.
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PMID:Limited heme synthesis in porphobilinogen deaminase-deficient mice impairs transcriptional activation of specific cytochrome P450 genes by phenobarbital. 1110 24

Heme oxygenase (HO-1, encoded by Hmox1) is an inducible protein activated in systemic inflammatory conditions by oxidant stress. Vascular injury is characterized by a local reparative process with inflammatory components, indicating a potential protective role for HO-1 in arterial wound repair. Here we report that HO-1 directly reduces vasoconstriction and inhibits cell proliferation during vascular injury. Expression of HO-1 in arteries stimulated vascular relaxation, mediated by guanylate cyclase and cGMP, independent of nitric oxide. The unexpected effects of HO-1 on vascular smooth muscle cell growth were mediated by cell-cycle arrest involving p21Cip1. HO-1 reduced the proliferative response to vascular injury in vivo; expression of HO-1 in pig arteries inhibited lesion formation and Hmox1-/- mice produced hyperplastic arteries compared with controls. Induction of the HO-1 pathway moderates the severity of vascular injury by at least two adaptive mechanisms independent of nitric oxide, and is a potential therapeutic target for diseases of the vasculature.
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PMID:Heme oxygenase-1 protects against vascular constriction and proliferation. 1138 95

Carbon monoxide and nitric oxide are two endogenously produced gases that can act as second messenger molecules. Heme oxygenase and nitric oxide synthase are the enzyme systems responsible for generating carbon monoxide and nitric oxide, respectively. Both carbon monoxide and nitric oxide share similar properties, such as the ability to activate soluble guanylate cyclase to increase cyclic GMP. It is becoming increasingly clear that these two gases do not always work independently, but rather can modulate each other's activity. Although much is known about the heme oxygenase/carbon monoxide and nitric oxide synthase/nitric oxide pathways, how these two important systems interact is less well understood. This review attempts to define the current known relationship between carbon monoxide and nitric oxide as it relates to their production and physiological function.
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PMID:Cross talk between carbon monoxide and nitric oxide. 1200 81

Heme oxygenase (HO) is the rate-limiting enzyme for the degradation of heme, a prooxidant, coming from a multitude of heme-containing proteins/enzymes. With the action of cytochrome P(450) reductase, HO cleaves the heme ring into biliverdin which is converted into bilirubin, both have been shown to have intrinsic radical scavenger activities. Iron is also released from the heme core and in its free form can act as a catalyst for oxidative stress damage or can be sequested by several iron-binding proteins. Under physiological conditions, the newly generated iron can be neutralized within the cell. The third product of the opening of the porphyrin ring is carbon monoxide, which role has been puzzling. It has been reported as a potential neuromodulator, it modulates guanylate cyclase activity and has vasodilation, anti-inflammatory and antiapoptotic effects. In the brain, HO2 accounts for the vast majority of HO activity. By decreasing HO2 activity, one would expect more neuronal damage after oxidative stress injury with possible direct implications to acute and chronic neurodegenerative disorders. Pharmacological ways to increase neuronal HO activity is likely to have therapeutic applications.
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PMID:Decreased activity of the antioxidant heme oxygenase enzyme: implications in ischemia and in Alzheimer's disease. 1205 65


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