Interferon-gamma plays a nonredundant role in mediating T cell-dependent outward vascular remodeling of allogeneic human coronary arteries

Vascular remodeling (change in vessel diameter) rather than intimal hyperplasia is the most important predictor of luminal loss in immune-mediated arterial injury, yet little is known about its mechanisms. Here, we show that outward vascular remodeling and intimal thickening, two manifestations of arteriosclerosis with opposing effects on luminal size, result from immune effector mechanisms that are T-cell dependent and interferon (IFN)-gamma mediated. In our in vivo model of human coronary artery injury by allogeneic peripheral blood mononuclear cells, both processes occur concurrently and are characterized by T-cell infiltrates with a predominantly IFN-gamma-producing cytokine profile. Neutralization of IFN-gamma inhibits the arterial and intimal expansion, whereas administration of IFN-gamma enhances these effects. The nonredundant role of IFN-gamma in T-cell-dependent remodeling of human coronary arteries demonstrated here presents a new therapeutic target for preservation of vessel lumen in arteriosclerosis.

Caveolin regulation of endothelial function

Caveolae are the sites in the cell membrane responsible for concentrating an array of signaling molecules critical for cell function. Recent studies have begun to identify the functions of caveolin-1, the 22-kDa caveolar protein that oligomerizes and inserts into the cytoplasmic face of the plasma membrane. Caveolin-1 appears to regulate caveolar internalization by stabilizing caveolae at the plasma membrane rather than controlling the shape of the membrane invagination. Because caveolin-1 is a scaffolding protein, it has also been hypothesized to function as a "master regulator" of signaling molecules in caveolae. Deletion of the caveolin-1 gene in mice resulted in cardiac hypertrophy and lung fibrosis, indicating its importance in cardiac and lung development. In the endothelium, caveolin-1 regulates nitric oxide signaling by binding to and inhibiting endothelial nitric oxide synthase (eNOS). Increased cytosolic Ca2+ or activation of the kinase Akt leads to eNOS activation and its dissociation from caveolin-1. Caveolae have also been proposed as the vesicle carriers responsible for transcellular transport (transcytosis) in endothelial cells. Transcytosis, the primary means of albumin transport across continuous endothelia, occurs by fission of caveolae from the membrane. This event is regulated by tyrosine phosphorylation of caveolin-1 and dynamin. As Ca2+ influx channels and pumps are localized in caveolae, caveolin-1 is also an important determinant of Ca2+ signaling in endothelial cells. Many of these findings were presented in San Diego, CA, at the 2003 Experimental Biology symposium "Caveolin Regulation of Endothelial Function" and are reviewed in this summary.

Regulation of survivin function by Hsp90

Pathways controlling cell proliferation and cell survival require flexible adaptation to environmental stresses. These mechanisms are frequently exploited in cancer, allowing tumor cells to thrive in unfavorable milieus. Here, we show that Hsp90, a molecular chaperone that is central to the cellular stress response, associates with survivin, an apoptosis inhibitor and essential regulator of mitosis. This interaction involves the ATPase domain of Hsp90 and the survivin baculovirus inhibitor of apoptosis repeat. Global suppression of the Hsp90 chaperone function or targeted Abmediated disruption of the survivin-Hsp90 complex results in proteasomal degradation of survivin, mitochondrial-dependent apoptosis, and cell cycle arrest with mitotic defects. These data link the cellular stress response to an antiapoptotic and mitotic checkpoint maintained by survivin. Targeting the survivin-Hsp90 complex may provide a rational approach for cancer therapy.

Phosphorylation of threonine 497 in endothelial nitric-oxide synthase coordinates the coupling of L-arginine metabolism to efficient nitric oxide production

There is evidence that endothelial nitric-oxide synthase (eNOS) is regulated by reciprocal dephosphorylation of Thr497 and phosphorylation of Ser1179. To examine the interrelationship between these sites, cells were transfected with wild-type (WT), T497A, T497D, S1179D, and T497A/S1179D eNOS and activity, NO release and eNOS localization were assessed. Although eNOS T497A, S1179D and T497A/S1179D eNOS had greater enzymatic activity than did WT eNOS in lysates, basal production of NO from cells was markedly reduced in cells transfected with T497A and T497A/S1179D eNOS but augmented in cells transfected with S1179D eNOS. Stimulating cells with ATP or ionophore normalized the loss of function seen with T497A and T497A/S1179D eNOS to levels observed with WT and S1179D eNOS, respectively. Despite these functional differences, the localization of eNOS mutants were similar to WT. Because both T497A and T497A/S1179D eNOS exhibited higher enzyme activity but reduced production of NO, we examined whether these mutations were "uncoupling" NO synthesis. T497A and T497A/S1179D eNOS generated 2-3 times more superoxide anion than WT eNOS, and both basal and stimulated interactions of T497A/S1179D eNOS with hsp90 were reduced in co-immunoprecipitation experiments. Thus, the phosphorylation/dephosphorylation of Thr497 may be an intrinsic switch mechanism that determines whether eNOS generates NO versus superoxide in cells.

Mesenteric vasoconstriction triggers nitric oxide overproduction in the superior mesenteric artery of portal hypertensive rats

BACKGROUND & AIMS

Vasoconstriction of the superior mesenteric artery (SMA) is the earliest hemodynamic event occurring after partial portal vein ligation (PVL). We tested the hypothesis that this early vasoconstriction of the SMA may initiate eNOS up-regulation in PVL.

METHODS

Portal hypertension with or without mesenteric vasoconstriction was induced by differentially calibrated stenosis of the portal vein (PVL-20G and PVL-18G, respectively). In a separate group of rats, mesenteric vasoconstriction was achieved by renal artery ligation. Sham-operated rats were used as controls. Effects of vasoconstriction of the SMA in PVL and RAL rats were evaluated by measuring perfusion pressure changes in isolated SMA beds in response to methoxamine, nitric oxide synthase activity, and eNOS protein expression. Mean arterial pressure, portal pressure, and SMA blood flow were measured by catheterization and Doppler flowmetry. SMA vascular resistance was calculated from arterial pressure, portal pressure, and SMA flow.

RESULTS

There was a significant increase in SMA vascular resistance in PVL-20G (2.33 +/- 0.13 vs. 1.22 +/- 0.03 mm Hg/% flow; P < 0.05) and RAL (2.32 +/- 0.18 vs. 1.18 +/- 0.02 mm Hg/% flow; P < 0.05) but not in PVL-18G, showing mesenteric vasoconstriction in both PVL-20G and RAL groups. The mesenteric vasculature of PVL-20G and RAL animals showed hyporeactivity to methoxamine (P < 0.01). Whereas both PVL groups were portal hypertensive (P < 0.01), RAL rats were not. The SMA hyporeactivity of PVL-20G and RAL rats was corrected by N(G)()-monomethyl-L-arginine, and nitric oxide synthase enzyme activity was significantly higher in PVL-20G and RAL rats (P < 0.05).

CONCLUSIONS

Mesenteric arterial vasoconstriction plays a triggering role in up-regulation of eNOS catalytic activity in the SMA of portal hypertensive rats.

Heat shock protein 90 and tyrosine kinase regulate eNOS NO* generation but not NO* bioactivity

An increase in the association of heat shock protein 90 (HSP90) with endothelial nitric oxide (NO) synthase (eNOS) is well recognized for increasing NO (NO*) production. Despite the progress in this field, the mechanisms by which HSP90 modulates eNOS remain unclear due, in part, to the fact that geldanamycin (GA) redox cycles to generate superoxide anion (O(2)(-*) and the fact that inhibiting HSP90 with GA or radicicol (RAD) destabilizes tyrosine kinases that rely on the chaperone for maturation. In this report, we determine the extent to which these side effects alter vascular and endothelial cell function in physiologically relevant systems and in cultured endothelial cells. Vascular endothelial growth factor (VEGF)-stimulated vascular permeability, as measured by Evans blue leakage in the ears of male Swiss mice in vivo, and acetylcholine-induced vasodilation of isolated, pressurized mandibular arterioles from male C57BL6 mice ex vivo were attenuated by N(omega)-nitro-L-arginine methyl ester (L-NAME), GA, and RAD. Z-1[N-(2-aminoethyl)-N-(2-ammonoethyl)amino]diazen-1-ium-1,2-dioate (DETA-NONOate), a slow releasing NO. donor, increased vasodilation of arterioles pretreated with GA, RAD, and L-NAME equally well except at 10(-5) M, the highest concentration used, where vasodilation was greater in pressurized arterioles treated with L-NAME than in arterioles pretreated with GA or RAD alone. Both GA and RAD reduced NO* release from stimulated endothelial cell cultures and increased O(2)(-*) production in the endothelium of isolated aortas by an L-NAME-inhibitable mechanism. Pretreatment with RAD increased stimulated O(2)(-*) production from eNOS, whereas pretreatment with genistein (GE), a broad-spectrum tyrosine kinase inhibitor, did not; however, pretreatment with GE + RAD resulted in a super-induced state of uncoupled eNOS activity upon stimulation. These data suggest that the tyrosine kinases, either directly or indirectly, and HSP90-dependent signaling pathways act in concert to suppress uncoupled eNOS activity.

Adeno-associated virus mediated gene delivery into coronary microvessels of chronically instrumented dogs

The objective of this study was to assess the potential of adeno-associated virus (AAV)-mediated gene delivery into coronary microvessels in vivo in a large animal. Ten mongrel dogs were chronically instrumented and allowed to recover for 10 days. Dogs were reanesthetized, and the aorta was constricted by a hydraulic occluder, whereby left ventricular (LV) pressure increased by 30% and left circumflex coronary artery blood flow by 50%. Recombinant AAV (serotype 2, CMV enhancer/chicken beta-actin promoter) encoding for green fluorescent protein (GFP) was injected as a bolus into the left atrium during aortic constriction at total titers of 1010 or 1012 infectious units. Dogs were followed for 2 (n = 4)or4wk(n = 6). Hemodynamics or body weight did not change. In LV tissue slices, a fluorescein-labeled antibody to GFP stained endothelial and smooth muscle cells but was absent in myocytes. To quantify transduction, slices were then stained with antibodies against alpha-smooth muscle actin or von Willebrand factor. Approximately 4% of arterioles and 2% of microvessels stained positive for anti-GFP independent from viral titer or duration. By regression analyses, the percent of vessels transfected was proportional to the increase in LV systolic pressure during occlusion. AAV is a potential vector for gene transfer into the coronary microcirculation in large animals, including perhaps humans.

Endothelial NO synthase phosphorylated at SER635 produces NO without requiring intracellular calcium increase

Shear stress stimulates NO production involving the Ca2+-independent mechanisms in endothelial cells. We have shown that exposure of bovine aortic endothelial cells (BAEC) to shear stress stimulates phosphorylation of eNOS at S635 and S1179 by the protein kinase A- (PKA-) dependent mechanisms. We examined whether phosphorylation of S635 of eNOS induced by PKA stimulates NO production in a calcium-independent manner. Expression of a constitutively active catalytic subunit of PKA (Cqr) in BAEC induced phosphorylation of S635 and S1179 residues and dephosphorylation of T497. Additionally, Cqr expression stimulated NO production, which could not be prevented by treating cells with the intracellular calcium chelator BAPTA-AM. To determine the role of each eNOS phosphorylation site in NO production, HEK-293 cells transfected with eNOS point mutants whereby S116, T497, S635, and S1179 were mutated to either A or D. Maximum NO production from S635D-expressing cells was significantly higher than that of either wild type or S635A in both basal and elevated [Ca2+]i conditions. More interestingly, S635D cells produced NO even when [Ca2+]i was nearly depleted by BAPTA-AM. We confirmed these results obtained in HEK-293 cells in BAEC transfected with S635D, S635A, or wild-type eNOS vector. These findings suggest that, once phosphorylated at S635 residue, eNOS produces NO without requiring any changes in [Ca2+]i. PKA-dependent phosphorylation of eNOS S635 and subsequent basal NO production in a Ca2+-independent manner may play an important role in regulating vascular biology and pathophysiology.

Chaperone-dependent regulation of endothelial nitric-oxide synthase intracellular trafficking by the co-chaperone/ubiquitin ligase CHIP

Endothelial nitric-oxide synthase (eNOS), the enzyme responsible for production of endothelial NO, is under tight and complex regulation. Proper cellular localization of eNOS is critical for optimal coupling of extracellular stimulation with NO production. In addition, the molecular chaperone Hsp90 interacts with eNOS and positively regulates eNOS activity. Hsp90 is modulated by physical interaction with its co-chaperones. CHIP (carboxyl terminus of Hsp70-interacting protein) is such a co-chaperone that remodels the Hsp90 heterocomplex and causes protein degradation of some Hsp90 substrates through the ubiquitin-protein isopeptide ligase activity of CHIP. Here we show that CHIP incorporated into the eNOS.Hsp90 complex and specifically decreased soluble eNOS levels in transiently transfected COS cells. Surprisingly, in contrast to the effects of the Hsp90 inhibitor geldanamycin, which induces eNOS ubiquitylation and its subsequent protein degradation, CHIP did not target eNOS for ubiquitylation and proteasome-dependent degradation. Instead, CHIP partitioned soluble eNOS into an insoluble and inactive cellular compartment, presumably through its co-chaperone activity. This effect seems to be due to displacement of eNOS from the Golgi apparatus, which is otherwise required for trafficking of eNOS to the plasmalemma and subsequent activation. Consistent with observations from overexpression studies, eNOS localization to the membrane and activity were increased in mouse lung endothelial cells lacking CHIP. Taken together, these results demonstrate a novel co-chaperone-dependent mechanism through which eNOS trafficking is regulated and suggest a potentially generalized role for CHIP in protein trafficking through the Golgi compartment.

Caveolin-1 can regulate vascular smooth muscle cell fate by switching platelet-derived growth factor signaling from a proliferative to an apoptotic pathway

BACKGROUND

Caveolin-1 is a regulator of signaling events originating from plasma membrane microdomains termed caveolae. This study was performed to determine the regulatory role of caveolin-1 on the proliferative events induced by platelet-derived growth factor (PDGF) in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Treatment of VSMCs with PDGF for 24 hours resulted in a loss of caveolin-1 protein expression and plasma membrane-associated caveolae, despite a 3-fold increase in caveolin-1 mRNA. Pretreatment of VSMCs with chloroquine, an inhibitor of lysosomal function, inhibited the PDGF-induced loss of caveolin-1. These studies demonstrated that caveolin-1 was a target of PDGF signaling events. Adenoviral overexpression of caveolin-1 was associated with a switch in PDGF-induced signaling events from a proliferative response to an apoptotic response. This overexpression inhibited PDGF-induced expression of cyclin D1 in the presence of unaffected mitogen-activated protein kinase activation.

CONCLUSIONS

Taken together, these studies suggest that caveolin-1 is an inhibitor of PDGF proliferative responses and might be capable of transforming PDGF-induced proliferative signals into death signals.

Influence of caveolin on constitutively activated recombinant eNOS: insights into eNOS dysfunction in BDL rat liver

Diminished endothelial nitric oxide (NO) synthase (eNOS)-derived NO production from the hepatic vascular endothelium contributes to hepatic vasoconstriction in portal hypertension. The aim of this study was to examine the mechanism of this process by testing the influence of a constitutively active form of eNOS (S1179DeNOS) in both primary and propagated liver cells in vitro and in the sham and bile duct ligated (BDL) rat liver in vivo, using an adenoviral vector encoding green fluorescent protein (AdGFP) and S1179DeNOS (AdS1179DeNOS). AdS1179DeNOS transduction augmented basal and agonist-stimulated NO generation in nonparenchymal liver cells. Sham rats transduced in vivo with AdS1179DeNOS evidenced a decreased pressor response to incremental doses of the vasoconstrictor methoxamine compared with sham rats transduced with AdGFP. However, BDL rats transduced with AdS1179DeNOS did not display improved vasodilatory responses as evidenced by similar flow-dependent pressure increases to that observed in BDL rats transduced with AdGFP, despite similar levels of viral transgene expression. We next examined the influence of the eNOS inhibitory protein caveolin on S1179DeNOS dysfunction in cirrhotic liver. Immunogold electron microscopic analysis of caveolin in BDL liver demonstrated prominent expression not only in liver endothelial cells, but also in hepatic stellate cells. In vitro studies in the LX2 hepatic stellate cell line demonstrate that caveolin precipitates recombinant S1179DeNOS in LX2 cells, that recombinant S1179DeNOS coprecipitates caveolin, and that binding is enhanced in the presence of overexpression of caveolin. Furthermore, caveolin overexpression inhibits recombinant S1179DeNOS activity. These studies indicate that recombinant S1179DeNOS protein functions appropriately in normal liver cells and tissue but evidences dysfunction in the cirrhotic rat liver and that caveolin expression and inhibition in BDL nonparenchymal cells, including hepatic stellate cells, may account for this dysfunction.

Abolition of arteriolar dilation but not constriction to histamine in cremaster muscle of eNOS-/- mice

Histamine increases the permeability of capillaries and venules but little is known of its precapillary actions on the control of tissue perfusion. Using gene ablation and pharmacological interventions, we tested whether histamine could increase muscle blood flow through stimulating nitric oxide (NO) release from microvascular endothelium. Vasomotor responses to topical histamine were investigated in second-order arterioles in the superfused cremaster muscle of anesthetized C57BL6 mice and null platelet endothelial cell adhesion molecule-1 (PECAM-1-/-) and null endothelial NO synthase (eNOS-/-) mice aged 8-12 wk. Neither resting (17 +/- 1 microm) nor maximum diameters (36 +/- 2 microm) were different between groups, nor was the constrictor response (approximately 5 +/- 1 microm) to elevating superfusate oxygen from 0 to 21%. For arterioles of C57BL6 and PECAM-1-/- mice, cumulative addition of histamine to the superfusate produced vasodilation (1 nM-1 microM; peak response, 9 +/- 1 microm) and then vasoconstriction (10-100 microM; peak response, 12 +/- 2 microm). In eNOS-/- mice, histamine produced only vasoconstriction. In C57BL6 and PECAM-1-/- mice, vasodilation was abolished with Nomega-nitro-l-arginine (30 microM); in all mice, vasoconstriction was abolished with nifedipine (1 microM). Vasomotor responses were eliminated with pyrilamine (1 microM; H1 receptor antagonist) yet remained intact with cimetidine (1 microM; H2 receptor antagonist). These findings illustrate that the biphasic vasomotor response of mouse cremaster arterioles to histamine is mediated through H1 receptors on endothelium (NO-dependent vasodilation) as well as smooth muscle (Ca2+ entry and constriction). Thus histamine can increase as well as decrease muscle blood flow, according to local concentration. However, when NO production is compromised, only vasoconstriction and flow reduction occur.

Transduction of the liver with activated Akt normalizes portal pressure in cirrhotic rats

BACKGROUND & AIMS

Portal hypertension in cirrhosis is secondary to an increase in hepatic resistance that occurs mainly through collagen deposition. However, recent evidence points to a major contribution by other factors, such as an intrahepatic reduction in nitric oxide production. Akt is a major activator of the endothelial nitric oxide synthase (eNOS) enzyme, but its potential role in intrahepatic resistance in cirrhosis is unknown. For this reason the aims of the present study were to determine whether there is an impaired Akt activation in cirrhotic livers and how this phenomenon relates to the decrease in NO production associated with portal hypertension.

METHODS

Cirrhosis was induced in rats by carbon tetrachloride inhalation. Protein abundance and phosphorylation status of Akt and eNOS were examined by Western blotting. The role of Akt in the liver of cirrhotic rats was investigated through infection with adenoviruses encoding either beta-galactosidase (beta-gal) or constitutively active Akt (myr-Akt).

RESULTS

The liver of cirrhotic animals showed a significant reduction in Akt and eNOS phosphorylation. Adenoviral delivery of myr-Akt restored eNOS phosphorylation and increased the intrahepatic concentration of guanosine 3',5'-cyclic monophosphate. These events were associated with normalization in portal pressure and a significant increase in mean arterial pressure after 3 days of adenoviral infection. In contrast, transduction of livers with beta-gal did not produce any change in these hemodynamic parameters.

CONCLUSIONS

myr-Akt gene therapy restored Akt activation and NO production in the cirrhotic liver, suggesting that this therapy may be useful for the treatment of portal hypertension.

Selective inhibition of tumor microvascular permeability by cavtratin blocks tumor progression in mice

Tumor vasculature is hyperpermeable to macromolecules compared to normal vasculature; however, the relationship between tumor hyperpermeability and tumor progression is poorly understood. Here we show that a cell-permeable peptide derived from caveolin-1, termed cavtratin, reduces microvascular hyperpermeability and delays tumor progression in mice. These antipermeability and antitumor actions of cavtratin occur in the absence of direct cytostatic or antiangiogenic effects. Cavtratin blocks microvascular permeability by inhibiting endothelial nitric oxide synthase (eNOS), as the antipermeability and antitumor actions of cavtratin are markedly diminished in eNOS knockout mice. Our results support the concepts that hyperpermeability of tumor blood vessels contributes to tumor progression and that blockade of eNOS may be exploited as a novel target for antitumor therapy.

The phosphorylation of caveolin-2 on serines 23 and 36 modulates caveolin-1-dependent caveolae formation

Caveolin-1 and -2 are the two major coat proteins found in plasma membrane caveolae of most of cell types. Here, by using adenoviral transduction of either caveolin-1 or caveolin-2 or both isoforms into cells lacking both caveolins, we demonstrate that caveolin-2 positively regulates caveolin-1-dependent caveolae formation. More importantly, we show that caveolin-2 is phosphorylated in vivo at two serine residues and that the phosphorylation of caveolin-2 is necessary for its actions as a positive regulator of caveolin-1 during organelle biogenesis in prostate cancer cells. Mutation of the primary phosphorylation sites on caveolin-2, serine 23 and 36, reduces the number of plasmalemma-attached caveolae and increases the accumulation of noncoated vesicles, but does not affect trafficking of caveolin-2, interaction with caveolin-1 or its biophysical properties. Thus, the phosphorylation of caveolin-2 is a novel mechanism to regulate the dynamics of caveolae assembly.

Compensatory phosphorylation and protein-protein interactions revealed by loss of function and gain of function mutants of multiple serine phosphorylation sites in endothelial nitric-oxide synthase

We examined the influence of individual serine phosphorylation sites in endothelial nitric-oxide synthase (eNOS) on basal and stimulated NO release, cooperative phosphorylation, and co-association with hsp90 and Akt. Mutation of the serine phosphorylation sites 116, 617, and 1179 to alanines affected the phospho-state of at least one other site, demonstrating cooperation between multiple phosphorylation events, whereas mutation of serine 635 to alanine did not cause compensation. Mutation of serines 116 and 617 to alanine promoted a greater protein-protein interaction with hsp90 and Akt and greater phosphorylation on serine 1179, the major site for Akt phosphorylation. More importantly, using alanine substitutions, Ser-116 is important for agonist, but not basal NO release, Ser-635 is important for basal, but not stimulated, Ser-617 negatively regulates basal and stimulated NO release, and Ser-1179 phosphorylation is stimulatory for both basal and agonist-mediated NO release. Using putative "gain of function" mutants (serine to aspartate) serines 635 and 1179 are important positive regulators of basal and stimulated NO release. S635D eNOS is the most efficacious, yielding 5-fold increases in basal and 2-fold increases in stimulated NO release from cells. However, S617A and S617D eNOS both increased NO release with opposite actions in NOS activity assays. Thus, multiple serine phosphorylation events regulate basal and stimulate NO release with Ser-635 and Ser-1179 being important positive regulatory sites and Ser-116 as a negative regulatory. Ser-617 may not be important for directly regulating NO release but is important as a modulator of phosphorylation at other sites and protein-protein interactions.

Cell-permeable peptides improve cellular uptake and therapeutic gene delivery of replication-deficient viruses in cells and in vivo

Small polybasic peptides derived from the transduction domains of certain proteins, such as the third alpha-helix of the Antennapedia (Antp) homeodomain, can cross the cell membrane through a receptor-independent mechanism. These cell-permeable molecules have been used as 'Trojan horses' to introduce biologically active cargo molecules such as DNA, peptides or proteins into cells. Using these cell-permeable peptides, we have developed an efficient and simple method to increase virally mediated gene delivery and protein expression in vitro and in vivo. Here, we show that cell-permeable peptides increase viral cell entry, improve gene expression at reduced titers of virus and improve efficacy of therapeutically relevant genes in vivo.

Endothelial nitric oxide synthase: the Cinderella of inflammation?

A hallmark of inflammation is increased vascular permeability. Increases in vascular permeability and the migration of inflammatory cells are linked to complex interactions of inflammatory mediators with the vascular endothelium. Normally, endothelial nitric oxide synthase (eNOS) produces a tonic amount of nitric oxide (NO), which is responsible for the homeostasis between the endothelium and surrounding tissues. However, most agonists that act on endothelial cells cause a series of post-translational modifications that influence eNOS activity. Furthermore, stimulation by shear stress, autacoids or growth factors either induces eNOS or shifts it to a more active state, which produces a burst of NO. Here, we highlight recent findings about eNOS and propose how new pharmacological tools can be used to dissect the involvement and contribution of eNOS to inflammatory responses.

Src kinase mediates phosphatidylinositol 3-kinase/Akt-dependent rapid endothelial nitric-oxide synthase activation by estrogen

17beta-Estradiol activates endothelial nitric oxide synthase (eNOS), enhancing nitric oxide (NO) release from endothelial cells via the phosphatidylinositol 3-kinase (PI3-kinase)/Akt pathway. The upstream regulators of this pathway are unknown. We now demonstrate that 17beta-estradiol rapidly activates eNOS through Src kinase in human endothelial cells. The Src family kinase specific-inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2) abrogates 17beta-estradiol- but not ionomycin-stimulated NO release. Consistent with these results, PP2 blocked 17beta-estradiol-induced Akt phosphorylation but did not inhibit NO release from cells transduced with a constitutively active Akt. PP2 abrogated 17beta-estradiol-induced activation of PI3-kinase, indicating that the PP2-inhibitable kinase is upstream of PI3-kinase and Akt. A 17beta-estradiol-induced estrogen receptor/c-Src association correlated with rapid c-Src phosphorylation. Moreover, transfection of kinase-dead c-Src inhibited 17beta-estradiol-induced Akt phosphorylation, whereas constitutively active c-Src increased basal Akt phosphorylation. Estrogen stimulation of murine embryonic fibroblasts with homozygous deletions of the c-src, fyn, and yes genes failed to induce Akt phosphorylation, whereas cells maintaining c-Src expression demonstrated estrogen-induced Akt activation. Estrogen rapidly activated c-Src inducing an estrogen receptor, c-Src, and P85 (regulatory subunit of PI3-kinase) complex formation. This complex formation results in the successive activation of PI3-kinase, Akt, and eNOS with consequent enhanced NO release, implicating c-Src as a critical upstream regulator of the estrogen-stimulated PI3-kinase/Akt/eNOS pathway.

Mice with targeted deletion of eNOS develop hyperdynamic circulation associated with portal hypertension

Systemic vasodilation is the initiating event of the hyperdynamic circulatory state, being most likely triggered by increased levels of vasodilators, primarily nitric oxide (NO). Endothelial NO synthase (eNOS) is responsible for this event. We tested the hypothesis that gene deletion of eNOS and inducible NOS (iNOS) may inhibit the development of the hyperdynamic circulatory state in portal hypertensive animals. To test this hypothesis, we used mice lacking eNOS (eNOS-/-) or eNOS/iNOS (eNOS/iNOS-/-) genes. A partial portal vein ligation (PVL) was used to induce portal hypertension. Sham-operated animals were used as a control. Hemodynamic characteristics were tested 2 wk after surgery. As opposed to our hypothesis, PVL also caused significant reduction in peripheral resistance in eNOS-/- compared with sham animals (0.33 +/- 0.02 vs. 0.41 +/- 0.03 mmHg. min x kg body wt x ml(-1); P = 0.04) and in eNOS/iNOS-/- animals with PVL compared with that of the sham-operated group (0.44 +/- 0.02 vs. 0.54 +/- 0.04; P = 0.03). This demonstrates that, despite gene deletion of eNOS, the knockout mice developed hyperdynamic circulation. Compensatory vasodilator molecule(s) are upregulated in place of NO in the systemic and splanchnic circulation in portal hypertensive animals.

Chronic treatment with nitric oxide-releasing aspirin reduces plasma low-density lipoprotein oxidation and oxidative stress, arterial oxidation-specific epitopes, and atherogenesis in hypercholesterolemic mice

The effects of chronic treatment with nitric oxide-containing aspirin (NO-aspirin, NCX-4016) in comparison with regular aspirin or placebo on the development of a chronic disease such as atherosclerosis were investigated in hypercholesterolemic low-density lipoprotein (LDL)-receptor-deficient mice. Male mice were assigned randomly to receive in a volume of 10 ml/kg either placebo (n = 10), 30 mg/kg/day NO-aspirin (n = 10), or 18 mg/kg/day of regular aspirin (n = 10). After 12 weeks of treatment, the computer-assisted imaging analysis revealed that NO-aspirin reduced the aortic cumulative lesion area by 39.8 +/- 12.3% compared with that of the placebo (P < 0.001). Regular aspirin did not reduce significantly aortic lesions (-5.1 +/- 2.3%) compared with the placebo [P = 0.867, not significant (NS)]. Furthermore, NO-aspirin reduced significantly plasma LDL oxidation compared with aspirin and placebo, as shown by the significant reduction of malondialdehyde content (P < 0.001) as well as by the prolongation of lag-time (P < 0.01). Similarly, systemic oxidative stress, measured by plasma isoprostanes, was significantly reduced by treatment with NCX-4016 (P < 0.05). More importantly, mice treated with NO-aspirin revealed by immunohistochemical analysis of aortic serial sections a significant decrease in the intimal presence of oxidation-specific epitopes of oxLDL (E06 monoclonal antibody, P < 0.01), and macrophages-derived foam cells (F4/80 monoclonal antibody, P < 0.05), compared with placebo or aspirin. These data indicate that enhanced NO release by chronic treatment with the NO-containing aspirin has antiatherosclerotic and antioxidant effects in the arterial wall of hypercholesterolemic mice.

Inhibitor of apoptosis protein survivin regulates vascular injury

Survivin (also termed Birc5) belongs to the family of genes known as inhibitors of apoptosis, and it has been implicated in both prevention of cell death and control of mitosis. The survivin pathway is exploited in cancer, but its potential role in vascular injury is unknown. Here, we show that balloon-mediated arterial injury in rabbits resulted in expression of survivin in vascular cells. Serum or PDGF-AB stimulated survivin expression in cultured smooth-muscle cells (SMCs), which suppressed apoptosis and prevented caspase activation. Adenoviral delivery of a phosphorylation-defective survivin mutant reversed the cytoprotective effect of PDGF in SMCs without affecting mitotic progression, suppressed neointimal formation in wire-injured mouse femoral arteries, and induced vascular cell apoptosis in vivo. These data identify survivin as a critical regulator of SMC apoptosis after acute vascular injury. Disrupting the survivin pathway may provide a novel therapy to limit pathological vessel-wall remodeling.

Nitric oxide-releasing aspirin decreases vascular injury by reducing inflammation and promoting apoptosis

Endothelial dysfunction, defined as a deficit in the bioavailability of nitric oxide (NO), occurs as sequelae of many vascular diseases; however, the utility of supplementing NO to obviate the extent of disease is understudied. Here, we examined if prolonged treatment with an NO-releasing form of aspirin (NO-ASA) can influence neointimal remodeling of femoral arteries of hypercholesterolemic ApoE (-/-) mice. Treatment of ApoE (-/-) mice with NO-ASA, but not aspirin (ASA), improved neointimal remodeling post-injury. NO-ASA treatment increased lumen diameters and reduced intimal-to-medial ratios of injured femoral arteries compared with ASA- or vehicle-treated mice. The reduction in lumen diameter in NO-ASA-treated mice was associated with a marked reduction in CD45-positive inflammatory cells and an increased number of TUNEL-positive cells. Thus, NO-ASA, by virtue of releasing NO, can reduce vascular inflammation and promote apoptosis during vascular remodeling associated with neointimal thickening.

Native low-density lipoprotein induces endothelial nitric oxide synthase dysfunction: role of heat shock protein 90 and caveolin-1

Although native LDL (n-LDL) is well recognized for inducing endothelial cell (EC) dysfunction, the mechanisms remain unclear. One hypothesis is n-LDL increases caveolin-1 (Cav-1), which decreases nitric oxide (*NO) production by binding endothelial nitric oxide synthase (eNOS) in an inactive state. Another is n-LDL increases superoxide anion (O(2)(*-)), which inactivates *NO. To test these hypotheses, EC were incubated with n-LDL and then analyzed for *NO, O(2)(*-), phospho-eNOS (S1179), eNOS, Cav-1, calmodulin (CaM), and heat shock protein 90 (hsp90). n-LDL increased NOx by more than 4-fold while having little effect on A23187-stimulated nitrite production. In contrast, n-LDL decreased cGMP under basal and A23187-stimulated conditions and increased O(2)(*-) by a mechanism that could be inhibited by L-nitroargininemethylester (L-NAME) and BAPTA/AM. n-LDL increased phospho-eNOS by 149%, eNOS by approximately 34%, and Cav-1 by 28%, and decreased the association of hsp90 with eNOS by 49%. n-LDL did not appear to alter eNOS distribution between membrane fractions (approximately 85%) and cytosol (approximately 15%). Only 3-6% of eNOS in membrane fractions was associated with Cav-1. These data support the hypothesis that n-LDL increases O(2)(*-), which scavenges *NO, and suggest that n-LDL uncouples eNOS activity by decreasing the association of hsp90 as an initial step in signaling eNOS to generate O(2)(*-).

Phosphorylation of eNOS initiates excessive NO production in early phases of portal hypertension

Akt, also known as protein kinase B, is a serine/threonine kinase. Akt becomes active when phosphorylated by the activation of receptor tyrosine kinases, G protein-coupled receptors, and mechanical forces such as shear stress. Studies in vitro have shown that Akt can directly phosphorylate endothelial nitric oxide (NO) synthase (eNOS) and activate the enzyme, leading to NO production. The aim of this study was to test the hypothesis that the phosphorylation of eNOS plays a role in the enhanced NO production observed in early portal hypertension. Male Sprague-Dawley rats were subjected to either sham or portal vein ligation (PVL), and mesenteric arterial beds were used for ex vivo perfusion studies. Mesenteric arterial beds from PVL rats had an approximately 60-70% decrease in response to methoxamine (an alpha(1)-agonist and vasoconstrictor) compared with the sham group (P < 0.01). When N(G)-monomethyl-L-arginine (a NOS inhibitor) was added to the perfusion, the difference in perfusion pressure between the two groups was abolished, suggesting that enhanced NO production in the PVL group blunted the response to the vasoconstrictor. The reduced responsiveness in PVL was not due to changes in eNOS expression but was due to an increase in enzyme-specific activity, suggesting posttranslational modification of eNOS. The phosphorylation of eNOS at Ser(1176) was significantly increased by twofold (P < 0.05) in the PVL group. Furthermore, PVL significantly increased Akt phosphorylation (an active form of Akt) by threefold (P < 0.05). When vessels were treated with wortmannin (10 nM) to block the phosphatidylinositol-3-OH-kinase/Akt pathway, NO-induced vasodilatation was significantly reduced. These results suggest that the phosphorylation of eNOS by Akt activates the enzyme and may be the first step leading to an initial increase in NO production in portal hypertension.

Domain mapping studies reveal that the M domain of hsp90 serves as a molecular scaffold to regulate Akt-dependent phosphorylation of endothelial nitric oxide synthase and NO release

Protein-protein interactions with the molecular chaperone hsp90 and phosphorylation on serine 1179 by the protein kinase Akt leads to activation of endothelial nitric oxide synthase. However, the interplay between these protein-protein interactions remains to be established. In the present study, we show that vascular endothelial growth factor stimulates the coordinated association of hsp90, Akt, and resultant phosphorylation of eNOS. Characterization of the domains of hsp90 required to bind eNOS, using yeast 2-hybrid, cell-based coprecipitation experiments, and GST-fusion proteins, revealed that the M region of hsp90 interacts with the amino terminus of eNOS and Akt. The addition of purified hsp90 to in vitro kinase assays facilitates Akt-driven phosphorylation of recombinant eNOS protein, but not a short peptide encoding the Akt phosphorylation site, suggesting that hsp90 may function as a scaffold for eNOS and Akt. In vivo, coexpression of adenoviral or the cDNA for hsp90 with eNOS promotes nitric oxide release; an effect eliminated using a catalytically functional phosphorylation mutant of eNOS. These results demonstrate that stimulation of endothelial cells with vascular endothelial growth factor recruits eNOS and Akt to an adjacent region on the same domain of hsp90, thereby facilitating eNOS phosphorylation and enzyme activation.

Functional reconstitution of endothelial nitric oxide synthase reveals the importance of serine 1179 in endothelium-dependent vasomotion

Phosphorylation of endothelial nitric oxide synthase (eNOS) at serine 1179 can activate the enzyme, leading to NO release. Because eNOS is important in regulating vascular tone, we investigated whether phosphorylation of this residue is involved in vasomotion. Adenoviral transduction of endothelial cells (ECs) with the phosphomimetic S1179DeNOS markedly increased basal and vascular endothelial cell growth factor (VEGF)-stimulated NO release compared with cells transduced with wild-type virus. Conversely, adenoviral transduction of ECs with the non-phosphorylatable S1179AeNOS suppressed basal and stimulated NO release. Using a novel method for luminal delivery of adenovirus, transduction of the endothelium of carotid arteries from eNOS knockout mice with S1179DeNOS completely restored NO-mediated dilatation to acetylcholine (ACh), whereas vasomotor responses in arteries transduced with S1179AeNOS were significantly attenuated. Basal NO release was also significantly reduced in arteries transduced with S1179AeNOS, compared with S1179DeNOS. Thus, our data directly demonstrate that phosphorylation of eNOS at serine 1179 is an important regulator of basal and stimulated NO release in ECs and in intact blood vessels.

Expression and function of recombinant S1179D endothelial nitric oxide synthase in canine cerebral arteries

BACKGROUND AND PURPOSE

Bovine endothelial nitric oxide synthase (eNOS) is phosphorylated directly by the protein kinase Akt at serine 1179. Mutation of this residue to the negatively charged aspartate (S1179DeNOS) increases nitric oxide (NO) production constitutively in the absence of agonist stimulus. The present study was designed to determine the effect of mutant S1179DeNOS gene expression on vasomotor function of canine cerebral arteries.

METHODS

Isolated basilar and middle cerebral arteries were exposed ex vivo (30 minutes at 37 degrees C) to an adenoviral vector (10(10) plaque-forming units per milliliter) encoding the S1179DeNOS gene (AdCMVS1179DeNOS), the wild-type eNOS gene (AdCMVeNOS), or the green fluorescent protein (GFP) reporter gene (AdCMVGFP). Twenty-four hours after transduction, arteries were suspended in an organ chamber for isometric force recording, and levels of cGMP were measured by radioimmunoassay.

RESULTS

Transgene protein expression was detected mainly in the vascular adventitia. In AdCMVS1179DeNOS-transduced arteries, basal levels of cGMP were significantly elevated compared with those in control (nontransduced), AdCMVGFP-, or AdCMVeNOS-transduced vessels (n=8; P<0.01). The elevation of cGMP was abolished by a NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), or by incubation in the calcium-free medium in the presence of calcium chelators. In AdCMVS1179DeNOS-transduced arteries, contractions to endothelin-1 (10(-10) to 10(-8) mol/L) were significantly reduced compared with those in control and AdCMVGFP-transduced arteries (n=7; P<0.05). The vasoconstrictor effect of endothelin-1 was restored in the presence of the NOS inhibitor L-NAME.

CONCLUSIONS

Our results suggest that in cerebral arteries, expression of recombinant S1179DeNOS increases basal production of NO and inhibits the vasoconstrictor effect of endothelin-1. This effect may have therapeutic application in prevention and treatment of cerebrovascular diseases.

Localization of endothelial nitric-oxide synthase phosphorylated on serine 1179 and nitric oxide in Golgi and plasma membrane defines the existence of two pools of active enzyme

The subcellular localization of endothelial nitric-oxide synthase (eNOS) is critical for optimal coupling of extracellular stimulation to nitric oxide production. Because eNOS is activated by Akt-dependent phosphorylation to produce nitric oxide (NO), we determined the subcellular distribution of eNOS phosphorylated on serine 1179 using a variety of methodologies. Based on sucrose gradient fractionation, phosphorylated-eNOS (P-eNOS) was found in both caveolin-1-enriched membranes and intracellular domains. Co-transfection of eNOS with Akt and stimulation of endothelial cells with vascular endothelial growth factor (VEGF) increased the ratio of P-eNOS to total eNOS but did not change the relative intracellular distribution between these domains. The proper localization of eNOS to intracellular membranes was required for agonist-dependent phosphorylation on serine 1179, since VEGF did not increase eNOS phosphorylation in cells transfected with a non-acylated, mistargeted form of eNOS. Confocal imaging of P-eNOS and total eNOS pools demonstrated co-localization in the Golgi region and plasmalemma of transfected cells and native endothelial cells. Finally, VEGF stimulated a large increase in NO localized in both the perinuclear region and the plasma membrane of endothelial cells. Thus, activated, phosphorylated eNOS resides in two cellular compartments and both pools are VEGF-regulated to produce NO.

Angiopoietin-1 negatively regulates expression and activity of tissue factor in endothelial cells

Normally, tissue factor (TF) is not expressed on the surface of endothelial cells, but its expression can be induced by vascular endothelial growth factor (VEGF) and tumor necrosis factor (TNF)-a. However, the signaling pathway(s) affecting this induction is unknown. Using human umbilical vein endothelial cells, we found that inhibitors of guanine-cytosine-rich DNA binding protein and nuclear factor (NF)-kB suppressed VEGF- and TNF-a-induced expression and activity of TF. However, unexpectedly, phosphatidylinositol (PI) 3'-kinase inhibitor enhanced the VEGF- and TNF-a-induced expression and activity of TF. Angiopoietin-1 (Ang1), a strong activator of intracellular PI 3'-kinase/Akt, inhibited the induction of TF by VEGF and TNF-a, whereas Ang1 itself did not produce any significant effect on TF. Selective activation (or inactivation) of PI 3'-kinase/Akt by using adenoviral transfer reduced (or enhanced) TNF-a-induced expression of TF mRNA and protein, regardless of Ang1 treatment. From these results, we conclude that Ang1 inhibits the up-regulation of TF expression, possibly through activation of PI 3'-kinase/Akt in endothelial cells. Ang1 may be useful as an inhibitor of VEGF- and TNF-a-induced coagulation, inflammation, and cancer progression.

Post-translational control of endothelial nitric oxide synthase: why isn't calcium/calmodulin enough?

Endothelial nitric oxide synthase (eNOS) is important for cardiovascular homeostasis, vessel remodeling, and angiogenesis. Given the impact of endothelium- derived nitric oxide (NO) in vascular biology, much work in the past several years has focused on the control of NO synthesis by regulatory proteins that influence its function. Indeed calcium-activated calmodulin is important for regulation of NOS activity. Herein we discuss why other proteins, in addition to calmodulin, are necessary for eNOS regulation and summarize the biology of negative and positive regulators of eNOS function in vitro, in cells, and in blood vessels.

Distinction between signaling mechanisms in lipid rafts vs. caveolae

The relative importance of lipid rafts vs. specialized rafts termed caveolae to influence signal transduction is not known. Here we show that in cells lacking caveolae, the dually acylated protein, endothelial nitric oxide synthase (eNOS), localizes to cholesterol-rich lipid raft domains of the plasma membrane. In these cells, expression of caveolin-1 (cav-1) stimulates caveolae biogenesis, promotes the interaction of cav-1 with eNOS, and the inhibition of NO release from cells. Interestingly, in cells where cav-1 does not drive caveolae assembly, despite equal levels of cav-1 and eNOS and localization of both proteins to raft domains of the plasmalemma, the physical interaction of eNOS with cav-1 is dramatically less resulting in less inhibition of NO release. Thus, cav-1 concentrated in caveolae, not in rafts, is in closer proximity to eNOS and is necessary for negative regulation of eNOS function, thereby providing the first clear example of spatial regulation of signaling in this organelle that is distinct from raft domains.

Dynamic regulation of metabolism and respiration by endogenously produced nitric oxide protects against oxidative stress

One of the many biological functions of nitric oxide is the ability to protect cells from oxidative stress. To investigate the potential contribution of low steady state levels of nitric oxide generated by endothelial nitric oxide synthase (eNOS) and the mechanisms of protection against H(2)O(2), spontaneously transformed human ECV304 cells, which normally do not express eNOS, were stably transfected with a green fluorescent-tagged eNOS cDNA. The eNOS-transfected cells were found to be resistant to injury and delayed death following a 2-h exposure to H(2)O(2) (50-150 microM). Inhibition of nitric oxide synthesis abolished the protective effect against H(2)O(2) exposure. The ability of nitric oxide to protect cells depended on the presence of respiring mitochondria as ECV304+eNOS cells with diminished mitochondria respiration (rho(-)) are injured to the same extent as nontransfected ECV304 cells and recovery of mitochondrial respiration restores the ability of nitric oxide to protect against H(2)O(2)-induced death. Nitric oxide also found to have a profound effect in cell metabolism, because ECV304+eNOS cells had lower steady state levels of ATP and higher utilization of glucose via the glycolytic pathway than ECV304 cells. However, the protective effect of nitric oxide against H(2)O(2) exposure is not reproduced in ECV304 cells after treatment with azide and oligomycin suggesting that the dynamic regulation of respiration by nitric oxide represent a critical and unrecognized primary line of defense against oxidative stress.

Akt-mediated phosphorylation of the G protein-coupled receptor EDG-1 is required for endothelial cell chemotaxis

The role of the protein kinase Akt in cell migration is incompletely understood. Here we show that sphingosine-1-phosphate (S1P)-induced endothelial cell migration requires the Akt-mediated phosphorylation of the G protein-coupled receptor (GPCR) EDG-1. Activated Akt binds to EDG-1 and phosphorylates the third intracellular loop at the T(236) residue. Transactivation of EDG-1 by Akt is not required for G(i)-dependent signaling but is indispensable for Rac activation, cortical actin assembly, and chemotaxis. Indeed, T236AEDG-1 mutant sequestered Akt and acted as a dominant-negative GPCR to inhibit S1P-induced Rac activation, chemotaxis, and angiogenesis. Transactivation of GPCRs by Akt may constitute a specificity switch to integrate rapid G protein-dependent signals into long-term cellular phenomena such as cell migration.

Akt down-regulation of p38 signaling provides a novel mechanism of vascular endothelial growth factor-mediated cytoprotection in endothelial cells

Vascular endothelial growth factor (VEGF) utilizes a phosphoinositide 3-kinase (PI 3-kinase)/Akt signaling pathway to protect endothelial cells from apoptotic death. Here we show that PI 3-kinase/Akt signaling promotes endothelial cell survival by inhibiting p38 mitogen-activated protein kinase (MAPK)-dependent apoptosis. Blockade of the PI 3-kinase or Akt pathways in conjunction with serum withdrawal stimulates p38-dependent apoptosis. Blockade of PI 3-kinase/Akt also led to enhanced VEGF activation of p38 and apoptosis. In this context, the pro-apoptotic effect of VEGF is attenuated by the p38 MAPK inhibitor SB203580. VEGF stimulation of endothelial cells or infection with an adenovirus expressing constitutively active Akt causes MEKK3 phosphorylation, which is associated with decreased MEKK3 kinase activity and down-regulation of MKK3/6 and p38 MAPK activation. Conversely, activation-deficient Akt decreases VEGF-stimulated MEKK3 phosphorylation and increases MKK/p38 activation. Activation of MKK3/6 is not dependent on Rac activation since dominant negative Rac does not decrease p38 activation triggered by inhibition of PI 3-kinase. Thus, cross-talk between the Akt and p38 MAPK pathways may regulate the level of cytoprotection versus apoptosis and is a new mechanism to explain the cytoprotective actions of Akt.

Acidic hydrolysis as a mechanism for the cleavage of the Glu(298)-->Asp variant of human endothelial nitric-oxide synthase

The 894G-->T polymorphism within exon 7 of the human endothelial nitric-oxide synthase (eNOS) gene codes for glutamate or aspartate, respectively, at residue 298 and has been associated with several diseases of cardiovascular origin. A recent report indicates that Asp(298)-eNOS (E298D) is cleaved intracellularly to 100- and 35-kDa fragments, suggesting a mechanism for reduced endothelial function. Here we have documented the precise cleavage site of the E298D variant as a unique aspartyl-prolyl (Asp(298)--Pro(299)) bond not seen in wild-type eNOS (Glu(298)). We show that E298D-eNOS, as isolated from cells and in vitro, is susceptible to acidic hydrolysis, and the 100-kDa fragment can be generated ex vivo by increasing temperature at low pH. Importantly, cleavage of E298D was eliminated using a sample buffer system designed to limit acidic hydrolysis of Asp--Pro bonds. These results argue against intracellular processing of E298D-eNOS and suggest that previously described fragmentation of E298D could be a product of sample preparation. We also found that eNOS turnover, NO production, and the susceptibility to cellular stress were not different in cells expressing WT versus E298D-eNOS. Finally, enzyme activities were identical for the respective recombinant enzymes. Thus, intracellular cleavage mechanisms are unlikely to account for associations between the exon 7 polymorphism and cardiovascular diseases.

The sonic hedgehog receptor patched associates with caveolin-1 in cholesterol-rich microdomains of the plasma membrane

The Hedgehog signaling pathway is involved in early embryonic patterning as well as in cancer; however, little is known about the subcellular localization of the Hedgehog receptor complex of Patched and Smoothened. Since Hh has been found in lipid rafts in Drosophila, we hypothesized that Patched and Smoothened might also be found in these cholesterol-rich microdomains. In this study, we demonstrate that both Smoothened and Patched are in caveolin-1-enriched/raft microdomains. Immunoprecipitation studies show that Patched specifically interacts with caveolin-1, whereas Smoothened does not. Fractionation studies show that Patched and caveolin-1 can be co-isolated from buoyant density fractions that represent caveolae/raft microdomains and that Patched and caveolin-1 co-localize by confocal microscopy. Glutathione S-transferase fusion protein experiments show that the interaction between Patched and caveolin-1 involves the caveolin-1 scaffolding domain and a Patched consensus binding site. Immunocytochemistry data and fractionation studies also show that Patched seems to be required for transport of Smoothened to the membrane. Depletion of plasmalemmal cholesterol influences the distribution of the Hh receptor complex in the caveolin-enriched/raft microdomains. These data suggest that caveolin-1 may be integral for sequestering the Hh receptor complex in these caveolin-enriched microdomains, which act as a scaffold for the interactions with the Hh protein.

Sphingosine 1-phosphate activates Akt, nitric oxide production, and chemotaxis through a Gi protein/phosphoinositide 3-kinase pathway in endothelial cells

Sphingosine 1-phosphate (SPP) binds to members of the endothelial differentiation gene family (EDG) of receptors and leads to diverse signaling events including cell survival, growth, migration and differentiation. However, the mechanisms of how SPP activates these proangiogenic pathways are poorly understood. Here we show that SPP signals through the EDG-1 receptor to the heterotrimeric G protein G(i), leading to activation of the serine/threonine kinase Akt and phosphorylation of the Akt substrate, endothelial nitric-oxide synthase (eNOS). Inhibition of G(i) signaling, and phosphoinositide 3-kinase (PI 3-kinase) activity resulted in a decrease in SPP-induced endothelial cell chemotaxis. SPP also stimulates eNOS phosphorylation and NO release and these effects are also attenuated by inhibition of G(i) signaling, PI 3-kinase, and Akt. However, inhibition of NO production did not influence SPP-induced chemotaxis but effectively blocked the chemotactic actions of vascular endothelial growth factor. Thus, SPP signals through G(i) and PI 3-kinase leading to Akt activation and eNOS phosphorylation.

Heat shock protein 90 mediates the balance of nitric oxide and superoxide anion from endothelial nitric-oxide synthase

The balance of nitric oxide (.NO) and superoxide anion (O(2)) plays an important role in vascular biology. The association of heat shock protein 90 (Hsp90) with endothelial nitric-oxide synthase (eNOS) is a critical step in the mechanisms by which eNOS generates.NO. As eNOS is capable of generating both.NO and O(2), we hypothesized that Hsp90 might also mediate eNOS-dependent O(2) production. To test this hypothesis, bovine coronary endothelial cells (BCEC) were pretreated with geldanamycin (GA, 10 microg/ml; 17.8 microm) and then stimulated with the calcium ionophore, (5 microm). GA significantly decreased -stimulated eNOS-dependent nitrite production (p < 0.001, n = 4) and significantly increased -stimulated eNOS-dependent O(2) production (p < 0.001, n = 8). increased phospho-eNOS(Ser-1179) levels by >1.6-fold over vehicle (V)-treated levels. Pretreatment with GA by itself or with increased phospho-eNOS levels. In unstimulated V-treated BCEC cultures low amounts of Hsp90 were found to associate with eNOS. Pretreatment with GA and/or increased the association of Hsp90 with eNOS. These data show that Hsp90 is essential for eNOS-dependent.NO production and that inhibition of ATP-dependent conformational changes in Hsp90 uncouples eNOS activity and increases eNOS-dependent O(2) production.

Can modulation of endothelial nitric oxide synthase explain the vasculoprotective actions of statins?

Statin-based drugs are the mainstay of therapy for coronary artery disease. Recent insights into the cellular mechanisms of this class of drugs suggest that modulation of nitric oxide synthesis contributes to their beneficial actions. These effects are independent of their lipid-lowering effects and result in enhanced nitric oxide release.

Suppression of vascular endothelial growth factor-mediated endothelial cell protection by survivin targeting

The protective genes that mediate endothelial cell (EC) survival during angiogenesis have not been completely characterized. Here, we show that an antisense oligonucleotide to the apoptosis inhibitor survivin suppressed de novo expression of survivin in ECs by vascular endothelial cell growth factor (VEGF). In contrast, the survivin antisense oligonucleotide did not affect anti-apoptotic bcl-2 levels in endothelium. When assessed in cell death assays, antisense targeting of survivin abolished the anti-apoptotic function of VEGF against tumor necrosis factor-alpha- or ceramide-induced cell death, enhanced caspase-3 activity, promoted the generation of a approximately 17-kd active caspase-3 subunit, and increased cleavage of the caspase substrate, polyADP ribose polymerase. In contrast, the survivin antisense oligonucleotide had no effect on EC viability in the absence of VEGF. Antisense oligonucleotides to platelet-endothelial cell adhesion molecule-1 (PECAM-1, CD31), lymphocyte function-associated molecule-3 (LFA-3, CD58), or intercellular adhesion molecule-1 (ICAM-1, CD54) did not reduce the anti-apoptotic function of VEGF in endothelium. When tested on other angiogenic activities mediated by VEGF, survivin antisense treatment induced rapid regression of three-dimensional vascular capillary networks, but did not affect EC migration/chemotaxis. These data suggest that the anti-apoptotic properties of VEGF during angiogenesis are primarily mediated by the induced expression of survivin in ECS: Manipulation of this pathway may increase EC viability in compensatory angiogenesis or facilitate EC apoptosis and promote vascular regression during tumor angiogenesis.

Direct interaction between endothelial nitric-oxide synthase and dynamin-2. Implications for nitric-oxide synthase function

Endothelial nitric-oxide synthase (eNOS) is regulated in part through specific protein interactions. Dynamin-2 is a large GTPase residing within similar membrane compartments as eNOS. Here we show that dynamin-2 binds directly with eNOS thereby augmenting eNOS activity. Double label confocal immunofluorescence demonstrates colocalization of eNOS and dynamin in both Clone 9 cells cotransfected with green fluorescent protein-dynamin and eNOS, as well as in bovine aortic endothelial cells (BAEC) expressing both proteins endogenously, predominantly in a Golgi membrane distribution. Immunoprecipitation of eNOS from BAEC lysate coprecipitates dynamin and, conversely, immunoprecipitation of dynamin coprecipitates eNOS. Additionally, the calcium ionophore, a reagent that promotes nitric oxide release, enhances coprecipitation of dynamin with eNOS in BAEC, suggesting the interaction between the proteins can be regulated by intracellular signals. In vitro studies demonstrate that glutathione S-transferase (GST)-dynamin-2 quantitatively precipitates both purified recombinant eNOS protein as well as in vitro transcribed (35)S-labeled eNOS from solution indicating a direct interaction between the proteins in vitro. Scatchard analysis of binding studies demonstrates an equilibrium dissociation constant (K(d)) of 27.6 nm. Incubation of purified recombinant eNOS protein with GST-dynamin-2 significantly increases eNOS activity as does overexpression of dynamin-2 in ECV 304 cells stably transfected with eNOS-green fluorescent protein. These studies demonstrate a direct protein-protein interaction between eNOS and dynamin-2, thereby identifying a new NOS-associated protein and providing a novel function for dynamin. These events may have relevance for eNOS regulation and trafficking within vascular endothelium.

In vivo delivery of the caveolin-1 scaffolding domain inhibits nitric oxide synthesis and reduces inflammation

Caveolin-1, the primary coat protein of caveolae, has been implicated as a regulator of signal transduction through binding of its "scaffolding domain" to key signaling molecules. However, the physiological importance of caveolin-1 in regulating signaling has been difficult to distinguish from its traditional functions in caveolae assembly, transcytosis, and cholesterol transport. To directly address the importance of the caveolin scaffolding domain in vivo, we generated a chimeric peptide with a cellular internalization sequence fused to the caveolin-1 scaffolding domain (amino acids 82-101). The chimeric peptide was efficiently taken up into blood vessels and endothelial cells, resulting in selective inhibition of acetylcholine (Ach)-induced vasodilation and nitric oxide (NO) production, respectively. More importantly, systemic administration of the peptide to mice suppressed acute inflammation and vascular leak to the same extent as a glucocorticoid or an endothelial nitric oxide synthase (eNOS) inhibitor. These data imply that the caveolin-1 scaffolding domain can selectively regulate signal transduction to eNOS in endothelial cells and that small-molecule mimicry of this domain may provide a new therapeutic approach.

Simvastatin upregulates coronary vascular endothelial nitric oxide production in conscious dogs

Statin drugs can upregulate endothelial nitric oxide (NO) synthase (eNOS) in isolated endothelial cells independent of lipid-lowering effects. We investigated the effect of short-term simvastatin administration on coronary vascular eNOS and NO production in conscious dogs and canine tissues. Mongrel dogs were instrumented under general anesthesia to measure coronary blood flow (CBF). Simvastatin (20 mg. kg(-1). day(-1)) was administered orally for 2 wk; afterward, resting CBF was found to be higher compared with control (P < 0.05) and veratrine- (activator of reflex cholinergic NO-dependent coronary vasodilation) and ACh-mediated coronary vasodilation were enhanced (P < 0.05). Response to endothelium-independent vasodilators, adenosine and nitroglycerin, was not potentiated. After simvastatin administration, plasma nitrate and nitrite (NO(x)) levels increased from 5.22 +/- 1.2 to 7. 79 +/- 1.3 microM (P < 0.05); baseline and agonist-stimulated NO production in isolated coronary microvessels were augmented (P < 0.05); resting in vivo myocardial oxygen consumption (MVO(2)) decreased from 6.8 +/- 0.6 to 5.9 +/- 0.4 ml/min (P < 0.05); NO-dependent regulation of MVO(2) in response to NO agonists was augmented in isolated myocardial segments (P < 0.05); and eNOS protein increased 29% and eNOS mRNA decreased 50% in aortas and coronary vascular endothelium. Short-term administration of simvastatin in dogs increases coronary endothelial NO production to enhance NO-dependent coronary vasodilation and NO-mediated regulation of MVO(2).

Membrane estrogen receptor engagement activates endothelial nitric oxide synthase via the PI3-kinase-Akt pathway in human endothelial cells

17beta-Estradiol (E(2)) is a rapid activator of endothelial nitric oxide synthase (eNOS). The product of this activation event, NO, is a fundamental determinant of cardiovascular homeostasis. We previously demonstrated that E(2)-stimulated endothelial NO release can occur without an increase in cytosolic Ca(2+). Here we demonstrate for the first time, to our knowledge, that E(2) rapidly induces phosphorylation and activation of eNOS through the phosphatidylinositol 3 (PI3)-kinase-Akt pathway. E(2) treatment (10 ng/mL) of the human endothelial cell line, EA.hy926, resulted in increased NO production, which was abrogated by the PI3-kinase inhibitor, LY294002, and the estrogen receptor antagonist ICI 182, 780. E(2) stimulated rapid Akt phosphorylation on serine 473. As has been shown for vascular endothelial growth factor, eNOS is an E(2)-activated Akt substrate, demonstrated by rapid eNOS phosphorylation on serine 1177, a critical residue for eNOS activation and enhanced sensitivity to resting cellular Ca(2+) levels. Adenoviral-mediated EA.hy926 transduction confirmed functional involvement of Akt, because a kinase-deficient, dominant-negative Akt abolished E(2)-stimulated NO release. The membrane-impermeant E(2)BSA conjugate, shown to bind endothelial cell membrane sites, also induced rapid Akt and consequent eNOS phosphorylation. Thus, engagement of membrane estrogen receptors results in rapid endothelial NO release through a PI3-kinase-Akt-dependent pathway. This explains, in part, the reduced requirement for cytosolic Ca(2+) fluxes and describes an important pathway relevant to cardiovascular pathophysiology.

Geldanamycin, an inhibitor of heat shock protein 90 (Hsp90) mediated signal transduction has anti-inflammatory effects and interacts with glucocorticoid receptor in vivo

Histamine, vascular endothelial growth factor, acetylcholine, oestrogen as well as fluid shear stress activates a mechanism that recruits heat shock protein 90 to the endothelial nitric oxide synthase. The interaction between Hsp90 and eNOS enhances the activation of the enzyme in cells and in intact blood vessels leading to NO production. Intraplantar administration of carrageenan (50 microl paw(-1)) to mice causes an oedema lasting 72 h. Geldanamycin (0.1, 0.3, 1 mg kg(-1)), a specific inhibitor of Hsp-90, that inhibits endothelium-dependent relaxations of the rat aorta, mesentery and middle artery inhibits carrageenan-induced mouse paw oedema in a dose dependent manner. Co-administration to mice of dexamethasone (1 mg kg(-1)) with geldanamycin (0.3 mg kg(-1)) at anti-inflammatory dose causes a loss of the total anti-inflammatory effect of each agent alone. RU 486 (10 mg kg(-1)), a well known glucocorticoid receptorial antagonist, does not inhibit oedema formation but prevents the anti-inflammatory action of dexamethasone (1 mg kg(-1)). Similarly, RU 486 prevents the anti-inflammatory action of geldanamycin (0.3 mg kg(-1)). In conclusion we have described for the first time that geldanamycin, an inhibitor of Hsp90 dependent signal transduction, is anti-inflammatory in vivo implying that Hsp90 is critical for pathways involved in carrageenan-induced paw oedema. In addition the ability of GA to block NO release and reduce oedema formation suggests a therapeutic rationale for specific inhibitors of Hsp90 as potential anti-inflammatory drugs.