3-Hydroxy-3-methylglutaryl-CoA reductase inhibitors block calcium-dependent tyrosine kinase Pyk2 activation by angiotensin II in vascular endothelial cells. involvement of geranylgeranylation of small G protein Rap1

Human urinary kininogenase reduces the endothelial injury by inhibiting Pyk2/MCU pathway

The injury of endothelial cells is one of the initiating factors in restenosis after endovascular treatment. Human urinary kallidinogenase (HUK) is a tissue kallikrein which is used for ischemia-reperfusion injury treatment. Studies have shown that HUK may be a potential therapeutic agent to prevent stenosis after vascular injury, however, the precise mechanisms have not been fully established. This study is to investigate whether HUK can protect endothelial cells after balloon injury or H2O2-induced endothelial cell damage through the proline-rich tyrosine kinase 2 (Pyk2)/mitochondrial calcium uniporter (MCU) pathway. Intimal hyperplasia, a decrease of pinocytotic vesicles and cell apoptosis were found in the common carotid artery balloon injury and H2O2-induced endothelial cell damage, Pyk2/MCU was also up-regulated in such pathological process. HUK could prevent these injuries partially via the bradykinin B2 receptor by inhibiting Pyk2/MCU pathway, which prevented the mitochondrial damage, maintained calcium balance, and eventually inhibited cell apoptosis. Furthermore, MCU expression was not markedly increased if Pyk2 was suppressed by shRNA technique in the H2O2 treatment group, and cell viability was significantly better than H2O2-treated only. In short, our results indicate that the Pyk2/MCU pathway is involved in endothelial injury induced by balloon injury or H2O2-induced endothelial cell damage. HUK plays an protective role by inhibiting the Pyk2/MCU pathway in the endothelial injury.

Pyk2/MCU Pathway as a New Target for Reversing Atherosclerosis

Objective: Multiple mechanisms including vascular endothelial cell damage have a critical role in the formation and development of atherosclerosis (AS), but the specific molecular mechanisms are not exactly clarified. This study aims to determine the possible roles of proline-rich tyrosine kinase 2 (Pyk2)/mitochondrial calcium uniporter (MCU) pathway in AS mouse model and H₂O₂-induced endothelial cell damage model and explore its possible mechanisms.

Approach and Results: The AS mouse model was established using apolipoprotein E-knockout (ApoE^–/–) mice that were fed with a high-fat diet. It was very interesting to find that Pyk2/MCU expression was significantly increased in the artery wall of atherosclerotic mice and human umbilical vein endothelial cells (HUVECs) attacked by hydrogen peroxide (H₂O₂). In addition, down-regulation of Pyk2 by short hairpin RNA (shRNA) protected HUVECs from H₂O₂ insult. Furthermore, treatment with rosuvastatin on AS mouse model and H₂O₂-induced HUVEC injury model showed a protective effect against AS by inhibiting the Pyk2/MCU pathway, which maintained calcium balance, prevented the mitochondrial damage and reactive oxygen species production, and eventually inhibited cell apoptosis.

Conclusion: Our results provide important insight into the initiation of the Pyk2/MCU pathway involved in AS-related endothelial cell damage, which may be a new promising target for atherosclerosis intervention.

Effects of mevalonate kinase interference on cell differentiation, apoptosis, prenylation and geranylgeranylation of human keratinocytes are attenuated by farnesyl pyrophosphate or geranylgeranyl pyrophosphate

Mevalonate kinase (MVK) mutations were previously identified in disseminated superficial actinic porokeratosis. However, the role of MVK in differentiation, apoptosis and prenylation of keratinocytes requires further investigation. Farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) of the mevalonate pathway attach to small G proteins, and serve as molecular switches in biochemical pathways. Therefore, the aim of the present study was to investigate the role of MVK in the expression of keratin 1 and involucrin, apoptosis, protein prenylation and the processing of small G proteins. HaCat human keratinocytes were transfected with viruses carrying MVK interference and overexpression vectors, respectively. The mRNA expression of MVK, keratin 1 and involucrin was detected by reverse transcription-quantitative PCR. Protein expression of MVK, keratin 1, involucrin, lamin A, HRAS, KRAS, NRAS, Rho E, Rho B, Rho A, RAC1 and cdc42 in HaCat cells was detected by western blotting. The apoptotic rates of HaCat cells and protein prenylation levels were examined by flow cytometry. The expression of MVK in HaCat cells was significantly decreased in the interference groups, and markedly increased in the overexpression group compared with the negative control groups. The mRNA and protein expression levels of keratin 1 and involucrin were significantly decreased following interference of MVK expression, and the decrease was markedly attenuated by FPP. Furthermore, the apoptotic rate was markedly increased following MVK interference, and the increase was significantly attenuated by GGPP. The overexpression of MVK significantly decreased the apoptotic rate of HaCat cells. The prenylation levels after MVK interference was notably decreased, which was markedly attenuated by GGPP. The overexpression of MVK significantly increased the prenylation levels of HaCat cells. FPP or GGPP reversed MVK interference-induced decrease in geranylgeranylation levels of lamin A, HRAS, KRAS, NRAS, Rho E, Rho B, Rho A, RAC1 and cdc42. In conclusion, MVK interference decreases the expression of differentiation markers, increases apoptosis, and decreases protein prenylation and geranylgeranylation levels in keratinocytes. These changes are attenuated by FPP or GGPP.

Integration of Rap1 and Calcium Signaling

Ca²⁺ is a universal intracellular signal. The modulation of cytoplasmic Ca²⁺ concentration regulates a plethora of cellular processes, such as: synaptic plasticity, neuronal survival, chemotaxis of immune cells, platelet aggregation, vasodilation, and cardiac excitation–contraction coupling. Rap1 GTPases are ubiquitously expressed binary switches that alternate between active and inactive states and are regulated by diverse families of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Active Rap1 couples extracellular stimulation with intracellular signaling through secondary messengers—cyclic adenosine monophosphate (cAMP), Ca²⁺, and diacylglycerol (DAG). Much evidence indicates that Rap1 signaling intersects with Ca²⁺ signaling pathways to control the important cellular functions of platelet activation or neuronal plasticity. Rap1 acts as an effector of Ca²⁺ signaling when activated by mechanisms involving Ca²⁺ and DAG-activated (CalDAG-) GEFs. Conversely, activated by other GEFs, such as cAMP-dependent GEF Epac, Rap1 controls cytoplasmic Ca²⁺ levels. It does so by regulating the activity of Ca²⁺ signaling proteins such as sarcoendoplasmic reticulum Ca²⁺-ATPase (SERCA). In this review, we focus on the physiological significance of the links between Rap1 and Ca²⁺ signaling and emphasize the molecular interactions that may offer new targets for the therapy of Alzheimer’s disease, hypertension, and atherosclerosis, among other diseases.

Inhibition of prenyltransferase activity by statins in both liver and muscle cell lines is not causative of cytotoxicity

As inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, statins are an important first-line treatment for hypercholesterolemia. However, a recognized side-effect of statin therapy is myopathy, which in severe cases can present as potentially fatal rhabdomyolysis. This represents an important impediment to successful statin therapy, and despite decades of research the molecular mechanisms underlying this side-effect remain unclear. Current evidence supports a role for reduced levels of mevalonate pathway intermediates, with the most accepted hypothesis being a reduction in isoprenoids formation, leading to faulty post-translational modifications of membrane-associated proteins. We have undertaken a comprehensive analysis of the impact of nine statins on two human cell lines; Huh7 hepatoma and RD rhabdomyosarcoma. In both cell lines, concentration-dependent inhibition of prenylation was observed for cerivastatin and simvastatin, which could be rescued with the pathway intermediate mevalonate; in general, muscle cells were more sensitive to this effect, as measured by the levels of unprenylated Rap1A, a marker for prenylation by geranylgeranyl transferase I. Concentration-dependent toxicity was observed in both cell lines, with muscle cells again being more sensitive. Importantly, there was no correlation between inhibition of prenylation and cell toxicity, suggesting they are not causally linked. The lack of a causal relationship was confirmed by the absence of cytotoxicity in all cell lines following exposure to specific inhibitors of geranylgeranyl transferases I and II, and farnesyl transferase. As such, we provide strong evidence against the commonly accepted hypothesis linking inhibition of prenylation and statin-mediated toxicity, with the two processes likely to be simultaneous but independent.

Pyk2 mediates endothelin-1 signaling via p130Cas/BCAR3 cascade and regulates human glomerular mesangial cell adhesion and spreading

Calcium-regulated non-receptor proline-rich tyrosine kinase 2 (Pyk2) is a critical mediator of endothelin-1 (ET-1) signaling in human glomerular mesangial cells (GMC). We aimed to identify which small G-protein is acting downstream of Pyk2. Dominant interfering Pyk2 construct, termed calcium regulated non kinase (CRNK) or green fluorescent protein (control) were expressed in GMC using adenovirus-mediated gene transfer. ET-1 stimulation resulted in a significant increase of Pyk2 phosphorylation accompanied by GTP-loading of Rap1 and RhoA. CRNK expression inhibited ET-1-induced autophosphorylation of endogenous Pyk2 and diminished Rap1, but not RhoA, activation. The mechanism linking Pyk2 and Rap1 included (1) increased autophosphorylation of Pyk2 associated with p130Cas, (2) augmented p130Cas Y165 and Y249 phosphorylation, and (3) enhanced p130Cas-BCAR3 complex formation. CRNK expression prevented p130Cas phosphorylation and attenuated p130Cas association with BCAR3. Downregulation of endogenous BCAR3 protein expression using an siRNA technique led to a significant decrease in Rap1 activation in response to ET-1. We observed that endogenous Pyk2 was important for GMC adhesion and spreading. Our data suggest that ET-1 stimulated the GTPase Rap1 (but neither RhoA nor Ras) by a mechanism involving Pyk2 activation and recruitment of the p130Cas/BCAR3 complex in GMC.

Inhibitory effect of simvastatin on the TNF-alpha- and angiotensin II-induced monocyte adhesion to endothelial cells is mediated through the suppression of geranylgeranyl isoprenoid-dependent ROS generation

Vascular endothelial cell activation by cytokines and other pro-inflammatory mediators is an initial event in atherosclerosis and in other vascular diseases. Simvastatin, a HMG-CoA reductase inhibitor, suppressed both tumor necrosis factor (TNF)-alpha- and angiotensin (Ang) II-induced monocyte adhesion to endothelial cells (an initial step in vascular inflammation) and reactive oxygen species (ROS) production. Diphenyleneiodonium and apocynin, both NADPH oxidase inhibitors, also suppressed TNF-alpha-induced ROS and monocyte-endothelial cell adhesion, demonstrating that TNF-alpha-induced monocyte adhesion is mediated through ROS produced by NADPH oxidase activation. Furthermore, exogenously applied mevalonate or geranylgeranylpyrophosphate in combination with simvastatin completely prevented the inhibitory effects of simvastatin on ROS generation and monocyte-endothelial cell adhesion by TNFalpha and Ang II. These results suggest that monocyte adhesion to endothelial cells induced by TNF-alpha or Ang II is mediated via the geranylgeranyl isoprenoid-dependent generation of ROS, and that this is inhibited by simvastatin.

Simvastatin suppresses lung inflammatory response in a rat cardiopulmonary bypass model

BACKGROUND

Inflammatory response in the lungs is a well-known complication after cardiopulmonary bypass (CPB). The main aims of our study were to explore whether pretreatment with simvastatin would inhibit toll-like receptor 4 expression and suppress lung inflammatory response in a rat CPB model.

METHODS

Male Sprague-Dawley rats were divided into four groups (n = 6 each): sham group; CPB (control group); CPB plus low-dose simvastatin (5 mg/kg daily [L-Sim group]); and CPB plus high-dose simvastatin (10 mg/kg daily [H-Sim group]). Blood samples were collected at the beginning and at the termination of CPB, and at 1, 2, 4, and 24 hours after operation. The bronchoalveolar lavage fluid and lungs were harvested 24 hours postoperatively.

RESULTS

The simvastatin-treated groups had significantly higher ratios of PaO(2)/FiO(2) and lower values of respiratory index than the control group. We observed that simvastatin reduced CPB-induced toll-like receptor 4 and nuclear factor-kappaB expressions in CPB groups (p < 0.01, versus control group). The levels of interleukin-6, tumor necrosis factor-alpha, and monocyte chemotactic protein-1 in serum, bronchoalveolar lavage fluid, and lung tissues increased in CPB groups, whereas pretreatment with simvastatins reduced these inflammatory marks in a dose-dependent manner (p < 0.01, versus control group). Furthermore, pretreatment with simvastatin had a lower lung injury score (p < 0.05, versus control group).

CONCLUSIONS

These findings suggest that simvastatin inhibited CPB-induced toll-like receptor 4 upregulation and nuclear factor-kappaB activation, efficaciously reduing the pulmonary inflammatory response after CPB.

Erythropoietin Receptor Signal Transduction Requires Protein Geranylgeranylation

Erythropoietin (Epo) acts through the erythropoietin receptor, a member of the type-1 cytokine receptor family, to influence survival, proliferation, and differentiation of erythroid progenitors. Epo stimulation of factor-dependent 32D cells results in phosphorylation of many proteins, including Janus kinase (Jak) 2, signal transducer and activator of transcription (Stat) 5, and extracellular signal-regulated kinase (Erk). Some of Epo-activated signaling proteins require isoprenylation, either farnesylation or geranylgeranylation, for post-translational modification. In this study, we sought to characterize the interplay between protein isoprenylation and Epo signal transduction. Using two different Epo-responsive cell lines, we found that depletion of mevalonate and its isoprenoid derivatives using the 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitor lovastatin impairs Epo signaling as assessed by phosphorylation of cellular substrates and inhibition of apoptosis. Interestingly, the effect of mevalonate depletion was prevented by adding back geranylgeranyl pyrophosphate but not farnesyl pyrophosphate. Furthermore, selective inhibition of protein geranylgeranylation mimicked the effect of lovastatin, whereas selective inhibition of farnesylation had no effect. These results indicate that protein geranylgeranylation and not farnesylation is important for proper Epo signal transduction.

The small GTPase Rac is involved in clustering of hippocampal neurons and fasciculation of their neurites

In hippocampal neurons cultured from brains of newborn rats, the glutamate receptor agonist N-methyl-D-aspartate induced the clustering of neuronal perikarya and the fasciculation of neurites. In addition, N-methyl-D-aspartate activated the small GTPase Rac1. Other stimuli of Rac activity, such as the Rho kinase inhibitors Y-27632, H-1152, and H89, as well as the cytotoxic necrotizing factor-1 from Escherichia coli, also caused neuronal clustering and neurite bundling. In neurons transiently transfected with dominant negative Rac1N17 neither N-methyl-D-aspartate nor Y-27632 induced clustering and fasciculation. In addition, the PI3-kinase inhibitors wortmannin and LY-294002 prevented these effects, as did a dominant negative form of p110PI3-Kgamma. Time-lapse microscopy showed that lethal toxin from Clostridium sordellii, which inhibits Rac, and wortmannin blocked the neuronal migration induced by Y-27632. In contrast, only lethal toxin reversed the clustering and fasciculation induced by pre-treatment with Y-27632. This effect of the toxin may be due to inactivation of Ras, since FTI-277, which prevents the farnesylation of Ras and thereby inactivates the GTPase, also dissolved the preformed clusters. We suggest that active Rac and a PI3-kinase synergistically induce neuronal migration, whereas a Ras isoform is responsible for the lasting attachment of neurons necessary for clustering and neurite fasciculation.

All hydrophobic HMG-CoA reductase inhibitors induce apoptotic death in rat pulmonary vein endothelial cells

3-Hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase inhibitors (statins) are effective in patients with hypercholesterolemia to reduce risk of cardiovascular diseases, because of not only their lowering cholesterol effects but also their pleiotropic effects, such as improvement of endothelial cell dysfunction. On the other hand, statins prevent cell proliferation of various cells, including endothelial cells. We examined effects of all statins available at present on the viability of cultured rat pulmonary vein endothelial cells. Lovastatin, simvastatin, atorvastatin, fluvastatin and cerivastatin, which are hydrophobic statins, markedly reduced cell viability associated with DNA fragmentation, DNA laddering and activation of caspase-3, suggesting apoptotic cell death. Pravastatin, which is a hydrophilic statin, however, did not induce cell apoptosis. Apoptosis induced by hydrophobic statins was associated with activation of apoptosis-related intracellular signal transduction systems; attenuation of localization of RhoA to the membrane, induction of Rac1, and increase in phosphorylation of c-Jun N-terminal kinase and c-Jun. Endothelial cell apoptosis is underlying the improvement of the endothelial dysfunction with hydrophobic statins.

Induction of connective tissue growth factor by angiotensin II: integration of signaling pathways

OBJECTIVE

Angiotensin II is recognized as one of the major mediators of cardiovascular pathology. Because connective tissue growth factor (CTGF) is involved in the pathophysiologic processes underlying fibrotic diseases, its regulation by angiotensin II was investigated.

METHODS AND RESULTS

In the 2-kidney, 1-clip model of renovascular hypertension, increased expression of CTGF was detectable in the hypertrophic left ventricle. By activation of angiotensin II type 1 receptors, angiotensin II caused rapid expression of CTGF mRNA and protein in a human fibroblast cell line. Activation of the p42/44 mitogen-activated protein (MAP) kinase signaling pathway proved to be essential for angiotensin II-stimulated CTGF expression. Inhibition of MAP kinase activation by forskolin prevented CTGF induction. Inhibition of the isoprenylation of small GTPases by simvastatin or pretreatment of the cells with toxin B reduced basal CTGF expression below detection limits and prevented induction by angiotensin II. Specific interference with RhoA signaling by Y27632 primarily reduced basal CTGF expression. There was no significant reduction of expression of angiotensin II type 1 receptors by simvastatin. These data indicate cooperation between the Rho signaling and the angiotensin II-activated MAP kinase pathways.

CONCLUSIONS

Direct induction of CTGF by angiotensin II is indicative of a role for CTGF in angiotensin II-mediated fibrosis and might be a target of antifibrotic interventions.

Fluvastatin enhances the inhibitory effects of a selective angiotensin II type 1 receptor blocker, valsartan, on vascular neointimal formation

BACKGROUND

The present studies were undertaken to investigate the potential effect of a hydroxymethylglutaryl coenzyme A reductase inhibitor (statin) to enhance the inhibitory effect of an angiotensin (Ang) II type 1 (AT1) receptor blocker (ARB) on vascular neointimal formation and to explore the cellular mechanism of cross-talk of the AT1 receptor and statin in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Neointimal formation and the proliferation of VSMCs induced by cuff placement around the femoral artery were significantly inhibited by treatment with an ARB, valsartan, at a dose of 0.1 mg x kg(-1) x d(-1) and with fluvastatin at a dose of 1 mg x kg(-1) x d(-1), which did not influence mean arterial blood pressure or plasma cholesterol level, whereas valsartan or fluvastatin alone at these doses did not affect neointimal formation or the proliferation of VSMCs. Pretreatment with fluvastatin (approximately 5 micromol/L) for 24 hours significantly inhibited Ang II (1 micromol/L)-mediated DNA synthesis and c-fos promoter activity in cultured VSMCs. Moreover, pretreatment of VSMCs with fluvastatin significantly inhibited Ang II-mediated extracellular signal-regulated kinase (ERK) activation and tyrosine- and serine-phosphorylation of signal transducer and activator of transcription (STAT)1 and STAT3. AT1 receptor-mediated recruitment of Rac-1 to Janus kinase (Jak) family/STATs was also inhibited by fluvastatin. Consistent with these in vitro results, phosphorylation of ERK, STAT1, and STAT3 was attenuated by the coadministration of valsartan and fluvastatin even at low doses in vivo.

CONCLUSION

These results suggest that the cholesterol-independent inhibition of AT1 receptor-mediated VSMC proliferation by statins may contribute to the beneficial effects of statins combined with an ARB on vascular diseases.

Extracellular signal-regulated kinase inhibition by statins inhibits neutrophil activation by ANCA

BACKGROUND

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) may modulate cellular inflammatory functions independent of serum cholesterol. We tested the hypothesis that statins decrease respiratory burst activity of human polymorphonuclear neutrophils (PMN) in response to anti-neutrophil cytoplasmic antibodies (ANCA).

METHODS

Neutrophils were isolated from healthy human volunteers, human immunoglobulins were isolated from patients with proteinase-3 (PR3)- and myeloperoxidase (MPO)-ANCA. Superoxide generation was measured by the ferricytochrome C assay and the nitro blue tetrazolium (NBT) test. ANCA antigen expression was measured by flow cytometry and phosphorylation of mitogen-activated protein kinase (MAPK) was assessed by Western blotting.

RESULTS

Cerivastatin and simvastatin inhibited respiratory burst activity to ANCA dose-dependently (1 to 25 micromol/L). Tumor necrosis factor-alpha (TNF-alpha)-primed neutrophils released 26.7 +/- 2.8 nmol O2-/0.75 x 106 PMN/45 min and 10 micromol/L simvastatin reduced this amount to 18.0 +/- 2.1 nmol. The inhibitory effect was confirmed by the NBT test. The respiratory burst decrease could not be reversed by 500 micromol/L mevalonic acid (MVA). In this assay, both statins also inhibited the response to human ANCA. PR3-ANCA resulted in 19.4 +/- 2.0 nmol O2- nmol. This amount was decreased to 6.0 +/- 1.2 nmol by preincubation with 10 micromol/L simvastatin (P < 0.01). For MPO-ANCA, the values were 22.6 +/- 2.8 nmol for controls versus 16.7 +/- 3.1 nmol with statin (P < 0.01). By FACS, simvastatin decreased TNF-alpha-mediated ANCA antigen translocation (from 219 +/- 33 to 180 +/- 35 MFI for PR3 and 24.0 +/- 2.4 to 18.3 +/- 1.1 for MPO). Finally, since p38 MAPK and ERK control TNF-alpha priming, we studied the effects of both statins on MAPK. Western blotting showed that statins inhibited TNF-alpha-induced ERK phosphorylation in a dose dependent fashion, but had no effect on p38.

CONCLUSION

These findings demonstrate that HMG-CoA reductase inhibitors decrease respiratory burst activity of human PMN in response to ANCA. This effect was independent of mevalonate, but involved inhibition of ERK activation during TNF-alpha priming. Our data suggest that HMG-CoA reductase inhibitors may help limit inflammatory responses.

New insights in the transcriptional activity and coregulator molecules in the arterial wall

A number of vascular diseases are associated with abnormal expression of genes that contribute to their pathophysiological and clinical manifestations, but at the same time offer potential therapeutic targets. One of the promising therapeutic approaches targets the pathophysiological pathways leading to aberrant gene activation, namely transcriptional activity and its molecular modulators (agonists, antagonists, coregulators, and nuclear receptors). The transcription factors can be divided into four classes (I-IV) classified by structural elements, like basic leucine zipper (bZIP) or basic helix-loop-helix (bHLH), which mediate their DNA binding activity but also determine the classes of drugs that can affect their activity. For example, statins modulate activation of the class-I transcription factor sterol responsive element-binding protein (SREBP), whose target genes including hydroxyl-methyl-glutaryl acetyl Coenzyme-A (HMG-CoA) reductase, HMG-CoA synthase, and the low-density lipoprotein receptor, all of which are involved in cholesterol and fatty acid metabolism. Similarly, insulin-like drugs target the nuclear receptor peroxisome-proliferator-activator-receptor (PPAR)-gamma (class-II), several anti-inflammatory drugs inhibit activation of nuclear factor kappa B (NFkappaB) (class-IV), while others (e.g. flavopiridol, rapamycin, and paclitaxel) target regulation of cell-cycle proteins. Increased understanding of the genetic and molecular basis of disease (e.g. transcriptional activity and its coregulation) will potentially enhance future diagnosis, treatment, and prevention of vascular diseases.

Simvastatin attenuates smooth muscle neointimal proliferation and pulmonary hypertension in rats

Hypertensive pulmonary vascular disease is characterized by abnormal proliferation of vascular endothelial and smooth muscle cells, leading to occlusion of pulmonary arterioles, pulmonary hypertension, right ventricular failure, and death. Compounds with antiproliferative effects on vascular endothelial and smooth muscle cells, such as 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, may prevent the development of experimental hypertensive pulmonary vascular disease. Pneumonectomized rats injected with monocrotaline at 7 days develop severe hypertensive pulmonary vascular disease with neointimal formation. Rats were randomized to receive either vehicle or treatment with the HMG-CoA reductase inhibitor simvastatin (2 mg/kg per day). By Day 35, rats that received vehicle had higher mean pulmonary arterial pressures (53 +/- 2 mm Hg) and right ventricular hypertrophy (right ventricle/[left ventricle plus septum] [RV/LV+S] = 0.78 +/- 0.09) than rats in Group PMS5-35 that received simvastatin from Day 5 to 35 (mean pulmonary arterial pressure = 27 +/- 3 mm Hg, RV/LV+S = 0.34 +/- 0.08; p < or = 0.001). Pulmonary vascular remodeling with neointimal formation consisting of vascular smooth muscle cells was more severe in vehicle-treated rats (vascular occlusion score, 1.98 +/- 0.02) than in Group PMS5-35 (vascular occlusion score, 0.59 +/- 0.46; p < 0.001). In addition, lung endothelial nitric oxide synthase gene expression was decreased in vehicle-treated animals but was restored toward normal levels in simvastatin-treated animals. Simvastatin attenuates monocrotaline-induced pulmonary vascular remodeling with neointimal formation, pulmonary arterial hypertension, and right ventricular hypertrophy in rats.

Thrombin-stimulated Pyk2 phosphorylation in human endothelium is dependent on intracellular calcium and independent of protein kinase C and Src kinases

G-protein-coupled receptor agonists (GPCAs) cause functional responses in endothelial cells including secretion, proliferation, and altering monolayer permeability. These events are mediated in part by activation of the p42/44 mitogen-activated protein kinase (MAPK) cascade. The cytosolic tyrosine kinase Pyk2 is postulated to link GPCA-induced changes in intracellular calcium to activation of the MAP kinase cascade. We have investigated the regulation of Pyk2 in human umbilical vein endothelial cells in response to GPCAs and show that (1) thrombin, a PAR-1 peptide, and histamine cause rapid concentration- and time-dependent phosphorylation on tyrosines 402 (Src kinase binding site), 881 (Grb2 binding site), and 580 (an autophosphorylation site), (2) thrombin-stimulated phosphorylation is dependent on intracellular calcium and independent of PKC and PI-3 kinase, and (3) inhibition of Src kinases has no significant effect on thrombin-stimulated phosphorylation, implying that tyrosine phosphorylation of Pyk2 is independent of Src binding.

HMG-CoA reductase inhibitors and the malignant cell: the statin family of drugs as triggers of tumor-specific apoptosis

The statin family of drugs target HMG-CoA reductase, the rate-limiting enzyme of the mevalonate pathway, and have been used successfully in the treatment of hypercholesterolemia for the past 15 years. Experimental evidence suggests this key biochemical pathway holds an important role in the carcinogenic process. Moreover, statin administration in vivo can provide an oncoprotective effect. Indeed, in vitro studies have shown the statins can trigger cells of certain tumor types, such as acute myelogenous leukemia, to undergo apoptosis in a sensitive and specific manner. Mechanistic studies show bcl-2 expression is down-regulated in transformed cells undergoing apoptosis in response to statin exposure. In addition, the apoptotic response is in part due to the depletion of the downstream product geranylgeranyl pyrophosphate, but not farnesyl pyrophosphate or other products of the mevalonate pathway including cholesterol. Clinically, preliminary phase I clinical trials have shown the achievable plasma concentration corresponds to the dose range that can trigger apoptosis of tumor types in vitro. Moreover, little toxicity was evident in vivo even at high concentrations. Clearly, additional clinical trials are warranted to further assess the safety and efficacy of statins as novel and immediately available anti-cancer agents. In this article, the experimental evidence supporting a role for the statin family of drugs to this new application will be reviewed.

Diversity of G protein-coupled receptor signaling pathways to ERK/MAP kinase

One of the most intriguing examples of cross talk between signaling systems is the interrelationship between G protein-coupled receptor and growth factor receptor pathways leading to activation of the ERK/MAP kinase phosphorylation cascade. This review focuses on the mechanism of this cross talk, denoting primarily signaling components known to occur in the G protein-coupled receptor branch of the MAP kinase pathways in neural cells. Recent evidence is presented on the existence of a plethora of pathways, due to the multiplicity of G protein-coupled receptors, their differential interaction with heterotrimeric G protein isoforms, various effectors and second messengers. In light of this rich diversity, the review will discuss different points of convergence of G protein-coupled receptor and growth factor receptor pathways that may feature a requirement for growth factor receptor transactivation, receptor internalization and scaffolds to assemble receptor, adaptor and anchoring proteins into multiprotein complexes.