Rho-associated kinase directly induces smooth muscle contraction through myosin light chain phosphorylation

Rho-kinase inhibitors as therapeutics: from pan inhibition to isoform selectivity

The emerging critical implications of Rho/Rho-kinase (ROCK) signaling in neurodegenerative diseases, glaucoma, renoprotection, diabetes and cancer have sparked growing interest in the pharmacological potential of ROCK inhibitors beyond their current application in cardiovascular disease. This article discusses the therapeutic benefits of novel ROCK inhibitors in development, and highlights the recent advances in the current understanding of disease-dependent and isoform-specific functions of ROCK and their potential impact on future therapeutic strategies.

ROCK1 functions as a suppressor of inflammatory cell migration by regulating PTEN phosphorylation and stability

Rho kinases belong to a family of serine/threonine kinases whose role in recruitment and migration of inflammatory cells is poorly understood. We show that deficiency of ROCK1 results in increased recruitment and migration of macrophages and neutrophils in vitro and in vivo. Enhanced migration resulting from ROCK1 deficiency is observed despite normal expression of ROCK2 and a significant reduction in overall ROCK activity. ROCK1 directly binds PTEN in response to receptor activation and is essential for PTEN phosphorylation and stability. In the absence of ROCK1, PTEN phosphorylation, stability, and its activity are significantly impaired. Consequently, increased activation of downstream targets of PTEN, including PIP3, AKT, GSK-3beta, and cyclin D1, is observed. Our results reveal ROCK1 as a physiologic regulator of PTEN whose function is to repress excessive recruitment of macrophages and neutrophils during acute inflammation.

UTP controls cell surface distribution and vasomotor activity of the human P2Y2 receptor through an epidermal growth factor receptor-transregulated mechanism

Extracellular nucleotides transmit signals into the cells through the P2 family of cell surface receptors. These receptors are amply expressed in human blood vessels and participate in vascular tone control; however, their signaling mechanisms remain unknown. Here we show that in smooth muscle cells of isolated human chorionic arteries, the activation of the P2Y(2) receptor (P2Y(2)R) induces not only its partition into membrane rafts but also its rapid internalization. Cholesterol depletion with methyl-beta-cyclodextrin reduced the association of the agonist-activated receptor into membrane rafts but did not affect either the UTP-mediated vasoconstrictions or the vasomotor responses elicited by both serotonin and KCl. Ex vivo perfusion of human chorionic artery segments with 1-10 mum UTP, a selective P2Y(2)R agonist, displaced the P2Y(2)R localization into membrane rafts within 1 min, a process preceded by the activation of both RhoA and Rac1 GTPases. AG1478, a selective and potent inhibitor of the epidermal growth factor receptor tyrosine kinase activity, not only blocked the UTP-induced vasomotor activity but also abrogated both RhoA and Rac1 activation, the P2Y(2)R association with membrane rafts, and its internalization. Altogether, these results show for the first time that the plasma membrane distribution of the P2Y(2)R is transregulated by the epidermal growth factor receptor, revealing an unsuspected functional interplay that controls both the membrane distribution and the vasomotor activity of the P2Y(2)R in intact human blood vessels.

Flavone Attenuates Vascular Contractions by Inhibiting RhoA/Rho Kinase Pathway

Our previous study demonstrated that flavone inhibits vascular contractions by decreasing the phosphorylation levelof the myosin phosphatase target subunit (MYPT1). In the present study, we hypothesized that flavone attenuates vascular contractions through the inhibition of the RhoA/Rho kinase pathway. Rat aortic rings were denuded of endothelium, mounted in organ baths, and contracted with either 30 nM U46619 (a thromboxane A2 analogue) or 8.0 mM NaF 30 min after pretreatment with either flavone (100 or 300 microM) or vehicle. We determined the phosphorylation level of the myosin light chain (MLC(20)), the myosin phophatase targeting subunit 1 (MYPT1) and the protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phophatase of 17-kDa (CPI17) by means of Western blot analysis. Flavone inhibited, not only vascular contractions induced by these contractors, but also the levels of MLC(20) phosphorylation. Furthermore, flavone inhibited the activation of RhoA which had been induced by either U46619 or NaF. Incubation with flavone attenuated U46619-or NaF-induced phosphorylation of MYPT1(Thr855) and CPI17(Thr38), the downstream effectors of Rho-kinase. In regards to the Ca(2+)-free solution, flavone inhibited the phosphorylation of MYPT1(Thr855) and CPI17(Thr38), as well as vascular contractions induced by U46619. These results indicate that flavone attenuates vascular contractions, at least in part, through the inhibition of the RhoA/Rho-kinase pathway.

Analysis of pulmonary vasodilator responses to SB-772077-B [4-(7-((3-amino-1-pyrrolidinyl)carbonyl)-1-ethyl-1H-imidazo(4,5-c)pyridin-2-yl)-1,2,5-oxadiazol-3-amine], a novel aminofurazan-based Rho kinase inhibitor

The effects of SB-772077-B [4-(7-((3-amino-1-pyrrolidinyl)carbonyl)-1-ethyl-1H-imidazo(4,5-c)pyridin-2-yl)-1,2,5-oxadiazol-3-amine], an aminofurazan-based Rho kinase inhibitor, on the pulmonary vascular bed and on monocrotaline-induced pulmonary hypertension were investigated in the rat. The intravenous injections of SB-772077-B decreased pulmonary and systemic arterial pressures and increased cardiac output. The decreases in pulmonary arterial pressure were enhanced when pulmonary vascular resistance was increased by U46619 [9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha)], hypoxia, or N(omega)-nitro-L-arginine methyl ester. SB-772077-B was more potent than Y-27632 [trans-4-[(1R)-1-aminoethyl]-N-4-pyridinyl-cyclohexanecarboxamide dihydrochloride] or fasudil [5-(1,4-diazepane-1-sulfonyl)isoquinoline] in decreasing pulmonary and systemic arterial pressures. The results with SB-772077-B, fasudil, and Y-27632 suggest that Rho kinase is constitutively active and is involved in the regulation of baseline tone and vasoconstrictor responses. Chronic treatment with SB-772077-B attenuated the increase in pulmonary arterial pressure induced by monocrotaline. The intravenous injection of SB-772077-B decreased pulmonary and systemic arterial pressures in rats with monocrotaline-induced pulmonary hypertension. The decreases in pulmonary arterial pressure in response to SB-772077-B in monocrotaline-treated rats were smaller than responses in U46619-infused animals, and the analysis of responses suggests that approximately 60% of the pulmonary hypertensive response is mediated by a Rho kinase-sensitive mechanism. The observation that Rho kinase inhibitors decrease pulmonary arterial pressure when pulmonary vascular resistance is increased by interventions such as hypoxia, U46619, angiotensin II, nitric-oxide synthase inhibition, and Bay K 8644 [S-(-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-[trifluoromethyl]phenyl)-3-pyridine carboxylic acid methyl ester] suggest that the vasodilatation is independent of the mechanisms used to increase intracellular calcium and promote vasoconstriction. The present results suggest that SB-772077-B would be beneficial in the treatment of pulmonary hypertensive disorders.

Smooth muscle signalling pathways in health and disease

Smooth muscle contractile activity is a major regulator of function of the vascular system, respiratory system, gastrointestinal system and the genitourinary systems. Malfunction of contractility in these systems leads to a host of clinical disorders, and yet, we still have major gaps in our understanding of the molecular mechanisms by which contractility of the differentiated smooth muscle cell is regulated. This review will summarize recent advances in the molecular understanding of the regulation of smooth muscle myosin activity via phosphorylation/dephosphorylation of myosin, the regulation of the accessibility of actin to myosin via the actin-binding proteins calponin and caldesmon, and the remodelling of the actin cytoskeleton. Understanding of the molecular 'players' should identify target molecules that could point the way to novel drug discovery programs for the treatment of smooth muscle disorders such as cardiovascular disease, asthma, functional bowel disease and pre-term labour.

The planar cell polarity pathway directs parietal endoderm migration

Parietal endoderm (PE) contributes to the yolk sac and is the first migratory cell type in the mammalian embryo. We can visualize PE migration in vitro using the F9 teratocarcinoma derived embryoid body outgrowth system and, show here that PE migration is directed by the non-canonical Wnt planar cell polarity (PCP) pathway via Rho/ROCK. Based on golgi apparatus localization and microtubule orientation, 68.6% of cells in control outgrowths are oriented in the direction of migration. Perturbation of Wnt signaling via sFRP treatment results in a loss of orientation coupled with an increase in cell migration. Inhibition of the PCP pathway at the level of Daam1 also results in a loss of cell orientation along with an increase in cell migration, as seen with sFRP treatment. Constitutively active Daam can inhibit the loss of orientation that occurs with sFRP treatment. We previously demonstrated that ROCK inhibition leads to an increase in cell migration, and we now show that these cells also lack oriented migration. Canonical Wnt signaling or the Rac arm of the PCP pathway does not appear to play a role in PE oriented migration. These data suggest the PCP pathway via Rho/ROCK modulates migration of PE.

Y27632, a Rho-activated kinase inhibitor, normalizes dysregulation in alpha1-adrenergic receptor-induced contraction of Lyon hypertensive rat artery smooth muscle

RhoA-activated kinase (ROK) is involved in the disorders of smooth muscle contraction found in hypertension model animals and patients. We examined whether the alpha1-adrenergic receptor agonist-induced ROK signal is perturbed in resistance small mesentery artery (SMA) of Lyon genetically hypertensive (LH) rats, using a ROK antagonist, Y27632. Smooth muscle strips of SMA and aorta were isolated from LH and Lyon normotensive (LN) rats. After Ca(2+)-depletion and pre-treatment with phenylephrine (PE), smooth muscle contraction was induced by serial additions of CaCl(2). In LH SMA Ca(2+) permeated cells to a lesser extent as compared with LN SMA, while CaCl(2)-induced contraction of LH SMA was greater than that of LN SMA, indicating a higher ratio of force to Ca(2+) in LH SMA contraction (Ca(2+) sensitization). No hyper-contraction was observed in LH aorta tissues. Treatment of LH SMA with Y27632 restored both Ca(2+) permeability and Ca(2+)-force relationship to levels seen for LN SMA. In response to PE stimulation, phosphorylation of CPI-17, a phosphorylation-dependent myosin phosphatase inhibitor protein, and MYPT1 at Thr853, the inhibitory phosphorylation site of the myosin phosphatase regulatory subunit, was increased in LN SMA, but remained unchanged in LH SMA. These results suggest that the disorder in ROK-dependent Ca(2+) permeability and Ca(2+)-force relationship is responsible for LH SMA hyper-contraction. Unlike other hypertensive models, the ROK-induced hyper-contractility of LH SMA is independent of MYPT1 and CPI-17 phosphorylation, which suggests that ROK-mediated inhibition of myosin phosphatase does not affect SMA hyper-contractility in LH SMA cells.

Targeting cerebrovascular Rho-kinase in stroke

BACKGROUND

Rho and Rho-associated kinase (ROCK) play pivotal roles in pathogenesis of vascular diseases including stroke. ROCK is expressed in all cell types relevant to stroke, and regulates a range of physiological processes.

OBJECTIVE

To provide an overview of ROCK as an experimental therapeutic target in cerebral ischemia, and the translational opportunities and obstacles in the prophylaxis and treatment of stroke.

METHODS

Relevant literature was reviewed.

RESULTS

ROCK activity is upregulated in chronic vascular risk factors such as diabetes, hyperlipidemia and hypertension, and more acutely by cerebral ischemia. ROCK activation is predicted to increase the risk of cerebral ischemia, and worsen the ischemic tissue outcome and functional recovery. Evidence suggests that ROCK inhibition is protective in models of cerebral ischemia. The benefit is mediated through multiple mechanisms.

CONCLUSION

ROCK is a promising therapeutic target in all stages of stroke.

Mechanotransduction in development: a growing role for contractility

Mechanotransduction research has focused historically on how externally applied forces can affect cell signalling and function. A growing body of evidence suggests that contractile forces that are generated internally by the actomyosin cytoskeleton are also important in regulating cell behaviour, and suggest a broader role for mechanotransduction in biology. Although the molecular basis for these cellular forces in mechanotransduction is being pursued in cell culture, researchers are also beginning to appreciate their contribution to in vivo developmental processes. Here, we examine the role for mechanical forces and contractility in regulating cell and tissue structure and function during development.

Substrate rigidity regulates Ca2+ oscillation via RhoA pathway in stem cells

Substrate rigidity plays crucial roles in regulating cellular functions, such as cell spreading, traction forces, and stem cell differentiation. However, it is not clear how substrate rigidity influences early cell signaling events such as calcium in living cells. Using highly sensitive Ca(2+) biosensors based on fluorescence resonance energy transfer (FRET), we investigated the molecular mechanism by which substrate rigidity affects calcium signaling in human mesenchymal stem cells (HMSCs). Spontaneous Ca(2+) oscillations were observed inside the cytoplasm and the endoplasmic reticulum (ER) using the FRET biosensors targeted at subcellular locations in cells plated on rigid dishes. Lowering the substrate stiffness to 1 kPa significantly inhibited both the magnitudes and frequencies of the cytoplasmic Ca(2+) oscillation in comparison to stiffer or rigid substrate. This Ca(2+) oscillation was shown to be dependent on ROCK, a downstream effector molecule of RhoA, but independent of actin filaments, microtubules, myosin light chain kinase, or myosin activity. Lysophosphatidic acid, which activates RhoA, also inhibited the frequency of the Ca(2+) oscillation. Consistently, either a constitutive active mutant of RhoA (RhoA-V14) or a dominant negative mutant of RhoA (RhoA-N19) inhibited the Ca(2+) oscillation. Further experiments revealed that HMSCs cultured on gels with low elastic moduli displayed low RhoA activities. Therefore, our results demonstrate that RhoA and its downstream molecule ROCK may mediate the substrate rigidity-regulated Ca(2+) oscillation, which determines the physiological functions of HMSCs.

Smooth muscle signalling pathways in health and disease

Smooth muscle contractile activity is a major regulator of function of the vascular system, respiratory system, gastrointestinal system and the genitourinary systems. Malfunction of contractility in these systems leads to a host of clinical disorders, and yet, we still have major gaps in our understanding of the molecular mechanisms by which contractility of the differentiated smooth muscle cell is regulated. This review will summarize recent advances in the molecular understanding of the regulation of smooth muscle myosin activity via phosphorylation/dephosphorylation of myosin, the regulation of the accessibility of actin to myosin via the actin-binding proteins calponin and caldesmon, and the remodelling of the actin cytoskeleton. Understanding of the molecular 'players' should identify target molecules that could point the way to novel drug discovery programs for the treatment of smooth muscle disorders such as cardiovascular disease, asthma, functional bowel disease and pre-term labour.

A major haplotype block at the rho-associated kinase 2 locus is associated with a lower risk of hypertension in a recessive manner: the HYPGENE study

The goals of our study were to evaluate the haplotype pattern at the Rho-associated kinase 2 (ROCK2) locus and prospectively test the association between the ROCK2 haplotype-tagging single-nucleotide polymorphisms (tagSNPs) with hypertension for verified incident hypertensive patients (n=607) and healthy, normotensive controls (n=586) in a HYPGENE study. Rho-associated kinases (ROCKs) play a central role in signaling pathways that are involved in vascular smooth muscle contraction and endothelial nitric oxide availability. Using a set of stringent criteria (minor allele frequency>or=0.05, pairwise r2>or=0.95), we identified 18 tagSNPs from the 109 SNPs available in the HapMap Caucasian data set. TagSNPs were genotyped using the Illumina BeadStation platform. The 18 tagSNPs consisted of two linkage disequilibrium (LD) blocks. A haplotype defined by four SNPs (rs965665, rs10178332, rs6755196, rs10929732) in LD block 2 was recessively associated with a lower risk of hypertension (p=0.003). Homozygotes for the minor alleles had an 85% lower risk of hypertension than carriers of the common allele. The associations were independent of baseline age, cardiorespiratory fitness, body mass index, sex, and follow-up time. The LD block 2 spans about 137 kb of genomic DNA at the 5'-end of the ROCK2 locus and covers exons encoding the kinase domain of the protein. Our data strongly suggest that a major haplotype block at the ROCK2 locus is recessively associated with a lower risk of hypertension. Identification of functional mutation(s) could thus help in the development of ROCK2-specific treatments.

Potent inhibition of cicatricial contraction in proliferative vitreoretinal diseases by statins

OBJECTIVE

Despite tremendous progress in vitreoretinal surgery, certain postsurgical complications limit the success in the treatment of proliferative vitreoretinal diseases (PVDs), such as proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). One of the most significant complications is the cicatricial contraction of proliferative membranes, resulting in tractional retinal detachment and severe vision loss. Novel pharmaceutical approaches are thus urgently needed for the management of these vision-threatening diseases. In the current study, we investigated the inhibitory effects of statins on the progression of PVDs.

RESEARCH DESIGN AND METHODS

Human vitreous concentrations of transforming growth factor-beta2 (TGF-beta2) were measured by enzyme-linked immunosorbent assay. TGF-beta2-and vitreous-dependent phosphorylation of myosin light chain (MLC), a downstream mediator of Rho-kinase pathway, and collagen gel contraction simulating cicatrical contraction were analyzed using cultured hyalocytes. Inhibitory effects of simvastatin on cicatrical contraction were assessed both in vitro and in vivo.

RESULTS

Human vitreous concentrations of TGF-beta2 were significantly higher in the samples from patients with PVD compared with those without PVD. Simvastatin inhibited TGF-beta2-dependent MLC phosphorylation and gel contraction in a dose- and time-dependent manner and was capable of inhibiting translocation of Rho protein to the plasma membrane in the presence of TGF-beta2. Vitreous samples from patients with PVD enhanced MLC phosphorylation and gel contraction, whereas simvastatin almost completely inhibited these phenomena. Finally, intravitreal injection of simvastatin dose-dependently prevented the progression of diseased states in an in vivo model of PVR.

CONCLUSIONS

Statins might have therapeutic potential in the prevention of PVDs.

Contact guidance mediated three-dimensional cell migration is regulated by Rho/ROCK-dependent matrix reorganization

Cells generate mechanical force to organize the extracellular matrix (ECM) and drive important developmental and reparative processes. Likewise, tumor cells invading into three-dimensional (3D) matrices remodel the ECM microenvironment. Importantly, we previously reported a distinct radial reorganization of the collagen matrix surrounding tumors that facilitates local invasion. Here we describe a mechanism by which cells utilize contractility events to reorganize the ECM to provide contact guidance that facilitates 3D migration. Using novel assays to differentially organize the collagen matrix we show that alignment of collagen perpendicular to the tumor-explant boundary promotes local invasion of both human and mouse mammary epithelial cells. In contrast, organizing the collagen matrix to mimic the ECM organization associated with noninvading regions of tumors suppresses 3D migration/invasion. Moreover, we demonstrate that matrix reorganization is contractility-dependent and that the Rho/Rho kinase pathway is necessary for collagen alignment to provide contact guidance. Yet, if matrices are prealigned, inhibiting neither Rho nor Rho kinase inhibits 3D migration, which supports our conclusion that Rho-mediated matrix alignment is an early step in the invasion process, preceding and subsequently facilitating 3D migration.

The Rho-Rock-Myosin signaling axis determines cell-cell integrity of self-renewing pluripotent stem cells

Background

Embryonic stem (ES) cells self-renew as coherent colonies in which cells maintain tight cell-cell contact. Although intercellular communications are essential to establish the basis of cell-specific identity, molecular mechanisms underlying intrinsic cell-cell interactions in ES cells at the signaling level remain underexplored.

Methodology/Principal Findings

Here we show that endogenous Rho signaling is required for the maintenance of cell-cell contacts in ES cells. siRNA-mediated loss of function experiments demonstrated that Rock, a major effector kinase downstream of Rho, played a key role in the formation of cell-cell junctional assemblies through regulation of myosin II by controlling a myosin light chain phosphatase. Chemical engineering of this signaling axis by a Rock-specific inhibitor revealed that cell-cell adhesion was reversibly controllable and dispensable for self-renewal of mouse ES cells as confirmed by chimera assay. Furthermore, a novel culture system combining a single synthetic matrix, defined medium, and the Rock inhibitor fully warranted human ES cell self-renewal independent of animal-derived matrices, tight cell contacts, or fibroblastic niche-forming cells as determined by teratoma formation assay.

Conclusions/Significance

These findings demonstrate an essential role of the Rho-Rock-Myosin signaling axis for the regulation of basic cell-cell communications in both mouse and human ES cells, and would contribute to advance in medically compatible xeno-free environments for human pluripotent stem cells.

Regulation of RhoA-dependent ROCKII activation by Shp2

Contractile forces mediated by RhoA and Rho kinase (ROCK) are required for a variety of cellular processes, including cell adhesion. In this study, we show that RhoA-dependent ROCKII activation is negatively regulated by phosphorylation at a conserved tyrosine residue (Y722) in the coiled-coil domain of ROCKII. Tyrosine phosphorylation of ROCKII is increased with cell adhesion, and loss of Y722 phosphorylation delays adhesion and spreading on fibronectin, suggesting that this modification is critical for restricting ROCKII-mediated contractility during these processes. Further, we provide evidence that Shp2 mediates dephosphorylation of ROCKII and, therefore, regulates RhoA-induced cell rounding, indicating that Shp2 couples with RhoA signaling to control ROCKII activation during deadhesion. Thus, reversible tyrosine phosphorylation confers an additional layer of control to fine-tune RhoA-dependent activation of ROCKII.

Modulation of enzymatic activities by n-3 polyunsaturated fatty acids to support cardiovascular health

Epidemiological evidence from Greenland Eskimos and Japanese fishing villages suggests that eating fish oil and marine animals can prevent coronary heart disease. Dietary studies from various laboratories have similarly indicated that regular fish oil intake affects several humoral and cellular factors involved in atherogenesis and may prevent atherosclerosis, arrhythmia, thrombosis, cardiac hypertrophy and sudden cardiac death. The beneficial effects of fish oil are attributed to their n-3 polyunsaturated fatty acid (PUFA; also known as omega-3 fatty acids) content, particularly eicosapentaenoic acid (EPA; 20:5, n-3) and docosahexaenoic acid (DHA; 22:6, n-3). Dietary supplementation of DHA and EPA influences the fatty acid composition of plasma phospholipids that, in turn, may affect cardiac cell functions in vivo. Recent studies have demonstrated that long-chain omega-3 fatty acids may exert beneficial effects by affecting a wide variety of cellular signaling mechanisms. Pathways involved in calcium homeostasis in the heart may be of particular importance. L-type calcium channels, the Na+-Ca2+ exchanger and mobilization of calcium from intracellular stores are the most obvious key signaling pathways affecting the cardiovascular system; however, recent studies now suggest that other signaling pathways involving activation of phospholipases, synthesis of eicosanoids, regulation of receptor-associated enzymes and protein kinases also play very important roles in mediating n-3 PUFA effects on cardiovascular health. This review is therefore focused on the molecular targets and signaling pathways that are regulated by n-3 PUFAs in relation to their cardioprotective effects.

Tumor necrosis factor-alpha antagonism improves vasodilation during hyperinsulinemia in metabolic syndrome

OBJECTIVE

Obesity is associated with chronic inflammation due to overproduction of proinflammatory cytokines, including tumor necrosis factor (TNF)-alpha. We assessed the effects of TNF-alpha neutralization by infliximab on vascular reactivity during hyperinsulinemia in obesity-related metabolic syndrome.

RESEARCH DESIGN AND METHODS

Vascular responses to intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) were assessed in patients with metabolic syndrome, before and after administration of infliximab.

RESULTS

Patients had blunted vasodilator responses to ACh and SNP during hyperinsulinemia compared with control subjects; a potentiation of the responsiveness to both ACh and SNP, however, was observed in patients following infliximab. The antioxidant vitamin C improved the vasodilator response to ACh in patients with metabolic syndrome, but its effect was not further enhanced by concurrent administration of infliximab.

CONCLUSIONS

TNF-alpha neutralization ameliorates vascular reactivity in metabolic syndrome during hyperinsulinemia, likely in relation to decreased oxidative stress, thereby suggesting an involvement of inflammatory cytokines in vascular dysfunction of these patients.

Regulation of sinusoidal perfusion in portal hypertension

Portal hypertension, a major complication of cirrhosis, is caused by both increased portal blood flow and augmented intrahepatic vascular resistance. Even though the latter is primarily caused by anatomical changes, it has become clear that dynamic factors contribute to the increased hepatic vascular resistance. The hepatic sinusoid is the narrowest vascular structure within the liver and is the principal site of blood flow regulation. The anatomical location of hepatic stellate cells, which embrace the sinusoids, provides a favorable arrangement for sinusoidal constriction, and for control of sinusoidal vascular tone and blood flow. Hepatic stellate cells possess the essential contractile apparatus for cell contraction and relaxation. Moreover, the mechanisms of stellate cell contraction are better understood, and many substances which influence contractility have been identified, providing a rationale and opportunity for targeting these cells in the treatment of portal hypertension in cirrhosis.

Activation of Rho kinase by TNF-alpha is required for JNK activation in human pulmonary microvascular endothelial cells

TNF-alpha induces complex signaling events in endothelial cells (ECs), leading to inflammatory gene transcription and junctional permeability increases. This study examined the activation of RhoA and Rho kinase induced by TNF-alpha in primary human pulmonary microvascular ECs and its role in regulating EC responses to TNF-alpha. TNF-alpha induced a time-dependent activation of RhoA and Rho kinase in these ECs. TNF-alpha also induced activation of JNK that peaked at 15 min and lasted for at least 3 h. Inhibition of Rho kinase using a specific pharmacological inhibitor, Y27632, prevented TNF-alpha-induced early and late JNK activation. Inhibition of RhoA protein expression using small-interfering RNA, however, did not prevent TNF-alpha-induced Rho kinase activation or JNK activation. Studies using MAPK kinase 4 (MKK4) small-interfering RNA showed that MKK4 was not required for TNF-alpha-induced early JNK activation and that Rho kinase modulated early JNK activation through MKK4-independent mechanisms. Rho kinase, however, modulated TNF-alpha-induced late JNK activation mainly through MKK4-dependent mechanisms. Activation of Rho kinase was required for JNK-dependent IL-6 secretion induced by TNF-alpha. Moreover, inhibition of Rho kinase prevented TNF-alpha-induced cytoskeletal changes and permeability increases. Inhibition of JNK activation, however, did not prevent TNF-alpha-induced cytoskeletal changes, suggesting that Rho kinase did not modulate cytoskeletal changes through JNK activation. Therefore, Rho kinase plays important roles in EC responses to TNF-alpha by regulating permeability increases and JNK-dependent IL-6 production during pulmonary inflammation.

Inhibition of ROCK activity allows InlF-mediated invasion and increased virulence of Listeria monocytogenes

Listeria monocytogenes is an intracellular bacterial pathogen that causes life-threatening disease. The mechanisms used by L. monocytogenes to invade non-professional phagocytic cells are not fully understood. In addition to the requirement of bacterial determinants, host cell conditions profoundly influence infection. Here, we have shown that inhibition of the RhoA/ROCK pathway by pharmacological inhibitors or RNA interference results in increased L. monocytogenes invasion of murine fibroblasts and hepatocytes. InlF, a member of the internalin multigene family with no known function, was identified as a L. monocytogenes-specific factor mediating increased host cell binding and entry. Conversely, activation of RhoA/ROCK activity resulted in decreased L. monocytogenes adhesion and invasion. Furthermore, virulence of wild-type bacteria during infection of mice was significantly increased upon inhibition of ROCK activity, whereas colonization and virulence of an inlF deletion mutant was not affected, thus supporting a role for InlF as a functional virulence determinant in vivo under specific conditions. In addition, inhibition of ROCK activity in human-derived cells enhanced either bacterial adhesion or adhesion and entry in an InlF-independent manner, further suggesting a host species or cell type-specific role for InlF and that additional bacterial determinants are involved in mediating ROCK-regulated invasion of human cells.

Chronic hypoxia induces Rho kinase-dependent myogenic tone in small pulmonary arteries

Myogenic tone in the pulmonary vasculature of normoxic adult animals is minimal or nonexistent. Whereas chronic hypoxia (CH) increases basal tone in pulmonary arteries, it is unclear if a portion of this elevated tone is due to development of myogenicity. Since basal arterial RhoA activity and Rho kinase (ROK) expression are augmented by CH, we hypothesized that CH elicits myogenic reactivity in pulmonary arteries through ROK-dependent vascular smooth muscle (VSM) Ca(2+) sensitization. To test this hypothesis, we assessed the contribution of ROK to basal tone and pressure-induced vasoconstriction in endothelium-disrupted pulmonary arteries [50-300 microm inner diameter (ID)] from control and CH [4 wk at 0.5 atmosphere (atm)] rats. Arteries were loaded with fura-2 AM to continuously monitor VSM intracellular Ca(2+) concentration ([Ca(2+)](i)). Basal VSM [Ca(2+)](i) was not different between groups. The ROK inhibitor, HA-1077 (100 nM to 30 microM), caused a concentration-dependent reduction of basal tone in CH arteries but had no effect in control vessels. In contrast, PKC inhibition with GF109203X (1 microM) did not alter basal tone. Furthermore, significant vasoconstriction in response to stepwise increases in intraluminal pressure (5-45 mmHg) was observed at 12, 15, 25, and 35 mmHg in arteries (50-200 microm ID) from CH rats. This myogenic reactivity was abolished by HA-1077 (10 microM) but not by GF109203X. VSM [Ca(2+)](i) was unaltered by HA-1077, GF109203X, or increases in pressure in either group. Myogenicity was not observed in larger vessels (200-300 microm ID). We conclude that CH induces myogenic tone in small pulmonary arteries through ROK-dependent myofilament Ca(2+) sensitization.

ROCK enzymatic assay

We describe the protocols for measuring Rho-associated coiled-coil-containing kinase (ROCK) activity in vitro. A His-tagged, constitutively active form of the protein (lacking C-terminal inhibitory domains) is expressed in baculovirus. The protein is purified by a combination of metal affinity, ion exchange, and size exclusion chromatography. Enzymatic activity is measured spectrophotometrically in a coupled assay format wherein a molecule of NADH is oxidized to NAD+ each time a phosphate is transferred by ROCK.

Flavone inhibits vascular contraction by decreasing phosphorylation of the myosin phosphatase target subunit

1. Flavonoids modulate vascular tone through an endothelium-dependent or -independent mechanism. Although a few mechanisms for endothelium-independent relaxation have been suggested, such as interference with protein kinase C or cAMP or cGMP phosphodiesterase, the inhibition of Ca(2+) release from intracellular stores or Ca(2+) influx from extracellular fluids, the mode of action of flavonoids remains elusive. 2. We hypothesized that treatment with flavone inhibits vascular smooth muscle contraction by decreasing the phosphorylation of the myosin phosphatase target subunit (MYPT1). 3. Rat aortic rings were denuded of endothelium, mounted in organ baths and contracted with U46619, a thromboxane A(2) analogue. 4. Flavone dose-dependently inhibited the U46619-induced contractile response and myosin light chain (MLC(20)) phosphorylation. At 10(-7) mol/L, U46619 induced vascular contraction with the concomitant phosphorylation of MYPT1 at Thr855, but not at Thr697. Incubation with flavone (100 or 300 micromol/L) for 30 min attenuated the phosphorylation of MYPT1(Thr855), but not MYPT1(Thr697). 5. It is concluded that treatment with flavone inhibits vascular smooth muscle contraction by decreasing the phosphorylation of the MYPT1. These results suggest that flavone causes endothelium-independent relaxation through, at least in part, the inhibition of p160 Rho-associated coiled-coil-containing protein kinase (ROCK) signalling.

Angiotensin II/AT2 receptor-induced vasodilation in stroke-prone spontaneously hypertensive rats involves nitric oxide and cGMP-dependent protein kinase

BACKGROUND

Angiotensin II (Ang II) induces vasodilation, in part, through angiotensin type 2 receptor (AT2R)-induced actions in conditions associated with angiotensin type 1 receptor (AT1R) blockade and AT2R upregulation. Ang II/AT2R-induced vasodilation involves nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-dependent processes. We previously demonstrated that AT2R-mediated effects involve inhibition of the RhoA/Rho kinase pathway. However, molecular mechanisms underlying this phenomenon are unknown.

AIMS

In the present in-vivo study we tested the hypothesis that AT2R-elicited vasodilation is associated with nitric oxide synthase (NOS) activation and NO production, and that a cGMP-dependent protein kinase (cGKI), which inactivates RhoA, is upregulated when stroke-prone spontaneously hypertensive rats (SHRSP) are treated with AT1R blockers.

METHODS

SHRSP and Wistar-Kyoto (WKY) rats were treated with the AT1R blocker valsartan for 14 days. Dilatory responses to Ang II with or without the NOS inhibitor N-nitro-L-arginine methyl ester (L-NAME) were performed in norepinephrine-precontracted vessels in the presence of valsartan. Expression of AT2R, endothelial NOS (eNOS) and cGKI was assessed by immunoblotting. NO bioavailability and NAD(P)H oxidase activity were evaluated by chemiluminescence.

RESULTS

Ang II elicited vasodilation in valsartan-treated SHRSP. L-NAME inhibited this effect, indicating a role for NO. eNOS expression and NO concentration were increased twofold by valsartan, only in SHRSP. Expression of cGKI was reduced in SHRSP and restored after valsartan treatment. NAD(P)H oxidase activity was approximately threefold higher in SHRSP versus WKY (P < 0.05) and reduced by valsartan.

CONCLUSIONS

Ang II, via AT2R, facilitates vasodilation through NOS/NO-mediated pathways and upregulation [corrected] of CGK1 [corrected] after chronic AT1R antagonism. These effects may contribute in part to beneficial actions of AT1R blockers in the treatment of hypertension.

Scaffold mediated regulation of MAPK signaling and cytoskeletal dynamics: a perspective

Cell migration is critical for many physiological processes and is often misregulated in developmental disorders and pathological conditions including cancer and neurodegeneration. MAPK signaling and the Rho family of proteins are known regulators of cell migration that exert their influence on cellular cytoskeleton during cell adhesion and migration. Here we review data supporting the view that localized ERK signaling mediated through recently identified scaffold proteins may regulate cell migration.

Postnatal maturation modulates relationships among cytosolic Ca2+, myosin light chain phosphorylation, and contractile tone in ovine cerebral arteries

The present study tests the hypothesis that age-related changes in patterns of agonist-induced myofilament Ca(2+) sensitization involve corresponding differences in the relative contributions of thick- and thin-filament regulation to overall myofilament Ca(2+) sensitivity. Posterior communicating cerebral arteries from term fetal and nonpregnant adult sheep were used in measurements of cytosolic Ca(2+), myosin light chain (MLC) phosphorylation, and contractile tensions induced by varying concentrations of K(+) or serotonin [5-hydroxytryptamine (5-HT)]. The results were used to assess the relative contributions of the relationships between cytosolic Ca(2+) and MLC phosphorylation (thick-filament reactivity), along with the relationships between MLC phosphorylation and contractile tension (thin-filament reactivity), to overall myofilament Ca(2+) sensitivity. For K(+)-induced contractions, both fetal and adult arteries exhibited similar basal myofilament Ca(2+) sensitivity. Despite this similarity, thick-filament reactivity was greater in fetal arteries, whereas thin-filament reactivity was greater in adult arteries. In contrast, 5-HT-induced contractions exhibited increased myofilament Ca(2+) sensitivity compared with K(+)-induced contractions for both fetal and adult cerebral arteries, and the magnitude of this effect was greater in fetal compared with adult arteries. When interpreted together with our previous studies of 5-HT-induced myofilament Ca(2+) sensitization, we attributed the present effects to agonist enhancement of thick-filament reactivity in fetal arteries mediated by G protein receptor activation of a PKC-independent but RhoA-dependent pathway. In adult arteries, agonist stimulation enhanced thin-filament reactivity was also probably mediated through G protein-coupled activation of RhoA-dependent and PKC-independent mechanisms. Overall, the present data demonstrate that agonist-enhanced myofilament Ca(2+) sensitivity can be partitioned into separate thick- and thin-filament effects, the magnitudes of which are different between fetal and adult cerebral arteries.

Sevoflurane, but not propofol, prevents Rho kinase-dependent contraction induced by sphingosylphosphorylcholine in the porcine coronary artery

BACKGROUND

Sphingosylphosphorylcholine may induce coronary vasospasm by the activation of Rho kinase. We designed the current study to examine the differential effects of anesthetics on Rho kinase activation induced by sphingosylphosphorylcholine in porcine coronary arteries.

METHODS

Rings of porcine coronary artery without endothelium were prepared in tissue bath containing modified Krebs-Ringer bicarbonate solution. Using isometric force recording, concentration-response curves in response to sphingosylphosphorylcholine were obtained in the absence or in the presence of sevoflurane, propofol, or a selective Rho kinase inhibitor Y27632, which was added 15 min before the application of sphingosylphosphorylcholine. Intracellular translocation of Rho A toward the plasma membrane and phosphorylation of the myosin-targeting subunit of myosin light chain phosphatase were also evaluated by Western blotting.

RESULTS

Sphingosylphosphorylcholine (10(-7) to 10(-5) M) produced contraction of the porcine coronary artery, which was abolished by a selective Rho kinase inhibitor Y27632 (2 x 10(-6) M). Sevoflurane (1.7%) reduced sphingosylphosphorylcholine-induced coronary artery constriction, and the higher concentration (3.4%) abolished it (P < 0.05). In contrast, propofol (3 x 10(-6) M and 10(-5) M) had no effect on coronary artery constriction due to sphingosylphosphorylcholine. Sevoflurane, but not propofol, reduced intracellular translocation of Rho A toward the plasma membrane. Sevoflurane and Y27632, but not propofol, similarly decreased (64.4% or 70.8% reduction, respectively, P < 0.05) phosphorylation of the myosin-targeting subunit of myosin light chain phosphatase.

CONCLUSIONS

Sphingosylphosphorylcholine induces coronary vasocontriction via activation of Rho kinase. Sevoflurane, but not propofol, inhibits this pathway, resulting in prevention of vasoconstriction.

Rho kinase is an effector underlying Ca2+-desensitizing hypoxic relaxation in porcine coronary artery

Acute hypoxia dilates most systemic arteries leading to increased tissue perfusion. We have previously shown that at high-stimulus conditions, porcine coronary artery was relaxed by hypoxia without a change in intracellular [Ca2+] ( 27 ). This Ca2+-desensitizing hypoxic relaxation (CDHR) was validated in permeabilized porcine coronary artery smooth muscle (PCASM) in which hypoxia decreased force and myosin regulatory light chain phosphorylation (p-MRLC) despite fixed [Ca2+] ( 10 ). Rho kinase-dependent phosphorylation of myosin phosphatase-targeting subunit 1 (p-MYPT1) is associated with decreased MRLC phosphatase activity and increased Ca2+ sensitivity of both p-MRLC and force. We recently reported that p-MYPT1 dephosphorylation was a key effector in CDHR ( 33 ). In the current study, we tested the hypothesis that Rho kinase and not p-MYPT1 phosphatase is the regulated enzyme involved in CDHR. We used α-toxin to permeabilize deendothelialized PCASM. CDHR was attenuated in contractions attributable to myosin light chain kinase (MLCK, in the presence of the Rho kinase inhibitor Y-27632). In contrast, hypoxia relaxed contractions attributable to Rho kinase phosphorylation of MYPT1 and MRLC or MRLC alone (in the presence of the MLCK inhibitor ML7). Using an in situ assay, we showed that Rho kinase activity, measured as thiophosphorylation of MYPT1 and MRLC, was nearly abolished by hypoxia. The in vitro activity of the catalytically active fragment of Rho kinase was not affected by hypoxia. Our evidence strongly implicates that hypoxia directly inhibits Rho kinase-dependent phosphorylation of MYPT1. This underlies the decreases in both p-MYPT1 and p-MRLC and thereby leads to the Ca2+-desensitizing hypoxic relaxation.

Ca2+ signaling in hypoxic pulmonary vasoconstriction: effects of myosin light chain and Rho kinase antagonists

Antagonists of myosin light chain (MLC) kinase (MLCK) and Rho kinase (ROK) are thought to inhibit hypoxic pulmonary vasoconstriction (HPV) by decreasing the concentration of phosphorylated MLC at any intracellular Ca(2+) concentration ([Ca(2+)](i)) in pulmonary arterial smooth muscle cells (PASMC); however, these antagonists can also decrease [Ca(2+)](i). To determine whether MLCK and ROK antagonists alter Ca(2+) signaling in HPV, we measured the effects of ML-9, ML-7, Y-27632, and HA-1077 on [Ca(2+)](i), Ca(2+) entry, and Ca(2+) release in rat distal PASMC exposed to hypoxia or depolarizing concentrations of KCl. We performed parallel experiments in isolated rat lungs to confirm the inhibitory effects of these agents on pulmonary vasoconstriction. Our results demonstrate that MLCK and ROK antagonists caused concentration-dependent inhibition of hypoxia-induced increases in [Ca(2+)](i) in PASMC and HPV in isolated lungs and suggest that this inhibition was due to blockade of Ca(2+) release from the sarcoplasmic reticulum and Ca(2+) entry through store- and voltage-operated Ca(2+) channels in PASMC. Thus MLCK and ROK antagonists might block HPV by inhibiting Ca(2+) signaling, as well as the actin-myosin interaction, in PASMC. If effects on Ca(2+) signaling were due to decreased phosphorylated myosin light chain concentration, their diversity suggests that MLCK and ROK antagonists may have acted by inhibiting myosin motors and/or altering the cytoskeleton in a manner that prevented achievement of required spatial relationships among the cellular components of the response.

Cellular regulation of basal tone in internal anal sphincter smooth muscle by RhoA/ROCK

Sustained contractions of smooth muscle cells (SMC) maintain basal tone in the internal anal sphincter (IAS). To examine the molecular bases for the myogenic tone in the IAS, the present studies focused on the role of RhoA/ROCK in the SMC isolated from the IAS vs. the adjoining phasic tissues of the rectal smooth muscle (RSM) and anococcygeus smooth muscle (ASM) of rat. We also compared cellular distribution of RhoA/ROCK, levels of RhoA-GTP, RhoA-Rho guanine nucleotide dissociation inhibitor (GDI) complex formation, levels of p(Thr696)-MYPT1, and SMC relaxation caused by RhoA inhibition. Levels of RhoA/ROCK were higher at the cell membrane in the IAS SMC compared with those from the RSM and ASM. C3 exoenzyme (RhoA inhibitor) and Y 27632 (ROCK inhibitor) caused a concentration-dependent relaxation of the IAS SMC. In addition, active ROCK-II (primary isoform of ROCK in SMC) caused further shortening in the IAS SMC. C3 exoenzyme increased RhoA-RhoGDI binding and reduced the levels of RhoA-GTP and p(Thr696)-MYPT1. ROCK inhibitor attenuated PKC-induced contractions in IAS SMC. Conversely, a PKC inhibitor (Gö 6850, which causes partial relaxation of the SMC) had no significant effect on ROCK-II-induced contractions. Further experiments showed the highest levels of RhoA, active form of RhoA (RhoA-GTP), ROCK-II, 20-kDa myosin regulatory light chain (MLC(20)), phospho-MYPT1, and phospho-MLC(20) in the IAS vs. RSM and ASM SMC. However, the trend was the reverse with the levels of inactive RhoA (GDP-RhoA-RhoGDI complex) and MYPT1. We conclude that RhoA/ROCK play a critical role in maintenance of spontaneous tone in the IAS SMC via inhibition of myosin light chain phosphatase.

A microfabricated platform probing cytoskeleton dynamics using multidirectional topographical cues

Cell migration, which involves complicated coordination of cytoskeleton elements and regulatory molecules, plays a central role in a large variety of biological processes from development, immune response to tissue regeneration. However, conventional methods to study in vitro cell migration are often limited to stimulating a cell along a single direction or at a single location. This restriction prevents a deeper understanding of the fundamental mechanisms that control the spatio-temporal dynamics of cytoskeleton. Here we report a novel microfabricated platform that enables a multi-directional stimulation to a cell using topographical cues. In this device, cells were seeded on a grid-patterned topographically structured surface composed of 2 microm wide and 2 microm high straight ridges. Because the size of a unit grid was smaller than a single cell, each cell was simultaneously experiencing contact guidance leading to different directions. The device showed that healthy cells preferred to align and migrate in the direction of the longer side of the grid. But cells with impaired intracelluar tension force generation exhibited multiple uncoordinated cell protrusions along guiding ridges in all directions. Our results demonstrate the importance of actomyosin network in long-range communication and regulation of local actin polymerization activities. This platform will find wide applications in investigations of signal transduction and regulation process in cell migration.

Selective adapter recruitment and differential signaling networks by VEGF vs. shear stress

Vascular endothelial cells are continuously exposed to mechanical and chemical stimuli, such as shear stress and VEGF, respectively. It is still not clear how cells perceive these stimuli and orchestrate their responses. Studying the molecular mechanism by which shear stress and VEGF regulate the signaling pathways in bovine endothelial aortic cells, we found that VEGF induced a rapid association of VEGF receptor 2 (Flk-1) with Nck beta, but shear stress did not have such an effect. SU1498 (a specific inhibitor of Flk-1) and Nck beta(nm) (a negative mutant of Nck beta) blocked the VEGF-induced ERK and JNK activities. Only SU1498, but not Nck beta(nm), inhibited the shear-induced ERK activity. Furthermore, neither SU1498 nor Nck beta(nm) had significant effects on the shear-induced JNK activity, which can be blocked by inhibitors of Src family kinase and ROCK kinase. Therefore, mechanical (shear stress) and chemical (VEGF) stimuli diverge at the receptor Flk-1 in terms of the recruitment of the adapter protein Nck beta, and they employ different components of the complex signaling network in regulating downstream molecules, e.g., ERK and JNK.

Development of Rho-kinase inhibitors for cardiovascular medicine

Rho-kinase (ROCK) is one of the downstream effectors of the small G-protein Rho. The Rho-ROCK pathway has an important role in mediating various cellular functions, including contraction, actin cytoskeleton organization, cell adhesion and motility, proliferation, cytokinesis and gene expression, all of which are involved in the pathogenesis of cardiovascular disease. Indeed, vascular smooth muscle cells, endothelial cells, adventitial cells, cardiomyocytes and nerve cells all undergo pathophysiological changes through the ROCK pathway. Abnormal activation of this pathway is associated with the pathogenesis of various cardiovascular diseases such as hypertension, coronary and cerebral vasospasm, restenosis, atherosclerosis, stroke and heart failure, although the roles of the ROCK isoforms (ROCK1 and ROCK2) remain to be elucidated. In this article, we review the information about the therapeutic importance of the ROCK pathway and summarize the current status of the development of ROCK inhibitors.

Rho-kinase dependent organization of stress fibers and focal adhesions in cultured fibroblasts

The activation of Rho-kinase is known to modulate the organization of the actin-based cytoskeletal systems, including the formation of stress fibers and focal adhesions. Rho-kinase likely plays a more crucial and complex role in the organization of actin-based cytoskeletal systems than in that of myosin light chain kinase (MLCK). In order to understand the role of Rho-kinase in the organization of stress fibers and focal adhesions, we treated cultured fibroblasts with a Rho-kinase inhibitor and analyzed the stress fiber and focal adhesion organization under conventional fluorescence microscopy and replica electron microscopy. Some of the cells were transfected with GFP-labeled paxillin, actin or alpha-actinin, and the effects of the inhibitor were monitored in the living cells. The Rho-kinase inhibitor caused disassembly of the stress fibers and focal adhesions in the central portion of the cell within 1 h. However, the stress fibers and focal adhesions located in the cell periphery were not as severely affected by the Rho-kinase inhibitor. The time-lapse video recording revealed that when these cells were washed with a fresh medium in order to remove the Rho-kinase inhibitor, the stress fibers and focal adhesions located in the center of the cell gradually reorganized and, within 1.5-2 h, the cells completely recovered. This observation strongly suggests that the activation of Rho-kinase plays an important role in the organization of the central stress fibers and focal adhesions.

Acto-myosin reorganization and PAR polarity in C. elegans

The symmetry-breaking event during polarization of C. elegansembryos is an asymmetric rearrangement of the acto-myosin network, which dictates cell polarity through the differential recruitment of PAR proteins. The sperm-supplied centrosomes are required to initiate this cortical reorganization. Several questions about this event remain unanswered: how is the acto-myosin network regulated during polarization and how does acto-myosin reorganization lead to asymmetric PAR protein distribution? As we discuss,recent studies show that C. elegans embryos use two GTPases, RHO-1 and CDC-42, to regulate these two steps in polarity establishment. Although RHO-1 and CDC-42 control distinct aspects of polarization, they function interdependently to regulate polarity establishment in C. elegansembryos.

Rho kinase in the regulation of cell death and survival

Rho kinase (ROCK) belongs to a family of serine/threonine kinases that are activated via interaction with Rho GTPases. ROCK is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, and proliferation. Recent studies have shown that ROCK plays an important role in the regulation of apoptosis in various cell types and animal disease models. Two ROCK isoforms, ROCK1 and ROCK2, are assumed to be function redundant, this based largely on kinase construct overexpression and chemical inhibitors (Y27632 and fasudil) which inhibit both ROCK1 and ROCK2. Gene targeting and RNA interference approaches allow further dissection of distinct cellular, physiological, and patho-physiological functions of the two ROCK isoforms. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of ROCK signaling in the regulation of apoptosis and highlights new findings from recently generated ROCK-deficient mice.

Pressor response induced by central angiotensin II is mediated by activation of Rho/Rho-kinase pathway via AT1 receptors

OBJECTIVES

The brain renin-angiotensin system plays an important role in cardiovascular regulation and the pathogenesis of hypertension. Angiotensin II activates the Rho/Rho-kinase pathway in vascular smooth muscle cells and cardiomyocytes in vitro. The aim of the present study was to determine whether angiotensin II in the brainstem activates the Rho/Rho-kinase pathway, and, if so, whether this mechanism is involved in the central pressor action of angiotensin II.

METHODS AND RESULTS

Angiotensin II infused intracisternally for 7 days in Wistar-Kyoto rats (WKY) increased systolic blood pressure (SBP) and urinary norepinephrine excretion. These responses were abolished by the co-infusion of Y-27632, a specific Rho-kinase inhibitor, or valsartan. The intracisternal infusion of Y-27632 or valsartan also reduced SBP and norepinephrine excretion in spontaneously hypertensive rats (SHR). Western blot analysis was performed to examine the expression levels of membranous RhoA and phosphorylated ezrin, radixin, and moesin (p-ERM), which reflects Rho/Rho-kinase activity. The expression levels of membranous RhoA and p-ERM in the brainstem were significantly greater in both angiotensin II-treated WKY and SHR than in vehicle-treated WKY. Valsartan reduced the expression levels of membranous RhoA and p-ERM in angiotensin II-treated WKY and SHR. Y-27632 reduced the expression levels of p-ERM in angiotensin II-treated WKY and SHR.

CONCLUSIONS

These results suggest that the pressor response induced by intracisternally infused angiotensin II is substantially mediated by the activation of the Rho/Rho-kinase pathway via AT1 receptors of the brainstem in WKY, and that this pathway might be involved in the hypertensive mechanisms of SHR.

Up-regulation of myometrial RHO effector proteins (PKN1 and DIAPH1) and CPI-17 (PPP1R14A) phosphorylation in human pregnancy is associated with increased GTP-RHOA in spontaneous preterm labor

RHO GTP-binding proteins are important regulators of actin-myosin interactions in uterine smooth muscle cells. Active (GTP-bound) RHOA binds to RHO-associated protein kinase (ROCK1), which inhibits the myosin-binding subunit (PPP1R12A) of myosin light chain phosphatase, leading to calcium-independent increases in myosin light chain phosphorylation and tension, which are termed "calcium sensitization." The RHO effector protein kinase N (PKN1) also increases calcium sensitization by phosphorylating the protein kinase C (PRKCB)-dependent protein CPI-17 (PPP1R14A) to inhibit the PPP1c subunit of myosin phosphatase. Moreover, other RHO proteins, such as RHOB, RHOD, and their effectors (DIAPH1 and DIAPH2), may modulate PKN1/ ROCK1 signaling to effect changes in myosin phosphatase activity and myosin light chain phosphorylation. The increases in contractile activity observed in term and preterm labor may be due to an increase in RHO activity and/or changes in RHO-related proteins. We found that the RHOA and RHOB mRNA levels in the myometrium were increased in pregnancy, although the expression levels of the RHOA and RHOB proteins did not change with pregnancy or labor. GTP-bound RHOA was increased in pregnancy, and this increase was significant in spontaneous preterm labor myometrium. PKN1 expression and PPP1R14A phosphorylation were dramatically increased in the pregnant myometrium. We also observed increases in DIAPH1 expression in spontaneous term and preterm labor myometrial tissues. The present study shows that human pregnancy is characterized by increases in PKN1 expression and PPP1R14A phosphorylation in the myometrium. Moreover, increases in GTP-bound RHOA and DIAPH1 expression may contribute to the increase in uterine activity in idiopathic preterm labor.

ArhGAP9, a novel MAP kinase docking protein, inhibits Erk and p38 activation through WW domain binding

We have identified human ArhGAP9 as a novel MAP kinase docking protein that interacts with Erk2 and p38alpha through complementarily charged residues in the WW domain of ArhGAP9 and the CD domains of Erk2 and p38alpha. This interaction sequesters the MAP kinases in their inactive states through displacement of MAP kinase kinases targeting the same sites. While over-expression of wild type ArhGAP9 caused MAP kinase activation by the epidermal growth factor receptor (EGFR) to be suppressed and preserved the actin stress fibres in quiescent Swiss 3T3 fibroblasts, over-expression of an ArhGAP9 mutant defective in MAP kinase binding restored EGFR-induced MAP kinase activation and resulted in significant disruption of the stress fibres, consistent with the role of Erk activation in disassembly of actin stress fibres. The interaction between ArhGAP9 and the MAP kinases represents a novel mechanism of cross-talk between Rho GTPase and MAP kinase signaling.

Diguanosine pentaphosphate: an endogenous activator of Rho-kinase possibly involved in blood pressure regulation

OBJECTIVE

Rho-kinase activity is increased in cardiovascular disease and in the pathophysiology of hypertension. Few endogenous factors are known that activate the Rho-kinase pathway. Stimulation of P2Y receptors activates the Rho-kinase pathway. Recently identified diguanosine pentaphosphate (Gp5G) possibly activates P2Y receptors. In this study, Gp5G was identified and quantified in human plasma. The influence of Gp5G on vascular tone was studied.

METHODS

Gp5G in human plasma was purified to homogeneity by several steps. Gp5G was quantified and identified by matrix-assisted laser desorption/ionization mass spectrometry and enzymatic analysis. The vasoactive effects of Gp5G were studied in the isolated perfused rat kidney and after intra-aortic application. Activation of Rho-kinase was measured using western blot analysis.

RESULTS

The plasma level of Gp5G in healthy donors is 9.47 +/- 4.97 nmol/l. Gp5G increases contractile responses induced by angiotensin II in a dose-dependent way [ED50 (-log mol) angiotensin II: 10.9 +/- 0.1; angiotensin II plus Gp5G (100 nmol/l): 11.5 +/- 0.1]. P2 receptor antagonists inhibited the Gp5G-induced increase in angiotensin II vasoconstriction. MRS2179, a selective P2Y1 receptor antagonist, had no effect on Gp5G-mediated angiotensin II potentiation. Rho-kinase inhibition by Y27632 abolished the Gp5G-induced increase of contractile responses to angiotensin II. Concentrations of 10 nmol/l Gp5G activated the translocation of RhoA from the cytosolic to the membranous fraction indicating the activation of Rho-kinase. The intra-aortic application of 100 pmol Gp5G significantly increased mean arterial blood pressure by 13.5 +/- 4.2 mmHg.

CONCLUSION

Gp5G is an endogenous activator of Rho-kinase, which might affect vascular tone control by Rho-kinase at physiological levels. Gp5G activates P2Y4&6 receptors, and might play a role in physiological and pathophysiological vascular tone control.

Roles of rho-associated kinase and oxidative stress in the pathogenesis of aortic stiffness

OBJECTIVES

The purpose of this study was to determine the relationship between Rho-associated kinase (ROCK) activity and aortic stiffness in humans.

BACKGROUND

Epidemiologic studies have shown that there is a relationship between aortic stiffness and cardiovascular complications. Recent evidence suggests that ROCK plays an important role in the process of atherosclerosis.

METHODS

We evaluated the forearm blood flow (FBF) response to sodium nitroprusside (SNP), a nitric oxide donor, acetylcholine (ACh), an endothelium-dependent vasodilator, and fasudil, a specific ROCK inhibitor, in 51 healthy male subjects (mean age 45.6 +/- 3.0 years). The FBF was measured by using a strain-gauge plethysmography. Carotid-femoral pulse wave velocity (cf-PWV) was measured to assess the aortic stiffness using a pulse wave velocimeter.

RESULTS

Intra-arterial infusion of SNP alone, ACh alone, or fasudil alone and after co-infusion of N(G)-monomethyl-L-arginine (L-NMMA), a nitric-oxide synthase inhibitor, significantly increased FBF in a dose-dependent manner (p < 0.01). Multivariate analysis showed that age and number of pack-years smoked were independent predictors of ROCK activity before or after co-infusion of L-NMMA (p < 0.01) and that age and ROCK activity before or after co-infusion of L-NMMA were independent predictors of cf-PWV (p < 0.01). The concentration of serum malondialdehyde-modified low-density lipoprotein, an index of oxidative stress, was significantly correlated with ROCK activity before and after co-infusion of L-NMMA and cf-PWV (p < 0.01).

CONCLUSIONS

These findings suggest that aging and accumulating smoking habit, which might induce excessive oxidative stress, are involved in ROCK activity in the vasculature, leading to an increase in aortic stiffness in humans.

Proplatelet formation is regulated by the Rho/ROCK pathway

Platelets are released by megakaryocytes (MKs) via cytoplasmic extensions called proplatelets, which require profound changes in the microtubule and actin organization. Here, we provide evidence that the Rho/ROCK pathway, a well-known regulator of actin cytoskeleton, acts as a negative regulator of proplatelet formation (PPF). Rho is expressed at a high level during the entire MK differentiation including human CD34(+) cells. Thrombopoietin stimulates its activity but at a higher extent in immature than in mature MKs. Overexpression of a dominant-negative or a spontaneously active RhoA leads to an increase or a decrease in PPF indicating that Rho activation inhibits PPF. This inhibitory effect is mediated through the main Rho effector, Rho kinase (ROCK), the inhibition of which also increases PPF. Furthermore, inhibition of Rho or ROCK in MKs leads to a decrease in myosin light chain 2 (MLC2) phosphorylation, which is required for myosin contractility. Interestingly, inhibition of the MLC kinase also decreases MLC2 phosphorylation while increasing PPF. Taken together, our results suggest that MLC2 phosphorylation is regulated by both ROCK and MLC kinase and plays an important role in platelet biogenesis by controlling PPF and fragmentation.

Statins may ameliorate pulmonary hypertension via RhoA/Rho-kinase signaling pathway

Statins are the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors that function as potent inhibitors of cholesterol biosynthesis and have been used for many years for the treatment of hypercholesterolemia. However, accumulating experimental and clinical studies have revealed that the health benefits associated with statins treatment, particularly those conferred on the cardiovascular system, were the cholesterol-independent. Because statins inhibit an early step in the cholesterol biosynthetic pathway, they also inhibit the synthesis of isoprenoids such as farnesylpyrophosphate and geranylgeranylpyrophosphate, which are important postranslational lipid attachments for intracellular signaling molecules such as the Rho GTPases. The isoprenylation of Rho is a prerequisite for Rho activation, facilitating its interaction with the plasma membrane, undergoing GDP-GTP exchange and be activated. Inhibition of RhoA geranylgeranylation by statins decreases membrane GTP-bound active RhoA and subsequent Rho-kinase activity. Activated RhoA via its downstream effector Rho-kinase is involved in a wide range of cellular functions, such as cell migration, proliferation and apoptosis. Recently, rising evidences suggested that RhoA/Rho-kinase pathway was essentially involved in various models of pulmonary hypertension and statins effectively ameliorated pulmonary hypertension. Based on this findings, we hypothesis that statins attenuate pulmonary hypertension via RhoA/Rho-kinase signaling pathway in vivo.