Arachidonic acid-induced Ca2+ sensitization of smooth muscle contraction through activation of Rho-kinase

Selective inhibition of neurogenic, but not agonist-induced contractions by phospholipase A2 inhibitors points to presynaptic phospholipase A2 functions in contractile neurotransmission to human prostate smooth muscle

BACKGROUND

Phospholipases A2 (PLA2 ) may be involved in α1 -adrenergic contraction by formation of thromboxane A2 in different smooth muscle types. However, whether this mechanism occurs with α1 -adrenergic contractions of the prostate, is still unknown. While α1 -adrenoceptor antagonists are the first line option for medical treatment of voiding symptoms in benign prostatic hyperplasia (BPH), improvements are limited, probably by nonadrenergic contractions including thromboxane A2 . Here, we examined effects of PLA2 inhibitors on contractions of human prostate tissues.

METHODS

Prostate tissues were obtained from radical prostatectomy. Contractions were induced by electric field stimulation (EFS) and by α1 -adrenergic agonists in an organ bath, after application of the cytosolic PLA2 inhibitors ASB14780 and AACOCF3, the secretory PLA2 inhibitor YM26734, the leukotriene receptor antagonist montelukast, or of solvent to controls.

RESULTS

Frequency-dependent contractions of human prostate tissues induced by EFS were inhibited by 25% at 8 Hz, 38% at 16 Hz and 37% at 32 Hz by ASB14780 (1 µM), and by 32% at 16 Hz and 22% at 32 Hz by AACOCF3 (10 µM). None of both inhibitors affected contractions induced by noradrenaline, phenylephrine or methoxamine. YM26734 (3 µM) and montelukast (0.3 and 1 µM) neither affected EFS-induced contractions, nor contractions by α1 -adrenergic agonists, while all contractions were substantially inhibited by silodosin (100 nM).

CONCLUSIONS

Our findings suggest presynaptic PLA2 functions in prostate smooth muscle contraction, while contractions induced by α1 -adrenergic agonists occur PLA2 -independent. Lacking sensitivity to montelukast excludes an involvement of PLA2 -derived leukotrienes in promotion of contractile neurotransmission.

Chylomicrons Regulate Lacteal Permeability and Intestinal Lipid Absorption

BACKGROUND

Lymphatic vessels are responsible for tissue drainage, and their malfunction is associated with chronic diseases. Lymph uptake occurs via specialized open cell-cell junctions between capillary lymphatic endothelial cells (LECs), whereas closed junctions in collecting LECs prevent lymph leakage. LEC junctions are known to dynamically remodel in development and disease, but how lymphatic permeability is regulated remains poorly understood.

METHODS

We used various genetically engineered mouse models in combination with cellular, biochemical, and molecular biology approaches to elucidate the signaling pathways regulating junction morphology and function in lymphatic capillaries.

RESULTS

By studying the permeability of intestinal lacteal capillaries to lipoprotein particles known as chylomicrons, we show that ROCK (Rho-associated kinase)-dependent cytoskeletal contractility is a fundamental mechanism of LEC permeability regulation. We show that chylomicron-derived lipids trigger neonatal lacteal junction opening via ROCK-dependent contraction of junction-anchored stress fibers. LEC-specific ROCK deletion abolished junction opening and plasma lipid uptake. Chylomicrons additionally inhibited VEGF (vascular endothelial growth factor)-A signaling. We show that VEGF-A antagonizes LEC junction opening via VEGFR (VEGF receptor) 2 and VEGFR3-dependent PI3K (phosphatidylinositol 3-kinase)/AKT (protein kinase B) activation of the small GTPase RAC1 (Rac family small GTPase 1), thereby restricting RhoA (Ras homolog family member A)/ROCK-mediated cytoskeleton contraction.

CONCLUSIONS

Our results reveal that antagonistic inputs into ROCK-dependent cytoskeleton contractions regulate the interconversion of lymphatic junctions in the intestine and in other tissues, providing a tunable mechanism to control the lymphatic barrier.

Conformational Change of Tetratricopeptide Repeats Region Triggers Activation of Phytochrome-Associated Protein Phosphatase 5

Phytochrome activity is not only controlled by light but also by post-translational modifications, e. g. phosphorylation. One of the phosphatases responsible for plant phytochrome dephosphorylation and thereby increased activity is the phytochrome-associated protein phosphatase 5 (PAPP5). We show that PAPP5 recognizes phospho-site mimicking mutants of phytochrome B, when being activated by arachidonic acid (AA). Addition of AA to PAPP5 decreases the α-helical content as tracked by CD-spectroscopy. These changes correspond to conformational changes of the regulatory tetratricopeptide repeats (TPR) region as shown by mapping data from hydrogen deuterium exchange mass spectrometry onto a 3.0 Å crystal structure of PAPP5. Surprisingly, parts of the linker between the TPR and PP2A domains and of the so-called C-terminal inhibitory motif exhibit reduced deuterium uptake upon AA-binding. Molecular dynamics analyses of PAPP5 complexed to a phyB phosphopeptide show that this C-terminal motif remains associated with the TPR region in the substrate bound state, suggesting that this motif merely serves for restricting the orientations of the TPR region relative to the catalytic PP2A domain. Given the high similarity to mammalian PP5 these data from a plant ortholog show that the activation mode of these PPP-type protein phosphatases is highly conserved.

Nonmuscle Myosin II Regulation Directs Its Multiple Roles in Cell Migration and Division

Nonmuscle myosin II (NMII) is a multimeric protein complex that generates most mechanical force in eukaryotic cells. NMII function is controlled at three main levels. The first level includes events that trigger conformational changes that extend the complex to enable its assembly into filaments. The second level controls the ATPase activity of the complex and its binding to microfilaments in extended NMII filaments. The third level includes events that modulate the stability and contractility of the filaments. They all work in concert to finely control force generation inside cells. NMII is a common endpoint of mechanochemical signaling pathways that control cellular responses to physical and chemical extracellular cues. Specific phosphorylations modulate NMII activation in a context-dependent manner. A few kinases control these phosphorylations in a spatially, temporally, and lineage-restricted fashion, enabling functional adaptability to the cellular microenvironment. Here, we review mechanisms that control NMII activity in the context of cell migration and division. Expected final online publication date for the Annual Review of Cell and Developmental Biology, Volume 37 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

New insights into RhoA/Rho-kinase signaling: a key regulator of vascular contraction

While Rho-signalling controlling vascular contraction is a canonical mechanism, with the modern approaches used in research, we are advancing our understanding and details into this pathway are often uncovered. RhoA-mediated Rho-kinase is the major regulator of vascular smooth muscle cells and a key player manoeuvring other functions in these cells. The discovery of new interactions, such as oxidative stress and hydrogen sulphide with Rho signalling are emerging addition not only in the physiology of the smooth muscle, but especially in the pathophysiology of vascular diseases. Likewise, the interplay between ageing and Rho-kinase in the vasculature has been recently considered. Importantly, in smooth muscle contraction, this pathway may also be affected by sex hormones, and consequently, sex-differences. This review provides an overview of Rho signalling mediating vascular contraction and focuses on recent topics discussed in the literature affecting this pathway such as ageing, sex differences and oxidative stress.

Rho-ROCK Signaling in Normal Physiology and as a Key Player in Shaping the Tumor Microenvironment

The Rho-ROCK signaling network has a range of specialized functions of key biological importance, including control of essential developmental processes such as morphogenesis and physiological processes including homeostasis, immunity, and wound healing. Deregulation of Rho-ROCK signaling actively contributes to multiple pathological conditions, and plays a major role in cancer development and progression. This dynamic network is critical in modulating the intricate communication between tumor cells, surrounding diverse stromal cells and the matrix, shaping the ever-changing microenvironment of aggressive tumors. In this chapter, we overview the complex regulation of the Rho-ROCK signaling axis, its role in health and disease, and analyze progress made with key approaches targeting the Rho-ROCK pathway for therapeutic benefit. Finally, we conclude by outlining likely future trends and key questions in the field of Rho-ROCK research, in particular surrounding Rho-ROCK signaling within the tumor microenvironment.

SHROOM2 inhibits tumor metastasis through RhoA-ROCK pathway-dependent and -independent mechanisms in nasopharyngeal carcinoma

SHROOM2 is a key mediator of RhoA–ROCK pathway that regulates cell motility and actin cytoskeleton organization. However, the functions of SHROOM2 beyond RhoA/ROCK signaling remain poorly understood. Here, we report that SHROOM2 not only participates in RhoA–ROCK-induced stress fiber formation and focal adhesion, but also had an unanticipated role in suppressing epithelial-to-mesenchymal transition (EMT) and tumor metastasis. Depletion of SHROOM2 in nasopharyngeal carcinoma (NPC) cells enhances mesenchymal characteristics and reduces epithelial markers, concomitant with increased motility, enabling the development of invasion and tumor metastasis, which are largely ROCK-independent, as ROCK inhibitor Y-27632 did not cause EMT phenotype; furthermore, combination of ROCK inhibition and SHROOM2 depletion resulted in the most robust increases in cell migration and invasion, indicating that SHROOM2 and ROCK work synergistically rather than epistatic. Analysis of clinical samples suggested that SHROOM2 is downregulated in NPC and the expression of SHROOM2 in metastatic NPC was even lower than in the primary tumors. Our findings uncover a non-canonical role of SHROOM2 as a potent antagonist for EMT and NPC metastasis.

Rho-Associated Coiled-Coil Kinase (ROCK) in Molecular Regulation of Angiogenesis

Identified as a major downstream effector of the small GTPase RhoA, Rho-associated coiled-coil kinase (ROCK) is a versatile regulator of multiple cellular processes. Angiogenesis, the process of generating new capillaries from the pre-existing ones, is required for the development of various diseases such as cancer, diabetes and rheumatoid arthritis. Recently, ROCK has attracted attention for its crucial role in angiogenesis, making it a promising target for new therapeutic approaches. In this review, we summarize recent advances in understanding the role of ROCK signaling in regulating the permeability, migration, proliferation and tubulogenesis of endothelial cells (ECs), as well as its functions in non-ECs which constitute the pro-angiogenic microenvironment. The therapeutic potential of ROCK inhibitors in angiogenesis-related diseases is also discussed.

Ginsenoside Rb1 inhibits autophagy through regulation of Rho/ROCK and PI3K/mTOR pathways in a pressure-overload heart failure rat model

Objective

This study was designed to explore the relationship between ginsenoside Rb1 (Grb1) and high-load heart failure (HF) in rats.

Methods

The parameters of cardiac systolic function (left ventricular posterior wall thickness (LVPWT), left ventricular internal diastolic diameter (LVID), fraction shortening (FS) and mitral valves (MVs)) of rat hearts in each group were inspected by echocardiogram. The expressions of rat myocardial contractile proteins, autophagy-related proteins and the activation of Rho/ROCK and PI3K/mTOR pathways were detected by Western blot.

Key findings

LVPWT, FS, MVs and the expression of myocardial contractile proteins α-MHC, apoptosis-related proteins Bcl-2 and signalling pathway involved proteins pAkt and mTOR were significantly reduced in the HF, HF+5 mg/kg Grb1 (HF+Grb1-5) and HF+Grb1+arachidonic acid (AA) groups with LVID, β-MHC, cell apoptosis, cell autophagy and Rho/ROCK significantly increased compared with the control group, of which the tendency was contrary to the HF+20 mg/kg Grb1 (HF+Grb1-20) group compared with the HF group (P < 0.05). In the HF+Grb1+AA group, there was no significant change in the above indexes compared with the HF group.

Conclusions

The results indicated that Grb1 can exert anti-HF function by inhibiting cardiomyocyte autophagy of rats through regulation of Rho/ROCK and PI3K/mTOR pathways.

Acute compressive stress activates RHO/ROCK-mediated cellular processes

The ability to rapidly respond to applied force underpins cell/tissue homeostasis. This response is mediated by mechanotransduction pathways that regulate remodeling and tension of the actomyosin cytoskeleton to counterbalance external forces. Enhanced extracellular matrix tension hyper-activates mechanotransduction and characterizes diseased states such as cancer, but is also required for normal epidermal regeneration. While the impact of extracellular matrix tension on signaling and cell biology are well appreciated, that of acute compressive force is under-studied. We show here that acute compressive force applied to cells and tissues in a native 3-dimensional context elevates RHOA-GTP levels and increases regulatory myosin phosphorylation, actomyosin contractility and tension via ROCK. In consequence, cell proliferation was increased, as was the expression of regulators of epithelial-mesenchymal transition. Pharmacological inhibition of ROCK abrogated myosin phosphorylation, but not RHOA activation. Our results strongly suggest that acute compressive stress impairs cellular homeostasis in a RHO/ROCK-dependent manner, with implications for disease states such as cancer.

Rho kinase signaling and cardiac physiology

Rho kinases (ROCKs) are the first discovered RhoA effectors that are now widely known for their effects on actin organization. Recent studies have shown that ROCKs play important roles in cardiac physiology. Abnormal activation of ROCKs participate in multiple cardiovascular pathological processes, including cardiac hypertrophy, apoptosis, fibrosis, systemic hypertension, and pulmonary hypertension. ROCK inhibitors, fasudil and statins, have shown beneficial cardiovascular effects in many animal studies, clinical trials, and applications. Here, we mainly discuss the current understanding of the physiological roles of Rho kinase signaling in the heart, and briefly summarize the roles of ROCKs in cardiac-related vascular dysfunctions. We will also discuss the clinical application of ROCK inhibitors.

Rho-Mancing to Sensitize Calcium Signaling for Contraction in the Vasculature: Role of Rho Kinase

Vascular smooth muscle contraction is an important physiological process contributing to cardiovascular homeostasis. The principal determinant of smooth muscle contraction is the intracellular free Ca²⁺ concentration, and phosphorylation of myosin light chain (MLC) by activated myosin light chain kinase (MLCK) in response to increased Ca²⁺ is the main pathway by which vasoconstrictor stimuli induce crossbridge cycling of myosin and actin filaments. A secondary pathway for vascular smooth muscle contraction that is not directly dependent on Ca²⁺ concentration, but rather mediating Ca²⁺ sensitization, is the RhoA/Rho kinase pathway. In response to contractile stimuli, the small GTPase RhoA activates its downstream effector Rho kinase which, in turn, promotes contraction via myosin light chain phosphatase (MLCP) inhibition. RhoA/Rho kinase-mediated MLCP inhibition occurs mainly by phosphorylation and inhibition of MYPT1, the regulatory subunit of MLCP, or by CPI-17-mediated inhibition of the catalytic subunit of MLCP. In this review, we describe the molecular mechanisms underlying the pivotal role exerted by Rho kinase on vascular smooth muscle contraction and discuss the main regulatory pathways for its activity.

Structure of the Shroom-Rho Kinase Complex Reveals a Binding Interface with Monomeric Shroom That Regulates Cell Morphology and Stimulates Kinase Activity

Shroom-mediated remodeling of the actomyosin cytoskeleton is a critical driver of cellular shape and tissue morphology that underlies the development of many tissues including the neural tube, eye, intestines, and vasculature. Shroom uses a conserved SD2 domain to direct the subcellular localization of Rho-associated kinase (Rock), which in turn drives changes in the cytoskeleton and cellular morphology through its ability to phosphorylate and activate non-muscle myosin II. Here, we present the structure of the human Shroom-Rock binding module, revealing an unexpected stoichiometry for Shroom in which two Shroom SD2 domains bind independent surfaces on Rock. Mutation of interfacial residues impaired Shroom-Rock binding in vitro and resulted in altered remodeling of the cytoskeleton and loss of Shroom-mediated changes in cellular morphology. Additionally, we provide the first direct evidence that Shroom can function as a Rock activator. These data provide molecular insight into the Shroom-Rock interface and demonstrate that Shroom directly participates in regulating cytoskeletal dynamics, adding to its known role in Rock localization.

Pathophysiological effects of RhoA and Rho-associated kinase on cardiovascular system

In past decades, growing evidence from basic and clinical researches reveal that small guanosine triphosphate binding protein ras homolog gene family, member A (RhoA) and its main effector Rho-associated kinase (ROCK) play central and complex roles in cardiovascular systems, and increasing RhoA and ROCK activity is associated with a broad range of cardiovascular diseases such as congestive heart failure, atherosclerosis, and hypertension. Favorable outcomes have been observed with ROCK inhibitors treatment. In this review, we briefly summarize the pathophysiological roles of RhoA/ROCK signaling pathway on cardiovascular system, displaying the potential benefits in the cardiovascular system with controlling RhoA/ROCK signaling pathway.

Immunobiological factors aggravating the fatty infiltration on tendons and muscles in rotator cuff lesions

Rotator cuff lesions (RCLs) are a common cause of shoulder pain and dysfunction. The rotator cuff tendons can degenerate and/or tear from the greater tuberosity of the humerus, which is associated with several anatomical, physiological, biochemical, and molecular changes in tendon and muscle. In this article, these pathways are critically reviewed and discussed with various management strategies of RCLs. The article also highlights the immunobiological responses following the RCL and the inherent repair mechanisms elicited by the body. The greatest difficulty in treating this pathology is that the muscle can undergo irreversible fatty infiltration in the setting of chronic tears that is associated with poor surgical outcomes. The article also investigates the key molecular pathways of the muscle homeostasis (mTOR, Rho kinase, AMPK, and Ca(2+)) with the energy metabolism to propose a possible mechanism for fatty infiltration. Future research is warranted to target the key players of these pathways in the management of fatty infiltration and thus RCL.

Calcium Sensitization Mechanisms in Gastrointestinal Smooth Muscles

An increase in intracellular Ca²⁺ is the primary trigger of contraction of gastrointestinal (GI) smooth muscles. However, increasing the Ca²⁺ sensitivity of the myofilaments by elevating myosin light chain phosphorylation also plays an essential role. Inhibiting myosin light chain phosphatase activity with protein kinase C-potentiated phosphatase inhibitor protein-17 kDa (CPI-17) and myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation is considered to be the primary mechanism underlying myofilament Ca²⁺ sensitization. The relative importance of Ca²⁺ sensitization mechanisms to the diverse patterns of GI motility is likely related to the varied functional roles of GI smooth muscles. Increases in CPI-17 and MYPT1 phosphorylation in response to agonist stimulation regulate myosin light chain phosphatase activity in phasic, tonic, and sphincteric GI smooth muscles. Recent evidence suggests that MYPT1 phosphorylation may also contribute to force generation by reorganization of the actin cytoskeleton. The mechanisms responsible for maintaining constitutive CPI-17 and MYPT1 phosphorylation in GI smooth muscles are still largely unknown. The characteristics of the cell-types comprising the neuroeffector junction lead to fundamental differences between the effects of exogenous agonists and endogenous neurotransmitters on Ca²⁺ sensitization mechanisms. The contribution of various cell-types within the tunica muscularis to the motor responses of GI organs to neurotransmission must be considered when determining the mechanisms by which Ca²⁺ sensitization pathways are activated. The signaling pathways regulating Ca²⁺ sensitization may provide novel therapeutic strategies for controlling GI motility. This article will provide an overview of the current understanding of the biochemical basis for the regulation of Ca²⁺ sensitization, while also discussing the functional importance to different smooth muscles of the GI tract.

The whole-genome expression analysis of peripheral blood mononuclear cells from aspirin sensitive asthmatics versus aspirin tolerant patients and healthy donors after in vitro aspirin challenge

Background

Up to 30 % of adults with severe asthma are hypersensitive to aspirin and no unambiguous theory exists which provides a satisfactory explanation for the occurrence of aspirin-induced asthma (AIA) in some asthmatic patients. Therefore, the aim of this study was to compare the AIA expression profile against aspirin tolerant asthma (ATA) and healthy volunteers (HV) profile in peripheral blood mononuclear cells (PBMCs) after in vitro aspirin challenge in Caucasian population.

Methods

PBMCs were separated from blood of three groups of subjects - 11 AIA, 7 ATA and 15 HV and then stimulated by either 2 μM lysine aspirin or 20 μM lysine as a control. Subsequently, RNA was isolated, transcribed into cDNA and subjected to microarray and qPCR studies. Simultaneously, protein was extracted from PBMCs and used in further immunoblotting analysis.

Results

The validation of results at mRNA level has shown only three genes, whose expression was significantly altered between comprising groups. mRNA expression of CNPY3 in PBMCs in AIA was significantly lower (-0.41 ± 2.67) than in HV (1.04 ± 2.69), (p = 0.02); mRNA expression of FOSL1 in PBMCs in AIA was also significantly decreased (-0.66 ± 2.97) as opposed to HV (0.31 ± 4.83), (p = 0.02). While mRNA expression of ERAS in PBMCs was increased (1.15 ± 0.23) in AIA in comparison to HV (-1.32 ± 0.41), (p = 0.03). At protein level the changed expression of one protein was confirmed. Protein expression of FOSL1 in PBMCs in AIA was both significantly lower (-0.86 ± 0.08) than in ATA (0.39 ± 0.42), (p = 0.046) and in HV (0.9 ± 0.27), (p = 0.007).

Conclusions

This pilot study implies a positive association between CNPY3, ERAS, FOSL1 and aspirin-intolerant asthma, suggesting that these findings would be useful for further investigations of NSAIDs mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-015-0305-4) contains supplementary material, which is available to authorized users.

Polyunsaturated fatty acid biosynthesis is involved in phenylephrine-mediated calcium release in vascular smooth muscle cells

Stimulation of vascular smooth muscle (VSM) α1-adrenoceptors induces myosin phosphorylation and vasoconstriction via mobilisation of intracellular calcium and production of specific eicosanoids. Polyunsaturated fatty acid (PUFA) biosynthesis in VSM cells is involved, although the precise mechanism is not known. To address this, we characterised PUFA biosynthesis in VSM cells and determined its role in intracellular calcium release and eicosanoid production. Murine VSM cells converted 18:2n-6 to longer chain PUFA including 22:5n-6. Δ6 (D6d) and Δ5 (D5d) desaturase, and elongase (Elovl) 5 were expressed. Elovl2 was not detected in human, mouse or rat VSM cells, or in rat or mouse aortae, but tit was not associated with hypermethylation of its promoter. D6d or D5d inhibition reduced 18:3n-6 and 20:4n-6 synthesis, respectively, and induced concentration-related decrease in phenylephrine-mediated calcium release, and in PGE2 and PGF2α secretion. Together these findings suggest that PUFA biosynthesis in VSM cells is involved in calcium release associated with vasoconstriction.

The interaction between Shroom3 and Rho-kinase is required for neural tube morphogenesis in mice

Shroom3 is an actin-associated regulator of cell morphology that is required for neural tube closure, formation of the lens placode, and gut morphogenesis in mice and has been linked to chronic kidney disease and directional heart looping in humans. Numerous studies have shown that Shroom3 likely regulates these developmental processes by directly binding to Rho-kinase and facilitating the assembly of apically positioned contractile actomyosin networks. We have characterized the molecular basis for the neural tube defects caused by an ENU-induced mutation that results in an arginine-to-cysteine amino acid substitution at position 1838 of mouse Shroom3. We show that this substitution has no effect on Shroom3 expression or localization but ablates Rock binding and renders Shroom3 non-functional for the ability to regulate cell morphology. Our results indicate that Rock is the major downstream effector of Shroom3 in the process of neural tube morphogenesis. Based on sequence conservation and biochemical analysis, we predict that the Shroom-Rock interaction is highly conserved across animal evolution and represents a signaling module that is utilized in a variety of biological processes.

Structure of a highly conserved domain of Rock1 required for Shroom-mediated regulation of cell morphology

Rho-associated coiled coil containing protein kinase (Rho-kinase or Rock) is a well-defined determinant of actin organization and dynamics in most animal cells characterized to date. One of the primary effectors of Rock is non-muscle myosin II. Activation of Rock results in increased contractility of myosin II and subsequent changes in actin architecture and cell morphology. The regulation of Rock is thought to occur via autoinhibition of the kinase domain via intramolecular interactions between the N-terminus and the C-terminus of the kinase. This autoinhibited state can be relieved via proteolytic cleavage, binding of lipids to a Pleckstrin Homology domain near the C-terminus, or binding of GTP-bound RhoA to the central coiled-coil region of Rock. Recent work has identified the Shroom family of proteins as an additional regulator of Rock either at the level of cellular distribution or catalytic activity or both. The Shroom-Rock complex is conserved in most animals and is essential for the formation of the neural tube, eye, and gut in vertebrates. To address the mechanism by which Shroom and Rock interact, we have solved the structure of the coiled-coil region of Rock that binds to Shroom proteins. Consistent with other observations, the Shroom binding domain is a parallel coiled-coil dimer. Using biochemical approaches, we have identified a large patch of residues that contribute to Shrm binding. Their orientation suggests that there may be two independent Shrm binding sites on opposing faces of the coiled-coil region of Rock. Finally, we show that the binding surface is essential for Rock colocalization with Shroom and for Shroom-mediated changes in cell morphology.

The influence of polyunsaturated fatty acids on the phospholipase D isoforms trafficking and activity in mast cells

The impact of polyunsaturated fatty acid (PUFA) supplementation on phospholipase D (PLD) trafficking and activity in mast cells was investigated. The enrichment of mast cells with different PUFA including α-linolenic acid (LNA), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), linoleic acid (LA) or arachidonic acid (AA) revealed a PUFA-mediated modulation of the mastoparan-stimulated PLD trafficking and activity. All PUFA examined, except AA, prevented the migration of the PLD1 to the plasma membrane. For PLD2 no PUFA effects on trafficking could be observed. Moreover, PUFA supplementation resulted in an increase of mastoparan-stimulated total PLD activity, which correlated with the number of double bonds of the supplemented fatty acids. To investigate, which PLD isoform was affected by PUFA, stimulated mast cells were supplemented with DHA or AA in the presence of specific PLD-isoform inhibitors. It was found that both DHA and AA diminished the inhibition of PLD activity in the presence of a PLD1 inhibitor. By contrast, only AA diminished the inhibition of PLD activity in the presence of a PLD2 inhibitor. Thus, PUFA modulate the trafficking and activity of PLD isoforms in mast cells differently. This may, in part, account for the immunomodulatory effect of unsaturated fatty acids and contributes to our understanding of the modulation of mast cell activity by PUFA.

Rho-associated coiled-coil kinase (ROCK) signaling and disease

The small Rho GTPase family of proteins, encompassing the three major G-protein classes Rho, Rac and cell division control protein 42, are key mitogenic signaling molecules that regulate multiple cancer-associated cellular phenotypes including cell proliferation and motility. These proteins are known for their role in the regulation of actin cytoskeletal dynamics, which is achieved through modulating the activity of their downstream effector molecules. The Rho-associated coiled-coil kinase 1 and 2 (ROCK1 and ROCK2) proteins were the first discovered Rho effectors that were primarily established as players in RhoA-mediated stress fiber formation and focal adhesion assembly. It has since been discovered that the ROCK kinases actively phosphorylate a large cohort of actin-binding proteins and intermediate filament proteins to modulate their functions. It is well established that global cellular morphology, as modulated by the three cytoskeletal networks: actin filaments, intermediate filaments and microtubules, is regulated by a variety of accessory proteins whose activities are dependent on their phosphorylation by the Rho-kinases. As a consequence, they regulate many key cellular functions associated with malignancy, including cell proliferation, motility and viability. In this current review, we focus on the role of the ROCK-signaling pathways in disease including cancer.

Signal transduction and modulating pathways in tryptamine-evoked vasopressor responses of the rat isolated perfused mesenteric bed

Tryptamine is an endogenous and dietary indoleamine-based trace amine implicated in cardiovascular pathologies, including hypertension, migraine and myocardial infarction. This study aimed at identifying the signalling pathways for the vasoconstrictor response to tryptamine in rat isolated perfused mesenteric arterial beds and co-released vasodilator modulators of tryptamine-mediated vasoconstriction. Tryptamine caused concentration-dependent vasoconstriction of the mesenteric bed, measured as increases in perfusion pressure. These were inhibited by the 5-HT_2A receptor antagonist, ritanserin, indicating mediation via 5-HT_2A receptors. The response was inhibited by the phospholipase C (PLC) and phospholipase A₂ (iPLA₂) inhibitors, U-73122 and PACOCF₃, suggesting involvement of phospholipase pathways. Activation of these pathways by tryptamine releases cyclooxygenase (COX) products since indomethacin (non-selective inhibitor of COX-1/2) and nimesulide (selective COX-2 inhibitor) reduced the vasoconstriction. The most likely COX vasoconstrictor product was prostaglandin PGE₂ since the responses to tryptamine were reduced by AH-6809, a non-selective EP₁ receptor antagonist. Involvement of the Rho-kinase pathway in the tryptamine-evoked vasoconstriction was also indicated by its reduction by the Rho-kinase inhibitors, Y-27,632 and fasudil. The tryptamine vasoconstriction is modulated by the co-released endothelial vasodilator, nitric oxide. Thus, circulating tryptamine can regulate mesenteric blood flow through a cascade of signalling pathways secondary to stimulation of 5-HT_2A receptors.

New insights into the regulation of myosin light chain phosphorylation in retinal pigment epithelial cells

The retinal pigment epithelium (RPE) plays an essential role in the function of the neural retina and the maintenance of vision. Most of the functions displayed by RPE require a dynamic organization of the acto-myosin cytoskeleton. Myosin II, a main cytoskeletal component in muscle and non-muscle cells, is directly involved in force generation required for organelle movement, selective molecule transport within cell compartments, exocytosis, endocytosis, phagocytosis, and cell division, among others. Contractile processes are triggered by the phosphorylation of myosin II light chains (MLCs), which promotes actin-myosin interaction and the assembly of contractile fibers. Considerable evidence indicates that non-muscle myosin II activation is critically involved in various pathological states, increasing the interest in studying the signaling pathways controlling MLC phosphorylation. Particularly, recent findings suggest a role for non-muscle myosin II-induced contraction in RPE cell transformation involved in the establishment of numerous retinal diseases. This review summarizes the current knowledge regarding myosin function in RPE cells, as well as the signaling networks leading to MLC phosphorylation under pathological conditions. Understanding the molecular mechanisms underlying RPE dysfunction would improve the development of new therapies for the treatment or prevention of different ocular disorders leading to blindness.

The pivotal role of airway smooth muscle in asthma pathophysiology

Asthma is characterized by the association of airway hyperresponsiveness (AHR), inflammation, and remodelling. The aim of the present article is to review the pivotal role of airway smooth muscle (ASM) in the pathophysiology of asthma. ASM is the main effector of AHR. The mechanisms of AHR in asthma may involve a larger release of contractile mediators and/or a lower release of relaxant mediators, an improved ASM cell excitation/contraction coupling, and/or an alteration in the contraction/load coupling. Beyond its contractile function, ASM is also involved in bronchial inflammation and remodelling. Whereas ASM is a target of the inflammatory process, it can also display proinflammatory and immunomodulatory functions, through its synthetic properties and the expression of a wide range of cell surface molecules. ASM remodelling represents a key feature of asthmatic bronchial remodelling. ASM also plays a role in promoting complementary airway structural alterations, in particular by its synthetic function.

Rho-kinase inhibition attenuates calcium-induced contraction in β-escin but not Triton X-100 permeabilized rabbit femoral artery

K+-depolarization (KCl) of smooth muscle has long been known to cause Ca2+-dependent contraction, but only recently has this G protein-coupled receptor (GPCR)-independent stimulus been associated with rhoA kinase (ROCK)-dependent myosin light chain (MLC) phosphatase inhibition and Ca2+ sensitization. This study examined effects of ROCK inhibition on the concentration-response curves (CRCs) generated in femoral artery by incrementally adding increasing concentrations of KCl to intact tissues, and Ca2+ to tissues permeabilized with Triton X-100, β-escin and α-toxin. For a comparison, tissue responses were assessed also in the presence of protein kinase C (PKC) and MLC kinase inhibition. The ROCK inhibitor H-1152 induced a strong concentration-dependent inhibition of a KCl CRC. A relatively low GF-109203X concentration (1 μM) sufficient to inhibit conventional PKC isotypes also inhibited the KCl CRC but did not affect the maximum tension. ROCK inhibitors had no effect on the Ca2+ CRC induced in Triton X-100 or α-toxin permeabilized tissues, but depressed the maximum contraction induced in β-escin permeabilized tissue. GF-109203X at 1 μM depressed the maximum Ca2+-dependent contraction induced in α-toxin permeabilized tissue and had no effect on the Ca2+ CRC induced in Triton X-100 permeabilized tissue. The MLC kinase inhibitor wortmannin (1 μM) strongly depression the Ca2+ CRCs in tissues permeabilized with Triton X-100, α-toxin and β-escin. H-1152 inhibited contractions induced by a single exposure to a submaximum [Ca2+] (pCa 6) in both rabbit and mouse femoral arteries. These data indicate that β-escin permeabilized muscle preserves GPCR-independent, Ca2+- and ROCK-dependent, Ca2+ sensitization.

Rho-kinase/ROCK: A key regulator of the cytoskeleton and cell polarity

Rho-associated kinase (Rho-kinase/ROCK/ROK) is an effector of the small GTPase Rho and belongs to the AGC family of kinases. Rho-kinase has pleiotropic functions including the regulation of cellular contraction, motility, morphology, polarity, cell division, and gene expression. Pharmacological analyses have revealed that Rho-kinase is involved in a wide range of diseases such as vasospasm, pulmonary hypertension, nerve injury, and glaucoma, and is therefore considered to be a potential therapeutic target. This review focuses on the structure, function, and modes of activation and action of Rho-kinase.

Key role of the RhoA/Rho kinase system in pulmonary hypertension

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Regulation of smooth muscle contraction by small GTPases

Next to changes in cytosolic [Ca(2+)], members of the Rho subfamily of small GTPases, in particular Rho and its effector Rho kinase, also known as ROK or ROCK, emerged as key regulators of smooth muscle function in health and disease. In this review, we will focus on the regulation of the contractile machinery by Rho/ROK signaling and its interaction with PKC and cyclic nucleotide signaling. We will briefly discuss the emerging evidence that remodeling of cortical actin is necessary for contraction.

Stimulatory effects of arachidonic acid on myosin ATPase activity and contraction of smooth muscle via myosin motor domain

We have been searching for a mechanism to induce smooth muscle contraction that is not associated with phosphorylation of the regulatory light chain (RLC) of smooth muscle myosin (Nakamura A, Xie C, Zhang Y, Gao Y, Wang HH, Ye LH, Kishi H, Okagaki T, Yoshiyama S, Hayakawa K, Ishikawa R, Kohama K. Biochem Biophys Res Commun 369: 135–143, 2008). In this article, we report that arachidonic acid (AA) stimulates ATPase activity of unphosphorylated smooth muscle myosin with maximal stimulation (Rmax) of 6.84 ± 0.51 relative to stimulation by the vehicle and with a half-maximal effective concentration (EC50) of 50.3 ± 4.2 μM. In the presence of actin, Rmax was 1.72 ± 0.08 and EC50 was 26.3 ± 2.3 μM. Our experiments with eicosanoids consisting of the AA cascade suggested that they neither stimulated nor inhibited the activity. Under conditions that did not allow RLC to be phosphorylated, AA stimulated contraction of smooth muscle tissue with an Rmax of 1.45 ± 0.07 and an EC50 of 27.0 ± 4.4 μM. In addition to the ATPase activities of the myosin, AA stimulated those of heavy meromyosin, subfragment 1 (S1), S1 from which the RLC was removed, and a recombinant heavy chain consisting of the myosin head. The stimulatory effects of AA on these preparations were about twofold. The site of AA action was indicated to be the step-releasing inorganic phosphate (Pi) from the reaction intermediate of the myosin-ADP-Pi complex. The enhancement of Pi release by AA was supported by computer simulation indicating that AA docked in the actin-binding cleft of the myosin motor domain. The stimulatory effect of AA was detectable with both unphosphorylated myosin and the myosin in which RLC was fully phosphorylated. The AA effect on both myosin forms was suggested to cause excess contraction such as vasospasm.

Importance of Rac1 signaling pathway inhibition in the pleiotropic effects of HMG-CoA reductase inhibitors

BACKGROUND

The pleiotropic effects of HMG-CoA reductase inhibitors (statins) are thought to be mediated through inhibition of small GTP-binding proteins; however, it remains to be examined whether clinical concentrations/doses of statins actually exert them.

METHODS AND RESULTS

In vitro studies with cultured human umbilical venous endothelial cells found that statins (atorvastatin, pitavastatin and pravastatin at 10 micromol/L) had no inhibitory effects on RhoA/Rho-kinase or Ras, but atorvastatin and pitavastatin inhibited membrane Rac1 expression. In animal studies of angiotensin II (AngII)-infused rats, atorvastatin showed only mild inhibitory effects on AngII-induced cardiovascular hypertrophy, whereas fasudil, a selective Rho-kinase inhibitor, significantly suppressed it. Statins had no inhibitory effects on RhoA/Rho-kinase, but inhibited both membrane and GTP-bound Rac1 in the heart, whereas fasudil only inhibited Rho-kinase activity. Furthermore, the combination of atorvastatin and fasudil showed more effective inhibitory effects than fasudil alone. Finally, in studies of normal healthy volunteers, clinical doses of pravastatin or atorvastatin (20 mg/day for 1 week) significantly inhibited Rac1, but not RhoA/Rho-kinase activity, in circulating leukocytes.

CONCLUSIONS

The pleiotropic effects of statins, if any, at their clinical doses are mediated predominantly through inhibition of the Rac1 signaling pathway.

Does eicosapentaenoic acid (EPA) inhibit cerebral vasospasm in patients after aneurysmal subarachnoid hemorrhage?

BACKGROUND

Cerebral vasospasm following subarachnoid hemorrhage (SAH) is a significant cause of morbidity and mortality and recent studies indicate that Rho-kinase plays an important role in the occurrence of such cerebral vasospasm. Eicosapentaenoic acid (EPA), an n-3 polyunsaturated fatty acid, inhibits sphingosylphosphorylcholine (SPC)-induced Rho-kinase activation in vitro, so this study examined whether EPA prevented cerebral vasospasm occurrence after SAH in patients.

METHODS

The trial population was 101 patients with SAH subjected to craniotomy and clip application. EPA was orally administered at a daily dose of 1800 mg EPA from day 4 to day 14 to 73 patients; the other 28 constituted the control group, receiving no EPA.

RESULTS

EPA significantly curtailed both the occurrence of symptomatic vasospasm (14% EPA group, 36% control, P = 0.019) and of cerebral infarction because of cerebral vasospasm (4% EPA group, 29% control, P = 0.001). Moreover, the percentage of patients with a clinically good outcome was significantly higher in the EPA group (85%, P = 0.022) than in control (64%); there were no deaths in the EPA group but three (11%) in control (P = 0.020).

CONCLUSION

These findings suggest EPA inhibits symptomatic cerebral vasospasm and cerebral infarction after SAH and also improves clinical prognosis.

Polyphenols modulate calcium-independent mechanisms in human arterial tissue-engineered vascular media

BACKGROUND

In the present study, an arterial tissue-engineered vascular media (TEVM) was produced from cultured human smooth muscle cells of the umbilical artery and we took advantage of this model to evaluate the regulation of contraction and the signalling pathways of polyphenols in arteries.

METHODS

Cultured human smooth muscle cells of the umbilical artery were used to produce arterial TEVMs. Contraction experiments were performed to determine intracellular targets involved in the modulation of contraction by polyphenols extract from red wine, Provinols (SEPPIC Groupe Air Liquide, Paris, France).

RESULTS

Smooth muscle cells in arterial TEVM displayed a differentiated phenotype as demonstrated by the expression of alpha-smooth muscle actin, a vascular smooth muscle-specific marker, and tissue contraction in response to vasoconstrictor and vasodilator agents. Contractions caused by histamine were associated with an increase in [Ca(2+)](i) and a Ca(2+)-independent signalling pathway. The latter pathway involved mechanisms sensitive to protein kinase C, myosin light chain kinase, and Rho-associated protein kinase inhibitors. The regulation of contraction induced by Provinols shows that treatment of arterial TEVM with this compound significantly decreased histamine-induced contraction. This effect was associated with the inhibition of the Rho-associated protein kinase pathway and the decrease in alpha-smooth muscle actin expression.

CONCLUSION

The use of arterial TEVM, brings new insights into the mechanisms by which polyphenols regulate vascular contraction in the human artery.

Interactions between the leucine-zipper motif of cGMP-dependent protein kinase and the C-terminal region of the targeting subunit of myosin light chain phosphatase

Nitric oxide induces vasodilation by elevating the production of cGMP, an activator of cGMP-dependent protein kinase (PKG). PKG subsequently causes smooth muscle relaxation in part via activation of myosin light chain phosphatase (MLCP). To date, the interaction between PKG and the targeting subunit of MLCP (MYPT1) is not fully understood. Earlier studies by one group of workers showed that the binding of PKG to MYPT1 is mediated by the leucine-zipper motifs at the N and C termini, respectively, of the two proteins. Another group, however, reported that binding of PKG to MYPT1 did not require the leucine-zipper motif of MYPT1. In this work we fully characterized the interaction between PKG and MYPT1 using biophysical techniques. For this purpose we constructed a recombinant PKG peptide corresponding to a predicted coiled coil region that contains the leucine-zipper motif. We further constructed various C-terminal MYPT1 peptides bearing various combinations of a predicted coiled coil region, extensions preceding this coiled coil region, and the leucine-zipper motif. Our results show, firstly, that while the leucine-zipper motif at the N terminus of PKG forms a homodimeric coiled coil, the one at the C terminus of MYPT1 is monomeric and non-helical. Secondly, the leucine-zipper motif of PKG binds to that of MYPT1 to form a heterodimer. Thirdly, when the leucine-zipper motif of MYPT1 is absent, the PKG leucine-zipper motif binds to the coiled coil region and upstream segments of MYPT1 via formation of a heterotetramer. These results provide rationalization of some of the findings by others using alternative binding analyses.

Role of Rho kinases in PKG-mediated relaxation of pulmonary arteries of fetal lambs exposed to chronic high altitude hypoxia

An increase in Rho kinase (ROCK) activity is implicated in chronic hypoxia-induced pulmonary hypertension. In the present study, we determined the role of ROCKs in cGMP-dependent protein kinase (PKG)-mediated pulmonary vasodilation of fetal lambs exposed to chronic hypoxia. Fourth generation pulmonary arteries were isolated from near-term fetuses ( approximately 140 days of gestation) delivered from ewes exposed to chronic high altitude hypoxia for approximately 110 days and from control ewes. In vessels constricted to endothelin-1, 8-bromoguanosine-cGMP (8-Br-cGMP) caused a smaller relaxation in chronically hypoxic (CH) vessels compared with controls. Rp-8-Br-PET-cGMPS, a PKG inhibitor, attenuated relaxation to 8-Br-cGMP in control vessels to a greater extent than in CH vessels. Y-27632, a ROCK inhibitor, significantly potentiated 8-Br-cGMP-induced relaxation of CH vessels and had only a minor effect in control vessels. The expression of PKG was increased but was not accompanied with an increase in the activity of the enzyme in CH vessels. The expression of type II ROCK and activity of ROCKs were increased in CH vessels. The phosphorylation of threonine (Thr)696 and Thr850 of the regulatory subunit MYPT1 of myosin light chain phosphatase was inhibited by 8-Br-cGMP to a lesser extent in CH vessels than in controls. The difference was eliminated by Y-27632. These results suggest that chronic hypoxia in utero attenuates PKG-mediated relaxation in pulmonary arteries, partly due to inhibition of PKG activity and partly due to enhanced ROCK activity. Increased ROCK activity may inhibit PKG action through increased phosphorylation of MYPT1 at Thr696 and Thr850.

Rho kinase, myosin-II, and p42/44 MAPK control extracellular matrix-mediated apical bile canalicular lumen morphogenesis in HepG2 cells

The molecular mechanisms that regulate multicellular architecture and the development of extended apical bile canalicular lumens in hepatocytes are poorly understood. Here, we show that hepatic HepG2 cells cultured on glass coverslips first develop intercellular apical lumens typically formed by a pair of cells. Prolonged cell culture results in extensive organizational changes, including cell clustering, multilayering, and apical lumen morphogenesis. The latter includes the development of large acinar structures and subsequent elongated canalicular lumens that span multiple cells. These morphological changes closely resemble the early organizational pattern during development, regeneration, and neoplasia of the liver and are rapidly induced when cells are cultured on predeposited extracellular matrix (ECM). Inhibition of Rho kinase or its target myosin-II ATPase in cells cultured on glass coverslips mimics the morphogenic response to ECM. Consistently, stimulation of Rho kinase and subsequent myosin-II ATPase activity by lipoxygenase-controlled eicosatetranoic acid metabolism inhibits ECM-mediated cell multilayering and apical lumen morphogenesis but not initial apical lumen formation. Furthermore, apical lumen remodeling but not cell multilayering requires basal p42/44 MAPK activity. Together, the data suggest a role for hepatocyte-derived ECM in the spatial organization of hepatocytes and apical lumen morphogenesis and identify Rho kinase, myosin-II, and MAPK as potentially important players in different aspects of bile canalicular lumen morphogenesis.

Attenuation of contractility in rat epididymal vas deferens by Rho kinase inhibitors

The involvement of Ca(2+) sensitization mediated through Rho kinase in the contractility of rat epididymal vas deferens was investigated using Rho kinase inhibitors, trans-4-[(1R)-1-aminoethyl]-N-4-pyridinilcyclohexanecarboxamide dihydrochloride (Y-27632) and 1-(5-isoquinolinesulphonyl)homopiperazine (HA 1077), in comparison with myosin light chain kinase (MLCK) inhibitors, wortmannin and 1-(5-chloronaphthalenesulphonyl)homopiperazine (ML-9) and agents that affect protein kinase C (PKC) and non-receptor tyrosine kinase intracellular signalling. 2 In Ca(2+)-free/ethyleneglycol-bis-(beta-aminoethylether)N,N,N('),N(')-tetraacetic acid (EGTA) (1 mM) medium, noradrenaline evoked sustained contractions. Y-27632 and HA 1077 caused a concentration-dependent inhibition and complete relaxation (IC(50), 1.08 and 1.75 microM respectively). The Ca(2+)-free contraction was reduced by wortmannin (10 microM) or ML-9 (10 microM) but not by inhibitors of diacylglycerol metabolism, 3-[2-[4[bis(4-Fluoropheny)methylene]-1-piperidinyl]-2,3-dihydro-2-thioxi-4(H)-quinazolinone (R59949) (10 microm) or 1,6-bis(cyclohexyloximinocarbonylamino)hexane (RHC-80267) (10 microM) or by the phospholipase A(2) (PLA(2)) inhibitor, quinacrine (up to 100 microM) or tyrosine kinase inhibitor, genistein (30 microM). 3 In the presence of Ca(2+) (2.5 mM), noradrenaline (100 microM) evoked rhythmic activity and biphasic tonic contractions. Y-27632 (1-10 microM) or HA 1077 (1-10 microM) reduced the amplitude of rhythmic activity and tonic contractions. ML-9 (10 microM) attenuated the occurrence of rhythmic activity and modestly reduced the tonic contractions. ML-9 (10 microM) combined with Y-27632 (10 microM) significantly reduced the tonic contractions. ML-9 (30 microM) alone (or combined with Y-27632 10 microM) suppressed the rhythmic activity and substantially reduced (or abolished) the tonic contractions. 4 Contractions evoked by high [K(+)](o) (120 mM) or alpha,beta-methylene ATP (10 microM) were reduced significantly by Y-27632 (1-3 microM) indicating that the Rho kinase signalling pathway is activated by direct tissue depolarization or by stimulation of ligand-gated P(2X) purinoceptors. 5 Collectively, these results indicate that Ca(2+)-sensitization mediated by Rho kinase is involved in agonist- or depolarization-induced contraction of rat epididymal vas deferens. It is the major contractile mechanism underlying noradrenaline-induced Ca(2+)-free responses. It contributes to Ca(2+)-dependent rhythmic contractility and optimizes the development of full contractile tension triggered through calmodulin/MLCK activation by stimulated influx of Ca(2+).

Nuclear Rho kinase, ROCK2, targets p300 acetyltransferase

Rho-associated coiled-coil protein kinase (ROCK) is an effector for the small GTPase Rho and plays a pivotal role in diverse cellular activities, including cell adhesion, cytokinesis, and gene expression, primarily through an alteration of actin cytoskeleton dynamics. Here, we show that ROCK2 is localized in the nucleus and associates with p300 acetyltransferase both in vitro and in cells. Nuclear ROCK2 is present in a large protein complex and partially cofractionates with p300 by gel filtration analysis. By immunofluorescence, ROCK2 partially colocalizes with p300 in distinct insoluble nuclear structures. ROCK2 phosphorylates p300 in vitro, and nuclear-restricted expression of constitutively active ROCK2 induces p300 phosphorylation in cells. p300 acetyltransferase activity is dependent on its phosphorylation status in cells, and p300 phosphorylation by ROCK2 results in an increase in its acetyltransferase activity in vitro. These observations suggest that nucleus-localized ROCK2 targets p300 for phosphorylation to regulate its acetyltransferase activity.

RhoA/Rho-kinase in erectile tissue: mechanisms of disease and therapeutic insights

Penile erection is a complicated event involving the regulation of corpus cavernosal smooth muscle tone. Recently, the small monomeric G-protein RhoA and its downstream effector Rho-kinase have been proposed to be important players for mediating vasoconstriction in the penis. RhoA/Rho-kinase increases MLC (myosin light chain) phosphorylation through inhibition of MLCP (MLC phosphatase) thereby increasing Ca2+ sensitivity. This review will outline the RhoA/Rho-kinase signalling pathway, including the upstream regulators, guanine nucleotide exchange factors, GDP dissociation inhibitors and GTPase-activating proteins. We also summarize the current knowledge about the physiological roles of RhoA/Rho-kinase in both male and female erectile tissues and its aberrations contributing to erectile dysfunction in several disease states. Understanding the RhoA/Rho-kinase signalling pathway in the regulation of erection is important for the development of therapeutic interventions for erectile dysfunction.

Altered arachidonic acid-mediated responses in the perfused kidney of the streptozotocin-induced diabetic rat

Using perfused kidneys isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we investigated the effects of arachidonic acid (AA) on perfusion pressure in the presence of methoxamine. AA elicited a transient contraction followed by a sustained relaxation in each group. The amplitude of contraction was smaller in the diabetic group than in the control group, whereas the amplitude of the sustained relaxation was greater in the former than in the latter group. In the diabetic group, the AA-induced sustained relaxation was completely inhibited by indomethacin [cyclooxygenase (COX) inhibitor], SKF525A [cytochrome P450 (CYP450) inhibitor], or clotrimazole (epoxygenase inhibitor), but not by furegrelate [thromboxane A(2) (TXA(2))-synthase inhibitor], SQ29548 (TXA(2)-receptor antagonist), or baicalein [lipoxygenase (LOX) inhibitor]. In the diabetic kidney, more-or-less additive inhibitions of the AA-induced relaxation were seen when indomethacin was given with either SKF525A or clotrimazole. These results suggest that in the STZ-induced diabetic perfused kidney, vasorelaxant metabolites derived from AA (probably COX and/or CYP450 metabolites) are increased, and may serve to regulate vascular tone.

Enhanced role for RhoA-associated kinase in adrenergic-mediated vasoconstriction in gracilis arteries from obese Zucker rats

Obesity, insulin resistance, dyslipidemia, and hypertension are components of the pathophysiological state known as metabolic syndrome. Adrenergic vasoconstriction is mediated through increases in cytosolic Ca2+ and the myofilaments' sensitivity to Ca2+. In many pathophysiological states, there is an enhanced role for Rho kinase (ROK)-mediated increases in Ca2+ sensitivity of the contractile apparatus. Thus we hypothesized that there is a greater role for ROK-mediated increases in Ca2+ sensitivity in alpha1-adrenergic vasoconstriction in arteries from obese Zucker (OZ) rats. Therefore, small gracilis muscle arteries from 11- to 12-wk-old and 16- to 18-wk-old lean and OZ rats were isolated, cannulated, and pressurized to 75 mmHg. For some experiments, vessels were loaded with fura 2-AM. Changes in luminal diameter and vessel wall Ca2+ concentration ([Ca2+]) were measured in response to phenylephrine (PE), the thromboxane mimetic U-46619, and KCl. alpha1-Adrenergic vasoconstriction was similar between 11- to 12-wk-old lean and obese animals and greater in older obese animals compared with controls. PE-induced increases in vascular smooth muscle cell [Ca2+] were blunted in OZ animals compared with lean controls in both age groups of animals. KCl and U-46619 elicited similar vasoconstriction and vascular smooth muscle cell [Ca2+] in both groups. ROK inhibition attenuated PE vasoconstriction to a greater degree in arteries from 11- to 12-wk-old OZ rats compared with lean animals; ROK inhibition in arteries from older rats right shifted both concentration-response curves to the same point. Total RhoA and ROKalpha protein expressions were similar between groups. These results suggest an enhanced role for the ROK pathway in alpha1-adrenergic vasoconstriction in metabolic syndrome.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Vascular smooth muscle function: The physiology and pathology of vasoconstriction

Vascular smooth muscle is the contractile component of arteries and veins. The control of contraction and relaxation is dependent upon intracellular and extracellular signals. Abnormal contractions can cause and or contribute to pathology such as hypertension, ischemia and infarction. In this review, we address the vascular pathogenesis associated with hypertension and subarachnoid hemorrhage induced cerebral vasospasm. Hypertension is a multifactorial disease with many causes and a profound impact on the cardiovascular system, whereas subarachnoid hemorrhage induced cerebral vasospasm is a pathological vasoconstriction often causing infarction that is thought to be 'caused' by a factor or factors in the CSF following the hemorrhage. However, the mechanism by which the vessels are constricted is unknown. Although the causes for these two pathological vasoconstrictions remain to be determined, we conclude that the common denominator is that these contractile changes result in pathology with devastating consequences to human health.

Regulation of smooth muscle calcium sensitivity: KCl as a calcium-sensitizing stimulus

KCl has long been used as a convenient stimulus to bypass G protein-coupled receptors (GPCR) and activate smooth muscle by a highly reproducible and relatively “simple” mechanism involving activation of voltage-operated Ca2+channels that leads to increases in cytosolic free Ca2+([Ca2+]i), Ca2+-calmodulin-dependent myosin light chain (MLC) kinase activation, MLC phosphorylation and contraction. This KCl-induced stimulus-response coupling mechanism is a standard tool-set used in comparative studies to explore more complex mechanisms generated by activation of GPCRs. One area where this approach has been especially productive is in studies designed to understand Ca2+sensitization, the relationship between [Ca2+]iand force produced by GPCR agonists. Studies done in the late 1980s demonstrated that a unique relationship between stimulus-induced [Ca2+]iand force does not exist: for a given increase in [Ca2+]i, GPCR activation can produce greater force than KCl, and relaxant agents can produce the opposite effect to cause Ca2+desensitization. Such changes in Ca2+sensitivity are now known to involve multiple cell signaling strategies, including translocation of proteins from cytosol to plasma membrane, and activation of enzymes, including RhoA kinase and protein kinase C. However, recent studies show that KCl can also cause Ca2+sensitization involving translocation and activation of RhoA kinase. Rather than complicating the Ca2+sensitivity story, this surprising finding is already providing novel insights into mechanisms regulating Ca2+sensitivity of smooth muscle contraction. KCl as a “simple” stimulus promises to remain a standard tool for smooth muscle cell physiologists, whose focus is to understand mechanisms regulating Ca2+sensitivity.