Rho/Rho-kinase mediated signaling in physiology and pathophysiology

H-1152 effects on intraocular pressure and trabecular meshwork morphology of rat eyes

PURPOSE

The aim of this study was to elucidate the effects of the Rho-kinase inhibitor, H-1152, on cultured human trabecular meshwork (HTM) cells, TM morphology, and intraocular pressure (IOP) in rats.

METHODS

Cultured HTM cells were treated with H-1152. Changes in cell morphology and the organization of the actin cytoskeleton and focal adhesions were evaluated by microscopy and immunofluorescence. H-1152 was administered topically to the eyes of conscious rats, and IOP was measured with a commercially available tonometer before and after treatment. The eyes were enucleated 1 h after treatment, fixed, and processed for morphologic analysis by light and electron microscopy.

RESULTS

Exposure of the cultured HTM cells to 20 microM of H-1152 induced elongation and separation of cells, deterioration, and loss of actin stress fibers and focal adhesions within 2 h. Topical administration of H-1152 resulted in a significant decrease in IOP from 0.5 to 6 h, with the maximum IOP reduction of 28.1% at 1 h post-treatment (P < 0.001; n = 10). H-1152 caused an expansion of the intercellular spaces and loss of extracellular material in the juxtacanalicular region of the TM in rat eyes.

CONCLUSIONS

The IOP-lowering effect of H-1152 in rat eyes is likely due to changes in TM-cell morphology, the actin cytoskeleton, and cellular adhesions in the conventional outflow pathway. H-1152 has potential as a new antiglaucoma medication.

Serofendic acid promotes stellation induced by cAMP and cGMP analogs in cultured cortical astrocytes

We investigated the effect of serofendic acid, a neuroprotective substance derived from fetal calf serum, on the morphological changes in cultured cortical astrocytes. Cultured astrocytes developed a stellate morphology with several processes following exposure to dibutylyl cAMP (dbcAMP), a membrane-permeable cAMP analog; 8-Br-cGMP, a membrane-permeable cGMP analog; or phorbol-12-myristate-13-acetate (PMA), a protein kinase C activator. Serofendic acid significantly accelerated the stellation induced by dbcAMP- and 8-Br-cGMP. In contrast, the PMA-induced stellation was not affected by serofendic acid. Next, we attempted to elucidate the mechanism underlying the dbcAMP-induced stellation and explore the site of action of serofendic acid. Both the stellation induced by dbcAMP and the promotional effect of serofendic acid were partially inhibited by KT5720, a specific protein kinase A (PKA) inhibitor. Furthermore, serofendic acid failed to facilitate the stellation induced by Y-27632, an inhibitor of Rho-associated kinase (ROCK). These results indicate that serofendic acid promotes dbcAMP- and 8-Br-cGMP-induced stellation and the promotional effect on dbcAMP-induced stellation is mediated at least partly by the regulation of PKA activity and not by controlling ROCK activity.

Rho-kinase contributes to sustained RhoA activation through phosphorylation of p190A RhoGAP

RhoA is transiently activated by specific extracellular signals such as endothelin-1 (ET-1) in vascular smooth muscle cells. RhoGAP negatively regulates RhoA activity: thus, RhoA becomes the GDP-bound inactive form afterward. Sustained activation of RhoA is induced with high doses of the extracellular signals and is implicated in certain diseases such as vasospasms. However, it remains largely unknown how prolonged activation of RhoA is induced. Here we show that Rho-kinase, an effector of RhoA, phosphorylated p190A RhoGAP at Ser(1150) and attenuated p190A RhoGAP activity in COS7 cells. Binding of Rnd to p190A RhoGAP is thought to enhance its activation. Phosphorylation of p190A RhoGAP by Rho-kinase impaired Rnd binding. Stimulation of vascular smooth muscle cells with a high dose of ET-1 provoked sustained RhoA activation and p190A RhoGAP phosphorylation, both of which were prohibited by a Rho-kinase inhibitor. The phosphomimic mutation of p190A RhoGAP weakened Rnd binding and RhoGAP activities. Taken together, these results suggest that ET-1 induces Rho-kinase activation and subsequent phosphorylation of p190A RhoGAP, leading to prolonged RhoA activation.

Novel molecular insights into RhoA GTPase-induced resistance to aqueous humor outflow through the trabecular meshwork

Impaired drainage of aqueous humor through the trabecular meshwork (TM) culminating in increased intraocular pressure is a major risk factor for glaucoma, a leading cause of blindness worldwide. Regulation of aqueous humor drainage through the TM, however, is poorly understood. The role of RhoA GTPase-mediated actomyosin organization, cell adhesive interactions, and gene expression in regulation of aqueous humor outflow was investigated using adenoviral vector-driven expression of constitutively active mutant of RhoA (RhoAV14). Organ-cultured anterior segments from porcine eyes expressing RhoAV14 exhibited significant reduction of aqueous humor outflow. Cultured TM cells expressing RhoAV14 exhibited a pronounced contractile morphology, increased actin stress fibers, and focal adhesions and increased levels of phosphorylated myosin light chain (MLC), collagen IV, fibronectin, and laminin. cDNA microarray analysis of RNA extracted from RhoAV14-expressing human TM cells revealed a significant increase in the expression of genes encoding extracellular matrix (ECM) proteins, cytokines, integrins, cytoskeletal proteins, and signaling proteins. Conversely, various ECM proteins stimulated robust increases in phosphorylation of MLC, paxillin, and focal adhesion kinase and activated Rho GTPase and actin stress fiber formation in TM cells, indicating a potential regulatory feedback interaction between ECM-induced mechanical strain and Rho GTPase-induced isometric tension in TM cells. Collectively, these data demonstrate that sustained activation of Rho GTPase signaling in the aqueous humor outflow pathway increases resistance to aqueous humor outflow through the trabecular pathway by influencing the actomyosin assembly, cell adhesive interactions, and the expression of ECM proteins and cytokines in TM cells.

Stimulation of lung carcinoma cell growth by fibronectin-integrin signalling

Throughout many countries, lung cancer will kill more people this year than malignancies related to breast, prostate, colon, liver, kidney and melanoma combined. Despite recent advances in understanding the molecular biology of lung carcinoma and the introduction of multiple new chemotherapeutic agents for its treatment, its dismal five-year survival rate (<15%) has not changed substantially. The lack of advancement in this area reflects the limited knowledge available concerning the factors that promote oncogenic transformation and proliferation of carcinoma cells in the lung. Malignant transformation plays a key role in tumor growth and invasion; however, other factors such as the surrounding stroma, local growth factors, vascularity, and systemic hormones are important contributors as well. We believe that the composition of the lung extracellular matrix is also important due to its ability to affect malignant cell behavior in vitro. The matrix glycoprotein fibronectin, for example, is highly expressed in chronic lung disorders where most lung carcinomas are identified. This document reviews information that implicates fibronectin in the stimulation of lung carcinoma cell growth. Data available to date indicate that by binding to specific integrin receptors expressed on the surface of tumor cells, fibronectin stimulates intracellular signals implicated in the pathobiology of lung carcinogenesis and lung tumor chemoresistance including mitogen-activated protein kinases, GTPases, and the PI3-kinase/Akt/mTOR pathway. Thus, integrin-mediated signals triggered by fibronectin in tumor cells represent promising targets for the development of novel anti-cancer strategies.

The role of the actomyosin system in regulating trabecular fluid outflow

Abnormally high resistance to aqueous humor drainage via the trabecular meshwork and Schlemm's canal is highly correlated with the development of primary open-angle glaucoma. Contractility of the actomyosin system in the trabecular cells or inner wall endothelium of Schlemm's canal is an important factor in the regulation of outflow resistance. Cytoskeletal agents, affecting F-actin integrity or actomyosin contractility, or gene therapies, employing overexpression of caldesmon or Rho-A inhibition, can decrease outflow resistance in the drainage pathway. In this review, we discuss the mechanisms underlying these and similar effects on trabecular outflow resistance in living animals and/or in cultured ocular anterior segments from enucleated animal or human eyes.

Fasudil-induced hypoxia-inducible factor-1alpha degradation disrupts a hypoxia-driven vascular endothelial growth factor autocrine mechanism in endothelial cells

Hypoxic response of endothelial cells (EC) is an important component of tumor angiogenesis. Especially, hypoxia-inducible factor-1 (HIF-1)-dependent EC-specific mechanism is an essential component of tumor angiogenesis. Recently, the Rho/Rho-associated kinase (ROCK) signaling has been shown to play a key role in HIF-1alpha induction in renal cell carcinoma and trophoblast. The present study was designed to investigate whether low oxygen conditions might modulate HIF-1alpha expression through the Rho/ROCK signaling in human umbilical vascular ECs (HUVEC). Pull-down assay showed that hypoxia stimulated RhoA activity. Under hypoxic conditions, HUVECs transfected with small interfering RNA of RhoA and ROCK2 exhibited decreased levels of HIF-1alpha protein compared with nontargeted small interfering RNA transfectants, whereas HIF-1alpha mRNA levels were not altered. One of ROCK inhibitors, fasudil, inhibited hypoxia-induced HIF-1alpha expression without altering HIF-1alpha mRNA expression. Furthermore, proteasome inhibitor prevented the effect of fasudil on HIF-1alpha expression, and polyubiquitination was enhanced by fasudil. These results suggested that hypoxia-induced HIF-1alpha expression is through preventing HIF-1alpha degradation by activating the Rho/ROCK signaling in ECs. Furthermore, hypoxia induced both vascular endothelial growth factor (VEGF) and VEGF receptor-2 expression through the Rho/ROCK/HIF-1alpha signaling in HUVECs. Thus, augmented VEGF/VEGF receptor-2 autocrine mechanism stimulated HUVEC migration under hypoxic conditions. In summary, the Rho/ROCK/HIF-1alpha signaling is an essential mechanism for hypoxia-driven, VEGF-mediated autocrine loop in ECs. Therefore, fasudil might have the antimigratory effect against ECs in tumor angiogenesis.

Rho kinases regulate corneal epithelial wound healing

We have previously shown that Rho small GTPase is required for modulating both cell migration and proliferation through cytoskeleton reorganization and focal adhesion formation in response to wounding. In the present study, we investigated the role of Rho kinases (ROCKs), major effectors of Rho GTPase, in mediating corneal epithelial wound healing. Both ROCK 1 and 2 were expressed and activated in THCE cells, an SV40-immortalized human corneal epithelial cell (HCEC) line, in response to wounding, lysophosphatidic acid, and heparin-binding EGF-like growth factor (HB-EGF) stimulations. The ROCK inhibitor Y-27632 efficiently antagonized ROCK activities without affecting Rho activation in wounded HCECs. Y-27632 promoted basal and HB-EGF-enhanced scratch wound healing and enhanced cell migration and adhesion to matrices, while retarded HB-EGF induced cell proliferation. E-cadherin- and beta-catenin-mediated cell-cell junction and actin cytoskeleton organization were disrupted by Y-27632. Y-27632 impaired the formation and maintenance of tight junction barriers indicated by decreased trans-epithelial resistance and disrupted occludin staining. We conclude that ROCK activities enhance cell proliferation, promote epithelial differentiation, but negatively modulate cell migration and cell adhesion and therefore play a role in regulating corneal epithelial wound healing.

The inhaled Rho kinase inhibitor Y-27632 protects against allergen-induced acute bronchoconstriction, airway hyperresponsiveness, and inflammation

Recently, we have shown that allergen-induced airway hyperresponsiveness (AHR) after the early (EAR) and late (LAR) asthmatic reaction in guinea pigs could be reversed acutely by inhalation of the Rho kinase inhibitor Y-27632. The present study addresses the effects of pretreatment with inhaled Y-27632 on the severity of the allergen-induced EAR and LAR, the development of AHR after these reactions, and airway inflammation. Using permanently instrumented and unrestrained ovalbumin (OA)-sensitized guinea pigs, single OA challenge-induced EAR and LAR, expressed as area under the lung function (pleural pressure, P(pl)) time-response curve, were measured, and histamine PC(100) (provocation concentration causing a 100% increase of P(pl)) values were assessed 24 h before, and at 6 and 24 h after, the OA challenge (after the EAR and LAR, respectively). Thirty minutes before and 8 h after OA challenge, saline or Y-27632 (5 mM) was nebulized. After the last PC(100) value, bronchoalveolar lavage (BAL) was performed, and the inflammatory cell profile was determined. It was demonstrated that inhalation of Y-27632 before allergen challenge markedly reduced the immediate allergen-induced peak rise in P(pl), without significantly reducing the overall EAR and LAR. Also, pretreatment with Y-27632 considerably protected against the development of AHR after the EAR and fully prevented AHR after the LAR. These effects could not be explained by a direct effect of Y-27632 on the histamine responsiveness, because of the short duration of the acute bronchoprotection of Y-27632 (<90 min). In addition, Y-27632 reduced the number of total inflammatory cells, eosinophils, macrophages, and neutrophils recovered from the BAL. Altogether, inhaled Y-27632 protects against acute allergen-induced bronchoconstriction, development of AHR after the EAR and LAR, and airway inflammation in an established guinea pig model of allergic asthma.

Pathways leading to phosphorylation of p450c17 and to the posttranslational regulation of androgen biosynthesis

Cytochrome P450c17 (P450c17) is the single enzyme that catalyzes steroid 17alpha-hydroxylase and 17,20 lyase activities and hence is the crucial decision-making step that determines the class of steroid made in a steroidogenic cell. Although both activities are catalyzed on a single active site, the ratio of these activities is regulated by posttranslational events. Serine phosphorylation of P450c17 increases 17,20 lyase activity by increasing the enzyme's affinity for its redox partner, P450 oxidoreductase. We searched for the relevant kinase(s) that phosphorylates P450c17 by microarray studies and by testing of kinase inhibitors. Microarrays show that 145 of the 278 known serine/threonine kinases are expressed in human adrenal NCI-H295A cells, only six of which were induced more than 2-fold by treatment with 8-Br-cAMP. Key components of the ERK1/2 and MAPK/ERK kinase (MEK)1/2 pathways, which have been implicated in the insulin resistance of PCOS, were not found in NCI-H295A cells, implying that these pathways do not participate in P450c17 phosphorylation. Treatment with various kinase inhibitors that probe the protein kinase A/phosphatidylinositol 3-kinase/Akt pathway and the calcium/calmodulin/MAPK kinase pathway had no effect on the ratio of 17,20 lyase activity to 17alpha-hydroxylase activity, appearing to eliminate these pathways as candidates leading to the phosphorylation of P450c17. Two inhibitors that target the Rho-associated, coiled-coil containing protein kinase (ROCK)/Rho pathway suppressed 17,20 lyase activity and P450c17 phosphorylation, both in NCI-H295A cells and in COS-1 cells transfected with a P450c17 expression vector. ROCK1 phosphorylated P450c17 in vitro, but that phosphorylation did not affect 17,20 lyase activity. We conclude that members of the ROCK/Rho pathway act upstream from the kinase that phosphorylates P450c17 in a fashion that augments 17,20 lyase activity, possibly acting to catalyze a priming phosphorylation.

ROCK and PRK-2 mediate the inhibitory effect of Y-27632 on polyglutamine aggregation

Polyglutamine expansion in huntingtin (Htt) and the androgen receptor (AR) causes untreatable neurodegenerative diseases. Y-27632, a therapeutic lead, reduces Htt and AR aggregation in cultured cells, and Htt-induced neurodegeneration in Drosophila. Y-27632 inhibits both Rho-associated kinases ROCK and PRK-2, making its precise intracellular target uncertain. Over-expression of either kinase increases Htt and AR aggregation. Three ROCK inhibitors (Y-27632, HA-1077, and H-1152P), and a specific ROCK inhibitory peptide reduce polyglutamine protein aggregation, as does knockdown of ROCK or PRK-2 by RNAi. RNAi also indicates that each kinase is required for the inhibitory effects of Y-27632 to manifest fully. These two actin regulatory kinases are thus involved in polyglutamine aggregation, and their simultaneous inhibition may be an important therapeutic goal.

Cellular functions of GEF-H1, a microtubule-regulated Rho-GEF: is altered GEF-H1 activity a crucial determinant of disease pathogenesis?

The Rho guanine nucleotide exchange factor GEF-H1 is uniquely regulated by microtubule binding and is crucial in coupling microtubule dynamics to Rho-GTPase activation in a variety of normal biological situations. Here, we review the roles of GEF-H1 in epithelial barrier permeability, cell motility and polarization, dendritic spine morphology, antigen presentation, leukemic cell differentiation, cell cycle regulation, and cancer. GEF-H1 might also contribute to pathophysiological signaling involved in leukemias, and in cancers associated with mutated p53 tumor suppressor gene, epithelial and endothelial cell dysfunction, infectious disease, and cardiac hypertrophy. We suggest that GEF-H1 could be a novel therapeutic target in multiple human diseases.

Mechanical homeostasis is altered in uterine leiomyoma

OBJECTIVE

Uterine leiomyoma produce an extracellular matrix (ECM) that is abnormal in its volume, content, and structure. Alterations in ECM can modify mechanical stress on cells and lead to activation of Rho-dependent signaling and cell growth. Here we sought to determine whether the altered ECM that is produced by leiomyoma was accompanied by an altered state of mechanical homeostasis.

STUDY DESIGN

We measured the mechanical response of paired leiomyoma and myometrial samples and performed immunogold, confocal microscopy, and immunohistochemical analyses.

RESULTS

Leiomyoma were significantly stiffer than matched myometrium. The increased stiffness was accompanied by alteration of the ECM, cell shape, and cytoskeleton in leiomyoma, compared with myometrial samples from the same uterus. Levels of AKAP13, a protein that is known to activate Rho, were increased in leiomyoma compared to myometrium. AKAP13 was associated with cytoskeletal filaments of immortalized leiomyoma cells.

CONCLUSION

Leiomyoma cells are exposed to increased mechanical loading and show structural and biochemical features that are consistent with the activation of solid-state signaling.

Effects of pharmacologic inhibition of protein geranylgeranyltransferase type I on aqueous humor outflow through the trabecular meshwork

PURPOSE

To determine the effects of inhibition of protein geranylgeranyltransferase type I (GGTase-I), which isoprenylates so-called CaaX proteins, including the GTP-binding proteins such as Rho GTPases and the betagamma subunits of heterotrimeric G-proteins, on aqueous humor outflow and trabecular meshwork cytoskeletal integrity.

METHODS

A selective small molecular inhibitor of GGTase-I, GGTI-DU40, was tested in this study to investigate its effects on actin cytoskeletal integrity, cell adhesions, cell-cell junctions, myosin II phosphosphorylation, and membrane localization of GTP-binding proteins in trabecular meshwork (TM) cells, using immunofluorescence detection and immunoblotting analysis. The effects of GGTI-DU40 on aqueous humor outflow were determined using organ-cultured, perfused anterior segments of porcine eyes.

RESULTS

In the TM cell lysates, GGTI-DU40 was confirmed to inhibit GGTase-I activity in a dose-dependent manner. TM cells treated with GGTI-DU40 displayed dose-dependent changes in cell morphology and reversible decreases in actin stress fibers, focal adhesions, and adherens junctions. Myosin light chain phosphorylation was decreased significantly, and membrane localization of isoprenylated small GTPases and Gbetagamma was impaired in drug-treated TM cells. Aqueous outflow facility was increased significantly in eyes perfused with GGTI-DU40.

CONCLUSIONS

These data demonstrate that inhibition of geranylgeranyl isoprenylation of CaaX proteins in the aqueous outflow pathway increases aqueous humor outflow, possibly through altered cell adhesive interactions and actin cytoskeletal organization in cells of the outflow pathway. This study indicates that the GGTase-I enzyme is a promising molecular target for lowering increased ocular pressure in glaucoma patients.

GEF-H1 couples nocodazole-induced microtubule disassembly to cell contractility via RhoA

The RhoA GTPase plays a vital role in assembly of contractile actin-myosin filaments (stress fibers) and of associated focal adhesion complexes of adherent monolayer cells in culture. GEF-H1 is a microtubule-associated guanine nucleotide exchange factor that activates RhoA upon release from microtubules. The overexpression of GEF-H1 deficient in microtubule binding or treatment of HeLa cells with nocodazole to induce microtubule depolymerization results in Rho-dependent actin stress fiber formation and contractile cell morphology. However, whether GEF-H1 is required and sufficient to mediate nocodazole-induced contractility remains unclear. We establish here that siRNA-mediated depletion of GEF-H1 in HeLa cells prevents nocodazole-induced cell contraction. Furthermore, the nocodazole-induced activation of RhoA and Rho-associated kinase (ROCK) that mediates phosphorylation of myosin regulatory light chain (MLC) is impaired in GEF-H1-depleted cells. Conversely, RhoA activation and contractility are rescued by reintroduction of siRNA-resistant GEF-H1. Our studies reveal a critical role for a GEF-H1/RhoA/ROCK/MLC signaling pathway in mediating nocodazole-induced cell contractility.

Rho-kinase and effects of Rho-kinase inhibition on the lower urinary tract

Altered smooth muscle cell contractility/tone contributes, at least in part, to the lower urinary tract symptoms (LUTS) seen in men with benign prostatic obstruction (BPO). Accordingly, many of the therapies to date have focused largely on blockade of individual membrane receptors to diminish smooth muscle contractility and provide symptomatic relief. This pharmacologic approach has been associated with variable results, limited efficacy, and untoward side effects. Such limited clinical success is not surprising given the plethora of neurotransmitters, neuromodulators, and hormones that are now known to modulate LUT smooth muscle cell tone. In the pursuit of improved treatment options, more recent investigations have focused attention on intracellular signal transduction events that represent convergence points for membrane receptor activation. In particular, calcium sensitization and the role of the Rho-kinase pathway has received much attention. In this report, we review the literature on the role of the Rho-kinase pathway in the modulation of LUT smooth muscle cell tone. In short, the available data support an important role for Rho-kinase in the physiologic and pathophysiologic regulation of LUT smooth muscle cell tone. Rho-kinase inhibitors thus appear to represent a potentially attractive therapeutic possibility for the treatment of LUTS.

Quantitative high-throughput cell-based assays for inhibitors of ROCK kinases

The serine/threonine kinases ROCK1 and ROCK2 are direct targets of activated rho GTPases, and aberrant rho/ROCK signaling has been implicated in a number of human diseases. We have developed novel methods for high-throughput assays of ROCK inhibitors that provide for quantitative evaluation of the ability of small molecules to inhibit the function of ROCK kinases in intact cells. Conditions for extraction of known phosphorylated substrates of ROCK were identified, and the involvement of ROCK in phosphorylation of these substrates was evaluated using small interfering RNA (siRNA). Of the potential substrates tested, MYPT1 was identified as a substrate whose phosphorylation was reduced markedly in the combined absence of ROCK1 and ROCK2 proteins, and ELISA methods were developed to allow quantitative measurement of the degree of phosphorylation of MYPT1 at residue T853 in cells grown in 96-well plates. These methods are amenable to high-throughput assays for identification of ROCK inhibitors within libraries of small molecules and can be used to compare compound potencies to prioritize compounds of interest for additional evaluation. These methods should be useful in drug discovery efforts directed toward identifying potent ROCK inhibitors for potential treatment of cancer, hypertension, or other diseases involving rho/ROCK signaling.

ROCK inhibition and CNTF interact on intrinsic signalling pathways and differentially regulate survival and regeneration in retinal ganglion cells

Functional regeneration in the CNS is limited by lesion-induced neuronal apoptosis and an environment inhibiting axonal elongation. A principal, yet unresolved question is the interaction between these two major factors. We thus evaluated the role of pharmacological inhibition of rho kinase (ROCK), a key mediator of myelin-derived axonal growth inhibition and CNTF, a potent neurotrophic factor for retinal ganglion cells (RGC), in models of retinal ganglion cell apoptosis and neurite outgrowth/regeneration in vitro and in vivo. Here, we show for the first time that the ROCK inhibitor Y-27632 significantly enhanced survival of RGC in vitro and in vivo. In vitro, the co-application of CNTF and Y-27632 potentiated the effect of either substance alone. ROCK inhibition resulted in the activation of the intrinsic MAPK pathway, and the combination of CNTF and Y-27632 resulted in even more pronounced MAPK activation. While CNTF also induced STAT3 phosphorylation, the additional application of ROCK inhibitor surprisingly diminished the effects of CNTF on STAT3 phosphorylation. ROCK activity was also decreased in an additive manner by both substances. In vivo, both CNTF and Y-27632 enhanced regeneration of RGC into the non-permissive optic nerve crush model and additive effects were observed after combination treatment. Further evaluation using specific inhibitors delineate STAT3 as a negative regulator of neurite growth and positive regulator of cell survival, while MAPK and Akt support neurite growth. These results show that next to neurotrophic factors ROCK inhibition by Y-27632 potently supports survival of lesioned adult CNS neurons. Co-administration of CNTF and Y-27632 results in additive effects on neurite outgrowth and regeneration. The interaction of intracellular signalling pathways may, however, attenuate more pronounced synergy and has to be taken into account for future treatment strategies.

Functional, genetic and bioinformatic characterization of a calcium/calmodulin kinase gene in Sporothrix schenckii

Background

Sporothrix schenckii is a pathogenic, dimorphic fungus, the etiological agent of sporotrichosis, a subcutaneous lymphatic mycosis. Dimorphism in S. schenckii responds to second messengers such as cAMP and calcium, suggesting the possible involvement of a calcium/calmodulin kinase in its regulation. In this study we describe a novel calcium/calmodulin-dependent protein kinase gene in S. schenckii, sscmk1, and the effects of inhibitors of calmodulin and calcium/calmodulin kinases on the yeast to mycelium transition and the yeast cell cycle.

Results

Using the PCR homology approach a new member of the calcium/calmodulin kinase family, SSCMK1, was identified in this fungus. The cDNA sequence of sscmk1 revealed an open reading frame of 1,221 nucleotides encoding a 407 amino acid protein with a predicted molecular weight of 45.6 kDa. The genomic sequence of sscmk1 revealed the same ORF interrupted by five introns. Bioinformatic analyses of SSCMK1 showed that this protein had the distinctive features that characterize a calcium/calmodulin protein kinase: a serine/threonine protein kinase domain and a calmodulin-binding domain. When compared to homologues from seven species of filamentous fungi, SSCMK1 showed substantial similarities, except for a large and highly variable region that encompasses positions 330 – 380 of the multiple sequence alignment. Inhibition studies using calmodulin inhibitor W-7, and calcium/calmodulin kinase inhibitors, KN-62 and lavendustin C, were found to inhibit budding by cells induced to re-enter the yeast cell cycle and to favor the yeast to mycelium transition.

Conclusion

This study constitutes the first evidence of the presence of a calcium/calmodulin kinase-encoding gene in S. schenckii and its possible involvement as an effector of dimorphism in this fungus. These results suggest that a calcium/calmodulin dependent signaling pathway could be involved in the regulation of dimorphism in this fungus. The results suggest that the calcium/calmodulin kinases of yeasts are evolutionarily distinct from those in filamentous fungi.

Plexin-B1 Utilizes RhoA and Rho Kinase to Promote the Integrin-dependent Activation of Akt and ERK and Endothelial Cell Motility

The semaphorins are a family of proteins originally identified as axon-guiding molecules in the developing nervous system that have been recently shown to regulate many cellular functions, including motility, in a variety of cell types. We have previously shown that in endothelial cells Semaphorin 4D acts through its receptor, Plexin-B1, to elicit a pro-angiogenic phenotype that involves the activation of the phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway. Here we show through the use of a receptor chimeric approach, Plexin-B1 mutants, and dominant negative and pharmacological inhibitors that this response is dependent upon the activation of RhoA and its downstream target, Rho kinase (ROK). Indeed, we demonstrate that in endothelial cells, Semaphorin 4D promotes the formation of focal adhesion complexes, stress fibers, and the phosphorylation of myosin light chain, a response that was abolished by the use of ROK inhibitors and absent from cells expressing Plexin-B1 mutant constructs incapable of signaling to RhoA. Stress fiber polymerization and contraction are in turn necessary for RhoA-dependent pro-angiogenic signaling through Plexin-B1. Furthermore, we observed that in endothelial cells Plexin-B1 promotes the integrin-mediated activation of Pyk2, resulting in the stimulation of PI3K, Akt, and ERK. These findings provide evidence that Plexin-B1 promotes endothelial cell motility through RhoA and ROK by regulating the integrin-dependent signaling networks that result in the activation of PI3K and Akt.

The future of the oral pharmacotherapy of male erectile dysfunction: things to come

The convincing clinical data on the use of the orally active phosphodiesterase inhibitors sildenafil, vardenafil and tadalafil for the treatment of male erectile dysfunction have boosted research activities on the physiology of the male erectile mechanism. This included both peripheral intracellular signal transduction in the corpus cavernosum as well as central brain and spinal cord pathways controlling penile erection. This work provided the basis for the development and introduction of several new therapeutic modalities into the management of erectile dysfunction, some of which are already offered to the patients. As the concept of 'taking a pill' as a cure for an illness or the relief of symptoms of a disease has become widely accepted by the consumers, the pharmacologic treatment of erectile dysfunction has primarily focussed on selective, orally available drugs acting by influencing intracellular or central regulatory mechanisms, combining a high response rate and the advantage of an on-demand intake. These agents are regarded as more efficacious, and have a faster onset of drug action in the target tissue and an improved effect to side-effect ratio. The purpose of this review is to describe the major novel and evolving pharmacologic advances in the field of oral pharmacotherapy for the treatment of male erectile dysfunction.

Fasudil inhibits vascular endothelial growth factor-induced angiogenesis in vitro and in vivo

Vascular endothelial growth factor (VEGF)-induced endothelial cell migration is an important component of tumor angiogenesis. Rho and Rho-associated kinase (ROCK) are key regulators of focal adhesion, stress fiber formation, and thus cell motility. Inhibitors of this pathway have been shown to inhibit endothelial cell motility and angiogenesis. In this study, we investigated the antiangiogenic effect of fasudil, one of the ROCK inhibitors. Fasudil inhibited VEGF-induced endothelial cell migration, viability, and tube formation in vitro in human umbilical vein endothelial cells. VEGF-induced endothelial cell migration was reduced by fasudil associated with loss of stress fiber formation, focal adhesion assembly, and with the suppression of tyrosine phosphorylation of focal adhesion proteins. Furthermore, fasudil inhibited VEGF-induced phosphorylation of myosin light chain, which is one of the main substrates of ROCK. Therefore, the effect of fasudil was suggested to be ROCK dependent. Fasudil not only inhibited VEGF-induced cell proliferation but also reversed the protective effect of VEGF on apoptosis, which resulted in the decrease of cell viability. Moreover, fasudil inhibited VEGF-induced angiogenesis in a directed in vivo angiogenesis assay. These data are the first demonstration that fasudil has antiangiogenic properties. Therefore, fasudil might be useful for the treatment of angiogenesis-related diseases, especially cancer.

Role of Rho-kinase in contractions of ureters from rabbits with unilateral ureteric obstruction

OBJECTIVE

To investigate the expression of two isoforms of Rho-kinase (ROCK) and its functional role in the pathophysiological control of smooth muscle contraction in rabbits with unilateral ureteric obstruction (UUO).

MATERIAL AND METHODS

Left UUO was created in 14 rabbits and eight other rabbits (controls) had sham operations. After 2 weeks all the rabbits were killed. Ureteric strips suspended in an organ bath were used for functional studies and the effects of Y-27632, a specific inhibitor of Rho-kinase, on spontaneous contractions and electrical field stimulation (EFS; 50 V, 1 ms, 16 Hz, for 20 s), carbachol- (10(-7)-10(-4)m), phenylephrine- (10(-7)-10(-4)m) and KCl- (50 mm) induced contractions were analysed. Western blotting was used to determine expression levels of Rho-kinase protein in the ureters of UUO and control rabbits.

RESULTS

In the functional analysis, the contractions induced by EFS, KCl, phenylephrine and carbachol in the ureteric strips from rabbits with UUO were significantly greater than those from the control rabbits. Y-27632 considerably suppressed the ureter contractile responses in both UUO and control rabbits. Western blot analysis showed that both ROCK-1 and ROCK-2 proteins were expressed in the rabbit ureter. In accordance with the functional studies, the expression levels of both ROCK-1 and ROCK-2 were significantly greater in the ureters of UUO rabbits than in the controls.

CONCLUSIONS

Y-27632 suppressed ureteric contractions in the rabbits with UUO. Western blot analysis also confirmed greater expression levels of ROCK-1 and ROCK-2 in the ureters of UUO rabbits. It is important to elucidate by which mechanisms the Rho-kinase pathway affects ureteric function after obstruction.

Rho GTPase/Rho kinase inhibition as a novel target for the treatment of glaucoma

Rho kinase (ROCK1 and ROCK2) is a serine/threonine kinase that serves as an important downstream effector of Rho GTPase, and plays a critical role in regulating the contractile tone of smooth muscle tissues in a calcium-independent manner. Several lines of experimental evidence indicate that modulating ROCK activity within the aqueous humor outflow pathway using selective inhibitors could achieve very significant benefits for the treatment of increased intraocular pressure in patients with glaucoma. The rationale for such an approach stems from experimental data suggesting that both ROCK and Rho GTPase inhibitors can increase aqueous humor drainage through the trabecular meshwork, leading to a decrease in intraocular pressure. In addition to their ocular hypotensive properties, inhibitors of both ROCK and Rho GTPase have been shown to enhance ocular blood flow, retinal ganglion cell survival and axon regeneration. These properties of the ROCK and Rho GTPase inhibitors indicate that targeting the Rho GTPase/ROCK pathway with selective inhibitors represents a novel therapeutic approach aimed at lowering increased intraocular pressure in glaucoma patients.

Rho-kinase phosphorylates eNOS at threonine 495 in endothelial cells

Endothelial nitric oxide synthase (eNOS) produces nitric oxide (NO), which is involved in various physiological functions of the cardiovascular system. eNOS is activated by dephosphorylation at Thr495 and phosphorylation at Ser1177. Inhibition of Rho-kinase, an effector of the small GTPase RhoA, leads to activation of Akt/PKB, which phosphorylates eNOS at Ser1177 and thereby promotes NO production. However, little is known about the effects of Rho-kinase on phosphorylation of Thr495. We here found that the constitutively active form of Rho-kinase phosphorylated eNOS at Thr495 in vitro. Expression of the constitutively active form of RhoA or Rho-kinase increased this phosphorylation in COS-7 cells. Addition of thrombin to cultured human umbilical vein endothelial cells induced phosphorylation of eNOS at Thr495. Treatment with Y27632, a Rho-kinase inhibitor, suppressed thrombin-induced phosphorylation at Thr495. These results indicate that Rho-kinase can directly phosphorylate eNOS at Thr495 to suppress NO production in endothelium.

Comparative pharmacological analysis of Rho-kinase inhibitors and identification of molecular components of Ca2+ sensitization in the rat lower urinary tract

We aimed to compare the expression and function of molecular components of the RhoA/Rho-kinase signaling pathway in the contractile responses of detrusor, trigonal and urethral smooth muscle, using selective Rho-kinase inhibitors. Contractility studies and molecular approaches were employed to demonstrate the expression patterns and functional activity of the RhoA/Rho-kinase signaling pathway in the lower urinary tract. Frequency-response curves (1-32 Hz) and concentration-response curves (CRC) to carbachol (CCh, 0.01-30 microM), phenylephrine (PE, 0.01-300 microM) and endothelin-1 (ET-1, 0.01-100 nM) were significantly attenuated (p<0.01) following incubation with the Rho-kinase inhibitors H-1152 (0.1-1 microM), Y-27632 (1-10 microM) or HA-1077 (10 microM). Addition of Rho-kinase inhibitors also markedly reduced (p<0.01) the contractions evoked by either KCl (80 mM) or alpha,beta-methylene ATP (alpha,beta-mATP, 10 microM). Among the Rho-kinase inhibitors tested, H-1152 was approximately 9-16 times more potent than Y-27632 or HA-1077. In addition, basal tone of detrusor and trigonal strips was reduced following addition of Y-27632 (10 microM), H-1152 (1 microM) and HA-1077 (10 microM). The expression of RhoA, RhoGDI, leukemia-associated RhoGEF (LARG) and p115RhoGEF was similar among the detrusor, trigone and urethra, whereas Rho-kinase alpha, Rho-kinase beta and PDZ-RhoGEF protein levels were significantly lower in the urethra. Components of the RhoA/Rho-kinase signaling are expressed in detrusor, trigonal and urethral smooth muscle and dynamically regulate contraction and tone. Manipulation of RhoGEF expression may provide further understanding of mechanisms involving Ca(2+) sensitization in the lower urinary tract.

Role of the small GTPase RhoA in the hypoxia-induced decrease of plasma membrane Na,K-ATPase in A549 cells

Hypoxia impairs alveolar fluid reabsorption by promoting Na,K-ATPase endocytosis, from the plasma membrane of alveolar epithelial cells. The present study was designed to determine whether hypoxia induces Na,K-ATPase endocytosis via reactive oxygen species (ROS)-mediated RhoA activation. In A549 cells, RhoA activation occurred within 15 minutes of cells exposure to hypoxia. This activation was inhibited in cells infected with adenovirus coding for gluthatione peroxidase (an H2O2 scavenger), in mitochondria depleted (rho0) cells or cells expressing decreased levels of the Rieske iron-sulfur protein (inhibitor of mitochondrial complex III), which suggests a role for mitochondrial ROS. Moreover, exogenous H2O2 treatment during normoxia mimicked the effects of hypoxia on RhoA, further supporting a role for ROS. Cells expressing dominant negative RhoA failed to endocytose the Na,K-ATPase during hypoxia or after H2O2 treatment. Na,K-ATPase endocytosis was also prevented in cells treated with Y-27632, a Rho-associated kinase (ROCK) inhibitor, and in cells expressing dominant negative ROCK. In summary, we provide evidence that in human alveolar epithelial cells exposed to hypoxia, RhoA/ROCK activation is necessary for Na,K-ATPase endocytosis via a mechanism that requires mitochondrial ROS.

Angiotensin II signal transduction through the AT1 receptor: novel insights into mechanisms and pathophysiology

The intracellular signal transduction of AngII (angiotensin II) has been implicated in cardiovascular diseases, such as hypertension, atherosclerosis and restenosis after injury. AT(1) receptor (AngII type-1 receptor), a G-protein-coupled receptor, mediates most of the physiological and pathophysiological actions of AngII, and this receptor is predominantly expressed in cardiovascular cells, such as VSMCs (vascular smooth muscle cells). AngII activates various signalling molecules, including G-protein-derived second messengers, protein kinases and small G-proteins (Ras, Rho, Rac etc), through the AT(1) receptor leading to vascular remodelling. Growth factor receptors, such as EGFR (epidermal growth factor receptor), have been demonstrated to be 'trans'-activated by the AT(1) receptor in VSMCs to mediate growth and migration. Rho and its effector Rho-kinase/ROCK are also implicated in the pathological cellular actions of AngII in VSMCs. Less is known about the endothelial AngII signalling; however, recent studies suggest the endothelial AngII signalling positively, as well as negatively, regulates the NO (nitric oxide) signalling pathway and, thereby, modulates endothelial dysfunction. Moreover, selective AT(1)-receptor-interacting proteins have recently been identified that potentially regulate AngII signal transduction and their pathogenic functions in the target organs. In this review, we focus our discussion on the recent findings and concepts that suggest the existence of the above-mentioned novel signalling mechanisms whereby AngII mediates the formation of cardiovascular diseases.

Rho kinase-mediated local cold-induced cutaneous vasoconstriction is augmented in aged human skin

Cutaneous vasoconstriction (VC), a critical thermoregulatory response to cold, is generally impaired with aging. However, the effects of aging on local cooling-induced VC and its underlying mechanisms are poorly understood. We tested whether aged skin exhibits attenuated localized cold-induced VC and whether Rho kinase-mediated cold-induced VC is augmented with age. Skin blood flow was monitored with laser Doppler flowmetry (LDF) on seven young and seven older subjects. Cutaneous vascular conductance (CVC; LDF/mean arterial pressure) was expressed as percentage change from baseline (%DeltaCVC(base)). In protocol 1, two forearm skin sites were cooled to six temperatures (31.5-19 degrees C) for 10 min each or two temperatures (29 degrees C, 24 degrees C) for 30 min each, with no age differences in the magnitude of VC. In protocol 2, three forearm skin sites were instrumented for intradermal microdialysis and cooled to 24 degrees C for 40 min. During minutes 1-5, there was no age difference in CVC responses at control sites (young: -45 +/- 6% vs. older: -46 +/- 3%, P > 0.9). Adrenoceptor antagonism (yohimbine + propranolol) abolished VC in young (to +15 +/- 13%, P < 0.05) but only partially inhibited VC in older subjects (to -23 +/- 6%, P < 0.05). Rho kinase inhibition plus adrenoceptor antagonism (yohimbine + propranolol + fasudil) abolished VC in both groups. During minutes 35-40, there was no age difference in control (young: -77 +/- 4% vs. older: -70 +/- 2%, P > 0.3) or adrenoceptor-antagonized responses (young: -61 +/- 3% vs. older: -55 +/- 2%, P > 0.3); however, Rho kinase inhibition plus adrenoceptor antagonism blocked more VC in older compared with young subjects (-19 +/- 11% vs. -35 +/- 3%, P < 0.05). Although its magnitude remains unaffected, cold-induced VC becomes less dependent on adrenergic and more dependent on Rho kinase signaling with advancing age.

Up-regulation of arginase activity contributes to attenuated reflex cutaneous vasodilatation in hypertensive humans

Reflex cutaneous vasodilatation is dependent on nitric oxide (NO), which is diminished in hypertension (HTN). Arginase may be up-regulated with HTN, which preferentially metabolizes L-arginine (L-arg), competing with NO-synthase (NOS)-mediated pathways and limiting NO synthesis. We hypothesized that NO-dependent vasodilatation would be attenuated in HTN skin, and arginase inhibition (A-I) alone or with concurrent l-arginine supplementation, would augment vasodilatation. Five microdialysis fibres were placed in skin of eight unmedicated subjects with HTN (mean arterial pressure (MAP), 112 +/- 1 mmHg) and nine age-matched normotensive (AMN) (MAP: 87 +/- 1 mmHg) men and women to serve as: control (C, Ringer solution), NOS inhibited (NOS-I, 10 mM L-NAME), A-I (5 mM BEC + 5 mM nor-NOHA), L-arg supplemented (L-arg, 10 mM L-arg), and combined A-I + L-arg. Reflex vasodilatation was induced by using a water-perfused suit to increase oral temperature (T(or)) 1.0 degrees C. Red cell flux was measured by laser-Doppler flowmetry over each site. Cutaneous vascular conductance was calculated (CVC = flux/MAP) and normalized to maximal CVC (28 mM SNP + local heating to 43 degrees C). The Delta%CVC(max) between the control and NOS-I site was calculated as the difference between C and NOS-I sites. Maximal CVC was attenuated in the HTN subjects by approximately 25% compared with AMN subjects (P<0.001). Throughout, whole body heating %CVC(max) was not different between the groups (HTN, 43 +/- 3%CVC(max) versus AMN, 45 +/- 3%CVC(max), P>0.05). NOS-I significantly decreased %CVC(max) in both groups but %CVC(max) was greater in the HTN group (HTN, 32 +/- 4%CVC(max) versus AMN, 23 +/- 3%CVC(max), P<0.05). The Delta%CVC(max) between the control and NOS-I sites was attenuated at DeltaT(or) > 0.5 degrees C in the HTN group (P < 0.001 versus AMN). A-I alone augmented %CVC(max) only in the HTN group (HTN, 65 +/- 5%CVC(max) versus AMN, 48 +/- 3%CVC(max), P<0.05). L-Arg alone did not affect %CVC(max) in either group (HTN, 49 +/- 5%CVC(max) versus AMN, 49 +/- 3%CVC(max), P > 0.05). Combined A-I + L-arg augmented %CVC(max) in both subject groups compared with their respective control sites (HTN, 60 +/- 7%CVC(max) versus AMN, 61 +/- 3%CVC(max), both P<0.05 versus respective control sites). Vasodilatation is attenuated with HTN due to decreased NO-dependent vasodilatation and can be augmented with arginase inhibition but not L-arg supplementation, suggesting that arginase is up-regulated with HTN.

Activation of platelet function through G protein-coupled receptors

Because of their ability to become rapidly activated at places of vascular injury, platelets are important players in primary hemostasis as well as in arterial thrombosis. In addition, they are also involved in chronic pathological processes including the atherosclerotic remodeling of the vascular system. Although primary adhesion of platelets to the vessel wall is largely independent of G protein-mediated signaling, the subsequent recruitment of additional platelets into a growing platelet thrombus requires mediators such as ADP, thromboxane A(2), or thrombin, which act through G protein-coupled receptors. Platelet activation via G protein-coupled receptors involves 3 major G protein-mediated signaling pathways that are initiated by the activation of the G proteins G(q), G(13), and G(i). This review summarizes recent progress in understanding the mechanisms underlying platelet activation and thrombus extension via G protein-mediated signaling pathways.

LUTS treatment: Future treatment options

Lower urinary tract symptoms (LUTS) are commonly divided into storage, voiding, and postmicturition symptoms, and may occur in both men and women. Male LUTS have historically been linked to benign prostatic hyperplasia (BPH), but are not necessarily prostate related. The focus of treatment for LUTS has thus shifted from the prostate to the bladder and other extraprostatic sites. LUTS include symptoms of the overactive bladder (OAB), which are often associated with detrusor overactivity. Treatment for LUTS suggestive of BPH has traditionally involved the use of alpha(1)-adrenoceptor (AR) antagonists; 5alpha-reductase inhibitors; and phytotherapy-however, several new therapeutic principles have shown promise. Selective beta(3)-adrenoceptor agonists and antimuscarinics are potentially useful agents for treating LUTS, particularly for storage symptoms secondary to outflow obstruction. Other agents of potential or actual importance are antagonists of P2X(3) receptors, botulinum toxin type A, endothelin (ET)-converting enzyme inhibitors, and drugs acting at vanilloid, angiotensin, and vitamin D(3) receptor sites. Drugs interfering with the nitric oxide/cGMP-cAMP pathway, Rho-kinase and COX inhibitors, as well as drugs targeting receptors and mechanisms within the CNS, are also of interest and deserving of further study for the treatment of LUTS.

Cold-induced cutaneous vasoconstriction is mediated by Rho kinase in vivo in human skin

Cutaneous vasoconstriction (VC) is the initial thermoregulatory response to cold exposure and can be elicited through either whole body or localized skin cooling. However, the mechanisms governing local cold-induced VC are not well understood. We tested the hypothesis that Rho kinase participates in local cold-induced cutaneous VC. In seven men and women (20-27 yr of age), up to four ventral forearm skin sites were instrumented with intradermal microdialysis fibers for localized drug delivery during cooling. Skin blood flow was monitored at each site with laser-Doppler flowmetry while local skin temperature was decreased and maintained at 24 degrees C for 40 min. Cutaneous vascular conductance (CVC; laser-Doppler flowmetry/mean arterial pressure) was expressed as percent change from 34 degrees C baseline. During the first 5 min of cooling, CVC decreased at control sites (lactated Ringer solution) to -45 +/- 6% (P < 0.001), increased at adrenoceptor-antagonized sites (yohimbine + propranolol) to 15 +/- 14% (P = 0.002), and remained unchanged at both Rho kinase-inhibited (fasudil) and adrenoceptor-antagonized + Rho kinase-inhibited sites (yohimbine + propranolol + fasudil) (-9 +/- 1%, P = 0.4 and -6 +/- 2%, P = 0.4, respectively). During the last 5 min of cooling, CVC further decreased at all sites when compared with baseline values (control, -77 +/- 4%, P < 0.001; adrenoceptor antagonized, -61 +/- 3%, P < 0.001; Rho kinase inhibited, -34 +/- 7%, P < 0.001; and adrenoceptor antagonized + Rho kinase inhibited sites, -35 +/- 3%, P < 0.001). Rho kinase-inhibited and combined treatment sites were significantly attenuated when compared with both adrenoceptor-antagonized (P < 0.01) and control sites (P < 0.0001). Rho kinase mediates both early- and late-phase cold-induced VC, supporting in vitro findings and providing a putative mechanism through which both adrenergic and nonadrenergic cold-induced VC occurs in an in vivo human thermoregulatory model.

Expression of RhoA in placenta of preeclampsia

In order to detect the expression of RhoA in placenta from normal pregnancy and preeclampsia and evaluate the role of RhoA in preeclampsia, the expression of RhoA in placenta collected from 40 preeclampsia patients and 20 normotensive controls was determined by immunohistochemistry and RT-PCR. RhoA was found in syncytiotrophoblasts and cytotrophoblasts. The mean density of RhoA protein in placental tissues of mild and severe preeclampsia groups was significantly higher than that in normal pregnancy. The expression level of RhoA mRNA in mild and severe preeclampsia groups was significantly higher than that of normal pregnancy. Increased expression of RhoA in placental tissues might play an important role in the pathogenesis of preeclampsia.

Inhalation of the Rho-kinase inhibitor Y-27632 reverses allergen-induced airway hyperresponsiveness after the early and late asthmatic reaction

Background

In guinea pigs, we have previously demonstrated that the contribution of Rho-kinase to airway responsiveness in vivo and ex vivo is enhanced after active sensitization with ovalbumin (OA). Using conscious, unrestrained OA-sensitized guina pigs, we now investigated the role of Rho-kinase in the development of airway hyperresponsiveness (AHR) after the allergen-induced early (EAR) and late asthmatic reaction (LAR) in vivo.

Methods

Histamine and PGF_2α PC₁₀₀-values (provocation concentrations causing 100% increase in pleural pressure) were assessed before OA-challenge (basal airway responsiveness) and after the OA-induced EAR (5 h after challenge) and LAR (23 h after challenge). Thirty minutes later, saline or the specific Rho-kinase inhibitor Y-27632 (5 mM, nebulizer concentration) were nebulized, after which PC₁₀₀-values were reassessed.

Results

In contrast to saline, Y-27632 inhalation significantly decreased the basal responsiveness toward histamine and PGF_2α before OA-challenge, as indicated by increased PC₁₀₀ -values. Both after the allergen-induced EAR and LAR, AHR to histamine and PGF_2α was present, which was reversed by Y-27632 inhalation. Moreover, there was an increased effectiveness of Y-27632 to reduce airway responsiveness to histamine and PGF_2α after the EAR and LAR as compared to pre-challenge conditions. Saline inhalations did not affect histamine or PGF_2α PC₁₀₀-values at all. Interestingly, under all conditions Y-27632 was significantly more effective in reducing airway responsiveness to PGF_2α as compared to histamine. Also, there was a clear tendency (P = 0.08) to a more pronounced degree of AHR after the EAR for PGF_2α than for histamine.

Conclusion

The results indicate that inhalation of the Rho-kinase inhibitor Y-27632 causes a considerable bronchoprotection to both histamine and PGF_2α. Moreover, the results are indicative of a differential involvement of Rho-kinase in the agonist-induced airway obstruction in vivo. Increased Rho-kinase activity contributes to the allergen-induced AHR to histamine and PGF_2α after both the EAR and the LAR, which is effectively reversed by inhalation of Y-27632. Therefore, Rho-kinase can be considered as a potential pharmacotherapeutical target in allergic asthma.

Airway smooth muscle as a regulator of immune responses and bronchomotor tone

The traditional view of airway smooth muscle (ASM) in asthma, as a purely contractile tissue, seems to be inadequate. Compelling evidence now suggests that ASM plays an important role in regulating bronchomotor tone, in perpetuating airway inflammation, and in remodeling of the airways. This article reviews three distinct functions of ASM cells: the process of excitation-contraction coupling, with a particular focus on the role of cytokines in modulating calcium responses; the processes of smooth muscle cell proliferation and migration; and the synthetic and immunomodulatory function of ASM cells. This article also discusses how altered synthetic function contributes to airway remodeling.

Rho-kinase inhibition in the therapy of cardiovascular disease

Rho is a GTPase known to be a major mediator in the formation of stress fibers and focal adhesions, cell morphology, and smooth muscle contraction. Its role in smooth muscle contraction has led to exploration into the connection between Rho-mediated kinase activity and cardiovascular disease. The role of Rho-kinase in calcium sensitization for vascular smooth muscle contraction has recently been characterized. Inappropriate coronary artery vasoconstriction resulting from increased Rho-kinase in the vascular system is likely involved in the pathogenesis of exercise-induced myocardial ischemia, spontaneous coronary artery spasm, and hypertension. In clinical trials, Rho-kinase inhibitors such as fasudil and Y-27632 have demonstrated antiischemic, antivasospastic, and antihypertensive effects. These compounds have also exhibited the ability to blunt progression of cardiomyocyte hypertrophy and cardiac remodeling in heart failure. As such, Rho-kinase inhibition represents a potential novel therapeutic approach in cardiovascular disease.

Structural analysis of protein kinase A mutants with Rho-kinase inhibitor specificity

Controlling aberrant kinase-mediated cellular signaling is a major strategy in cancer therapy; successful protein kinase inhibitors such as Tarceva and Gleevec verify this approach. Specificity of inhibitors for the targeted kinase(s), however, is a crucial factor for therapeutic success. Based on homology modeling, we previously identified four amino acids in the active site of Rho-kinase that likely determine inhibitor specificities observed for Rho-kinase relative to protein kinase A (PKA) (in PKA numbering: T183A, L49I, V123M, and E127D), and a fifth (Q181K) that played a surprising role in PKA-PKB hybrid proteins. We have systematically mutated these residues in PKA to their counterparts in Rho-kinase, individually and in combination. Using four Rho-kinase-specific, one PKA-specific, and one pan-kinase-specific inhibitor, we measured the inhibitor-binding properties of the mutated proteins and identify the roles of individual residues as specificity determinants. Two combined mutant proteins, containing the combination of mutations T183A and L49I, closely mimic Rho-kinase. Kinetic results corroborate the hypothesis that side-chain identities form the major determinants of selectivity. An unexpected result of the analysis is the consistent contribution of the individual mutations by simple factors. Crystal structures of the surrogate kinase inhibitor complexes provide a detailed basis for an understanding of these selectivity determinant residues. The ability to obtain kinetic and structural data from these PKA mutants, combined with their Rho-kinase-like selectivity profiles, make them valuable for use as surrogate kinases for structure-based inhibitor design.

Therapeutic concepts for hypoxic pulmonary vasoconstriction involving ion regulation and the smooth muscle contractile apparatus

Hypoxic pulmonary vasoconstriction (HPV) and pulmonary hypertension present a common and formidable clinical problem for practicing intensivists, thoracic, transplant, and trauma surgeons. The Redox Theory for the mechanisms of HPV has provided researchers with a new understanding of the etiology behind HPV that has opened the door to many new avenues of therapy for the disease. Potassium channels have been proposed to be the main mediator contributing to HPV, and treatment concepts that attempt to manipulate the function and number of those channels have been explored. Additionally, attempts to transfer genes that express the formation of specific potassium channels directly into pulmonary hypertensive lungs have proven to be very promising. Finally, rho kinase (ROK) has been discovered to play a very central role in the formation of hypoxia-induced pulmonary hypertension, and the advent of very specific ROK inhibitors has shown positive clinical results. The purposes of this review are to: (1) briefly discuss some of the basic mechanisms that undergird HPV, including the Redox Theory for the mechanisms of HPV; (2) address current research involving treatments concepts related to ion channels; (3) report on research involving gene therapy to combat pulmonary hypertension; and (4) examine potential therapeutic avenues associated with inhibition of rho kinase.

Myosin-based contraction is not necessary for cardiac c-looping in the chick embryo

During the initial phase of cardiac looping, known as c-looping, the heart bends and twists into a c-shaped tube with the convex outer curvature normally directed toward the right side of the embryo. Despite intensive study for more than 80 years, the biophysical mechanisms that drive and regulate looping remain poorly understood, although some investigators have speculated that differential cytoskeletal contraction supplies the driving force for c-looping. The purpose of this investigation was to test this hypothesis. To inhibit contraction, embryonic chick hearts at stages 10-12 (10-16 somites, 33-48 h) were exposed to the myosin inhibitors 2,3-butanedione monoxime (BDM), ML-7, Y-27632, and blebbistatin. Experiments were conducted in both whole embryo culture and, to focus on bending alone, isolated heart culture. Measurements of heart stiffness and phosphorylation of the myosin regulatory light chains showed that BDM, Y-27632, and blebbistatin significantly reduced myocardial contractility, while ML-7 had a lesser effect. None of these drugs significantly affected looping during the studied stages. These results suggest that active contraction is not required for normal c-looping of the embryonic chick heart between stages 10 and 12.

Vascular endothelial growth factor stimulates neurite outgrowth from cerebral cortical neurons via Rho kinase signaling

Vascular endothelial growth factor (VEGF),which is prominently involved in angiogenesis, also exerts direct effects on neurons, leading to neurite extension, neuroprotection, and neurogenesis. However, the signal transduction pathways employed by VEGF in neurons are incompletely understood. We investigated the molecular mechanisms through which VEGF stimulates neurogenesis in primary cultures of rat cerebral cortical neurons. VEGF increased neurite outgrowth, measured using a colorimetric assay for cresyl violet staining of neuronal processes, with half-maximal enhancement at 10 ng/mL and maximal, approximately 60% enhancement at 30-100 ng/mL. The effect of VEGF was not reproduced by VEGF-B or placental growth factor, but was blocked by SU1498, consistent with a VEGFR2 receptor-mediated process. VEGF-induced neurite outgrowth was also blocked by the ROK inhibitor Y27632 and the Rho inhibitors sulindac and Clostridium botulium exoenzyme C3, and was accompanied by Y27632-sensitive phosphorylation of cofilin, a downstream mediator of Rho/ROK signaling. We conclude that VEGF promotes neurite outgrowth from cerebral cortical neurons by interacting with VEGFR2 and activating Rho/ROK signaling pathways.

folded gastrulation, cell shape change and the control of myosin localization

The global cell movements that shape an embryo are driven by intricate changes to the cytoarchitecture of individual cells. In a developing embryo, these changes are controlled by patterning genes that confer cell identity. However, little is known about how patterning genes influence cytoarchitecture to drive changes in cell shape. In this paper, we analyze the function of the folded gastrulation gene (fog), a known target of the patterning gene twist. Our analysis of fog function therefore illuminates a molecular pathway spanning all the way from patterning gene to physical change in cell shape. We show that secretion of Fog protein is apically polarized, making this the earliest polarized component of a pathway that ultimately drives myosin to the apical side of the cell. We demonstrate that fog is both necessary and sufficient to drive apical myosin localization through a mechanism involving activation of myosin contractility with actin. We determine that this contractility driven form of localization involves RhoGEF2 and the downstream effector Rho kinase. This distinguishes apical myosin localization from basal myosin localization, which we find not to require actinomyosin contractility or FOG/RhoGEF2/Rho-kinase signaling. Furthermore, we demonstrate that once localized apically, myosin continues to contract. The force generated by continued myosin contraction is translated into a flattening and constriction of the cell surface through a tethering of the actinomyosin cytoskeleton to the apical adherens junctions. Our analysis of fog function therefore provides a direct link from patterning to cell shape change.