Identification of calponin as a novel substrate of Rho-kinase

Potentiation of active force by cyclic strain in sheep carotid arterial smooth muscle

The ability to generate force in large arteries is known to be augmented by cyclic strain that mimics the mechanically dynamic in vivo environment associated with blood pressure fluctuation experienced by these arteries. Cyclic strain does not induce a contractile response, like that observed in the myogenic response seen in small arteries, but prompts a substantial increase in the response to electrical stimulation. We coined this phenomenon "force potentiation." Because protein kinase C (PKC) and rho-kinase (ROCK) are known to play a role in increasing contractility of arterial smooth muscle by inhibition of myosin light chain phosphatase, and integrin-link kinase (ILK) is crucial in mechanotransduction, we examined how inhibition of these kinases affected force potentiation in sheep carotid artery. We found that phosphorylation of the regulatory myosin light chain was enhanced by cyclic strain, but the enhancement was observed only in activated, not in relaxed muscle. Inhibition of ROCK diminished force potentiation and active isometric force, likely due to the disinhibition of myosin light chain phosphatase. Inhibition of PKC abolished force potentiation without an effect on active force, suggesting a more exclusive role of PKC (compared with ROCK) in mediating force potentiation. Inhibition of ILK had a similar effect as PKC inhibition, suggesting that ILK may be an upstream kinase for PKC activation by mechanical stimuli. Taken together, the findings suggest that ILK, PKC, and ROCK are important kinases in the signal transduction pathway that mediate the effect of mechanical strain on force potentiation.NEW & NOTEWORTHY When subjected to mechanical strain, smooth muscle from large arteries has the ability to increase its force generation (force potentiation), which could be important in autoregulation of blood pressure. This phenomenon, however, does not involve a myogenic response, such as the one seen in small arteries and arterioles. Our work shows the involvement of ILK, PKC, and ROCK in the signal transduction pathway that mediates the force-potentiating effect of mechanical strain in large arteries.

Functional tuning of Vascular L-type Ca2+ channels

Vascular smooth muscle contraction is intimately tied to membrane potential and the rise in intracellular Ca2+ enabled by the opening of L-type Ca2+ channels. While voltage is often viewed as the single critical factor gating these channels, research is starting to reveal a more intricate scenario whereby their function is markedly tuned. This emerging concept will be the focus of this three-part review, the first part articulating the mechanistic foundation of contractile development in vascular smooth muscle. Part two will extend this foundational knowledge, introducing readers to functional coupling and how neighboring L-type Ca2+ channels work cooperatively through signaling protein complexes, to facilitate their open probability. The final aspect of this review will discuss the impact of L-type Ca2+ channel trafficking, a process tied to cytoskeleton dynamics. Cumulatively, this brief manuscript provides new insight into how voltage, along with channel cooperativity and number, work in concert to tune Ca2+ responses and smooth muscle contraction.

In vivo dissection of Rhoa function in vascular development using zebrafish

The small monomeric GTPase RHOA acts as a master regulator of signal transduction cascades by activating effectors of cellular signaling, including the Rho-associated protein kinases ROCK1/2. Previous in vitro cell culture studies suggest that RHOA can regulate many critical aspects of vascular endothelial cell (EC) biology, including focal adhesion, stress fiber formation, and angiogenesis. However, the specific in vivo roles of RHOA during vascular development and homeostasis are still not well understood. In this study, we examine the in vivo functions of RHOA in regulating vascular development and integrity in zebrafish. We use zebrafish RHOA-ortholog (rhoaa) mutants, transgenic embryos expressing wild type, dominant negative, or constitutively active forms of rhoaa in ECs, pharmacological inhibitors of RHOA and ROCK1/2, and Rock1 and Rock2a/b dgRNP-injected zebrafish embryos to study the in vivo consequences of RHOA gain- and loss-of-function in the vascular endothelium. Our findings document roles for RHOA in vascular integrity, developmental angiogenesis, and vascular morphogenesis in vivo, showing that either too much or too little RHOA activity leads to vascular dysfunction.

ROCK 1 and 2 affect the spatial architecture of 3D spheroids derived from human corneal stromal fibroblasts in different manners

The objective of the current study was to examine the roles of ROCK1 and 2 on the spatial architecture of human corneal stroma. We examined the effects of a pan-ROCK inhibitor (pan-ROCK-i), ripasudil, and a ROCK2 inhibitor (ROCK2-i), KD025 on the expression of genes that encode for ECM proteins including collagen (COL) 1, 4, 6, and fibronectin (FN), their regulators, a tissue inhibitor of metalloproteinase (TIMP) 1-4, matrix metalloproteinase (MMP) 2, 9 and 14, and ER stress-related factors of two- and three-dimensional (2D and 3D) cultures of human corneal stroma fibroblasts (HCSFs), and the physical properties of 3D HCSF spheroids. A gene expression analysis using ROCK-is indicated that KD025 (ROCK2 selective ROCK inhibitor) induced more significant changes than Rip (ripasudil, pan-ROCK inhibitor), suggesting that ROCK2 might be more extensively involved in the metabolism of ECM proteins and cell architectures of the 2D cultured HCSFs than ROCK1. In terms of the physical properties, size and stiffness of the 3D HCSFs spheroids, Rip caused a significant enlargement and this enhancement was concentration-dependent while KD025 also exerted a similar but less pronounced effect. In contrast, Rip and KD025 modulated physical stiffness differently, in that Rip caused a substantial decrease and KD025 caused an increase. Such diverse effects between Rip and KD025 were also observed for the gene expressions of ECM proteins, their regulators, and ER-stress related factors. The findings presented herein suggest that the ROCK1 and 2 influence the spatial architecture of 3D HCFS spheroids in different manners.

Identification of hepatocellular carcinoma-related genes associated with macrophage differentiation based on bioinformatics analyses

Macrophage differentiation is associated with tumorigenesis, including the tumorigenesis of hepatocellular carcinoma (HCC). Herein, we explored the value of macrophage differentiation-associated genes (MDGs) in the prognosis of HCC using data from The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC) databases. We performed multivariate Cox regression analyses to identify the hub genes affecting HCC patient prognoses. The correlations between hub genes and macrophage differentiation and immune checkpoint inhibitors (PD-1, PD-L1, and CTLA4) were investigated. Finally, the potential mechanism was examined with gene set enrichment analysis (GSEA). In total, seventeen differentially expressed MDGs were obtained after intersecting data from the two databases. Multivariate analysis indicated that CDC42 expression was an independent prognostic indicator in both databases. Furthermore, CDC42 showed a strong correlation with the tumor infiltration levels of immune cells in HCC tissue. Correlation analysis revealed that CDC42 expression was positively associated with M2 macrophage markers and immune checkpoint inhibitors, which indicated that CDC42 expression might be related to M2 macrophage differentiation and HCC cell immune tolerance. Finally, GSEA showed that CDC42 expression was most significantly related to the Wnt signaling pathway. In conclusion, this study showed that CDC42 expression might be an important MDG in HCC and may prove to be a new gene for studying macrophage differentiation in HCC. Abbreviations: HCC: hepatocellular carcinoma; TCGA: The Cancer Genome Atlas; ICGC: International Cancer Genome Consortium; GSEA: gene set enrichment analysis; GO: Gene Ontology; KEGG: Kyoto Encyclopedia of Genes and Genomes; ROC: receiver operating characteristic; K-M: Kaplan-Meier; AUC: the area under the ROC curve; TNM: Tumor size/lymph nodes/distance metastasis.

The Formation of Melanocyte Apoptotic Bodies in Vitiligo and the Relocation of Vitiligo Autoantigens under Oxidative Stress

Background

Oxidative stress has a vital role in the early stages of vitiligo. Autoantigens released from apoptotic melanocytes (MC) under oxidative stress are involved in the presentation and recognition of antigens. However, the transport of autoantigens to the cell surface and their release to the extracellular environment are still unclear. Apoptotic bodies (ABs) have always been considered as a key source of immunomodulators and autoantigens. Yet, the role of ABs in the immune mechanism of vitiligo is still unknown.

Purpose

To explore whether MC's autoantigens translocate into ABs during oxidative stress-induced apoptosis and study the molecular mechanisms underlying autoantigen migration and AB formation.

Methods

PIG3V (an immortalized human vitiligo melanocyte cell line) were treated with H₂O₂, and ABs were separated. Transmission electron microscopy, flow cytometry, Western blot, mass spectrometry, and other methods were used to determine the relocation of specific antigens in PIG3V cells to ABs. After pretreatment with specific inhibitors (Rho kinase (Y-27632), myosin light chain kinase (MLCK, ML-9), pan-caspase (zVAD-FMK), and JNK (SP600125)), the pathway of autoantigen translocation into ABs and the formation of apoptotic bodies were determined.

Results

When treated with 0.8 mM H₂O₂, ABs were released from these cells. Autoantigens such as tyrosinase-related protein 1 (TYRP-1) and cleavage nuclear membrane antigen Lamin A/C (Asp230) were concentrated in ABs. The expression of autoantigens and the formation of ABs increased in a time- and dose-dependent manner after treatment with H₂O₂, while the application of specific inhibitors inhibited the formation of apoptotic bodies, i.e., the expression of antigens.

Conclusion

Vitiligo autoantigens translocate into ABs in the process of apoptosis induced by oxidative stress. The cytoskeletal protein activation pathway and the JNK-related apoptosis pathway are involved in the transport of autoantigens and the formation of ABs. ABs may be the key bridge between MC cell apoptosis and cellular immunity.

Pan-ROCK and ROCK2 Inhibitors Affect Dexamethasone-Treated 2D- and 3D-Cultured Human Trabecular Meshwork (HTM) Cells in Opposite Manners

Effects of a pan-ROCK-inhibitor, ripasudil (Rip), and a ROCK2 inhibitor, KD025 on dexamethasone (DEX)-treated human trabecular meshwork (HTM) cells as a model of steroid-induced glaucoma were investigated. In the presence of Rip or KD025, DEX-treated HTM cells were subjected to permeability analysis of 2D monolayer by transendothelial electrical resistance (TEER) and FITC–dextran permeability, physical properties, size and stiffness analysis (3D), and qPCR of extracellular matrix (ECM), and their modulators. DEX resulted in a significant increase in the permeability, as well as a large and stiff 3D spheroid, and those effects were inhibited by Rip. In contrast, KD025 exerted opposite effects on the physical properties (down-sizing and softening). Furthermore, DEX induced several changes of gene expressions of ECM and their modulators were also modulated differently by Rip and KD025. The present findings indicate that Rip and KD025 induced opposite effects toward 2D and 3D cell cultures of DEX-treated HTM cells.

Diverse effects of pan-ROCK and ROCK2 inhibitors on 2 D and 3D cultured human trabecular meshwork (HTM) cells treated with TGFβ2

A pan-ROCK-inhibitor, ripasudil (Rip), and a ROCK2 inhibitor, KD025, were used To study the effects of Rho-associated coiled-coil containing protein kinase (ROCK)1 and 2 on two-dimensional (2D) and three-dimensional (3D) cultures of a TGFβ2-treated human trabecular meshwork (HTM) cells. In the presence of 5 ng/mL TGFβ2, the effects of these inhibitors were characterized by transendothelial electrical resistance (TEER), FITC-dextran permeability, and the size and stiffness of 3D sphenoids, the expression of extracellular matrix (ECM) including collagen1, 4 and 6, and fibronectin, α-smooth muscle actin, a tissue inhibitor of metalloproteinase (TIMP)1–4, and matrix metalloproteinase (MMP)2, 9 and 14. TGFβ2 caused a significant increase in the TEER values, and decrease in FITC-dextran permeability, as well as a decrease in the sizes and stiffness of the 3D sphenoids. In the presence of ROCK inhibitors, the TGFβ2-induced effects of the TEER and FITC-dextran permeability were inhibited, especially by KD025. Rip induced a significant increase in sizes and a decrease in the stiffness of the TGFβ2-treated 3D sphenoids, although the effects of KD025 were weaker. Gene expressions of most of the ECMs, TIMP2 and MMP9 of 2D and 3D HTM cells were significantly up-regulated by TGFβ2. Those were significantly and differently modulated by Rip or KD025.

A rapid degradation of calponin 2 is required for cytokinesis

Calponin 2 is an actin cytoskeleton-associated protein and plays a role in regulating cell motility-related functions such as phagocytosis, migration, and division. We previously reported that overexpression of calponin 2 inhibits the rate of cell proliferation. To investigate the underlying mechanism, our present study found that the levels of endogenous calponin 2 in NIH3T3 and HEK293 cells rapidly decreased before cell division characterized by an absence at the actin contractile ring. In cells lacking endogenous calponin 2, transfective expression of GFP-fusion calponin 2 inhibited cell proliferation similar to that of nonfusion calponin 2. Fluorescent imaging studies of mitotic cells indicated that a proper level of calponin 2 expression and effective degradation during cytokinesis are necessary for normal cell division. Computer-assisted dynamic image analysis of dividing cells revealed that overexpression of calponin 2 significantly affects motility and shape behaviors of cells only on the interval from the start of anaphase to the start of cytokinesis, i.e., the pre-cytokinesis phase, but not on the interval from the start of cytokinesis to 50% completion of cytokinesis. The pre-cytokinesis degradation of calponin 2 was attenuated by MG132 inhibition of the ubiquitin proteasome and inhibitor of protein kinase C (PKC), suggesting that PKC phosphorylation-triggered degradation of calponin 2 could determine the rate of cytokinesis. The novel role of calponin 2 in regulating the rate of cytokinesis may be targeted for therapeutic applications such as in an inhibition of malignant tumor growth.

Biochemical Features and Physiological Roles of hNP22 in the Central Nervous System

hNP22, a novel neuron-specific protein that interacts with both actin filaments and microtubules, was found to be highly homologous to the smooth muscle cell cytoskeleton-associated proteins human SM22α and rat acidic calponin. In recent years, functions of hNP22 such as the promotion of neural differentiation and enhancement of neural plasticity, have been described, as well as potential roles of hNP22 in schizophrenia and alcohol-related brain damage (ARBD). Because of the potential roles of hNP22 in neuronal processes and its potential implications in diseases, hNP22 has emerged as a research target. In this paper, we review the gene structure, possible modifications, and functions of the hNP22 protein, as well as its potential clinical significance. Based on its physical structure and previous studies, we speculate that hNP22 has potential biological functions in neurological disorders, such as schizophrenia and ARBD.

Calponin-3 deficiency augments contractile activity, plasticity, fibrogenic response and Yap/Taz transcriptional activation in lens epithelial cells and explants

The transparent ocular lens plays a crucial role in vision by focusing light on to the retina with loss of lens transparency leading to impairment of vision. While maintenance of epithelial phenotype is recognized to be essential for lens development and function, knowledge of the identity of different molecular mechanisms regulating lens epithelial characteristics remains incomplete. This study reports that CNN-3, the acidic isoform of calponin, an actin binding contractile protein, is expressed preferentially and abundantly relative to the basic and neutral isoforms of calponin in the ocular lens, and distributes predominantly to the epithelium in both mouse and human lenses. Expression and MEKK1-mediated threonine 288 phosphorylation of CNN-3 is induced by extracellular cues including TGF-β2 and lysophosphatidic acid. Importantly, siRNA-induced deficiency of CNN3 in lens epithelial cell cultures and explants results in actin stress fiber reorganization, stimulation of focal adhesion formation, Yap activation, increases in the levels of α-smooth muscle actin, connective tissue growth factor and fibronectin, and decreases in E-cadherin expression. These results reveal that CNN3 plays a crucial role in regulating lens epithelial contractile activity and provide supporting evidence that CNN-3 deficiency is associated with the induction of epithelial plasticity, fibrogenic activity and mechanosensitive Yap/Taz transcriptional activation.

Metallothionein-2 is associated with the amelioration of asthmatic pulmonary function by acupuncture through protein phosphorylation

BACKGROUND

Acupuncture has long been used for asthma treatment but the underlying mechanism remains unclear. Previous study showed that metallothionein-2 (MT-2) was significantly decreased in asthmatic lung tissue. However, the relationship between acupuncture treatment and MT-2 expression during asthma is still unknown, and the detailed effect analysis of MT-2 on phosphorylation in airway smooth muscle cells (ASMCs) is also unclear.

METHODS

The acupuncture effect on pulmonary resistance (RL) was investigated in a rat model of asthma, and the mRNA and protein levels of MT-2 in lung tissue were detected. Primary ASMCs were isolated and treated with MT-2 recombinant protein to study the MT-2 effects on ASMC relaxation. A Phospho Explorer antibody microarray was applied to detect protein phosphorylation changes associated with MT-2-induced ASMC relaxation. Bioinformatic analysis were performed with PANTHER database, DAVID and STRING. Phosphorylation changes in key proteins were confirmed by Western blot.

RESULTS

Acupuncture significantly reduced RL at 2-5 min (P < 0.05 vs asthma) in asthmatic rats. Acupuncture continued to increase MT-2 mRNA expression in lung tissue for up to 14 days (P < 0.05 vs asthma). The MT-2 protein expression was significantly decreased in the asthmatic rats (P < 0.05 vs control), while MT-2 protein expression was significantly increased in the asthmatic model group treated with acupuncture (P < 0.05 vs asthma). Primary ASMCs were successfully isolated and recombinant MT-2 protein (100, 200, 400 ng/ml) significantly relaxed ASMCs (P < 0.05 vs control). MT-2 induced phosphorylation changes in 51 proteins. Phosphorylation of 14 proteins were upregulated while 37 proteins were downregulated. PANTHER classification revealed eleven functional groups, and the phosphorylated proteins were identified as transferases (27.8 %), calcium-binding proteins (11.1 %), etc. DAVID functional classification showed that the phosphorylated proteins could be attributed to eight functions, including protein phosphorylation and regulation of GTPase activity. STRING protein-protein interaction network analysis showed that Akt1 was one of the most important hubs for the phosphorylated proteins. The phosphorylation changes of Akt1 and CaMK2β were consistent in both the Phospho Explorer antibody microarray and Western blot.

CONCLUSION

Acupuncture can significantly ameliorate RL, and the MT-2 mRNA and protein levels in lung tissue are increased during treatment. MT-2 significantly relaxes ASMCs and induces a series of protein phosphorylation. These phosphorylation changes, including Akt1 and CaMK2β, may play important roles in the therapeutic effects of acupuncture on asthma.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

Cnn3 regulates neural tube morphogenesis and neuronal stem cell properties

Calponin 3 (Cnn3) is a member of the Cnn family of actin-binding molecules that is highly expressed in the mammalian brain and has been shown to control dendritic spine morphology, density, and plasticity by regulating actin cytoskeletal reorganization and dynamics. However, little is known about the role of Cnn3 during embryonic development. In this study, we analyzed mutant animals deficient in Cnn3 to gain a better understanding of its role in brain morphogenesis. Embryos lacking Cnn3 exhibited massive malformation of the developing brain including exoencephaly, closure defects at the rostral neural tube, and strong enlargement of brain tissue. In wild-type animals, we found Cnn3 being localized to the apical lining of the neuroepithelium in close vicinity to beta-Catenin and N-cadherin. By performing immunohistochemistry on beta-Catenin and p-Smad, and furthermore taking advantage of Wnt-reporter animals, we provide evidence that the loss of Cnn3 during development can affect signaling pathways crucial for correct morphogenesis of the neural tube. In addition, we used embryonic neurosphere cultures to investigate the role of Cnn3 in embryonic neuronal stem cells (NSC). Here, we observed that Cnn3 deficiency in NSCs increased the number of newly formed neurospheres and increased neurosphere size without perturbing their differentiation potential. Together, our study provides evidence for an important role of Cnn3 during development of the embryonic brain and in regulating NSC function.

Role of ROCK2 in CD4+ cells in allergic airways responses in mice

BACKGROUND

Rho kinases (ROCKs) contribute to allergic airways disease. ROCKs also play a role in lymphocyte proliferation and migration.

OBJECTIVE

To determine the role of ROCK2 acting within CD4+ cells in allergic airways responses.

METHODS

ROCK2-haploinsufficient (ROCK2+/- ) and wild-type mice were sensitized with ovalbumin (OVA). ROCK2+/- mice then received either CD4+ cells from ROCK2-sufficient OVA TCR transgenic (OT-II) mice or saline i.v. 48 h before challenge with aerosolized OVA. Wild-type mice received saline before challenge. Allergic airways responses were measured 48 h after the last challenge. Allergic airways responses were also assessed in mice lacking ROCK2 only in CD4+ cells (ROCK2CD4Cre mice) vs. control (CD4-Cre and ROCK2flox/flox ) mice.

RESULTS

OVA-induced increases in bronchoalveolar lavage lymphocytes, eosinophils, IL-13, IL-5, and eotaxin were reduced in ROCK2+/- vs. wild-type mice, as were airway hyperresponsiveness and mucous hypersecretion. In ROCK2+/- mice, adoptive transfer with CD4+ cells from OT-II mice restored effects of OVA on lymphocytes, eosinophils, IL-13, IL-5, and mucous hypersecretion to wild-type levels, whereas eotaxin and airway hyperresponsiveness were not affected. ROCK2 inhibitors reduced IL-13-induced release of eotaxin from airway smooth muscle (ASM), similar to effects of these inhibitors on ASM contractility. Despite the ability of adoptive transfer to restore allergic airways inflammation in ROCK2-insufficient mice, allergic inflammation was not different in ROCK2CD4Cre vs. control mice.

CONCLUSION

ROCK2 contributes to allergic airways responses likely via effects within ASM cells and within non-lymphocyte cells involved in lymphocyte activation and migration into the airways.

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.

Calponin isoforms CNN1, CNN2 and CNN3: Regulators for actin cytoskeleton functions in smooth muscle and non-muscle cells

Calponin is an actin filament-associated regulatory protein expressed in smooth muscle and many types of non-muscle cells. Three homologous genes, CNN1, CNN2 and CNN3, encoding calponin isoforms 1, 2, and 3, respectively, are present in vertebrate species. All three calponin isoforms are actin-binding proteins with functions in inhibiting actin-activated myosin ATPase and stabilizing the actin cytoskeleton, while each isoform executes different physiological roles based on their cell type-specific expressions. Calponin 1 is specifically expressed in smooth muscle cells and plays a role in fine-tuning smooth muscle contractility. Calponin 2 is expressed in both smooth muscle and non-muscle cells and regulates multiple actin cytoskeleton-based functions. Calponin 3 participates in actin cytoskeleton-based activities in embryonic development and myogenesis. Phosphorylation has been extensively studied for the regulation of calponin functions. Cytoskeleton tension regulates the transcription of CNN2 gene and the degradation of calponin 2 protein. This review summarizes our knowledge learned from studies over the past three decades, focusing on the evolutionary lineage of calponin isoform genes, their tissue- and cell type-specific expressions, structure-function relationships, and mechanoregulation.

Statins in Asthma: Potential Beneficial Effects and Limitations

Asthma's sustenance as a global pandemic, across centuries, can be attributed to the lack of an understanding of its workings and the inability of the existing treatment modalities to provide a long lasting cure without major adverse effects. The discovery of statins boosted by a better comprehension of the pathophysiology of asthma in the past few decades has opened up a potentially alternative line of treatment that promises to be a big boon for the asthmatics globally. However, the initial excellent results from the preclinical and animal studies have not borne the results in clinical trials that the scientific world was hoping for. In light of this, this review analyzes the ways by which statins could benefit in asthma via their pleiotropic anti-inflammatory properties and explain some of the queries raised in the previous studies and provide recommendations for future studies in this field.

Genome-wide identification of miR-200 targets reveals a regulatory network controlling cell invasion

The microRNAs of the miR-200 family maintain the central characteristics of epithelia and inhibit tumor cell motility and invasiveness. Using the Ago-HITS-CLIP technology for transcriptome-wide identification of direct microRNA targets in living cells, along with extensive validation to verify the reliability of the approach, we have identified hundreds of miR-200a and miR-200b targets, providing insights into general features of miRNA target site selection. Gene ontology analysis revealed a predominant effect of miR-200 targets in widespread coordinate control of actin cytoskeleton dynamics. Functional characterization of the miR-200 targets indicates that they constitute subnetworks that underlie the ability of cancer cells to migrate and invade, including coordinate effects on Rho-ROCK signaling, invadopodia formation, MMP activity, and focal adhesions. Thus, the miR-200 family maintains the central characteristics of the epithelial phenotype by acting on numerous targets at multiple levels, encompassing both cytoskeletal effectors that control actin filament organization and dynamics, and upstream signals that locally regulate the cytoskeleton to maintain cell morphology and prevent cell migration.

Cytoskeletal reorganization evoked by Rho-associated kinase- and protein kinase C-catalyzed phosphorylation of cofilin and heat shock protein 27, respectively, contributes to myogenic constriction of rat cerebral arteries

Our understanding of the molecular events contributing to myogenic control of diameter in cerebral resistance arteries in response to changes in intravascular pressure, a fundamental mechanism regulating blood flow to the brain, is incomplete. Myosin light chain kinase and phosphatase activities are known to be increased and decreased, respectively, to augment phosphorylation of the 20-kDa regulatory light chain subunits (LC20) of myosin II, which permits cross-bridge cycling and force development. Here, we assessed the contribution of dynamic reorganization of the actin cytoskeleton and thin filament regulation to the myogenic response and serotonin-evoked constriction of pressurized rat middle cerebral arteries. Arterial diameter and the levels of phosphorylated LC(20), calponin, caldesmon, cofilin, and HSP27, as well as G-actin content, were determined. A decline in G-actin content was observed following pressurization from 10 mm Hg to between 40 and 120 mm Hg and in three conditions in which myogenic or agonist-evoked constriction occurred in the absence of a detectable change in LC20 phosphorylation. No changes in thin filament protein phosphorylation were evident. Pressurization reduced G-actin content and elevated the levels of cofilin and HSP27 phosphorylation. Inhibitors of Rho-associated kinase and PKC prevented the decline in G-actin; reduced cofilin and HSP27 phosphoprotein content, respectively; and blocked the myogenic response. Furthermore, phosphorylation modulators of HSP27 and cofilin induced significant changes in arterial diameter and G-actin content of myogenically active arteries. Taken together, our findings suggest that dynamic reorganization of the cytoskeleton involving increased actin polymerization in response to Rho-associated kinase and PKC signaling contributes significantly to force generation in myogenic constriction of cerebral resistance arteries.

Airway smooth muscle in asthma: linking contraction and mechanotransduction to disease pathogenesis and remodelling

Asthma is an obstructive airway disease, with a heterogeneous and multifactorial pathogenesis. Although generally considered to be a disease principally driven by chronic inflammation, it is becoming increasingly recognised that the immune component of the pathology poorly correlates with the clinical symptoms of asthma, thus highlighting a potentially central role for non-immune cells. In this context airway smooth muscle (ASM) may be a key player, as it comprises a significant proportion of the airway wall and is the ultimate effector of acute airway narrowing. Historically, the contribution of ASM to asthma pathogenesis has been contentious, yet emerging evidence suggests that ASM contractile activation imparts chronic effects that extend well beyond the temporary effects of bronchoconstriction. In this review article we describe the effects that ASM contraction, in combination with cellular mechanotransduction and novel contraction-inflammation synergies, contribute to asthma pathogenesis. Specific emphasis will be placed on the effects that ASM contraction exerts on the mechanical properties of the airway wall, as well as novel mechanisms by which ASM contraction may contribute to more established features of asthma such as airway wall remodelling.

Rho/Rho-associated coiled-coil forming kinase pathway as therapeutic targets for statins in atherosclerosis

SIGNIFICANCE

The 3-hydroxy-methylglutaryl coenzyme A reductase inhibitors or statins are important therapeutic agents for lowering serum cholesterol levels. However, recent studies suggest that statins may exert atheroprotective effects beyond cholesterol lowering. These so-called "pleiotropic effects" include effects of statins on vascular and inflammatory cells. Thus, it is important to understand whether other signaling pathways that are involved in atherosclerosis could be targets of statins, and if so, whether individuals with "overactivity" of these pathways could benefit from statin therapy, regardless of serum cholesterol level.

RECENT ADVANCES

Statins inhibit the synthesis of isoprenoids, which are important for the function of the Rho/Rho-associated coiled-coil containing kinase (ROCK) pathway. Indeed, recent studies suggest that inhibition of the Rho/ROCK pathway by statins could lead to improved endothelial function and decreased vascular inflammation and atherosclerosis. Thus, the Rho/ROCK pathway has emerged as an important target of statin therapy for reducing atherosclerosis and possibly cardiovascular disease.

CRITICAL ISSUES

Because atherosclerosis is both a lipid and an inflammatory disease, it is important to understand how inhibition of Rho/ROCK pathway could contribute to statins' antiatherosclerotic effects.

FUTURE DIRECTIONS

The role of ROCKs (ROCK1 and ROCK2) in endothelial, smooth muscle, and inflammatory cells needs to be determined in the context of atherogenesis. This could lead to the development of specific ROCK1 or ROCK2 inhibitors, which could have greater therapeutic benefits with less toxicity. Also, clinical trials will need to be performed to determine whether inhibition of ROCKs, with and without statins, could lead to further reduction in atherosclerosis and cardiovascular disease.

Calponin 3 regulates stress fiber formation in dermal fibroblasts during wound healing

Skin wound healing is an intricate process involving various cell types and molecules. In granulation tissue, fibroblasts proliferate and differentiate into myofibroblasts and generate mechanical tension for wound closure and contraction. Actin stress fibers formed in these cells, especially those containing α-smooth muscle actin (α-SMA), are the central machinery for contractile force generation. In the present study, calponin 3 (CNN3), which has a phosphorylation-dependent actin-binding property, was identified in the molecular mechanism underlying stress fiber formation. CNN3 was expressed by fibroblasts/myofibroblasts in the proliferation phase of wound healing, and was associated with α-SMA in stress fibers formed by cultured dermal fibroblasts. CNN3 expression was post-transcriptionally regulated by tension, as demonstrated by disruption of actin filament organization under floating culture or blebbistatin treatment. CNN3 knockdown in primary fibroblasts impaired stress fiber formation, resulting in a phenotype of decreased cellular dynamics such as cell motility and contractile ability. These findings indicate that CNN3 participates in actin stress fiber remodeling, which is required for cell motility and contraction of dermal fibroblasts in the wound healing process.

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.

Calponin 2 acts as an effector of noncanonical Wnt-mediated cell polarization during neural crest cell migration

Neural crest cells (NCCs) migrate throughout the embryo to differentiate into cell types of all germ layers. Initial directed NCC emigration relies on planar cell polarity (PCP), which through the activity of the small GTPases RhoA and Rac governs the actin-driven formation of polarized cell protrusions. We found that the actin binding protein calponin 2 (Cnn2) was expressed in protrusions at the leading edge of migratory NCCs in chicks and frogs. Cnn2 knockdown resulted in NCC migration defects in frogs and chicks and randomized outgrowth of cell protrusions in NCC explants. Morphant cells showed central stress fibers at the expense of the peripheral actin network. Cnn2 acted downstream of Wnt/PCP, as migration defects induced by dominant-negative Wnt11 or inhibition of RhoA function were rescued by Cnn2 knockdown. These results suggest that Cnn2 modulates actin dynamics during NCC migration as an effector of noncanonical Wnt/PCP signaling.

Rock-dependent calponin 3 phosphorylation regulates myoblast fusion

Myogenesis occurs during embryonic development as well as regeneration following postnatal muscle fiber damage. Herein, we show that acidic calponin or calponin 3 (CNN3) regulates both myoblast cell fusion and muscle-specific gene expressions. Overexpression of CNN3 impaired C2C12 cell fusion, whereas CNN3 gene knockdown promoted skeletal myosin expression and fusion. CNN3 was phosphorylated at Ser293/296 in the C-terminal region. The basal inhibitory property of CNN3 against myoblast differentiation was enhanced by Ser293/296Ala mutation or deletion of the C-terminal region, and this inhibition was reversed by Ser293/296Asp mutation. Ser293/296 phosphorylation was required for CNN3 to bind actin and was dependent on Rho-associated kinases 1/2 (ROCK 1/2). Gene knockdown of ROCK1/2 suppressed CNN3 phosphorylation and impaired myoblast fusion, and these effects were partially attenuated by additional CNN3 overexpression of Ser293/296Asp CNN3. These findings indicated that CNN3 phosphorylation by ROCK blunts CNN3's inhibitory effects on muscle cell differentiation and fusion. In muscle tissues, satellite cells, but not mature myofibrils, expressed CNN3. CNN3 was also expressed and phosphorylated during myotube induction in isolated muscle satellite cells. Taken together, these results indicate that CNN3 is a downstream regulator of the ROCK signaling pathway for myogenesis.

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.

Peptide substrates for Rho-associated kinase 2 (Rho-kinase 2/ROCK2)

Peptide substrates sensitive for a certain protein kinase could be important for new-drug development and to understand the mechanism of diseases. Rho-associated kinase (Rho-kinase/ROCK) is a serine/threonine kinase, and plays an important part in cardiovascular disease, migration and invasion of tumor cells, and in neurological disorders. The purpose of this study was to find substrates with high affinity and sensitivity for ROCK2. We synthesized 136 peptide substrates from protein substrates for ROCK2 with different lengths and charged peptides. Incorporation of (32)P [counts per minute (CPM)] for each peptide substrate was determined by the radiolabel assay using [γ-(32)P]ATP. When the top five peptide substrates showing high CPMs (R4, R22, R133, R134, and R135) were phosphorylated by other enzymes (PKA, PKCα, and ERK1), R22, R133, and R135 displayed the highest CPM level for ROCK2 compared with other enzymes, whereas R4 and R134 showed similar CPM levels for ROCK2 and PKCα. We hypothesize that R22, R133, and R135 can be useful peptide substrates for ROCK2.

Role of Rho kinase isoforms in murine allergic airway responses

Inhibition of Rho-associated coiled-coil forming kinases (ROCKs) reduces allergic airway responses in mice. The purpose of this study was to determine the roles of the two ROCK isoforms, ROCK1 and ROCK2, in these responses. Wildtype (WT) mice and heterozygous ROCK1 and ROCK2 knockout mice (ROCK1(+/-) and ROCK2(+/-), respectively) were sensitised and challenged with ovalbumin. ROCK expression and activation were assessed by western blotting. Airway responsiveness was measured by forced oscillation. Bronchoalveolar lavage was performed and the lungs were fixed for histological assessment. Compared with WT mice, ROCK1 and ROCK2 expression were 50% lower in lungs of ROCK1(+/-) and ROCK2(+/-) mice, respectively, without changes in the other isoform. In WT lungs, ROCK activation increased after ovalbumin challenge and was sustained for several hours. This activation was reduced in ROCK1(+/-) and ROCK2(+/-) lungs. Airway responsiveness was comparable in WT, ROCK1(+/-), and ROCK2(+/-) mice challenged with PBS. Ovalbumin challenge caused airway hyperresponsiveness in WT, but not ROCK1(+/-) or ROCK2(+/-) mice. Lavage eosinophils and goblet cell hyperplasia were significantly reduced in ovalbumin-challenged ROCK1(+/-) and ROCK2(+/-) versus WT mice. Ovalbumin-induced changes in lavage interleukin-13, interleukin-5 and lymphocytes were also reduced in ROCK1(+/-) mice. In conclusion, both ROCK1 and ROCK2 are important in regulating allergic airway responses.

Long-term diabetic complications may be ameliorated by targeting Rho kinase

This review addresses the roles of Rho/Rho-kinase (ROCK) pathway in the pathogenesis of diabetes complications. Diabetes can cause many serious complications and can result in physical disability or even increased mortality. However, there are not many effective ways to treat these complications. The small guanosine-5'-triphosphate-binding protein Rho and its downstream target Rho-kinase mediate important cellular functions, such as cell morphology, motility, secretion, proliferation, and gene expression. Recently, the Rho/Rho-kinase pathway has attracted a great deal of attention in diabetes-related research. These studies have provided evidence that the activity and gene expression of Rho-kinase are upregulated in some tissues in animal models of type 1 or type 2 diabetes and in cell lines cultured with high concentrations of glucose. Inhibitors of Rho-kinase could prevent or ameliorate the pathological changes in diabetic complications. The inhibitory effects of statins on the Rho/Rho-kinase signalling pathway may also play a role in the prevention of diabetic complications. However, the precise molecular mechanism by which the Rho/Roh-kinase pathway participates in the development or progression of diabetic complications has not been extensively investigated. This article evaluates the relationship between Rho/Roh-kinase activation and diabetic complications, as well as the roles of Roh-kinase inhibitors and statins in the complications of diabetes, with the objective of providing a novel target for the treatment of long-term diabetic complications.

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.

Rho kinase II phosphorylation of the lipoprotein receptor LR11/SORLA alters amyloid-beta production

LR11, also known as SorLA, is a mosaic low-density lipoprotein receptor that exerts multiple influences on Alzheimer disease susceptibility. LR11 interacts with the amyloid-β precursor protein (APP) and regulates APP traffic and processing to amyloid-β peptide (Aβ). The functional domains of LR11 suggest that it can act as a cell surface receptor and as an intracellular sorting receptor for trans-Golgi network to endosome traffic. We show that LR11 over-expressed in HEK293 cells is radiolabeled following incubation of cells with [(32)P(i)]orthophosphate. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was used to discover putative LR11 interacting kinases. Rho-associated coiled-coil containing protein kinase (ROCK) 2 was identified as a binding partner and a candidate kinase acting on LR11. LR11 and ROCK2 co-immunoprecipitate from post-mortem human brain tissue and drug inhibition of ROCK activity reduces LR11 phosphorylation in vivo. Targeted knockdown of ROCK2 with siRNA decreased LR11 ectodomain shedding while simultaneously increasing intracellular LR11 protein level. Site-directed mutagenesis of serine 2206 in the LR11 cytoplasmic tail reduced LR11 shedding, decreased LR11 phosphorylation in vitro, and abrogated LR11 mediated Aβ reduction. These findings provide direct evidence that LR11 is phosphorylated in vivo and indicate that ROCK2 phosphorylation of LR11 may enhance LR11 mediated processing of APP and amyloid production.

Calponin 3 regulates actin cytoskeleton rearrangement in trophoblastic cell fusion

Cell-cell fusion is an intriguing differentiation process, essential for placental development and maturation. A proteomic approach identified a cytoplasmic protein, calponin 3 (CNN3), related to the fusion of BeWo choriocarcinoma cells. CNN3 was expressed in cytotrophoblasts in human placenta. CNN3 gene knockdown promoted actin cytoskeletal rearrangement and syncytium formation in BeWo cells, suggesting CNN3 to be a negative regulator of trophoblast fusion. Indeed, CNN3 depletion promoted BeWo cell fusion. CNN3 at the cytoplasmic face of cytoskeleton was dislocated from F-actin with forskolin treatment and diffused into the cytoplasm in a phosphorylation-dependent manner. Phosphorylation sites were located at Ser293/296 in the C-terminal region, and deletion of this region or site-specific disruption of Ser293/296 suppressed syncytium formation. These CNN3 mutants were colocalized with F-actin and remained there after forskolin treatment, suggesting that dissociation of CNN3 from F-actin is modulated by the phosphorylation status of the C-terminal region unique to CNN3 in the CNN family proteins. The mutant missing these phosphorylation sites displayed a dominant negative effect on cell fusion, while replacement of Ser293/296 with aspartic acid enhanced syncytium formation. These results indicated that CNN3 regulates actin cytoskeleton rearrangement which is required for the plasma membranes of trophoblasts to become fusion competent.

Rho-associated kinase plays a role in rabbit urethral smooth muscle contraction, but not via enhanced myosin light chain phosphorylation

The involvement of Rho-associated kinase (ROK) in activation of rabbit urethral smooth muscle contraction was investigated by examining the effects of two structurally distinct inhibitors of ROK, Y27632 and H1152, on the contractile response to electric field stimulation, membrane depolarization with KCl, and α1-adrenoceptor stimulation with phenylephrine. Both compounds inhibited contractions elicited by all three stimuli. The protein kinase C inhibitor GF109203X, on the other hand, had no effect. Urethral smooth muscle strips were analyzed for phosphorylation of three potential direct or indirect substrates of ROK: 1) myosin regulatory light chains (LC20) at S19, 2) the myosin-targeting subunit of myosin light chain phosphatase (MYPT1) at T697 and T855, and 3) cofilin at S3. The following results were obtained: 1) under resting tension, LC20 was phosphorylated to 0.65±0.02 mol Pi/mol LC20 (n=21) at S19; 2) LC20 phosphorylation did not change in response to KCl or phenylephrine; 3) ROK inhibition had no effect on LC20 phosphorylation in the absence or presence of contractile stimuli; 4) under resting conditions, MYPT1 was partially phosphorylated at T697 and T855 and cofilin at S3; 5) phosphorylation of MYPT1 and cofilin was unaffected by KCl or phenylephrine; and 6) KCl- and phenylephrine-induced contraction-relaxation cycles did not correlate with actin polymerization-depolymerization. We conclude that ROK plays an important role in urethral smooth muscle contraction, but not via inhibition of MLCP or polymerization of actin.

Hyaluronan-CD44 interaction promotes c-Src-mediated twist signaling, microRNA-10b expression, and RhoA/RhoC up-regulation, leading to Rho-kinase-associated cytoskeleton activation and breast tumor cell invasion

Dysregulation of microRNAs is observed in many cancers, including breast cancer. In particular, miR-10b appears to play an important role in tumor cell invasion and breast cancer progression. In this study, we investigated hyaluronan (HA)-induced CD44 (a primary HA receptor) interaction with c-Src kinase and the transcriptional factor, Twist, in breast tumor cells (MDA-MB-231 cells). Our results indicate that HA binding to CD44 promotes c-Src kinase activation, which, in turn, increases Twist phosphorylation, leading to the nuclear translocation of Twist and transcriptional activation. Further analyses reveal that miR-10b is controlled by an upstream promoter containing the Twist binding site(s), whereas ChIP assays demonstrate that stimulation of miR-10b expression by HA/CD44-activated c-Src is Twist-dependent in breast tumor cells. This process results in the reduction of a tumor suppressor protein (HOXD10), RhoA/RhoC up-regulation, Rho-kinase (ROK) activation, and breast tumor cell invasion. Treatment of MDA-MB-231 cells with PP2 (a c-Src inhibitor) or Twist-specific siRNAs effectively blocks HA-mediated Twist signaling events, abrogates miR-10b production, and increases HOXD10 expression. Subsequently, this c-Src/Twist signaling inhibition causes down-regulation of RhoA/RhoC expression and impairment of ROK-regulated cytoskeleton function (e.g. tumor cell invasion). To further evaluate the role of miR-10b in RhoGTPase signaling, MDA-MB-231 cells were also transfected with a specific anti-miR-10b inhibitor in order to silence miR-10b expression and block its target functions. Our results demonstrate that anti-miR-10b inhibitor not only enhances HOXD10 expression but also abrogates HA/CD44-mediated tumor cell behaviors in breast tumor cells. Taken together, these findings indicate that the HA-induced CD44 interaction with c-Src-activated Twist plays a pivotal role in miR-10b production, leading to the down-regulation of tumor suppressor protein (HOXD10), RhoGTPase-ROK activation, and tumor cell invasion. All of these events are critical prerequisite steps for the acquisition of metastatic properties by human breast cancer cells.

Involvement of reactive oxygen species in thrombin-induced pulmonary vasoconstriction

RATIONALE

Pulmonary vascular thrombosis and thrombotic arteriopathy are common pathological findings in pulmonary arterial hypertension. Thrombin may thus play an important role in the pathogenesis and pathophysiology of pulmonary arterial hypertension.

OBJECTIVES

The present study aimed to elucidate the contractile effect of thrombin in the pulmonary artery and clarify its underlying mechanisms.

METHODS

The changes in cytosolic Ca²(+) concentrations ([Ca²(+)](i)), 20-kD myosin light chain (MLC20) phosphorylation, and contraction were monitored in the isolated porcine pulmonary artery. The production of reactive oxygen species (ROS) was evaluated by fluorescence imaging.

MEASUREMENTS AND MAIN RESULTS

In the presence of extracellular Ca²(+), thrombin induced a sustained contraction accompanied by an increase in [Ca²(+)](i) and the phosphorylation of MLC20. In the absence of extracellular Ca²(+), thrombin induced a contraction without either [Ca²(+)](i) elevation or MLC20 phosphorylation. This Ca²(+)- and MLC20 phosphorylation-independent contraction was mimicked by hydrogen peroxide and inhibited by N-acetyl cysteine. Fluorescence imaging revealed thrombin to induce the production of ROS. A Rho-kinase inhibitor, Y27632, inhibited not only the thrombin-induced Ca²(+)- and MLC20 phosphorylation-dependent contraction, but also the Ca²(+)- and MLC20 phosphorylation-independent contraction and the ROS production. These effects of thrombin were mimicked by a proteinase-activated receptor 1 (PAR₁)-activating peptide.

CONCLUSIONS

This study elucidated the Ca²(+)- and MLC20 phosphorylation-independent ROS-mediated noncanonical mechanism as well as Ca²(+)- and MLC20 phosphorylation-dependent canonical mechanism that are involved in the thrombin-induced PAR₁-mediated pulmonary vasoconstriction. Rho-kinase was suggested to play multiple roles in the development of thrombin-induced pulmonary vasoconstriction.

Tail-suspended mice lacking calponin H1 experience decreased bone loss

Calponin h1 (CNh1) is an actin-binding protein originally isolated from vascular smooth muscle and has been reported to suppress bone formation. We are therefore curious how CNh1 is involved in bone loss that is caused by space flight in microgravity. We assessed the effects of tail suspension (TS) in C57BL/6J wild (CN+/+) and CNh1-deleted (CN-/-) mice to elucidate the role of CNh1 in bone loss under weightless conditions. Bone mineral density (BMD) of tibiae was measured by single energy X-ray absorptiometry, and bone volume fraction (BV/TV), mineral apposition rate (MAR), and bone formation rate (BFR/BS) were measured by bone histomorphometry. BMD, BV/TV, MAR, and BFR/BS were lower in CN+/+ mice with TS than in those without. In the CN-/- group, however, the decrease in each of these parameters by TS was ameliorated. Decreases in serum osteocalcin levels by TS in CN+/+ mice were attenuated in CN-/- mice. Furthermore, urinary deoxypyridinolin (DPD), an indicator of bone resorption, was increased in CN+/+ mice following TS, but not in CN-/- mice. In transfection experiments, the degree of induction of bone formation markers, alkaline phosphatase (ALP) activity and bone morphogenetic protein (BMP)-4 mRNA expression, under stimulation with BMP-2, was lower in MC3T3-E1 mouse osteoblast-like cells expressing CNh1 than that in mock transfected cells. Notably, the BMP-2-induced ALP activity was decreased by CNh1 expression, which was partially rescued by treatment with the Rho kinase inhibitor Y27632. Taken together, these results indicate that CNh1 is responsible for weightlessness-induced bone loss in part through Rho signaling pathway.

Rho kinase and hypertension

Arterial hypertension is a multifactorial disease that is characterised by increased peripheral vascular resistance often accompanied by smooth muscle cell hypertrophy and proliferation. Rho kinases (ROCKs) are the most extensively studied effectors of the small G-protein RhoA and abnormalities in RhoA/ROCK signalling have been observed in various cardiovascular disease including hypertension. The RhoA/ROCK-pathway is a key player in different smooth muscle cell functions including contractility, proliferation and migration. Furthermore, there is extensive crosstalk between RhoA/ROCK- and NO-signalling. Therefore, not only ROCK inhibitors but also NO-donators or pleiotropic agents like statins exert their beneficial effects on the cardiovascular system at least in part via Rho/Rho-kinase.

RhoGTPases and Rho-effectors in hepatocellular carcinoma metastasis: ROCK N'Rho move it

Hepatocellular carcinoma (HCC) is an intractable disease with an extremely high mortality rate. Metastasis is the major factor of liver failure, tumour recurrence and death in HCC patients. Unfortunately, no promising curative therapy for HCC metastasis is available as yet; therefore, treatment for advanced HCC still remains a formidable challenge. A large body of evidence has demonstrated that the RhoGTPases/Rho-effector pathway plays important roles in mediating HCC metastasis based on their foremost functions in orchestrating the cell cytoskeletal reorganization. This review will first discuss the general principles of cancer metastasis and cancer cell movement with a particular focus on HCC.We will then summarize the implications of various members in the RhoGTPases/Rho-effectors signalling cascade including the upstream RhoGTPase regulators RhoGTPases and Rho-effectors and their downstream targets in HCC metastasis. Finally, we will discuss the therapeutic insight of targeting the RhoGTPases/Rho-effector pathway in HCC. Taken together, the literature demonstrates the importance of the RhoGTPases/Rho-effector signalling pathway in HCC metastasis and marks the necessity to have a more thorough knowledge of this complicated signalling network in order to develop novel therapeutic strategies for HCC patients.

RhoA/ROCK signaling is essential for multiple aspects of VEGF-mediated angiogenesis

The small GTPase RhoA and its downstream effectors, ROCK1 and ROCK2, regulate a number of cellular processes, including cell motility, proliferation, survival, and permeability. Pharmacological inhibitors of the Rho pathway reportedly block angiogenesis; however, the molecular details of this inhibition are largely unknown. We demonstrate that vascular endothelial growth factor-A (VEGF) rapidly induces RhoA activation in endothelial cells (ECs). Moreover, the pharmacological inhibition of ROCK1/2 using 10 microM Y-27632 (the IC(50) for this compound in ECs) strongly disrupts vasculogenesis in pluripotent embryonic stem cell cultures, VEGF-mediated regenerative angiogenesis in ex vivo retinal explants, and VEGF-mediated in vitro EC tube formation. Furthermore, using small interfering RNA knockdown and mouse heterozygote knockouts of ROCK1 and ROCK2, we provide data indicating that VEGF-driven angiogenesis is largely mediated through ROCK2. These data demonstrate that Rho/ROCK signaling is an important mediator in a number of angiogenic processes, including EC migration, survival, and cell permeability, and suggest that Rho/ROCK inhibition may prove useful for the treatment of angiogenesis-related disorders.

Pressure-dependent contribution of Rho kinase-mediated calcium sensitization in serotonin-evoked vasoconstriction of rat cerebral arteries

Our understanding of the cellular signalling mechanisms contributing to agonist-induced constriction is almost exclusively based on the study of conduit arteries. Resistance arteries/arterioles have received less attention as standard biochemical approaches lack the necessary sensitivity to permit quantification of phosphoprotein levels in these small vessels. Here, we have employed a novel, highly sensitive Western blotting method to assess: (1) the contribution of Ca(2+) sensitization mediated by phosphorylation of myosin light chain phosphatase targeting subunit 1 (MYPT1) and the 17 kDa PKC-potentiated protein phosphatase 1 inhibitor protein (CPI-17) to serotonin (5-HT)-induced constriction of rat middle cerebral arteries, and (2) whether there is any interplay between pressure-induced myogenic and agonist-induced mechanisms of vasoconstriction. Arterial diameter and levels of MYPT1 (T697 and T855), CPI-17 and 20 kDa myosin light chain subunit (LC(20)) phosphorylation were determined following treatment with 5-HT (1 micromol l(1)) at 10 or 60 mmHg in the absence and presence of H1152 or GF109203X to suppress the activity of Rho-associated kinase (ROK) and protein kinase C (PKC), respectively. Although H1152 and GF109203X suppressed 5-HT-induced constriction and reduced phospho-LC(20) content at 10 mmHg, we failed to detect any increase in MYPT1 or CPI-17 phosphorylation. In contrast, an increase in MYPT1-T697 and MYPT1-T855 phosphorylation, but not phospho-CPI-17 content, was apparent at 60 mmHg following exposure to 5-HT, and the phosphorylation of both MYPT1 sites was sensitive to H1152 inhibition of ROK. The involvement of MYPT1 phosphorylation in the response to 5-HT at 60 mmHg was not dependent on force generation per se, as inhibition of cross-bridge cycling with blebbistatin (10 micromol l(1)) did not affect phosphoprotein content. Taken together, the data indicate that Ca(2+) sensitization owing to ROK-mediated phosphorylation of MYPT1 contributes to 5-HT-evoked vasoconstriction only in the presence of pressure-induced myogenic activation. These findings provide novel evidence of an interplay between myogenic- and agonist-induced vasoconstriction in cerebral resistance arteries.

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.

Ca2+ sensitization via phosphorylation of myosin phosphatase targeting subunit at threonine-855 by Rho kinase contributes to the arterial myogenic response

Ca(2+) sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure-induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) required to sustain this view is not currently available. Here, we determined whether Ca(2+) sensitization pathways involving Rho kinase (ROK)- and PKC-dependent phosphorylation of MYPT1 and CPI-17, respectively, contribute to the myogenic response of rat middle cerebral arteries. ROK inhibitors (Y27632, 0.03-10 micromol l(-1); H1152, 0.001-0.3 micromol l(-1)) and PKC inhibitors (GF109203X, 3 micromol l(-1); Gö6976; 10 micromol l(-1)) suppressed myogenic vasoconstriction between 40 and 120 mmHg. An improved, highly sensitive 3-step Western blot method was developed for detection and quantification of MYPT1 and CPI-17 phosphorylation. Increasing pressure from 10 to 60 or 100 mmHg significantly increased phosphorylation of MYPT1 at threonine-855 (T855) and myosin light chain (LC(20)). Phosphorylation of MYPT1 at threonine-697 (T697) and CPI-17 were not affected by pressure. Pressure-evoked elevations in MYPT1-T855 and LC(20) phosphorylation were reduced by H1152, but MYPT1-T697 phosphorylation was unaffected. Inhibition of PKC with GF109203X did not affect MYPT1 or LC(20) phosphorylation at 100 mmHg. Our findings provide the first direct, biochemical evidence that a Ca(2+) sensitization pathway involving ROK-dependent phosphorylation of MYPT1 at T855 (but not T697) and subsequent augmentation of LC(20) phosphorylation contributes to myogenic control of arterial diameter in the cerebral vasculature. In contrast, suppression of the myogenic response by PKC inhibitors cannot be attributed to block of Ca(2+) sensitization mediated by CPI-17 or MYPT1 phosphorylation.

Calponin control of cerebrovascular reactivity: therapeutic implications in brain trauma

Calponin (Cp) is an actin-binding protein first characterized in chicken gizzard smooth muscle (SM). This review discusses the role of Cp in mediating SM contraction, the biochemical process by which Cp facilitates SM contraction and the function of Cp in the brain. Recent work on the role of Cp in pathological states with emphasis on traumatic brain injury is also discussed. Based on past and present data, the case is presented for targeting Cp for novel genetic and pharmacological therapies aimed at improving outcome following traumatic brain injury (TBI).

Direct association of calponin with specific domains of PKC-alpha

Calponin contributes to the regulation of smooth muscle contraction through its interaction with F-actin and inhibition of the actin-activated Mg-ATPase activity of phosphorylated myosin. Previous studies have shown that the contractile agonist acetylcholine induced a direct association of translocated calponin and PKC-alpha in the membrane. In the present study, we have determined the domain of PKC-alpha involved in direct association with calponin. In vitro binding assay was carried out by incubating glutathione S-transferase-calponin aa 92-229 with His-tagged proteins of individual domains and different combinations of domains of PKC-alpha. Calponin was found to bind directly to the full-length PKC-alpha. Calponin bound to C2 and C4 domains but not to C1 and C3 domains of PKC-alpha. When incubated with proteins of different combination of domains, calponin bound to C2-C3, C3-C4, and C2-C3-C4 but not to C1-C2 or C1-C2-C3. To determine whether these in vitro bindings mimic the in vivo associations, and in vivo binding assay was performed by transfecting colonic smooth muscle cells with His-tagged proteins of individual domains and different combinations of domains of PKC-alpha. Coimmunoprecipitation of calponin with His-tagged truncated forms of PKC-alpha showed that C1-C2, C1-C2-C3, C2-C3, and C3-C4 did not associate with calponin. Calponin associated only with full-length PKC-alpha and with C2-C3-C4 in cells in the resting state, and this association increased upon stimulation with acetylcholine. These data suggest that calponin bound to fragments that may mimic the active form of PKC-alpha and that the functional association of PKC-alpha with calponin requires both C2 and C4 domains during contraction of colonic smooth muscle cells.

Calponin in non-muscle cells

Calponin is an actin filament-associated regulatory protein expressed in smooth muscle and non-muscle cells. Calponin is an inhibitor of the actin-activated myosin ATPase. Three isoforms of calponin have been found in the vertebrates. Whereas the role of calponin in regulating smooth muscle contractility has been extensively investigated, the function and regulation of calponin in non-muscle cells is much less understood. Based on recent progresses in the field, this review focuses on the studies of calponin in non-muscle cells, especially its regulation by cytoskeleton tension and function in cell motility. The ongoing research has demonstrated that calponin plays a regulatory role in non-muscle cell motility. Therefore, non-muscle calponin is an attractive target for the control of cell proliferation, migration and phagocytosis, and the treatment of cancer metastasis.

Rho kinase (ROCK) inhibitors

The Rho kinase (ROCK) isoforms, ROCK1 and ROCK2, were initially discovered as downstream targets of the small GTP-binding protein Rho. Because ROCKs mediate various important cellular functions such as cell shape, motility, secretion, proliferation, and gene expression, it is likely that this pathway will intersect with other signaling pathways known to contribute to cardiovascular disease. Indeed, ROCKs have already been implicated in the regulation of vascular tone, proliferation, inflammation, and oxidative stress. However, it is not entirely clear how ROCKs are regulated, what some of their downstream targets are, and whether ROCK1 and ROCK2 mediate different cellular functions. Clinically, inhibition of ROCK pathway is believed to contribute to some of the cardiovascular benefits of statin therapy that are independent of lipid lowering (ie, pleiotropic effects). To what extent ROCK activity is inhibited in patients on statin therapy is not known, but it may have important clinical implications. Indeed, several pharmaceutical companies are already actively engaged in the development of ROCK inhibitors as the next generation of therapeutic agents for cardiovascular disease because evidence from animal studies suggests the potential involvement of ROCK in hypertension and atherosclerosis.

Rho kinases in cardiovascular physiology and pathophysiology

Rho kinases (ROCKs) are the first and the best-characterized effectors of the small G-protein RhoA. In addition to their effect on actin organization, or through this effect, ROCKs have been found to regulate a wide range of fundamental cell functions such as contraction, motility, proliferation, and apoptosis. Abnormal activation of the RhoA/ROCK pathway has been observed in major cardiovascular disorders such as atherosclerosis, restenosis, hypertension, pulmonary hypertension, and cardiac hypertrophy. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of ROCK signaling and its roles in cardiovascular physiology and pathophysiology.