Calponin is required for agonist-induced signal transduction--evidence from an antisense approach in ferret smooth muscle

Mechanoregulation and function of calponin and transgelin

It is well known that chemical energy can be converted to mechanical force in biological systems by motor proteins such as myosin ATPase. It is also broadly observed that constant/static mechanical signals potently induce cellular responses. However, the mechanisms that cells sense and convert the mechanical force into biochemical signals are not well understood. Calponin and transgelin are a family of homologous proteins that participate in the regulation of actin-activated myosin motor activity. An isoform of calponin, calponin 2, has been shown to regulate cytoskeleton-based cell motility functions under mechanical signaling. The expression of the calponin 2 gene and the turnover of calponin 2 protein are both under mechanoregulation. The regulation and function of calponin 2 has physiological and pathological significance, as shown in platelet adhesion, inflammatory arthritis, arterial atherosclerosis, calcific aortic valve disease, post-surgical fibrotic peritoneal adhesion, chronic proteinuria, ovarian insufficiency, and tumor metastasis. The levels of calponin 2 vary in different cell types, reflecting adaptations to specific tissue environments and functional states. The present review focuses on the mechanoregulation of calponin and transgelin family proteins to explore how cells sense steady tension and convert the force signal to biochemical activities. Our objective is to present a current knowledge basis for further investigations to establish the function and mechanisms of calponin and transgelin in cellular mechanoregulation.

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.

Matrix Metalloproteinase-2 Activity is Associated with Divergent Regulation of Calponin-1 in Conductance and Resistance Arteries in Hypertension-induced Early Vascular Dysfunction and Remodelling

Matrix metalloproteinase (MMP)-2 participates in hypertension-induced maladaptive vascular remodelling by degrading extra- and intracellular proteins. The consequent extracellular matrix rearrangement and phenotype switch of vascular smooth muscle cells (VSMCs) lead to increased cellular migration and proliferation. As calponin-1 degradation by MMP-2 may lead to VSMC proliferation during hypertension, the hypothesis of this study is that increased MMP-2 activity contributes to early hypertension-induced maladaptive remodelling in conductance and resistance arteries via regulation of calponin-1. The main objective was to analyse whether MMP-2 exerts similar effects on the structure and function of the resistance and conductance arteries during early hypertension. Two-kidney, one-clip (2K-1C) hypertensive male rats and corresponding controls were treated with doxycycline (30 mg/kg/day) or water until reaching one week of hypertension. Systolic blood pressure was increased in 2K-1C rats, and doxycycline did not reduce it. Aortas and mesenteric arteries were analysed. MMP-2 activity and expression were increased in both arteries, and doxycycline reduced it. Significant hypertrophic remodelling and VSMC proliferation were observed in aortas but not in mesenteric arteries of 2K-1C rats. The contractility of mesenteric arteries to phenylephrine was increased in 2K-1C rats, and doxycycline prevented this alteration. The potency of phenylephrine to contract aortas of 2K-1C rats was increased, and doxycycline decreased it. Whereas calponin-1 expression was increased in 2K-1C mesenteric arteries, calponin-1 was reduced in aortas. Doxycycline treatment reverted changes in calponin-1 expression. MMP-2 contributes to hypertrophic remodelling in aortas by decreasing calponin-1 levels, which may result in VSMC proliferation. On the other hand, MMP-2-dependent increased calponin-1 in mesenteric arteries may contribute to vascular hypercontractility in 2K-1C rats. Divergent regulation of calponin-1 by MMP-2 may be an important mechanism that leads to maladaptive vascular effects in hypertension.

Loss of calponin h1 confers anoikis resistance and tumor progression in the development of high-grade serous carcinoma originating from the fallopian tube epithelium

Increasing evidence indicates that ovarian high-grade serous carcinoma (HGSC) originates from the fallopian tube epithelium and metastasizes to the ovary as the secondary site. A working hypothesis is that detached tubal HGSC cells survive anoikis and implant on the ovary. In this study, we found that downregulation of calponin h1 (CNN1) is necessary for the anoikis survival and cell transformation. CNN1 was progressively downregulated in cells and tissues representing different stages of HGSC development from fallopian tube epithelium (FTE). Knock down of CNN1 in immortalized human FTE cells conferred gains of resistance to anoikis and transformation phenotypes including anchorage independent growth (AIG) and xenograft tumorigenesis in NSG mice. Conversely, overexpression of CNN1 in RAS-transformed FTE cells resulted in an almost complete loss of AIG and tumorigenesis. Besides, there was a dramatic change of cell morphology from a polygonal, raised appearance to a round and flattened one. Increase in cell adhesion to laminin and collagen, and reduction in cell motility, anoikis resistance and invasiveness were also observed. A microarray analysis revealed upregulation of genes involved in cytoskeleton stabilization and signal transduction, and downregulation of genes involved in cytokine and chemokine activities. The study disclosed multiple tumor suppressor roles of CNN1 in the development of HGSC from the fallopian tube, and loss of CNN1 expression is crucial for its metastasis to a new site.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Mechanisms of Vascular Smooth Muscle Contraction and the Basis for Pharmacologic Treatment of Smooth Muscle Disorders

The smooth muscle cell directly drives the contraction of the vascular wall and hence regulates the size of the blood vessel lumen. We review here the current understanding of the molecular mechanisms by which agonists, therapeutics, and diseases regulate contractility of the vascular smooth muscle cell and we place this within the context of whole body function. We also discuss the implications for personalized medicine and highlight specific potential target molecules that may provide opportunities for the future development of new therapeutics to regulate vascular function.

Modulation of Kinin B2 Receptor Signaling Controls Aortic Dilatation and Rupture in the Angiotensin II-Infused Apolipoprotein E-Deficient Mouse

OBJECTIVE

Abdominal aortic aneurysm (AAA) is an important cause of mortality in older adults. Activity of the local kallikrein-kinin system may be important in cardiovascular disease. The effect of kinin B2 receptor (B2R) agonist and antagonist peptides on experimental AAA was investigated.

APPROACH AND RESULTS

AAA was induced in apolipoprotein E-deficient mice via infusion of angiotensin II (1.0 μg/kg per minute SC). B2R agonists or antagonists were given via injection (2 mg/kg IP) every other day. The B2R agonist (B9772) promoted aortic rupture in response to angiotensin II associated with an increase in neutrophil infiltration of the aorta in comparison to controls. Mice receiving a B2R/kinin B1 receptor antagonist (B9430) were relatively protected from aortic rupture. Neutrophil depletion abrogated the ability of the B2R agonist to promote aortic rupture. Progression of angiotensin II-induced aortic dilatation was inhibited in mice receiving a B2R antagonist (B9330). Secretion of metalloproteinase-2 and -9, osteoprotegerin, and osteopontin by human AAA explant was reduced in the presence of the B2R antagonist (B9330). B2R agonist and antagonist peptides enhanced and inhibited, respectively, angiotensin II-induced neutrophil activation and aortic smooth muscle cell inflammatory phenotype. The B2R antagonist (B9330; 5 μg) delivered directly to the aortic wall 1 week post-AAA induction with calcium phosphate in a rat model reduced aneurysm growth associated with downregulation of aortic metalloproteinase-9.

CONCLUSIONS

B2R signaling promotes aortic rupture within a mouse model associated with the ability to stimulate inflammatory phenotypes of neutrophils and vascular smooth muscle cells. B2R antagonism could be a potential therapy for AAA.

Cortical actin regulation modulates vascular contractility and compliance in veins

Most cardiovascular research focuses on arterial mechanisms of disease, largely ignoring venous mechanisms. Here we examine ex vivo venous stiffness, spanning tissue to molecular levels, using biomechanics and magnetic microneedle technology, and show for the first time that venous stiffness is regulated by a molecular actin switch within the vascular smooth muscle cell in the wall of the vein. This switch connects the contractile apparatus within the cell to adhesion structures and facilitates stiffening of the vessel wall, regulating blood flow return to the heart. These studies also demonstrate that passive stiffness, the component of total stiffness not attributable to vascular smooth muscle activation, is severalfold lower in venous tissue than in arterial tissue. We show here that the activity of the smooth muscle cells plays a dominant role in determining total venous stiffness and regulating venous return. The literature on arterial mechanics is extensive, but far less is known about mechanisms controlling mechanical properties of veins. We use here a multi-scale approach to identify subcellular sources of venous stiffness. Portal vein tissue displays a severalfold decrease in passive stiffness compared to aortic tissues. The α-adrenergic agonist phenylephrine (PE) increased tissue stress and stiffness, both attenuated by cytochalasin D (CytoD) and PP2, inhibitors of actin polymerization and Src activity, respectively. We quantify, for the first time, cortical cellular stiffness in freshly isolated contractile vascular smooth muscle cells using magnetic microneedle technology. Cortical stiffness is significantly increased by PE and CytoD inhibits this increase but, surprisingly, PP2 does not. No detectable change in focal adhesion size, measured by immunofluorescence of FAK and zyxin, accompanies the PE-induced changes in cortical stiffness. Probing with phospho-specific antibodies confirmed activation of FAK/Src and ERK pathways and caldesmon phosphorylation. Thus, venous tissue stiffness is regulated both at the level of the smooth muscle cell cortex, via cortical actin polymerization, and by downstream smooth muscle effectors of Src/ERK signalling pathways. These findings identify novel potential molecular targets for the modulation of venous capacitance and venous return in health and disease.

Osteoprotegerin deficiency limits angiotensin II-induced aortic dilatation and rupture in the apolipoprotein E-knockout mouse

OBJECTIVE

Mounting evidence links osteoprotegerin with cardiovascular disease. Elevated serum and aortic tissue osteoprotegerin are associated with the presence and growth of abdominal aortic aneurysm in humans; however, a role for osteoprotegerin in abdominal aortic aneurysm pathogenesis remains to be shown. We examined the functional significance of osteoprotegerin in aortic aneurysm using an Opg-deficient mouse model and in vitro investigations.

APPROACH AND RESULTS

Homozygous deletion of Opg in apolipoprotein E-deficient mice (ApoE(-/-)Opg(-/-)) inhibited angiotensin II-induced aortic dilatation. Survival free from aortic rupture was increased from 67% in ApoE(-/-)Opg(+/+) controls to 94% in ApoE(-/-)Opg(-/-) mice (P=0.040). Serum concentrations of proinflammatory cytokines/chemokines, and aortic expression for cathepsin S (CTSS), matrix metalloproteinase 2, and matrix metalloproteinase 9 after 7 days (early-phase) of angiotensin II infusion were significantly reduced in ApoE(-/-)Opg(-/-) mice compared with ApoE(-/-)Opg(+/+) controls. In addition, aortic expression of markers for an inflammatory phenotype in aortic vascular smooth muscle cells in response to early-phase of angiotensin II infusion was significantly lower in Opg-deficient mice. In vitro, human abdominal aortic aneurysm vascular smooth muscle cells produced more CTSS and exhibited increased CTSS-derived elastolytic activity than healthy aortic vascular smooth muscle cells, whereas recombinant human osteoprotegerin stimulated CTSS-dependent elastase activity in aortic vascular smooth muscle cells.

CONCLUSIONS

These findings support a role for osteoprotegerin in aortic aneurysm through upregulation of CTSS, matrix metalloproteinase 2, and matrix metalloproteinase 9 within the aorta, promoting an inflammatory phenotype in aortic vascular smooth muscle cells in response to angiotensin II.

Regulation of PKC autophosphorylation by calponin in contractile vascular smooth muscle tissue

Protein kinase C (PKC) is a key enzyme involved in agonist-induced smooth muscle contraction. In some cases, regulatory phosphorylation of PKC is required for full activation of the enzyme. However, this issue has largely been ignored with respect to PKC-dependent regulation of contractile vascular smooth muscle (VSM) contractility. The first event in PKC regulation is a transphosphorylation by PDK at a conserved threonine in the activation loop of PKC, followed by the subsequent autophosphorylation at the turn motif and hydrophobic motif sites. In the present study, we determined whether phosphorylation of PKC is a regulated process in VSM and also investigated a potential role of calponin in the regulation of PKC. We found that calponin increases the level of in vitro PKCα phosphorylation at the PDK and hydrophobic sites, but not the turn motif site. In vascular tissues, phosphorylation of the PKC hydrophobic site, but not turn motif site, as well as phosphorylation of PDK at S241 increased in response to phenylephrine. Calponin knockdown inhibits autophosphorylation of cellular PKC in response to phenylephrine, confirming results with recombinant PKC. Thus these results show that autophosphorylation of PKC is regulated in dVSM and calponin is necessary for autophosphorylation of PKC in VSM.

Molluscan smooth catch muscle contains calponin but not caldesmon

We isolated Ca(2+)-regulated thin filaments from the smooth muscle of the mussel Crenomytilus grayanus and studied the protein composition of different preparations from this muscle: whole muscle, heat-stable extract, fractions from heat-stable extract, thin filaments and intermediate stages of thin filaments purification. Among the protein components of the above-listed preparations, we did not find caldesmon (CaD), although two isoforms of a calponin-like (CaP-like) protein, which along with CaD is characteristic of vertebrate smooth muscle, were present in thin filaments. Thus, CaD is not Ca(2+)-regulator of thin filaments of this muscle. On the other hand, the mussel CaP-like protein is also not such Ca(2+)-regulator since we have shown that this protein can be selectively removed from isolated mussel thin filaments without loss of their Ca(2+)-sensitivity. We suggest that thin filaments in the smooth catch muscle possess other type of Ca(2+)-regulation, different from that in vertebrate smooth muscles.

The phosphoinositide 3'-kinase p110δ modulates contractile protein production and IL-6 release in human airway smooth muscle

Transforming growth factor (TGF) β1 increases pro-inflammatory cytokines and contractile protein expression by human airway smooth muscle (ASM) cells, which could augment airway inflammation and hyperresponsiveness. Phosphoinositide 3' kinase (PI3K) is one of the signaling pathways implicated in TGFβ1 stimulation, and may be altered in asthmatic airways. This study compared the expression of PI3K isoforms by ASM cells from donors with asthma (A), chronic obstructive pulmonary disease (COPD), or neither disease (NA), and investigated the role of PI3K isoforms in the production of TGFβ1 induced pro-inflammatory cytokine and contractile proteins in ASM cells. A cells expressed higher basal levels of p110δ mRNA compared to NA and COPD cells; however COPD cells produced more p110δ protein. TGFβ1 increased 110δ mRNA expression to the same extent in the three groups. Neither the p110δ inhibitor IC87114 (1, 10, 30 µM), the p110β inhibitor TGX221 (0.1, 1, 10 µM) nor the PI3K pan inhibitor LY294002 (3, 10 µM) had any effect on basal IL-6, calponin or smooth muscle α-actin (α-SMA) expression. However, TGFβ1 increased calponin and α-SMA expression was inhibited by IC87114 and LY294002 in all three groups. IC87114, TGX221, and LY294002 reduced TGFβ1 induced IL-6 release in a dose related manner in all groups of ASM cells. PI3K p110δ is important for TGFβ1 induced production of the contractile proteins calponin and α-SMA and the proinflammatory cytokine IL-6 in ASM cells, and may therefore be relevant as a potential therapeutic target to treat both inflammation and airway remodeling.

Phosphorylation of h1 calponin by PKC epsilon may contribute to facilitate the contraction of uterine myometrium in mice during pregnancy and labor

BACKGROUND

The timely onset of powerful uterine contractions during parturition occurs through thick and thin filament interactions, similar to other smooth muscle tissues. Calponin is one of the thin filament proteins. Phosphorylation of calponin induced by PKC-epsilon can promote the contraction of vascular smooth muscle. While the mechanism by which calponin regulates the contraction of pregnant myometrium has rarely been explored. Here, we explore whether PKC-epsilon/h1 calponin pathway contribute to regulation of myometrial contractility and development of parturition.

METHODS

We detected the expression of h1 calponin, phosphorylated h1 calponin, PKC-epsilon and phosphorylated PKC-epsilon in the different stages of mice during pregnancy and in labor by the method of western blot and recorded the contraction activity of myometrium strips at the 19th day during pregnancy with different treatments by the organ bath experiments.

RESULTS

The level of the four proteins including h1 calponin, phosphorylated h1 calponin, PKC-epsilon and phosphorylated PKC-epsilon was significantly increased in pregnant mice myometrium as compared with that in nonpregnant mice. The ratios of phosphorylated h1 calponin/h1 calponin and phosphorylated PKC-epsilon/PKC-epsilon were reached the peak after the onset of labor in myometrium in the mice. After the treatment of more than 10(9-) mol/L Psi-RACK (PKC-epsilon activator), the contractility of myometrium strips from mice was reinforced and the level of phosphorylated h1 calponin increased at the same time which could be interrupted by the specific inhibitor of PKC-epsilon. Meanwhile, the change of the ratio of phosphorylated h1 calponin/h1 calponin was consistent with that of contraction force of mice myometrium strips.

CONCLUSIONS

These data suggest that in mice myometrium, phosphorylation of h1 calponin induced by the PKC-epsilon might facilitate the contraction of uterine in labor and regulate pregnant myometrial contractility.

MEKK1-MKK4-JNK-AP1 pathway negatively regulates Rgs4 expression in colonic smooth muscle cells

BACKGROUND

Regulator of G-protein Signaling 4 (RGS4) plays an important role in regulating smooth muscle contraction, cardiac development, neural plasticity and psychiatric disorder. However, the underlying regulatory mechanisms remain elusive. Our recent studies have shown that upregulation of Rgs4 by interleukin (IL)-1β is mediated by the activation of NFκB signaling and modulated by extracellular signal-regulated kinases, p38 mitogen-activated protein kinase, and phosphoinositide-3 kinase. Here we investigate the effect of the c-Jun N-terminal kinase (JNK) pathway on Rgs4 expression in rabbit colonic smooth muscle cells.

METHODOLOGY/PRINCIPAL FINDINGS

Cultured cells at first passage were treated with or without IL-1β (10 ng/ml) in the presence or absence of the selective JNK inhibitor (SP600125) or JNK small hairpin RNA (shRNA). The expression levels of Rgs4 mRNA and protein were determined by real-time RT-PCR and Western blot respectively. SP600125 or JNK shRNA increased Rgs4 expression in the absence or presence of IL-1β stimulation. Overexpression of MEKK1, the key upstream kinase of JNK, inhibited Rgs4 expression, which was reversed by co-expression of JNK shRNA or dominant-negative mutants for MKK4 or JNK. Both constitutive and inducible upregulation of Rgs4 expression by SP600125 was significantly inhibited by pretreatment with the transcription inhibitor, actinomycin D. Dual reporter assay showed that pretreatment with SP600125 sensitized the promoter activity of Rgs4 in response to IL-1β. Mutation of the AP1-binding site within Rgs4 promoter increased the promoter activity. Western blot analysis confirmed that IL-1β treatment increased the phosphorylation of JNK, ATF-2 and c-Jun. Gel shift and chromatin immunoprecipitation assays validated that IL-1β increased the in vitro and ex vivo binding activities of AP1 within rabbit Rgs4 promoter.

CONCLUSION/SIGNIFICANCE

Activation of MEKK1-MKK4-JNK-AP1 signal pathway plays a tonic inhibitory role in regulating Rgs4 transcription in rabbit colonic smooth muscle cells. This negative regulation may aid in maintaining the transient level of RGS4 expression.

Stimulus-specific activation and actin dependency of distinct, spatially separated ERK1/2 fractions in A7r5 smooth muscle cells

A proliferative response of smooth muscle cells to activation of extracellular signal regulated kinases 1 and 2 (ERK1/2) has been linked to cardiovascular disease. In fully differentiated smooth muscle, however, ERK1/2 activation can also regulate contraction. Here, we use A7r5 smooth muscle cells, stimulated with 12-deoxyphorbol 13-isobutylate 20-acetate (DPBA) to induce cytoskeletal remodeling or fetal calf serum (FCS) to induce proliferation, to identify factors that determine the outcomes of ERK1/2 activation in smooth muscle. Knock down experiments, immunoprecipitation and proximity ligation assays show that the ERK1/2 scaffold caveolin-1 mediates ERK1/2 activation in response to DPBA, but not FCS, and that ERK1/2 is released from caveolin-1 upon DPBA, but not FCS, stimulation. Conversely, ERK1/2 associated with the actin cytoskeleton is significantly reduced after FCS, but not DPBA stimulation, as determined by Triton X fractionation. Furthermore, cytochalasin treatment inhibits DPBA, but not FCS-induced ERK1/2 phosphorylation, indicating that the actin cytoskeleton is not only a target but also is required for ERK1/2 activation. Our results show that (1) at least two ERK1/2 fractions are regulated separately by specific stimuli, and that (2) the association of ERK1/2 with the actin cytoskeleton regulates the outcome of ERK1/2 signaling.

Scaffolding proteins and non-proliferative functions of ERK1/2

Studies of ERK1/2 generally focus on the regulation of nuclear ERK1/2 function mainly related to proliferation, whereas less attention has been drawn to the role ERK1/2 plays in the cytosol. Scaffolding proteins for ERK1/2 have been shown to control the time point and also the intracellular location of ERK1/2 activation. Hence, by concentrating ERK1/2 within subcellular compartments, scaffolding proteins restrict the substrate specificity of ERK1/2 and thus optimize the cell response for specific signal transduction programs in order to manipulate specific cellular functions. We have presented evidence that the F-actin binding protein calponin represents a new type of ERK1/2 scaffold, controlling the activation of a subfraction of ERK1/2 which is connected solely to contractile and/or migratory events in a cell.

PKC regulates alpha(1)-adrenoceptor-mediated contractions and baseline Ca(2+) sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high altitude hypoxia

Chronic hypoxia has a profound effect on uterine artery adaptation to pregnancy. The present studies tested the hypothesis that pregnant kinase C (PKC) differentially regulates alpha(1)-adrenoceptor-mediated contractions and Ca(2+) sensitivity in the uterine arteries of nonpregnant and pregnant sheep acclimatized to high altitude hypoxia. Uterine arteries were isolated from nonpregnant (NPUA) and near-term pregnant (PUA) ewes maintained at high altitude (3801 m, Pao(2) approximately 60 torr) for 110 days. Phorbol 12,13-dibutyrate (PDBu) decreased phenylephrine-induced contractions in PUA but not in NPUA, which was partly inhibited by the PKC inhibitor GF109203X. Additionally, GF109203X shifted the concentration-response curve of phenylephrine-induced contractions to the right in PUA. In beta-escin-permeabilized arteries, Ca(2+)-induced increases in 20-kDa myosin light chain phosphorylation (MLC(20)-P) were similar in NPUA and PUA. However, Ca(2+) produced a concentration-dependent increase in the ratio of tension to MLC(20)-P in PUA, as compared with NPUA. PKC inhibition decreased Ca(2+)-induced contractions in both NPUA and PUA. PDBu induced contractions of PUA in the absence of changes in MLC(20)-P, which was not affected by PD098059. There was a significant increase in the basal activity of PKCvarepsilon in PUA, but not in NPUA, in hypoxic sheep, as compared with normoxic animals. The results demonstrate that the inhibitory effect of PKC on alpha(1)-adrenoceptor-mediated contractions of uterine arteries is preserved in pregnant sheep at high altitude. However, the PKC-mediated thin-filament regulatory pathway is upregulated, resulting in increased baseline Ca(2+) sensitivity in the uterine artery during pregnancy at high altitude.

h3/Acidic calponin: an actin-binding protein that controls extracellular signal-regulated kinase 1/2 activity in nonmuscle cells

Migration of fibroblasts is important in wound healing. Here, we demonstrate a role and a mechanism for h3/acidic calponin (aCaP, CNN3) in REF52.2 cell motility, a fibroblast line rich in actin filaments. We show that the actin-binding protein h3/acidic calponin associates with stress fibers in the absence of stimulation but is targeted to the cell cortex and podosome-like structures after stimulation with a phorbol ester, phorbol-12,13-dibutyrate (PDBu). By coimmunoprecipitation and colocalization, we show that extracellular signal-regulated kinase (ERK)1/2 and protein kinase C (PKC)alpha constitutively associate with h3/acidic calponin and are cotargeted with h3/acidic calponin in the presence of PDBu. This targeting can be blocked by a PKC inhibitor but does not require phosphorylation of h3/acidic calponin at the PKC sites S175 or T184. Knockdown of h3/acidic calponin results in a loss of PDBu-mediated ERK1/2 targeting, whereas PKCalpha targeting is unaffected. Caldesmon is an actin-binding protein that regulates actomyosin interactions and is a known substrate of ERK1/2. Both ERK1/2 activity and nonmuscle l-caldesmon phosphorylation are blocked by h3/acidic calponin knockdown. Furthermore, h3/acidic calponin knockdown inhibits REF52.2 migration in an in vitro wound healing assay. Our findings are consistent with a model whereby h3/acidic calponin controls fibroblast migration by regulation of ERK1/2-mediated l-caldesmon phosphorylation.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

Upregulation of RGS4 expression by IL-1beta in colonic smooth muscle is enhanced by ERK1/2 and p38 MAPK and inhibited by the PI3K/Akt/GSK3beta pathway

Initial Ca(2+)-dependent contraction of intestinal smooth muscle is inhibited upon IL-1beta treatment. The decrease in contraction reflects the upregulation of regulator of G protein signaling-4 (RGS4) via the canonical inhibitor of NF-kappaB kinase-2 (IKK2)/IkappaB-alpha/NF-kappaB pathway. Here, we show that the activation of various protein kinases, including ERK1/2, p38 MAPK, and phosphoinositide 3-kinase (PI3K), differentially modulates IL-1beta-induced upregulation of RGS4 in rabbit colonic muscle cells. IL-1beta treatment caused a transient phosphorylation of ERK1/2 and p38 MAPK. It also caused the phosphorylation of Akt and glycogen synthase kinase-3beta (GSK3beta), sequential downstream effectors of PI3K. Pretreatment with PD-98059 (an ERK inhibitor) and SB-203580 (a p38 MAPK inhibitor) significantly inhibited IL-1beta-induced RGS4 expression. In contrast, LY-294002 (a PI3K inhibitor) augmented, whereas GSK3beta inhibitors inhibited, IL-1beta-induced RGS4 expression. PD-98059 blocked IL-1beta-induced phosphorylation of IKK2, degradation of IkappaB-alpha, and phosphorylation and nuclear translocation of NF-kappaB subunit p65, whereas SB-203580 had a marginal effect, implying that the effect of ERK1/2 is exerted on the canonical IKK2/IkappaB-alpha/p65 pathway of NF-kappaB activation but that the effect of p38 MAPK may not predominantly involve NF-kappaB signaling. The increase in RGS4 expression enhanced by LY-294002 was accompanied by an increase in the phosphorylation of IKK2/IkappaB-alpha/p65 and blocked by pretreatment with inhibitors of IKK2 (IKK2-IV) and IkappaB-alpha (MG-132). Inhibition of GSK3beta abolished IL-1beta-induced phosphorylation of IKK2/p65. These findings suggest that ERK1/2 and p38 MAPK enhance IL-1beta-induced upregulation of RGS4; the effect of ERK1/2 reflects its ability to promote IKK2 phosphorylation and increase NF-kappaB activity. GSK3beta acts normally to augment the activation of the canonical NF-kappaB signaling. The PI3K/Akt/GSK3beta pathway attenuates IL-1beta-induced upregulation of RGS4 expression by inhibiting NF-kappaB activation.

Smooth muscle signalling pathways in health and disease

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

Interleukin-10 attenuates vascular responses to endothelin-1 via effects on ERK1/2-dependent pathway

Interleukin-10 (IL-10) is an anti-inflammatory cytokine with protective actions on the vasculature. On the other hand, endothelin (ET)-1 has potent vasoconstrictor, mitogenic, and proinflammatory activities, which have been implicated in the pathophysiology of a number of cardiovascular diseases. We hypothesized that, in a condition where ET-1 expression is upregulated, i.e., on infusion of TNF-alpha, IL-10 confers vascular protection from ET-1-induced injury. Aortic rings and first-order mesenteric arteries from male C57BL/6 (WT) and IL-10-knockout (IL-10(-/-)) mice were treated with human recombinant TNF-alpha (220 ng x kg(-1) x day(-1)) or vehicle (saline) for 14 days. TNF-alpha infusion significantly increased blood pressure in IL-10(-/-), but not WT, mice. TNF-alpha augmented vascular ET-1 mRNA expression in arteries from WT and IL-10(-/-) mice. ET type A (ET(A)) receptor expression was increased in arteries from IL-10(-/-) mice, and TNF-alpha infusion did not change vascular ET(A) receptor expression in control or IL-10(-/-) mice. Aorta and mesenteric arteries from TNF-alpha-infused IL-10(-/-) mice displayed increased contractile responses to ET-1, but not the ET type B receptor agonist IRL-1620. The ET(A) receptor antagonist atrasentan completely abolished responses to ET-1 in aorta and mesenteric vessels, whereas the ERK1/2 inhibitor PD-98059 abrogated increased contractions to ET-1 in arteries from TNF-alpha-infused IL-10(-/-) mice. Infusion of TNF-alpha, as well as knockdown of IL-10 (IL-10(-/-)), induced an increase in total and phosphorylated ERK1/2. These data demonstrate that IL-10 counteracts ET(A)-mediated vascular responses to ET-1, as well as activation of the ERK1/2 pathway.

Smooth muscle signalling pathways in health and disease

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

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.

Regulation of Ca2+/calmodulin kinase II by a small C-terminal domain phosphatase

We present here the identification and characterization of an SCP3 (small C-terminal domain phosphatase-3) homologue in smooth muscle and show, for the first time, that it dephosphorylates CaMKII [Ca(2+)/CaM (calmodulin)-dependent protein kinase II]. SCP3 is a PP2C (protein phosphatase 2C)-type phosphatase that is primarily expressed in vascular smooth muscle tissues and specifically binds to the association domain of the CaMKIIgamma G-2 variant. The dephosphorylation is site-specific, excluding the Thr(287) associated with Ca(2+)/CaM-independent activation of the kinase. As a result, the autonomous activity of CaMKIIgamma G-2 is not affected by the phosphatase activity of SCP3. SCP3 co-localizes with CaMKIIgamma G-2 on cytoskeletal filaments, but is excluded from the nucleus in differentiated vascular smooth muscle cells. Upon depolarization-induced Ca(2+) influx, CaMKIIgamma G-2 is activated and dissociates from SCP3. Subsequently, CaMKIIgamma G-2 is targeted to cortical adhesion plaques. We show here that SCP3 regulates phosphorylation sites in the catalytic domain, but not those involved in regulation of kinase activation. This selective dephosphorylation by SCP3 creates a constitutively active kinase that can then be differentially regulated by other phosphorylation-dependent regulatory mechanisms.

The pro-apoptotic protein Par-4 facilitates vascular contractility by cytoskeletal targeting of ZIPK

Par-4 (prostate apoptosis response 4) is a pro-apoptotic protein and tumour suppressor that was originally identified as a gene product up-regulated during apoptosis in prostate cancer cells. Here, we show, for the first time, that Par-4 is expressed and co-localizes with the actin filament bundles in vascular smooth muscle. Furthermore, we demonstrate that targeting of ZIPK to the actin filaments, as observed upon PGF-2α stimulation, is inhibited by the presence of a cell permeant Par-4 decoy peptide. The same decoy peptide also significantly inhibits PGF-2α induced contractions of smooth muscle tissue. Moreover, knockdown of Par-4 using antisense morpholino nucleotides results in significantly reduced contractility, and myosin light chain and myosin phosphatase target subunit phosphorylation. These results indicate that Par-4 facilitates contraction by targeting ZIPK to the vicinity of its substrates, myosin light chain and MYPT, which are located on the actin filaments. These results identify Par-4 as a novel regulator of myosin light chain phosphorylation in differentiated, contractile vascular smooth muscle.

Characterization of protein kinase pathways responsible for Ca2+ sensitization in rat ileal longitudinal smooth muscle

We investigated the protein kinases responsible for myosin regulatory light chain (LC20) phosphorylation and regulation of myosin light chain phosphatase (MLCP) activity during microcystin (phosphatase inhibitor)-induced contraction at low Ca2+ concentrations of rat ileal smooth muscle stretched in the longitudinal axis. Application of 1 microM microcystin induced LC20 diphosphorylation and contraction of beta-escin-permeabilized rat ileal smooth muscle at pCa 9. The PKC inhibitor GF-109203x, the MEK inhibitor PD-98059, and the p38 MAPK inhibitor SB-203580 significantly reduced this contraction. These inhibitory effects were abolished when the microcystin concentration was increased to 10 muM, indicating that application of these kinase inhibitors generated an increase in MLCP activity. GF-109203x and PD-98059, but not SB-203580, significantly decreased the phosphorylation level of the myosin-targeting subunit of MLCP, MYPT1, at Thr-697 (rat sequence) during microcystin-induced contraction at pCa 9. On the other hand, SB-203580, but not GF-109203x or PD-98059, significantly reduced the phosphorylation level of the PKC-potentiated phosphatase inhibitor of 17 kDa (CPI-17). A zipper-interacting protein kinase (ZIPK) inhibitor (SM1 peptide) and a Rho-associated kinase inhibitor (Y-27632) had little effect on microcystin-induced contraction at pCa 9. In conclusion, PKC, ERK1/2, and p38 MAPK pathways facilitate microcystin-induced contraction at low Ca2+ concentrations by contributing to the inhibition of MLCP activity either through phosphorylation of MYPT1 or CPI-17 [probably mediated by integrin-linked kinase (ILK)]. ILK and not ZIPK is likely to be the protein kinase responsible for LC20 diphosphorylation during microcystin-induced contraction of rat ileal smooth muscle at pCa 9, similar to its recently described role in vascular smooth muscle. The negative regulation of MLCP by PKC and MAPKs during microcystin-induced contraction at pCa 9, which is not observed in vascular smooth muscle, may be unique to phasic smooth muscle.

Spontaneous Contraction of Pseudoglandular-Stage Human Airspaces Is Associated with the Presence of Smooth Muscle-α-Actin and Smooth Muscle-Specific Myosin Heavy Chain in Recently Differentiated Fetal Human Airway Smooth Muscle

BACKGROUND

Recent investigations demonstrating that pseudoglandular-stage airspaces contract spontaneously suggest that the production of contractile proteins by airway wall smooth muscle (ASM) is an important factor in the functional and structural differentiation of ASM.

AIMS

Ouraim was to determine if smooth muscle (SM)-myosin heavy chain (MHC) myofilaments, the 'motor' underlying SM contraction, and SM-alpha-actin myofilaments were distributed simultaneously in pseudoglandular-stage human lungs and to further define the nature of fetal airway contractions.

METHODS

Immunohistochemically stained sections of fetal lung (14 fetuses, 10.1-17 weeks gestation) were analysed by computer-assisted morphometry to determine airspace dimensions and detect SM-MHC- and SM-alpha-actin-ASM. Lung tissue from the same fetuses was also placed in explant culture to observe airway contractions using videomicroscopy. We found that the smallest airspaces were just as likely to be invested by a layer of SM-MHC-positive ASM as by a layer of SM-alpha-actin-positive ASM. In addition, larger airways or airways from more mature fetal lungs were more likely to be invested by either SM-MHC- or SM-alpha-actin-positive ASM. Spontaneous airspace contractions were peristalsis-like and variable in amplitude. The time interval between contractions was temperature dependent (mean+/-SEM, 44+/-7.5 s at 37 degrees C), shortened by carbachol and increased by nitric oxide (NO)-donating drugs.

CONCLUSIONS

These observations suggest that ASM differentiation is characterised by the simultaneous production of SM-alpha-actin and SM-MHC myofilaments and that the presence of these proteins is likely to be responsible for cholinergic- and NO-sensitive spontaneous contractions of fetal human airspaces.

A critical role for calponin 2 in vascular development

Calponin 2 (h2 calponin, CNN2) is an actin-binding protein implicated in cytoskeletal organization. We have found that the expression of calponin 2 is relatively restricted to vasculature from 16 to 30 h post-fertilization during zebrafish (Danio rerio) development. Forty-eight hours after injecting antisense morpholino oligos against calponin 2 into embryos at the 1-4-cell stage, zebrafish demonstrated various cardiovascular defects, including sluggish axial and head circulation, absence of circulation in intersegmental vessels and in the dorsal longitudinal anastomotic vessel, enlarged cerebral ventricles, and pericardial edema, in addition to an excess bending, spiraling tail and twisting of the caudal fin. Knockdown of calponin 2 in the Tg(fli1:EGFP)(y1) zebrafish line (in which a fli1 promoter drives vascular-specific enhanced green fluorescent protein expression) indicated that diminished calponin 2 expression blocked the proper migration of endothelial cells during formation of intersegmental vessels. In vitro studies showed that basic fibroblast growth factor-induced human umbilical vein endothelial cell migration was down-regulated by knockdown of calponin 2 expression using an antisense adenovirus, and overexpression of calponin 2 enhanced migration and hastened wound healing. These events were correlated with activation of mitogen-activated protein kinase; moreover, inhibition of this pathway blocked the promigratory effect of calponin 2. Collectively, these data suggest that calponin 2 plays an important role in the migration of endothelial cells both in vivo and in vitro and that its expression is critical for proper vascular development.

Smooth muscle archvillin: a novel regulator of signaling and contractility in vascular smooth muscle

The mechanisms by which protein kinase C (PKC) and extracellular-signal-regulated kinases (ERK1/2) govern smooth-muscle contractility remain unclear. Calponin (CaP), an actin-binding protein and PKC substrate, mediates signaling through ERK1/2. We report here that CaP sequences containing the CaP homology (CH) domain bind to the C-terminal 251 amino acids of smooth-muscle archvillin (SmAV), a new splice variant of supervillin, which is a known actin- and myosin-II-binding protein. The CaP-SmAV interaction is demonstrated by reciprocal yeast two-hybrid and blot-overlay assays and by colocalization in COS-7 cells. In differentiated smooth muscle, endogenous SmAV and CaP co-fractionate and co-translocate to the cell cortex after stimulation by agonist. Antisense knockdown of SmAV in tissue inhibits both the activation of ERK1/2 and contractions stimulated by either agonist or PKC activation. This ERK1/2 signaling and contractile defect is similar to that observed in CaP knockdown experiments. In A7r5 smooth-muscle cells, PKC activation by phorbol esters induces the reorganization of endogenous, membrane-localized SmAV and microfilament-associated CaP into podosome-like structures that also contain F-actin, nonmuscle myosin IIB and ERK1/2. These results indicate that SmAV contributes to the regulation of contractility through a CaP-mediated signaling pathway, involving PKC activation and phosphorylation of ERK1/2.

Inhibition of protein kinase C-mediated contraction by Rho kinase inhibitor fasudil in rabbit aorta

Protein kinase C (PKC) activation by a phorbol ester increases myosin light chain (MLC(20)) phosphorylation through inhibition of MLC phosphatase (MLCP) and enhances contraction of vascular smooth muscle. We investigated whether Rho kinase, which is known to inhibit MLCP, is involved in the MLC(20) phosphorylation caused by a phorbol ester, 12-deoxyphorbol 13-isobutyrate (DPB), in rabbit aortas. DPB (1 microM) increased MLC(20) phosphorylation and tension. The Rho kinase inhibitor fasudil (10 microM) inhibited the DPB-induced contraction and decreased the MLC(20) phosphorylation at Ser19, a site phosphorylated by MLC kinase, although it did not affect the phosphorylation of total MLC(20). Rinsing a 65.4 mM KCl-contracted aorta with Ca(2+)-free, EGTA solution caused rapid dephosphorylation of MLC(20) and relaxation. When DPB was present in the rinsing solution, the MLC(20) dephosphorylation and the relaxation were inhibited. In this protocol, Ro31-8220 (10 microM), a PKC inhibitor, suppressed the phosphorylation of total MLC(20) and Ser19 induced by DPB. Fasudil also inhibited the Ser19 phosphorylation to a degree similar to Ro31-8220 and accelerated relaxation, which was less than the relaxation caused by Ro31-8220. The phospholipase A(2) inhibitor ONO-RS-082 (5 microM) inhibited the DPB-induced Ser19 phosphorylation but only transiently decreased the tension, suggesting the involvement of arachidonic acid in the phosphorylation and the existence of a MLC(20) phosphorylation-independent mechanism. When fasudil was combined with ONO-RS-082, fasudil exerted additional inhibition of the tension without further inhibition of the Ser19 phosphorylation. DPB phosphorylated the 130 kDa myosin binding subunit (MBS) of MLCP and fasudil inhibited the phosphorylation. These data suggest that the inhibition by fasudil of DPB-induced contraction and phosphorylation of MLC(20) at the MLC kinase-targeted site is a result of inhibition of Rho kinase. Thus, the PKC-dependent Ca(2+)-sensitization of vascular smooth muscle involves Rho kinase. A MLC(20) phosphorylation-independent mechanism is also involved in the Ca(2+)-sensitization.

Isoform switching from SM-B to SM-A myosin results in decreased contractility and altered expression of thin filament regulatory proteins

We previously generated an isoform-specific gene knockout mouse in which SM-B myosin is permanently replaced by SM-A myosin. In this study, we examined the effects of SM-B myosin loss on the contractile properties of vascular smooth muscle, specifically peripheral mesenteric vessels and aorta. The absence of SM-B myosin leads to decreased velocity of shortening and increased isometric force generation in mesenteric vessels. Surprisingly, the same changes occur in aorta, which contains little or no SM-B myosin in wild-type animals. Calponin and activated mitogen-activated protein kinase expression is increased and caldesmon expression is decreased in aorta, as well as in bladder. Light chain-17b isoform (LC(17b)) expression is increased in aorta. These results suggest that the presence or absence of SM-B myosin is a critical determinant of smooth muscle contraction and that its loss leads to additional changes in thin filament regulatory proteins.

Direct association and translocation of PKC-alpha with calponin

Calponin has been implicated in the regulation of smooth muscle contraction through its interaction with F-actin and inhibition of the actin-activated MgATPase activity of phosphorylated myosin. Calponin has also been shown to interact with PKC. We have studied the interaction of calponin with PKC-alpha and with the low molecular weight heat-shock protein (HSP)27 in contraction of colonic smooth muscle cells. Particulate fractions from isolated smooth muscle cells were immunoprecipitated with antibodies to calponin and Western blot analyzed with antibodies to HSP27 and to PKC-alpha. Acetylcholine induced a sustained increase in the immunocomplexing of calponin with HSP27 and of calponin with PKC-alpha in the particulate fraction, indicating an association of the translocated proteins in the membrane. To examine whether the observed interaction in vivo is due to a direct interaction of calponin with PKC-alpha, a cDNA of 1.3 kb of human calponin gene was PCR amplified. PCR product encoding 622 nt of calponin cDNA (nt 351-972 corresponding to amino acids 92-229) was expressed as fusion glutathione S-transferase (GST) protein in the vector pGEX-KT. We have studied the direct association of GST-calponin fusion protein with recombinant PKC-alpha in vitro. Western blot analysis of the fractions collected after elution with reduced glutathione buffer (pH 8.0) show a coelution of GST-calponin with PKC-alpha, indicating a direct association of GST-calponin with PKC-alpha. These data suggest that there is a direct association of translocated calponin and PKC-alpha in the membrane and a role for the complex calponin-PKC-alpha-HSP27, in contraction of colonic smooth muscle cells.

Alpha1-adrenergic signaling mechanisms in contraction of resistance arteries

Our goal in this review is to provide a comprehensive, integrated view of the numerous signaling pathways that are activated by alpha(1)-adrenoceptors and control actin-myosin interactions (i.e., crossbridge cycling and force generation) in mammalian arterial smooth muscle. These signaling pathways may be categorized broadly as leading either to thick (myosin) filament regulation or to thin (actin) filament regulation. Thick filament regulation encompasses both "Ca(2+) activation" and "Ca(2+)-sensitization" as it involves both activation of myosin light chain kinase (MLCK) by Ca(2+)-calmodulin and regulation of myosin light chain phosphatase (MLCP) activity. With respect to Ca(2+) activation, adrenergically induced Ca(2+) transients in individual smooth muscle cells of intact arteries are now being shown by high resolution imaging to be sarcoplasmic reticulum-dependent asynchronous propagating Ca(2+) waves. These waves differ from the spatially uniform increases in [Ca(2+)] previously assumed. Similarly, imaging during adrenergic activation has revealed the dynamic translocation, to membranes and other subcellular sites, of protein kinases (e.g., Ca(2+)-activated protein kinases, PKCs) that are involved in regulation of MLCP and thus in "Ca(2+) sensitization" of contraction. Thin filament regulation includes the possible disinhibition of actin-myosin interactions by phosphorylation of CaD, possibly by mitogen-activated protein (MAP) kinases that are also translocated during adrenergic activation. An hypothesis for the mechanisms of adrenergic activation of small arteries is advanced. This involves asynchronous Ca(2+) waves in individual SMC, synchronous Ca(2+) oscillations (at high levels of adrenergic activation), Ca(2+) sparks, "Ca(2+)-sensitization" by PKC and Rho-associated kinase (ROK), and thin filament mechanisms.

Role of ERK1/2 in uterine contractility and preterm labor in rats

The present study tested the hypothesis that ERK activation is an essential step in the onset of labor in a rat model of preterm labor. The administration of RU-486, an antiprogesterone agent, to rats induced preterm delivery 22.2 +/- 0.24 h after treatment. Changes in basal signaling events were studied in myometrial tissue from CO(2)-euthanized rats. Rats treated with RU-486 displayed a dramatically increased in vitro uterine contractility compared with gestational stage-matched, sham-treated rats. In vitro contractility was not significantly different from that during spontaneous labor. During RU-486-induced preterm labor, as previously described for spontaneous labor, ERK phosphorylation levels increased, as did phosphorylation of caldesmon at Ser(789), an ERK phosphorylation site. Also, a small but significant increase in 20-kDa myosin light chain phosphorylation was seen at a constant intracellular pCa of 7. When rats were chronically treated with an agent that prevents ERK activation, U-0126, the onset of RU-486-induced preterm labor was delayed in a statistically significant manner. Chronic in vivo treatment with U-0126 also significantly inhibited the RU-486-induced increase in in vitro contractility and ERK and caldesmon phosphorylation but did not alter the RU-486-induced increase in 20-kDa myosin light chain phosphorylation. These data indicate that ERK activation is a component of the multiple events leading to the development of labor in this rat model. We suggest that the ERK pathway could possibly be used to identify targets for the development of a novel class of tocolytic agents.

Caveolin-1 regulates contractility in differentiated vascular smooth muscle

Caveolin is a principal component of caveolar membranes. In the present study, we utilized a decoy peptide approach to define the degree of involvement of caveolin in PKC-dependent regulation of contractility of differentiated vascular smooth muscle. The primary isoform of caveolin in ferret aorta vascular smooth muscle is caveolin-1. Chemical loading of contractile vascular smooth muscle tissue with a synthetic caveolin-1 scaffolding domain peptide inhibited PKC-dependent increases in contractility induced by a phorbol ester or an alpha agonist. Peptide loading also resulted in a significant inhibition of phorbol ester-induced adducin Ser662 phosphorylation, an intracellular monitor of PKC kinase activity, ERK1/2 activation, and Ser789 phosphorylation of the actin binding protein caldesmon. alpha-Agonist-induced ERK1-1/2 activation was also inhibited by the caveolin-1 peptide. Scrambled peptide-loaded tissues or sham-loaded tissues were unaffected with respect to both contractility and signaling. Depolarization-induced activation of contraction was not affected by caveolin peptide loading. Similar results with respect to contractility and ERK1/2 activation during exposure to the phorbol ester or the alpha-agonist were obtained with the cholesterol-depleting agent methyl-beta-cyclodextrin. These results are consistent with a role for caveolin-1 in the coordination of signaling leading to the regulation of contractility of smooth muscle.

Suppression of peritoneal dissemination through protecting mesothelial cells from retraction by cancer cells

In a previous study, we demonstrated that calponin h1 suppressed tumor growth of transformed cells and that the peritonitis carcinomatosa induced by mouse B16-F10 melanoma (F10) cells was more extensive in calponin h1-deficient (CN(-/-)) mice with fragility of mesothelial (MS) cells than in their calponin h1-wild (CN(+/+)) counterparts. In our study, we assessed the therapeutic effect of calponin h1 on peritoneal dissemination. F10 cells were overlaid on the cultured CN(+/+) or CN(-/-) MS cells and the effect of calponin h1 on retraction of MS cells was evaluated. Then, an adenoviral vector with the calponin h1 gene (AdGFP-CN) inserted was constructed and was applied to CN(-/-) MS cells or CN(-/-) mouse peritoneum to investigate its suppressive effect on the peritoneal dissemination caused by F10 cells. Greater retraction and invasion of F10 cells were observed in CN(-/-) MS than in CN(+/+) cells in vitro, while down-regulation of calponin h1 was observed in CN(+/+) MS cells prior to the invasion of F10 cells. Infecting CN(-/-) MS cells with AdGFP-CN prevented their retraction and the invasion of F10 cells. Peritoneal dissemination was prominently suppressed in AdGFP-CN-infected CN(-/-) mice, and the survival of those mice was significantly prolonged. Thus, calponin h1 functioned to protect host MS cells from the invasion of F10 cells.

Impaired arterial pressure regulation during exercise due to enhanced muscular vasodilatation in calponin knockout mice

Calponin is known to be an actin binding protein in smooth muscle, inhibiting actomyosin ATPase activity in vitro. We previously reported that alpha-adrenergic vasoconstriction in calponin knockout (KO) mice was reduced compared with that in wild-type C57BL/6J (WT) mice and, as a compensation, arterial baroreflex sensitivity in KO mice was enhanced at rest. In the present study, we assessed arterial pressure regulation in WT and KO mice during graded treadmill exercise at 5, 10, and 15 m min-1. Mean arterial pressure (MAP) in KO mice fluctuated more than that in WT mice at every speed of exercise with two-fold higher variances (P < 0.001). The baroreflex sensitivity (Delta HR/Delta MAP) in WT mice (n = 6), determined from the heart rate response (Delta HR) to spontaneous change in MAP (Delta MAP), was -5.1 +/- 0.6 beats min-1 mmHg-1 (mean +/- S.E.M.) at rest and remained unchanged at -5.0 +/- 0.9 beats min-1 mmHg-1 during exercise (P < 0.01), while that in KO mice (n = 6) was -9.9 +/- 1.7 beats min-1 mmHg-1 at rest, significantly higher than that in WT mice (P < 0.001), and was reduced to -4.7 +/- 0.4 beats min-1 mmHg-1 during exercise (P < 0.01), not significantly different from that in WT mice. In another experiment, we measured muscle blood flow (MBF) in the thigh by laser-Doppler flowmetry, electromyogram (EMG), and MAP during voluntary locomotion in KO (n = 7) and WT (n = 7) mice. Muscle vascular conductance, MBF/MAP, started to increase immediately after locomotion, judged from EMG, and reached 50% of the maximum after the time of 2.3 +/- 0.2 s in KO mice, shorter than 5.8 +/- 0.6 s in WT mice (P < 0.001). Prior administration of alpha-adrenergic blockade (phentolamine) shortened the time in WT mice to that in KO mice (P < 0.001), but did not shorten the time in KO mice. Thus, impaired MAP regulation in KO mice during exercise was caused by a blunted muscle vascular alpha-adrenergic contractile response and by the attenuated HR response to spontaneous change in MAP due to reduced baroreflex sensitivity.

Downregulation of profilin with antisense oligodeoxynucleotides inhibits force development during stimulation of smooth muscle

The actin-regulatory protein profilin has been shown to regulate the actin cytoskeleton and the motility of nonmuscle cells. To test the hypothesis that profilin plays a role in regulating smooth muscle contraction, profilin antisense or sense oligodeoxynucleotides were introduced into the canine carotid smooth muscle by a method of reversible permeabilization, and these strips were incubated for 2 days for protein downregulation. The treatment of smooth muscle strips with profilin antisense oligodeoxynucleotides inhibited the expression of profilin; it did not influence the expression of actin, myosin heavy chain, and metavinculin/vinculin. Profilin sense did not affect the expression of these proteins in smooth muscle tissues. Force generation in response to stimulation with norepinephrine or KCl was significantly lower in profilin antisense-treated muscle strips than in profilin sense-treated strips or in muscle strips not treated with oligodeoxynucleotides. The depletion of profilin did not attenuate increases in phosphorylation of the 20-kDa regulatory light chain of myosin (MLC20) in response to stimulation with norepinephrine or KCl. The increase in F-actin/G-actin ratio during contractile stimulation was significantly inhibited in profilin-deficient smooth muscle strips. These results suggest that profilin is a necessary molecule of signaling cascades that regulate carotid smooth muscle contraction, but that it does not modulate MLC20 phosphorylation during contractile stimulation. Profilin may play a role in the regulation of actin polymerization or organization in response to contractile stimulation of smooth muscle.

Expression and purification of the h1 and h2 isoforms of calponin

Three homologous calponin isoforms, named h1, h2, and acidic calponins, have been found in birds and mammals. Based primarily on studies of chicken gizzard smooth muscle (h1) calponin, calponin has been identified as a family of actin-associated proteins that inhibit actomyosin ATPase activity. Evolutionary divergence of the calponin isoforms suggests differentiated function. While the role of h1 calponin in smooth muscle contraction is under investigation, h2 calponin has been shown regulating the function of actin cytoskeleton. Using cloned cDNA, we expressed mammalian h1 and h2 calponins in Escherichia coli. We have developed effective methods to purify biologically active h1 and h2 calponin proteins from transformed bacterial culture. The purified calponin isoform proteins were used to generate monoclonal antibodies that reveal epitopic structure difference between h1 and h2 calponins. Together with their differential expression in tissues and during development, the structural diversity of h1 and h2 calponins suggests non-redundant physiological function. Nevertheless, h1 and h2 calponins bind F-actin with similar affinity, indicating a conserved mechanism for their role in regulating actin filaments in smooth muscle and non-muscle cells.

Role of Crk-associated substrate in the regulation of vascular smooth muscle contraction

A pool of actin monomers is induced to polymerize into actin filaments during contractile stimulation of smooth muscle. The inhibition of actin dynamics by actin polymerization inhibitors depresses active force generation in smooth muscle. In this study, we hypothesized that Crk-associated substrate plays a role in the regulation of contraction and actin dynamics in vascular smooth muscle. Antisense or sense oligodeoxynucleotides for Crk-associated substrate were introduced into carotid smooth muscle tissues by chemical loading. The treatment of smooth muscle strips with antisense oligodeoxynucleotides inhibited the expression of Crk-associated substrates; it did not influence the expression of actin, myosin heavy chain, and paxillin. Sense oligodeoxynucleotides did not affect the expression of these proteins in smooth muscle tissues. Force generation in response to stimulation with norepinephrine or KCl was significantly lower in antisense-treated muscle strips than in sense-treated strips or in muscle strips not treated with oligodeoxynucleotides. The downregulation of Crk-associated substrate did not attenuate increases in phosphorylation of the 20-kDa regulatory light chain of myosin in response to stimulation with norepinephrine. The increase in F-actin/G-actin ratio during contractile stimulation was significantly inhibited in antisense-treated smooth muscle strips. Contractile activation of smooth muscle increased the association of profilin with actin monomers; the depletion of Crk-associated substrate inhibited the increases in the profilin-actin complex in response to contractile stimulation. These results suggest that Crk-associated substrate is a necessary molecule of signaling cascades that regulate active force generation in smooth muscle. This molecule may regulate actin dynamics in smooth muscle in response to contractile stimulation.

Differential functional properties of calmodulin-dependent protein kinase IIgamma variants isolated from smooth muscle

Six variants of calmodulin-dependent protein kinase IIgamma were isolated from a ferret-aorta smooth-muscle cDNA library. Variant G-2 is generated by a novel alternative polyadenylation, utilizing a site contained in an intron. The last 77 residues of the association domain are replaced with 99 residues of a unique sequence containing Src homology 3-domain-binding motifs, which alter catalytic activity. Variant C-2 has an eight-residue deletion in an ATP-binding motif and does not autophosphorylate Thr(286), but does phosphorylate exogenous substrate. Two variants, B and J, autodephosphorylate. Four variants differing only in the variable domain have differing catalytic activities, despite identical sequences in the catalytic domains. Thus structural features determined by variable and association domains are important for the catalytic activity of calmodulin-dependent protein kinase II.

Ca2+-dependent and Ca2+-independent regulation of smooth muscle contraction

An increase in the cytosolic Ca2+ concentration is a prerequisite in activation of contractile activity of smooth muscle. The shape of the Ca2+-signal is determined by spatial distribution and kinetics of Ca2+-binding sites in the cell. The increase in cytosolic Ca2+ activates myosin light chain kinase (MLCK) which in turn phosphorylates the regulatory light chains of myosin II. This Ca2+-dependent MLC20 phosphorylation is modulated in a Ca2+-independent manner by inhibiting the constitutive active myosin light chain phosphatase mediated by the monomeric GTPase Rho and the Rho-associated kinase as well as protein kinase C or by increasing its activity through cGMP. Furthermore, the activity of MLCK may be decreased due to phosphorylation by CaM kinase II and perhaps p21 activated protein kinase. Hence, smooth muscle tone appears to be regulated by a network of activating and inactivating intracellular signaling cascades which not only show a temporal but also a spatial activation pattern.

Enhanced baroreflex sensitivity in free-moving calponin knockout mice

Calponin is an actin binding protein in vascular smooth muscle that modifies contractile responses. However, its role in mean arterial pressure (MAP) regulation has not been clarified. To assess this, MAP and heart rate (HR) were measured in calponin knockout (KO) mice, and the results were compared with those in wild-type (WT) mice. The measurements were performed every 100 ms during a 60-min free-moving state each day for 3 days. Mice in both groups rested during approximately 70% of the total measuring period. The mean HR during rest was significantly lower in KO mice than in WT mice but with no significant difference in MAP between the groups. The change in HR response (deltaHR) to spontaneous change in MAP (deltaMAP) varied in a wider range in KO mice with an 80% increase in the coefficient of variation for HR (P < 0.05), whereas MAP in KO mice was controlled in a narrow range similar to that in WT mice. The baroreflex sensitivity (deltaHR/deltaMAP), determined from the change in HR to the spontaneous change in MAP, was twofold higher in KO mice than that in WT mice (P < 0.01), whereas there were no significant differences in the baroreflex sensitivity determined by intravascular administration of phenylephrine and sodium nitroprusside between the two groups (P > 0.1). The MAP response to the administrated doses of phenylephrine in KO mice was reduced to one-half of that in WT mice (P < 0.01) but with no significant difference in the response to sodium nitroprusside between the groups. The differences in HR variability and the spontaneous baroreflex sensitivity between the two groups completely disappeared after carotid sinus denervation. These results suggest that the higher variability in HR for KO mice was caused by the increased spontaneous arterial baroreflex sensitivity, though not detected by the intra-arterial administration of the drug, and that the higher variability of HR may be a compensatory adaptation to the blunted alpha-adrenergic response of peripheral vessels to sympathetic nervous activity.

Essential role of rho kinase in the Ca2+ sensitization of prostaglandin F(2alpha)-induced contraction of rabbit aortae

Inhibition of dephosphorylation of the 20 kDa myosin light chain (MLC(20)) is an important mechanism for the Ca(2+)-induced sensitization of vascular smooth muscle contraction. We investigated whether this mechanism operates in prostaglandin F(2alpha) (PGF(2alpha))-induced contraction of rabbit aortic smooth muscle and, if so, whether protein kinase C (PKC) or rho-associated kinase (rho kinase) contribute to the inhibition of dephosphorylation. In normal medium, PGF(2alpha) (10 microM) increased the phosphorylation of MLC(20) and developed tension. The rho-kinase inhibitors fasudil and hydroxyfasudil inhibited these changes, despite having no effect on a phorbol-ester-induced MLC(20) phosphorylation. After treatment with verapamil or chelation of external Ca(2+) with EGTA, PGF(2alpha) increased the MLC(20) phosphorylation and tension without an increase in [Ca(2+)](i), all of which were sensitive to fasudil and hydroxyfasudil. ML-9, a MLC kinase inhibitor, quickly reversed the KCl-induced MLC(20) phosphorylation and contraction to the resting level. However, fractions of PGF(2alpha)-induced contraction and MLC(20) phosphorylation were resistant to ML-9 but were sensitive to fasudil. Ro31-8220 (10 microM), a PKC inhibitor, did not affect the phosphorylation of MLC(20) and the tension caused by PGF(2alpha), thus excluding the possibility of the involvement of PKC in the PGF(2alpha)-induced MLC(20) phosphorylation. PGF(2alpha) increased phosphorylation at Thr654 of the myosin binding subunit (MBS) of myosin phosphatase, which is a target of rho kinase, and fasudil decreased the phosphorylation. These data suggest that the PGF(2alpha)-induced contraction is accompanied by the inhibition of MLC(20) dephosphorylation through rho kinase-induced MBS phosphorylation, leading to Ca(2+) sensitization of contraction. An actin-associated mechanism may also be involved in the PGF(2alpha)-induced sensitization.

ERK1/2-mediated phosphorylation of myometrial caldesmon during pregnancy and labor

We used a timed-pregnant rat model to track changes in myometrial contractility during pregnancy and labor and to correlate these changes with upstream signaling events. Myometrium was harvested from CO(2)-euthanized rats. Although contraction amplitudes increased at 16 and 20 days of pregnancy, contraction incidence and area under the force curve were inhibited, consistent with the myometrial quiescence of pregnancy. The Ca(2+) sensitivity of contraction was decreased at 20 days of pregnancy and this was partially reversed in labor. The protein content of h-caldesmon (h-CaD) was increased in pregnancy. A 40-fold increase in the signal from a phospho-CaD antibody specific for phosphorylation at an ERK1/2 site occurred during labor. ERK1/2 activation increased significantly at the onset of labor. Myosin light chain phosphorylation (LC20-P) increased significantly in labor compared with the nonpregnant state. Thus we conclude that the increase in CaD protein content during pregnancy may contribute to a suppression of the contractility of pregnant myometrium. Conversely, CaD phosphorylation, through an ERK1/2-mediated signaling pathway, as well as an increase in basal LC20-P, is suggested to contribute to the reversal of inhibition and promote contraction of the uterus during labor.

Organ culture as a useful method for studying the biology of blood vessels and other smooth muscle tissues

The benefit of organ culture is to retain the original structural relationship between various cell species and their interactions and enable us to study the long-term effects of exogenous stimuli. Organ culture methods have been used especially in the studies of the proliferative vascular diseases, such as atherosclerosis and restenosis. We describe here that organ culture is a useful in vitro method to study the biology of vascular and other smooth muscle organs.