Ca2+/calmodulin-dependent protein kinase IV activates cysteine-rich protein 1 through adjacent CRE and CArG elements

Role of CRP2-MRTF interaction in functions of myofibroblasts

Inflammatory response induces phenotypic modulation of fibroblasts into myofibroblasts. Although transforming growth factor-βs (TGF-βs) evoke such transition, the details of the mechanism are still unknown. Here, we report that a LIM domain protein, cysteine-and glycine-rich protein 2 (CSRP2 [CRP2]) plays a vital role in the functional expression profile in myofibroblasts and cancer-associated fibroblasts (CAFs). Knock-down of CRP2 severely inhibits the expression of smooth muscle cell (SMC) genes, cell motility, and CAF-mediated collective invasion of epidermoid carcinoma. We elucidate the following molecular bases: CRP2 directly binds to myocardin-related transcription factors (MRTF-A/B [MRTFs]) and serum response factor (SRF) and stabilizes the MRTF/SRF/CArG-box complex to activate SMC gene expression. Furthermore, a three-dimensional structural analysis of CRP2 identifies the amino acids required for the CRP2-MRTF-A interaction. Polar amino acids in the C-terminal half (serine-152, glutamate-154, serine-155, threonine-156, threonine-157, and threonine-159 in human CRP2) are responsible for direct binding to MRTF-A. On the other hand, hydrophobic amino acids outside the consensus sequence of the LIM domain (tryptophan-139, phenylalanine-144, leucine-153, and leucine-158 in human CRP2) play a role in stabilizing the unique structure of the LIM domain.Key words: CRP2, 3D structure, myocardin-related transcription factor, myofibroblast, cancer-associated fibroblasts.

Calcium Signalling in Heart and Vessels: Role of Calmodulin and Downstream Calmodulin-Dependent Protein Kinases

Cardiovascular disease is the major cause of death worldwide. The success of medication and other preventive measures introduced in the last century have not yet halted the epidemic of cardiovascular disease. Although the molecular mechanisms of the pathophysiology of the heart and vessels have been extensively studied, the burden of ischemic cardiovascular conditions has risen to become a top cause of morbidity and mortality. Calcium has important functions in the cardiovascular system. Calcium is involved in the mechanism of excitation-contraction coupling that regulates numerous events, ranging from the production of action potentials to the contraction of cardiomyocytes and vascular smooth muscle cells. Both in the heart and vessels, the rise of intracellular calcium is sensed by calmodulin, a protein that regulates and activates downstream kinases involved in regulating calcium signalling. Among them is the calcium calmodulin kinase family, which is involved in the regulation of cardiac functions. In this review, we present the current literature regarding the role of calcium/calmodulin pathways in the heart and vessels with the aim to summarize our mechanistic understanding of this process and to open novel avenues for research.

Identification of ASB7 as ER stress responsive gene through a genome wide in silico screening for genes with ERSE

The endoplasmic reticulum (ER) not only performs its basic function of regulating calcium homeostasis, lipid biosynthesis, folding, modifying and transporting proteins but also plays a decisive role in regulating multiple cellular processes ranging from cell growth and differentiation to apoptosis and autophagy. Disturbances in ER homeostasis initiate the unfolded protein response (UPR) implicated in the pathogenesis of many human diseases. Drugging the UPR components for therapeutic interventions has received considerable attention. The purpose of this study is to identify genes that are previously unsuspected to be regulated under ER stress. Because ER stress-inducible gene expression is majorly regulated under ERSE elements, we screened human genome by adopting an in silico approach using ERSE elements (I, II, III) as probes and identified 337 candidate genes. Having knowledge of the importance of E3 ubiquitin ligase in the ERAD machinery; we validated our preliminary search by focusing on one of the hits i.e. ASB7 gene that encodes E3 ubiquitin ligase. In HeLa cells, we found that pharmacological induction of ER stress led to an increase in the expression of ASB7 with simultaneous activation of UPR pathways. Although knockdown of ASB7 expression leads to significant reduction in GRP78 and CHOP mRNA levels, it did not protect cells from ER stress-induced cell death. Also, an up-regulation in the expression of pro-inflammatory genes like TNF-α and IL-1β in ASB7 knockdown cells was observed under ER stress. Collectively, our findings suggest that ASB7 is regulated under ER stress and this study also identifies several other genes that could apparently be regulated under ER stress.

Excitation-Contraction Coupling and Excitation-Transcription Coupling in Blood Vessels: Their Possible Interactions in Hypertensive Vascular Remodeling

Vascular smooth muscle cells (VSMC) display considerable phenotype plasticity which can be studied in vivo on vascular remodeling which occurs during acute or chronic vascular injury. In differentiated cells, which represent contractile phenotype, there are characteristic rapid transient changes of intracellular Ca2+ concentration ([Ca2+]i), while the resting cytosolic [Ca2+]i concentration is low. It is mainly caused by two components of the Ca2+ signaling pathways: Ca2+ entry via L-type voltage-dependent Ca2+ channels and dynamic involvement of intracellular stores. Proliferative VSMC phenotype is characterized by long-lasting [Ca2+]i oscillations accompanied by sustained elevation of basal [Ca2+]i. During the switch from contractile to proliferative phenotype there is a general transition from voltage-dependent Ca2+ entry to voltage-independent Ca2+ entry into the cell. These changes are due to the altered gene expression which is dependent on specific transcription factors activated by various stimuli. It is an open question whether abnormal VSMC phenotype reported in rats with genetic hypertension (such as spontaneously hypertensive rats) might be partially caused by a shift from contractile to proliferative VSMC phenotype.

Downregulation of L-type Ca2+ channel in rat mesenteric arteries leads to loss of smooth muscle contractile phenotype and inward hypertrophic remodeling

L-type Ca2+ channels (LTCCs) are important for vascular smooth muscle cell (VSMC) contraction, as well as VSMC differentiation, as indicated by loss of LTCCs during VSMC dedifferentiation. However, it is not clear whether loss of LTCCs is a primary event underlying phenotypic modulation or whether loss of LTCCs has significance for vascular structure. We used small interference RNA (siRNA) transfection in vivo to investigate the role of LTCCs in VSMC phenotypic expression and structure of rat mesenteric arteries. siRNA reduced LTCC mRNA and protein expression in rat mesenteric arteries 3 days after siRNA transfection to 12.7 ± 0.7% and 47.3 ± 13%, respectively: this was associated with an increased resting intracellular Ca2+ concentration ([Ca2+]i). Despite the high [Ca2+]i, the contractility was reduced (tension development to norepinephrine was 3.5 ± 0.2 N/m and 0.8 ± 0.2 N/m for sham-transfected and downregulated arteries respectively; P < 0.05). Expression of contractile phenotype marker genes was reduced in arteries downregulated for LTCCs. Phenotypic changes were associated with a 45% increase in number of VSMCs and a consequent increase of media thickness and media area. Ten days after siRNA transfection arterial structure was again normalized. The contractile responses of LTCC-siRNA transfected arteries were elevated in comparison with matched controls 10 days after transfection. The study provides strong evidence for causal relationships between LTCC expression and VSMC contractile phenotype, as well as novel data addressing the complex relationship between VSMC contractility, phenotype, and vascular structure. These findings are relevant for understanding diseases, associated with phenotype changes of VSMC and vascular remodeling, such as atherosclerosis and hypertension.

Vascular smooth muscle cell phenotype is defined by Ca2+-dependent transcription factors

Ca(2+) is an important second messenger in vascular smooth muscle cells (VSMCs). Therefore, VSMCs exercise tight control of the intracellular Ca(2+) concentration ([Ca(2+)]i) by expressing a wide repertoire of Ca(2+) channels and transporters. The presence of several pathways for Ca(2+) influx and efflux provides many possibilities for controlling [Ca(2+)]i in a spatial and temporal manner. Intracellular Ca(2+) has a dual role in VSMCs; first, it is necessary for VSMC contraction; and, second, it can activate multiple transcription factors. These factors are cAMP response element-binding protein, nuclear factor of activated T lymphocytes, and serum response factor. Furthermore, it was recently reported that the C-terminus of voltage-dependent L-type Ca(2+) calcium channels can regulate transcription in VSMCs. Transcription regulation in VSMCs modulates the expression patterns of genes, including genes coding for contractile and cytoskeleton proteins, and those promoting proliferation and cell growth. Depending on their gene expression, VSMCs can exist in different functional states or phenotypes. The majority of healthy VSMCs show a contractile phenotype, characterized by high contractile ability and a low proliferative rate. However, VSMCs can undergo phenotypic modulation with different physiological and pathological stimuli, whereby they start to proliferate, migrate, and synthesize excessive extracellular matrix. These events are associated with injury repair and angiogenesis, but also with the development of cardiovascular pathologies, such as atherosclerosis and hypertension. This review discusses the currently known Ca(2+)-dependent transcription factors in VSMCs, their regulation by Ca(2+) signalling, and their role in the VSMC phenotype.

CRP1, a protein localized in filopodia of growth cones, is involved in dendritic growth

The cysteine-rich protein (CRP) family is a subgroup of LIM domain proteins. CRP1, which cross-links actin filaments to make actin bundles, is the only CRP family member expressed in the CNS with little known about its function in nerve cells. Here, we report that CRP1 colocalizes with actin in the filopodia of growth cones in cultured rat hippocampal neurons. Knockdown of CRP1 expression by short hairpin RNA interference results in inhibition of filopodia formation and dendritic growth in neurons. Overexpression of CRP1 increases filopodia formation and neurite branching, which require its actin-bundling activity. Expression of CRP1 with a constitutively active form of Cdc42, a GTPase involved in filopodia formation, increases filopodia formation in COS-7 cells, suggesting cooperation between the two proteins. Moreover, we demonstrate that neuronal activity upregulates CRP1 expression in hippocampal neurons via Ca²⁺ influx after depolarization. Ca²⁺/calmodulin-dependent protein kinase IV (CaMKIV) and cAMP response element binding protein mediate the Ca²⁺-induced upregulation of CRP1 expression. Furthermore, CRP1 is required for the dendritic growth induced by Ca²⁺ influx or CaMKIV. Together, these data are the first to demonstrate a role for CRP1 in dendritic growth.

Loss of the serum response factor cofactor, cysteine-rich protein 1, attenuates neointima formation in the mouse

OBJECTIVE

Cysteine-rich protein (CRP) 1 and 2 are cytoskeletal lin-11 isl-1 mec-3 (LIM)-domain proteins thought to be critical for smooth muscle differentiation. Loss of murine CRP2 does not overtly affect smooth muscle differentiation or vascular function but does exacerbate neointima formation in response to vascular injury. Because CRPs 1 and 2 are coexpressed in the vasculature, we hypothesize that CRPs 1 and 2 act redundantly in smooth muscle differentiation.

METHODS AND RESULTS

We generated Csrp1 (gene name for CRP1) null mice by genetic ablation of the Csrp1 gene and found that mice lacking CRP1 are viable and fertile. Smooth muscle-containing tissues from Csrp1-null mice are morphologically indistinguishable from wild-type mice and have normal contractile properties. Mice lacking CRPs 1 and 2 are viable and fertile, ruling out functional redundancy between these 2 highly related proteins as a cause for the lack of an overt phenotype in the Csrp1-null mice. Csrp1-null mice challenged by wire-induced arterial injury display reduced neointima formation, opposite to that seen in Csrp2-null mice, whereas Csrp1/Csrp2 double-null mice produce a wild-type response.

CONCLUSIONS

Smooth muscle CRPs are not essential for normal smooth muscle differentiation during development, but may act antagonistically to modulate the smooth muscle response to pathophysiological stress.

Protein kinase A-regulated assembly of a MEF2{middle dot}HDAC4 repressor complex controls c-Jun expression in vascular smooth muscle cells

Vascular smooth muscle cells (VSMCs) maintain the ability to modulate their phenotype in response to changing environmental stimuli. This phenotype modulation plays a critical role in the development of most vascular disease states. In these studies, stimulation of cultured vascular smooth muscle cells with platelet-derived growth factor resulted in marked induction of c-jun expression, which was attenuated by protein kinase Cdelta and calcium/calmodulin-dependent protein kinase inhibition. Given that these signaling pathways have been shown to relieve the repressive effects of class II histone deacetylases (HDACs) on myocyte enhancer factor (MEF) 2 proteins, we ectopically expressed HDAC4 and observed repression of c-jun expression. Congruently, suppression of HDAC4 by RNA interference resulted in enhanced c-jun expression. Consistent with these findings, mutation of the MEF2 cis-element in the c-jun promoter resulted in promoter activation during quiescent conditions, suggesting that the MEF2 cis-element functions as a repressor in this context. Furthermore, we demonstrate that protein kinase A attenuates c-Jun expression by promoting the formation of a MEF2.HDAC4 repressor complex by inhibiting salt-inducible kinase 1. Finally, we document a physical interaction between c-Jun and myocardin, and we document that forced expression of c-Jun represses the ability of myocardin to activate smooth muscle gene expression. Thus, MEF2 and HDAC4 act to repress c-Jun expression in quiescent VSMCs, protein kinase A enhances this repression, and platelet-derived growth factor derepresses c-Jun expression through calcium/calmodulin-dependent protein kinases and novel protein kinase Cs. Regulation of this molecular "switch" on the c-jun promoter may thus prove critical for toggling between the activated and quiescent VSMC phenotypes.

Transforming growth factor beta up-regulates cysteine-rich protein 2 in vascular smooth muscle cells via activating transcription factor 2

CRP2 (cysteine-rich protein) is a vascular smooth muscle cell (VSMC)-expressed LIM-only protein. CRP2 associates with the actin cytoskeleton and interacts with transcription factors in the nucleus to mediate smooth muscle cell gene expression. Using Csrp2 (gene symbol of the mouse CRP2 gene)-deficient mice, we previously demonstrated that an absence of CRP2 enhances VSMC migration and increases neointima formation following arterial injury. Despite its importance in vascular injury, the molecular mechanisms controlling CRP2 expression in VSMC are largely unknown. Transforming growth factor beta (TGFbeta), a key factor present in the vessel wall in the early phases of arterial response to injury, plays an important role in modulating lesion formation. Because both CRP2 and TGFbeta are mediators of VSMC responses, we examined the possibility that TGFbeta might regulate CRP2 expression. TGFbeta significantly induced CRP2 mRNA and protein expression in VSMCs. Promoter analysis identified a conserved cAMP-responsive element (CRE)-like site (TAACGTCA) in the Csrp2 promoter that was critical for basal promoter activity and response to TGFbeta. Gel mobility shift assays revealed that mainly ATF2 bound to this CRE-like element, and mutation of the CRE sequences abolished binding. TGFbeta enhanced the activation of ATF2, leading to increased phospho-ATF2 levels within the DNA-protein complexes. Furthermore, ATF2-transactivated Csrp2 promoter activity and TGFbeta enhanced this activation. In addition, a phosphorylation-negative ATF2 mutant construct decreased basal and TGFbeta-mediated Csrp2 promoter activity. Our results show for the first time in VSMC that TGFbeta activates ATF2 phosphorylation and Csrp2 gene expression via a CRE promoter element.

Retinoic acid induces caspase-8 transcription via phospho-CREB and increases apoptotic responses to death stimuli in neuroblastoma cells

Caspase-8 is frequently deleted or silenced in neuroblastoma and other solid tumor such as medulloblastoma and small cell lung carcinoma. Caspase-8 expression can be re-established in neuroblastoma cell lines by treatment with demethylating agents or with IFN-gamma. Here we show that four different retinoic acid (RA) derivatives also increase caspase-8 protein expression in neuroblastoma, medulloblastoma and small cell lung carcinoma cell lines. This increase in protein expression is mirrored by an increase in RNA expression in NB cells. However, the promoter region of the caspase-8 gene was not responsible for the induction of caspase-8 expression. Rather, we identified another intronic region containing a CREB binding site that was required for maximal induction of caspase-8 via RA. DNA-protein interaction assays revealed increased phospho-CREB binding to this response element in RA-treated NB cells. Furthermore, mutations of the CREB binding site completely blocked caspase-8 induction in the luciferase reporter system assay and transfection of dominant-negative form of CREB repressed the up-regulation of caspase-8 by RA. Importantly, RA-released cells maintained caspase-8 expression for at least 2-5 days and were more sensitive to doxorubicin and TNFalpha. Thus, RA treatment in conjunction with TNFalpha and/or subsets of cytotoxic agents may have therapeutic benefits.

Impact of 5-HT3 receptor blockade on colonic haemodynamic responses to ischaemia and reperfusion in the rat

5-HT(3) receptor antagonists are clinically available for treating patients with irritable bowel syndrome (IBS) but their use is restricted because of a link with some episodes of ischaemic colitis. However, the role of 5-HT3 receptors in regulating colonic blood flow has not been systematically investigated. Thus, we examined acute and chronic treatment with alosetron, a potent and selective antagonist of the 5-HT3 receptor, on baseline colonic blood flow and haemodynamic responses during occlusion and reactive hyperaemia in the pentobarbitone-anaesthetized rat. Colonic haemodynamics were assessed using ultrasonic recordings of superior mesenteric blood flow (MBF) and laser Doppler recordings of colonic vascular perfusion (VP). Blood pressure (BP) was also monitored and in some experiments tissue oxygen was detected polarographically. Alosetron (10, 30, 100 microg kg(-1), i.v.) had no effect on baseline haemodynamics nor responses to nitric oxide synthase inhibition with N(omega)-nitro-l-arginine methyl ester (l-NAME) (16 mg kg(-1)). Arterial occlusion (5 min) reduced MBF (-98.6 +/- 0.6%) and VP (-70.7 +/- 5.4%) followed by a post-occlusion reactive hyperaemia (MBF = +94.5 +/- 19.1%; VP = +60.0 +/- 22.3%) the magnitude of which was unchanged following acute (30 microg kg(-1)) or chronic alosetron administration (0.5 mg kg(-1) twice daily, 5 days). Alosetron did not significantly alter baseline colonic blood flow in the anaesthetized rat; nor did it interfere with vascular control mechanisms activated during occlusion and reactive hyperaemia.

Modulation of peristalsis by NK3receptor antagonism in guinea-pig isolated ileum is revealed as intraluminal pressure is raised

1. NK(3) tachykinin receptors mediate slow excitatory transmission in the enteric nervous system and play a role in reflexes induced by the intestinal stretch or mucosal compression. However, there is little evidence to suggest that these receptors are important in peristalsis. We have examined the effects of the NK(3) receptor antagonist, talnetant, on peristalsis in guinea-pig isolated ileum induced by optimal and by supra-maximal distension pressures. 2. At the guinea-pig NK(3) receptor, talnetant was shown to have high affinity (pK(B) 8.8) and selectivity over the guinea-pig NK(1) and NK(2) receptors. 3. Peristaltic waves in the ileum elicited by optimal distension pressures (1-3 cmH(2)O) were unaffected by talnetant at a supra-maximal concentration (250 nm). 4. Distension at a higher pressure (4 cmH(2)O) induced peristalsis in which there was incomplete closure of the lumen during each peristaltic wave and an increase in the periods of inactivity observed between bursts of peristaltic activity. The addition of talnetant (250 nm) increased the number of peristaltic events by reducing these periods of inactivity and thus, increased the productivity of the peristaltic reflex. 5. The data suggest that NK(3) receptors are not involved in the modulation of peristaltic movements by physiological stimuli, but they may have a role in modulation of reflexes in extreme or pathological conditions.

The expression of CSRP2 encoding the LIM domain protein CRP2 is mediated by TGF-β in smooth muscle and hepatic stellate cells

Transforming growth factor-beta (TGF-beta) is a cytokine implicated in differentiation of smooth muscle cells and other mesenchymal-derived cells. During hepatic fibrogenesis, TGF-beta has a pivotal role in the initiation, promotion, and progression of transdifferentiation of hepatic stellate cells into myofibroblasts that play a central role in the synthesis of extracellular matrix components. Both, smooth muscle and activated hepatic stellate cells, express smooth muscle alpha-actin, the calponin-related protein SM22alpha, and CSRP2 encoding the cysteine- and glycine-rich LIM domain protein 2 (CRP2). The aim of the present study was to determine whether the expression of CSRP2 is influenced by TGF-beta. Stimulation as well as sequestering experiments demonstrated that TGF-beta markedly influences CSRP2 gene activity. Inhibition experiments using the ALK5 inhibitor SB-431542 further reveal that the transcriptional stimulation of the CSRP2 gene is mediated via the ALK5/Smad2/Smad3 signalling pathway. By use of bisulfite genomic analysis of CpG islands within the 5' regulatory regions we could exclude methylation-associated silencing, previously found to be responsible for the transcriptional inactivity of CSRP2 in a variety of human cancer cells and in a multistage carcinogenesis model, as a cause for CSRP2 inactivity in hepatocytes or fully transdifferentiated myofibroblasts.

Excitation-transcription coupling in arterial smooth muscle

The primary function of the vascular smooth muscle cell (SMC) is contraction for which SMCs express a selective repertoire of genes (eg, SM alpha-actin, SM myosin heavy chain [SMMHC], myocardin) that ultimately define the SMC from other muscle cell types. Moreover, the SMC exhibits extensive phenotypic diversity and plasticity, which play an important role during normal development, repair of vascular injury, and in vascular disease states. Diverse signals modulate ion channel activity in the sarcolemma of SMCs, resulting in altered intracellular calcium (Ca) signaling, activation of multiple intracellular signaling cascades, and SMC contraction or relaxation, a process known as "excitation-contraction coupling" (EC-coupling). Over the past 5 years, exciting new studies have shown that the same signals that regulate EC-coupling in SMCs are also capable of regulating SMC-selective gene expression programs, a new paradigm coined "excitation-transcription coupling" (ET-coupling). This article reviews recent progress in our understanding of the mechanisms by which ET-coupling selectively coordinates the expression of distinct gene subsets in SMCs by disparate transcription factors, including CREB, NFAT, and myocardin, via selective kinases. For example, L-type voltage-gated Ca2+ channels modulate SMC differentiation marker gene expression, eg, SM alpha-actin and SMMHC, via Rho kinase and myocardin and also regulate c-fos gene expression independently via CaMK. In addition, we discuss the potential role of IK channels and TRPC in ET-coupling as potential mediators of SMC phenotypic modulation, ie, negatively regulate SMC differentiation marker genes, in vascular disease.

Differential activation of mitogen-activated protein kinases in ischemic and nitroglycerin-induced preconditioning

Previous studies have shown that the cardioprotective effect of ischemic preconditioning (IPC) can be mimicked pharmacologically with clinically relevant agents, including nitric oxide (NO) donors. However, whether pharmacological preconditioning shares the same molecular mechanism with IPC is not fully elucidated. The present study aimed to determine the activation of mitogen-activated protein kinases (MAPKs) (ERK1/2, p38 MAPK and p46/p54 JNKs) during ischemia and at reperfusion in nitroglycerin-induced preconditioning as compared to IPC and to correlate this with the conferred cardioprotection in anesthetized rabbits. Sixty minutes of intravenous administration of nitroglycerin was capable of inducing both early and late phase preconditioning in anesthetized rabbits, as it was expressed by the reduction of infarct size. Despite the cardioprotective effect conferred by both ischemic and nitroglycerin-induced preconditioning, there was a differential phosphorylation of MAPKs between the studied groups. p38 MAPK was activated early in ischemia in both ischemic and the early nitroglycerin-induced preconditioning while JNKs were markedly increased only after IPC. Furthermore, in these groups, ERK1/2 were activated during reperfusion. A different profile was observed in the late preconditioning induced by nitroglycerin with increased p38 MAPK and ERK1/2 phosphorylation during late ischemia. No activation of JNKs was observed at any time point in this group. It seems that activation of individual MAPK subfamilies depends on the nature of preconditioning stimulus.

Excitation-transcription coupling in smooth muscle

Calcium (Ca2+) signals affect virtually every biological process, including both contraction and gene transcription in smooth muscle. Ca2+-regulated gene transcription is known to be important for both physiological and pathological responses in smooth muscle. The aim of this review is to discuss the current understanding of gene transcription regulated by excitation through Ca2+ signalling using a comparison of the two most characterized Ca2+-regulated transcription factors in smooth muscle, Ca2+-cyclic AMP response element binding protein (CREB) and nuclear factor of activated T-cells (NFAT). Recent studies have shown commonalities and differences in the regulation of CREB and NFAT through both voltage- and non-voltage-gated Ca2+ channels that lead to expression of smooth muscle cell specific differentiation markers as well as markers of proliferation. New insights into the regulation of specific genes through companion elements on the promoters of Ca2+-regulated genes have led to new models for transcriptional regulation by Ca2+ that are defined both by the source and duration of the Ca2+ signal and the composition of enhancer elements found within the regulatory regions of specific genes. Thus the combination of signalling pathways elicited by particular Ca2+ signals affect selective promoter elements that are key to the ultimate pattern of gene transcription.