Caroline P D Wheeler-Jones

Transcription

1 1366 Take the online multiple hoie questions assoiated with this artile (see page 1374) T Basi siene CELL SIGNALLING IN THE CARDIOVASCULAR SYSTEM: AN OVERVIEW Caroline P D Wheeler-Jones Heart 2005; 91: doi: /hrt he ardiovasular system is a highly omplex, well organised system in whih signal transdution plays ritial physiologial and pathophysiologial roles. The ellular elements of the heart and vasular wall are equipped with an array of speifi reeptors and with omplex intraellular mahinery that failitates and drives appropriate responses to extraellular stimuli. Understanding the mehanisms through whih extraellular stimuli modify the funtions of ells in the heart and vasular wall gives valuable insights into how perturbations of signalling systems an ause pathologial situations. This knowledge will allow the identifiation of novel moleular targets for pharmaologial intervention and will assist the future development of therapeuti strategies for managing ardiovasular disorders. This brief review will give a general overview of some major intraellular signalling systems operative in ells omprising the heart and vasulature, with partiular emphasis on the pleiotropi roles of protein kinases as regulators of ell behaviour. SENSING THE SIGNAL: THE ROLE OF G PROTEIN COUPLED RECEPTORS Cells must be able to monitor and respond appropriately to hanges in their extraellular environment, a proess that is often termed stimulus-response oupling. Signal transdution (ell signalling) systems allow ells to detet hanges in their extraellular milieu and to mount appropriate responses. Although numerous types of reeptor systems have evolved to detet extraellular stimuli, the family of reeptors that transmit signals through the ativation of heterotrimeri GTP binding proteins (G proteins) are important in many different tissues and play prominent roles in ells and tissues of the ardiovasular system. These proteins represent the largest group of ell surfae reeptors enoded by the mammalian genome (. 1% of human genes), and in the ardiovasular system G protein oupled reeptors (GPCRs) are impliated in more or less every regulatory event. Thus, signalling through GPCRs regulates the degree of peripheral arterial resistane, aspets of renal funtion, the rate and fore of myoardial ontration, and ardia hypertrophy. 1 GPCRs involved in normal ardiovasular funtion inlude those that respond to angiotensin II (AT 1 reeptors), to endothelin-1 (ET 1B reeptors), and to epinephrine and norepinephrine (a and b adrenergi reeptors). These reeptors are expressed on ardia myoytes, vasular smooth musle ells (VSMC) and endothelial ells, and signalling through them orhestrates the normal physiologial ontrol of vasular tone, heart rate, and ontratility. Moreover, sine angiotensin II, endothelin-1, and adrenergi agonists promote the growth of ardiomyoytes, stimulate vasular smooth musle ell (VSMC) proliferation, and modify endothelial ell funtion, signalling through their reeptors an also ontribute to the pathologial hanges exemplified by exessive ardia hypertrophy, atheroslerosis, and hypertension. GPCR agonists promote the interation of their respetive reeptors with a G protein heterotrimer omprising a, b, and subunits (fig1). 2 This interation subsequently promotes exhange of GTP for GDP on the G a subunit, auses subunit dissoiation, and thereby drives the ativation or inhibition of one or more effetor moleules by the free G a or G b subunits. These effetor moleules, whih inlude enzymes (for example, adenylate ylases; phospholipases) and ion hannels, regulate the generation of seond messenger moleules whih at through multiple mehanisms to trigger hanges in ell funtion. 3 4 By far the most important funtion for seond Correspondene to: messengers is to regulate the degree of phosphorylation of intraellular proteins, and this is now Dr Caroline P D Wheeler- reognised as the most general regulatory proess adopted by eukaryoti ells. 5 Protein Jones, Department of phosphorylation is a dynami equilibrium and seond messengers an alter the equilibrium by Veterinary Basi Sienes, Royal Veterinary College, promoting phosphorylation of protein substrates by ativating protein kinases, or by reversing this Royal College Street, London proess through protein phosphatases (fig 2). Disease an result from dysregulation of the NW1 0TU, UK; wheeler@rv. a.uk kinase(s) that trigger the ritial phosphorylation events assoiated with ativation of the system or with those that terminate the signal. 2 Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

2 Figure 1 Basi omponents of a G protein oupled reeptors (GPCR) signalling system. The basi omponents of a GPCR signalling system are the reeptor, a G protein, and an effetor moleule. The type of G protein employed, the subunits involved, and the effetors reruited are dependent upon the agonist and the ell type. For example, the AT 1 reeptor is the prinipal GPCR through whih angiotensin II modifies ardiovasular ell funtion. In this system, angiotensin II binding to the AT 1 reeptor ativates a G protein known as G q/11 whih subsequently stimulates ativity of the effetor moleule phospholipase C (PLC). This enzyme hydrolyses a membrane phospholipid (phosphatidylinositol 4,5-bisphosphate) to generate inositol (1,4,5)-trisphosphate (IP 3 ) and diaylglyerol (DAG). These moleules (termed seond messengers ) respetively raise the intraellular onentration of alium, and ativate protein kinase C. This signalling system is also triggered by ativation of the endothelin reeptor (ET 1B ), or by binding of adrenaline (epinephrine) to the a 1 -adrenoreeptor. In ontrast, stimulation of b-adrenergi reeptors in the heart or vasulature auses G as to ativate the effetor moleule adenylate ylase, leading to an elevation of the intraellular yli AMP onentration and to the onsequent ativation of AMP dependent protein kinase (PKA). Termination (down regulation) of GPCR mediated signalling events involves a family of G protein oupled reeptor kinases (GRKs). These enzymes phosphorylate ativated reeptors, promoting their unoupling from G proteins and initiating their subsequent internalisation. 2 SENSING THE SIGNAL: THE ROLE OF PROTEIN PHOSPHORYLATION Regulation of the phosphorylation of proteins is a entral omponent of all signal transdution pathways in ells of the ardiovasular system, making these moleules attrative targets for pharmaologial intervention. The realisation that around 3% of the human genome enodes for kinases and phosphatases, and the growing evidene that mutations and dysregulation of protein kinases play ausal roles in human disease further endorses the essential regulatory roles of these ell signalling elements. 6 A highly important feature of protein phosphorylation is its reversible ontrol; protein substrates are phosphorylated by kinases and dephosphorylated by phosphatases (fig 2). Thus, hanging kinase ativity, phosphatase ativity, or both an regulate the extent of phosphorylation of a substrate. The reversible phosphorylation events that are triggered by a ligand binding to its reeptor modify protein funtion, and thus ell behaviour, in numerous ways. For example, suh signals an alter the biologial ativity of a protein by hanging its onformation, an disrupt or enhane its interation with other regulatory moleules, or an hange its ellular loation. Protein kinases atually mediate most of the signal transdution in eukaryoti ells. Furthermore, the substrates of protein kinases are often ell speifi, whih helps to explain why there are distint effets of different signals in different tissues. These enzymes use adenosine triphosphate (ATP) to donate a phosphate group to partiular amino aid residues within their target substrates. Targeting kinases (and phosphatases) to ellular loations lose to their substrates also ensures very tight regulation of phosphorylation event. 7 Broadly speaking, kinases an be onveniently 1367 Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

3 1368 Figure 2 The Yin and Yang of protein phosphorylation. One the ell pereives an extraellular signal through one of its reeptor systems this will lead to a hange in kinase ativity(ies), and/or a hange in phosphatase ativity(ies) within the ell. Protein kinases use ellular ATP to donate phosphate groups to endogenous proteins. Consensus sequenes within proteins diret kinases to phosphorylate the orret amino aid residue within the substrate protein(s). Conversely, protein phosphatases remove phosphate groups from proteins and hene terminate or limit signals transdued through kinase pathways. In some instanes reeptors have intrinsi phosphatase, rather than kinase, ativity suh that ligand binding will lead diretly to de-phosphorylation of a protein that is normally onstitutively phosphorylated. This will ultimately lead to a hange in its funtion or loalisation, whih will then ulminate in altered ell behaviour. divided into three ategories based upon the speifi amino aid residues that they phosphorylate. SERINE/THREONINE KINASES Serine/threonine kinases, as their name suggests, phosphorylate either serine or threonine residues within their target proteins. Many members of this subgroup are omponents of signalling pathways that are essential for normal funtioning of the ardiovasular system (fig 3). Protein kinase A (PKA), for example, so alled beause it is a yli AMP (adenosine monophosphate) dependent kinase, plays ritial roles in mediating the effets of adrenergi stimulation on the heart and vasulature. 8 Similarly, GMP (guanosine monophosphate) dependent protein kinase (PKG) is a entral omponent of the pathway through whih nitri oxide, an endothelial derived vasodilator moleule, dereases vasular tone. 9 Protein kinase C is another serine/threonine kinase that is urrently reeiving a great deal of attention in the ardiovasular field. The protein kinase C (PKC) family omprises 10 isoforms that are divided into three groups based upon their different ativation requirements. Members of the onventional PKC family (a, b I, b II, and ) are alium dependent and are ativated by diaylglyerol (DAG) and phorbol esters. In ontrast, enzymes in the so alled novel PKC family (d, e, g, and h) are alium independent, and members of the atypial family (f and l) are not ativated by either alium or DAG. 10 Ativation of PKCs is important in ishaemi preonditioning of the myoardium, a phenomenon where brief exposure to ishaemia protets against a further ishaemi insult. In partiular, PKCe ativity is a ritial mediator of preonditioning and may protet against myoardial ell death by phosphorylating proteins that regulate the expression of protetive genes, or by phosphorylating, and thereby inhibiting, the ativities of proteins that promote programmed ell death. In ontrast, overexpression of ative PKCe an promote pathologial hypertrophy. Similarly, PKCa may be involved in GPCR mediated signalling in normal hearts, but when present in exessive amounts an impair ventriular systoli and diastoli funtion TYROSINE KINASES Protein tyrosine kinases (PTKs) phosphorylate tyrosine residues within proteins. These moleules have been subdivided into two ategories, reeptor tyrosine kinases (RTKs), of whih at least 13 families have been desribed, and nonreeptor PTKs, of whih at least nine families are urrently defined. 16 Growth fator reeptors, suh as those for epidermal growth fator (EGF), vasular endothelial growth fator (VEGF), and ErbB-2 are members of the RTK family, and ligand binding in these instanes promotes physiologial ell growth and proliferation (for example, during wound healing) as well as supporting aberrant ell growth in aners. These reeptors use their intrinsi tyrosine kinase ativity to reruit and ativate other proteins and hene trigger downstream signalling events that have many similarities to those eliited by ativation of GPCRs. Thus, following ligand binding, the RTKs autophosphorylate and the resulting phosphorylated tyrosine residues at as highly seletive binding sites for SH2 (Sr homology domain 2) ontaining proteins. Upon reruitment these proteins Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

4 Figure 3 Pivotal roles for serine/threonine kinases in ells of the ardiovasular system. Serine/threonine kinases are entral omponents of a number of important ell speifi signalling pathways operative in, for example, ardia myoytes and vasular smooth musle ells. (A) Adrenergi stimulation of ardiomyoytes through b 1 adrenoreeptors promotes G s a mediated ativation of adenylate ylase, generation of the seond messenger AMP, and ativation of AMP dependent protein kinase (protein kinase A). One ativated, protein kinase A phosphorylates numerous endogenous substrates (many of them ion hannels) whih failitate the rate of depolarisation, elevation of intraellular alium, and the ytoskeletal effets that together ulminate in inreased myoyte ontratility and a raised heart rate. (B) In vasular smooth musle ells, endothelial derived nitri oxide (NO) diretly ativates the effetor moleule guanylate ylase (GC) leading to the prodution of GMP and diret ativation of GMP dependent protein kinase (protein kinase G). The enzymati ativity of protein kinase G results in the ativation of myosin light hain (MLC) phosphatase that dephosphorylates MLC and auses vasular smooth musle relaxation. Protein kinase G also targets many other substrates (for example, voltage dependent alium hannels; phospholipase C) whose phosphorylation ulminates in a redued intraellular alium level and hene diminished vessel wall ontration. (C) Preonditioning stimuli in ardia musle (for example, brief exposure to ishaemia) ause an NO dependent ativation of protein kinase Ce. It is thought that PKCe disables pro-apoptoti proteins and also phosphorylates a number of transription fators leading to inreased expression of protetive genes in the myoardium. transdue signals through hanges in their own enzymati ativity or by reruiting other proteins. Among the SH2 ontaining proteins are effetor moleules (for example, phospholipase C), whose ativation leads to further downstream signalling through PKC and mitogen ativated protein kinase (MAPK) asades (see below). Like GPCRs, RTKs play important roles in ells of the ardiovasular system and are prinipally involved in initiating signalling events that ontrol ell growth, proliferation, and differentiation. Signalling through ErbB2 in ardiomyoytes, for example, promotes intraellular events that protet against the development of dilated ardiomyopathy. Importantly, patients reeiving anti-erbb2 antibodies as a aner treatment develop ardia dysfuntion as a side effet, highlighting the ritial role of these reeptor kinases in regulating normal ardiomyoyte behaviour. 17 Among the non-reeptor PTKs are the Sr, JAK (Janus kinase), and FAK (foal adhesion kinase) families. The Sr family omprises eight mammalian members (Sr, Yes, Fgr, Fyn, Lk, Lyn, Hk, and Blk) whih ontain SH2 domains adjaent to their atalyti domain. Sine GPCRs do not possess intrinsi tyrosine kinase ativity, these reeptors trigger ativation of many of these non-reeptor tyrosine kinases to initiate their intraellular signalling programmes. PROTEIN KINASE CASCADES: MIXED KINASE SIGNALS The existene of protein kinase asades, in whih a hain of phosphorylation events ours, was established 35 years ago with the disovery that PKA phosphorylates and ativates phosphorylase kinase in response to elevated AMP. 18 Protein kinase asades are extremely useful in signal transdution mehanisms as they allow for amplifiation, feedbak, rosstalk, and branhing. This, in turn, allows a limited number of enzymes to regulate very preisely a large number of ellular proesses. In this respet, the most important group of serine/threonine kinases, upon whih many other signals onverge, and whose ativities regulate numerous events in ells of the ardiovasular system, are the mitogen ativated protein kinases. 4 The basi assembly of an MAPK asade omprises three sequential kinases: an MAPK, an MAPK kinase (MKK), and an MAPK kinase kinase (MKKK) (fig 4) MKKKs are ativated either by phosphorylation via MAPK kinase kinase kinases (MKKKKs) or by interation with small GTP binding proteins of the Ras or Rho families. MKKKs are serine/ threonine kinases that phosphorylate, and thus ativate, the subsequent kinase in the pathway, an MKK. MKKs, some of whih are referred to as MEKs (MAPK/ERK ativating 1369 Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

5 1370 Heart: first published as /hrt on 14 September Downloaded from Figure 4 Organisation of MAP kinase asades. MAP kinase asades are exemplified by the lassial MAPK asade. In this signalling pathway ligand binding to a GPCR triggers ativation of the asade by promoting the generation of seond messengers and by reruiting adaptor moleules and non-reeptor tyrosine kinases. This results in ativation of a MAPK kinase kinase kinase and subsequent phosphorylation and ativation of raf, a MAPK kinase kinase. Raf an then phosphorylate the dual speifiity kinase MEK (an MAPK kinase) whih diretly phosphorylates ERK1/2 (a MAPK). Negative feedbak then allows for signal dampening or desensitisation. Within the lassial MAPK asade ERK1/2 promotes the indution of dual speifiity MAPK phosphatases (MKP-1 and-2), thus initiating its own deativation and limiting ellular responses in the absene of ontinued stimulus input. 19 There is also growing evidene of rosstalk between the different MAPK pathways. For example, it is thought that the proliferative effet of vasular endothelial growth fator on endothelial ells requires the sequential ativation of ERK1/2 and JNKs. 20 These studies have been strongly influened by the availability of seletive pharmaologial tools that blok the MAPKs themselves or target upstream omponents of the various asades. 21 on 8 Otober 2018 by guest. Proteted by opyright.

6 kinase), are unusual in that they reognise and phosphorylate speifi threonine and tyrosine residues in their substrates (the MAPKs) and are hene known as dual speifiity kinases. The final kinases in the three module asade are the MAPKs themselves, whih phosphorylate serine/threonine residues in many endogenous substrates. Ativation of MAPKs often results in their rapid movement to the nuleus. Thus, through their effets on phosphorylation, these kinases diretly affet the ativities of key ytoplasmi moleules (for example, phospholipase A 2 (PLA 2 ) enzymes) and modify aute ellular funtions, as well as promoting phosphorylation of nulear proteins (for example, transription fators) and thereby exerting more hroni effets by influening gene expression. 22 Other moleules ( saffolds ), that have yet to be fully defined and haraterised, failitate optimal signalling through these pathways by physially linking the kinase omponents of the various asades together and therefore maintaining the seletivity and speifiity of signal transdution from membrane to nuleus. 23 The mammalian MAPKs are divided into at least five families: ERK1/2 (extraellular regulated kinases), the p38 mapks, the -jun N-terminal kinases (JNKs), ERK3/4, and ERK5. The most widely studied MAPKs of reent years are ERK1/2, whih are omponents of the so alled lassial MAPK asade. These enzymes were the first MAPKs to be identified in mammalian ells as serine/ threonine kinases that phosphorylated a omponent of the ell ytoskeleton following exposure of adipoytes to insulin, another growth fator that uses an RTK as its reeptor. 24 Although a key funtion of ERK1/2 is to ontrol ell proliferation, differentiation, and survival via transription fator ativation, these MAPKs have also been impliated in many other aute events in ardiovasular ells, inluding the release of vasoative moleules from the endothelium, 25 and vasular smooth musle ell ontration in resistane vessels. 26 Thus, in endothelial ells ERK1/2 phosphorylates an isoform of the effetor moleule PLA 2, whih leaves arahidoni aid from membrane phospholipids. Cylooxygenase enzymes then onvert arahidoni aid into prostaglandin H 2, whih is a substrate for the various synthase enzymes that generate a range of other prostaglandins, inluding prostaylin (PGI 2 ). Sine PGI 2 is a vasodilator, suppresses platelet reativity, and inhibits vasular smooth musle ell proliferation, endothelial ERK1/2 ativation diretly ontributes to limiting the degree of vasular smooth musle ontration, thromboti events in the vasulature, and smooth musle ell growth, all of whih an our to exess in a number of ardiovasular disorders inluding hypertension and atheroslerosis. In vasular smooth musle, ERK1/2 phosphorylates the high moleular weight form of the ontratile regulatory protein aldesmon, suggesting that these kinases are also diretly involved in regulating the normal ontratile properties of the vasular wall. 26 ERK1/2 and JNK ativities are also inreased in vessels from hypertensive animals, demonstrating that aberrant expression and ativation of these MAPKs may also be assoiated with vessel pathology. One major funtion of ardia myoytes that depends upon ERK1/2 ativation is hypertrophi growth. Myoardial hypertrophy is an adaptive proess that ours in response to both physiologial and pathologial stimuli inluding angiotensin II, endothelin-1, and ateholamines. All of these mediators, as well as mehanial stress, stimulate ERK1/2 ativation in ardia myoytes and use this pathway to trigger the ytoplasmi and nulear events that failitate enhaned protein synthesis and hypertrophi ell growth. Interestingly, another signalling moleule that is thought to be important for hypertrophi growth of myoytes is the phosphatase alineurin. 27 Calineurin is a alium ativated phosphatase that atalyses the dephosphorylation of ytoplasmi transription fators known as NFATs (nulear fators of ativated T ells). In ardiomyoytes, this dephosphorylation event allows movement of NFATs into the nuleus where they ooperate with other transription fators to drive altered transription of hypertrophi genes. GPCR ligands that raise intraellular alium, inluding angiotensin II, ateholamines, and endothelin-1, an all ativate the alineurin pathway as well as the lassial MAPK asade, thus illustrating how phosphorylation and dephosphorylation events an interat to regulate the hypertophi phenotype in ardia musle. These kinase/phosphatase pathways may be important both for the physiologial ardia hypertrophy observed in the athleti (trained) heart, and for the pathophysiologial hypertrophy harateristi of failing hearts with inreased workloads. Moreover, reent evidene indiates that alineurin promotes the release of pro-inflammatory mediators from VSMCs, 28 suggesting that alineurin mediated dephosphorylation events may also have pathophysiologial signifiane in the vasular wall. The ERK1/2 pathway is not the only MAPK asade that has funtional signifiane in the ardiovasular system, and the p38 mapks are also involved in a range of ellular funtions. 29 Thus, during inflammation adhesion moleule expression on endothelial ells is neessary for the tethering and transendothelial migration of leuoytes. Expression of these adhesion moleules is highly dependent upon ativation of p38 mapk, whih phosphorylates the transription fators required for transriptional ativation of their genes. p38 mapk exists in several isoforms and these may have distint funtions, espeially in ardia tissue. For example, ishaemia/reperfusion ativates p38 mapk a but inhibits p38 mapk b. 30 In addition, ativation of p38 mapk a promotes apoptosis of ardiomyoytes whereas p38 mapk b indues ardiomyoyte hypertrophy. 31 The role of the JNKs has been less well studied but these MAPKs are also impliated in ardia hypertrophy and heart failure. 32 There is also inreasing evidene in ells of the ardiovasular system that GPCRs and RTKs an talk to eah other to oordinate intraellular signalling events. For example, angiotensin II an diretly promote ardiomyoyte growth by transativating the epidermal growth fator (EGF) reeptor and therefore triggering the distal ERK1/2-dependent signalling events that are important for the regulation of hypertrophi gene transription (fig 5). Transativation of growth fator reeptors is now beoming reognised as a novel form of signal transdution utilised by GPCRs. 33 Thus, targeting growth fator reeptors and hene the signalling events downstream of reeptor ativation may prove to be a benefiial means of ahieving inhibition of mitogeni signalling in response to a range of GPCRs. 34 SUMMARY AND PERSPECTIVES Cells involved in regulating homeostasis in the ardiovasular system respond to hanges in their loal environment by using a range of extraellular reeptors, of whih the GPCRs are the most important. Signal reognition is transdued into a ellular 1371 Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

7 1372 Figure 5 Kinases and phosphatases ontribute to ardia myoyte hypertrophy. Raised onentrations of angiotensin II, a powerful vasoonstritor, have been impliated in a number of pathologies assoiated with hypertension inluding atheroslerosis and ardia hypertrophy. 16 In the heart, angiotensin II ats through the G protein G q/11 to stimulate phospholipase C (PLC) and generate IP 3 and DAG. These events inrease the intraellular onentration of alium and ativate PKC. Non-reeptor tyrosine kinases suh as Sr and Pyk2 are also impliated in the hypertrophi response to angiotensin II, along with ativation of the alium dependent phosphatase alineurin. GPCRs in a number of ardiovasular ells an make extensive use of growth fator reeptors to initiate signalling programmes and this is partiularly evident in ardia myoytes where several of these intermediary moleules are involved in ontrolling angiotensin II mediated transativation of the epidermal growth fator (EGF) reeptor. Current evidene suggests that AT 1 reeptor mediated transativation of the EGF reeptor on ardia myoytes involves stimulation of the ativities of a family of membrane assoiated metalloprotease enzymes (ADAMs). These ultimately leave EGF reeptor ligands (suh as heparin binding EGF) from their membrane assoiated preursors whih releases them for interation with their reeptors. Stimulation of EGF reeptors then triggers ativation of several other signalling pathways in the myoytes inluding the MAP kinases. Phosphatase and kinase ativities regulate a number of ytosoli and nulear phosphorylation events whih together ontrol the hypertrophi gene transription responsible for driving ventriular hypertrophy. response (physiologial or pathologial) through intraellular transdution mehanisms that onverge on the regulation of the phosphorylation state of intraellular proteins by a range of protein kinase and protein phosphatase enzymes. It seems likely that subtle defets in these mehanisms may lead to a number of ardiovasular pathologies. This brief desription of some signal transdution pathways in the ardiovasular system an only srath the surfae of what are exeedingly omplex regulatory mehanisms. The omplexity is important beause it allows ells to at in onert to maintain homeostasis by responding rapidly to small and flutuating hanges in the inoming environmental signals, while the rosstalk between signalling pathways allows oordinated responses to multiple different and sometimes opposing signals. However, the omplexity and rosstalk may also be responsible for hroni pathologial Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

8 Glossary of terms Adenylate ylases: effetor enzymes that turn ATP into yli AMP whih, in turn, regulates ell funtion Adhesion moleule(s): protein moleules expressed on the surfae of ells to enable diret interation between neighbouring ells (inluding, but not limited to, adhesion) Arahidoni aid: a long hain, unsaturated fatty aid whih is generated by phospholipases, and whih an be turned into a range of other seond messengers Diaylglyerol: a lipid seond messenger that an ativate protein kinases whih is generated by phospholipases Effetor (moleule): an intraellular moleule (usually protein or lipid) that interats with the intraellular part of a ell surfae reeptor and transmits information from the reeptor into the ell Diaylglyerol: a lipid seond messenger that an ativate protein kinases whih is generated by phospholipases Heterotrimeri: a omplex protein that omprises three (trimeri) different (hetero) subunit proteins Isoforms: a family of proteins with similar struture and funtion but oded for by different genes, probably evolved by gene dupliation. Phorbol ester: a tumour promoting hemial derived from plant seeds that an substitute for diaylglyerol in ativating protein kinases Phospholipases: effetor enzymes that leave lipid moleules in the plasma membrane to generate intraellular signals that regulate ell funtion Phosphorylate/phosphorylation: the enzyme mediated hemial modifiation of proteins by ovalently attahing phosphate to speifi amino aids in the protein, whih alters the struture and funtion of the protein (Protein) kinases: enzymes that phosphorylate proteins (Protein) phosphatases: enzymes that remove phosphate from speifi amino aids in proteins (de-phosphorylate), thus reversing the effets of protein kinases Transription fator: a nulear protein that regulates gene expression by binding to speifi sites in genomi DNA hanges in the ardiovasular system. These signalling asades are dynami, with onstant ativation and deativation by protein (de)phosphorylation, allowing the system to ahieve equilibrium where ell funtion is optimum for the prevailing environmental onditions. Under these irumstanes small, but hroni, alterations in this omplex signalling network ould result in a shift in the equilibrium favouring the development of pathologial onditions suh as, for example, ardia hypertrophy. The existene of families of kinases and phosphatases and the realisation that individual members of a family may play opposing physiologial roles is a partiularly hallenging onept that must inform future therapeuti development. The good news is that our understanding of the signal transdution pathways in the ardiovasular system has inreased enormously over the past two deades. The identifiation of protein kinases and phosphatases as key elements in these pathways make them attrative moleular targets for future drug development. In partiular, the intimate involvement of the MAPK family of enzymes (and their assoiated phosphatases) in physiologial and pathologial ardiovasular proesses suggests that they may offer useful therapeuti targets for preventing or reversing aberrant ell growth in failing hearts. Our inreasingly detailed understanding of the inner mehanisms of ells omprising the ardiovasular system may soon lead to targeted and tailored therapies for previously ill defined disorders. In ompliane with EBAC/EACCME guidelines, all authors partiipating in Eduation in Heart have dislosed potential onflits of interest that might ause a bias in the artile REFERENCES 1 Dzimiri N. Reeptor rosstalk. Impliations for ardiovasular funtion, disease and therapy. Eur J Biohem 2002;269: A omprehensive review detailing the omplexities underlying reeptor mediated signalling in the heart and vessels. This review provides good overage of the various G protein oupled reeptors operative in vasular and ardia ells, the interations between them, and how this rosstalk regulates funtional outome. 2 Krupnik JG, Benovi JL. The role of reeptor kinases and arrestins in G protein-oupled reeptor regulation. Ann Rev Pharmaol Toxiol 1998;38: This artile reviews the speifi roles of two families of saffolding moleules involved in organising G protein oupled signalling systems. 3 Cabrera-Vera TM, Vanhauwe J, Thomas TO, et al. Insights into G protein struture, funtion, and regulation. Endor Rev 2003;24: A detailed review of G proteins and G protein mediated signalling. 4 Gutkind JS. Regulation of mitogen-ativated protein kinase signalling networks by G protein-oupled reeptors. Siene stke ( gi/ontent/full/oc_sigtrans;2000/40/re1). An exellent review overing all the basi aspets of G protein ativation along with details of the diverse signalling pathways linked to ativation of G protein oupled reeptors. 5 Cohen P. The origins of protein phosphorylation. Nature Cell Biol 2002;4:E A brief historial perspetive on the disovery of protein phosphorylation and dephosphorylation as important regulatory mehanisms in eukaryoti ells. 6 Manning G, Whyte DB, Martinez R, et al. The protein kinase omplement of the human genome. Siene 2002;298: Identifiation of protein kinase genes and their assoiation with disease loi. 7 Ruehr ML, Russell MA, Bond M. A-kinase anhoring protein targeting of protein kinase A in the heart. J Mol Cell Cardiol 2004;37: A review of the PKA pathway in ardia myoytes and the roles of saffolding proteins (AKAPs) in regulating ativation of PKA mediated phosphorylation events. 8 Rokman HA, Koh WJ, Lefkowitz RJ. Seven-transmembrane-spanning reeptors and heart funtion. Nature 2002;415: This review gives an up to date overage of the important GPCRs in ardia ells, the intraellular signalling events assoiated with their ativation, and the mehanisms involved in signal termination. The review fouses partiularly on b adrenergi reeptors. 9 Linoln TM, Dey N, Sellak H. GMP-dependent protein kinase signalling mehanisms in smooth musle: from the regulation of tone to gene expression. J Appl Physiol 2001;91: A short informative review on the potential dual role of GMP dependent protein kinases as regulators of tone in normal vessels, and of the phenotypi hanges assoiated with vasular smooth musle ells in diseased vessels. 10 Parker PJ, Murray-Rust J. PKC at a glane. J Cell Si 2004;117: A brief but informative ommentary on PKC isoforms. This artile is aompanied by a poster insert that details the mehanisms involved in PKC ativation. 11 Gray MO, Karliner JS, Mohly-Rosen D. A seletive e protein kinase C antagonist inhibits protetion of ardia myoytes from hypoxia-indued ell death. J Biol Chem 1997;272: This artile suggests that ative PKCe is protetive in ardia ells. 12 Baines PC, Zhang J, Wang GW, et al. Mitohondrial PKCe and MAPK form signalling modules in the murine heart. Cir Res 2002;90: This paper provides evidene that PKCe and MAPKs form protein omplexes that failitate signalling through phosphorylation asades. 13 Pyle WG, Chen Y, Hofmann PA. Cardioprotetion through a PKC-dependent derease in myofilament ATPase. Am J Physiol 2003;285:H Gray MO, Zhou H-Z, Shaffhalter-Zoppoth I, et al. Preservation of baseline hemodynami funtion and loss of induible ardioprotetion in adult mie laking protein kinase C. J Biol Chem 2004;279: Hahn HS, Marreez Y, Odley A, et al. Protein kinase Ca negatively regulates systoli and diastoli funtion in pathologial hypertrophy. Cir Res 2003;93: Evidene that PCKa ativation an exert detrimental effets in the failing heart. 16 Yin G, Yan C, Berk BC. Angiotensin II signaling pathways mediated by tyrosine kinases. Int J Biohem Cell Biol 2003;35: A review of the many tyrosine kinases involved in angiotensin II mediated signalling events. 17 Crone SA, Zhao Y-Y, Fan L, et al. ErbB2 is essential in the prevention of dilated ardiomyopathy. Nature Med 2002;8: These authors generated mie with a ventriular restrited deletion of the reeptor tyrosine kinase ErbB2. As these mie aged they showed notable ventriular wall thinning, hamber dilation, and dereased ontratility ompared to hearts from normal mie of the same age. Cardia myoytes isolated from the ErbB2 defiient mie were also 1373 Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.

9 1374 more suseptible to a toxi stimulus. These data explain why some breast aner patients treated with hereptin, a monolonal antibody direted against the extraellular domain of ErbB2, develop ardiomyopathy. 18 DeLange RJ, Kemp RG, Riley WD, et al. Ativation of skeletal musle phosphorylase kinase by adenosine triphosphate and 39, 59-monophosphate. J Biol Chem 1968;243: An early demonstration of the existene of phosphorylation asades in mammalian ells. 19 Brondello J-M, Brunet A, Pouyssegur J, et al. The dual speifiity mitogenativated protein kinase phosphatases-1 and -2 are indued by the p42/ p44 MAPK asade. J Biol Chem 1997;272: This paper shows that ativation of the lassial MAPK asade leads to indution of phosphatase enzymes that dephosphorylate ERK1/2, thus terminating ERK-mediated phosphorylation events. 20 Pedram A, Razandi M, Levin ER. Extraellular signal-regulated protein kinase/jun kinase ross-talk underlies vasular endothelial ell growth fatorindued endothelial ell proliferation. J Biol Chem 1998;273: English JM, Cobb MH. Pharmaologial inhibitors of MAPK pathways. Trends Pharm Si 2002;23: Brand NJ, Barton PJR. Myoardial moleular biology: an introdution. Heart 2002;87: Burak WR, Shaw AS. Signal transdution: hanging on a saffold. Curr Opin Cell Biol 2000;12: A short review on the role of saffolding proteins in ontrolling MAPK asades. 24 Ray LB, Sturgill TW. Rapid stimulation by insulin of a serine/threonine kinase in 3T3-L1 adipoytes that phosphorylates mirotubule-assoiated protein 2 in vitro. Pro Natl Aad Si USA 1987;84: Houliston RA, Pearson JD, Wheeler-Jones CPD. Agonist-speifi ross talk between ERKs and p38 mapk regulates PGI 2 synthesis in endothelium. Am J Physiol Cell Physiol 2001;281:C This paper shows that ommuniation between two MAPK asades regulates the release of the vasodilator moleule prostaylin from human endothelial ells. MULTIPLE CHOICE QUESTIONS Eduation in Heart Interative ( 26 Adam LP, Franklin MT, Raff GJ, et al. Ativation of mitogen-ativated protein kinase in porine arotid arteries. Cir Res 1995;76: Wilkins BJ, Molkentin JD. Calineurin and ardia hypertrophy: where have we been? Where are we going? J Physiol 2002;541:1 8. A short ritial review on the role of alineurin as a mediator of ardia myoyte growth. 28 Satonaka H, Suzuki E, Nishimatsu H, et al. Calineurin promotes the expression of monoyte hemoattratant protein-1 in vasular myoytes and mediates vasular inflammation. Cir Res 2004;94: This paper shows that fored expression of the phosphatases alineurin in vasular smooth musle ells auses release of inflammatory mediators. 29 Nebreda AR, Porras A. p38 MAP kinases: beyond the stress response. Trends Biohem Si 2000;25: A onise aount of the reported roles for p38 mapks in ell growth, survival, and differentiation. 30 Saurin AT, Martin JL, Heads RJ, et al. The role of differential ativation of p38- mitogen-ativated protein kinase in preonditioned ventriular myoytes. FASEB J 2000;14: Wang Y, Huang S, Sah VP, et al. Cardia musle ell hypertrophy and apoptosis indued by distint members of the p38 mitogen-ativated protein kinase family. J Biol Chem 1998;273: Shultz R, Aker S, Belosjorow S, et al. Stress kinase phosphorylation is inreased in paing-indued heart failure in rabbits. Am J Physiol Heart Cir Physiol 2003;285:H Shah BH, Catt KJ. Matrix metalloproteinase-dependent EGF reeptor ativation in hypertension and left ventriular hypertrophy. Trends Endorinol Metab 2004;15: Fore T, Kuida K, Namhuk M, et al. Inhibitors of protein kinase signaling pathways. Emerging therapies for ardiovasular disease. Cirulation 2004;109: A thorough review of the kinase inhibitors urrently in linial trials and perspetives on the development of kinase inhibitors for treating disorders of the ardiovasular system. There are six multiple hoie questions assoiated with eah Eduation in Heart artile (these questions have been written by the authors of the artiles). Eah artile is submitted to EBAC (European Board for Areditation in Cardiology; for 1 hour of external CPD redit. How to find the MCQs: Clik on the Online Learning: [Take interative ourse] link on the table of ontents for the issue online or on the Eduation in Heart olletion ( Free aess: This link will take you to the BMJ Publishing Group s online learning website. Your Heart Online user name and password will be reognised by this website. As a Heart subsriber you have free aess to these MCQs but you must register on the site so you an trak your learning ativity and reeive redit for ompleted ourses. How to get aess: If you have not yet ativated your Heart Online aess, please do so by visiting and entering your six digit (all numeri) ustomer number (found above your address label with your print opy). If you have any trouble ativating or using the site please ontat subsriptions@bmjgroup.om Case based Heart: You might also be interested in the interative ases published in assoiation with Heart ( Heart: first published as /hrt on 14 September Downloaded from on 8 Otober 2018 by guest. Proteted by opyright.