Abstract. The development of functional blood and lymphatic vessels requires spatio-temporal coordination of the production and release of growth factors such as vas-

The mitogen-activated protein kinases (MAPKs) pathways are highly organized signaling systems that transduce extracellular signals into a variety of intracellular responses. In this context, it is currently poorly understood how kinases constituting these signaling cascades are assembled and activated in response to receptor stimulation to generate specific cellular responses. Here, we show that AKAP-Lbc, an A-kinase anchoring protein (AKAP) with an intrinsic Rho-specific guanine nucleotide exchange factor activity, is critically involved in the activation of the p38␣ MAPK downstream of ␣ 1b -adrenergic receptors (␣ 1b -ARs). Our results indicate that AKAP-Lbc can assemble a novel transduction complex containing the RhoA effector PKN␣, MLTK, MKK3, and p38␣, which integrates signals from ␣ 1b -ARs to promote RhoA-dependent activation of p38␣. In particular, silencing of AKAP-Lbc expression or disrupting the formation of the AKAP-Lbc⅐p38␣ signaling complex specifically reduces ␣ 1 -AR-mediated p38␣ activation without affecting receptor-mediated activation of other MAPK pathways. These findings provide a novel mechanistic hypothesis explaining how assembly of macromolecular complexes can specify MAPK signaling downstream of ␣ 1 -ARs.2 are seven-transmembrane domain receptors coupled to heterotrimeric G proteins of the G q and G 12 /G 13 family (1, 2). Evidence accumulated over the last years indicate that these receptors, besides their well known implication in controlling vascular contractility, glucose metabolism, genitourinary functions, and behavioral responses (3), are also crucially involved in the regulation of various pathological cardiovascular remodeling processes including vascular smooth muscle cell hypertrophy, proliferation, and migration in response to injury (4, 5) as well as cardiac hypertrophy (6 -8). It is now evident that mitogen-activated protein kinases (MAPKs) signaling pathways play a central role in mediating many of these pathological responses (1, 9 -11).MAPKs are proline-directed serine/threonine kinases that induce the majority of their physiological effects through phosphorylation and activation of transcription factors and the regulation of the expression of specific sets of genes (12). Mammalian MAPKs can be subdivided into five families including ERK1/2, JNK, p38, ERK3/4, and ERK5, which display different biological functions (12). MAPK signaling cascades are organized into functional signaling modules of three kinases in which a MAP kinase kinase kinase (MAPKKK) phosphorylates and activates a MAP kinase kinase (MAPKK) that, in turn, phosphorylates and activates a MAPK (13). The modular organization of the pathway is controlled by scaffolding proteins that can bind each of the kinases (13). Although the implication of MAPK pathways in the pathophysiological responses induced by ␣ 1 -ARs has been extensively studied it is currently unknown how MAPK signaling modules are assembled and activated in response to ␣1-AR stimulation to generate specific cellular responses.Several evidences ...

bIn response to stress, the heart undergoes a remodeling process associated with cardiac hypertrophy that eventually leads to heart failure. A-kinase anchoring proteins (AKAPs) have been shown to coordinate numerous prohypertrophic signaling pathways in cultured cardiomyocytes. However, it remains to be established whether AKAP-based signaling complexes control cardiac hypertrophy and remodeling in vivo. In the current study, we show that AKAP-Lbc assembles a signaling complex composed of the kinases PKN, MLTK, MKK3, and p38␣ that mediates the activation of p38 in cardiomyocytes in response to stress signals. To address the role of this complex in cardiac remodeling, we generated transgenic mice displaying cardiomyocyte-specific overexpression of a molecular inhibitor of the interaction between AKAP-Lbc and the p38-activating module. Our results indicate that disruption of the AKAP-Lbc/p38 signaling complex inhibits compensatory cardiomyocyte hypertrophy in response to aortic banding-induced pressure overload and promotes early cardiac dysfunction associated with increased myocardial apoptosis, stress gene activation, and ventricular dilation. Attenuation of hypertrophy results from a reduced protein synthesis capacity, as indicated by decreased phosphorylation of 4E-binding protein 1 and ribosomal protein S6. These results indicate that AKAP-Lbc enhances p38-mediated hypertrophic signaling in the heart in response to abrupt increases in the afterload. In response to increased workload or pathological insults, the heart undergoes a remodeling process associated with cardiomyocyte hypertrophy (1). This response is initially compensatory and causes the ventricular mass to increase as a means of maintaining normal cardiac output. However, concomitant reactivation of a fetal gene program profoundly alters cardiac contractility, calcium handling, and myocardial energetics, which in the long term leads to increased cardiomyocyte death, replacement fibrosis, and heart failure (2).A-kinase anchoring proteins (AKAPs) constitute a family of scaffolding proteins that tether the cyclic AMP (cAMP)-dependent protein kinase A (PKA), as well as other signaling enzymes, at focal points within cells to ensure the coordination of specific signal transduction events (3, 4). Evidence collected over the last few years indicates that AKAPs coordinate numerous prohypertrophic signaling pathways in cultured cardiomyocytes (neonatal ventricular myocytes [NVMs]) (5-7). However, so far, no study has addressed the implication of these anchoring proteins in cardiac hypertrophy in vivo.Previous work has identified an anchoring protein expressed in cardiomyocytes, termed AKAP-Lbc, which acts as a RhoA selective guanine nucleotide exchange factor (GEF) (8) and serves as a scaffold for multiple signaling enzymes regulating cardiomyocyte growth (9-12). Silencing of AKAP-Lbc expression in rat NVMs strongly reduces RhoA activation and hypertrophic responses induced by GPCR agonists (9, 10), suggesting a link between AKAPLbc-mediated RhoA activation...

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Several noncardiac drugs have been linked to cardiac safety concerns, highlighting the importance of post‐marketing surveillance and continued evaluation of the benefit‐risk of long‐established drugs. Here, we examine the risk of QT prolongation and/or torsade de pointes (TdP) associated with the use of hydroxyzine, a first generation sedating antihistamine. We have used a combined methodological approach to re‐evaluate the cardiac safety profile of hydroxyzine, including: (1) a full review of the sponsor pharmacovigilance safety database to examine real‐world data on the risk of QT prolongation and/or TdP associated with hydroxyzine use and (2) nonclinical electrophysiological studies to examine concentration‐dependent effects of hydroxyzine on a range of human cardiac ion channels. Based on a review of pharmacovigilance data between 14th December 1955 and 1st August 2016, we identified 59 reports of QT prolongation and/or TdP potentially linked to hydroxyzine use. Aside from intentional overdose, all cases involved underlying medical conditions or concomitant medications that constituted at least 1 additional risk factor for such events. The combination of cardiovascular disorders plus concomitant treatment of drugs known to induce arrhythmia was identified as the greatest combined risk factor. Parallel patch‐clamp studies demonstrated hydroxyzine concentration‐dependent inhibition of several human cardiac ion channels, including the ether‐a‐go‐go‐related gene (hERG) potassium ion channels. Results from this analysis support the listing of hydroxyzine as a drug with “conditional risk of TdP” and are in line with recommendations to limit hydroxyzine use in patients with known underlying risk factors for QT prolongation and/or TdP.