Role of G beta-subunit in angiotensin II-type 1 receptor signaling

Dual Blockade of TGF-β Receptor and Endothelin Receptor Synergistically Inhibits Angiotensin II-Induced Myofibroblast Differentiation: Role of AT1R/Gαq-Mediated TGF-β1 and ET-1 Signaling

Angiotensin II (Ang II) upregulates transforming growth factor-beta1 (TGF-β1) and endothelin-1 (ET-1) in various types of cells, and all of them act as profibrotic mediators. However, the signal transduction of angiotensin II receptor (ATR) for upregulation of TGF-β1 and ET-1, and their effectors that play an essential role in myofibroblast differentiation, are not fully understood. Therefore, we investigated the ATR networking with TGF-β1 and ET-1 and identified the signal transduction of these mediators by measuring the mRNA expression of alpha-smooth muscle actin (α-SMA) and collagen I using qRT-PCR. Myofibroblast phenotypes were monitored by α-SMA and stress fiber formation with fluorescence microscopy. Our findings suggested that Ang II induced collagen I and α-SMA synthesis and stress fiber formation through the AT₁R/G_αq axis in adult human cardiac fibroblasts (HCFs). Following AT₁R stimulation, G_αq protein, not G_βγ subunit, was required for upregulation of TGF-β1 and ET-1. Moreover, dual inhibition of TGF-β and ET-1 signaling completely inhibited Ang II-induced myofibroblast differentiation. The AT₁R/G_αq cascade transduced signals to TGF-β1, which in turn upregulated ET-1 via the Smad- and ERK1/2-dependent pathways. ET-1 consecutively bound to and activated endothelin receptor type A (ET_AR), leading to increases in collagen I and α-SMA synthesis and stress fiber formation. Remarkably, dual blockade of TGF-β receptor and ETR exhibited the restorative effects to reverse the myofibroblast phenotype induced by Ang II. Collectively, TGF-β1 and ET-1 are major effectors of AT₁R/G_αq cascade, and therefore, negative regulation of TGF-β and ET-1 signaling represents a targeted therapeutic strategy for the prevention and restoration of cardiac fibrosis.

Label-free cell signaling pathway deconvolution of angiotensin type 1 receptor reveals time-resolved G-protein activity and distinct AngII and AngIIIIV responses

Angiotensin II (AngII) type 1 receptor (AT₁R) is a G protein-coupled receptor known for its role in numerous physiological processes and its implication in many vascular diseases. Its functions are mediated through G protein dependent and independent signaling pathways. AT₁R has several endogenous peptidic agonists, all derived from angiotensinogen, as well as several synthetic ligands known to elicit biased signaling responses. Here, surface plasmon resonance (SPR) was used as a cell-based and label-free technique to quantify, in real time, the response of HEK293 cells stably expressing the human AT₁R. The goal was to take advantage of the integrative nature of this assay to identify specific signaling pathways in the features of the response profiles generated by numerous endogenous and synthetic ligands of AT₁R. First, we assessed the contributions of Gq, G12/13, Gi, Gβγ, ERK1/2 and β-arrestins pathways in the cellular responses measured by SPR where Gq, G12/Rho/ROCK together with β-arrestins and ERK1/2 were found to play significant roles. More specifically, we established a major role for G12 in the early events of the AT₁R-dependent response, which was followed by a robust ERK1/2 component associated to the later phase of the signal. Interestingly, endogenous AT₁R ligands (AngII, AngIII and AngIV) exhibited distinct responses signatures with a significant increase of the ERK1/2-like components for both AngIII and AngIV, which points toward possibly distinct physiological roles for the later. We also tested AT₁R biased ligands, all of which affected both the early and later events. Our results support SPR-based integrative cellular assays as a powerful approach to delineate the contribution of specific signaling pathways for a given cell response and reveal response differences associated with ligands with distinct pharmacological properties.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

JANUS under stress--role of JAK/STAT signaling pathway in vascular diseases

They were more than just another kinases (JAK), when they were first described in the late 80s and named JAK kinases. The mandatory role of this novel family of dual active janus kinases (JAK) and their substrates the signal transducers and activators of transcription (STAT) was demonstrated in mice who died during embryogenesis when lacking a functional allele, e.g. that of JAK2. Initially, the JAK/STAT signaling pathway was discovered as the primary mediator of intracellular signaling induced by interferon in hematopoietic and immune cells. Nowadays, it is well accepted that JAK kinases and STAT proteins are constitutively expressed in the vessel wall in a cell type specific manner and transfer intracellular signaling events of various receptor families, e.g. that of cytokines, growth factors and vasoactive peptides such as angiotensin II (Ang II) or endothelin. The potential impact of the JAK/STAT signaling pathway on cardiovascular pathophysiology and disease development arise from reports describing that JAKs may bind directly to the angiotensin II type I (AT(1)) receptor, thereby enhancing their phosphorylation in various cell types of the vessel wall. More interestingly, these signaling events are modulated by NAD(P)H oxidase-derived superoxide anions which directly phosphorylate JAK2 and thereby control JAK2 activity. A potential impact was also described for atherosclerotic plaque development in which the activation of JAKs and STATs seems to be critical. Based on these observations, we here review the role of the JAK/STAT signaling pathways as critical regulator for cardiovascular disease development, i.e. atherosclerotic plaque progression or the manifestation of arterial hypertension.

Pleiotropic AT1 receptor signaling pathways mediating physiological and pathogenic actions of angiotensin II

Angiotensin II (Ang II) activates a wide spectrum of signaling responses via the AT1 receptor (AT1R) that mediate its physiological control of blood pressure, thirst, and sodium balance and its diverse pathological actions in cardiovascular, renal, and other cell types. Ang II-induced AT1R activation via Gq/11 stimulates phospholipases A2, C, and D, and activates inositol trisphosphate/Ca2+ signaling, protein kinase C isoforms, and MAPKs, as well as several tyrosine kinases (Pyk2, Src, Tyk2, FAK), scaffold proteins (G protein-coupled receptor kinase-interacting protein 1, p130Cas, paxillin, vinculin), receptor tyrosine kinases, and the nuclear factor-kappaB pathway. The AT1R also signals via Gi/o and G11/12 and stimulates G protein-independent signaling pathways, such as beta-arrestin-mediated MAPK activation and the Jak/STAT. Alterations in homo- or heterodimerization of the AT1R may also contribute to its pathophysiological roles. Many of the deleterious actions of AT1R activation are initiated by locally generated, rather than circulating, Ang II and are concomitant with the harmful effects of aldosterone in the cardiovascular system. AT1R-mediated overproduction of reactive oxygen species has potent growth-promoting, proinflammatory, and profibrotic actions by exerting positive feedback effects that amplify its signaling in cardiovascular cells, leukocytes, and monocytes. In addition to its roles in cardiovascular and renal disease, agonist-induced activation of the AT1R also participates in the development of metabolic diseases and promotes tumor progression and metastasis through its growth-promoting and proangiogenic activities. The recognition of Ang II's pathogenic actions is leading to novel clinical applications of angiotensin-converting enzyme inhibitors and AT1R antagonists, in addition to their established therapeutic actions in essential hypertension.

Angiotensin II signaling pathways mediated by tyrosine kinases

Angiotensin II (AngII) plays a critical role in control of cardiovascular and renal homeostasis. In addition to its physiological action as a vasoconstrictor, growing evidence supports the notion that AngII contributes to cardiovascular diseases such as hypertension, atherosclerosis, and heart failure. The physiological and pathological actions of AngII in adults are mediated largely via the AngII type 1 receptor (AT1R), a heterotrimeric G-protein-coupled receptor (GPCR). Besides coupling with heterotrimeric G proteins to activate phospholipase C-beta (PLC-beta), AT1R also activates receptor tyrosine kinases (PDGF-R, EGF-R and IGF-R) and non-receptor tyrosine kinases (Src, Fyn, Yes, proline-rich tyrosine kinase 2 (Pyk2), focal adhesion kinase (FAK) and JAK2). These tyrosine kinases play critical roles in AngII-stimulated cell signal events.

Stats: transcriptional control and biological impact

Extracellular proteins bound to cell-surface receptors can change nuclear gene expression patterns in minutes, with far-reaching consequences for development, cell growth and homeostasis. The signal transducer and activator of transcription (STAT) proteins are among the most well studied of the latent cytoplasmic signal-dependent transcription-factor pathways. In addition to several roles in normal cell decisions, dysregulation of STAT function contributes to human disease, making the study of these proteins an important topic of current research.