Angiotensin II Inhibits Insulin Receptor Signaling in Adipose Cells.

Angiotensin II (Ang II) is a critical regulator of insulin signaling in the cardiovascular system and metabolic tissues. However, in adipose cells, the regulatory role of Ang II on insulin actions remains to be elucidated. The effect of Ang II on insulin-induced insulin receptor (IR) phosphorylation, Akt activation, and glucose uptake was examined in 3T3-L1 adipocytes.

CRF Receptor Signaling via the ERK1/2-MAP and Akt Kinase Cascades: Roles of Src, EGF Receptor, and PI3-Kinase Mechanisms.

In the present study, we determined the cellular regulators of ERK1/2 and Akt signaling pathways in response to human CRF receptor (CRFR) activation in transfected COS-7 cells. We found that Pertussis Toxin (PTX) treatment or sequestering Gβγ reduced CRFR-mediated activation of ERK1/2, suggesting the involvement of a G-linked cascade. Neither G/PKA nor G/PKC were associated with ERK1/2 activation.

GnRH agonist reduces estrogen receptor dimerization in GT1-7 cells: evidence for cross-talk between membrane-initiated estrogen and GnRH signaling.

17β-estradiol (E2), a key participant on the initiation of the LH surge, exerts both positive and negative feedback on GnRH neurons. We sought to investigate potential interactions between estrogen receptors alpha (ERα) and beta (ERβ) and gonadotropin releasing hormone receptor (GnRH-R) in GT1-7 cells. Radioligand binding studies demonstrated a significant decrease in saturation E2 binding in cells treated with GnRH agonist.

Angiotensin II induces vascular endocannabinoid release, which attenuates its vasoconstrictor effect via CB1 cannabinoid receptors.

In the vascular system angiotensin II (Ang II) causes vasoconstriction via the activation of type 1 angiotensin receptors. Earlier reports have shown that in cellular expression systems diacylglycerol produced during type 1 angiotensin receptor signaling can be converted to 2-arachidonoylglycerol, an important endocannabinoid. Because activation of CB(1) cannabinoid receptors (CB(1)R) induces vasodilation and reduces blood pressure, we have tested the hypothesis that Ang II-induced 2-arachidonoylglycerol release can modulate its vasoconstrictor action in vascular tissue.

Regulation of endocannabinoid release by G proteins: a paracrine mechanism of G protein-coupled receptor action.

In the past years, the relationship between the endocannabinoid system (ECS) and other hormonal and neuromodulatory systems has been intensively studied. G protein-coupled receptors (GPCRs) can stimulate endocannabinoid (eCB) production via activation of G(q/11) proteins and, in some cases, G(s) proteins. In this review, we summarize the pathways through which GPCR activation can trigger eCB release, as well as the best known examples of this process throughout the body tissues.

The relationship between pulsatile GnRH secretion and cAMP production in immortalized GnRH neurons.

In perifused immortalized GnRH neurons (GT1-7), simultaneous measurements of GnRH and cAMP revealed that the secretory profiles for both GnRH and cAMP are pulsatile. An analysis of GnRH and cAMP pulses in 16 independent experiments revealed that 25% of pulses coincide. Inversion of the peak and nadir levels was found in 33% and random relationship between GnRH and cAMP found in 42% of analyzed pulses.

Expression and function of ATIP/MTUS1 in human prostate cancer cell lines.

Background: We have previously demonstrated Ang II type 2 (AT(2)-) receptor-mediated inhibition of EGF-induced prostate cancer cell growth in androgen-dependent (LNCaP) and independent (PC3) prostate cancer cell lines.

Methods: To explore the signaling pathways involved in this inhibitory effect, we examined the interaction of the AT(2)-receptor with its novel regulatory partner ATIP using real time PCR, over-expression, siRNA and [(3)H]thymidine incorporation assays.

Results: The results in human prostate cancer cell lines demonstrate the presence of ATIP in both cell lines examined, and suggest that (i) the AT(2)-receptor through an interaction with ATIP mediates an anti-growth factor effect in both androgen-dependent and androgen-independent cell lines; (ii) ATIP expression decreases as the rate of cell growth and androgen-independence increase; and (iii) EGF may act on cell growth in part by reducing the content of ATIP present in the cells.

Mechanisms of angiotensin II-induced ERK1/2 activation in fetal cardiomyocytes.

Fetal cardiomyocytes have been utilized in studies on myocardial repair in the damaged hearts of rodents and other species. Changes in angiotensin II (Ang II) receptor expression, especially decline of its type II receptor (AT2), are known to occur during the growth of cardiomyocytes from fetus to adult. However, the extent to which changes in the signaling pathways of Ang II type I (AT1) and AT2 receptors via p42/44 mitogen-activated protein kinase (ERK1/2) activation affect the physiological and pathophysiological functions in cardiomyocytes has not been defined.

Angiotensin-induced EGF receptor transactivation inhibits insulin signaling in C9 hepatic cells.

To investigate the potential interactions between the angiotensin II (Ang II) and insulin signaling systems, regulation of IRS-1 phosphorylation and insulin-induced Akt activation by Ang II were examined in clone 9 (C9) hepatocytes. In these cells, Ang II specifically inhibited activation of insulin-induced Akt Thr(308) and its immediate downstream substrate GSK-3alpha/beta in a time-dependent fashion, with approximately 70% reduction at 15 min. These inhibitory actions were associated with increased IRS-1 phosphorylation of Ser(636)/Ser(639) that was prevented by selective blockade of EGFR tyrosine kinase activity with AG1478.

The hypothalamic GnRH pulse generator: multiple regulatory mechanisms.

Pulsatile secretion of gonadotropin-releasing hormone (GnRH) release is an intrinsic property of hypothalamic GnRH neurons. Pulse generation has been attributed to multiple specific mechanisms, including spontaneous electrical activity of GnRH neurons, calcium and cAMP signaling, a GnRH receptor autocrine regulatory component, a GnRH concentration-dependent switch in GnRH receptor (GnRH-R) coupling to specific G proteins, the expression of G protein-coupled receptors (GPCRs) and steroid receptors, and homologous and heterologous interactions between cell membrane receptors expressed in GnRH neurons. The coexistence of multiple regulatory mechanisms for pulsatile GnRH secretion provides a high degree of redundancy in maintaining this crucial component of the mammalian reproductive process.

Pulsatile GnRH secretion: roles of G protein-coupled receptors, second messengers and ion channels.

The pulsatile secretion of GnRH from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to multiple G proteins. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca(2+)- and cAMP-dependent signaling and GnRH neuronal firing.

Identification of the invariant chain (CD74) as an angiotensin AGTR1-interacting protein.

Little is known about the protein-protein interactions that regulate the trafficking of the angiotensin II type I receptor (AGTR1) through the biosynthetic pathway. The membrane-proximal region of the cytoplasmic tail of the AGTR1 has been identified by site-directed mutagenesis studies as an essential site for normal AGTR1 folding and surface expression. Based on yeast two-hybrid screening of a human kidney cDNA library with the AGTR1 carboxyl-terminal tail as a bait, we identified the invariant chain (CD74) as a novel interacting protein.

Converse regulatory functions of estrogen receptor-alpha and -beta subtypes expressed in hypothalamic gonadotropin-releasing hormone neurons.

Estradiol (E(2)) acts as a potent feedback molecule between the ovary and hypothalamic GnRH neurons, and exerts both positive and negative regulatory actions on GnRH synthesis and secretion. However, the extent to which these actions are mediated by estrogen receptors (ERs) expressed in GnRH neurons has been controversial. In this study, Single-cell RT-PCR revealed the expression of both ERalpha and ERbeta isoforms in cultured fetal and adult rat hypothalamic GnRH neurons.

Differential signaling pathways in angiotensin II- and epidermal growth factor-stimulated hepatic C9 cells.

Caveolin1 (Cav1) is an important component of the plasmamembrane microdomains, such as caveolae/lipid rafts, that are associated with angiotensin II type 1 (AT(1)) and epidermal growth factor (EGF) receptors in certain cell types. The interactions of Cav1 with other signaling molecules that mediate AT(1) receptor function were analyzed in angiotensin II (Ang II)- and EGF-stimulated hepatic C9 cells. This study demonstrated that cholesterol-rich domains mediate the actions of early upstream signaling molecules such as Src and intracellular Ca(2+) in cells stimulated by Ang II, but not by EGF, and that Cav1 has a scaffolding role in the process of mitogen-activated protein kinase activation.

Appearance of angiotensin II expression in non-basal epithelial cells is an early feature of malignant change in human prostate.

Background: Despite increasing interest in the renin-angiotensin system in cancer, little is known about angiotensin II (Ang II) expression in human prostate tumors.

Methods: Using immunohistochemistry, we examined Ang II expression in prostate cancer (Gleason grades 2-5), benign prostatic hyperplasia (BPH), and high-grade prostatic intraepithelial neoplasia (HGPIN).

Results: Ang II was present in proliferating neoplastic cells in HGPIN, in malignant cells in all grades of prostate cancer examined, in basal but not luminal epithelial cells in BPH, and in the cytoplasm of LNCaP, DU145, and PC3 prostate cancer cells.

Mechanism of angiotensin II-induced superoxide production in cells reconstituted with angiotensin type 1 receptor and the components of NADPH oxidase.

The mechanism of angiotensin II (Ang II)-induced superoxide production was investigated with HEK293 or Chinese hamster ovary cells reconstituted with the angiotensin type 1 receptor (AT(1)R) and NADPH oxidase (either Nox1 or Nox2) along with a pair of adaptor subunits (either NOXO1 with NOXA1 or p47(phox) with p67(phox)). Ang II enhanced the activity of both Nox1 and Nox2 supported by either adaptor pair, with more effective activation of Nox1 in the presence of NOXO1 and NOXA1 and of Nox2 in the presence of p47(phox) and p67(phox). Expression of several AT(1)R mutants showed that interaction of the receptor with G proteins but not that with beta-arrestin or with other proteins (Jak2, phospholipase C-gamma1, SH2 domain-containing phosphatase 2) that bind to the COOH-terminal region of AT(1)R, was necessary for Ang II-induced superoxide production.

Expression of a functional g protein-coupled receptor 54-kisspeptin autoregulatory system in hypothalamic gonadotropin-releasing hormone neurons.

The G protein-coupled receptor 54 (GPR54) and its endogenous ligand, kisspeptin, are essential for activation and regulation of the hypothalamic-pituitary-gonadal axis. Analysis of RNA extracts from individually identified hypothalamic GnRH neurons with primers for GnRH, kisspeptin-1, and GPR54 revealed expression of all three gene products. Also, constitutive and GnRH agonist-induced bioluminescence resonance energy transfer between Renilla luciferase-tagged GnRH receptor and GPR54 tagged with green fluorescent protein, expressed in human embryonic kidney 293 cells, revealed heterooligomerization of the two receptors.

Interactions between conserved residues in transmembrane helices 2 and 7 during angiotensin AT1 receptor activation.

Site-directed mutagenesis studies and independent molecular modeling studies were combined to investigate the network of inter-residue interactions within the transmembrane region of the angiotensin AT(1a) receptor. Site-directed mutagenesis was focused on residues Tyr292, Asn294, Asn295, and Asn298 in transmembrane helix 7, and the conserved Asp74 in helix 2 and other polar residues. Functional interactions between pairs of residues were evaluated by determining the effects of single and double-reciprocal mutations on agonist-induced AT(1a) receptor activation.

Mechanisms of endothelin-1-induced MAP kinase activation in adrenal glomerulosa cells.

G protein-coupled receptors (GPCRs) such as angiotensin II, bradykinin and endothelin-1 (ET-1) are critically involved in the regulation of adrenal function, including aldosterone production from zona glomerulosa cells. Whereas, substantial data are available on the signaling mechanisms of ET-1 in cardiovascular tissues, such information in adrenal glomerulosa cells is lacking. Bovine adrenal glomerulosa (BAG) cells express receptors for endothelin-1 (ET-1) and their stimulation caused phosphorylation of Src (at Tyr416), proline-rich tyrosine kinase (Pyk2 at Tyr402), extracellularly regulated signal kinases (ERK1/2), and their dependent proteins, p90 ribosomal S6 kinase (RSK-1) and CREB.

Protein phosphatase 5 as a negative key regulator of Raf-1 activation.

Growth factors such as the epidermal growth factor cause sequential activation of receptor tyrosine kinases, adaptor molecules and the Raf-MEK-ERK pathway. The kinetics and intensity of these signals are dependent on the balance between phosphorylation and dephosphorylation of these molecules by numerous kinases and phosphatases, respectively. Recently, protein phosphatase 5 has been characterized as a key dephosphorylation regulator of Raf-1 activation in growth factor-mediated signaling, leading to attenuation of the MEK-ERK cascade.

Essential role of G protein-gated inwardly rectifying potassium channels in gonadotropin-induced regulation of GnRH neuronal firing and pulsatile neurosecretion.

Activation of the luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor (LHR) in cultured hypothalamic cells and immortalized GnRH (gonadotropin-releasing hormone) neurons (GT1-7 cells) transiently stimulates and subsequently inhibits cAMP production and pulsatile GnRH release. The marked and delayed impairment of cAMP signaling and episodic GnRH release in GT1-7 cells is prevented by pertussis toxin (PTX). This, and the LH-induced release of membrane-bound Galpha(s) and Galpha(i3) subunits, are indicative of differential G protein coupling to the LHR.

Dependence of GnRH-induced phosphorylation of CREB and BAD on EGF receptor transactivation in GT1-7 neuronal cells.

The hypothalamic neuropeptide, gonadotropin releasing hormone (GnRH), is a primary regulatory factor in the neuroendocrine control of reproduction. The GnRH decapeptide is released in an episodic manner from hypothalamic GnRH neurons, which are known to express GnRH receptors. Here we examined the signaling pathways by which autocrine GnRH stimulation generates cell survival and proliferative signals in hypothalamic GT1-7 cells.

TACE-dependent EGF receptor activation in angiotensin-II-induced kidney disease.

Angiotensin II (Ang II) has been implicated in the development of cardiovascular disorders and chronic kidney disease (CKD). Ang II causes renal lesions through the activation of tumor necrosis factor (TNF)-alpha-converting enzyme (TACE, also called a disintegrin and a metalloproteinase domain 17) and the release of transforming growth factor (TGF)-alpha, which binds to and activates the epidermal growth factor receptor. Renal lesions such as glomerulosclerosis, tubular atrophy, fibrosis, mononuclear cell infiltration and proteinuria following chronic Ang II infusion are substantially reduced in mice lacking TGF-alpha and those given a specific TACE inhibitor.