Arginine vasopressin stimulates mesangial cell proliferation by activating the epidermal growth factor receptor

Arginine vasopressin hormone receptor antagonists in experimental autoimmune encephalomyelitis rodent models: A new approach for human multiple sclerosis treatment

Multiple sclerosis (MS) is a chronic demyelinating and neurodegenerative disease that affects the central nervous system. MS is a heterogeneous disorder of multiple factors that are mainly associated with the immune system including the breakdown of the blood-brain and spinal cord barriers induced by T cells, B cells, antigen presenting cells, and immune components such as chemokines and pro-inflammatory cytokines. The incidence of MS has been increasing worldwide recently, and most therapies related to its treatment are associated with the development of several secondary effects, such as headaches, hepatotoxicity, leukopenia, and some types of cancer; therefore, the search for an effective treatment is ongoing. The use of animal models of MS continues to be an important option for extrapolating new treatments. Experimental autoimmune encephalomyelitis (EAE) replicates the several pathophysiological features of MS development and clinical signs, to obtain a potential treatment for MS in humans and improve the disease prognosis. Currently, the exploration of neuro-immune-endocrine interactions represents a highlight of interest in the treatment of immune disorders. The arginine vasopressin hormone (AVP) is involved in the increase in blood−brain barrier permeability, inducing the development and aggressiveness of the disease in the EAE model, whereas its deficiency improves the clinical signs of the disease. Therefore, this present review discussed on the use of conivaptan a blocker of AVP receptors type 1a and type 2 (V1a and V2 AVP) in the modulation of immune response without completely depleting its activity, minimizing the adverse effects associated with the conventional therapies becoming a potential therapeutic target in the treatment of patients with multiple sclerosis.

G-Protein Coupled Receptor Signaling and Mammalian Target of Rapamycin Complex 1 Regulation

The mammalian target of rapamycin (mTOR) senses upstream stimuli to regulate numerous cellular functions such as metabolism, growth, and autophagy. Increased activation of mTOR complex 1 (mTORC1) is typically observed in human disease and continues to be an important therapeutic target. Understanding the upstream regulators of mTORC1 will provide a crucial link in targeting hyperactivated mTORC1 in human disease. In this mini-review, we will discuss the regulation of mTORC1 by upstream stimuli, with a specific focus on G-protein coupled receptor signaling to mTORC1. SIGNIFICANCE STATEMENT: mTORC1 is a master regulator of many cellular processes and is often hyperactivated in human disease. Therefore, understanding the molecular underpinnings of G-protein coupled receptor signaling to mTORC1 will undoubtedly be beneficial for human disease.

Regulation of mTORC1 by Upstream Stimuli

The mammalian target of rapamycin (mTOR) is an evolutionary conserved Ser/Thr protein kinase that senses multiple upstream stimuli to control cell growth, metabolism, and autophagy. mTOR is the catalytic subunit of mTOR complex 1 (mTORC1). A significant amount of research has uncovered the signaling pathways regulated by mTORC1, and the involvement of these signaling cascades in human diseases like cancer, diabetes, and ageing. Here, we review advances in mTORC1 regulation by upstream stimuli. We specifically focus on how growth factors, amino acids, G-protein coupled receptors (GPCRs), phosphorylation, and small GTPases regulate mTORC1 activity and signaling.

Arginine Vasopressin Modulates Ion and Acid/Base Balance by Regulating Cell Numbers of Sodium Chloride Cotransporter and H+-ATPase Rich Ionocytes

Arginine vasopressin (Avp) is a conserved pleiotropic hormone that is known to regulate both water reabsorption and ion balance; however, many of the mechanisms underlying its effects remain unclear. Here, we used zebrafish embryos to investigate how Avp modulates ion and acid–base homeostasis. After incubating embryos in double-deionized water for 24 h, avp mRNA expression levels were significantly upregulated. Knockdown of Avp protein expression by an antisense morpholino oligonucleotide (MO) reduced the expression of ionocyte-related genes and downregulated whole-body Cl⁻ content and H⁺ secretion, while Na⁺ and Ca²⁺ levels were not affected. Incubation of Avp antagonist SR49059 also downregulated the mRNA expression of sodium chloride cotransporter 2b (ncc2b), which is a transporter responsible for Cl⁻ uptake. Correspondingly, avp morphants showed lower NCC and H⁺-ATPase rich (HR) cell numbers, but Na⁺/K⁺-ATPase rich (NaR) cell numbers remained unchanged. avp MO also downregulated the numbers of foxi3a- and p63-expressing cells. Finally, the mRNA expression levels of calcitonin gene-related peptide (cgrp) and its receptor, calcitonin receptor-like 1 (crlr1), were downregulated in avp morphants, suggesting that Avp might affect Cgrp and Crlr1 for modulating Cl⁻ balance. Together, our results reveal a molecular/cellular pathway through which Avp regulates ion and acid–base balance, providing new insights into its function.

Noncanonical effects of vasopressin in angiogenesis

The molecular action of vasopressin depends on the localization of hormonal receptors. The basic physiological effects of vasopressin are manifested in the blood vasculature, renal inner medulla and brain. To date, new information concerning the tissue-specific spreading of vasopressin receptors has been accumulated, and it needs to be summarized. Platelets and endotheliocytes expressing V1a and V2 receptor types, respectively, are related to less investigated targets of the hormone. Vasopressin induces the initial reversible stage of platelet activation, required for interaction with intercellular matrix proteins. Platelet adhesion on endothelium activates cellular secretion of growth factors and enzymes for intercellular matrix glucosamine metabolism. Platelet hyaluronidase HYAL2 hydrolyses high-molecular hyaluronic acid to shorter fragments. Unlike intact hyaluronic acid with a molecular weight of several megadaltons, generally showing distinctive antiangiogenic properties, intermediate fractions of hyaluronan hydrolysis in a range from 2.5 to 200 kilodaltons have a stimulating effect on angiogenesis. Intercellular contacts between platelets and endotheliocytes are stabilized due to adhesive transmembrane glycoprotein PECAM-1 interaction. Resulting PECAM-1 heterodimers acquire conformation with high affinity to integrins αvβ3. Integrin activation forms contact links between endothelium and fibrillar proteins. Activated endotheliocytes secrete von Willebrand factor and P-selectin. These proteins are accumulated in Weibel–Palade bodies. Vasopressin stimulates cAMP-dependent ACAP-regulated exocytosis of Weibel–Palade bodies. von Willebrand factor possesses adhesive properties and additionally accelerates interaction of cells with the intercellular matrix. Adhesion on fibrillar collagen and membrane glycoproteins in cooperation with effects of PECAM-1–αvβ3 integrin complexes fixes cell aggregates in the surrounding interstitium and promotes proliferating endotheliocyte migration in according to the direction of local growth factor gradients during angiogenesis. Neurohormonal regulation of platelet and endotheliocyte secretory activity functionally link proliferation and migration of endotheliocytes during angiogenesis and integrate it according to the adaptive capacity of the entire organism.

Arginine vasopressin (AVP): a review of its historical perspectives, current research and multifunctional role in the hypothalamo-hypophysial system

INTRODUCTION

This publication reviews the function of arginine vasopressin and focuses on the morphologic and functional correlation between the hormone and its effect on stress, the hypophysial-adrenocortical axis, neuroimmune responses, renal function and corticotroph pituitary tumors.

MATERIALS AND METHODS

A literature review was performed using various search engines for information regarding the morphology and the multifunctional role of arginine vasopressin.

RESULTS

Although a large number of studies were published discussing these interactions, there are several important areas that are still obscure.

CONCLUSION

The questions of how does arginine vasopressin affect the morphology and function of these various areas, and how does the secretion of ACTH and adrenocortical hormones influence the morphology of arginine vasopressin-producing cells and their hormone secretion requires further investigation.

Substance-specific importance of EGFR for vascular smooth muscle cells motility in primary culture

Besides their importance for the vascular tone, vascular smooth muscle cells (VSMC) also contribute to pathophysiological vessel alterations. Various G-protein coupled receptor ligands involved in vascular dysfunction and remodeling can transactivate the epidermal growth factor receptor (EGFR) of VSMC, yet the importance of EGFR transactivation for the VSMC phenotype is incompletely understood. The aims of this study were (i) to characterize further the importance of the VSMC-EGFR for proliferation, migration and marker gene expression for inflammation, fibrosis and reactive oxygen species (ROS) homeostasis and (ii) to test the hypothesis that vasoactive substances (endothelin-1, phenylephrine, thrombin, vasopressin and ATP) rely differentially on the EGFR with respect to the abovementioned phenotypic alterations. In primary, aortic VSMC from mice without conditional deletion of the EGFR, proliferation, migration, marker gene expression (inflammation, fibrosis and ROS homeostasis) and cell signaling (ERK 1/2, intracellular calcium) were analyzed. VSMC-EGFR loss reduced collective cell migration and single cell migration probability, while no difference between the genotypes in single cell velocity, chemotaxis or marker gene expression could be observed under control conditions. EGF promoted proliferation, collective cell migration, chemokinesis and chemotaxis and leads to a proinflammatory gene expression profile in wildtype but not in knockout VSMC. Comparing the impact of five vasoactive substances (all reported to transactivate EGFR and all leading to an EGFR dependent increase in ERK1/2 phosphorylation), we demonstrate that the importance of EGFR for their action is substance-dependent and most apparent for crowd migration but plays a minor role for gene expression regulation.

A review of the nonpressor and nonantidiuretic actions of the hormone vasopressin

The pressor and antidiuretic actions of arginine vasopressin (AVP) have been well documented. This review focuses on the less widely appreciated actions of AVP which also have important physiologic functions and when better understood may provide important insights into common disease states. These actions include effects on pain perception and bone structure as well as important relationships to the varied components of metabolic syndrome. These include effects on blood glucose, lipid levels, and blood pressure. AVP may also play a role in the progression of chronic kidney disease and effect physiologic changes relating to aging, abnormal social behavior, and cognitive function. Important cellular responses including cell proliferation, inflammation, and control of infection and their relationship to AVP are described. Finally, the effects of AVP on hemostasis and the hypothalamic-pituitary-adrenal axis are noted. The goal of this summary of the various actions of AVP is to direct attention to the potential benefits of research in these underemphasized areas of importance.

An electrocardiographic, molecular and biochemical approach to explore the cardioprotective effect of vasopressin and milrinone against phosphide toxicity in rats

The present study was conducted to identify the protective effect of vasopressin (AVP) and milrinone on cardiovascular function, mitochondrial complex activities, cellular ATP reserve, oxidative stress, and apoptosis in rats poisoned by aluminum phosphide (AlP). Rats were divided into five groups (n = 12) including control, AlP (12.5 mg/kg), AlP + AVP (2.0 Units/kg), AlP + milrinone (0.25 mg/kg) and AlP + AVP + milrinone. After treatment, the animals were connected to an electronic cardiovascular monitoring device to monitor electrocardiographic (ECG) parameter. Finally, oxidative stress biomarkers, mitochondrial complex activities, ADP/ATP ratio and apoptosis were evaluated on the heart tissues. Results indicated that AlP administration induced ECG abnormalities along with a decline in blood pressure and heart rate. AVP and milrinone significantly ameliorated these changes in all treated groups. Considerable protective effects on oxidative stress biomarkers, complex IV activity, ADP/ATP ratio and caspase-3 and -9 activities in treated groups were also found. These findings were supported by flow cytometry assay of cardiomyocytes. In conclusion, administration of AVP and milrinone, not only improve cardiovascular functions in AlP poisoned rats in the short time, but after a long time can also restore mitochondrial function and ATP level and reduce the oxidative damage, which prevent cardiomyocytes from entering the apoptotic phase.

Antagonism of the prostaglandin E2 EP1 receptor in MDCK cells increases growth through activation of Akt and the epidermal growth factor receptor

The actions of prostaglandin E2 (PGE2) in the kidney are mediated by G protein-coupled E-prostanoid (EP) receptors, which affect renal growth and function. This report examines the role of EP receptors in mediating the effects of PGE2 on Madin-Darby canine kidney (MDCK) cell growth. The results indicate that activation of Gs-coupled EP2 and EP4 by PGE2 results in increased growth, while EP1 activation is growth inhibitory. Indeed, two EP1 antagonists (ONO-8711 and SC51089) stimulate, rather than inhibit, MDCK cell growth, an effect that is lost following an EP1 knockdown. Similar observations were made with M1 collecting duct and rabbit kidney proximal tubule cells. ONO-8711 even stimulates growth in the absence of exogenous PGE2, an effect that is prevented by ibuprofen (indicating a dependence upon endogenous PGE2). The involvement of Akt was indicated by the observation that 1) ONO-8711 and SC51089 increase Akt phosphorylation, and 2) MK2206, an Akt inhibitor, prevents the increased growth caused by ONO-8711. The involvement of the EGF receptor (EGFR) was indicated by 1) the increased phosphorylation of the EGFR caused by SC51089 and 2) the loss of the growth-stimulatory effect of ONO-8711 and SC51089 caused by the EGFR kinase inhibitor AG1478. The growth-stimulatory effect of ONO-8711 was lost following an EGFR knockdown, and transduction of MDCK cells with a dominant negative EGFR. These results support the hypothesis that 1) signaling via the EP1 receptor involves Akt as well as the EGFR, and 2), EP1 receptor pharmacology may be employed to prevent the aberrant growth associated with a number of renal diseases.

Vasopressin activates Akt/mTOR pathway in smooth muscle cells cultured in high glucose concentration

Mammalian target of rapamycin (mTOR) complex is a key regulator of autophagy, cell growth and proliferation. Here, we studied the effects of arginine vasopressin (AVP) on mTOR activation in vascular smooth muscle cells cultured in high glucose concentration. AVP induced the mTOR phosphorylation in A-10 cells grown in high glucose, in contrast to cells cultured in normal glucose; wherein, only basal phosphorylation was observed. The AVP-induced mTOR phosphorylation was inhibited by a PI3K inhibitor. Moreover, the AVP-induced mTOR activation inhibited autophagy and increased thymidine incorporation in cells grown in high glucose. This increase was abolished by rapamycin which inhibits the mTORC1 complex formation. Our results suggest that AVP stimulates mTOR phosphorylation by activating the PI3K/Akt signaling pathway and, subsequently, inhibits autophagy and raises cell proliferation in A-10 cells maintained in high glucose concentration.

Vasopressin V1a and V1b Receptors: From Molecules to Physiological Systems

The neurohypophysial hormone arginine vasopressin (AVP) is essential for a wide range of physiological functions, including water reabsorption, cardiovascular homeostasis, hormone secretion, and social behavior. These and other actions of AVP are mediated by at least three distinct receptor subtypes: V1a, V1b, and V2. Although the antidiuretic action of AVP and V2 receptor in renal distal tubules and collecting ducts is relatively well understood, recent years have seen an increasing understanding of the physiological roles of V1a and V1b receptors. The V1a receptor is originally found in the vascular smooth muscle and the V1b receptor in the anterior pituitary. Deletion of V1a or V1b receptor genes in mice revealed that the contributions of these receptors extend far beyond cardiovascular or hormone-secreting functions. Together with extensively developed pharmacological tools, genetically altered rodent models have advanced the understanding of a variety of AVP systems. Our report reviews the findings in this important field by covering a wide range of research, from the molecular physiology of V1a and V1b receptors to studies on whole animals, including gene knockout/knockdown studies.

Enhanced angiotensin-converting enzyme 2 attenuates angiotensin II-induced collagen production via AT1 receptor-phosphoinositide 3-kinase-Akt pathway

Recent reports support a protective role for angiotensin-converting enzyme 2 (ACE2) against glomerular diseases, especially by decreasing of extracellular matrix (ECM) proteins. However, the mechanism regulating this effect appears to be complex and poorly understood. Our aim was to investigate whether or not ACE2 ameliorates the profibrotic effects of Ang II-mediated, Akt-dependent pathways in the mouse mesangial cell line, MES-13.Gene transfer of ACE2 suppressed Ang II-activated Akt-phosphorylation, accompanied by a decreased level of collagen type I in cells. In addition, Ang II-induced collagen type I synthesis in MES-13s by activating the Ang II/AT-1R-PI3K pathway. This transactivation was dependent on cAMP/Epac but not on PKA. TGF-βRI played a pivotal role in this signaling pathway inducing collagen deposition effects which could be reversed by ACE2 gene transfer in MES-13 cells. The results revealed that gene transfer of ACE2 regulated Ang II-mediated AT1R-TGFβRI-PI3K-Akt signaling and involved the synthesis of collagen. The beneficial effect of ACE2 overexpression appeared to result mainly from blocking phosphorylation of Akt in mesangial cells, suggesting that the ACE2 gene might be a novel therapeutic target for glomerular diseases.

Androgen Receptor regulation of Vitamin D receptor in response of castration-resistant prostate cancer cells to 1α-Hydroxyvitamin D5 - a calcitriol analog

Calcitriol (1,25(OH)(2)D3) is cytostatic for prostate cancer (CaP), but had limited therapeutic utility due to hypercalcemia-related toxicities, leading to the development of low-calcemic calcitriol analogs. We show that one analog, 1-α-Hydroxyvitamin-D5 (1α(OH)D5), induced apoptosis in castration-sensitive LNCaP prostate cancer cells, but unlike calcitriol, did not increase androgen receptor (AR) transcriptional activity. LNCaP-AI, a castrate-resistant (CRCaP) LNCaP subline, was resistant to 1α(OH)D5 in the presence of androgens; however, androgen withdrawal (AWD), although ineffective by itself, sensitized LNCaP-AI cells to 1α(OH)D5. Investigation of the mechanism revealed that the vitamin D receptor (VDR), which mediates the effects of 1α(OH)D5, is downregulated in LNCaP-AI cells compared to LNCaP in the presence of androgens, whereas AWD restored VDR expression. Since LNCaP-AI cells expressed higher AR compared to LNCaP and AWD decreased AR, this indicated an inverse relationship between VDR and AR. Further, AR stimulation (by increased androgen) suppressed VDR, while AR downregulation (by ARsiRNA) stimulated VDR levels and sensitized LNCaP-AI cells to 1α(OH)D5 similar to AWD. Another cell line, pRNS-1-1, although isolated from a normal prostate, had lost AR expression in culture and adapted to androgen-independent growth. These cells expressed the VDR and were sensitive to 1α(OH)D5, but restoration of AR expression suppressed VDR levels and induced resistance to 1α(OH)D5 treatment. Taken together, these results demonstrate negative regulation of VDR by AR in CRCaP cells. This effect is likely mediated by prohibitin (PHB), which was inhibited by AR transcriptional activity and stimulated VDR in CRCaP, but not castrate-sensitive cells. Therefore, in castration sensitive cells, although the AR negatively regulates PHB, this does not affect VDR expression, whereas in CRCaP cells, negative regulation of PHB by the AR results in concomitant negative regulation of the VDR by the AR. These data demonstrate a novel mechanism by which 1α(OH)D5 prolong the effectiveness of AWD in CaP cells.

Vasopressin protects hippocampal neurones in culture against nutrient deprivation or glutamate-induced apoptosis

Vasopressin (VP) secreted within the brain modulates neuronal function by acting as a neurotransmitter. Recent studies show that VP prevents serum deprivation-induced apoptosis in the neuronal cell line, H32. To determine whether VP is anti-apoptotic in hippocampal neurones, primary cultures of these neurones were used to examine the effect of VP on neuronal culture supplement (B27) deprivation-, or glutamate-induced apoptosis, and the signalling pathways mediating the effects. Removal of B27 supplement from the culture medium for 24 h or the addition of glutamate (3-10μm) decreased neuronal viability (P<0.05) and increased Tdt-mediated dUTP nick-end labelling (TUNEL) staining and caspase-3 activity (P<0.05), which is consistent with apoptotic cell death. VP (10 nm) reduced B27 deprivation- or glutamate-induced cell death (P<0.05). These anti-apoptotic effects of VP were completely blocked by a V1 but not a V2 receptor antagonist, indicating that they are mediated via V1 VP receptors. The anti-apoptotic effect of VP in neurones involves activation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) and inositol trisphosphate/protein kinase B (Akt) signalling pathways. This was shown by the transient increases in phospho-ERK and phospho-Akt after incubation with VP revealed by western blot analyses, and the ability of specific inhibitors to reduce the inhibitory effect of VP on caspase-3 activity and TUNEL staining by 70% and 35%, respectively (P<0.05). These studies demonstrate that VP has anti-apoptotic actions in hippocampal neurones, an effect that is mediated by the MAPK/ERK and phosphatidylinositol-3 kinase/Akt signalling pathways. The ability of VP to reduce nutrient deprivation or glutamate overstimulation-induced neuronal death suggests that VP acts as a neuroprotective agent within the brain.

The parvocellular vasopressinergic system and responsiveness of the hypothalamic pituitary adrenal axis during chronic stress

Vasopressin (VP) secreted from parvocellular neurons of the hypothalamic paraventricular nucleus (PVN) stimulates pituitary adrenocorticotropic hormone (ACTH) secretion, through interaction with receptors of the V1b subtype (V1bR) in the pituitary corticotroph, mainly by potentiating the stimulatory effects of corticotrophin-releasing hormone (CRH). Chronic stress paradigms associated with corticotroph hyperresponsiveness lead to preferential expression of hypothalamic VP over CRH and upregulation of pituitary V1bR, suggesting that VP has a primary role during adaptation of the hypothalamic pituitary adrenal (HPA) axis to long-term stimulation. However, studies using pharmacological or genetic ablation of V1bR have shown that VP is required for full ACTH responses to some stressors, but not for the sensitization of ACTH responses to a novel stress observed during chronic stress. Studies using minipump infusion of a peptide V1 antagonist in long-term adrenalectomized rats have revealed that VP mediates proliferative responses in the pituitary. Nevertheless, only a minor proportion of cells undergoing mitogenesis co-express markers for differentiated corticotrophs or precursors, suggesting that new corticotrophs are recruited from yet undifferentiated cells. The overall evidence supports a limited role of VP regulating acute ACTH responses to some acute stressors and points to cell proliferation and pituitary remodelling as alternative roles for the marked increases in parvocellular vasopressinergic activity during prolonged activation of the HPA axis.

Regulation of androgen receptor transcriptional activity by rapamycin in prostate cancer cell proliferation and survival

The mTOR (mammalian target of rapamycin) inhibitor rapamycin caused growth arrest in both androgen-dependent and androgen-independent prostate cancer cells; however, long-term treatment induced resistance to the drug. The aim of this study was to investigate methods that can overcome this resistance. Here, we show that rapamycin treatment stimulated androgen receptor (AR) transcriptional activity, whereas suppression of AR activity with the antiandrogen bicalutamide sensitized androgen-dependent, as well as AR-sensitive androgen-independent prostate cancer cells, to growth inhibition by rapamycin. Further, the combination of rapamycin and bicalutamide, but not the individual drugs, induced significant levels of apoptosis in prostate cancer cells. The net effect of rapamycin is determined by its individual effects on the mTOR complexes mTORC1 (mTOR/raptor/GbetaL) and mTORC2 (mTOR/rictor/sin1/GbetaL). Inhibition of both mTORC1 and mTORC2 by rapamycin-induced apoptosis, whereas rapamycin-stimulation of AR transcriptional activity resulted from the inhibition of mTORC1, but not mTORC2. The effect of rapamycin on AR transcriptional activity was mediated by the phosphorylation of the serine/threonine kinase Akt, which also partially mediated apoptosis induced by rapamycin and bicalutamide. These results indicate the presence of two parallel cell-survival pathways in prostate cancer cells: a strong Akt-independent, but rapamycin-sensitive pathway downstream of mTORC1, and an AR-dependent pathway downstream of mTORC2 and Akt, that is stimulated by mTORC1 inhibition. Thus, the combination of rapamycin and bicalutamide induce apoptosis in prostate cancer cells by simultaneously inhibiting both pathways and hence would be of therapeutic value in prostate cancer treatment.

Vasopressin up-regulates the expression of growth-related immediate-early genes via two distinct EGF receptor transactivation pathways

Activation of V(1a) receptor triggers the expression of growth-related immediate-early genes (IEGs), including c-Fos and Egr-1. We found that pre-treatment of rat vascular smooth muscle A-10 cell line with the EGF receptor inhibitor AG1478 or the over-expression of an EGFR dominant negative mutant (HEBCD533) blocked the vasopressin-induced expression of IEGs, suggesting that activation of these early genes mediated by V(1a) receptor is via transactivation of the EGF receptor. Importantly, the inhibition of the metalloproteinases, which catalyzed the shedding of the EGF receptor agonist HB-EGF, selectively blocked the vasopressin-induced expression c-Fos. On the other hand, the inhibition of c-Src selectively blocked the vasopressin-induced expression of Egr-1. Interestingly, in contrast to the expression of c-Fos, the expression of Egr-1 was mediated via the Ras/MEK/MAPK-dependent signalling pathway. Vasopressin-triggered expression of both genes required the release of intracellular calcium, activation of PKC and beta-arrestin 2. These findings demonstrated that vasopressin up-regulated the expression of c-Fos and Erg-1 via transactivation of two distinct EGF receptor-dependent signalling pathways.

Delivery of recombinant adeno-associated virus-mediated human tissue kallikrein for therapy of chronic renal failure in rats

The tissue kallikrein-kinin system is important in regulating cardiovascular and renal function, and dysregulation of the system has been implicated in heart and kidney pathologies. These findings suggest that if balance can be restored to the kallikrein-kinin axis, then associated disease progression may be attenuated. To test this hypothesis, recombinant adeno-associated virus (rAAV)-mediated human tissue kallikrein (HK) expression was induced in a rodent model of chronic renal failure involving 5/6 nephrectomy (nephrectomy plus 70% reduction of remaining kidney). rAAV-HK treatment attenuated the rise in blood pressure, glomerular sclerosis, and tubulointerstitial injury observed in this model. rAAV-HK treatment also attenuated renal function decline as measured by urinary microalbumin, osmolarity, and cGMP levels. Reverse transcriptase-polymerase chain reaction analysis showed that rAAV-HK-treated rats had higher levels of bradykinin receptor-2 (B(2)R) and dopamine receptor-1 mRNAs. In contrast, angiotensin II receptor-1, endothelin receptor-A, and vasopressin receptor-2 mRNAs were markedly downregulated in kidneys from HK-treated rats. Bradykinin induced similar changes in receptor levels and prevented transforming growth factor-beta(1)-induced tubulointerstitial fibrosis. The effects of bradykinin could be reversed with the B(2)R antagonist HOE-140. Together, these findings suggest that restoration of the kallikrein-kinin system reduces kidney injury and protects renal function in 5/6-nephrectomized rats via changes in the expression and activation of G protein-coupled receptors including B(2)R.

Pharmacological characterization of RWJ-676070, a dual vasopressin V(1A)/V(2) receptor antagonist

The dysregulation of arginine vasopressin (AVP) release and activation of vasopressin V(1A) and V(2) receptors may play a role in disease. The in vitro and in vivo pharmacology of RWJ-676070, a potent, balanced antagonist of both the V(1A) and V(2) receptors is described. RWJ-676070 binding and intracellular functional antagonist activity was characterized using cells expressing V(1A), V(1B) or V(2) receptors. Its inhibition of V(1A) receptor-mediated contraction of vascular rings and platelet aggregation was determined. V(2) receptor-medated aquaresis was determined in rats, dogs and monkeys. V(1A) receptor-mediated inhibitory activity was assessed in vivo in a vasopressin-induced hypertension model and in normotensive rats and in two hypertensive rat models. RWJ-676070 inhibited AVP binding to human V(1A) and V(2) receptors (Ki=1 and 14 nM, respectively). RWJ-676070 inhibited V(1A) receptor-induced intracellular calcium mobilization and V(2) receptor-induced cAMP accumulation with Ki values of 14 nM and 13 nM, respectively. The compound was slightly less potent against rat V(1A) receptors. RWJ-676070 inhibited V(1A) receptor-mediated vasoconstriction in rat and dog vascular rings and AVP-induced human platelet aggregation. Dose dependent aquaresis was demonstrated in rats, dogs and monkeys following oral administration. RWJ-676070 inhibited AVP-induced hypertension in rats but had no effect on arterial pressure in normotensive and spontaneously hypertensive rats but did decrease arterial pressure in Dahl, salt-sensitive hypertensive rats. RWJ-676070 is a new, potent antagonist of V(1A) and V(2) receptors that may be useful for treatment of diseases benefiting from balanced inhibition of both V(1A) and V(2) receptors.

Anti-apoptotic actions of vasopressin in H32 neurons involve MAP kinase transactivation and Bad phosphorylation

Vasopressin (VP) secreted within the brain modulates neuronal function acting as a neurotransmitter. Based on the observation that VP prevented serum deprivation-induced cell death in the neuronal cell line, H32, which expresses endogenous V1 receptors, we tested the hypothesis that VP has anti-apoptotic properties. Flow cytometry experiments showed that 10 nM VP prevented serum deprivation-induced cell death and annexin V binding. Serum deprivation increased caspase-3 activity in a time and serum concentration dependent manner, and VP prevented these effects through interaction with receptors of V1 subtype. The signaling pathways mediating the anti-apoptotic effect of VP involve mitogen activated protein (MAP) kinase and extracellular signal-regulated kinases (ERK), Ca(2+)/calmodulin dependent kinase (CaMK) and protein kinase C (PKC). Western blot analyses revealed time-dependent decreases of Bad phosphorylation and increases in cytosolic levels of cytochrome c following serum deprivation, effects which were prevented by 10 nM VP. These data demonstrate that activation of endogenous V1 VP receptors prevents serum deprivation-induced apoptosis, through phosphorylation-inactivation of the pro-apoptotic protein, Bad, and consequent decreases in cytosolic cytochrome c and caspase-3 activation. The data suggest that VP has anti-apoptotic activity in neurons and that VP may act as a neuroprotective agent in the brain.

G protein-coupled receptor-induced Akt activity in cellular proliferation and apoptosis

Akt (also known as protein kinase B) plays an integral role in many intracellular signaling pathways activated by a diverse array of extracellular signals that target several different classes of membrane-bound receptors. Akt plays a particularly prominent part in signaling networks that result in the modulation of cellular proliferation, apoptosis and survival. Thus, the overexpression of Akt subtypes has been measured in a number of cancer types, and dominant-negative forms of Akt can trigger apoptosis and reduce the survival of cancer cells. G protein-coupled receptors act as cell-surface detectors for a diverse spectrum of biological signals and are able to activate or inhibit Akt via several direct and indirect means. In this review, we shall document how G protein-coupled receptors are able to control Akt activity and examine the resulting biochemical and physiological changes, with particular emphasis on cellular proliferation, apoptosis and survival.

Vasopressin mediates mitogenic responses to adrenalectomy in the rat anterior pituitary

To determine whether increased vasopressinergic activity during chronic stress or adrenalectomy mediates trophic changes in the corticotroph, we examined the effect of peripheral V1 receptor blockade in rats, using the antagonist, dGly[Phaa1,D-tyr(et), Lys, Arg]vasopressin (VP), on the number of pituitary cells taking up bromodeoxyuridine (BrdU) and cells containing immunoreactive ACTH (irACTH). Adrenalectomy significantly increased the number of BrdU- and ACTH-labeled cells at 3 and 6 d, and a much larger increase was observed at 28 d. Minipump infusion of V1 antagonist for 28 d, at doses blocking the increases in ACTH and corticosterone induced by exogenous VP, prevented the increases in BrdU incorporation, but not irACTH cells observed 28 d after adrenalectomy. Unexpectedly, colocalization of BrdU with ACTH-positive cells was minor (about three cells per pituitary section), and this was unaffected by adrenalectomy or V1 antagonist infusion. In contrast, adrenalectomy for 6 or 14 d failed to increase BrdU incorporation or irACTH cells in V1b receptor knockout mice while inducing the expected increase in wild-type mice. The data show that VP is required for pituitary mitogenesis after adrenalectomy but, at least in rats, not for increasing the number of corticotrophs. The lack of colocalization of ACTH in mitotic cells suggests that recruitment of corticotrophs during adrenalectomy occurs from undifferentiated cells.

Alteration of glucose homeostasis in V1a vasopressin receptor-deficient mice

Arginine-vasopressin (AVP) is known to be involved in maintaining glucose homeostasis, and AVP-resistance is observed in poorly controlled non-insulin-dependent diabetes mellitus subjects, resulting in a lowered plasma volume. Recently we reported that V1a vasopressin receptor-deficient (V1aR(-/-)) mice exhibited a decreased circulating blood volume and hypermetabolism of fat accompanied with impaired insulin-signaling. Here we further investigated the roles of the AVP/V1a receptor in regulating glucose homeostasis and plasma volume using V1aR(-/-) mice. The plasma glucose levels at the baseline or during a glucose tolerance test were higher in V1aR(-/-) than wild-type (WT) mice. Moreover, a hyperinsulinemic-euglycemic clamp revealed that the glucose infusion rate was significantly lower in V1aR(-/-) mice than in WT mice and that hepatic glucose production was higher in V1aR(-/-) mice than WT mice. In contrast to the increased hepatic glucose production, the liver glycogen content was decreased in the mutant mice. These results indicated that the mutant mice had impaired glucose tolerance. Furthermore, feeding V1aR(-/-) mice a high-fat diet accompanied by increased calorie intake resulted in significantly overt obesity in comparison with WT mice. In addition, we found that the circulating plasma volume and aldosterone level were decreased in V1aR(-/-) mice, although the plasma AVP level was increased. These results suggested that the effect of AVP on water recruitment was disturbed in V1aR(-/-) mice. Thus, we demonstrated that one of the AVP-resistance conditions resulting from deficiency of the V1a receptor leads to decreased plasma volume as well as impaired glucose homeostasis, which can progress to obesity under conditions of increased calorie intake.

A 90 kDa fragment of filamin A promotes Casodex-induced growth inhibition in Casodex-resistant androgen receptor positive C4-2 prostate cancer cells

Prostate tumors are initially dependent on androgens for growth, but the majority of patients treated with anti-androgen therapy progress to androgen-independence characterized by resistance to such treatment. This study investigates a novel role for filamin A (FlnA), a 280 kDa cytoskeletal protein (consisting of an actin-binding domain (ABD) followed by 24 sequential repeats), in androgen-independent (AI) growth. Full-length FlnA is cleaved to 170 kDa (ABD+FlnA1-15) and 110 kDa fragments (FlnA16-24); the latter is further cleaved to a 90 kDa fragment (repeats 16-23) capable of nuclear translocation and androgen receptor (AR) binding. Here, we demonstrate that in androgen-dependent LNCaP prostate cancer cells, the cleaved 90 kDa fragment is localized to the nucleus, whereas in its AI subline C4-2, FlnA failed to cleave and remained cytoplasmic. Transfection of FlnA16-24 cDNA in C4-2 cells restored expression and nuclear localization of 90 kDa FlnA. Unlike LNCaP, C4-2 cells proliferate in androgen-reduced medium and in the presence of the AR-antagonist Casodex. They also exhibit increased Akt phosphorylation compared to LNCaP, which may contribute to their AI phenotype. Nuclear expression of 90 kDa FlnA in C4-2 cells decreased Akt phosphorylation, prevented proliferation in androgen-reduced medium and restored Casodex sensitivity. This effect was inhibited by constitutive activation of Akt indicating that FlnA restored Casodex sensitivity in C4-2 cells by decreasing Akt phosphorylation. In addition, FlnA-specific siRNA which depleted FlnA levels, but not control siRNA, induced resistance to Casodex in LNCaP cells. Our results demonstrate that expression of nuclear FlnA is necessary for androgen dependence in these cells.

Molecular mechanisms mediating the G protein-coupled receptor regulation of cell cycle progression

G protein-coupled receptors are key regulators of cellular communication, mediating the efficient coordination of a cell's responses to extracellular stimuli. When stimulated these receptors modulate the activity of a wide range of intracellular signalling pathways that facilitate the ordered development, growth and reproduction of the organism. There is now a growing body of evidence examining the mechanisms by which G protein-coupled receptors are able to regulate the expression, activity, localization and stability of cell cycle regulatory proteins that either promote or inhibit the initiation of DNA synthesis. In this review, we will detail the intracellular pathways that mediate the G protein-coupled receptor regulation of cellular proliferation, specifically the progression from the G1 phase to the S phase of the cell cycle.

Vasopressin stimulates Na-dependent phosphate transport and calcification in rat aortic smooth muscle cells

We investigated the effect of arginine vasopressin (AVP) on inorganic phosphate (Pi) transport in A-10 rat aortic vascular smooth muscle cells (VSMCs). AVP time- and dose-dependently stimulated Na-dependent Pi transport in A-10 cells. This stimulatory effect of AVP on Pi transport was markedly suppressed by V1 receptor antagonist. A protein kinase C (PKC) inhibitor calphostin C partially suppressed the stimulatory effect of AVP. The selective inhibitors of c-Jun-NH2-terminal mitogen-activated protein (MAP) kinase (Jun kinase) attenuated AVP-induced Pi transport, but Erk kinase or p38 MAP kinase inhibitors did not. Wortmannin, a phosphatidylinositol (PI) 3-kinase inhibitor, suppressed AVP-induced Pi transport. Rapamycin, a selective inhibitor of S6 kinase, reduced this effect of AVP, while Akt kinase inhibitor did not. The combination of inhibitors for PKC, Jun kinase and PI 3-kinase completely suppressed the AVP-enhanced Pi transport. Furthermore, AVP rescued the VSMC from high phosphate-induced cell death and enhanced mineralization of these cells. In summary, these results suggest that AVP stimulates both Na-dependent Pi transport and mineralization in VSMCs. The mechanism is mediated by the activation of multiple signaling pathways including PKC, PI 3-kinase, S6 kinase and Jun kinase.

A proteomic screen identified stress-induced chaperone proteins as targets of Akt phosphorylation in mesangial cells

The serine-threonine kinase Akt regulates mesangial cell apoptosis, proliferation, and hypertrophy. To define Akt signaling pathways in mesangial cells, we performed a functional proteomic screen for rat mesangial cell proteins phosphorylated by Akt. A group of chaperone proteins, heat shock protein (Hsp) 70, Hsp90alpha, Hsp90beta, Glucose-regulated protein (Grp) Grp78, Grp94, and protein disulfide isomerase (PDI) were identified as potential Akt substrates by two techniques: (a) in vitro phosphorylation of mesangial cell lysate by recombinant active Akt followed by protein separation by SDS-PAGE or 2-DE and phosphoprotein identification by peptide mass fingerprinting using MALDI-MS, or (b) immunoblot analysis of proteins from PDGF-stimulated mesangial cells using an anti-Akt phospho-motif antibody. In vitro kinase reactions using recombinant proteins confirmed that Akt phosphorylates Hsp70, Hsp90alpha and beta, Grp94, and PDI. Immunoprecipitation of Akt from mesangial cell lysate coprecipitated Grp78 and Hsp70. PDGF stimulation of mesangial cells caused an acidic shift in the isoelectric point of Hsp70, Hsp90, and PDI that was dependent on PI-3K activity for Hsp70 and Hsp90. The data suggest that Akt-mediated phosphorylation of stress-induced chaperones represents a mechanism for regulation of chaperone function during mesangial cell responses to physiologic and pathologic stimuli.

Gas6 induces Akt/mTOR-mediated mesangial hypertrophy in diabetic nephropathy

BACKGROUND

We have already reported Gas6 is involved in glomerular hypertrophy observed in diabetic nephropathy. However, the molecular mechanisms involved in glomerular hypertrophy are still unknown, especially in vivo.

METHODS

In vivo, diabetes was induced in rats and mice by streptozotocin (STZ) and the activation of the Akt/mTOR pathway in glomeruli was examined. In vitro, mesangial hypertrophy was assessed by [(3)H]leucine incorporation and measuring cell areas.

RESULTS

Akt, p70 S6 kinase, and 4E-BP-1 were induced and phosphorylated in rat glomerular lysates after 12 weeks of STZ injection when mesangial and glomerular hypertrophy was observed. We then examined the role of Gas6 by treating STZ-rats with warfarin, and found that warfarin treatment inhibited the phosphorylation of these molecules as well as the hypertrophy. We next examined whether high glucose stimulation can induce the expression of Gas6/Axl in mesangial cells. Stimulation of the cells with 25 mmol/L of glucose increased the expression of Gas6/Axl and mesangial cell size compared with that with 5.6 mmol/L of glucose. This hypertrophic effect was abolished in mesangial cells derived from Gas6 knockout mice. We also found that LY294002 and rapamycin blocked Gas6-induced activation of the Akt/mTOR pathway and mesangial hypertrophy. Furthermore, less phosphorylated Akt-positive or 4E-BP-1-positive areas were found in STZ-treated Gas6 knockout mice than in STZ-treated wild-type mice.

CONCLUSION

Our study indicates that the Akt/mTOR pathway is a key signaling cascade in Gas6-mediated mesangial and glomerular hypertrophy and revealed a crucial role of Gas6/Axl and the Akt/mTOR pathway in the development of diabetic nephropathy.

Akt mediates mechanical strain-induced collagen production by mesangial cells

Increased glomerular hydrostatic pressure is an important determinant of glomerulosclerosis and can be modeled by in vitro exposure of mesangial cells to cyclic mechanical strain. Stretched mesangial cells increase extracellular matrix protein production, the hallmark of glomerulosclerosis. Recent data indicate that the serine/threonine kinase Akt may be involved in matrix modulation. Thus, Akt activation and matrix synthesis in stretched mesangial cells were studied. Exposure of mesangial cells to 1 Hz cyclic strain led to prompt Akt activation, which was biphasic to 24 h. Activation was dependent on signaling through phosphatidylinositol-3-kinase and required EGF receptor transactivation. Inhibition of signaling through the PDGF receptor, Src kinase, or cytoskeletal disruption failed to prevent strain-induced Akt activation. Collagen type 1A1 transcript expression, promoter activation, and protein secretion were increased by stretch at 24 h and were dependent on phosphatidylinositol-3 kinase. Overexpression of dominant-negative Akt inhibited strain-induced collagen 1A1 production. Conversely, overexpression of constitutively active Akt led to increased collagen 1A1 upregulation and secretion. Finally, Akt activation was observed in the glomeruli of remnant rat kidneys, a model marked by increased intraglomerular pressure. The authors conclude that mechanical strain induces Akt activation in mesangial cells through a mechanism requiring phosphatidylinositol-3-kinase and EGF receptor transactivation. Type 1 collagen production is dependent on Akt and can be induced by Akt overexpression. Akt activation is observed in remnant kidneys in vivo. Thus, the role of Akt in progression of chronic hemodynamic glomerular disease is worthy of further exploration.

beta-Adrenergic-responsive activation of extracellular signal-regulated protein kinases in salivary cells: role of epidermal growth factor receptor and cAMP

The beta-adrenergic receptor agonist isoproterenol exerts growth-promoting effects on salivary glands. In this study, activation of ERKs, members of the mitogen-activated protein kinase family, by isoproterenol was examined in a human salivary gland cell line (HSY). Immunoblot analysis indicated that isoproterenol (10(-5) M) induced transient activation of ERK1/2 (4.4-fold relative to basal at 10 min) similar to that caused by EGF (6.7 fold). Isoproterenol, like EGF, also induced phosphorylation of the EGF receptor. However, inhibition of EGF receptor phosphorylation by the tyrphostin AG-1478 only partially attenuated isoproterenol-induced ERK phosphorylation, whereas EGF-responsive ERK activation was completely blocked. The G(i) inhibitor pertussis toxin also caused partial inhibition of isoproterenol-stimulated ERK activation. The cAMP analog 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP) and the cAMP-elevating agents IBMX and cholera toxin produced transient ERK1/2 activation, similar to the effect of isoproterenol, in HSY cells. The stimulatory effects of isoproterenol and cAMP on ERK phosphorylation were not reduced by the PKA inhibitor H-89, whereas the Src family inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidase (PP2) and transfection of a dominant-negative Src construct diminished isoproterenol-induced ERK activation. Isoproterenol induced marked overexpression of the cell growth-related adhesion molecule CD44, and this effect of isoproterenol was abolished by the ERK pathway inhibitor PD-98059. In summary, we show a dual mechanism of isoproterenol-induced ERK phosphorylation in HSY cells-one pathway mediated by EGF receptor transactivation and the other by an EGF receptor-independent pathway possibly mediated by cAMP. Our results also suggest that isoproterenol-induced growth of salivary tissue may involve ERK-mediated CD44 expression.

Contribution of PKC-dependent and -independent processes in temporal ERK regulation by ET-1, PDGF, and EGF in rat myometrial cells

Endothelin-1 (ET-1), platelet-derived growth factor (PDGF), and epidermal growth factor (EGF) stimulated thymidine incorporation with different efficiency (PDGF ≫ EGF = ET-1) in rat myometrial cells. They also stimulated ERK activation, which culminated at 5 min and then declined to reach a plateau (at 45 min: EGF > 90%, PDGF = 50%, and ET-1 < 10% of maximum). Inhibition and downregulation of PKC demonstrated that ERK activation at 5 min involved PKCδ and -ζ for ET-1 and PKCα plus another PKC isoform for PDGF. By contrast, the EGF response did not involve PKC. Stimulation of Ras was more important with EGF than with PDGF, with ET-1 being the weakest activator. The simultaneous incubation of the cells with EGF and ET-1 potentiated the ERK activation at 5 min and mimicked the plateau phase obtained with PDGF. Under these conditions thymidine incorporation was comparable to that induced by PDGF. Taken together, our results indicated that the kinetic profile of ERK activation and its impact on cell proliferation can be modulated by the differential involvement of PKC isoforms and the amplitude of Ras activation.

Role of protein kinase C in arginine vasopressin-stimulated ERK and p70S6 kinase phosphorylation

We previously showed in rat renal glomerular mesangial cells, that arginine vasopressin (AVP)-stimulated cell proliferation was mediated by epidermal growth factor receptor (EGF-R) transactivation, and activation (phosphorylation) of ERK1/2 and p70S6 kinase (Ghosh et al. [2001]: Am J Physiol Renal Physiol 280:F972-F979]. In this paper, we extend these observations and show that different protein kinase C (PKC) isoforms play different roles in mediating AVP-stimulated ERK1/2 and p70S6 kinase phosphorylation and cell proliferation. AVP treatment for 0-60 min stimulated the serine/threonine phosphorylation of PKC isoforms alpha, delta, epsilon, and zeta. The activation of PKC was dependent on EGF-R and phosphatidylinositol 3-kinase (PI3K) activation. In addition, inhibition of conventional and novel PKC isoforms by chronic (24 h) exposure to phorbol 12-myristate 13-acetate (PMA) inhibited AVP-induced activation of ERK and p70S6 kinase as well as EGF-R phosphorylation. Rottlerin, a specific inhibitor of PKCdelta, inhibited both ERK and p70S6 kinase phosphorylation and cell proliferation. In contrast, a PKCepsilon translocation inhibitor decreased ERK1/2 activation without affecting p70S6 kinase or cell proliferation, while a dominant negative PKCzeta (K281W) cDNA delayed p70S6 kinase activation without affecting ERK1/2. On the other hand, Gö6976, an inhibitor of conventional PKC isoforms, did not affect p70S6 kinase, but stimulated ERK1/2 phosphorylation without affecting cell proliferation. Our results indicate that PKCdelta plays an important role in AVP-stimulated ERK and p70S6 kinase activation and cell proliferation.

Changes in cellular composition of kidney collecting duct cells in rats with lithium-induced NDI

Lithium treatment for 4 wk caused severe polyuria, dramatic downregulation in aquaporin-2 (AQP-2) expression, and marked decrease in AQP-2 immunoreactivity with the appearance of a large number of cells without AQP-2 labeling in the collecting ducts after lithium treatment. Surprisingly, this was not all due to an increase in AQP-2-negative principal cells, because double immunolabeling revealed that the majority of the AQP-2-negative cells displayed [H(+)]ATPase labeling, which identified them as intercalated cells. Moreover, multiple [H(+)]ATPase-labeled cells were adjacent, which was never seen in control rats. Quantitation confirmed a significant decrease in the fraction of collecting duct cells that exhibited detectable AQP-2 labeling compared with control rats: in cortical collecting ducts, 40 +/- 3.4 vs. 62 +/- 1.8% of controls (P < 0.05; n = 4) and in inner medullary collecting ducts, 58 +/- 1.6 vs. 81 +/- 1.3% of controls (P < 0.05; n = 4). In parallel, a significant increase in the fraction of intercalated ([H(+)]ATPase-positive) cells was shown. Urine output, whole kidney AQP-2 expression, cellular organization, and the fractions of principal and intercalated cells in cortex and inner medulla returned to control levels after 4 wk on a lithium-free diet following 4 wk on a lithium-containing diet. In conclusion, lithium treatment not only decreased AQP-2 expression, but dramatically and reversibly reduced the fraction of principal cells and altered the cellular organization in collecting ducts. These effects are likely to be important in lithium-induced nephrogenic diabetes insipidus.

Endothelin-1 activates mesangial cell ERK1/2 via EGF-receptor transactivation and caveolin-1 interaction

Endothelin-1 (ET-1) stimulates glomerular mesangial cell proliferation and extracellular matrix protein transcription through an ERK1/2-dependent pathway. In this study, we determined whether ET-1 activation of glomerular mesangial cell ERK1/2 is mediated through EGF receptor (EGF-R) transactivation and whether intact caveolae are required. We showed that ET-1 stimulated tyrosine phosphorylation of the EGF-R in primary cultured, growth-arrested rat mesangial cells. In response to ET-1, ERK1/2 phosphorylation was increased by 27 +/- 1-fold and attenuated by AG-1478, a specific EGF-R inhibitor, to 9 +/- 1-fold. Moreover, filipin III and beta-cyclodextrin, two cholesterol-depleting drugs known to disrupt caveolae, significantly reduced ET-1-induced phosphorylation of ERK1/2. In addition, preincubation of mesangial cells with a myristoylated peptide that binds to the caveolin-1 scaffolding domain diminished ET-1 activation of ERK1/2. ET-1 caused interaction of caveolin-1 with phosphorylated ERK1/2 identified by coimmunoprecipitation. Activation of ERK1/2 and its interaction with caveolin-1 were reduced by AG-1478, beta-cyclodextrin, or inhibition of PKC. Phosphorylated ERK1/2 localized at focal adhesion complexes along with phospho-caveolin-1, suggesting specific sites of compartmentalization of these signaling molecules. Hence, ET-1 activates mesangial cell ERK1/2 predominantly through a pathway involving EGF-R transactivation, leading to a mechanism involving attachment to caveolin-1, presumably in caveolae.

Mesangial cell proliferation inhibitors for the treatment of proliferative glomerular disease

Mesangial cells (MC) serve a number of functions in the renal glomerular capillary including structural support of the capillary tuft, modulation of glomerular hemodynamics, and a phagocytic function allowing removal of macromolecules and immune complexes. The proliferation of MC is a prominent feature of glomerular disease including IgA nephropathy, membranoproliferative glomerulonephritis, lupus nephritis, and diabetic nephropathy. In experimental animal models of nephritis, MC proliferation frequently precedes and is linked to the increase of extracellular matrix in the mesangium and glomerulosclerosis. Reduction of MC proliferation in glomerular disease models by treatment with heparin, low-protein diet, or antibodies to platelet-derived growth factor (PDGF), have been shown to reduce extracellular matrix expansion and glomerulosclerotic changes. Therefore, MC proliferation inhibitors may offer therapeutic opportunities for the treatment of proliferative glomerular disease. It is also known that the MC proliferation is inhibited by many kinds of pharmacological drugs, for example, angiotensin converting enzyme (ACE) inhibitors, leukotriene D(4) (LTD(4)) antagonists, PDGF inhibitors, matrix metalloproteinases (MMP) inhibitors, 3-hydroxy-3 methyl glutaryl-coenzymeA (HMG-CoA) inhibitors, cyclin-dependent kinases (CDK) inhibitors, and others. This review summarizes the recently reported MC proliferation inhibitors with their pharmacological properties on the basis of their chemical structures.

ET-1 stimulates ERK signaling pathway through sequential activation of PKC and Src in rat myometrial cells

In this study, we analyzed in rat myometrial cells the signaling pathways involved in the endothelin (ET)-1-induced extracellular signal-regulated kinase (ERK) activation required for the induction of DNA synthesis. We found that inhibition of protein kinase C (PKC) by Ro-31-8220 abolished ERK activation. Inhibition of phospholipase C (PLC) by U-73122 or of phosphoinositide (PI) 3-kinase by wortmannin partially reduced ERK activation. A similar partial inhibition was observed after treatment with pertussis toxin or PKC downregulation by phorbol ester treatment. The effect of wortmannin was additive with that produced by PKC downregulation but not with that due to pertussis toxin. These results suggest that both diacylglycerol-sensitive PKC, activated by PLC products, and diacylglycerol-insensitive PKC, possibly activated by a G(i)-PI 3-kinase-dependent process, are involved in ET-1-induced ERK activation. These two pathways were found to be activated mainly through the ET(A) receptor subtype. ET-1 and phorbol ester stimulated Src activity in a PKC-dependent manner, both responses being abolished in the presence of Ro-31-8220. Inhibition of Src kinases by PP1 abrogated phorbol ester- and ET-1-induced ERK activation. Finally, ET-1 activated Ras in a PP1- and Ro-31-8220-sensitive manner. Altogether, our results indicate that ET-1 induces ERK activation in rat myometrial cells through the sequential stimulation of PKC, Src, and Ras.