Angiotensin II-induced activation of p21-activated kinase 1 requires Ca2+ and protein kinase Cδ in vascular smooth muscle cells

Coptisine inhibits neointimal hyperplasia through attenuating Pak1/Pak2 signaling in vascular smooth muscle cells without retardation of re-endothelialization

BACKGROUND AND AIMS

Vascular injury-induced endothelium-denudation and profound vascular smooth muscle cells (VSMCs) proliferation and dis-regulated apoptosis lead to post-angioplasty restenosis. Coptisine (CTS), an isoquinoline alkaloid, has multiple beneficial effects on the cardiovascular system. Recent studies identified it selectively inhibits VSMCs proliferation. However, its effects on neointimal hyperplasia, re-endothelialization, and the underlying mechanisms are still unclear.

METHODS

Cell viability was assayed by 3-[4,5-dimethylthiazole-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and cell counting kit-8 (CCK-8). Cell proliferation and apoptosis were measured by flow cytometry and immunofluorescence of Ki67 and TUNEL. Quantitative phosphoproteomics (QPP) was employed to screen CTS-responsive phosphor-sites in the key regulators of cell proliferation and apoptosis. Neointimal hyperplasia was induced by balloon injury of rat left carotid artery (LCA). Adenoviral gene transfer was conducted in both cultured cells and LCA. Re-endothelialization was evaluated by Evan's blue staining of LCA.

RESULTS

1) CTS had strong anti-proliferative and pro-apoptotic effects in cultured rat VSMCs, with the EC50 4∼10-folds lower than that in endothelial cells (ECs). 2) Rats administered with CTS, either locally to LCA's periadventitial space or orally, demonstrated a potently inhibited balloon injury-induced neointimal hyperplasia, but had no delaying effect on re-endothelialization. 3) The QPP results revealed that the phosphorylation levels of Pak1S144/S203, Pak2S20/S197, Erk1T202/Y204, Erk2T185/Y187, and BadS136 were significantly decreased in VSMCs by CTS. 4) Adenoviral expression of phosphomimetic mutants Pak1D144/D203/Pak2D20/D197 enhanced Pak1/2 activities, stimulated the downstream pErk1T202/Y204/pErk2T185/Y187/pErk3S189/pBadS136, attenuated CTS-mediated inhibition of VSMCs proliferation and promotion of apoptosis in vitro, and potentiated neointimal hyperplasia in vivo. 5) Adenoviral expression of phosphoresistant mutants Pak1A144/A203/Pak2A20/A197 inactivated Pak1/2 and totally simulated the inhibitory effects of CTS on platelet-derived growth factor (PDGF)-stimulated VSMCs proliferation and PDGF-inhibited apoptosis in vitro and neointimal hyperplasia in vivo. 6) LCA injury significantly enhanced the endogenous phosphorylation levels of all but pBadS136. CTS markedly attenuated all the enhanced levels.

CONCLUSIONS

These results indicate that CTS is a promising medicine for prevention of post-angioplasty restenosis without adverse impact on re-endothelialization. CTS-directed suppression of pPak1S144/S203/pPak2S20/S197 and the subsequent effects on downstream pErk1T202/Y204/pErk2T185/Y187/pErk3S189 and pBadS136 underline its mechanisms of inhibition of VSMCs proliferation and stimulation of apoptosis. Therefore, the phosphor-sites of Pak1S144/S203/Pak2S20/S197 constitute a potential drug-screening target for fighting neointimal hyperplasia restenosis.

AT1 receptor signaling pathways in the cardiovascular system

The importance of the renin angiotensin aldosterone system in cardiovascular physiology and pathophysiology has been well described whereas the detailed molecular mechanisms remain elusive. The angiotensin II type 1 receptor (AT1 receptor) is one of the key players in the renin angiotensin aldosterone system. The AT1 receptor promotes various intracellular signaling pathways resulting in hypertension, endothelial dysfunction, vascular remodeling and end organ damage. Accumulating evidence shows the complex picture of AT1 receptor-mediated signaling; AT1 receptor-mediated heterotrimeric G protein-dependent signaling, transactivation of growth factor receptors, NADPH oxidase and ROS signaling, G protein-independent signaling, including the β-arrestin signals and interaction with several AT1 receptor interacting proteins. In addition, there is functional cross-talk between the AT1 receptor signaling pathway and other signaling pathways. In this review, we will summarize an up to date overview of essential AT1 receptor signaling events and their functional significances in the cardiovascular system.

The p21-activated kinase, PAK2, is important in the activation of numerous pancreatic acinar cell signaling cascades and in the onset of early pancreatitis events

In a recent study we explored Group-1-p21-activated kinases (GP.1-PAKs) in rat pancreatic acini. Only PAK2 was present; it was activated by gastrointestinal-hormones/neurotransmitters and growth factors in a PKC-, Src- and small-GTPase-mediated manner. PAK2 was required for enzyme-secretion and ERK/1-2-activation. In the present study we examined PAK2's role in CCK and TPA-activation of important distal signaling cascades mediating their physiological/pathophysiological effects and analyzed its role in pathophysiological processes important in early pancreatitis. In rat pancreatic acini, PAK2-inhibition by the specific, GP.1.PAK-inhibitor, IPA-3-suppressed cholecystokinin (CCK)/TPA-stimulated activation of focal-adhesion kinases and mitogen-activated protein-kinases. PAK2-inhibition reversed the dual stimulatory/inhibitory effect of CCK/TPA on the PI3K/Akt/GSK-3β pathway. However, its inhibition did not affect PKC activation. PAK2-inhibition protected acini from CCK-induced ROS-generation; caspase/trypsin-activation, important in early pancreatitis; as well as from cell-necrosis. Furthermore, PAK2-inhibition reduced proteolytic-activation of PAK-2p34, which is involved in programmed-cell-death. To ensure that the study did not only rely in the specificity of IPA-3 as a PAK inhibitor, we used two other approaches for PAK inhibition, FRAX597 a ATP-competitive-GP.1-PAKs-inhibitor and infection with a PAK2-dominant negative(DN)-Advirus. Those two approaches confirmed the results obtained with IPA-3. This study demonstrates that PAK2 is important in mediating CCK's effect on the activation of signaling-pathways known to mediate its physiological/pathophysiological responses including several cellular processes linked to the onset of pancreatitis. Our results suggest that PAK2 could be a new, important therapeutic target to consider for the treatment of diseases involving deregulation of pancreatic acinar cells.

Critical role of actin-associated proteins in smooth muscle contraction, cell proliferation, airway hyperresponsiveness and airway remodeling

Asthma is characterized by airway hyperresponsiveness and airway remodeling, which are largely attributed to increased airway smooth muscle contractility and cell proliferation. It is known that both chemical and mechanical stimulation regulates smooth muscle contraction. Recent studies suggest that contractile activation and mechanical stretch induce actin cytoskeletal remodeling in smooth muscle. However, the mechanisms that control actin cytoskeletal reorganization are not completely elucidated. This review summarizes our current understanding regarding how actin-associated proteins may regulate remodeling of the actin cytoskeleton in airway smooth muscle. In particular, there is accumulating evidence to suggest that Abelson tyrosine kinase (Abl) plays a critical role in regulating airway smooth muscle contraction and cell proliferation in vitro, and airway hyperresponsiveness and remodeling in vivo. These studies indicate that Abl may be a novel target for the development of new therapy to treat asthma.

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.

Gastrointestinal hormones/neurotransmitters and growth factors can activate P21 activated kinase 2 in pancreatic acinar cells by novel mechanisms

P-21-activated kinases (PAKs) are serine/threonine kinases comprising six isoforms divided in two groups, group-I (PAK1-3)/group-II (PAK4-6) which play important roles in cell cytoskeletal dynamics, survival, secretion and proliferation and are activated by diverse stimuli. However, little is known about PAKs ability to be activated by gastrointestinal (GI) hormones/neurotransmitters/growth-factors. We used rat pancreatic acini to explore the ability of GI-hormones/neurotransmitters/growth-factors to activate Group-I-PAKs and the signaling cascades involved. Only PAK2 was present in acini. PAK2 was activated by some pancreatic growth-factors [EGF, PDGF, bFGF], by secretagogues activating phospholipase-C (PLC) [CCK, carbachol, bombesin] and by post-receptor stimulants activating PKC [TPA], but not agents only mobilizing cellular calcium or increasing cyclic AMP. CCK-activation of PAK2 required both high- and low-affinity-CCK1-receptor-state activation. It was partially reduced by PKC- or Src-inhibition, but not with PI3K-inhibitors (wortmannin, LY294002) or thapsigargin. IPA-3, which prevents PAK2 binding to small-GTPases partially inhibited PAK2-activation, as well as reduced CCK-induced ERK1/2 activation and amylase release induced by CCK or bombesin. This study demonstrates pancreatic acini, possess only one Group-I-PAK, PAK2. CCK and other GI-hormones/neurotransmitters/growth-factors activate PAK2 via small GTPases (CDC42/Rac1), PKC and SFK but not cytosolic calcium or PI3K. CCK-activation of PAK2 showed several novel features being dependent on both receptor-activation states, having PLC- and PKC-dependent/independent components and small-GTPase-dependent/independent components. These results show that PAK2 is important in signaling cascades activated by numerous pancreatic stimuli which mediate their various physiological/pathophysiological responses and thus could be a promising target for the development of therapies in some pancreatic disorders such as pancreatitis.

Novel roles of PAK1 in the heart

Our work and others’ over the past few years have led to the identification of new roles of PAK1 in cardiac physiology, such as the regulation of cardiac ion channel and actomyosin function. More recent studies have revealed that PAK1-deficient mice were vulnerable to cardiac hypertrophy and readily progress to failure under sustained pressure overload and susceptible to ischemia/reperfusion injury. Our further study indicated that the PAK1 activator FTY720 was able to prevent this pressure overload-induced hypertrophy in wild-type mice without compromising their cardiac functions. A cardiac protective effect against ischemia/reperfusion injury by FTY720 was also observed in both rat and mouse models by us and others. Thus, these studies suggest that PAK1 is more important in the heart than previously thought, in particular a therapeutic potential of PAK1 activators. In the future, in-depth investigations are required to further substantiate our hypotheses on mechanisms for PAK1 function in the heart and to explore a therapeutic potential of FTY720 and other PAK1 activators in heart disease conditions.

Preeclampsia serum-induced collagen I expression and intracellular calcium levels in arterial smooth muscle cells are mediated by the PLC-γ1 pathway

In women with preeclampsia (PE), endothelial cell (EC) dysfunction can lead to altered secretion of paracrine factors that induce peripheral vasoconstriction and proteinuria. This study examined the hypothesis that PE sera may directly or indirectly, through human umbilical vein ECs (HUVECs), stimulate phospholipase C-γ1-1,4,5-trisphosphate (PLC-γ1-IP₃) signaling, thereby increasing protein kinase C-α (PKC-α) activity, collagen I expression and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in human umbilical artery smooth muscle cells (HUASMCs). HUASMCs and HUVECs were cocultured with normal or PE sera before PLC-γ1 silencing. Increased PLC-γ1 and IP₃ receptor (IP₃R) phosphorylation was observed in cocultured HUASMCs stimulated with PE sera (P<0.05). In addition, PE serum significantly increased HUASMC viability and reduced their apoptosis (P<0.05); these effects were abrogated with PLC-γ1 silencing. Compared with normal sera, PE sera increased [Ca²⁺]_i in cocultured HUASMCs (P<0.05), which was inhibited by PLC-γ1 and IP₃R silencing. Finally, PE sera-induced PKC-α activity and collagen I expression was inhibited by PLC-γ1 small interfering RNA (siRNA) (P<0.05). These results suggest that vasoactive substances in the PE serum may induce deposition in the extracellular matrix through the activation of PLC-γ1, which may in turn result in thickening and hardening of the placental vascular wall, placental blood supply shortage, fetal hypoxia–ischemia and intrauterine growth retardation or intrauterine fetal death. PE sera increased [Ca²⁺]_i and induced PKC-α activation and collagen I expression in cocultured HUASMCs via the PLC-γ1 pathway.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

Klotho endows hepatoma cells with resistance to anoikis via VEGFR2/PAK1 activation in hepatocellular carcinoma

Klotho was originally characterized as an aging suppressor gene that predisposed Klotho-deficient mice to premature aging-like syndrome. Although Klotho was recently reported to exhibit tumor suppressive properties during various malignant transformations, the functional role and molecular mechanism of Klotho in hepatocarcinogenesis remains poorly understood. In our present study, immunohistochemical Klotho staining levels in a clinical follow-up of 52 hepatoma patients were significantly associated with liver cirrhosis, tumor multiplicity and venous invasion. The overall survival rate of hepatoma patients with high Klotho expression was significantly lower than those patients with low Klotho expression. Moreover, Klotho overexpression increased cellular migration, anchorage-independent growth, and anoikis resistance in hepatoma cells. Klotho overexpression elevated p21-activated kinase 1 (PAK1) expression and shRNA-mediated PAK1 knockdown and kinase activity inhibition with kinase dead mutant PAK1 K299R coexpression or allosteric inhibitor IPA3 treatment reversed anoikis resistance in Klotho-overexpressed hepatoma cells. More importantly, the pivotal significance of upregulated VEGFR2 protein levels mediated by Klotho expression was confirmed by VEGFR2 inhibitor Axitinib and blocking antibody treatment in hepatoma cells. Axitinib treatment sensitized anoikis was reversed by constitutive active mutant PAK1 T423E coexpression in Klotho-overexpressed hepatoma cells. Conversely, knockdown of Klotho reduced VEGFR2/PAK1 dependent anoikis resistance, which could be reversed by PAK1 T423E. These results revealed a novel oncogenic function of Klotho in promoting anoikis resistance via activating VEGFR2/PAK1 signaling, thus facilitating tumor migration and invasion during hepatoma progression, which could provide a putative molecular mechanism for tumor metastasis.

Reciprocal regulation of Rac1 and PAK-1 by HIF-1alpha: a positive-feedback loop promoting pulmonary vascular remodeling

Pulmonary vascular remodeling associated with pulmonary hypertension is characterized by media thickening, disordered proliferation, and in situ thrombosis. The p21-activated kinase-1 (PAK-1) can control growth, migration, and prothrombotic activity, and the hypoxia-inducible transcription factor HIF-1alpha was associated with pulmonary vascular remodeling. Here we studied whether PAK-1 and HIF-1alpha are linked in pulmonary vascular remodeling. PAK-1 was expressed in the media of remodeled pulmonary vessels from patients with pulmonary vasculopathy and was upregulated, together with its upstream regulator Rac1 and HIF-1alpha in lung tissue from lambs with pulmonary vascular remodeling. PAK-1 and Rac1 were activated by thrombin involving calcium, thus resulting in enhanced generation of reactive oxygen species (ROS) in human pulmonary artery smooth muscle cells (PASMCs). Activation of PAK-1 stimulated HIF activity and HIF-1alpha expression involving ROS and NF-kappaB, enhanced the expression of the HIF-1 target gene plasminogen activator inhibitor-1, and stimulated PASMC proliferation. Importantly, HIF-1 itself bound to the Rac1 promoter and enhanced Rac1 and PAK-1 transcription. Thus, PAK-1 and its activator Rac1 are novel HIF-1 targets that may constitute a positive-feedback loop for induction of HIF-1alpha by thrombin and ROS, thus explaining elevated levels of PAK-1, Rac1, and HIF-1alpha in remodeled pulmonary vessels.

Regulation of phagocyte NADPH oxidase by hydrogen peroxide through a Ca(2+)/c-Abl signaling pathway

The importance of H(2)O(2) as a cellular signaling molecule has been demonstrated in a number of cell types and pathways. Here we explore a positive feedback mechanism of H(2)O(2)-mediated regulation of the phagocyte respiratory burst NADPH oxidase (NOX2). H(2)O(2) induced a dose-dependent stimulation of superoxide production in human neutrophils, as well as in K562 leukemia cells overexpressing NOX2 system components. Stimulation was abrogated by the addition of catalase, the extracellular Ca(2+) chelator BAPTA, the T-type Ca(2+) channel inhibitor mibefradil, the PKCdelta inhibitor rottlerin, or the c-Abl nonreceptor tyrosine kinase inhibitor imatinib mesylate or by overexpression of a dominant-negative form of c-Abl. H(2)O(2) induced phosphorylation of tyrosine 311 on PKCdelta and this activating phosphorylation was blocked by treatment with rottlerin, imatinib mesylate, or BAPTA. Rac GTPase activation in response to H(2)O(2) was abrogated by BAPTA, imatinib mesylate, or rottlerin. In conclusion, H(2)O(2) stimulates NOX2-mediated superoxide generation in neutrophils and K562/NOX2 cells via a signaling pathway involving Ca(2+) influx and c-Abl tyrosine kinase acting upstream of PKCdelta. This positive feedback regulatory pathway has important implications for amplifying the innate immune response and contributing to oxidative stress in inflammatory disorders.

p21-activated kinase 1 participates in vascular remodeling in vitro and in vivo

Vascular smooth muscle cell hypertrophy, proliferation, or migration occurs in hypertension, atherosclerosis, and restenosis after angioplasty, leading to pathophysiological vascular remodeling. Angiotensin II and platelet-derived growth factor are well-known participants of vascular remodeling and activate a myriad of downstream protein kinases, including p21-activated protein kinase (PAK1). PAK1, an effector kinase of small GTPases, phosphorylates several substrates to regulate cytoskeletal reorganization. However, the exact role of PAK1 activation in vascular remodeling remains to be elucidated. Here, we have hypothesized that PAK1 is a critical target of intervention for the prevention of vascular remodeling. Adenoviral expression of dominant-negative PAK1 inhibited angiotensin II-stimulated vascular smooth muscle cell migration. It also inhibited vascular smooth muscle cell proliferation induced by platelet-derived growth factor. PAK1 was activated in neointima of the carotid artery after balloon injury in the rat. Moreover, marked inhibition of the neointima hyperplasia was observed in a dominant-negative PAK1 adenovirus-treated carotid artery after the balloon injury. Taken together, these results suggest that PAK1 is involved in both angiotensin II and platelet-derived growth factor-mediated vascular smooth muscle cell remodeling, and inactivation of PAK1 in vivo could be effective in preventing pathophysiological vascular remodeling.

Involvement of betaPIX in angiotensin II-induced migration of vascular smooth muscle cells

Angiotensin II (Ang II) stimulates migration of vascular smooth muscle cell (VSMC) in addition to its contribution to contraction and hypertrophy. It is well established that Rho GTPases regulate cellular contractility and migration by reorganizing the actin cytoskeleton. Ang II activates Rac1 GTPase, but its upstream guanine nucleotide exchange factor (GEF) remains elusive. Here, we show that Ang II-induced VSMC migration occurs in a betaPIX GEF-dependent manner. betaPIX-specific siRNA treatment significantly inhibited Ang II-induced VSMC migration. Ang II activated the catalytic activity of betaPIX towards Rac1 in dose- and time-dependent manners. Activity reached a peak at 10 min and declined close to a basal level by 30 min following stimulation. Pharmacological inhibition with specific kinase inhibitors revealed the participation of protein kinase C, Src family kinase, and phosphatidylinositol 3-kinase (PI3-K) upstream of betaPIX. Both p21-activated kinase and reactive oxygen species played key roles in cytoskeletal reorganization downstream of betaPIX-Rac1. Taken together, our results suggest that betaPIX is involved in Ang II-induced VSMC migration.

Intra- and extrarenal arteries exhibit different profiles of contractile responses in high glucose conditions

BACKGROUND AND PURPOSE

The renal artery (RA) has been extensively investigated for the assessment of renal vascular function/dysfunction; however, few studies have focused on the intrarenal vasculature.

EXPERIMENTAL APPROACH

We devised a microvascular force measurement system, which allowed us to measure contractions of interlobar arteries (ILA), isolated from within the mouse kidney and prepared without endothelium.

KEY RESULTS

KCl (50 mM) induced similar force development in the aorta and RA but responses in the ILA were about 50% lower. Treatment of RA with 10 microM phenylephrine (PE), 10 nM U46619 (thromboxane A(2) analogue) or 10 microM prostaglandin F(2 alpha) elicited a response greater than 150% of that induced by KCl. In ILA, 10 nM U46619 elicited a response that was 130% of the KCl-induced response; however, other agonists induced levels similar to that induced by KCl. High glucose conditions (22.2 mM glucose) significantly enhanced responses in RA and ILA to PE or U46619 stimulation. This enhancement was suppressed by rottlerin, a calcium-independent PKC inhibitor, indicating that glucose-dependent, enhanced small vessel contractility in the kidney was linked to the activation of calcium-independent PKC.

CONCLUSION AND IMPLICATIONS

Extra- and intrarenal arteries exhibit different profiles of agonist-induced contractions. In ILA, only U46619 enhanced small vessel contractility in the kidney, which might lead to renal dysfunction and nephropathy through reduced intrarenal blood flow rate. A model has been established, which will allow the assessment of contractile responses of intrarenal arteries from murine models of renal disease, including type 2 diabetes.

Diosmetin induces human osteoblastic differentiation through the protein kinase C/p38 and extracellular signal-regulated kinase 1/2 pathway

INTRODUCTION

The survival of osteoblasts is one of the determinants of the development of osteoporosis. This study is the first to investigate the osteoblastic differentiation induced by diosmetin, a flavonoid derivative, in osteoblastic cell lines MG-63, hFOB, and MC3T3-E1 and bone marrow stroma cell line M2-10B4.

MATERIALS AND METHODS

Osteoblastic differentiation was determined by assaying alkaline phosphatase (ALP) activity and mineralization degree and measuring various osteoblast-related markers using ELISA. Expression and phosphorylation of Runt-related transcription factor 2 (Runx2), protein kinase Cdelta (PKCdelta), extracellular signal-regulated kinase (ERK), p38, and c-jun-N-terminal kinase (JNK) was assessed by immunoblot. Rac1 activity was determined by immunoprecipitation, and Runx2 activity was assessed by EMSA. Genetic inhibition was performed by small hairpin RNA plasmids or small interfering RNA (siRNA) transfection.

RESULTS

Diosmetin exhibited an effect on osteoblastic maturation and differentiation by means of ALP activity, osteocalcin, osteopontin, and type I collagen production, as well as Runx2 upregulation. Induction of differentiation by diosmetin was associated with increased PKCdelta phosphorylation and the activations of Rac1 and p38 and ERK1/2 kinases. Blocking PKCdelta by siRNA inhibition significantly decreased osteoblastic differentiation by inhibiting Rac1 activation and subsequently attenuating the phosphorylation of p38 and ERK1/2. In addition, blocking p38 and ERK1/2 by siRNA transfection also suppressed diosmetin-induced cell differentiation.

CONCLUSIONS

In this study, we show that diosmetin induced osteoblastic differentiation through the PKCdelta-Rac1-MEK3/6-p38 and PKCdelta-Rac1-MEK1/2- ERK1/2-Runx2 pathways and that it is a promising agent for treating osteoporosis.

Intermediate filaments in smooth muscle

The intermediate filament (IF) network is one of the three cytoskeletal systems in smooth muscle. The type III IF proteins vimentin and desmin are major constituents of the network in smooth muscle cells and tissues. Lack of vimentin or desmin impairs contractile ability of various smooth muscle preparations, implying their important role for smooth muscle force development. The IF framework has long been viewed as a fixed cytostructure that solely provides mechanical integrity for the cell. However, recent studies suggest that the IF cytoskeleton is dynamic in mammalian cells in response to various external stimulation. In this review, the structure and biological properties of IF proteins in smooth muscle are summarized. The role of IF proteins in the modulation of smooth muscle force development and redistribution/translocation of signaling partners (such as p130 Crk-associated substrate, CAS) is depicted. This review also summarizes our latest understanding on how the IF network may be regulated in smooth muscle.

PKCdelta regulates the stimulation of vascular endothelial factor mRNA translation by angiotensin II through hnRNP K

Angiotensin II (Ang II)-induced renal injury is partly mediated by growth factors such as VEGF. We have previously shown that Ang II rapidly increases VEGF protein synthesis in proximal tubular epithelial (MCT) cells by augmenting mRNA translation, which is partly dependent on activation and binding of hnRNP K to 3' untranslated region (UTR) of VEGF mRNA. Regulation of hnRNP K activation by PKCdelta was studied in MCT cells. Transfection with a PKCdelta siRNA inhibited hnRNP K Ser302 phosphorylation and activation, and reduced Ang II stimulation of VEGF synthesis. Inhibition of PKCdelta with röttlerin also prevented binding of hnRNP K to VEGF mRNA and reduced the efficiency of VEGF mRNA translation. In db/db mice at 2 weeks of type 2 diabetes, VEGF expression was increased, which was due not to increase in transcription but to augmented translation of VEGF mRNA. Augmented VEGF expression was associated with increased binding of hnRNP K to VEGF mRNA. c-src and PKCdelta activities and hnRNP K phosphorylation on Ser302 in renal cortex of db/db mice were increased compared to control mice. We conclude: Ang II-induced VEGF mRNA translation is associated with activation of hnRNP K in MCT cells. In the signaling pathway leading to hnRNP K activation induced by Ang II, PKCdelta is downstream of c-src. PKCdelta-mediated phosphorylation of hnRNP K is required for Ang II stimulation of VEGF mRNA translation. In mice with type 2 diabetes, src and PKCdelta activation and hnRNP K phosphorylation correlate with increased VEGF mRNA translation and kidney hypertrophy. 3' UTR events are important in regulation of VEGF expression in models of renal injury.

Physiologic properties and regulation of the actin cytoskeleton in vascular smooth muscle

Vascular smooth muscle tone plays a fundamental role in regulating blood pressure, blood flow, microcirculation, and other cardiovascular functions. The cellular and molecular mechanisms by which vascular smooth muscle contractility is regulated are not completely elucidated. Recent studies show that the actin cytoskeleton in smooth muscle is dynamic, which regulates force development. In this review, evidence for actin polymerization in smooth muscle upon external stimulation is summarized. Protein kinases such as Abelson tyrosine kinase, focal adhesion kinase, Src, and mitogen-activated protein kinase have been documented to coordinate actin polymerization in smooth muscle. Transmembrane integrins have also been reported to link to signaling pathways modulating actin dynamics. The roles of Rho family of the small proteins that bind to guanosine triphosphate (GTP), also known as GTPases, and the actin-regulatory proteins, including Crk-associated substrate, neuronal Wiskott-Aldrich Syndrome protein, the Arp2/3 complex, and profilin, and heat shock proteins in regulating actin assembly are discussed. These new findings promote our understanding on how smooth muscle contraction is regulated at cellular and molecular levels.

Novel role of protein kinase C-delta Tyr 311 phosphorylation in vascular smooth muscle cell hypertrophy by angiotensin II

We have shown previously that activation of protein kinase C-delta (PKC delta) is required for angiotensin II (Ang II)-induced migration of vascular smooth muscle cells (VSMCs). Here, we have hypothesized that PKC delta phosphorylation at Tyr(311) plays a critical role in VSMC hypertrophy induced by Ang II. Immunoblotting was used to monitor PKC delta phosphorylation at Tyr(311), and cell size and protein measurements were used to detect hypertrophy in VSMCs. PKC delta was rapidly (0.5 to 10.0 minutes) phosphorylated at Tyr(311) by Ang II. This phosphorylation was markedly blocked by an Src family kinase inhibitor and dominant-negative Src but not by an epidermal growth factor receptor kinase inhibitor. Ang II-induced Akt phosphorylation and hypertrophic responses were significantly enhanced in VSMCs expressing PKC delta wild-type compared with VSMCs expressing control vector, whereas the enhancements were markedly diminished in VSMCs expressing a PKC delta Y311F mutant. Also, these responses were significantly inhibited in VSMCs expressing kinase-inactive PKC delta K376A compared with VSMCs expressing control vector. From these data, we conclude that not only PKC delta kinase activation but also the Src-dependent Tyr(311) phosphorylation contributes to Akt activation and subsequent VSMC hypertrophy induced by Ang II, thus signifying a novel molecular mechanism for enhancement of cardiovascular diseases induced by Ang II.

Angiotensin II signal transduction through the AT1 receptor: novel insights into mechanisms and pathophysiology

The intracellular signal transduction of AngII (angiotensin II) has been implicated in cardiovascular diseases, such as hypertension, atherosclerosis and restenosis after injury. AT(1) receptor (AngII type-1 receptor), a G-protein-coupled receptor, mediates most of the physiological and pathophysiological actions of AngII, and this receptor is predominantly expressed in cardiovascular cells, such as VSMCs (vascular smooth muscle cells). AngII activates various signalling molecules, including G-protein-derived second messengers, protein kinases and small G-proteins (Ras, Rho, Rac etc), through the AT(1) receptor leading to vascular remodelling. Growth factor receptors, such as EGFR (epidermal growth factor receptor), have been demonstrated to be 'trans'-activated by the AT(1) receptor in VSMCs to mediate growth and migration. Rho and its effector Rho-kinase/ROCK are also implicated in the pathological cellular actions of AngII in VSMCs. Less is known about the endothelial AngII signalling; however, recent studies suggest the endothelial AngII signalling positively, as well as negatively, regulates the NO (nitric oxide) signalling pathway and, thereby, modulates endothelial dysfunction. Moreover, selective AT(1)-receptor-interacting proteins have recently been identified that potentially regulate AngII signal transduction and their pathogenic functions in the target organs. In this review, we focus our discussion on the recent findings and concepts that suggest the existence of the above-mentioned novel signalling mechanisms whereby AngII mediates the formation of cardiovascular diseases.

Small GTP-binding proteins and mitogen-activated protein kinases as promising therapeutic targets of vascular remodeling

PURPOSE OF REVIEW

To summarize the most recent findings concerning the targeting of mitogen-activated protein kinases and small GTP-binding proteins toward vascular remodeling together with molecular mechanisms of their activations in vascular pathophysiology.

RECENT FINDINGS

In addition to targeting the classical Ras/extracellular signal-regulated kinase cascade, Rho-kinase inhibitors, as well as the HMG-CoA reductase inhibitors, or 'statins', have pleiotropic efficacy for experimental cardiovascular diseases that involve inhibition of the signal transduction cascades originated by the small GTP-binding proteins such as Rho and Rac. Moreover, the underlying molecular mechanisms of the activation of these small GTP-binding proteins and downstream mitogen-activated protein kinases in cardiovascular tissue and cells have recently been better characterized. Additionally, gene-targeting studies in animal models are revealing select roles of the isoforms of these signaling proteins in the pathophysiology of cardiovascular disease. This is exemplified by the role of c-Jun NH(2)-terminal kinases in mediating atherosclerosis and diabetes.

SUMMARY

Characterization of the function of small GTP-binding proteins, mitogen-activated protein kinases and their effectors in cardiovascular pathophysiology can be readily identified by using select inhibitors, dominant-negative gene transfer and the generation of select gene-targeted animals. These findings strongly support the notion that small GTP-binding proteins and mitogen-activated protein kinases are promising therapeutic targets toward cardiovascular diseases.

Epidermal growth factor stimulates Rac1 and p21-activated kinase in vascular smooth muscle cells

Epidermal growth factor (EGF) has been shown to be a potent mitogen for vascular smooth muscle cells (VSMC) both in vitro and in vivo, thus contributing to the development of atherosclerosis and hypertension. Stimulation of Rho-family GTPases Rac/Cdc42 exerts pleiotropic cellular effects and have been demonstrated to contribute to EGF-induced proliferation in other cell systems. However, the effect of EGF on Rac/Cdc42 activation is unknown for VSMC. In the present report, we evaluated stimulation of Rac/Cdc42 by EGF in VSMC performing PAK-PBD binding assay. EGF treatment of VSMC induced time and concentration dependent binding of GTP-bound Rac1 to PAK-PBD peaking at 1 min and showing sustained activation up to 15 min. However, stimulation of Cdc42 could not be demonstrated. To further evaluate downstream effectors of Rac1 stimulation of p21-activated kinase (PAK) and c-Jun N-terminal kinase (JNK) by EGF was determined. In VSMC, EGF sequentially stimulated PAK, peaking at 5 min, and JNK, peaking at 15 min. Pretreatment of VSMC by EGF receptor specific tyrosine kinase inhibitor AG1478 and non-specific tyrosine kinase inhibitor genistein inhibited EGF-induced activation of Rac1, PAK and JNK, whereas tyrosine kinase inhibitors specific for Src (PP1) and specific for platelet-derived growth factor (AG1296) had no effect. Specific inhibition or Rac1 by NSC23766 attenuated EGF-induced [(3)H] thymidine incorporation in VSMC. Our data provide evidence for EGF-induced Rac1 activation and implicate PAK and JNK as downstream targets of Rac1 in EGF signal transduction in VSMC.

Involvement of transient receptor potential canonical 1 (TRPC1) in angiotensin II-induced vascular smooth muscle cell hypertrophy

Angiotensin II (Ang II) induces vascular smooth muscle cell (VSMC) hypertrophy as one of the major events leading to atherosclerosis. Increased Ca(2+) entry is an important stimulus for VSMC hypertrophy, but the association with Ang II remains to be determined. Transient receptor potential canonical 1 (TRPC1) forms store-operated Ca(2+) (SOC) channels that are involved in Ca(2+) homeostasis. Our aim was to ascertain the potential involvement of TRPC1 in Ang II-induced VSMC hypertrophy. For this purpose, we used cultured human coronary artery smooth muscle cells (hCASMCs). Store-operated Ca(2+) entry (SOCE) increased in the Ang II-induced hypertrophied cells, and SOC channel blocker inhibited the Ang II-induced hypertrophic response. Although hCASMCs constitutively expressed TRPC1, C3, C4, C5, and C6, only TRPC1 increased in response to Ang II stimulation. TRPC1 siRNA decreased SOCE and prevented Ang II-induced hypertrophy. We found NF-kappaB binding sites in the 5'-regulatory region of the human TRPC1 gene. An electrophoretic mobility shift assay showed that Ang II increased the TRPC1 promoter's NF-kappaB binding activity. Co-treatment with NF-kappaB decoy oligonucleotides not only reduced TRPC1 expression, but also inhibited the hypertrophic responses. In conclusion, our data suggest that Ang II and subsequent NF-kappaB activation induces hCASMC hypertrophy through an enhancement of TRPC1 expression.

Mechanism of endothelial nitric oxide synthase phosphorylation and activation by thrombin

Thrombin has been shown to activate endothelial NO synthase (eNOS) leading to endothelium-dependent vasorelaxation. In addition to its activation by Ca2+/calmodulin, eNOS has several regulatory sites. Ser1179 phosphorylation of eNOS by the phosphatidylinositol 3-kinase-dependent Akt stimulates its catalytic activity. In this study, we have elucidated the signaling mechanism of thrombin-induced phosphorylation of eNOS in the regulation of NO production. Immunoblot analysis showed that thrombin rapidly phosphorylates eNOS at Ser1179 in cultured bovine aortic endothelial cells. Also, thrombin was unable to stimulate eNOS if the Ser1179 was mutated to Ala. Akt is phosphorylated in response to thrombin at Ser473 at a later time point than eNOS. In this regard, a phosphatidylinositol 3-kinase inhibitor, LY294002, blocked Akt phosphorylation without affecting eNOS phosphorylation and cGMP production by thrombin. The Ca2+ ionophore A23187 stimulated eNOS phosphorylation, as well as cGMP production, and pretreatment with intracellular or extracellular Ca2+ chelators inhibited thrombin-induced eNOS phosphorylation and cGMP production. Moreover, infection of bovine aortic endothelial cell with adenovirus encoding dominant-negative mutants of protein kinase C (PKC) and PKC or pretreatment of bovine aortic endothelial cells with PKC inhibitors revealed that PKC is indispensable for thrombin-induced eNOS phosphorylation and activation. From these data, we concluded that thrombin induces the Ser1179 phosphorylation-dependent eNOS activation through a Ca2+-dependent, PKC-sensitive, but phosphatidylinositol 3-kinase/Akt-independent pathway.

Activation of endothelial nitric oxide synthase by the angiotensin II type 1 receptor

Enhanced angiotensin II (AngII) action has been implicated in endothelial dysfunction that is characterized as decreased nitric oxide availability. Although endothelial cells have been reported to express AngII type 1 (AT1) receptors, the exact role of AT1 in regulating endothelial NO synthase (eNOS) activity remains unclear. We investigated the possible regulation of eNOS through AT1 in bovine aortic endothelial cells (BAECs) and its functional significance in rat aortic vascular smooth muscle cells (VSMCs). In BAECs infected with adenovirus encoding AT1 and in VSMCs infected with adenovirus encoding eNOS, AngII rapidly stimulated phosphorylation of eNOS at Ser1179. This was accompanied with increased cGMP production. These effects were blocked by an AT1 antagonist. The cGMP production was abolished by a NOS inhibitor as well. To explore the importance of eNOS phosphorylation, VSMCs were also infected with adenovirus encoding S1179A-eNOS. AngII did not stimulate cGMP production in VSMCs expressing S1179A. However, S1179A was able to enhance basal NO production as confirmed with cGMP production and enhanced vasodilator-stimulated phosphoprotein phosphorylation. Interestingly, S1179A prevented the hypertrophic response similar to wild type in VSMCs. From these data, we conclude that the AngII/AT1 system positively couples to eNOS via Ser1179 phosphorylation in ECs and VSMCs if eNOS and AT1 coexist. However, basal level NO production may be sufficient for prevention of AngII-induced hypertrophy by eNOS expression. These data demonstrate a novel molecular mechanism of eNOS regulation and function and thus provide useful information for eNOS gene therapy under endothelial dysfunction.

Critical role of vimentin phosphorylation at Ser-56 by p21-activated kinase in vimentin cytoskeleton signaling

Phosphorylation and spatial reorganization of the vimentin network have been implicated in mediating smooth muscle contraction, cell migration, and mitosis. In this study, stimulation of cultured smooth muscle cells with 5-hydroxytryptamine (5-HT) induced PAK1 phosphorylation at Thr-423 (an indication of p21-activated kinase (PAK) activation). Treatment with PAK led to disassembly of wild-type (but not mutant S56A) vimentin filaments as assessed by an in vitro filament assembly assay. Furthermore, stimulation with 5-HT resulted in the dissociation of Crk-associated substrate (CAS; an adapter protein associated with smooth muscle force development) from cytoskeletal vimentin. Expression of mutant S56A vimentin in cells inhibited the increase in phosphorylation at Ser-56 and in the ratios of soluble to insoluble vimentin (an index of vimentin disassembly) and the dissociation of CAS from cytoskeletal vimentin in response to 5-HT activation compared with cells expressing wild-type vimentin. Because CAS may be involved in PAK activation, PAK phosphorylation was evaluated in cells expressing the S56A mutant. Expression of mutant S56A vimentin depressed PAK phosphorylation at Thr-423 induced by 5-HT. Expression of the S56A mutant also inhibited the spatial reorientation of vimentin filaments in cells in response to 5-HT stimulation. Our results suggest that vimentin phosphorylation at Ser-56 may inversely regulate PAK activation possibly via the increase in the amount of soluble CAS upon agonist stimulation of smooth muscle cells. Additionally, vimentin phosphorylation at this position is critical for vimentin filament spatial rearrangement elicited by agonists.

ADAM17 Mediates Epidermal Growth Factor Receptor Transactivation and Vascular Smooth Muscle Cell Hypertrophy Induced by Angiotensin II

BACKGROUND

Angiotensin II (Ang II) promotes growth of vascular smooth muscle cells (VSMCs) via epidermal growth factor (EGF) receptor (EGFR) transactivation mediated through a metalloprotease-dependent shedding of heparin-binding EGF-like growth factor (HB-EGF). However, the identity of the metalloprotease responsible for this process remains unknown.

METHODS AND RESULTS

To identify the metalloprotease required for Ang II-induced EGFR transactivation, primary cultured aortic VSMCs were infected with retrovirus encoding dominant negative (dn) mutant of ADAM10 or ADAM17. EGFR transactivation induced by Ang II was inhibited in VSMCs infected with dnADAM17 retrovirus but not with dnADAM10 retrovirus. However, Ang II comparably stimulated intracellular Ca2+ elevation and JAK2 tyrosine phosphorylation in these VSMCs. In addition, dnADAM17 inhibited HB-EGF shedding induced by Ang II in A10 VSMCs expressing the AT1 receptor. Moreover, Ang II enhanced protein synthesis and cell volume in VSMCs infected with control retrovirus, but not in VSMCs infected with dnADAM17 retrovirus.

CONCLUSIONS

ADAM17 activated by the AT1 receptor is responsible for EGFR transactivation and subsequent protein synthesis in VSMCs. These findings demonstrate a previously missing molecular mechanism by which Ang II promotes vascular remodeling.

4-Hydroxynonenal signalling to apoptosis in isolated rat hepatocytes: the role of PKC-delta

4-Hydroxynonenal, a significant aldehyde end product of membrane lipid peroxidation with numerous biochemical activities, has consistently been detected in various human diseases. Concentrations actually detectable in vivo (0.1-5 microM) have been shown to up-regulate different genes and modulate various enzyme activities. In connection with the latter aspect, we show here that, in isolated rat hepatocytes, 1 microM 4-hydroxynonenal selectively activates protein kinase C-delta, involved in apoptosis of many cell types; it also induces very early activation of Jun N-terminal kinase, in parallel increasing activator protein-1 DNA-binding activity in a time-dependent manner and triggering apoptosis after only 120 min treatment. These phenomena are likely protein kinase C-delta-dependent, being significantly reduced or annulled by cell co-treatment with rottlerin, a selective inhibitor of protein kinase C-delta. We suggest that 4-hydroxynonenal may induce apoptosis through activation of protein kinase C-delta and of Jun N-terminal kinase, and consequent up-regulation of activator protein-1 DNA binding.