Angiotensin II stimulates p21-activated kinase in vascular smooth muscle cells: role in activation of JNK

Attenuation of Angiotensin II-Induced Hypertension in BubR1 Low-Expression Mice Via Repression of Angiotensin II Receptor 1 Overexpression

Background Angiotensin II (Ang II) can cause hypertension and tissue impairment via AGTR1 (Ang II receptor type 1), particularly in renal proximal tubule cells, and can cause DNA damage in renal cells via nicotinamide adenine dinucleotide phosphate oxidase. BubR1 (budding uninhibited by benzimidazole-related 1) is a multifaceted kinase that functions as a mitotic checkpoint. BubR1 expression can be induced by Ang II in smooth muscle cells in vitro, but the relationship between systemic BubR1 expression and the Ang II response is unclear. Methods and Results Twenty 24-week-old male BubR1 low-expression mice (BubR1^L/L mice) and age-matched BubR1^+/+ mice were used in this study. We investigated how Ang II stimulation affects BubR1^L/L mice. The elevated systolic blood pressure caused by Ang II stimulation in BubR1^+/+ mice was significantly attenuated in BubR1^L/L mice. Additionally, an attenuated level of Ang II-induced perivascular fibrosis was observed in the kidneys of BubR1^L/L mice. Immunohistochemistry revealed that the overexpression of AGTR1 induced by Ang II stimulation was repressed in BubR1^L/L mice. We evaluated AGTR1 and Nox-4 (nicotinamide adenine dinucleotide phosphate oxidase-4) levels to determine the role of BubR1 in the Ang II response. Results from in vitro assays of renal proximal tubule cells suggest that treatment with small interfering RNA targeting BubR1 suppressed Ang II-induced overexpression of AGTR1. Similarly, the upregulation in Nox4 and Jun N-terminal kinase induced by Ang II administration was repressed by treatment with small interfering RNA targeting BubR1. Conclusions Ang II-induced hypertension is caused by AGTR1 overexpression in the kidneys via the upregulation of BubR1 and Nox4.

Activation of the STAT3/microRNA-21 pathway participates in angiotensin II-induced angiogenesis

Angiotensin II (AngII) facilitates angiogenesis that is associated with the continuous progression of atherosclerotic plaques, but the underlying mechanisms are still not fully understood. Several microRNAs (miRNAs) have been shown to promote angiogenesis; however, whether miRNAs play a crucial role in AngII-induced angiogenesis remains unclear. This study evaluated the functional involvement of miRNA-21 (miR-21) in the AngII-mediated proangiogenic response in human microvascular endothelial cells (HMECs). We found that AngII exerted a proangiogenic role, indicated by the promotion of proliferation, migration, and tube formation in HMECs. Next, miR-21 was found to be upregulated in AngII-treated HMECs, and its specific inhibitor potently blocked the proangiogenic effects of AngII. Subsequently, we focused on the constitutive activation of STAT3 in the AngII-mediated proangiogenic process. Bioinformatic analysis indicated that STAT3 acted as a transcription factor initiating miR-21 expression, which was verified by ChIP-PCR. A reporter assay further identified three functional binding sites of STAT3 in the miR-21 promoter region. Moreover, phosphatase and tensin homolog (PTEN) was recognized as a target of miR-21, and STAT3 inhibition restored AngII-induced reduction in PTEN. Similarly, the STAT3/miR-21 axis was shown to mediate AngII-provoked angiogenesis in vivo, which was demonstrated by using the appropriate inhibitors. Our data suggest that AngII was involved in proangiogenic responses through miR-21 upregulation and reduced PTEN expression, which was, at least in part, linked to STAT3 signaling. The present study provides novel insights into AngII-induced angiogenesis and suggests potential treatment strategies for attenuating the progression of atherosclerotic lesions and preventing atherosclerosis complications.

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.

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.

Identification of Hic-5 as a novel scaffold for the MKK4/p54 JNK pathway in the development of abdominal aortic aneurysms

BACKGROUND

Although increased amounts of reactive oxygen species in the pathogenesis of abdominal aortic aneurysm (AAA) are well documented, the precise molecular mechanisms by which reactive oxygen species induce AAAs have not been fully elucidated. This study focused on the role of hydrogen peroxide-inducible clone 5 (Hic-5), which is induced by hydrogen peroxide and transforming growth factor-β, in the cellular signaling of AAA pathogenesis.

METHODS AND RESULTS

Using the angiotensin II-induced AAA model in Apoe(-/-) mice, we showed that Apoe(-/-)Hic-5(-/-) mice were completely protected from AAA formation and aortic rupture, whereas Apoe(-/-) mice were not. These features were similarly observed in smooth muscle cell-specific Hic-5-deficient mice. Furthermore, angiotensin II treatment induced Hic-5 expression in a reactive oxygen species-dependent manner in aortic smooth muscle cells in the early stage of AAA development. Mechanistic studies revealed that Hic-5 interacted specifically with c-Jun N-terminal kinase p54 and its upstream regulatory molecule mitogen-activated protein kinase kinase 4 as a novel scaffold protein, resulting in the expression of membrane type 1 matrix metalloproteinase and matrix metalloproteinase 2 activation in aortic smooth muscle cells.

CONCLUSION

Hic-5 serves as a novel scaffold protein that specifically activates the mitogen-activated protein kinase kinase 4/p54 c-Jun N-terminal kinase pathway, thereby leading to the induction and activation of matrix metalloproteinases in smooth muscle cells and subsequent AAA formation. Our study provided a novel therapeutic option aimed at inhibiting the mitogen-activated protein kinase kinase 4-Hic-5-p54 c-Jun N-terminal kinase pathway in the vessel wall, particularly through Hic-5 inhibition, which may be used to produce more precise and effective therapies.

Angiotensin II-induced MMP-2 activity and MMP-14 and basigin protein expression are mediated via the angiotensin II receptor type 1-mitogen-activated protein kinase 1 pathway in retinal pigment epithelium: implications for age-related macular degeneration

Accumulation of various lipid-rich extracellular matrix (ECM) deposits under the retinal pigment epithelium (RPE) has been observed in eyes with age-related macular degeneration (AMD). RPE-derived matrix metalloproteinase (MMP)-2, MMP-14, and basigin (BSG) are major enzymes involved in the maintenance of ECM turnover. Hypertension (HTN) is a systemic risk factor for AMD. It has previously been reported that angiotensin II (Ang II), one of the most important hormones associated with HTN, increases MMP-2 activity and its key regulator, MMP-14, in RPE, inducing breakdown of the RPE basement membrane, which may lead to progression of sub-RPE deposits. Ang II exerts most of its actions by activating the mitogen-activated protein kinase (MAPK) signaling pathway. Herein is explored the MAPK signaling pathway as a potential key intracellular modulator of Ang II-induced increase in MMP-2 activity and MMP-14 and BSG protein expression. It was observed that Ang II stimulates phosphorylation of extracellular signal-regulated kinase (ERK) and p38 MAPK in RPE cells and ERK/p38 and Jun N-terminal kinase (JNK) in mice. These effects were mediated by Ang II type 1 receptors. Blockade of ERK or p38 MAPK abrogated the increase in MMP-2 activity and MMP-14 and BSG proteins in ARPE-19 cells. A better understanding of the molecular events by which Ang II induces ECM dysregulation is of critical importance to further define its contribution to the progression of sub-RPE deposits in AMD patients with HTN.

Krüppel-like factor (KLF) 5 mediates cyclin D1 expression and cell proliferation via interaction with c-Jun in Ang II-induced VSMCs

AIM

To elucidate how krüppel-like factor (KLF5) activates cyclin D1 expression in Ang II-induced vascular smooth muscle cells (VSMC) proliferation.

METHODS

An adenoviral vector containing the full-length cDNA of KLF5 and a recombinant plasmid expressing c-Jun were constructed. MTT assay and flow cytometric analysis were used to determine the effect of Ang II on cell growth. The luciferase assay and chromatin immunoprecipitation were used to detect the relationship between KLF5 and c-Jun in transactivation of cyclin D1 gene expression.

RESULTS

Ang II upregulated the expression of KLF5 with concurrent acceleration of the cell cycle progression in VSMCs. Ang II induced KLF5 activation via the ERK and p38 MAPK pathways triggered by AT-1 receptor. High DNA binding activity and functional interaction of KLF5 and c-Jun were found in Ang II-induced VSMCs. Cotransfection of KLF5 and c-Jun expression vectors significantly increased cyclin D1 promoter activity.

CONCLUSION

KLF5 is a downstream signal of the ERK 1/2 and p38 MAPK pathways, and activates the transcription of cyclin D1 gene via functional interaction with c-Jun in Ang II-induced VSMC proliferation.

Peptide hormone regulation of angiogenesis

It is now apparent that regulation of blood vessel growth contributes to the classical actions of hormones on development, growth, and reproduction. Endothelial cells are ideally positioned to respond to hormones, which act in concert with locally produced chemical mediators to regulate their growth, motility, function, and survival. Hormones affect angiogenesis either directly through actions on endothelial cells or indirectly by regulating proangiogenic factors like vascular endothelial growth factor. Importantly, the local microenvironment of endothelial cells can determine the outcome of hormone action on angiogenesis. Members of the growth hormone/prolactin/placental lactogen, the renin-angiotensin, and the kallikrein-kinin systems that exert stimulatory effects on angiogenesis can acquire antiangiogenic properties after undergoing proteolytic cleavage. In view of the opposing effects of hormonal fragments and precursor molecules, the regulation of the proteases responsible for specific protein cleavage represents an efficient mechanism for balancing angiogenesis. This review presents an overview of the actions on angiogenesis of the above-mentioned peptide hormonal families and addresses how specific proteolysis alters the final outcome of these actions in the context of health and disease.

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.

Angiotensin II regulation of adrenocortical gene transcription

Angiotensin II (Ang II) is the key peptide hormone in the renin-angiotensin-aldosterone system (RAAS). Its ability to regulate levels of circulating aldosterone relies on actions on adrenal glomerulosa cells. Many of the Ang II effects on glomerulosa cells involve a precisely coordinated regulation of signaling cascades and gene expression. The development of genome-wide gene arrays has allowed the definition of transcriptome-wide effects of Ang II in adrenocortical cells. Analysis of the Ang II gene targets reveals broad effects on cellular gene expression, particularly the rapid induction of numerous transcription factors that may regulate long-term steroid metabolism and cell growth/proliferation. Herein we discuss the Ang II-induced genes in adrenocortical cells and review the progress in defining the role of these genes in zona glomerulosa function.

Rho/Rho kinase is a key enzyme system involved in the angiotensin II signaling pathway of liver fibrosis and steatosis

BACKGROUND AND AIM

The molecular mechanisms underlying the involvement of the renin-angiotensin system in hepatic fibrosis are unclear. Recently, it was reported that a Rho kinase inhibitor prevented fibrosis of various tissues and that the Rho/Rho kinase pathway was involved in the renin-angiotensin system of vascular smooth muscle cells. In this study, the involvement of the Rho/Rho kinase pathway on angiotensin II signaling in liver fibrogenesis and generation of steatosis was investigated.

METHODS

Rats were fed a choline-deficient/L-amino acid-defined (CDAA) diet continuously and treated with a Rho kinase inhibitor, Y-27632, and an angiotensin II receptor blocker, TCV-116. Liver histology and hepatic stellate cell activation were analyzed. Free radical production was detected by 4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine immunostaining and the expression of tumor necrosis factor-alpha was examined. Isolated hepatic stellate cells were pretreated with a Rho kinase inhibitor, Y-27632, or an angiotensin II receptor blocker, CV-11974, and stimulated with angiotensin II, and mRNA expression of transforming growth factor-beta and alpha-smooth muscle actin was analyzed.

RESULTS

Both the angiotensin II receptor blocker and the Rho kinase inhibitor improved fibrosis and steatosis of the liver in CDAA-fed rats. The increase in the number of hepatocytes positive for 4-hydroxynonenal and 8-hydroxy-2'-deoxyguanosine in CDAA-fed rats was significantly prevented by the angiotensin II receptor blocker and the Rho kinase inhibitor. The levels of tumor necrosis factor-alpha mRNA in the liver of CDAA-fed rats were significantly increased and this increase was significantly inhibited by treatment with the angiotensin II receptor blocker and the Rho kinase inhibitor. mRNA expression of transforming growth factor-beta and alpha-smooth muscle actin stimulated by angiotensin II was also significantly suppressed by these two drugs.

CONCLUSION

These results suggest that the Rho/Rho kinase pathway is at least partly involved in the renin-angiotensin system and plays an important role in hepatic fibrosis and steatosis.

Novel roles of intracrine angiotensin II and signalling mechanisms in kidney cells

Angiotensin II (Ang II) has powerful sodium-retaining, growth-promoting and pro- inflammatory properties in addition to its physiological role in maintaining body salt and fluid balance and blood pressure homeostasis. Increased circulating and local tissue Ang II is one of the most important factors contributing to the development of sodium and fluid retention, hypertension and target organ damage. The importance of Ang II in the pathogenesis of hypertension and target organ injury is best demonstrated by the effectiveness of angiotensin- converting enzyme (ACE) inhibitors and AT1-receptor antagonists in treating hypertension and progressive renal disease including diabetic nephropathy. The detrimental effects of Ang II are mediated primarily by the AT1-receptor, while the AT2-receptor may oppose the AT1-receptor. The classical view of the AT1-receptor-mediated effects of Ang II is that the agonist binds its receptors at the cell surface, and following receptor phosphorylation, activates downstream signal transduction pathways and intracellular responses. However, evidence is emerging that binding of Ang II to its cell surface AT1-receptors also activates endocytotic (or internalisation) processes that promote trafficking of both the effector and the receptor into intracellular compartments. Whether internalised Ang II has important intracrine and signalling actions is not well understood. The purpose of this article is to review recent advances in Ang II research with focus on the mechanisms underlying high levels of intracellular Ang II in proximal tubule cells and the contribution of receptor-mediated endocytosis of extracellular Ang II. Further attention is devoted to the question whether intracellular and/or internalised Ang II plays a physiological role by activating cytoplasmic or nuclear receptors in proximal tubule cells. This information may aid future development of drugs to prevent and treat Ang II-induced target organ injury in cardiovascular and renal diseases by blocking intracellular and/or nuclear actions of Ang II.

STAT1 and STAT3 as intracellular regulators of vascular remodeling

The roles of signal transducers and activators of transcription (STAT) proteins are widely discussed in the pathogenesis of cardiovascular diseases. It is highly probable that STAT1 and STAT3 are activated during proliferation and inflammation inside atheromatous plaques. Luminal surfaces of endothelium become thrombogenic because of STAT1-dependent induction of MHC II and STAT3-regulated recruitment of phospholipase A2. As with STAT1, STAT3 seems to mediate stimulation of vascular wall cells by VEGF, HGF, and Ang II. STAT3 can contribute to counteracting apoptosis by eventual cooperation with c-fos and the bcl-xl gene. As pharmacological agents called statins are reported to regulate activities of STAT proteins, these signal messenger proteins could serve as targets for anti-atherogenic therapy. We attempted to review the role of STAT1 and STAT3 proteins in vascular remodeling.

Effects of AT1 receptor-mediated endocytosis of extracellular Ang II on activation of nuclear factor-kappa B in proximal tubule cells

Angiotensin II (Ang II) exerts powerful proinflammatory and growth effects on the development of Ang II-induced hypertensive glomerulosclerosis and tubulo-interstitial fibrosis. The proinflammatory and growth actions of Ang II are primarily mediated by activation of cell surface type 1 receptors (AT(1)) and the transcription factor nuclear factor-kappaB (NF-kappaB). However, binding of cell surface receptors by extracellular Ang II also induces receptor-mediated endocytosis of the agonist-receptor complex in renal cells. The purpose of the present study was to determine whether AT(1) receptor-mediated endocytosis of extracellular Ang II is required for Ang II-induced NF-kappaB activation and subsequent proliferation of rabbit renal proximal tubule cells. Expression of AT(1) (primarily AT(1a) or human AT(1)) receptors in these cells was confirmed by Western blot, showing that transfection of a human AT(1) receptor-specific 20-25 nucleotide siRNA knocked down more than 70% of AT(1) receptor protein (P < 0.01). Stimulation of proximal tubule cells by Ang II (1 nM) induced fourfold increases in NF-kappaB activity (P < 0.01). The Ang II-increased NF-kappaB activity was significantly attenuated by coadministration of losartan (10 microM), an AT(1) receptor-selective blocker, or colchicine (1 microM), a selective cytoskeleton microtubule inhibitor known to block receptor-mediated endocytosis (P < 0.01). Furthermore, Ang II significantly increased (3)H-thymidine incorporation (>55%, P < 0.01), an index of cell proliferation and DNA synthesis, and the effect was also attenuated by coadministration of losartan and colchicine (P < 0.01). Our results therefore suggest that AT(1) receptor-mediated endocytosis of extracellular Ang II may be required for Ang II-induced NF-kappaB activation and subsequent cell proliferation in renal proximal tubule cells.

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.

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

The renin-angiotensin system is a central component of the physiological and pathological responses of cardiovascular system. Its primary effector hormone, angiotensin II (ANG II), not only mediates immediate physiological effects of vasoconstriction and blood pressure regulation, but is also implicated in inflammation, endothelial dysfunction, atherosclerosis, hypertension, and congestive heart failure. The myriad effects of ANG II depend on time (acute vs. chronic) and on the cells/tissues upon which it acts. In addition to inducing G protein- and non-G protein-related signaling pathways, ANG II, via AT(1) receptors, carries out its functions via MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases [PDGF, EGFR, insulin receptor], and nonreceptor tyrosine kinases [Src, JAK/STAT, focal adhesion kinase (FAK)]. AT(1)R-mediated NAD(P)H oxidase activation leads to generation of reactive oxygen species, widely implicated in vascular inflammation and fibrosis. ANG II also promotes the association of scaffolding proteins, such as paxillin, talin, and p130Cas, leading to focal adhesion and extracellular matrix formation. These signaling cascades lead to contraction, smooth muscle cell growth, hypertrophy, and cell migration, events that contribute to normal vascular function, and to disease progression. This review focuses on the structure and function of AT(1) receptors and the major signaling mechanisms by which angiotensin influences cardiovascular physiology and pathology.

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

ANG II promotes remodeling of vascular smooth muscle cells (VSMCs) in cardiovascular diseases. It has been shown to activate p21-activated kinase (PAK)1, a critical component of signaling pathways implicated in growth and migration. However, the detailed signaling mechanism by which ANG II induces PAK1 activation in VSMCs remains unclear. Therefore, we have examined the mechanism required for activation of PAK1 by ANG II in VSMCs. ANG II, through activation of the ANG II type 1 receptor, rapidly promotes phosphorylation of PAK1 in VSMCs via a pathway independent of transactivation of the epidermal growth factor receptor. Using selective agonists and inhibitors, we demonstrated that mobilization of intracellular Ca2+ and PKCδ activation are required for ANG II-induced PAK1 phosphorylation. Rottlerin, a PKCδ inhibitor, significantly blocked ANG II-induced PAK1 phosphorylation. Further support for this notion was provided through infection of VSMCs with adenovirus encoding a dominant-negative (dn)PKCδ, which also markedly reduced phosphorylation of PAK1 by ANG II. In this pathway, Ca2+ acts upstream of PKCδ because a Ca2+ ionophore rapidly induced PKCδ phosphorylation at Tyr311 and Ca2+-dependent PAK1 phosphorylation was blocked by rottlerin. In addition, dnPYK-2, dnRac, and antioxidants inhibited ANG II-induced PAK1 phosphorylation, suggesting that PYK-2, Rac, and reactive oxygen species are involved in the upstream signaling. Finally, dnPAK1 markedly inhibited ANG II-induced protein synthesis in VSMCs. These data provide a novel signaling pathway by which ANG II may contribute to vascular remodeling.

Angiotensin II stimulates protein synthesis and inhibits proliferation in primary cultures of rat adrenal glomerulosa cells

Angiotensin II (Ang II) is one of the most important stimuli of rat adrenal glomerulosa cells. The aim of the present study was to investigate whether Ang II can stimulate cell proliferation and/or hypertrophy and investigate pathways and intracellular targets. A 3-d treatment with Ang II (5-100 nm), through the Ang II type 1 receptor subtype, abolished cell proliferation observed in control cells but increased protein synthesis. Preincubation with PD98059 (a MAPK kinase inhibitor) abolished basal proliferation and had no effect on basal protein synthesis but did reverse the effect of Ang II on protein synthesis. The p38 MAPK inhibitor SB203580 reversed the inhibitory effect on cell proliferation and abolished the increase in protein synthesis, whereas the c-Jun N-terminal kinase inhibitor SP600125 had no effect. Time-course studies revealed that Ang II stimulated phosphorylation of both p42/p44mapk and p38 MAPK but did not activate c-Jun N-terminal kinase. Ang II had no effect on the level of cyclin E expression but increased the expression of the cyclin-dependent kinase, p27Kip1, an effect abolished in cells preincubated with SB203580 and PD98059. In conclusion, in cultured rat glomerulosa cells, a 3-d treatment with Ang II increases protein synthesis, with a concomitant decrease in proliferation. These effects are mediated by both the p42/p44mapk and p38 MAPK pathways, which increase expression of the steroidogenic enzymes, steroidogenic acute regulatory protein and 3beta-hydroxysteroid dehydrogenase and p27Kip1, a protein known to block the cell cycle in G1 phase. Together these results support the key role of Ang II as a stimulus of steroid synthesis rather than a proliferating factor.

Oxidative stress in the infarcted heart: role of de novo angiotensin II production

This study aimed to elucidate whether angiotensin (Ang) II generated de novo at the infarct site regulates the redox state of inflammatory cells participating in cardiac repair. On days 3-28 following ligation of the rat left coronary artery, we addressed at the infarct site: (a) the appearance and cellular origin of oxidative stress by monitoring the expression (mRNA and protein) of gp91phox (a subunit of superoxide producing NADPH oxidase) and the antioxidant superoxide dismutase (SOD), together with the presence of 3-nitrotyrosine (a marker of oxidative stress); (b) the presence of components requisite to Ang peptide generation; and (c) response to treatment with losartan (Los, 10mg/kg/day). We found at the infarct site, macrophage-derived oxidative stress appears during week 1 coincident with the appearance of components requisite to AngII generation and activity in these cells. Based on observed response to AT1 receptor antagonism with Los, we would suggest de novo AngII, in an autocrine manner, participates in the induction of oxidative stress while suppressing the expression of antioxidant defenses.

Effect of angiotensin II type 2 receptor blockade on mitogen activated protein kinases during myocardial ischemia-reperfusion

Mitogen-activated protein kinases (MAPKs) have been implicated during ischemia-reperfusion (IR) and angiotensin II (AngII) type 2 receptor (AT2R) blockade has been shown to induce cardioprotection involving protein kinase Cepsilon (PKCepsilon) signaling after IR. We examined whether the 3 major MAPKs, p38, c-Jun NH2-terminal kinase (JNK-1 and JNK-2), and extracellular signal regulated kinases (ERK-1 and ERK-2) are activated after IR and whether treatment with the AT2R antagonist PD123,319 (PD) alters their expression. Isolated rat hearts were randomized to control (aerobic perfusion, 80 min), IR (no drug; 50 min of perfusion, 30 min global ischemia and 30 min reperfusion; working mode), and IR + PD (0.3 micromol/l) and left ventricular (LV) work was measured. We measured LV tissue content of p38, p-p38, p-JNK-1 (54 kDa), p-JNK-2 (46 kDa), p-ERK-1 (44 kDa), p-ERK-2 (42 kDa) and PKCepsilon proteins by immunoblotting and cGMP by enzyme immunoassay. IR resulted in significant LV dysfunction, increase in p-p38 and p-JNK-1/-2, no change in p-ERK-1/-2 or PKCepsilon, and decrease in cGMP. PD improved LV recovery after IR, induced a slight increase in p-p38 (p < 0.01 vs. control), normalized p-JNK-1, did not change p-ERK-1/-2, and increased PKCepsilon and cGMP. The overall results suggest that p38 and JNK might play a significant role in acute IR injury and the cardioprotective effect of AT2R blockade independent of ERK. The activation of p38 and JNKs during IR may be linked, in part, to AT2R stimulation.

Identification of Nck interacting proteins in vascular smooth muscle cells

The adaptor molecule Nck has been demonstrated to mediate Angiotensin II (AngII)-induced stimulation of p21-activated kinase (PAK) and c-Jun NH2-terminal kinase (JNK) in vascular smooth muscle cells (VSMC). We have previously demonstrated, that immunoprecipitation of Nck from VSMC stimulated by AngII yielded an unidentified 100 kD phosphotyrosine (pTyr) protein. The present study was aimed at identifying the Nck-associated 100 kD pTyr protein in VSMC. Several candidate proteins of appropriate size, that had been shown previously either to bind to Nck or had been implicated in signal transduction pathways leading to activation of PAK or JNK were tested for association with Nck in VSMC. The first candidate protein we tested was Git1, which did not bind to Nck in VSMC upon stimulation by AngII. However, we identified dynamin as a 100 kD protein that was bound to Nck in VSCM via interaction with the third Nck-SH3 domain. However, dynamin was not tyrosine phosphorylated by AngII treatment and seemed to be distinct from the 100 kD phosphotyrosine protein that was found in Nck immunoprecipitates. Future work will now have to identify the Nck-associated 100 kD pTyr protein and functional studies will have to address its role in AngII signaling.

Mesenteric artery remodeling and effects of imidapril and irbesartan on it in spontaneously hypertensive rats

AIM: To investigate the remodeling of mesenteric artery and the expression of TGF-β₁, c-Jun in mesenteric artery and effects of imidapril and irbesartan on the remodeling in spontaneously hypertensive rats (SHR).

METHODS: Thirty SHR (male/female, 21/9), aged 13 wk, were randomly divided into 3 groups (7 male rats and 3 female rats each group): SHR group, imidapril group (imidapril 3 mg/kg·d was given in drinking water for 14 wk), and irbesartan group (irbesartan 50 mg/kg·d was given in drinking water foe 14 wk). Ten homogenous Wistar Kyoto rats, 5 males and 5 females, weighing 206 ± 49 g, were selected as normal control group (WKY group). Systolic pressure was measured on day 1, 2, 4, 6, 8, 10, 12 and 14 during the experiment and the rats were killed at the end of the experiment. Angiotensin II (Ang II) level in plasma and mesenteric arteries was measured by radioimmunoassay. The morphology of the secondary branches of mesenteric artery were examined by light microscopy and electron microscopy. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression of transforming growth factor TGF-β₁ and c-Jun mRNA.

RESULTS: Compared with imidapril group and irbesartan group, the blood pressure was remarkably increased in SHR group. Ang II level in plasma and mesenteric arteries in SHR group was the same or lower than that in WKY group, and was higher in irbesartan group and lower in imidapril group. The remodeling of mesenteric arteries in SHR group was mostly obvious among the 4 groups. The ratio of TGF-β₁ absorbed light value to GAPDH absorbed light value in the SHR group was 0.887 ± 0.019, which was significantly higher than that in WKY group, imidapril group, and irbesartan group with the ratios of 0.780 ± 0.018, 0.803 ± 0.005, and 0.847 ± 0.017, respectively (P < 0.01). Ang II level in plasma and mesenteric arteries in imidapril group was significantly lower than that in irbesartan group (P < 0.05). The c-Jun absorbed light value/GAPDH absorbed light value of mesenteric arteries in the SHR group was 0.850 ± 0.015, which was significantly higher than that in the WKY, imidapril, and irbesartan groups (0.582 ± 0.013, 0.743 ± 0.012, and 0.789 ± 0.013, respectively, P < 0.01), and was significantly lower in imidapril group than in irbesartan group (P < 0.05).

CONCLUSION: Imidapril and irbesartan can not only control blood pressure but also inhibit mesenteric arteries remodeling and mRNA expression of TGF-β₁, c-Jun in SHR. Imidapril is more effective than irbesartan.

Effect of angiotensin II type 2 receptor blockade on activation of mitogen-activated protein kinases after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

The stress-responsive mitogen-activated protein kinases (MAPKs) (p38-MAPK, c-Jun NH2-terminal kinase [JNK-1 and JNK-2], and extracellular signal regulated kinases [ERK-1 and ERK-2]) might be involved in angiotensin II (AII)-induced ischemia-reperfusion injury. Cardioprotection induced by AII type 1 (AT1) and type 2 (AT2) receptor blockade during ischemia-reperfusion is associated with protein kinase Cepsilon (PKCepsilon), nitric oxide, and cyclic guanosine monophosphate (cGMP) signaling. Our aim was to assess the effect of selective AT1 and AT2 receptor blockade with losartan and PD123,319, respectively, on MAPK expression after ischemia-reperfusion in isolated working rat hearts.

METHODS

Groups of six hearts were subjected to global ischemia (30 minutes) followed by reperfusion (30 minutes) and exposed to no drug/no ischemia-reperfusion (control), ischemia-reperfusion/no drug, and ischemia-reperfusion with losartan (1 microM), or PD123,319 (0.3 microM) and additional groups. AT1/AT2 receptor expression, MAPKs, PKCepsilon, and cGMP, and changes in mechanical function were measured. Western blotting was done on left ventricular tissue for AT1/AT2, p38/phosphorylated-p38 (p-p38), phosphorylated (p)-JNK-1/-2, phosphorylated (p)-ERK-1/-2, and PKCepsilon proteins; Northern blots for AT1/AT2 mRNA; and enzyme immunoassay for cGMP.

RESULTS

Compared with controls, ischemia-reperfusion induced significant left ventricular dysfunction, decreased AT2 protein and mRNA, increased p-p38 and p-JNK-1/-2, did not change p-ERK-1/-2 or PKCepsilon, and decreased cGMP. PD123,319 improved left ventricular recovery after ischemia-reperfusion, increased AT2 protein and mRNA, mildly increased p-p38, normalized p-JNK-1, did not change p-ERK-1/-2, and increased PKCepsilon and cGMP. Losartan did not change p-p38, increased p-JNK-1, and did not change pERK-1/-2, PKCepsilon, or cGMP.

CONCLUSIONS

The overall results suggest that the activation of p38-MAPK and JNK might be linked to AII signaling and play a significant role in acute ischemia-reperfusion injury as well as in the cardioprotective effect of AT2 receptor blockade.

Pyk2- and Src-dependent tyrosine phosphorylation of PDK1 regulates focal adhesions

3-Phosphoinositide-dependent protein kinase 1 (PDK1) is a signal integrator that activates the AGC superfamily of serine/threonine kinases. PDK1 is phosphorylated on tyrosine by oxidants, although its regulation by agonists that stimulate G-protein-coupled receptor signaling pathways and the physiological consequences of tyrosine phosphorylation in this setting have not been fully identified. We found that angiotensin II stimulates the tyrosine phosphorylation of PDK1 in vascular smooth muscle in a calcium- and c-Src-dependent manner. The calcium-activated tyrosine kinase Pyk2 acts as a scaffold for Src-dependent phosphorylation of PDK1 on Tyr9, which permits phosphorylation of Tyr373 and -376 by Src. This critical function of Pyk2 is further supported by the observation that Pyk2 and tyrosine-phosphorylated PDK1 colocalize in focal adhesions after angiotensin II stimulation. Importantly, infection of smooth muscle cells with a Tyr9 mutant of PDK1 inhibits angiotensin II-induced tyrosine phosphorylation of paxillin and focal adhesion formation. These observations identify a novel interaction between PDK1 and Pyk2 that regulates the integrity of focal adhesions, which are major compartments for integrating signals for cell growth, apoptosis, and migration.

Biology of the p21-activated kinases

The p21-activated kinases (PAKs) 1-3 are serine/threonine protein kinases whose activity is stimulated by the binding of active Rac and Cdc42 GTPases. Our understanding of the regulation and biology of these important signaling proteins has increased tremendously since their discovery in the mid-1990s. PAKs 1-3 are activated by a variety of GTPase-dependent and -independent mechanisms. This complexity reflects the contributions of PAK function in many cellular signaling pathways and the need to carefully control PAK action in a highly localized manner. PAKs serve as important regulators of cytoskeletal dynamics and cell motility, transcription through MAP kinase cascades, death and survival signaling, and cell-cycle progression. Consequently, PAKs have also been implicated in a number of pathological conditions and in cell transformation. We propose here a key role for PAK action in coordinating the dynamics of the actin and microtubule cytoskeletons during directional motility of cells, as well as in other functions requiring cytoskeletal polarization.

Inhibition of contraction and myosin light chain phosphorylation in guinea-pig smooth muscle by p21-activated kinase 1

The p21-activated protein kinases (PAKs) have been implicated in cytoskeletal rearrangements and modulation of non-muscle contractility. Little, however, is known about the role of the PAK family members in smooth muscle contraction. Therefore, we investigated the effect of the predominant isoform in vascular smooth muscle cells, PAK1, on contraction and phosphorylation of the regulatory light chains of myosin (r-MLC) in Triton-skinned guinea-pig smooth muscle. We also investigated which of the three putative substrates at the contractile apparatus - MLCK, caldesmon or r-MLC - is phosphorylated by PAK1 in smooth muscle tissue. Incubation of Triton-skinned carotid artery and taenia coli from guinea-pig with an active mutant of PAK1 in relaxing solution for 30-60 min resulted in inhibition of submaximal force by about 50 %. The mechanism of inhibition of force was studied in the Triton-skinned taenia coli. In this preparation, inhibition of force was associated with a respective inhibition of r-MLC phosphorylation. In the presence of the myosin phosphatase inhibitor, microcystin-LR (10 microM), the rate of contraction and r-MLC phosphorylation elicited at pCa 6.79 were both decreased. Because under these conditions the rate of r-MLC phosphorylation is solely dependent on MLCK activity, this result suggests that the inhibitory effect of PAK1 on steady-state force and r-MLC phosphorylation is due to inhibition of MLCK. In line with this, we found that MLCK was significantly phosphorylated by PAK1 while there was very little 32P incorporation into caldesmon. PAK1 phosphorylated isolated r-MLC but not those in the skinned fibres or in purified smooth muscle myosin II. In conclusion, these results suggest that PAK1 attenuates contraction of skinned smooth muscle by phosphorylating and inhibiting MLCK.

Localization of p21-activated protein kinase gamma-PAK/Pak2 in the endoplasmic reticulum is required for induction of cytostasis

The intracellular localization and physiological functions of the p21-activated protein kinase gamma-PAK have been examined in human embryonic kidney 293T and COS-7 cells. At 1-4 days post-transfection, cell division is inhibited by the expression of wild type (WT) gamma-PAK and the mutant S490A, whereas cells expressing S490D and the inactive mutants K278R and T402A grow exponentially, indicating a role for gamma-PAK in the induction of cytostasis. WT gamma-PAK and S490A are localized in a region surrounding the nucleus identified as the endoplasmic reticulum (ER), as determined by immunofluorescence, whereas K278R, T402A, and S490D lack localization. As shown by sucrose density gradient centrifugation, WT gamma-PAK, S490A, and endogenous gamma-PAK are distributed among the high density (ER-associated), intermediate density, and low density fractions, whereas the mutants that do not inhibit cell division are present only as soluble enzyme. The amount of endogenous gamma-PAK associated with the particulate fractions is increased 4-fold when cell division is inhibited by ionizing radiation. gamma-PAK in the ER and intermediate density fractions has high specific activity and is active, whereas the soluble form of gamma-PAK has low activity and is activable. The importance of localization of gamma-PAK is supported by data with the C-terminal mutants S490D and Delta 488; these mutants have high levels of protein kinase activity but do not induce cytostasis and are not bound to the ER. A model for the induction of cytostasis by gamma-PAK through targeting of gamma-PAK to the ER is presented in which gamma-PAK activity and Ser-490 are implicated in the regulation of cytostasis.

Emerging functions of p21-activated kinases in human cancer cells

The p21 activated kinases (Paks), an evolutionarily conserved family of serine/threonine kinases, are important for a variety of cellular functions including cell morphogenesis, motility, survival, mitosis, and angiogenesis. Paks are widely expressed in numerous tissues and are activated by growth factors and extracellular signals through GTPase-dependent and -independent mechanisms. Overexpression of Paks in epithelial cancer cells has been shown to increase migration potential, increase anchorage independent growth, and cause abnormalities in mitosis. Dysregulation of Paks has been reported in several human tumors and neurodegenerative diseases. A growing list of novel Pak interacting proteins has opened up exciting avenues of investigation by which to understand the functions of Paks in tumorigenesis. In this review, we will summarize the current knowledge of the Paks family with respect to emerging cellular functions and possible contributions to cancer.

Recent advances in angiotensin II signaling

Angiotensin II (Ang II) is a multifunctional hormone that influences the function of cardiovascular cells through a complex series of intracellular signaling events initiated by the interaction of Ang II with AT1 and AT2 receptors. AT1 receptor activation leads to cell growth, vascular contraction, inflammatory responses and salt and water retention, whereas AT2 receptors induce apoptosis, vasodilation and natriuresis. These effects are mediated via complex, interacting signaling pathways involving stimulation of PLC and Ca2+ mobilization; activation of PLD, PLA2, PKC, MAP kinases and NAD(P)H oxidase, and stimulation of gene transcription. In addition, Ang II activates many intracellular tyrosine kinases that play a role in growth signaling and inflammation, such as Src, Pyk2, p130Cas, FAK and JAK/STAT. These events may be direct or indirect via transactivation of tyrosine kinase receptors, including PDGFR, EGFR and IGFR. Ang II induces a multitude of actions in various tissues, and the signaling events following occupancy and activation of Ang receptors are tightly controlled and extremely complex. Alterations of these highly regulated signaling pathways may be pivotal in structural and functional abnormalities that underlie pathological processes in cardiovascular diseases such as cardiac hypertrophy, hypertension and atherosclerosis.

Involvement of p44/42 mitogen-activated protein kinases in regulating angiotensin II- and endothelin-1-induced contraction of rat thoracic aorta

In order to elucidate the signal transduction pathway of vascular smooth muscle contraction induced by the activation of receptors for angiotensin II and endothelin-1, we examined whether tyrosine kinases and mitogen-activated protein (MAP) kinases are involved in the development of force of contraction in the rat aorta. Isolated aortic smooth muscles without endothelium were incubated in a modified Krebs-Henseleit solution and stimulated with angiotensin II (100 nM) or endothelin-1 (10 nM). A tyrosine kinase inhibitor genistein (10 microM) reduced the angiotensin II- and endothelin-1-induced aortic contraction, while 10 microM of daidzein (an inactive analogue of genistein) did not. The K(+) depolarization-induced contraction was not attenuated by 10 microM of genistein. Selective inhibitors of MAP kinase/extracellular signal-regulated kinase (Erk) kinase (MEK) such as PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] and U0126 [1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene] inhibited the angiotensin II- and endothelin-1-induced vasocontraction. The p44/42 MAP kinases were phosphorylated in cultured aortic smooth muscle cells and in physiologically contracted aortic vessels stimulated with angiotensin II and endothelin-1 for 5 min. The angiotensin II- and endothelin-1-induced phosphorylations of p44/42 MAP kinases were inhibited by PD98059 as well as U0126 in the intact aorta. These results suggest that the activation of genistein-sensitive tyrosine kinases and p44/42 MAP kinases is involved in the angiotensin II- and endothelin-1-induced rat aortic contraction.

Cyclosporin A inhibits angiotensin II-induced c-Jun NH(2)-terminal kinase activation but not protein synthesis in vascular smooth muscle cells

Angiotensin II activates three major mitogen-activated protein kinases (MAPK) in vascular smooth muscle cells. Although other angiotensin II-induced MAPKs activation require transactivation of a growth factor receptor, the detailed mechanism by which angiotensin II activates c-Jun NH(2)-terminal kinase (JNK) remains unclear. Here, an immunosuppressant, cyclosporin A but not FK506, selectively inhibited angiotensin II-induced JNK activation in vascular smooth muscle cells. However, cyclosporin A had no inhibitory effect on angiotensin II-induced protein synthesis. Thus, angiotensin II-induced JNK activation but not protein synthesis is mediated by a mechanism sensitive to cyclosporin A, which is independent from calcineurin in vascular smooth muscle cells.

Paxillin-dependent paxillin kinase linker and p21-activated kinase localization to focal adhesions involves a multistep activation pathway

The precise temporal-spatial regulation of the p21-activated serine-threonine kinase PAK at the plasma membrane is required for proper cytoskeletal reorganization and cell motility. However, the mechanism by which PAK localizes to focal adhesions has not yet been elucidated. Indirect binding of PAK to the focal adhesion protein paxillin via the Arf-GAP protein paxillin kinase linker (PKL) and PIX/Cool suggested a mechanism. In this report, we demonstrate an essential role for a paxillin-PKL interaction in the recruitment of activated PAK to focal adhesions. Similar to PAK, expression of activated Cdc42 and Rac1, but not RhoA, stimulated the translocation of PKL from a generally diffuse localization to focal adhesions. Expression of the PAK regulatory domain (PAK1-329) or the autoinhibitory domain (AID 83-149) induced PKL, PIX, and PAK localization to focal adhesions, indicating a role for PAK scaffold activation. We show PIX, but not NCK, binding to PAK is necessary for efficient focal adhesion localization of PAK and PKL, consistent with a PAK-PIX-PKL linkage. Although PAK activation is required, it is not sufficient for localization. The PKL amino terminus, containing the PIX-binding site, but lacking paxillin-binding subdomain 2 (PBS2), was unable to localize to focal adhesions and also abrogated PAK localization. An identical result was obtained after PKLDeltaPBS2 expression. Finally, neither PAK nor PKL was capable of localizing to focal adhesions in cells overexpressing paxillinDeltaLD4, confirming a requirement for this motif in recruitment of the PAK-PIX-PKL complex to focal adhesions. These results suggest a GTP-Cdc42/GTP-Rac triggered multistep activation cascade leading to the stimulation of the adaptor function of PAK, which through interaction with PIX provokes a functional PKL PBS2-paxillin LD4 association and consequent recruitment to focal adhesions. This mechanism is probably critical for the correct subcellular positioning of PAK, thereby influencing the ability of PAK to coordinate cytoskeletal reorganization associated with changes in cell shape and motility.

Lysophosphatidic acid stimulates p21-activated kinase in vascular smooth muscle cells

Lysophosphatidic acid (LPA) has been shown to be a potent mitogen for vascular smooth muscle cells. Src-dependent transactivation of receptor tyrosine kinases has been previously demonstrated to mediate LPA-induced activation of MAP kinase ERK1/2. Furthermore, generation of reactive oxygen species (ROS) by LPA is also known to contribute to MAP kinase activation. Rho family small G-proteins Rac and Cdc42, and their immediate downstream effector p21-activated kinase (PAK), have been demonstrated to mediate important effects on the cytoskeleton that are relevant for cell migration and proliferation. In the present report we evaluated stimulation of PAK by LPA in rat aortic vascular smooth muscle cells (VSMC) by PAK immunocomplex MBP in-gel kinase assay. LPA increased PAK activity 3-fold, peaking at 5 min and showing sustained activation up to 45 min. Inhibition of tyrosine kinases by pretreatment of VSMC with genistein or specific inhibition of Src by PP1 greatly diminished LPA-induced PAK activation, whereas specific inhibition of PDFG- and EGF receptor kinase by tyrphostin AG1296 and AG1478 had no effect. Furthermore, inhibition of Galpha(i) by pertussis toxin and inhibition of NADH/NADPH oxidase by diphenylene iodonium also diminished LPA-induced stimulation of PAK. This is the first study to demonstrate that LPA activates PAK. In VSMC, PAK activation by LPA is mediated by Galpha(i) and is dependent on Src, whereas EGF- or PDGF receptor transactivation are not involved. Furthermore, generation of ROS is required for LPA-induced activation of PAK.

Cyclooxygenase-2 in myocardium stimulation by angiotensin-II in cultured cardiac fibroblasts and role at acute myocardial infarction

Myocardial infarction is followed by a complex repair process that includes a significant role for inflammatory cells. Cyclooxygenase-2 (COX-2) plays a key role in mediating inflammation. Contribution of COX-2 to inflammatory response following myocardial infarction is less certain. In an effort to evaluate the function of COX-2 and prostaglandin E(2)(PGE(2)) in myocardial infarction, we examined the role of COX-2 after angiotensin II (Ang II) stimulation in cardiac fibroblasts and in rats with experimental myocardial infarction (MI). We combined Western blot analysis and enzyme immunoassay to demonstrate COX-2 expression and PGE(2)release in cardiac fibroblasts. Isolated cardiac fibroblasts were stimulated with Ang II. Unstimulated fibroblasts showed no COX-2 protein expression. Fibroblasts stimulated with Ang II showed a strong time-dependent expression of COX-2 protein. The p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580 but not the p42/44 MAPK-inhibitor PD98059 suppressed Ang II-induced COX-2 protein expression. COX-2 expression correlated with a significantly increased PGE(2)release from cardiac fibroblasts. The COX-2 specific inhibitor NS-398 suppressed the Ang II-stimulated PGE(2)production. We then investigated COX-2 expression and inflammatory cell infiltration in our rat model of myocardial infarction. MI was produced by coronary artery ligation in adult female Wistar rats. The period of coronary artery occlusion was 96 h. The selective COX-2 inhibitor rofecoxib (3 mg/kg/d), administered orally, was given one day before MI and continued for four days. Western blotting showed expression of COX-2 protein in the area of necrosis and the infarct border zone. Immunofluorescence analysis showed macrophage infiltration as well as fibroblast proliferation in the infarct border zone of 4-d infarcted tissue and a significantly reduced cell invasion and fibroblast proliferation in infarcted tissue of rats treated with rofecoxib. MI size at day 4 was comparable in untreated and treated rats. In conclusion, we demonstrate that pharmacological interference with prostaglandin synthesis in myocardial infarction is associated with reduced myocardial invasion of inflammatory cells.

Angiotensin receptors: signaling, vascular pathophysiology, and interactions with ceramide

Angiotensin II (ANG II) is a pleiotropic vasoactive peptide that binds to two distinct receptors: the ANG II type 1 (AT(1)) and type 2 (AT(2)) receptors. Activation of the renin-angiotensin system (RAS) results in vascular hypertrophy, vasoconstriction, salt and water retention, and hypertension. These effects are mediated predominantly by AT(1) receptors. Paradoxically, other ANG II-mediated effects, including cell death, vasodilation, and natriuresis, are mediated by AT(2) receptor activation. Our understanding of ANG II signaling mechanisms remains incomplete. AT(1) receptor activation triggers a variety of intracellular systems, including tyrosine kinase-induced protein phosphorylation, production of arachidonic acid metabolites, alteration of reactive oxidant species activities, and fluxes in intracellular Ca(2+) concentrations. AT(2) receptor activation leads to stimulation of bradykinin, nitric oxide production, and prostaglandin metabolism, which are, in large part, opposite to the effects of the AT(1) receptor. The signaling pathways of ANG II receptor activation are a focus of intense investigative effort. We critically appraise the literature on the signaling mechanisms whereby AT(1) and AT(2) receptors elicit their respective actions. We also consider the recently reported interaction between ANG II and ceramide, a lipid second messenger that mediates cytokine receptor activation. Finally, we discuss the potential physiological cross talk that may be operative between the angiotensin receptor subtypes in relation to health and cardiovascular disease. This may be clinically relevant, inasmuch as inhibitors of the RAS are increasingly used in treatment of hypertension and coronary heart disease, where activation of the RAS is recognized.

Inability of serotonin to activate the c-Jun N-terminal kinase and p38 kinase pathways in rat aortic vascular smooth muscle cells

BACKGROUND

Serotonin (5-HT, 5-hydroxytryptamine) activates the Extracellular Signal-Regulated Kinase (ERK)/ Mitogen-Activated Protein Kinase (MAPK) pathways, in vascular smooth muscle cells. Parallel MAPK pathways, the c-Jun N-terminal Kinase (JNK) and p38 pathway, are activated by stimulators of the ERK/MAPK pathway. We hypothesized that 5-HT would activate the JNK and p38 pathways in rat vascular smooth muscle cells.

RESULTS

Results were determined using standard Western analysis and phosphospecific JNK and p38 antibodies. No significant activation by 5-HT (10(-9) - 10(-5) M; 30 min) of the JNK or p38 pathways, as measured by protein phosphorylation, was observed in any of these experiments. These experiments were repeated in the presence of the serine/threonine phosphatase inhibitor okadaic acid (1 uM) and the tyrosine phosphatase inhibitor sodium orthovanadate (1 uM) to maximize any observable signal. Even under these optimized conditions, no activation of the JNK or p38 pathways by 5-HT was observed. Time course experiments (5-HT 10(-5) M; 5 min, 15 min, 30 min and 60 min) showed no significant activation of JNK after incubation with 5-HT at any time point. However, we detected strong activation of JNK p54 and p46 (5- and 7 fold increases in bands p54 and p46, respectively over control levels) by anisomycin (500 ng/ml, 30 min). Similarly, a JNK activity assay failed to reveal activation of JNK by 5-HT, in contrast to the strong stimulation by anisomycin.

CONCLUSION

Collectively, these data support the conclusion that 5-HT does not activate the JNK or p38 pathways in rat vascular smooth muscle cells.

Essential role for extracellular Ca(2+) in JNK activation by mechanical stretch in bladder smooth muscle cells

Mechanical stretch has been implicated in phenotypic changes as an adaptive response to stretch stress physically loaded in bladder smooth muscle cells (BSMCs). To investigate stretch-induced signaling, we examined the mitogen-activated protein kinase (MAPK) family using rat primary BSMCs. When BSMCs were subjected to sustained mechanical stretch using collagen-coated silicon membranes, activation of c-Jun NH(2)-terminal kinase (JNK) was most relevant among three subsets of MAPK family members: the activity was elevated from 5 min after stretch and peaked at 10 min with an 11-fold increase. Activation of p38 was weak compared with that of JNK, and ERK was not activated at all. JNK activation by mechanical stretch was totally dependent on extracellular Ca(2+) and inhibited by Gd(3+), a blocker of stretch-activated (SA) ion channels. Nifedipine and verapamil, inhibitors for voltage-dependent Ca(2+) channels, had no effect on this JNK activation. Moreover, none of the inhibitors pertussis toxin, genistein, wortmannin, or calphostin C affected stretch-induced JNK activation, indicating that G protein-coupled and tyrosine kinase receptors are unlikely to be involved in this JNK activation. On the other hand, W-7, a calmodulin inhibitor, and cyclosporin A, a calcineurin inhibitor, prevented JNK activation by stretch. These results suggest a novel pathway for stretch-induced activation of JNK in BSMCs: mechanical stretch evokes Ca(2+) influx via Gd(3+)-sensitive SA Ca(2+) channels, resulting in JNK activation under regulation in part by calmodulin and calcineurin.

Unique regulation of c-Jun N-terminal kinase by PYK2/CAK-beta in angiotensin II-stimulated vascular smooth muscle cells

Activation of tyrosine kinases is believed to play a central role in angiotensin II (AngII) signaling. Here, we have investigated whether a tyrosine kinase, PYK2, is functionally involved in AngII-induced c-Jun N-terminal kinase (JNK) activation in vascular smooth muscle cells (VSMCs). Adenovirus expressing PYK2 kinase-inactive mutant K457A or a tyrosine phosphorylation site mutant Y402F was transfected in VSMCs. AngII-induced JNK phosphorylation was markedly enhanced by K457A, whereas it was suppressed by Y402F. Protein synthesis induced by AngII was also enhanced by K457A and inhibited by Y402F. In this regard, K457A suppressed PYK2 kinase activation by AngII, whereas it enhanced AngII-induced PYK2 Tyr(402) phosphorylation. By contrast, Y402F inhibited PYK2 Tyr(402) phosphorylation, whereas it markedly enhanced AngII-induced PYK2 kinase activation. Thus, we conclude that PYK2 kinase activity negatively regulates JNK activation and protein synthesis, whereas Tyr(402) phosphorylation positively regulates these events in AngII-stimulated VSMCs, suggesting a unique role of PYK2 in mediating vascular remodeling.

Angiotensin II-induced stimulation of p21-activated kinase and c-Jun NH2-terminal kinase is mediated by Rac1 and Nck

p21-activated kinase (PAK) has been shown to be an upstream mediator of JNK in angiotensin II (AngII) signaling. Little is known regarding other signaling molecules involved in activation of PAK and JNK by AngII. Rho family GTPases Rac and Cdc42 have been shown to enhance PAK activity by binding to p21-binding domain of PAK (PAK-PBD). In vascular smooth muscle cells (VSMC) AngII stimulated Rac1 binding to GST-PAK-PBD fusion protein. Pretreatment of VSMC by genistein inhibited AngII-induced Rac1 activation, whereas Src inhibitor PP1 had no effect. Inhibition of protein kinase C by phorbol 12,13-dibutyrate pretreatment also decreased AngII-mediated activation of Rac1. The adaptor molecule Nck has been shown previously to mediate PAK activation by facilitating translocation of PAK to the plasma membrane. In VSMC AngII stimulated translocation of Nck and PAK to the membrane fraction. Overexpression of dominant-negative Nck in Chinese hamster ovary (CHO) cells, stably expressing the AngII type I receptor (CHO-AT1), inhibited both PAK and JNK activation by AngII, whereas it did not affect ERK1/2. Finally, dominant-negative Nck inhibited AngII-induced DNA synthesis in CHO-AT1 cells. Our data provide evidence for Rac1 and Nck as upstream mediators of PAK and JNK in AngII signaling and implicate JNK in AngII-induced growth responses.

Mildly oxidized low-density lipoprotein acts synergistically with angiotensin II in inducing vascular smooth muscle cell proliferation

OBJECTIVES

Considerable attention has been focused on both mildly oxidized low-density lipoprotein (mox-LDL) and highly oxidized LDL (ox-LDL) as important risk factors for cardiovascular disease. Further, angiotensin II (Ang II) appears to play a crucial role in the development of hypertension and atherosclerosis. We assessed the effect of oxidatively modified LDL and its major oxidative components, i.e., hydrogen peroxide (H2O2), lysophosphatidylcholine (LPC), and 4-hydroxy-2-nonenal (HNE) and their interaction with Ang II on vascular smooth muscle cell (VSMC) DNA synthesis.

METHODS

Growth-arrested rabbit VSMCs were incubated in serum-free medium with different concentrations of native LDL, mox-LDL, ox-LDL, H2O2, LPC, or HNE with or without Ang II. DNA synthesis in VSMCs was measured by [3H]thymidine incorporation.

RESULTS

Ang II stimulated DNA synthesis in a dose-dependent manner with a maximal effect at a concentration of 1 micromol/l (173%). Ang II (0.5 micromol/l) amplified the effect of native LDL at 500 ng/ml, ox-LDL at 100 ng/ml, and mox-LDL at 50 ng/ml on DNA synthesis (108 to 234%, 124 to 399%, 129 to 433%, respectively). H2O2 had a maximal effect at a concentration of 5 micromol/l (177%), LPC at 15 micromol/l (156%), and HNE at 0.5 micromol/l (137%). Low concentrations of H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) also acted synergisitically with Ang II (0.5 micromol/l) in inducing DNA synthesis to 308, 304, or 238%, respectively. Synergistic interactions of Ang II (0.5 micromol/l) with mox-LDL, ox-LDL (both 50 ng/ml), H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) on DNA synthesis were completely reversed by the combined use of probucol (10 micromol/l), a potent antioxidant and candesartan (0.1 micromol/l), an AT1 receptor antagonist.

CONCLUSIONS

Our results suggest that mox-LDL, ox-LDL, and their major components H2O2, LPC, and HNE act synergistically with Ang II in inducing VSMC DNA synthesis. A combination of antioxidants with AT1 receptor blockade may be effective in the treatment of VSMC proliferative disorders associated with hypertension and atherosclerosis.

Activation of MAPKs by angiotensin II in vascular smooth muscle cells. Metalloprotease-dependent EGF receptor activation is required for activation of ERK and p38 MAPK but not for JNK

In cultured vascular smooth muscle cells (VSMC), the vasculotrophic factor, angiotensin II (AngII) activates three major MAPKs via the G(q)-coupled AT1 receptor. Extracellular signal-regulated kinase (ERK) activation by AngII requires Ca(2+)-dependent "transactivation" of the EGF receptor that may involve a metalloprotease to stimulate processing of an EGF receptor ligand from its precursor. Whether EGF receptor transactivation also contributes to activation of other members of MAPKs such as p38MAPK and c-Jun N-terminal kinase (JNK) by AngII remains unclear. In the present study, we have examined the effects of a synthetic metalloprotease inhibitor BB2116, and the EGF receptor kinase inhibitor AG1478 on AngII-induced activation of MAPKs in cultured VSMC. BB2116 markedly inhibited ERK activation induced by AngII or the Ca(2+) ionophore without affecting the activation by EGF or PDGF. BB2116 as well as HB-EGF neutralizing antibody inhibited the EGF receptor transactivation by AngII, suggesting a critical role of HB-EGF in the metalloprotease-dependent EGF receptor transactivation. In addition to the ERK activation, activation of p38MAPK and JNK by AngII was inhibited by an AT1 receptor antagonist, RNH6270. and EGF markedly activate p38MAPK, whereas but not EGF markedly activates JNK, indicating the possible contribution of the EGF receptor transactivation to the p38MAPK activation. The findings that both BB2116 and AG1478 specifically inhibited activation of p38MAPK but not JNK by AngII support this hypothesis. From these data, we conclude that ERK and p38MAPK activation by AngII requires the metalloprotease-dependent EGF receptor transactivation, whereas the JNK activation is regulated without involvement of EGF receptor transactivation.

The effect of angiotensin II on mitogen-activated protein kinase in human cardiomyocytes

The role of angiotensin II (Ang II)-receptors on mitogen-activated protein kinase (MAPK) activation in cardiomyocytes remains controversial. Therefore, the current study was designed to investigate the actions of AT(1)- and AT(2)-receptors on Ang II-induced extracellular signal-regulated kinase (ERK), p38 and the c-Jun N-terminal kinase (JNK) MAPK activities in human cardiomyocytes. Human cardiac tissue was obtained from open-heart surgery (n=6). The cardiac tissue was minced and incubated in the special tissue culture system for 24 hours in the absence or presence of Ang II (10(-7) M). These studies were repeated with the AT(1)-receptor antagonist losartan (10(-6) M) or the AT(2)-receptor antagonist PD-123319 (10(-6) M). Immunohistochemical staining and Western blot analysis with phospho-antibodies were performed to determine ERK, JNK and p38 activities. Ang II increased ERK and p38 activities in human cardiomyocytes. The effects of Ang II were abolished by losartan and enhanced by PD-123319. Co-incubation with both losartan and PD-123319 resulted in a decrease of ERK and p38 activities in cardiomyocytes. The immunohistochemical staining of JNK showed no significant differences between Ang II alone, Ang II plus losartan and Ang II plus PD-123319 groups. In conclusion, Ang II has a potent effect on ERK and p38 MAPK activities in cardiomyocytes, by acting through AT(1)-receptors. This effect of Ang II is modified by AT(2)-receptors. Therefore, Ang II, via AT(1)- and AT(2)-receptor stimulation, has a distinct effect on MAPK activity in cardiomyocytes.

Ca(2+)-dependent activation of c-jun NH(2)-terminal kinase in primary rabbit proximal tubule epithelial cells

Previous work from this laboratory demonstrated that arachidonic acid activates c-jun NH(2)-terminal kinase (JNK) through oxidative intermediates in a Ca(2+)-independent manner (Cui X and Douglas JG. Arachidonic acid activates c-jun N-terminal kinase through NADPH oxidase in rabbit proximal tubular epithelial cells. Proc Natl Acad Sci USA 94: 3771-3776, 1997.). We now report that JNK can also be activated via a Ca(2+)-dependent mechanism by agents that increase the cytosolic Ca(2+) concentration (Ca(2+) ionophore A(23187), Ca(2+)-ATPase inhibitor thapsigargin) or deplete intracellular Ca(2+) stores [intracellular Ca(2+) chelator 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM]. The activation of JNK by BAPTA-AM occurs despite a decrease in cytosolic Ca(2+) concentration as detected by the indicator dye fura 2, but appears to be related to Ca(2+) metabolism, because modification of BAPTA with two methyl groups increases not only the chelation affinity for Ca(2+), but also the potency for JNK activation. BAPTA-AM stimulates Ca(2+) influx across the plasma membrane, and the resulting local Ca(2+) increases are probably involved in activation of JNK because Ca(2+) influx inhibitors (SKF-96365, nifedipine) and lowering of the free extracellular Ca(2+) concentration with EGTA reduce the BAPTA-induced JNK activation.