Genistein, a tyrosine kinase inhibitor, reduces Ca2+ mobilization in swine carotid media

Vascular effects of phytoestrogens and alternative menopausal hormone therapy in cardiovascular disease

Phytoestrogens are estrogenic compounds of plant origin classified into different groups including isoflavones, lignans, coumestans and stilbenes. Isoflavones such as genistein and daidzein are the most studied and most potent phytoestrogens, and are found mainly in soy based foods. The effects of phytoestrogens are partly mediated via estrogen receptors (ERs): ERα, ERβ and possibly GPER. The interaction of phytoestrogens with ERs is thought to induce both genomic and non-genomic effects in many tissues including the vasculature. Some phytoestrogens such as genistein have additional non-ER-mediated effects involving signaling pathways such as tyrosine kinase. Experimental studies have shown beneficial effects of phytoestrogens on endothelial cells, vascular smooth muscle, and extracellular matrix. Phytoestrogens may also affect other pathophysiologic vascular processes such as lipid profile, angiogenesis, inflammation, tissue damage by reactive oxygen species, and these effects could delay the progression of atherosclerosis. As recent clinical trials showed no vascular benefits or even increased risk of cardiovascular disease (CVD) and CV events with conventional menopausal hormone therapy (MHT), phytoestrogens are being considered as alternatives to pharmacologic MHT. Epidemiological studies in the Far East population suggest that dietary intake of phytoestrogens may contribute to the decreased incidence of postmenopausal CVD and thromboembolic events. Also, the WHO-CARDIAC study supported that consumption of high soybean diet is associated with lower mortalities from coronary artery disease. However, as with estrogen, there has been some discrepancy between the experimental studies demonstrating the vascular benefits of phytoestrogens and the data from clinical trials. This is likely because the phytoestrogens clinical trials have been limited in many aspects including the number of participants enrolled, the clinical end points investigated, and the lack of long-term follow-up. Further investigation of the cellular mechanisms underlying the vascular effects of phytoestrogens and careful evaluation of the epidemiological evidence and clinical trials of their potential vascular benefits would put forward the use of phytoestrogens as an alternative MHT for the relief of menopausal symptoms and amelioration of postmenopausal CVD.

Cardiac oxytocin receptor blockade stimulates adverse cardiac remodeling in ovariectomized spontaneously hypertensive rats

An increasing amount of evidence demonstrates the beneficial role of oxytocin (OT) in the cardiovascular system. Similar actions are attributed to genistein, an isoflavonic phytoestrogen. The treatment with genistein activates the OT system in the aorta of ovariectomized (OVX) Sprague-Dawley (SD) rats. The objective of this study was to determine the effects of low doses of genistein on the OT-induced effects in rat hypertension. The hypothesis tested was that treatment of OVX spontaneously hypertensive rats (SHRs) with genistein improves heart structure and heart work through a mechanism involving the specific OT receptor (OTR). OVX SHRs or SD rats were treated with genistein (in microg/g body wt sc, 10 days) in the presence or absence of an OT antagonist (OTA) [d(CH(2))(5), Tyr(Me)(2), Orn(8)]-vasotocin or a nonspecific estrogen receptor antagonist (ICI-182780). Vehicle-treated OVX rats served as controls. RT-PCR and Western blot analysis demonstrated that left ventricular (LV) OTR, downregulated by ovariectomy, increased in response to genistein. In SHRs or SD rats, this effect was blocked by OTA or ICI-182780 administration. The OTR was mainly localized in microvessels expressing the CD31 marker and colocalized with endothelial nitric oxide synthase. In SHRs, the genistein-stimulated OTR increases were associated with improved fractional shortening, decreased blood pressure (12 mmHg), decreased heart weight-to-body weight ratio, decreased fibrosis, and lowered brain natriuretic peptide in the LV. The prominent finding of the study is the detrimental effect of OTA treatment on the LV of SHRs. OTA treatment of OVX SHRs resulted in a dramatic worsening of ejection fractions and an augmented fibrosis. In conclusion, these results demonstrate that cardiac OTRs are involved in the regulation of cardiac function of OVX SHRs. The decreases of OTRs may contribute to cardiac pathology following menopause.

Inducible IL-23p19 expression in human microglia via p38 MAPK and NF-kappaB signal pathways

Activated microglia can release a variety of proinflammatory cytokines that play a crucial role in the pathogenesis of multiple sclerosis (MS). IL-23, a novel proinflammatory cytokine, is required for the induction of experimental autoimmune encephalomyelitis. Previously we demonstrated that IL-23 is expressed in MS lesions and that microglia are one cellular source of IL-23 in MS patients. In the present study we investigated the inducible expression and regulation of p19, a key subunit of IL-23, in human microglia. We demonstrated the inducible expression of IL-23p19 by lipopolysaccharide-stimulated microglial cells. Using signaling pathway-specific inhibitors, we showed that blocking p38 MAP kinase or NF-kappaB signaling pathway significantly reduced p19 expression in microglia. The regulatory role of p38 MAP kinase in p19 expression was further confirmed by decreased expression in microglia transduced with dominant-negative p38. We concluded that the p38 MAP kinase and NF-kappaB signaling pathways play an important role in regulation of IL-23p19 expression on human microglia, and are thus potential therapeutic targets in the treatment of MS.

Protein kinases in vascular smooth muscle tone--role in the pulmonary vasculature and hypoxic pulmonary vasoconstriction

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism that in the normal animal diverts blood away from poorly ventilated areas of the lung, thereby maintaining optimal ventilation-perfusion matching. In global hypoxia however, such as in respiratory disease or at altitude, it causes detrimental increases in pulmonary vascular resistance and pulmonary artery (PA) pressure. The precise intracellular pathways and mechanisms underlying HPV remain unclear, although it is now recognised that both an elevation in smooth muscle intracellular [Ca2+] and a concomitant increase in Ca2+ sensitivity are involved. Several key intracellular protein kinases have been proposed as components of the signal transduction pathways leading to development of HPV, specifically Rho kinase, non-receptor tyrosine kinases (NRTK), p38 mitogen activated protein (MAP) kinase, and protein kinase C (PKC). All of these have been implicated to a greater or lesser extent in pathways leading to Ca2+ sensitisation, and in some cases regulation of intracellular [Ca2+] as well. In this article, we review the role of these key protein kinases in the regulation of vascular smooth muscle (VSM) constriction, applying what is known in the systemic circulation to the pulmonary circulation and HPV. We conclude that the strongest evidence for direct involvement of protein kinases in the mechanisms of HPV concerns a central role for Rho kinase in Ca2+ sensitisation, and a potential role for Src-family kinases in both modulation of Ca2+ entry via capacitative Ca2+ entry (CCE) and activation of Rho kinase, though others are likely to have indirect or modulatory influences. In addition, we speculate that Src family kinases may provide a central interface between the proposed hypoxia-induced generation of reactive oxygen species by mitochondria and both the elevation in intracellular [Ca2+] and Rho kinase mediated Ca2+ sensitisation.

Comparison of the effects of isoflurane and sevoflurane on protein tyrosine phosphorylation-mediated vascular contraction

BACKGROUND

Isoflurane induces greater effects on vasodilation and decreasing blood pressure than sevoflurane. Tyrosine kinase-catalyzed protein tyrosine phosphorylation plays an important role in regulating vascular smooth muscle contraction. The aim of the present study was to compare the effects of isoflurane and sevoflurane on tyrosine phosphorylation-mediated vascular constriction, by assessing the degree of sodium orthovanadate (Na(3)VO(4), tyrosine phosphatase inhibitor)-induced contraction and protein tyrosine phosphorylation of rat aortic smooth muscle.

METHODS

Na(3)VO(4)-induced contraction and protein tyrosine phosphorylation of rat aortic smooth muscle were measured in the presence of genistein, a tyrosine kinase inhibitor, and different concentrations of isoflurane and sevoflurane, using isometric force measurement and Western blot, respectively.

RESULTS

Na(3)VO(4) (10(-4) M) induced sustained contraction and tyrosine phosphorylation of substrates that were both markedly attenuated in the presence of genistein (5 x 10(-5) M). Isoflurane and sevoflurane dose-dependently (1, 2, 3 MAC) attenuated the Na(3)VO(4)-induced contraction (P < 0.05-0.005, n = 8), with a greater degree of inhibition by isoflurane than sevoflurane at 2 MAC (P < 0.01) and 3 MAC (P < 0.05). Both anesthetics also attenuated the total band density of the Na(3)VO(4)-induced, tyrosine-phosphorylated substrates in a concentration-dependent manner (P < 0.05-0.005, n = 4), with much greater attenuation by isoflurane than sevoflurane at 1 and 2 MAC (P < 0.05), respectively.

CONCLUSION

The results of the present study demonstrate that isoflurane exhibits a greater degree of inhibition on the Na(3)VO(4)-stimulated contraction and protein tyrosine phosphorylation of rat aortic smooth muscle compared with sevoflurane. These findings suggest that isoflurane depresses the protein tyrosine phosphorylation-mediated contraction of vascular smooth muscle to a greater degree than sevoflurane.

Receptor-operated Ca2+ influx and its association with the Src family in secretagogue-stimulated pancreatic acini

We investigated signal transduction between receptor-operated Ca(2+) influx (ROCI) and Src-related nonreceptor protein tyrosine kinase (PTK) in rat pancreatic acini. CCK and the Ca(2+) ionophore enhanced the Src-related PTK activity, whereas the high-affinity CCK-A receptor agonists, fibroblast growth factor (FGF), and the protein kinase C (PKC) activator had no or little effect. This increase was abolished by eliminating [Ca(2+)](o), loading of the intracellular Ca(2+) chelator, and administering the PTK inhibitor genistein. While genistein inhibited extracellular Ca(2+) or Mn(2+) entry induced by CCK and carbachol, it did not affect intracellular Ca(2+) release and oscillations. CCK dose-dependently increased the Src phosphotransferase activity, which was abolished by inhibitors of G(q) protein, phospholipase C (PLC), and Src, but not by the calmodulin kinase (CaMK) inhibitor. Intensities of the Src band and amounts of tyrosine phosphorylated Src were enhanced by CCK stimulation. Thus, Src cascades appear to be coupled to the low-affinity CCK-A receptor and utilize G(q)-PLC pathways for their activation, independent of PKC and CaMK cascades. The low-affinity CCK-A receptor regulates ROCI via mediation of Src-related PTK and activates Src pathways to cause [Ca(2+)](o)-dependent pancreatic exocytosis.

Sensitivity of rabbit aorta and mesenteric artery to norepinephrine: role of tyrosine kinases

We tested the hypothesis that the differential sensitivity of rabbit aorta and mesenteric artery to norepinephrine is due to tyrosine kinase activity. The EC50 of aorta to norepinephrine was 6.5 times more sensitive than that in mesenteric artery. Basal myosin light chain phosphorylation was significantly greater in aorta as compared to mesenteric artery. Vanadate increased norepinephrine sensitivity significantly more in mesenteric artery than aorta, whereas genistein had the opposite effect. Basal phosphotyrosine levels were significantly higher in aorta than in mesenteric artery, the percentage increase in total tyrosine phosphorylated protein was significantly higher in mesenteric artery. These results suggest that the higher basal phosphotyrosine levels in the aorta may be responsible for the higher basal level of myosin light chain phosphorylation and this may be the basis for the higher sensitivity of the aorta to norepinephrine when compared with the mesenteric artery.

Prostaglandin F(2alpha) stimulates tyrosine phosphorylation of phospholipase C-gamma1

In this study, we investigated the ability of prostaglandin F(2alpha) (PGF(2alpha)) to induce tyrosine phosphorylation of phospholipase C-gamma1 (PLC-gamma1) in cat iris sphincter smooth muscle (CISM) cells. PGF(2alpha)(1 microM) stimulated PLC-gamma1 tyrosine phosphorylation in a time- and dose-dependent manner with a maximum increase of 3-fold at 0.5min. The protein tyrosine kinase inhibitors, genistein, and tyrphostin A-25, blocked the stimulatory effects of PGF(2alpha), suggesting involvement of protein tyrosine kinase activity in the physiological actions of the PGF(2alpha). Furthermore, PGF(2alpha)-induced p42/p44 MAP kinase activation was also completely blocked by protein tyrosine kinase inhibitors. In summary, these findings show that PGF(2alpha) stimulates tyrosine phosphorylation of PLC-gamma1 in CISM cells and indicate that PGF(2alpha)-stimulated tyrosine phosphorylation is responsible for an early signal transduction event.

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.

Tyrosine kinase participates in vasoconstriction through a Ca(2+)- and myosin light chain phosphorylation-independent pathway

This study was undertaken to determine the role of tyrosine kinase on intracellular Ca(2+) ([Ca(2+)](i)), myosin light chain (MLC) phosphorylation, and contraction caused by norepinephrine (NE) in rat aorta. NE induced a sustained contraction with an increase of [Ca(2+)](i). On the other hand, NE increased the phosphorylation of the 20 kDa MLC transiently. Pretreatment with genistein and tyrophostin 25, tyrosine kinase inhibitors, significantly inhibited NE-induced contraction, but did not affect the increase of [Ca(2+)](i) and MLC phosphorylation. These results suggest that tyrosine kinase may regulate the NE-mediated contraction without altering [Ca(2+)](i) and MLC phosphorylation in rat aorta.

Regulation of ion channels by protein tyrosine phosphorylation

Ion channels are regulated by protein phosphorylation and dephosphorylation of serine, threonine, and tyrosine residues. Evidence for the latter process, tyrosine phosphorylation, has increased substantially since this topic was last reviewed. In this review, we present a comprehensive summary and synthesis of the literature regarding the mechanism and function of ion channel regulation by protein tyrosine kinases and phosphatases. Coverage includes the majority of voltage-gated, ligand-gated, and second messenger-gated channels as well as several types of channels that have not yet been cloned, including store-operated Ca2+ channels, nonselective cation channels, and epithelial Na+ and Cl- channels. Additionally, we discuss the critical roles that channel-associated scaffolding proteins may play in localizing protein tyrosine kinases and phosphatases to the vicinity of ion channels.

Dietary soy exerts an antihypertensive effect in spontaneously hypertensive female rats

This study tested the hypothesis that dietary soy would attenuate the development of hypertension in female spontaneously hypertensive rats (SHR). Female SHR and control Wistar-Kyoto rats were obtained at 4 wk of age, randomly assigned to either an ovariectomized (OVX) group or a sham-operated group, and placed on a soy diet or control casein diet. After a minimum of 8 wk on their respective diets, mean arterial pressure (MAP) and heart rate (HR) were recorded before and after inhibition of nitric oxide synthase, air-jet stress, or ganglionic blockade. The major finding of this study is that MAP was reduced in the OVX SHR consuming soy diet compared with the casein-fed controls (150 +/- 4 vs. 164 +/- 3 mmHg). Plasma genistein concentrations were increased in the soy-fed OVX SHR (1.23 +/- 0.31 microM) compared with the casein-fed OVX SHR (nondetectable). However, there was no difference in plasma genistein concentrations between sham-operated and OVX SHR (1.37 +/- 0.42 vs. 1.23 +/- 0.31 microM). Inhibition of nitric oxide synthase increased MAP and decreased HR in all groups; diet did not affect this response. Air-jet stress increased MAP and HR in all groups. However, these responses were exaggerated in the soy-fed SHR. Finally, ganglionic blockade abolished the antihypertensive effect of soy diet in the OVX SHR. These findings indicate that dietary soy exerts an antihypertensive effect in OVX SHR. This effect does not involve the nitric oxide system but may be related to an as yet undefined interaction with the autonomic nervous system.

Integrins and mechanotransduction of the vascular myogenic response

This review summarizes what is currently known about the role of integrins in the vascular myogenic response. The myogenic response is the rapid and maintained constriction of a blood vessel in response to pressure elevation. A role for integrins in this process has been suggested because these molecules form an important mechanical link between the extracellular matrix and the vascular smooth muscle cytoskeleton. We briefly summarize evidence for a general role of integrins in mechanotransduction. We then describe the integrin subunit combinations known to exist in smooth muscle and the vascular wall matrix proteins that may interact with these integrins. We then discuss the effects of integrin-specific peptides and antibodies on vascular tone and on calcium entry mechanisms in vascular smooth muscle. Because integrin function is linked to the cytoskeleton, we discuss evidence for the role of the cytoskeleton in determining myogenic responsiveness. Finally, we analyze evidence that integrin-linked signaling pathways, such as those involving protein tyrosine phosphorylation cascades and mitogen-activated protein kinases, are required for myogenic tone.

Depletion of focal adhesion kinase by antisense depresses contractile activation of smooth muscle

Focal adhesion kinase (FAK) undergoes tyrosine phosphorylation in response to the contractile stimulation of tracheal smooth muscle. We hypothesized that FAK may play an important role in signaling pathways that regulate smooth muscle contraction. FAK antisense or FAK sense was introduced into muscle strips by reversible permeabilization, and strips were incubated with antisense or sense for 7 days. Antisense decreased FAK expression compared with that in untreated and sense-treated tissues, but it did not affect the expression of vinculin or myosin light chain kinase. Increases in force, intracellular free Ca2+ and myosin light chain phosphorylation in response to stimulation with ACh or KCl were depressed in FAK-depleted tissues, but FAK depletion did not affect the activation of permeabilized tracheal muscle strips with Ca2+. The tyrosine phosphorylation of paxillin, a substrate for FAK, was also significantly reduced in FAK-depleted strips. We conclude that FAK is a necessary component of the signaling pathways that regulate smooth muscle contraction and that FAK plays a role in regulating intracellular free Ca2+ and myosin light chain phosphorylation.

Tyrosine kinase involvement in renal arteriolar constrictor responses to angiotensin II

Experiments were performed to test the hypothesis that tyrosine kinase activity contributes to renal arteriolar contractile responses to angiotensin (Ang) II. Rats were subjected to short-term enalaprilat treatment to decrease endogenous Ang II formation before tissue was harvested for experiments with the in vitro blood-perfused juxtamedullary nephron technique. Acute surgical papillectomy was used to avoid the indirect afferent arteriolar effect of Ang II that arises through increased tubuloglomerular feedback sensitivity. Arteriolar lumen diameter responses to 1 and 10 nmol/L Ang II were monitored by videomicroscopic methods before and during treatment with various tyrphostin compounds: 100 micromol/L AG18 (broad-spectrum tyrosine kinase inhibitor), 100 nmol/L AG1478 (selective epidermal growth factor receptor tyrosine kinase inhibitor), or 100 micromol/L AG9 (inactive analog). Baseline afferent arteriolar lumen diameter averaged 23.5+/-1.2 micrometer and was not influenced by any tyrphostin. Ang II (10 nmol/L) decreased afferent diameter by 11.1+/-1.0 micrometer under untreated conditions, a response that was not altered by AG9 but significantly blunted by AG18 (34+/-9% inhibition) or AG1478 (52+/-8% inhibition). AG18 did not suppress afferent arteriolar contractile responses to membrane depolarization (20 to 55 mmol/L K(+ )bath). Efferent arteriolar baseline diameter averaged 24.1+/-0.8 micrometer and was unaltered by AG18 or AG1478; however, efferent diameter responses to 10 nmol/L Ang II were diminished 52+/-10% by AG18 and 51+/-13% by AG1478. These observations indicate that Ang II signaling in renal afferent and efferent arteriolar vascular smooth muscle is either mediated or modulated by tyrosine kinase activity, including that of the epidermal growth factor receptor tyrosine kinase.

Dietary soy-derived isoflavone phytoestrogens. Could they have a role in coronary heart disease prevention?

Soy protein-containing foods are a rich source of isoflavone phytoestrogens, such as genistein and daidzein. There is great interest in these substances, as lower rates of chronic diseases, including coronary heart disease, have been associated with high dietary intake of soy-containing foods. Soy phytoestrogens bind weakly to estrogen receptors, and some bind more strongly to estrogen receptor-beta compared with estrogen receptor-alpha. A meta-analysis has indicated that isoflavone phytoestrogens lowered plasma cholesterol concentrations in subjects with initially elevated levels, but had little effect in subjects with normal cholesterol concentrations. These substances reportedly may also have beneficial effects on arterial endothelial function. In addition to these potentially antiatherogenic effects, many laboratories are investigating other possible mechanisms, including antioxidative and antiproliferative properties of these substances. We have shown that dietary supplementation with soy-derived isoflavones reduced the in vitro oxidation susceptibility of low-density lipoprotein (LDL). To further explore this phenomenon, we incorporated genistein and daidzein into LDL molecules in vitro with the aid of an artificial transfer system. However, it was necessary to convert the isoflavone molecules to fat-soluble derivatives, fatty acid esters (analogous to esterified endogenous estrogens, which are known to occur in vivo), to achieve significant incorporation. The LDLs containing esterified isoflavones were shown to be less susceptible to oxidation in vitro than native LDL. We also employed U937 cell cultures for investigating the effects of isoflavone-containing LDLs on cell proliferation. Some of these LDLs exhibited antiproliferative effects in cultured U937 cells. In summary, lipophilic phytoestrogen derivatives could be incorporated into LDLs, increasing their oxidation resistance and antiproliferative efficacy ex vivo, both of which are, in theory, antiatherogenic effects. Further studies are needed to assess to what extent analogous effects could be produced in vivo and whether such substances have a role in hormone replacement and coronary heart disease prevention in postmenopausal women.

Effects of VEGF on Ca(2+)-transient in cultured lymphatic endothelial cells and mechanical activity of isolated lymph vessels

We investigated the effects of vascular endothelial growth factor (VEGF(165)) on [Ca(2+)](i)-transient in cultured lymphatic endothelial cells (LEC) and mechanical activity of isolated dog thoracic ducts. VEGF (0.1-10 ng/ml) caused a dose-dependent increase of the [Ca(2+)](i) in LEC. Pretreatment with 10(-5) M genistein or 5x10(-6) M herbimycin A produced a significant reduction of the VEGF-induced [Ca(2+)](i)-transient. In the presence of 10(-6) M thapsigargin, VEGF caused no significant effect on the [Ca(2+)](i)-transient. Pretreatment with Ca(2+)-free solution containing 0.1 mM EGTA produced no significant effect on the peak increase of [Ca(2+)](i) induced by 0.1 or 10 ng/ml VEGF, but significantly depressed the sustained part of [Ca(2+)](i) observed at the higher concentration of VEGF. The VEGF (0.1-10 ng/ml) caused a significant dilation of the isolated lymph vessels with intact endothelium, which were precontracted with U46,619. The 10 ng/ml VEGF-induced dilation was significantly reduced by 3 x 10(-5) M N(omega)-nitro-L-arginine methyl ester (L-NAME). The action of L-NAME was inhibited by the simultaneous application of 10(-3) M L-arginine. Mechanical rubbing of the endothelium also caused significant inhibition of the VEGF-induced dilation. The findings suggest that VEGF(165) may activate the receptor-related tyrosine kinase and cause the release of Ca(2+) from the inositol 1,4, 5-triphosphate-sensitive intracellular Ca(2+) stores in LEC. VEGF(165) also produces endothelium-dependent nitric oxide-mediated dilation of the precontracted isolated lymph vessels.

Tyrosine kinase-dependent calcium signaling in airway smooth muscle cells

Contractile agonists may stimulate mitogenic responses in airway smooth muscle by mechanisms that involve tyrosine kinases. The role of contractile agonist-evoked activation of tyrosine kinases in contractile signaling is not clear. We addressed this issue using cultured rat airway smooth muscle cells. In these cells, serotonin (5-HT, 1 microM) caused contraction (quantitated by a decrease in cell area), which was blocked by the tyrosine kinase inhibitor genistein (40 microM). Genistein and tyrphostin 23 (40 and 10 microM, respectively) significantly decreased 5-HT-evoked peak Ca(2+) responses, and the effect of genistein could be observed in the absence of extracellular Ca(2+). The specific inhibitor of mitogen-activated protein kinase kinase PD-98059 (30 microM) had no significant effect on peak Ca(2+) levels. Western analysis of cell extracts revealed that 5-HT caused a significant increase in tyrosine phosphorylation of proteins with molecular masses of approximately 70 kDa within 10 s of stimulation but no measurable tyrosine phosphorylation of the gamma isoform of phospholipase C (PLC-gamma). Tyrosine phosphorylation was inhibited by genistein. Furthermore, genistein (40 microM) significantly attenuated 5-HT-induced inositol phosphate production. We conclude that in airway smooth muscle contractile agonists acting on G protein-coupled receptors may activate tyrosine kinase(s), which in turn modulate calcium signaling by affecting, directly or indirectly, PLC-beta activity. It is unlikely that PLC-gamma or the mitogen-activated protein kinase pathway is involved in Ca(2+) signaling to 5-HT.

Genistein attenuates peritoneal metastasis of azoxymethane-induced intestinal adenocarcinomas in Wistar rats

The effects of the soybean isoflavonoid genistein on the development of bombesin-enhanced peritoneal metastasis from intestinal adenocarcinomas induced by azoxymethane (AOM) were investigated in male inbred Wistar rats. From the beginning of the experiment, rats were given 10 weekly s.c. injections of AOM (7.4 mg/kg body weight) and s.c. injections of bombesin (40 microg/kg body weight) every other day, and from week 16, s.c. injections of genistein (5 or 10 mg/kg body weight) every other day until the end of the experiment in week 45. Bombesin significantly increased the incidence of intestinal tumors and of cancer metastasis to the peritoneum. Although genistein administered at either dose had little or no effect on the enhancement of intestinal carcinogenesis by bombesin or on the location, histologic type, depth of involvement, labeling index, or growth pattern of intestinal cancers, it significantly decreased the incidence of cancer metastasis. Genistein also significantly decreased the incidence of lymphatic vessel invasion of adenocarcinomas, which was enhanced by bombesin. Our findings indicate that genistein attenuates cancer metastasis by inhibiting cancer cell invasion into lymphatic vessels through activities that do not affect the growth of intestinal cancers.

Activation of tyrosine kinase pathway by vanadate in gallbladder smooth muscle

Vanadate, an inhibitor of tyrosine phosphatase activity, might induce gallbladder contraction through the stimulation of the tyrosine kinase pathway. The aim of this study was to characterize the effects of vanadate in the guinea pig gallbladder smooth muscle. Vanadate exerts contractile effects which are not mediated by neurotransmitter release. The tyrosine kinase inhibitor genistein nearly abolished vanadate contraction, suggesting that an increase in protein tyrosine phosphorylation mediates the actions of vanadate. This suggestion was confirmed by Western blot analysis. Vanadate contractions were reduced in the presence of methoxyverapamil or in Ca(2+)-free medium, suggesting that vanadate may induce Ca(2+) influx. Neither inactivation of the Na(+)/K(+) pump nor reversal of the Na(+)/Ca(2+) exchanger can account for vanadate's actions. Vanadate contractile effects were reduced by indomethacin, as well as mepacrine, the inhibitor of phospholipase A(2), but were not affected by phospholipase C inhibitors. Neither inhibitors of diacylglycerol lipase nor protein kinase C reduced the response induced by vanadate. These data indicate that the effects of vanadate on smooth muscle are mainly mediated by protein tyrosine phosphorylation and reveal a new link between tyrosine phosphorylation and arachidonic acid metabolism in the control of gallbladder smooth muscle contraction.

Tyrosine kinase inhibitors modulate agonist-induced vasodilation in the hamster cheek pouch

The purpose of this study was to determine whether inhibitors of tyrosine kinase attenuate vasodilation elicited by endogenously elaborated and exogenously applied nitric oxide in the in situ peripheral microcirculation. Using intravital microscopy, we found that pretreatment with genistein (1.0 microM) and tyrphostin 25 (10.0 microM), two structurally unrelated tyrosine kinase inhibitors, significantly attenuated acetylcholine-, bradykinin- and nitroglycerin-induced dilation of second-order arterioles (51 +/- 1 microm) in the in situ hamster cheek pouch (P < 0.05). Both inhibitors nearly abrogated acetylcholine-induced responses but only partially blocked bradykinin- and nitroglycerin-induced vasodilation. Genistein and tyrphostin 25 alone had no significant effects on resting arteriolar diameter and on adenosine-induced vasodilation in the cheek pouch. On balance, these data indicate that tyrosine kinase inhibitors attenuate endogenously elaborated and exogenously applied nitric oxide-induced vasodilation in the in situ hamster cheek pouch. However, the extent of tyrosine kinase inhibitor-sensitive pathway involvement in this response appears to be agonist dependent.

Signaling mechanisms underlying the vascular myogenic response

The vascular myogenic response refers to the acute reaction of a blood vessel to a change in transmural pressure. This response is critically important for the development of resting vascular tone, upon which other control mechanisms exert vasodilator and vasoconstrictor influences. The purpose of this review is to summarize and synthesize information regarding the cellular mechanism(s) underlying the myogenic response in blood vessels, with particular emphasis on arterioles. When necessary, experiments performed on larger blood vessels, visceral smooth muscle, and even striated muscle are cited. Mechanical aspects of myogenic behavior are discussed first, followed by electromechanical coupling mechanisms. Next, mechanotransduction by membrane-bound enzymes and involvement of second messengers, including calcium, are discussed. After this, the roles of the extracellular matrix, integrins, and the smooth muscle cytoskeleton are reviewed, with emphasis on short-term signaling mechanisms. Finally, suggestions are offered for possible future studies.

Inhibition of Ca2+-dependent contraction in swine carotid artery by myosin kinase inhibitors

Experiments were designed to examine the efficacy of the MLCK inhibitors wortmannin and ML-9 in intact smooth muscle to determine whether contractile agonists can induce a Ca(2+) and myosin light chain phosphorylation-independent contraction. Both wortmannin and ML-9 reduced active stress in a dose-dependent manner. Both inhibitors interfered with Ca2+ mobilization in either the K(+)-depolarized or agonist activated swine carotid media at concentrations greater than 10 microM. Wortmannin reduced MRLC phosphorylation and stress to resting levels in stimulated tissues while Ca2+ remained above resting levels. There was no evidence for Ca2+ and MRLC phosphorylation-independent stress generation in swine arterial smooth muscle.

Role of tyrosine phosphorylation in the regulation of cerebral vascular tone in newborn pig in vivo

The role of tyrosine phosphorylation was investigated using protein tyrosine phosphatase inhibitors in newborn pigs equipped with a cranial window in vivo. We tested the hypothesis that cyclooxygenase and nitric oxide (NO) synthase are physiological targets for tyrosine phosphorylation in cerebral circulation. Phenylarsine oxide dilated pial arterioles and increased prostacyclin and prostaglandin E2 in cortical periarachnoid fluid; these responses were inhibited by indomethacin. Nomega-nitro-L-arginine methyl ester (L-NAME) and Nomega-nitro-L-arginine (L-NNA) inhibited the vasodilation to phenylarsine oxide; the effects of NO synthase inhibitors and indomethacin were additive. Cyclooxygenase-mediated vascular responses were assessed using topical application of arachidonic acid. Phenylarsine oxide and sodium orthovanadata potentiated vasodilation and prostanoid synthesis in response to arachidonic acid. Nomega-nitro-L-arginine methyl ester and Nomega-nitrol-arginine did not affect vasodilation or prostanoid production in response to arachidonic acid, indicating no cross talk between cyclooxygenase and NO synthase. These data indicate that cyclooxygenase and NO synthase are physiological targets for tyrosine phosphorylation in the cerebral circulation of newborn pigs.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Tyrosine kinase inhibitors suppress prostaglandin F2alpha-induced phosphoinositide hydrolysis, Ca2+ elevation and contraction in iris sphincter smooth muscle

We investigated the effects of the protein tyrosine kinase inhibitors, genistein, tyrphostin 47, and herbimycin on prostaglandin F2alpha- and carbachol-induced inositol-1,4,5-trisphosphate (IP3) production, [Ca2+]i mobilization and contraction in cat iris sphincter smooth muscle. Prostaglandin F2alpha and carbachol induced contraction in a concentration-dependent manner with EC50 values of 0.92 x 10(-9) and 1.75 x 10(-8) M, respectively. The protein tyrosine kinase inhibitors blocked the stimulatory effects of prostaglandin F2alpha, but not those evoked by carbachol, on IP3 accumulation, [Ca2+]i mobilization and contraction, suggesting involvement of protein tyrosine kinase activity in the physiological actions of the prostaglandin. Daidzein and tyrphostin A, inactive negative control compounds for genistein and tyrphostin 47, respectively, were without effect. Latanoprost, a prostaglandin F2alpha analog used as an antiglaucoma drug, induced contraction and this effect was blocked by genistein. Genistein (10 microM) markedly reduced (by 67%) prostaglandin F2alpha-stimulated increase in [Ca2+]i but had little effect on that of carbachol in cat iris sphincter smooth muscle cells. Vanadate, a potent inhibitor of protein tyrosine phosphatase, induced a slow gradual muscle contraction in a concentration-dependent manner with an EC50 of 82 microM and increased IP3 generation in a concentration-dependent manner with an EC50 of 90 microM. The effects of vanadate were abolished by genistein (10 microM). Wortmannin, a myosin light chain kinase inhibitor, reduced prostaglandin F2alpha- and carbachol-induced contraction, suggesting that the involvement of protein tyrosine kinase activity may lie upstream of the increases in [Ca2+]i evoked by prostaglandin F2alpha. Further studies aimed at elucidating the role of protein tyrosine kinase activity in the coupling mechanism between prostaglandin F2alpha receptor activation and increases in intracellular Ca2+ mobilization and identifying the tyrosine-phosphorylated substrates will provide important information about the role of protein tyrosine kinase in the mechanism of smooth muscle contraction, as well as about the mechanism of the intraocular pressure lowering effect of the prostaglandin in glaucoma patients.

Receptor-operated calcium influx mediated by protein tyrosine kinase pathways

Calcium influx from the extracellular space elicited by activation of heterotrimeric G protein-coupled and heptahelical receptors plays a critical role in transmembrane signal transduction in a wide variety of cell systems. In nonexcitable cells, the precise voltage-independent mechanism by which calcium enters the cell remains unknown. Multiple mechanisms appear to be operating in different cell types (1-3): 1. G protein-operated calcium influx, 2. Second messenger-operated calcium influx, 3. Capacitative calcium influx, and 4. Phosphorylation of calcium channels. Receptor-operated calcium channels have a fundamental role in stimulus-secretion coupling in many different cells, but these channels remain to be purified and cloned. This review proposes that receptor-operated calcium influx is mediated by protein tyrosine kinase pathways. The function of protein tyrosine kinase pathways and their interactions with other receptor-operated calcium influx mechanisms are described.

Genistein elicits biphasic effects on L-type Ca2+ current in feline atrial myocytes

A perforated patch recording method was used to determine the effects of genistein (Gen), a protein tyrosine kinase (PTK) inhibitor, on basal L-type Ca2+ current (ICa,L) in feline atrial myocytes. Gen (50 microM) elicited biphasic changes in ICa,L: an initial inhibition (-55 +/- 4%; phase 1) followed by a secondary stimulation (34 +/- 9%; phase 2) of ICa,L. Withdrawal of Gen elicited a further potentiation of ICa,L (152 +/- 19%; phase 3) above control (n = 46). In general, phase 1 inhibition and phase 3 potentiation varied directly with Gen concentration, and phase 2 stimulation exhibited biphasic concentration-dependent changes compared with control. When cells were dialyzed using a ruptured patch recording method, Gen elicited only inhibition of ICa,L; phases 2 and 3 were abolished. Vanadate (1 mM), an inhibitor of protein tyrosine phosphatase, abolished both Gen-induced inhibition and stimulation of ICa,L. Daidzein (50 microM), a weakly active analog of Gen, exerted no significant effects on ICa,L, and withdrawal of daidzein failed to potentiate ICa,L. In a few cells, Gen elicited a prominent vanadate-sensitive stimulation of ICa,L in the absence of any significant inhibition of ICa,L. Gen-induced changes in ICa,L were unaffected by either 100 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester (AM) or 1 microM ryanodine, agents that alter intracellular Ca2+; 4 microM H-89 or 50 microM Rp diastereomer of adenosine 3',5'-monophosphothioate (RP-cAMPS), inhibitors of protein kinase A (PKA); 0.1 microM calphostin C or 2 microM chelerythrine, inhibitors of protein kinase C (PKC); or 100 microM NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide (NO) synthase. We conclude that in feline atrial myocytes, Gen acts via membrane-bound PTKs to inhibit ICa,L and via cytosolic PTKs to stimulate ICa,L. Gen-induced changes in ICa,L are not related to changes in intracellular Ca2+ or to secondary interactions with either PKA, PKC, or NO signaling pathways. These results indicate that in atrial myocytes ICa,L is regulated by two independent and competing PTK signaling mechanisms.

Role of tyrosine kinase in dilator responses of rat basilar artery in vivo

We tested the hypothesis that dilator responses of the basilar artery to endothelium-dependent vasodilators are mediated by activation of tyrosine kinase in vivo. Using a cranial window in anesthetized rats, we examined responses of the basilar artery to acetylcholine and bradykinin. Topical application of acetylcholine and bradykinin increased diameter of the basilar artery in a concentration-related manner. Genistein, an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but inhibited vasodilatation in response to acetylcholine and bradykinin, without affecting vasodilatation produced by sodium nitroprusside. Tyrphostin 47, another inhibitor of tyrosine kinase, attenuated acetylcholine-induced dilatation of the basilar artery without affecting vasodilatation in response to sodium nitroprusside. Tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect acetylcholine-induced vasodilatation. Sodium orthovanadate, an inhibitor of tyrosine phosphatase, enhanced acetylcholine-induced dilatation of the basilar artery. These results suggest that dilator responses of the basilar artery to endothelium-dependent agonists, acetylcholine and bradykinin, are mediated in large part by activation of tyrosine kinase. Because vasodilatation produced by these agonists is mediated primarily by nitric oxide, activation of tyrosine kinase may have an important role in nitric oxide production in the basilar artery in vivo.

Role of tyrosine kinase in serotonin-induced constriction of the basilar artery in vivo

BACKGROUND AND PURPOSE

Serotonin is one of the most potent constrictors of cerebral blood vessels and is implicated in several pathological conditions, including migraine and cerebral ischemia. Recent evidence has suggested that tyrosine kinase is involved in vasocontractile responses. The objective of this study was to test the hypothesis that activation of tyrosine kinase contributes to serotonin-induced constriction of the basilar artery in vivo.

METHODS

Using a cranial window in anesthetized Sprague-Dawley rats, we examined effects of inhibitors of tyrosine kinase and tyrosine phosphatase on constrictor responses of the basilar artery to serotonin in vivo.

RESULTS

Serotonin (10(-8), 10(-7), and 10(-6) mol/L) produced constriction of the basilar artery by 12+/-2%, 27+/-2%, and 37+/-3%, respectively. Genistein (3 x 10(-6) mol/L), an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but attenuated serotonin-induced vasoconstriction (P<.05 versus control responses). Daidzein, an inactive analogue of genistein, did not affect serotonin-induced constriction of the basilar artery. Tyrphostin 47 (10(-5) mol/L), another inhibitor of tyrosine kinase, also attenuated serotonin-induced vasoconstriction, and tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect the vasoconstriction. Sodium orthovanadate (10(-5) mol/L), an inhibitor of tyrosine phosphatase, enhanced serotonin-induced vasoconstriction. Phorbol 12,13-dibutyrate, a direct activator of protein kinase C, also caused constriction of the basilar artery, which was not affected by genistein or sodium orthovanadate.

CONCLUSIONS

These results suggest that serotonin-induced constriction of the basilar artery is mediated, at least in part, by activation of tyrosine kinase in vivo.

Stimulation of G-protein coupled receptors in vascular smooth muscle cells induces tyrosine kinase dependent increases in calcium without tyrosine phosphorylation of phospholipase C gamma-1

It is often believed that increases in intracellular Ca2+ ([Ca2+]i) resulting from stimulation of G-protein coupled receptors in vascular smooth muscle cells (VSMC) require activation of the beta1 isoform of phospholipase C (PLC). However, recent studies showed that rat aortic VSMC do not express PLC beta-1 and that stimulation with angiotensin-II induces tyrosine kinase dependent increases in [Ca2+]i and tyrosine phosphorylation of PLC gamma-1. Whether this pathway is activated by other vasoactive agents that stimulate G-protein coupled receptors is unknown. Here, we show that A10 VSMC express PLC beta-2, PLC beta-3, PLC delta-1, and PLC gamma-1. The cells also expressed Galpha(q/11). However, neither PLC beta-1 nor PLC beta-4 was detected. Stimulation with angiotensin-II, vasopressin, serotonin, or endothelin induced tyrosine kinase dependent increases in [Ca2+]i. However, tyrosine phosphorylation of PLC gamma-1 did not occur. In contrast, stimulation with platelet derived growth factor increased [Ca2+]i and tyrosine phosphorylation of PLC gamma-1. The results show that tyrosine phosphorylation of PLC gamma-1 is not required for tyrosine kinase dependent increases in [Ca2+]i resulting from stimulation of diverse G-protein coupled receptors in VSMC.

Phyto-oestrogens and Western diseases

Incidences of breast, colorectal and prostate cancer are high in the Western world compared to countries in Asia. We have postulated that the Western diet compared to the semivegetarian diet in some Asian countries may alter hormone production, metabolism or action at the cellular level by some biochemical mechanisms. Our interest has been focused on two groups of hormone-like diphenolic phyto-oestrogens of dietary origin, the lignans and isoflavonoids abundant in plasma of subjects living in areas with low cancer incidence. The precursors of the biologically active compounds detected in man are found in soybean products, whole-grain cereal food, seeds, and berries. The plant lignan and isoflavonoid glycosides are converted by intestinal bacteria to hormone-like compounds. The weakly oestrogenic diphenols formed influence sex-hormone production, metabolism and biological activity, intracellular enzymes, protein synthesis, growth factor action, malignant cell proliferation, differentiation, cell adhesion and angiogenesis in such a way as to make them strong candidates for a role as natural cancer-protective compounds. Their effect on some of the most important steroid biosynthetic enzymes may result in beneficial modulation of hormone concentrations and action in the cells preventing development of cancer. Owing to their oestrogenic activity they reduce hot flushes and vaginal dryness in postmenopausal women and may to some degree inhibit osteoporosis, but alone they may be insufficient for complete protection. Soy intake prevents oxidation of the low-density lipoproteins in vitro when isolated from soy-treated individuals and affect favourably plasma lipid concentrations. Animal experiments provide evidence suggesting that both lignans and isoflavonoids may prevent the development of cancer as well as atherosclerosis. However, in some of these experiments it has not been possible to separate the phyto-oestrogen effect from the effect of other components in the food. The isoflavonoids and lignans may play a significant inhibitory role in cancer development particularly in the promotional phase of the disease, but recent evidence points also to a role in the initiation stage of carcinogenesis. At present, however, no definite recommendations can be made as to the dietary amounts needed for prevention of disease. This review deals with all the above-mentioned aspects of phyto-oestrogens.

Activation of cardiac chloride conductance by the tyrosine kinase inhibitor, genistein

1. Genistein (GST), an inhibitor of protein tyrosine kinase (PTK), Na3VO4 (VO4), an inhibitor of phosphotyrosine phosphatase (PTPase), and forskolin (FSK), an activator of the cyclic AMP-dependent, cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel, were applied to guinea-pig ventricular myocytes to probe for a possible role of tyrosine phosphorylation in the regulation of cardiac Cl- channels. 2. Myocytes in the standard whole-cell configuration were pulsed to various potentials and Cl- current (ICl) measured as the difference from control background current. GST (1-500 microM) activated a current that had similar biophysical properties (time- and voltage-independent; Cl(-)-dependent reversal potential and outward rectification) as ICl activated by 5 microM FSK. The EC50 for activation of Cl- conductance (gCl) by GST was approximately 100 microM, and gCl activated by GST (500 microM) was as large as gCl activated by maximally-effective FSK (5 microM). Daidzein, a GST analogue with little effect on PTK, was at least one order less effective than GST. 3. GST responses were rapidly and reversibly inhibited by 0.1-1 mM VO4 treatments that had little effect on FSK-activated ICl. 4. Niflumic acid (100-200 microM) reversibly depressed GST (100 microM)-activated gCl by 55%. 5. GST (50 microM) strongly incremented current in myocytes with cyclic AMP-dependent CFTR ICl already activated by maximally-effective FSK 5 microM. 6. Based on these results, and on evidence of a synergistic interaction between GST and FSK, we conclude that inhibition of tyrosine phosphorylation by GST causes an activation of cardiac CFTR that is not mediated by an elevation of cyclic AMP.