Non-receptor cytosolic protein tyrosine kinases from various rat tissues

Hypoglycemic, Hypolipidemic, and Wound Healing Potential of Quercetin in Streptozotocin-Induced Diabetic Rats

Background:

Among the dietary polyphenolic, quercetin is the most common compound available in vegetables and fruits. The phytochemicals are used to treat diabetic wounds and diabetes, and specifically dietary polyphenols are being extensively studied for their anti-inflammatory and antioxidant abilities.

Objective:

The objective of the study was to assess the hypoglycemic, hypolipidemic, and wound healing potential of quercetin in streptozotocin (STZ)-induced diabetic Wistar rats.

Materials and Methods:

Induction of diabetes was done by intraperitoneally administration of STZ at the dose of 55 mg/kg in Wistar rats. An excision wound was created in diabetic rats that were treated with quercetin (100 mg/kg) orally and quercetin ointment topically to evaluate the antidiabetic and wound healing potential of quercetin.

Results:

Repeated oral administration of quercetin along with topical application of quercetin ointment in diabetic rats normalized the altered blood glucose, hydroxyproline, and glucosamine levels. Topical application of quercetin ointment alone on the excised wound was sufficient enough to heal the wound area in diabetic rats.

Conclusions:

The result of the present study indicates that quercetin produces hypoglycemic effect in STZ-induced diabetic rats and normalized plasma lipids and protein profiles. Besides, this quercetin also has an excellent wound healing property when applied topically on the wound area in diabetic rats.

SUMMARY

Quercetin has hypoglycaemic and hypolipidemic potential in streptozotocin induced diabetes in wistar rats

Dermal application along with oral administrations of quercetin has more effective in wound healing in diabetic animals

Histopathological studies of pancreas, skin and liver shows significant reduction in archaeological alterations on quercetin administrations in diabetic rats.

Abbreviation used: STZ: Streptozotocin; CMC: Carboxy methyl cellulose; HDL: High density lipoproteins; LDL: low density lipoproteins.

Tyrosine phosphorylation modulates the vascular responses of mesenteric arteries from human colorectal tumors

The aim of this study was to analyze whether tyrosine phosphorylation in tumoral arteries may modulate their vascular response. To do this, mesenteric arteries supplying blood flow to colorectal tumors or to normal intestine were obtained during surgery and prepared for isometric tension recording in an organ bath. Increasing tyrosine phosphorylation with the phosphatase inhibitor, sodium orthovanadate produced arterial contraction which was lower in tumoral than in control arteries, whereas it reduced the contraction to noradrenaline in tumoral but not in control arteries and reduced the relaxation to bradykinin in control but not in tumoral arteries. Protein expression of VEGF-A and of the VEGF receptor FLT1 was similar in control and tumoral arteries, but expression of the VEGF receptor KDR was increased in tumoral compared with control arteries. This suggests that tyrosine phosphorylation may produce inhibition of the contraction in tumoral mesenteric arteries, which may increase blood flow to the tumor when tyrosine phosphorylation is increased by stimulation of VEGF receptors.

α-Synuclein, leucine-rich repeat kinase-2, and manganese in the pathogenesis of Parkinson disease

Parkinson disease (PD) is the most common movement disorder. It is characterized by bradykinesia, postural instability, resting tremor, and rigidity associated with the progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Another pathological hallmark of PD is the presence of α-synuclein proteiniacous inclusions, known as Lewy bodies and Lewy neurites, in some of the remaining dopaminergic neurons. Mounting evidence indicates that both genetic and environmental factors contribute to the etiology of PD. For example, genetic mutations (duplications, triplications or missense mutations) in the α-synuclein gene can lead to PD, but even in these patients, age-dependent physiological changes or environmental exposures appear to be involved in disease presentation. Several additional alterations in many other genes have been established to either cause or increase the risk of parkinson disease. More specifically, autosomal dominant missense mutations in the gene for leucine-rich repeat kinase 2 (LRRK2/PARK8) are the most common known cause of PD. Recently it was shown that G2019S, the most common diseasing-causing mutant of LRRK2, has dramatic effects on the kinase activity of LRRK2: while activity of wild-type LRRK2 is inhibited by manganese, the G2019S mutation abrogates this inhibition. Based on the in vitro kinetic properties of LRRK2 in the presence of manganese, we proposed that LRRK2 may be a sensor of cytoplasmic manganese levels and that the G2019S mutant has lost this function. This finding, alongside a growing number of studies demonstrating an interaction between PD-associated proteins and manganese, suggest that dysregulation of neuronal manganese homeostasis over a lifetime can play an important role in the etiology of PD.

The G2019S pathogenic mutation disrupts sensitivity of leucine-rich repeat kinase 2 to manganese kinase inhibition

Mutations in leucine-rich repeat kinase-2 (LRRK2) are the most common cause of late-onset Parkinson disease. Previously, we showed that the G2019S pathogenic mutation can cause a dramatic increase (approximately 10-fold) in kinase activity, far above other published studies. A notable experimental difference was the use of Mn-ATP as a substrate. Therefore, the effects of metal cation-ATP cofactors on LRRK2 kinase activity were investigated. It is shown, using several divalent metal cations, that only Mg(2+) or Mn(2+) can support LRRK2 kinase activity. However, for wild-type, I2020T, and R1441C LRRK2, Mn(2+) was significantly less effective at supporting kinase activity. In sharp contrast, both Mn(2+) and Mg(2+) were effective at supporting the activity of G2019S LRRK2. These divergent effects associated with divalent cation usage and the G2019S mutation were predominantly because of differences in catalytic rates. However, LRRK2 was shown to have much lower (approximately 40-fold) ATP K(m) for Mn-ATP compared with Mg-ATP. Consequently, sub-stoichiometric concentrations of Mn(2+) can act to inhibit the kinase activity of wild-type, but not G2019S LRRK2 in the presence of Mg(2+) . From these findings, a new model is proposed for a possible function of LRRK2 and the consequence of the G2019S LRRK2 pathogenic mutation.

Tungsten effects on phosphate-dependent biochemical pathways are species and liver cell line dependent

Tungsten, in the form of tungstate, polymerizes with phosphate, and as extensive polymerization occurs, cellular phosphorylation and dephosphorylation reactions may be disrupted, resulting in negative effects on cellular functions. A series of studies were conducted to evaluate the effect of tungsten on several phosphate-dependent intracellular functions, including energy cycling (ATP), regulation of enzyme activity (cytosolic protein tyrosine kinase [cytPTK] and tyrosine phosphatase), and intracellular secondary messengers (cyclic adenosine monophosphate [cAMP]). Rat noncancerous hepatocyte (Clone-9), rat cancerous hepatocyte (H4IIE), and human cancerous hepatocyte (HepG2) cells were exposed to 1-1000 mg/l tungsten (in the form of sodium tungstate) for 24 h, lysed, and analyzed for the above biochemical parameters. Cellular ATP levels were not significantly affected in any cell line. After 4 h, tungsten significantly decreased cytPTK activity in Clone-9 cells at >or= 18 mg/l, had no effect in H4IIE cells, and significantly increased cytPTK activity by 70% in HepG2 cells at >or= 2 mg/l. CytPTK displayed a slight hormetic response to tungsten after 24-h exposure yet returned to normal after 48-h exposure. Tungsten significantly increased cAMP by over 60% in Clone-9 cells at >or= 100 mg/l, significantly increased cAMP in H4IIE cells at only 100 mg/l, and significantly increased cAMP in HepG2 cells between 1-100 mg/l but at much more modest levels (8-20%). In conclusion, these data indicate that tungsten produces complex results that must be carefully interpreted in the context of their respective animal models, as well as the phenotype of the cell lines (i.e., normal vs. cancerous).

Interactions of methoxyacetic acid with androgen receptor

Endocrine disruptive compounds (EDC) alter hormone-stimulated, nuclear receptor-dependent physiological and developmental processes by a variety of mechanisms. One recently identified mode of endocrine disruption is through hormone sensitization, where the EDC modulates intracellular signaling pathways that control nuclear receptor function, thereby regulating receptor transcriptional activity indirectly. Methoxyacetic acid (MAA), the primary, active metabolite of the industrial solvent ethylene glycol monomethyl ether and a testicular toxicant, belongs to this EDC class. Modulation of nuclear receptor activity by MAA could contribute to the testicular toxicity associated with MAA exposure. In the present study, we evaluated the impact of MAA on the transcriptional activity of several nuclear receptors including the androgen receptor (AR), which plays a pivotal role in the development and maturation of spermatocytes. AR transcriptional activity is shown to be increased by MAA through a tyrosine kinase signaling pathway that involves PI3-kinase. In a combinatorial setting with AR antagonists, MAA potentiated the AR response without significantly altering the EC(50) for androgen responsiveness, partially alleviating the antagonistic effect of the anti-androgens. Finally, MAA treatment of TM3 mouse testicular Leydig cells markedly increased the expression of Cyp17a1 and Shbg while suppressing Igfbp3 expression by ~90%. Deregulation of these genes may alter androgen synthesis and action in a manner that contributes to MAA-induced testicular toxicity.

Src family tyrosine kinases mediate contraction of rat isolated tail arteries in response to a hyposmotic stimulus

OBJECTIVE

Hypotonic solutions cause vasoconstriction in rat tail arteries, due largely to activation of L-type calcium channels (CaV1.2). We studied possible roles of tyrosine kinases, particularly src family kinases (SFK) and extracellular signal-related kinases (ERK1/2), in this response.

METHODS

Rat tail arteries were mounted on a myograph for measurement of isometric force. Arteries were bathed in isosmotic physiological saline solution (300 mOsm/l) containing 50 mmol/l mannitol and were stimulated by a hyposmotic solution containing 0 mmol/l mannitol (PSS-M). Activation of tyrosine kinases and ERK1/2 by hyposmotic solution was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting on rat tail artery lysates with specific phospho-antibodies.

RESULTS

Western blotting showed SFK src and yes present in rat tail artery. PSS-M increased tyrosine phosphorylation of several proteins, including SFK and ERK1/2. Genistein blocked phosphorylation of SFK and ERK1/2 by PSS-M. In isolated arteries PSS-M caused a contraction inhibited by the tyrosine kinase inhibitor, genistein, and three structurally different selective SFK inhibitors, herbimycin-A, PP1 and SU6656. Mitogen-activated protein kinase kinase inhibitor PD98059 or selective inhibitors of platelet-derived growth factor receptor (AG1296) and epidermal growth factor receptor (AG1478) had no effect on contraction induced by a hypotonic solution.

CONCLUSIONS

Hyposmotic conditions activate SFK, src and yes, and contract rat tail artery by a SFK-dependent mechanism. ERK1/2 are activated by the hypotonic solution, but do not play a role in the contractile response. SFK modulation of CaV1.2 may be an important mechanism mediating vasoconstriction to mechanical stimuli in vascular smooth muscle.

Interactions between NMDA receptors and mGlu5 receptors expressed in HEK293 cells

1 Ca2+ imaging was used to investigate interactions between responses induced by N-methyl-D-aspartate (NMDA; 15 microm) and (RS)-3,5-dihydroxyphenyl-glycine (DHPG; 30 microm) in human embryonic kidney (HEK) 293 cells, transiently transfected with rat recombinant NR1a, NR2A and mGlu5a cDNA. 2 Responses to NMDA were reversibly depressed by DHPG from 244+/-14 to 194+/-12% of baseline. Treatment with thapsigargin (1 microm, 10 min) prevented this effect. 3 After thapsigargin pretreatment, repeated applications of NMDA showed a gradual rundown in amplitude over a period of several hours, and were unaffected by DHPG. 4 Continuous perfusion with staurosporine (0.1 microm), after thapsigargin pretreatment, converted the run-down to a small increase in NMDA responses to 123+/-6 % of baseline. DHPG induced a further and sustained potentiation of NMDA responses to 174+/-12% of the initial baseline. 5 The protein tyrosine kinase (PTK) inhibitors genistein (50 microm) and 3-(4-chlorophenyl)1-(1,1-dimethylethyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (PP2; 1 microm) inhibited the staurosporine- and DHPG-induced potentiation of NMDA responses. 6 The protein phosphatase (PTP) inhibitors orthovanadate (100 microm) and phenyl arsine oxide (PAO, 1 microm) facilitated the staurosporine-evoked potentiation of NMDA responses and occluded DHPG-induced potentiation. 7 In conclusion, complex interactions can be demonstrated between mGlu5 and NMDA receptors expressed in HEK293 cells. There is a negative inhibitory influence of Ca2+ release and PKC activation. Inhibition of these processes reveals a tonic, mGlu5 receptor and PTK-dependent potentiation of NMDA receptors that can be augmented by either stimulating mGlu5 receptors or by inhibiting PTPs.

Effect of tyrosine kinase blockade on norepinephrine-induced cytosolic calcium response in rat afferent arterioles

We used genistein (Gen) and tyrphostin 23 (Tyr-23) to evaluate the importance of tyrosine phosphorylation in norepinephrine (NE)-induced changes in intracellular free calcium concentration ([Ca(2+)](i)) in rat afferent arterioles. [Ca(2+)](i) was measured in microdissected arterioles using ratiometric photometry of fura 2 fluorescence. The control [Ca(2+)](i) response to NE (1 microM) consisted of a rapid initial peak followed by a plateau phase sustained above baseline. Pretreatment with the tyrosine kinase inhibitor Tyr-23 (50 microM, 10 min) caused a slow 40% increase in baseline [Ca(2+)](i). Tyr-23 attenuated peak and plateau responses to NE, both by approximately 70%. In the absence of extracellular Ca(2+) (0 Ca), Tyr-23 reduced the immediate [Ca(2+)](i) response to NE by approximately 60%, indicative of mobilization of internal stores, and abolished the plateau phase. In other arterioles, the [Ca(2+)](i) response to depolarization induced by KCl (50 mM) was not attenuated by Tyr-23, indicating no direct effect on L-type Ca(+) channels activated by depolarization. The Ca(2+) channel blocker nifedipine (1 microM) inhibited the NE response by approximately 50%; the effects of nifedipine and Tyr-23 were not additive. Nifedipine had no inhibitory effect after Tyr-23 pretreatment, indicating Tyr-23 inhibition of Ca(2+) entry. Another tyrosine kinase inhibitor, Gen (5 and 50 microM), did not affect baseline [Ca(2+)](i). High-dose Gen inhibited the peak and plateau response to NE by 87 and 75%, respectively; low-dose Gen attenuated both responses by approximately 20%. In 0 Ca, Gen (50 microM) abolished the immediate [Ca(2+)](i) mobilization response. Combined nifedipine and Gen (50 microM) inhibited the rapid NE response by approximately 90% in the presence of extracellular Ca(2+). Gen (50 microM) also inhibited by 60% the [Ca(2+)](i) response to 50 mM KCl, indicating a direct interaction with voltage-sensitive, L-type Ca(2+) entry channels. These results indicate that tyrosine phosphorylation is an important link in the chain of events leading to alpha-adrenoceptor-induced Ca(2+) recruitment (both entry and release) in afferent arteriolar smooth muscle cells. Furthermore, different blockers of tyrosine kinase appear to have different modes of action in renal microvessels.

Intraluminal pressure stimulates MAPK phosphorylation in arterioles: temporal dissociation from myogenic contractile response

Members of the MAPK family of enzymes, p42/44 and p38, have been implicated in both the regulation of contractile function and growth responses in vascular smooth muscle. We determined whether such kinases are activated during the arteriolar myogenic response after increases in intraluminal pressure. Particular emphasis was placed on temporal aspects of activation to determine whether such phosphorylation events parallel the known time course for myogenic contraction. Experiments used single cannulated arterioles isolated from the cremaster muscle of rats with some vessels loaded with the fluorescent Ca2+-sensitive dye fura 2 (2 microM). The p42/44 inhibitor PD-98059 (50 microM) caused vasodilation but did not prevent pressure-induced myogenic constriction. The vasodilator response was accompanied by decreased smooth muscle intracellular Ca2+. Western blotting revealed a significant increase in the level of phosphorylation of p42/44 15 min after the application of a 30- to 100-mmHg pressure step. Phosphorylation of p42/44 was a late event that appeared to be temporally dissociated from contraction, which was complete within 1-5 min. EGF (80 nM) caused marked phosphorylation of p42/44 but only acted as a weak vasoconstrictor. The p38 inhibitor SB-203580 (10 microM) did not alter baseline diameter, nor did it prevent myogenic vasoconstriction. Consistent with these observations, SB-203580 did not cause a measurable change in intracellular Ca2+. The results demonstrate activation of the p42/44 class of MAPK resulting from increased transmural pressure. Such activation is, however, dissociated from the acute pressure-induced vasoconstrictor response in terms of time course and may represent the activation of compensatory, but parallel, pathways, including those related to growth and remodeling.

Life in the slow lane: molecular mechanisms of estivation

Estivation is a state of aerobic hypometabolism used by organisms to endure seasonally arid conditions, often in desert environments. Estivating species are often active for only a few weeks each year to feed and breed and then retreat to estivate in sheltered sites, often underground. In general, estivation includes a strong reduction in metabolic rate, a primary reliance on lipid oxidation to fuel metabolism, and methods of water retention, both physical (e.g. cocoons) and metabolic (e.g. urea accumulation). The present review focuses on several aspects of metabolic adaptation during estivation including changes in the activities of enzymes of intermediary metabolism and antioxidant defenses, the effects of urea on estivator enzymes, enzyme regulation by reversible protein phosphorylation, protein kinases and phosphatases involved in signal transduction mechanisms, and the role of gene expression in estivation. The focus is on two species: the spadefoot toad, Scaphiopus couchii, from the Arizona desert; and the land snail, Otala lactea, a native of the Mediterranean region. The mechanisms of metabolic depression in estivators are similar to those seen in hibernation and anaerobiosis, and contribute to the development of a unified set of biochemical principles for the control of metabolic arrest in nature.

Coupling of M2 muscarinic receptor to L-type Ca channel via c-src kinase in rabbit colonic circular smooth muscle

BACKGROUND & AIMS

The L-type Ca(2+) channel is a major pathway for Ca(2+) influx in colonic smooth muscle and is modulated by endogenous levels of nonreceptor tyrosine kinase, c-src. Tyrosine kinases are also activated by G-protein-coupled receptors (GPCR). This study determined whether muscarinic receptor couples to Ca(2+) channels via c-src kinase.

METHODS

Currents were measured in rabbit colonic smooth muscle cells and in transfected HEK293 cells by patch-clamp technique. Tyrosyl phosphorylated proteins were detected by Western blots and the interaction of c-src with the c-terminus of alpha subunit of Ca(2+) channel was determined by a GST pull-down assay.

RESULTS

Methacholine (10 micromol/L) enhanced Ca(2+) channel currents by 30% under conditions whereby the M(3) receptor pathway was blocked by either 4-DAMP or by intracellular dialysis with anti-Galphaq antibody. Similar effects were observed by blocking intracellular Ca(2+) release with heparin. Enhancement was abolished by intracellular anti-Galphai antibody and by the c-src inhibitor, PP2 but unaffected by the inactive analog PP3. Immunoblot with anti-src antibody revealed increased src phosphorylation by muscarinic receptor stimulation. Purified c-src directly associated with the c-terminus of alpha1c subunit of the Ca(2+) channel. In M(2) receptor transfected HEK293 cells, currents were enhanced 2-fold by carbachol.

CONCLUSIONS

These studies demonstrate stimulation of Ca(2+) current in colonic smooth muscle cells by M2 receptor coupled to Galphai-G protein and c-src activation. They also suggest a central role of c-src kinase in the cross-talk between tyrosine kinase receptor and GPCR.

Cellular signalling in arteriolar myogenic constriction: involvement of tyrosine phosphorylation pathways

1. An increase in transmural pressure in arterioles results in a shortening of vascular smooth muscle cells, with subsequent constriction of the vessel. The mechanisms underlying this myogenic contraction are not fully understood; however, the obligatory role of increases in intracellular [Ca(2+)] and myosin light chain phosphorylation have been demonstrated. 2. The myogenic response shows a relationship with smooth muscle cell membrane potential and influx of extracellular Ca(2+) through voltage-operated Ca(2+) channels (VOCC). Mechanically sensitive channels and possibly release of Ca(2+) from intracellular stores may play a role. However, there are other components of myogenic contraction that cannot be explained by a Ca(2+)-MLCK mechanism, for example the initial sensing of alterations in transmural pressure, whether sustained myogenic constriction involves myofilament Ca(2+) sensitization or remodelling of the vessel wall in response to a maintained increase in transmural pressure. 3. In an attempt to investigate these areas, recent studies have examined a role for tyrosine phosphorylation pathways in pressure-induced contraction of arterioles. In rat pressurized cremaster arterioles, tyrosine kinase inhibitors dilated vessels showing spontaneous myogenic tone and tyrosine phosphatase inhibitors caused vasoconstriction. However, pressure-induced myogenic constriction of vessels persisted in the presence of these agents. Biochemical studies revealed that phosphotyrosine formed at a relatively slow rate (significant after 5 min, with maximal increase after approximately 15 min) in response to increased vessel transmural pressure, in contrast with myosin light chain phosphorylation or the time-course of myogenic constriction itself (maximum within 1 min). 4. Taken together, these observations support the idea of a role for tyrosine phosphorylation pathways in longer-term responses to increased transmural pressure rather than acute myogenic constriction. Phosphotyrosine formation was also more closely correlated to vessel wall tension (pressure x diameter) than the diameter of the arterioles alone. The identity of the tyrosine-phosphorylated proteins requires further investigation; however, there is some evidence supporting roles for cSrc-type tyrosine kinases and p44 mitogen-activated protein kinase. The longer-term responses of blood vessels to increased transmural pressure that may involve tyrosine phosphorylation pathways include maintenance of myogenic constriction and vessel wall remodelling.

Mechanisms underlying pervanadate-induced contraction of rat cremaster muscle arterioles

The current study examined the role of extracellular Ca2+, calmodulin and myosin light-chain kinase (MLCK) in pervanadate-induced constriction of cannulated, pressurized rat cremaster arterioles. Pervanadate (0.03-100 microM) induced a concentration-dependent constriction of arterioles that was significantly attenuated (P<0.05) by the tyrosine kinase inhibitor tyrphostin 47 (30 microM). The L-type voltage-sensitive Ca2+ channel antagonists verapamil (10 microM) and nifedipine (1 microM) dilated vessels possessing myogenic tone but had no demonstrable effect on pervanadate constriction, while a higher concentration of nifedipine (10 microM) reduced constriction by approximately 50%. Pervanadate-induced contractions were reduced by the calmodulin inhibitor W-7 (N-(6-aminohexyl)-chloro-1-naphtalene sulphonamide, 50 microM) and the MLCK inhibitor ML-7 (1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine, 10 or 30 microM). Removal of extracellular Ca2+ abolished the contractile effect of pervanadate. Measurement of changes in arteriolar wall [Ca2+] using the Ca2+ sensitive dye Fura-2 showed that pervanadate did not increase [Ca2+] during arteriolar constriction. These observations suggest that pervanadate-induced contraction of smooth muscle in the cremaster arteriole involves Ca2+/calmodulin-dependent myosin phosphorylation and possibly sensitization of the contractile apparatus to Ca2+.

Different Forms of Vanadate on Sugar Transport in Insulin Target and Nontarget Cells

The effects of several vanadates (ie, orthovanadate, pervanadate, and two stable peroxovanadium compounds) on basal and insulin-stimulated 2-DG transport in insulin target and nontarget cell lines are reported, herein. In nontarget cells, exposure to vanadates (5 x 10(-6) to 10(-4) mol/L) resulted in 2-DG transport stimulatory responses similar to those observed in 2-DG transport post exposure to 667 nmol/L insulin alone, or insulin in combination with vanadates. In 3T3-L1 adipocytes and L6 myotubes, exposure to a vanadate compound or 67 nmol/L insulin, stimulated 2-DG transport dramatically. Again, this effect on stimulated transport was similar to 2-DG transport post-treatment with the effective vanadates in combination with insulin. While pervanadate or stable peroxovanadates stimulated 2-DG transport at 10(-5) to 10(-6) mol/L, orthovanadate up to 10(-4) mol/L was not effective in stimulating 2-DG transport in any of the cell lines tested. The data indicate that the various peroxovanadates are clearly superior insulin mimetics while a more limited insulin mimesis is observed with orthovanadate over a wide variety of cell types.

Tyrosine phosphorylation following alterations in arteriolar intraluminal pressure and wall tension

Arterioles respond to increased transmural pressure with myogenic constriction. The present study investigated the role of tyrosine phosphorylation in myogenic activity. Cannulated segments of a rat cremaster arteriole were fixed under pressure, followed by incubation with fluorescein isothiocyanate (FITC)-conjugated anti-phosphotyrosine. Smooth muscle cell fluorescence intensity was measured with the use of confocal laser-scanning microscopy. Anti-phosphotyrosine fluorescence intensity in muscle cells of arterioles maintained at 100 mmHg was reduced by the tyrosine kinase inhibitor tyrphostin A47 (30 microM) and increased by the tyrosine phosphatase inhibitor pervanadate (100 microM). In time-course experiments, anti-phosphotyrosine fluorescence increased slowly (over 5 min) after an acute increase in intraluminal pressure, and was dissociated from myogenic contraction (within 1 min). In contrast, angiotensin II (0.1 microM) caused rapid constriction and increased tyrosine phosphorylation. Anti-phosphotyrosine fluorescence was also pressure dependent (10-100 mmHg). Abolition of myogenic activity, either through removal of extracellular Ca2+, or exposure to verapamil (5 microM) or forskolin (0.1 microM) caused a further increase in anti-phosphotyrosine fluorescence. We conclude that transmural pressure and/or wall tension in arterioles causes increased tyrosine phosphorylation; however, this is not involved in the acute phase of myogenic constriction but may be involved in later responses, such as sustained myogenic tone or mechanisms possibly related to growth.

Type 1 protein tyrosine kinases in Chinese breast carcinomas: a clinicopathologic study

Immunostaining for epidermal growth factor receptor (EGFR), c-erbB-2, c-erbB-3, c-erbB-4, ER, and PR was performed in 107 cases of primary breast carcinomas from Anyang, China. The expression rates of EGFR, c-erbB-2, c-erbB-3 and c-erbB-4 in this series were 43.9%, 36%, 27%, and 45.8%, respectively, and a stronger c-erbB-4 staining of "normal" glandular structures inside tumors and in the vicinity of tumor clusters was confirmed. Larger tumor size, lymph node metastases, and higher histologic grade in invasive ductal carcinomas were shown to be statistically valuable negative prognostic factors, and c-erbB-2 expression was also weakly associated with a poor prognosis no matter what the nodal status. The expressions of c-erbB-4 and ER in invasive ductal carcinomas were inversely associated with histologic grade of the tumors. Associations between the expression of c-erbB-4 and ER (p = 0.001) and the expression of ER and PR study (p = 0.004) were found in the present study. No significant associations between the expressions of EGFR, c-erbB-3, c-erbB-4, ER, and PR and overall survival were detected. The expression of c-erbB-4 in the node negative group was, however, associated with a better prognosis, indicating a different role of c-erbB-4 protein in breast tumor development than other EGFR family members have. Int J Surg Pathol 9(3):177-187, 2001

Insulin-stimulated hydrogen peroxide reversibly inhibits protein-tyrosine phosphatase 1b in vivo and enhances the early insulin action cascade

The insulin signaling pathway is activated by tyrosine phosphorylation of the insulin receptor and key post-receptor substrate proteins and balanced by the action of specific protein-tyrosine phosphatases (PTPases). PTPase activity, in turn, is highly regulated in vivo by oxidation/reduction reactions involving the cysteine thiol moiety required for catalysis. Here we show that insulin stimulation generates a burst of intracellular H(2)O(2) in insulin-sensitive hepatoma and adipose cells that is associated with reversible oxidative inhibition of up to 62% of overall cellular PTPase activity, as measured by a novel method using strictly anaerobic conditions. The specific activity of immunoprecipitated PTP1B, a PTPase homolog implicated in the regulation of insulin signaling, was also strongly inhibited by up to 88% following insulin stimulation. Catalase pretreatment abolished the insulin-stimulated production of H(2)O(2) as well as the inhibition of cellular PTPases, including PTP1B, and was associated with reduced insulin-stimulated tyrosine phosphorylation of its receptor and high M(r) insulin receptor substrate (IRS) proteins. These data provide compelling new evidence for a redox signal that enhances the early insulin-stimulated cascade of tyrosine phosphorylation by oxidative inactivation of PTP1B and possibly other tyrosine phosphatases.

Effects of protein tyrosine kinase inhibitors on voltage-operated calcium channel currents in vascular smooth muscle cells and pp60(c-src) kinase activity

1. Tyrosine kinases have been proposed as regulators of voltage-operated calcium channels. The effects of a range of structurally different inhibitors of protein tyrosine kinases (PTK) were examined on voltage-operated calcium channel currents (I(Ba)) and pp60(c-src) kinase (c-src) activity in vitro. 2. I(Ba) was measured in single myocytes isolated from rabbit ear artery by conventional whole cell voltage-clamp techniques. The activity of purified human c-src was measured in vitro using a non-radioactive assay. 3. Bath application of tyrphostin-23 and genistein (non-selective PTK inhibitors), bistyrphostin (a receptor-PTK-selective inhibitor) and PP1 (a src family-selective inhibitor) inhibited I(Ba) in a concentration-dependent manner over a range of test membrane potentials. Intracellular application of peptide-A, a peptide inhibitor of c-src also inhibited currents. Inhibitor potency series against I(Ba) was PP1 > genistein > tyrphostin 23 > bistyrphostin. 4. Tyrphostin-23, genistein, PP1, and peptide-A shifted the steady-state inactivation curves in a hyperpolarized direction without altering their slope. The inhibitors had no significant effects on I(Ba) activation calculated from current-voltage relationships. 5. The agents inhibited c-src activity in a concentration-dependent manner. The order of potency was PP1 > genistein > peptide-A > tyrphostin-23 > bistyrphostin. The IC(50) for inhibition of c-src activity was similar to the IC(50) for inhibition of I(Ba) in all cases. 6. Western blot analysis with a specific antibody to c-src showed the presence of this cytoplasmic tyrosine kinase in rabbit ear artery cells. 7. A range of structurally dissimilar inhibitors of PTKs inhibit I(Ba) and c-src activity with similar potency. These data provide further evidence implicating endogenous c-src in the modulation of L-type calcium channels in vascular smooth muscle cells.

Tissue specific expression of Yrk kinase: implications for differentiation and inflammation

The Src family of proto-oncogenes is a highly conserved group of non-receptor tyrosine kinases with very similar, but not identical, tissue distributions and functions. Yrk is a recently discovered new member of this family. Here we report the patterns of expression of this kinase in a variety of chicken tissues during development and after hatching, and experiments that correlate some of the observed patterns of expression with potential functions. The results show that the Yrk protein is primarily found in neuronal and epithelial cells and in monocyte/macrophages. In neuronal tissues of hatched chicks, Yrk is expressed in Purkinje cells, in the gigantocellularis of the brain-stem, and in retinal ganglion cells. In addition, staining for this kinase is also seen as thread-like and punctate patterns suggesting staining in neurites and growth cones. Epithelial cells express Yrk in the stomach during late developmental stages and after hatching but, in other epithelia such as in the peridermis, intestine and kidney, expression is high during development but low (skin) or undetectable (intestine and kidney) after hatching. These results suggest that Yrk may have several functional roles, specifically in cell migration and or differentiation during neuronal and epithelial cell development and in maintenance of the differentiated phenotype. In this study we also show that significant levels of Yrk are detected in monocytes of the blood and in tissue macrophages. Analysis of chicken hematopoietic cell lines confirmed the expression of Yrk in cells of monocyte/macrophage lineage and show for the first time in experimentally-induced inflammation that Yrk kinase activity is high during the period of monocyte infiltration, raising the possibility that this kinase plays a role in inflammation and/or response to injury.

Rat testicular Src: normal distribution and involvement in ethylene glycol monomethyl ether-induced apoptosis

Kinase activities were previously proposed to be central to germ cell apoptosis induced by ethylene glycol monomethyl ether (EGME) and its active metabolite methoxyacetic acid (MAA). We evaluated the role of tyrosine kinase pp60(c-src) in control and EGME-treated adult rat testis in vivo, as well as in vitro using cultured adult rat seminiferous tubules treated with MAA. In normal testicular tissue, immunoreactivity of Src was mostly detected in Sertoli cell cytoplasm and reached the maximum level around the lumen at spermiation. Src localization was confirmed by immunostaining of cocultures of Sertoli and germ cells and was further confirmed by electron microscopic observation that immunoreactivity was predominant in Sertoli cell cytoplasm as well as occasionally at the Sertoli/germ cell junctions. A single dose of 200 mg/kg EGME induced an increase of Src immunoexpression in both epithelium and interstitium in rat testis. Eight hours after treatment, an intensive immunostaining of Src began to be observed specifically in the cytoplasm of the dying spermatocytes. The apoptotic changes were replicated by exposure of 5 mM MAA in the adult rat seminiferous tubule culture model. Furthermore, spermatocyte degeneration was significantly prevented by cotreatment with 0.1 microM geldanamycin, 10 microM herbimycin A, or 10 microM PP2, which are inhibitors of Src activity. These data collectively suggest that pp60(c-src) mediates Sertoli-germ cell interaction in physiological events, and may play an important role in EGME/MAA-induced germ cell apoptosis.

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.