Pervanadate stimulates amylase release and protein tyrosine phosphorylation of paxillin and p125(FAK) in differentiated AR4-2J pancreatic acinar cells

Hyperphosphorylated FAK Delocalizes from Focal Adhesions to Membrane Ruffles

Cell adhesion and migration are key determinants in tumor metastasis. Adherence of tumor cell to the extracellular matrix is mediated via integrin containing focal adhesions (FAs). Binding of integrins to ECM triggers phosphorylation of two major components of FAs, focal adhesion kinase (FAK) and Src, activating downstream signaling pathway which leads to FA disassembly and cell migration. In this paper, we analyze how phosphorylation of FAK regulates its trafficking at FAs in living human astrocytoma cells. Upon pervanadate-induced FAK phosphorylation, phosphorylated FAK appeared highly expressed at newly formed membrane ruffles. This effect was abolished in presence of the specific Src inhibitor PP2. Our findings demonstrate that upon phosphorylation, FAK delocalizes from FAs to membrane ruffles.

Enhanced expression of interleukin-18 in serum and pancreas of patients with chronic pancreatitis

AIM: To investigate interleukin-18 (IL-18) in patients with chronic panreatitis (CP).

METHODS: We studied 29 patients with CP and 30 healthy controls. Peripheral blood mononuclear cells (PBMC) were isolated and incubated with 50 mmol/L ethanol, lipopolysaccharide (LPS) (doses 25 g/L, 250 g/L, 2500 g/L) and both agents for 24 h. Levels of IL-18 in the supernatants, and levels of IL-18, IL-12, interferon (IFN)-γ and soluble CD14 in the serum were analysed by ELISA technique. Expression of IL-18 in PBMC was investigated by reverse-transcription (RT)-PCR. IL-18 protein levels in CP tissue and in normal pancreas were studied by ELISA technique. IL-18 levels in PBMC and pancreatic tissue were determined by Westernblot. Immunohistochemistry for pancreatic IL-18 expression was performed.

RESULTS: In patients, IL-18 serum levels were significantly enhanced by 76% (mean: 289.9 ± 167.7 ng/L) compared with controls (mean: 165.2 ± 43.6 ng/L; P < 0.0005). IL-12 levels were enhanced by 25% in patients (18.3 ± 7.3 ng/L) compared with controls (14.7 ± 6.8 ng/L, P = 0.0576) although not reaching the statistical significance. IFN-γ and soluble CD14 levels were not increased. In vitro, LPS stimulated significantly and dose-dependently IL-18 secretion from PBMC. Incubation with ethanol reduced LPS-stimulated IL-18 secretion by about 50%. The mRNA expression of IL-18 in PBMC and the response of PBMC to ethanol and LPS was similar in CP patients and controls. In PBMC, no significant differences in IL-18 protein levels were detected between patients and controls. IL-18 protein levels were increased in CP tissues compared to normal pancreatic tissues. IL-18 was expressed by pancreatic acinar cells and by infiltrating inflammatory cells within the pancreas.

CONCLUSION: IL-18 originates from the chronically inflammed pancreas and appears to be involved in the fibrotic destruction of the organ.

Methods for the detection of paxillin post-translational modifications and interacting proteins by mass spectrometry

Methods for the simultaneous identification of interacting proteins and post-translational modifications of the focal adhesion adapter protein, paxillin, are presented. The strategy includes (1) lower-level, transient transfection of FLAG-GFP-Paxillin into HEK293 cells, (2) incubation of cells with phosphatase inhibitors prior to lysis, (3) purification of paxillin by anti-FLAG immunoprecipitation, (4) analysis of peptides generated from on-beads digestion using LTQ-FT or LTQ-ETD mass spectrometry, and (5) enrichment of phosphopeptide methyl esters with IMAC. Using the above strategies, we identify 29 phosphorylation sites (19 novel and 10 previously reported) and a novel glycosylation site on Ser 74. Furthermore, with this method, we simultaneously detect 10 co-purifying proteins which are present in focal adhesion complexes. Extension of these methods to other substrates should facilitate generation of global phosphorylation maps and protein-protein interactions for any protein of interest.

Low-dose exposure of intestinal epithelial cells to formaldehyde results in MAP kinase activation and molecular alteration of the focal adhesion protein paxillin

We investigated the potential pathophysiological role of non-lethal formaldehyde concentrations on human intestinal epithelial HT-29 cells. Expression levels of actin, tubulin and detectable cytokeratin isoforms 5, 13, 18, 19 and 20 were not affected after 24h of exposure to 1mM formaldehyde. By contrast, cellular organization of cytoskeletal constituents was already changed after 60 min. Within 15 min, formaldehyde induced profound tyrosine phosphorylation of the focal adhesion protein paxillin and of proteins at about 120-130 kDa. Concomitantly, phosphorylation of ERK-1/2 and p38 MAP kinase occurred. Paxillin was not only tyrosine phosphorylated but underwent a sustained molecular weight shift representing serine/threonine phosphorylation that was independent of MAP kinase activity and EGF-R-mediated signalling. Our data show that exposure of intestinal epithelial cells to low-dose formaldehyde is followed by rapid and profound signalling events. The data suggest a modifier role of environmental or endogenous formaldehyde for epithelial cell functions.

Ethanol modifies the actin cytoskeleton in rat pancreatic acinar cells--comparison with effects of CCK

BACKGROUND

One of the early events leading to alcoholic pancreatitis seems to be the effect of ethanol on stimulus-secretion coupling. This study examines ethanol-induced modifications of filamentous actin (F-actin) content and localization in acini, the resulting alpha-amylase secretion and the role of protein kinase C (PKC) activity in these processes.

METHODS

Freshly isolated acini were treated with different concentrations of ethanol or cholecystokinin octapeptide (CCK-8) for different periods. F-actin was localized by confocal laser scanning microscopy; its quantity was determined fluorometrically, and the alpha-amylase secretion was measured.

RESULTS

Ethanol caused F-actin reorganization resembling the effects of supramaximal CCK-8 stimulation and of direct PKC activation by phorbol-12-myristate-13-acetate. The polyphasic time course of the F-actin content also resembled that under supramaximal CCK-8 stimulation and was counteracted by inhibition of PKC. The PKC inhibitor bisindolylmaleimide I did not increase the ethanol- induced alpha-amylase secretion, but the suboptimally CCK-8-stimulated secretion via high-affinity receptors.

CONCLUSION

Ethanol, like supramaximal CCK-8 concentrations, inhibits acinar secretion by reorganization of the actin cytoskeleton via PKC activation. This effect is suggested to be mediated by low-affinity CCK-A receptors. Together with the ethanol-induced stimulation of early steps of stimulus-secretion coupling, this may be a pancreas-damaging mechanism resembling that in experimental hyperstimulation pancreatitis.

Tyrosine phosphatase PTP1B modulates store-operated calcium influx

We have studied modulation of "store-operated calcium influx" by tyrosine phosphatases in the pancreatic acinar cell line AR42J and in HEK 293 cells. We show that inhibition of tyrosine phosphatases by bis-(N,N-dimethyl-hydroxamido) hydrooxovanadate (DMHV) leads to an increase in Ca(2+) release-activated Ca(2+) (CRAC) entry. This effect can be blocked in the presence of 2-aminoethyldiphenyl borate (2-APB). Furthermore, transfection of HEK 293 cells with the human wild-type tyrosine phosphatase PTP1B leads to inhibition of CRAC influx, whereas transfection with the substrate-trapping mutant of PTP1B (D181A) slightly increases Ca(2+) influx. It also decreases enzymatic activity of PTP1B as compared to non-transfected cells. Our data suggest that CRAC influx is modulated by tyrosine phosphorylation and dephosphorylation which involves the tyrosine phosphatase PTP1B.

Tensile stress-dependent collagen XII and fibronectin production by fibroblasts requires separate pathways

The intracellular mechanisms controlling mechano-dependent production of the two extracellular matrix proteins collagen XII and fibronectin were analyzed. Fibroblasts were cultured on either tensed (attached) or released (floating) collagen type-I gels, respectively. Collagen XII and fibronectin production was three- to fivefold higher under tensed than under released conditions. The general inhibitor of tyrosine phosphorylation, genistein (50 microM), and the MAP kinase inhibitor PD98059 (20 microM) selectively reduced collagen XII accumulation by tensed cultures. Addition of PD98059, but not genistein, downregulated tensile stress-induced tyrosine phosphorylation levels of ERK1/2 and focal adhesion kinase. Staurosporine as well as pretreatment with phorbol ester, which constitute means to downregulate classical and novel PKC activity, specifically blocked collagen XII but not fibronectin accumulation in tensed fibroblasts. ERK1/2 phosphorylation levels were not affected by staurosporine treatment. Chronic exposure to the protein kinase C inhibitors bisindolylmaleimide and calphostin C blocked increased production of both fibronectin and collagen XII from cells under tension. The data manifest that the mechano-dependent production of collagen XII and fibronectin requires separate pathways. The FAK-ERK1/2 pathway, a genistein-sensitive tyrosine kinase, and a distinct classical/novel PKC appear selectively required for increased production of collagen XII in cells under tensile stress, whereas fibronectin induction is regulated by a different PKC-dependent pathway.

Homologous and heterologous regulation of somatostatin receptor 2

We previously demonstrated that phosphorylation of somatostatin receptor 2A (sst2A) is rapidly increased in transfected cells both by agonist and by the protein kinase C (PKC) activator phorbol myristate acetate (PMA). Here, we investigate whether PKC-mediated receptor phosphorylation is involved in the homologous or heterologous regulation of endogenous sst2 receptors in AR42J pancreatic acinar cells upon stimulation by agonist or by cholecystokinin (CCK) or bombesin (BBS). Somatostatin, PMA, CCK, and BBS all increased sst2A receptor phosphorylation 5- to 10-fold within minutes. Somatostatin binding also caused rapid internalization of the ligand-receptor complex, and PMA, CCK, and BBS all stimulated this internalization further. Additionally, sst2 receptor-mediated inhibition of adenylyl cyclase was desensitized by all treatments. Somatostatin, as well as peptidic (SMS201-995) and nonpeptidic (L-779,976) sst2 receptor agonists increased the EC(50) for somatostatin inhibition 20-fold. In contrast, pretreatment with BBS, CCK, or PMA caused a modest 2-fold increase in the EC(50) for cyclase inhibition. Whereas the PKC inhibitor GF109203X abolished sst2A receptor phosphorylation by CCK, BBS, and PMA, it did not alter the effect of somatostatin, demonstrating that these reactions were catalyzed by different kinases. Consistent with a functional role for PKC-mediated receptor phosphorylation, GF109203X prevented PMA stimulation of sst2 receptor internalization. Surprisingly, however, GF109203X did not inhibit BBS and CCK stimulation of sst2A receptor endocytosis. These results demonstrate that homologous and heterologous hormones induce sst2A receptor phosphorylation by PKC-independent and -dependent mechanisms, respectively, and produce distinct effects on receptor signaling and internalization. In addition, the heterologous hormones also modulate sst2 receptor internalization by a novel mechanism that is independent of receptor phosphorylation.

Differential activation of p42ERK2 and p125FAK by cholecystokinin and bombesin in the secretion and proliferation of the pancreatic amphicrine cell line AR42J

BACKGROUND

AR42J rat pancreatic acinar carcinoma cells have retained the potential to secrete digestive enzymes in addition to their ability to proliferate upon stimulation with regulatory peptides. We investigated the involvement of p42ERK2 and p125FAK (extracellular signal-regulated protein kinase and focal adhesion protein kinase, respectively) by cholecystokinin and bombesin stimulation with regard to secretion and mitogenesis.

METHODS

The p42ERK2 activity was measured by kinase assay and the activation of p125FAK by antiphosphotyrosine Western blot analysis of p125FAK immunoprecipitates. The expression of both kinases was determined by Western blot analysis, the amylase secretion by colorimetry, and the DNA synthesis by [3H]thymidine incorporation.

RESULTS

p42ERK2 and p125FAK were activated by cholecystokinin and bombesin with maximum stimulation at concentrations above 10 nM. Bombesin was a weaker activator of p42ERK2 and p125FAK, causing only half of the kinase activity induced by stimulation with cholecystokinin. PD98059 was shown to inhibit p42ERK2, while tyrphostin 25 blocked p125FAK tyrosine phosphorylation. Preincubation of AR42J cells with PD98059 or tyrphostin 25 was without influence on cholecystokinin- or bombesin-stimulated secretion in normal or 72-hour dexamethasone-pretreated cells. In contrast, inhibition of both protein kinases leads to reduced cholecystokinin-stimulated [3H]thymidine incorporation rates.

CONCLUSIONS

Cholecystokinin induced proliferation of AR42J cells by strong activation of p42ERK2 and p125FAK. Bombesin failed to stimulate DNA synthesis, probably due to its reduced potency to stimulate these kinases. Both protein kinases are not implicated in the process of enzyme secretion.

Role of p38 MAP kinase in diperoxovanadate-induced phospholipase D activation in endothelial cells

We previously demonstrated that diperoxovanadate (DPV), a synthetic peroxovanadium compound and cell-permeable oxidant that acts as a protein tyrosine phosphatase inhibitor and insulinomimetic, increased phospholipase D (PLD) activation in endothelial cells (ECs). In this report, the regulation of DPV-induced PLD activation by mitogen-activated protein kinases (MAPKs) was investigated. DPV activated extracellular signal-regulated kinase, c-Jun NH2-terminal kinase (JNK), and p38 MAPK in a dose- and time-dependent fashion. Treatment of ECs with p38 MAPK inhibitors SB-203580 and SB-202190 or transient transfection with a p38 dominant negative mutant mitigated the PLD activation by DPV but not by phorbol ester. SB-202190 blocked DPV-mediated p38 MAPK activity as determined by activated transcription factor-2 phosphorylation. Immunoprecipitation of PLD from EC lysates with PLD1 and PLD2 antibodies revealed both PLD isoforms associated with p38 MAPK. Similarly, PLD1 and PLD2 were detected in p38 immunoprecipitates from control and DPV-challenged ECs. Binding assays demonstrated interaction of glutathione S-transferase-p38 fusion protein with PLD1 and PLD2. Both PLD1 and PLD2 were phosphorylated by p38 MAPK in vitro, and DPV increased phosphorylation of PLD1 and PLD2 in vivo. However, phosphorylation of PLD by p38 failed to affect PLD activity in vitro. These results provide evidence for p38 MAPK-mediated regulation of PLD in ECs.

Intracellular signaling mechanisms activated by cholecystokinin-regulating synthesis and secretion of digestive enzymes in pancreatic acinar cells

The intracellular signaling mechanisms by which cholecystokinin (CCK) and other secretagogues regulate pancreatic acinar function are more complex than originally realized. CCK couples through heterotrimeric G proteins of the Gq family to lead to an increase in intracellular free Ca2+, which shows spatial and temporal patterns of signaling. The actions of Ca2+ are mediated in part by activation of a number of Ca2+-activated protein kinases and the protein phosphatase calcineurin. By the process of exocytosis the intracellular messengers Ca2+, diacylglycerol, and cAMP activate the release of the zymogen granule content in a manner that is poorly understood. This fusion event most likely involves SNARE and Rab proteins present on zymogen granules and cellular membrane domains. More likely related to nonsecretory aspects of cell function, CCK also activates three MAPK cascades leading to activation of ERKs, JNKs, and p38 MAPK. Although the function of these pathways is not well understood, ERKs are probably related to cell growth, and through phosphorylation of hsp27, p38 can affect the actin cytoskeleton. The PI3K (phosphatidylinositol 3-kinase)-mTOR (mammalian target of rapamycin) pathway is important for regulation of acinar cell protein synthesis because it leads to both activation of p70S6K and regulation of the availability of eIF4E in response to CCK. CCK also activates a number of tyrosyl phosphorylation events including that of p125FAK and other proteins associated with focal adhesions.

Hormone-stimulated calcium release is inhibited by cytoskeleton-disrupting toxins in AR4-2J cells

We have studied the role of the actin cytoskeleton in bombesin-induced inositol 1,4,5-trisphosphate (IP(3))-production and Ca(2+)release in the pancreatic acinar tumour cell line AR4-2J. Intracellular and extracellular free Ca(2+)concentrations were measured in cell suspensions, using Fura-2. Disruption of the actin cytoskeleton by pretreatment of the cells with latrunculin B (10 microM), cytochalasin D (10 microM) or toxin B from Clostridium difficile (20 ng/ml) for 5-29 h led to inhibition of both, bombesin-stimulated IP(3)-production and Ca(2+)release. The toxins had no effect on binding of bombesin to its receptor, on Ca(2+)uptake into intracellular stores and on resting Ca(2+)levels. Ca(2+)mobilization from intracellular stores, induced by thapsigargin (100 nM) or IP(3)(1 microM) was not impaired by latrunculin B. In latrunculin B-pretreated cells inhibition of both, bombesin-stimulated IP(3)- production and Ca(2+)release was partly suspended in the presence of aluminum fluoride, an activator of G-proteins. Aluminum fluoride had no effect on basal IP(3)and Ca(2+)levels of control and toxin-pretreated cells. We conclude that disruption of the actin cytoskeleton impairs coupling of the bombesin receptor to its G-protein, resulting in inhibition of phospholipase C-activity with subsequent decreases in IP(3)-production and Ca(2+)release.

Enhancement of Ca2+-induced noradrenaline release by vanadate in PC12 cells: possible involvement of tyrosine phosphorylation

Tyrosine phosphorylation has been shown to participate in the signal cascade after receptor stimulation with neurotransmitters and neurotrophins. However, the role of tyrosine phosphorylation in the process(es) of neurotransmitter release has not been well established. The effects of orthovanadate (Na3VO4), an inhibitor of protein-tyrosine phosphatases, on cytosolic free Ca2+ concentrations ([Ca2+]i), phosphotyrosine accumulation and noradrenaline (NA) release in neurosecretory PC12 cells were investigated. Addition of Na3VO4 enhanced ionomycin-stimulated [3H]NA release in a concentration-dependent manner, although Na3VO4 alone had no effect. Na3VO4 also enhanced [3H]NA release induced by P2 receptor stimulation with adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) or by depolarization with 50 mM KCl, which stimulated a [Ca2+]i increase. A cell permeable inhibitor of protein-tyrosine phosphatases, L-p-bromotetramisole oxalate, at 0.3 mM enhanced ionomycin-stimulated [3H]NA release, although pervanadate had no effect. Addition of 5 mM Na3VO4 stimulated phosphotyrosine accumulation in several protein bands such as p130cas, but did not increase [Ca2+]i in PC12 cells. These findings suggest that the tyrosine phosphorylation pathway regulates Ca2+-stimulated NA release without changes of [Ca2+]i in PC12 cells.

ATP depletion increases tyrosine phosphorylation of beta-catenin and plakoglobin in renal tubular cells

This study examines the hypothesis that the loss of integrity of the junctional complex induced by ATP depletion is related to alterations in tyrosine phosphorylation of the adherens junction proteins beta-catenin and plakoglobin. ATP depletion of cultured mouse proximal tubular (MPT) cells induces a marked increase in tyrosine phosphorylation of both beta-catenin and plakoglobin. The tyrosine phosphatase inhibitor vanadate has the same effect in ATP-replete (control) monolayers, whereas genistein, a tyrosine kinase inhibitor, reduces phosphorylation of both proteins in ATP-replete monolayers and prevents the hyperphosphorylation of these proteins with ATP depletion. This study also demonstrates that the fall in the transepithelial resistance of MPT monolayers induced by ATP depletion can be reproduced by treatment of ATP-replete monolayers with vanadate, whereas genistein substantially ameliorates the fall in transepithelial resistance induced by ATP depletion. Also, using immunofluorescence microscopy it was demonstrated that ATP depletion results in a marked diminution of E-cadherin staining in the basolateral membrane of MPT cells. Vanadate mimics this effect of ATP depletion, whereas genistein ameliorates the reduction in the intensity of E-cadherin staining induced by ATP depletion. Because it is has been well established that hyperphosphorylation of the catenins leads to dissociation of the adherens junction and to dysfunction of the junctional complex, it is proposed that the increase in tyrosine phosphorylation of catenins observed in MPT cells during ATP depletion contributes to the loss of function of the junctional complex associated with sublethal injury.

Neurohumoral control of the exocrine pancreas

Recent advances in the study of pancreatic exocrine secretion are reviewed, with an emphasis on neurohumoral mechanisms. In the past year, cDNA for the human pancreatic sodium-bicarbonate cotransporter was cloned, and the expressed protein was localized to pancreatic acini and ductal cells. Recent information suggests that the cholecystokinin B receptor has a role in pancreatic amylase release. Further evidence supports the concept of a protease-sensitive negative feedback mechanism regulating pancreatic exocrine secretion. Study of the expression of the receptors responsible for the regulation of pancreatic function has proven fruitful in the determination of the molecular mechanisms of hormone signal transduction and desensitization. Studies of peptide 1, pituitary adenylate cyclase-activating peptide, and gastrin-releasing peptide have shown how these peptides participate in the regulation of pancreatic secretion and have provided information on intracellular signaling pathways obtained using rat pancreatic tumor cells. Neural regulation via cholinergic receptors in isolated pancreatic acini and the mechanisms responsible for other neurotransmitters, such as calcitonin gene-related peptide, histamine, and dopamine, are reviewed. This review highlights recent discoveries in the neurohumoral regulation of pancreatic exocrine secretion.

Intracellular regulatory mechanisms in pancreatic acinar cellular function

The intracellular mechanisms regulating pancreatic acinar cell function are more complex than previously realized. This is probably due in part to the need to match the biosynthetic and secretory functions of the cells. Much information is available on how secretagogue receptors acutely couple through heterotrimeric G proteins to increase intracellular messengers, particularly cytoplasmic free Ca(2+), although details are still being worked out. Less is known about how Ca(2+) signals to induce fusion of zymogen granules with the apical plasma membrane. Investigation has focused on the proteins of the zymogen granule membrane, and several novel proteins have recently been identified. In addition, understanding of the three MAP kinase cascades, the mTOR-p70S6 kinase pathway, and the focal adhesion kinase pathway in acinar cells is increasing. The functions of these pathways in acini have been linked to mitogenesis, protein synthesis, and regulation of the cytoskeleton.

Oxidizing effects of vanadate on calcium mobilization and amylase release in rat pancreatic acinar cells

The effects of vanadate were examined by monitoring intracellular free calcium concentration ([Ca2+]i) and amylase secretion in collagenase-dispersed rat pancreatic acinar cells. Vanadate increased [Ca2+]i by mobilizing calcium from agonist-releasable intracellular calcium stores, since this increase was observed in the absence of extracellular calcium and vanadate failed to increase [Ca2+]i after treatment with thapsigargin in calcium-free medium. Moreover, pretreatment of acinar cells with vanadate prevented the cholecystokinin octapeptide (CCK-8)-induced signal of [Ca2+]i, whereas co-incubation with CCK-8 potentiated the plateau phase of calcium response to CCK-8 without modifying the transient calcium spike. The effects of vanadate on calcium mobilization were reversed by the presence of the sulfhydryl reducing agent dithiothreitol. Vanadate also activated the calcium influx, since an additional enhancement of calcium influx induced by thapsigargin-evoked intracellular store depletion was observed and vanadate reversed the inhibitory effect of lanthanum (an inhibitor of calcium entry) into acinar cells. In addition, vanadate evoked a concentration-dependent release of amylase from pancreatic acinar cells and moreover, reduced the secretory response to CCK-8. We conclude that, in pancreatic acinar cells, vanadate releases calcium from the agonist-releasable intracellular calcium pool and consequently induces amylase secretion. These effects are likely due to the oxidizing effects of this compound.

Hydrogen peroxide stimulates tyrosine phosphorylation of focal adhesion kinase in vascular endothelial cells

Reactive oxygen species (ROS) are implicated in the pathophysiology of several vascular disorders including atherosclerosis. Although the mechanism(s) of ROS-induced vascular damage remains unclear, there is increasing evidence for ROS-mediated modulation of signal transduction pathways. Exposure of bovine pulmonary artery endothelial cells to hydrogen peroxide (H(2)O(2)) enhanced tyrosine phosphorylation of 60- to 80- and 110- to 130-kDa cellular proteins, which were determined by immunoprecipitation with specific antibodies focal adhesion kinase (p125(FAK)) and paxillin (p68). Brief exposure of cells to a relatively high concentration of H(2)O(2) (1 mM) resulted in a time- and dose-dependent tyrosine phosphorylation of FAK, which reached maximum levels within 10 min (290% of basal levels). Cytoskeletal reorganization as evidenced by the appearance of actin stress fibers preceded H(2)O(2)-induced tyrosine phosphorylation of FAK, and the microfilament disruptor cytochalasin D also attenuated the tyrosine phosphorylation of FAK. Treatment of BPAECs with 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetraacetic acid-AM attenuated H(2)O(2)-induced increases in intracellular Ca(2+) but did not show any consistent effect on H(2)O(2)-induced tyrosine phosphorylation of FAK. Several tyrosine kinase inhibitors, including genistein, herbimycin, and tyrphostin, had no detectable effect on tyrosine phosphorylation of FAK but attenuated the H(2)O(2)-induction of mitogen-activated protein kinase activity. We conclude that H(2)O(2)-induced increases in FAK tyrosine phosphorylation may be important in H(2)O(2)-mediated endothelial cell activation.

Inhibition of amylase secretion from differentiated AR4-2J pancreatic acinar cells by an actin cytoskeleton controlled protein tyrosine phosphatase activity

Disruption of the actin cytoskeleton in AR4-2J pancreatic acinar cells led to an increase in cytosolic protein tyrosine phosphatase activity, abolished bombesin-induced tyrosine phosphorylation and reduced bombesin-induced amylase secretion by about 45%. Furthermore, both tyrosine phosphorylation and amylase secretion induced by phorbol ester-induced activation of protein kinase C were abolished. An increase in the cytosolic free Ca2+ concentration by the Ca2+ ionophore A23187 had no effect on tyrosine phosphorylation but induced amylase release. Only when added together with phorbol ester, the same level of amylase secretion as with bombesin was reached. This amylase secretion was inhibited by about 40%, by actin cytoskeleton disruption similar to that induced by bombesin. We conclude that actin cytoskeleton-controlled protein tyrosine phosphatase activity downstream of protein kinase C activity regulates tyrosine phosphorylation which in part is involved in bombesin-stimulated amylase secretion.