Involvement of Src family tyrosine kinase in apoptosis of human neutrophils induced by protozoan parasite Entamoeba histolytica

Tyrosine kinases are one of the most important regulators for intracellular signal transduction related to inflammatory responses. However, there are no reports describing the effects of tyrosine kinases on neutrophil apoptosis induced by Entamoeba histolytica. In this study, isolated human neutrophils from peripheral blood were incubated with live trophozoites in the presence or absence of tyrosine kinase inhibitors. Entamoeba-induced receptor shedding of CD16 and PS externalization in neutrophils were inhibited by pre-incubation of neutrophils with the broad-spectrum tyrosine kinase inhibitor genistein or the Src family kinase inhibitor PP2. Entamoeba-induced ROS production was also inhibited by genistein or PP2. Moreover, genistein and PP2 blocked the phosphorylation of ERK and p38 MAPK in neutrophils induced by E. histolytica. These results suggest that Src tyrosine kinases may participate in the signaling event for ROS-dependent activation of MAPKs during neutrophil apoptosis induced by E. histolytica.     

Tyrosine Kinases Are Required for Catecholamine Secretion and Mitogen-Activated Protein Kinase Activation in Bovine Adrenal Chromaffin Cells

Abstract: Nicotine-induced catecholamine secretion in bovine adrenomedullary chromaffin cells is accompanied by rapid tyrosine phosphorylation of multiple cellular proteins, most notably the mitogen-activated protein kinases (MAPKs). The requirement for activation of tyrosine kinases and MAPKs in chromaffin cell exocytosis was investigated using a panel of tyrosine kinase inhibitors. Genistein and tyrphostin 23, two compounds that inhibit tyrosine kinases by distinct mechanisms, were found to inhibit secretion by >90% in cells stimulated by nicotine, 55 m M KCI, or the Ca²⁺ ionophore A23187. Inhibition of secretion induced by all three secretagogues correlated with a block in both protein tyrosine phosphorylation and activation of the MAPKs and their activators (MEKs) in situ. However, neither genistein nor tyrphostin 23 inhibited the activities of the MAPKs or MEKs in vitro. These results indicate that the target(s) of inhibition lie down-stream of Ca²⁺ influx and upstream of MEK activation. This Ca²⁺-activated tyrosine kinase activity could not be accounted for entirely by c-Src or Fyn (two nonreceptor tyrosine kinases that are expressed abundantly in chromaffin cells), because their in vitro kinase activities were not inhibited by tyrphostin 23 and only partially inhibited by genistein. These results demonstrate that an unidentified Ca²⁺-activated tyrosine kinase(s) is required for MAPK activation and exocytosis in chromaffin cells and suggest that MAPK participates in the regulation of secretion.     

Requirement of protein tyrosine kinase and phosphatase activities for human sperm exocytosis

The acrosome is a membrane-limited granule that overlies the nucleus of the mature spermatozoon. In response to physiological or pharmacological stimuli, sperm undergo calcium-dependent exocytosis termed the acrosome reaction, which is an absolute prerequisite for fertilization. Protein tyrosine phosphorylation and dephosphorylation are a mechanisms by which multiple cellular events are regulated. Here we report that calcium induces tyrosine phosphorylation in streptolysin O (SLO)-permeabilized human sperm. As expected, pretreatment with tyrphostin A47-a tyrosine kinase inhibitor-abolishes the calcium effect. Interestingly, the calcium-induced increase in tyrosine phosphorylation has a functional correlate in sperm exocytosis. Masking of phosphotyrosyl groups with a specific antibody or inhibition of tyrosine kinases with genistein, tyrphostin A47, and tyrphostin A51 prevent the acrosome reaction. By reversibly sequestering intra-acrosomal calcium with a photo-inhibitable chelator, we show a requirement for protein tyrosine phosphorylation late in the exocytotic pathway, after the efflux of intra-acrosomal calcium. Both mouse and human sperm contain highly active tyrosine phosphatases. Importantly, this activity declines when sperm are incubated under capacitating conditions. Inhibition of tyrosine phosphatases with pervanadate, bis(N,N-dimethylhydroxoamido)hydroxovanadate, ethyl-3,4-dephostatin, and phenylarsine oxide prevents the acrosome reaction. Our results show that both tyrosine kinases and phosphatases play a central role in sperm exocytosis.     

Noncatalytic Inhibition of Cyclic Nucleotide–gated Channels by Tyrosine Kinase Induced by Genistein

Rod photoreceptor cyclic nucleotide–gated (CNG) channels are modulated by tyrosine phosphorylation. Rod CNG channels expressed in Xenopus oocytes are associated with constitutively active protein tyrosine kinases (PTKs) and protein tyrosine phosphatases that decrease and increase, respectively, the apparent affinity of the channels for cGMP. Here, we examine the effects of genistein, a competitive inhibitor of the ATP binding site, on PTKs. Like other PTK inhibitors (lavendustin A and erbstatin), cytoplasmic application of genistein prevents changes in the cGMP sensitivity that are attributable to tyrosine phosphorylation of the CNG channels. However, unlike these other inhibitors, genistein also slows the activation kinetics and reduces the maximal current through CNG channels at saturating cGMP. These effects occur in the absence of ATP, indicating that they do not involve inhibition of a phosphorylation event, but rather involve an allosteric effect of genistein on CNG channel gating. This could result from direct binding of genistein to the channel; however, the time course of inhibition is surprisingly slow (>30 s), raising the possibility that genistein exerts its effects indirectly. In support of this hypothesis, we find that ligands that selectively bind to PTKs without directly binding to the CNG channel can nonetheless decrease the effect of genistein. Thus, ATP and a nonhydrolyzable ATP derivative competitively inhibit the effect of genistein on the channel. Moreover, erbstatin, an inhibitor of PTKs, can noncompetitively inhibit the effect of genistein. Taken together, these results suggest that in addition to inhibiting tyrosine phosphorylation of the rod CNG channel catalyzed by PTKs, genistein triggers a noncatalytic interaction between the PTK and the channel that allosterically inhibits gating.     

Volume-sensitive tyrosine kinases regulate liver cell volume through effects on vesicular trafficking and membrane Na+ permeability

In liver cells, the influx of Na+ mediated by nonselective cation (NSC) channels in the plasma membrane contributes importantly to regulation of cell volume. Under basal conditions, channels are closed; but both physiologic (e.g. insulin) and pathologic (e.g. oxidative stress) stimuli that are known to stimulate tyrosine kinases are associated with large increases in membrane Na+ permeability to approximately 80 pA/pF or more. Consequently, the purpose of these studies was to evaluate whether volume-sensitive tyrosine kinases mediate cell volume increases through effects on the activity or distribution of NSC channel proteins. In HTC hepatoma cells, decreases in cell volume evoked by hypertonic exposure increased total cellular tyrosine kinase activity approximately 20-fold. Moreover, hypertonic exposure (320-400 mosM) was followed after a delay by NSC channel activation and partial recovery of cell volume toward basal values (regulatory volume increase (RVI)). The tyrosine kinase inhibitors genistein and erbstatin prevented both NSC channel activation and RVI. Similarly, hypertonic exposure resulted in an increase in p60(c-src) activity, and intracellular dialysis with recombinant p60(c-src) led to activation of NSC currents in the absence of an osmolar gradient. Utilizing FM1-43 fluorescence, exposure to hypertonic media caused a rapid increase in the rate of exocytosis of approximately 40% (p < 0.01), and genistein inhibited both exocytosis and channel activation. These findings indicate that volume-sensitive increases in p60(c-src) and/or related tyrosine kinases play a key role in the regulation of membrane Na+ permeability, suggesting that increases in the NSC conductance may be mediated in part through rapid recruitment of a distinct pool of channel-containing vesicles.     

Effect of genistein alone and in combination with okadaic acid on the cell cycle resumption of mouse oocytes

Our biopharmacological approach suggests that the now well-documented inhibitory effects of genistein on the maturation of mammalian oocytes do not seem to be related to its effect on tyrosine kinases. Indeed, we show that both tyrphostin B46 and Lavendustin A, two selective inhibitors of protein tyrosine kinases, fail to inhibit meiosis reinitiation. According to recent findings, the G2/M arrest induced by genistein could be due to inhibition of the kinase activity of cdc2. We were therefore mainly interested in dissecting the cytological effects of genistein on mouse primary and secondary oocytes. Genistein exerts the same cytological effects as IBMX on primary oocytes: their germinal vesicle is maintained in a central position, the cytoplasmic microtubule network is stabilized, the central GV immobilization is overcome by demecolcine and they complete normal maturation after their transfer to culture medium. The GV-arresting activity of genistein is also bypassed by OA but combination of both drugs results in a dramatic reorganization of the cytoskeleton leading to a huge membrane bulging, which is quite different to apoptotic-related blebbing. MAP Kinase activation is correlated with meiosis reinitiation. When applied after GVBD has taken place, genistein does not inhibit MAPK activation, metaphase spindle formation and metaphase-to-anaphase transition, but prevents the barrel-shaped MI spindle from undergoing its peripheral migration and the oocytes from extruding their first polar body. It may thus be concluded that the checkpoint control for anaphase onset is unaffected by the drug. On the contrary, our results suggest that spindle anaphase A to spindle anaphase B transition, spindle degradation, mid-body formation and cytokinesis are triggered by a genistein-sensitive mechanism that might be a mid-anaphase checkpoint. Finally, we confirm that genistein induces transition to interphase in metaphase II oocytes but never induces cortical granule exocytosis, the cytoplasmic hallmark of activation.     

Inhibition of protein tyrosine phosphatases suppresses P-selectin exocytosis in activated human platelets

P-selectin (CD62P), a cell adhesion molecule for most leukocytes, is stored in the alpha-granules of platelets and the Weibel-Palade bodies of endothelial cells. Upon thrombogenic and inflammatory challenges, P-selectin is rapidly expressed, by exocytosis, on activated platelets and stimulated endothelial cells. However, little is known for the molecular mechanisms governing the regulation of the rapid mobilization of P-selectin in these cells. Here we show that phenylarsine oxide (PAO) and diamide (both were inhibitors for protein tyrosine phosphatases), but not genistein (an inhibitor for protein tyrosine kinases), adenosine, wortmannin and LY294002 (all were inhibitors for phosphatidylinositol 3- and 4-kinases), could inhibit P-selectin exocytosis on activated platelets and could abolish the P-selectin mediated aggregation of activated platelets to neutrophils. However, PAO did not attenuate the P-selectin mediated adhesion of human promyeloid HL-60 cells on the stimulated endothelial cells under flow conditions. Further, PAO had no detectable effects on the exocytosis of P-selectin in the stimulated endothelial cells. These results indicate that protein tyrosine phosphatases are necessary for P-selectin exocytosis on the activated platelets, but not on the stimulated endothelial cells, and suggest that inhibitors for protein tyrosine phosphatases may be potentially valuable for treatment of platelet/leukocyte aggregation.     

Genistein inhibits Ca2+ influx and glutamate release from hippocampal synaptosomes: putative non-specific effects

The role of protein tyrosine kinases on glutamate release was investigated by determining the effect of broad range inhibitors of tyrosine kinases on the release of glutamate from rat hippocampal synaptosomes. We found that lavendustin A and herbimycin A did not inhibit glutamate release stimulated by 15 mM KCl, but genistein, also a broad range inhibitor of tyrosine kinases did inhibit the intracellular Ca(2+) concentration response to KCl and, concomitantly, decreased glutamate release evoked by the same stimulus, in a dose-dependent manner. These effects were not observed with the inactive analogue genistin. Therefore, we investigated the mechanism whereby genistein modulates Ca(2+) influx and glutamate release. Studies with voltage-gated Ca(2+) channel inhibitors showed that omega-conotoxin GVIA did not further inhibit glutamate release or the Ca(2+) influx stimulated by KCl in the presence of genistein. This tyrosine kinase inhibitor and omega-agatoxin IVA had a partially additive effect on those events. Nitrendipine did not reduce significantly the KCl-induced responses. Genistein further reduced Ca(2+) influx in response to KCl in the presence of nitrendipine, omega-conotoxin GVIA and omega-agatoxin IVA, simultaneously. The effect of tyrosine phosphatase inhibitors was also tested on the influx of Ca(2+) and on glutamate release stimulated by KCl-depolarization. We found that the broad range inhibitors sodium orthovanadate and dephostatin did not significantly affect these KCl-evoked events.Our results suggest that genistein inhibits glutamate release and Ca(2+) influx in response to KCl independently of tyrosine kinase inhibition, and that tyrosine kinases and phosphatases are not key regulators of glutamate release in hippocampal nerve terminals.     

Nitric Oxide Synthase Expression in Glial Cells: Suppression by Tyrosine Kinase Inhibitors

Abstract: Rat brain glial cells have the capacity to express a calcium-independent form of nitric oxide synthase (iNOS). To test if iNOS induction required tyrosine kinase activity, we made use of genistein, a selective inhibitor of tyrosine kinases. In both primary astrocyte cultures and C6 glioma cells, the presence of genistein prevented both lipopolysaccharide- and cytokine-induced NOS activity in a dose-dependent manner. The presence of tyrphostin-25 (10 µ M ), which is highly specific for tyrosine kinases, also blocked iNOS induction. Additional characterization showed that genistein blocked iNOS induction in a dose-dependent manner (IC₅₀ of ∼ 40 µ M ), that the continuous presence of genistein was not necessary to observe inhibition, and that preincubation with genistein led to higher levels of inhibition than the simultaneous addition of genistein and inducers. The decrease in iNOS activity due to genistein was accompanied by a decrease in iNOS mRNA level as detected by a specific PCR assay. These results indicate that induction of astroglial iNOS expression requires tyrosine kinase activity.     

Are tyrosine kinases involved in mediating contraction-stimulated muscle glucose transport?

Muscle contractions and insulin stimulate glucose transport into muscle by separate pathways. The contraction-mediated increase in glucose transport is mediated by two mechanisms, one involves the activation of 5'-AMP-activated protein kinase (AMPK) and the other involves the activation of calcium/calmodulin-dependent protein kinase II (CAMKII). The steps leading from the activation of AMPK and CAMKII to the translocation of GLUT4 to the cell surface have not been identified. Studies with the use of the tyrosine kinase inhibitor genistein suggest that one or more tyrosine kinases could be involved in contraction-stimulated glucose transport. The purpose of the present study was to determine the involvement of tyrosine kinases in contraction-stimulated glucose transport in rat soleus and epitrochlearis muscles. Contraction-stimulated glucose transport was completely prevented by pretreatment with genistein (100 microM) and the related compound butein (100 microM). However, the structurally distinct tyrosine kinase inhibitors 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyridine and herbimycin did not reduce contraction-stimulated glucose transport. Furthermore, genistein and butein inhibited glucose transport even when muscles were exposed to these compounds after being stimulated to contract. Muscle contractions did not result in increases in tyrosine phosphorylation of proteins such as proline-rich tyrosine kinase and SRC. These results provide evidence that tyrosine kinases do not mediate contraction-stimulated glucose transport and that the inhibitory effects of genistein on glucose transport result from direct inhibition of the glucose transporters at the cell surface.     

Protein kinase activation and protein phosphorylation in Naegleria fowleri amebae in response to normal human serum

Activation of signal transduction pathways in response to serum complement in Naegleria fowleri amebae was investigated. We examined the activation of protein kinases and changes in the phosphorylation state of proteins in N. fowleri stimulated by normal human serum (NHS). To determine differences in phosphorylation of proteins when amebae were exposed to NHS or heat inactivated serum (HIS) lacking complement, amebae were labeled with [32P] orthophosphate. An increase in phosphorylation of relatively low molecular weight proteins was noted in N. fowleri incubated in NHS with a concomitant decrease in phosphorylation of high molecular mass polypeptides. To investigate whether serine/threonine or tyrosine kinases were stimulated by NHS, amebae were treated with protein kinase inhibitors H7, staurosporine or genistein, prior to serum exposure and examined for susceptibility to complement. Treatment with each of these inhibitors resulted in increased complement lysis. Incubation of N. fowleri with genistein specifically inhibited tyrosine phosphorylation of proteins stimulated by NHS. A tyrosine kinase activity assay using exogenous polyGlu-Tyr substrate demonstrated differential activation of tyrosine kinases in amebae treated with NHS when compared to treatment with HIS. The results suggest that activation of protein kinases and subsequent protein phosphorylation are important in mediating complement resistance in N. fowleri.     

Src family tyrosine kinases differentially modulate exocytosis from rat brain nerve terminals

We have studied the role of src family tyrosine kinases in regulating synaptic transmitter release from rat brain synaptosomes by using two assays that measure different aspects of synaptic vesicle exocytosis: glutamate release (that directly measures exocytosis of vesicle contents) and release of FM 2-10 styryl dye (that is proportional to the time the synaptic vesicle is fused to the plasma membrane). Depolarisation was induced by KCl (30 mM) or 4-aminopyridine (4AP: 0.3mM) to induce release by full fusion (FF) exocytosis, or by 1 mM 4AP to induce release by both FF and kiss-and-run (KR)-like exocytosis. The src family selective inhibitor, PP1 (10 microM), increased KCl and 0.3 mM 4AP-evoked Ca2+ -dependent release of glutamate, but had little effect upon exocytosis evoked by 1mM 4AP. PP1 did not affect the release of FM 2-10 under any of the depolarisation conditions used. PP1 also had no effect on overall intracellular calcium levels, as measured by FURA2, suggesting that the effects of the inhibitor are downstream of calcium entry. At the same concentration the inactive analogue of this compound, PP3, had no effect on any measure. Immunoblotting with an antibody to phosphotyrosine revealed that phosphorylation of many synaptosomal proteins was reduced by PP1. The immunoreactivity of three protein bands increased upon depolarisation and this increase was blocked by PP1. Phosphorylation of src at tyrosine-416 was reduced by PP1 but changes in its phosphorylation did not correlate with the effects of PP1 on release. These results suggest one or more members of the src family of tyrosine kinases is a negative regulator of the KR mode of exocytosis in synaptosomes, perhaps by tonically inhibiting KR under normal stimulation conditions.     

Protein kinase implication in prolactin signaling in bovine oocyte-cumulus complexes

The mechanisms of prolactin signal transduction in generative and somatic cells of mammalian ovarian follicles are poorly understood. In this work, participation of tyrosine kinases and protein kinase C in mediation of the previously revealed modulating effects of prolactin on the nuclear maturation of bovine oocytes and the morphologic and functional state of surrounding cumulus cells in vitro has been investigated. It was found that a tyrosine kinase inhibitor genistein suppresses the stimulating action of prolactin on the completion of oocyte nuclear maturation and cumulus expansion, whereas a protein kinase C inhibitor calpostin C does not affect the hormonal effect. Furthermore, both genistein and calpostin C inhibited the inducing influence of prolactin on the proliferative activity of cumulus cells. At the same time, the retarding action of prolactin on destructive processes in cumulus cells was blocked only in the presence of calpostin C. These results show that the stimulating influence of prolactin on oocyte nuclear maturation accompanied by cumulus expansion is achieved with participation of tyrosine kinases, whereas the modulating action of the hormone on the functional state of cumulus cells depends on activation both of tyrosine kinases and protein kinase C.     

The Tyrosine Kinase Inhibitor Genistein Increases Endogenous Dopamine Release from Normal and Weaver Mutant Mouse Striatal Slices

Abstract: Protein tyrosine kinases that are known to have major roles in the control of cell growth and transformation are abundant and have numerous phosphoprotein substrates in the adult CNS. Although less well characterized than serine/threonine kinases, tyrosine kinases are also concentrated in the synapse. The effect of genistein, a selective inhibitor of tyrosine kinase activity, was examined on the in vitro release of endogenous dopamine (DA) from superfused mouse striatal slices. Fractional release of DA was significantly increased over basal release levels by genistein (100 and 200 µ M ). The effect was concentration dependent and rapidly reversible on washout of the kinase inhibitor. No significant change from basal release levels was observed with two structural analogues of genistein that do not inhibit tyrosine kinase activity at the same concentration. We have previously described alterations in basal and evoked DA release from the striatum of the weaver ( wv/wv ) mutant mouse, and genotypic differences in fractional release were also observed with genistein stimulation. The total evoked release was 25–50% greater from the wv/wv striatum. These results suggest a modulatory role for tyrosine kinase activity in neurotransmitter release and perhaps an alteration of kinase-regulated mechanisms in the DA-deficient wv/wv striatum.     

Reversible protein tyrosine phosphorylation affects pollen germination and pollen tube growth via the actin cytoskeleton

Summary. Phenylarsine oxide (PAO) and genistein are two well-known specific inhibitors of tyrosine phosphatases and kinases, respectively, that have been used in the functional analysis of the status of protein phosphotyrosine in different cell types. Our experiments showed that both PAO and genistein arrested pollen germination and pollen tube growth and led to the malformation of the pollen tubes, although genistein had a lesser effect. The malformations of the pollen tubes caused by PAO and genistein were, however, quite different. In addition, it was found that the rate of pollen germination and tube growth recovered to a certain extent when phalloidin was present during PAO treatment, but not when it was present during genistein treatment. Furthermore, PAO treatment also had a great effect on the dynamic organization of filamentous actin in the pollen grain and pollen tube, while genistein only caused reorganization of actin at the turning point of the pollen tube. Our results suggest that reversible protein tyrosine phosphorylation is a crucial step in pollen germination and pollen tube growth, but that tyrosine kinases and phosphatases may have different effects which may function through the reorganization of the actin cytoskeleton. Correspondence and reprints: Key Laboratory of Cell Proliferation and Regulation Biology of the Ministry of Education, College of Life Science, Beijing Normal University, Beijing 100875, People’s Republic of China.     

Genistein directly inhibits GLUT4-mediated glucose uptake in 3T3-L1 adipocytes

The isoflavone-derivative genistein is commonly applied as an inhibitor of tyrosine kinases. In this report we analyze the effect of genistein on insulin-stimulated glucose uptake in 3T3-L1 adipocytes. In these cells insulin-induced glucose uptake is primarily mediated by the GLUT4 glucose transporter. We observed that pre-treatment with genistein did not affect insulin-induced tyrosine kinase activity of the insulin receptor or activation of protein kinase B. On the other hand, genistein acted as a direct inhibitor of insulin-induced glucose uptake in 3T3-L1 adipocytes with an IC(50) of 20 microM. We conclude that apart from acting as a general tyrosine kinase inhibitor, genistein also affects the function of other proteins such as the GLUT4 transporter. These data suggest that caution must be applied when interpreting data on the involvement of tyrosine kinase activity in glucose uptake in 3T3-L1 adipocytes.     

Effect of tyrosine kinase inhibition on basal and epidermal growth factor-stimulated human Caco-2 enterocyte sheet migration and proliferation

Mucosal healing requires enterocyte migration (restitution) supplemented by proliferation. Proliferation and migration may be studied independently by thymidine uptake and proliferation-blocked cell migration using human Caco-2 enterocyte monolayers in culture. Since epidermal growth factor (EGF) promotes mucosal healing and the EGF receptor is a tyrosine kinase, we hypothesized that tyrosine kinases might therefore modulate enterocyte migration and proliferation. The tyrosine kinase inhibitors genistein and 2, 5-dihydroxymethylcinnamate, which block kinase ATP-binding and substrate-binding sites, respectively, were studied alone and with EGF. Proliferation was blocked with mitomycin. Although each inhibitor decreased basal and EGF-stimulated monolayer expansion when cell proliferation occurred, neither genistein nor 2, 5-dihydroxymethylcinnamate decreased migration when proliferation was blocked. However, each inhibitor prevented EGF stimulation of proliferation-blocked migration and thymidine uptake. More substantial inhibition of basal proliferation by genistein correlated with increased protein-linked DNA breaks, which may reflect nonspecific inhibition of DNA topoisomerase activity by genistein. The more specific 2,5-dihydroxymeth-ylcinnamate blocked changes in the α2 integrin subunit organization which may modulate EGF-stimulated migration. Antiproliferative effects of tyrosine kinase inhibitors decrease basal monolayer expansion but true basal enterocyte migration appears independent of tyrosine kinase regulation. However, a specific tyrosine kinase-dependent modulation of cell-matrix interaction inhibits EGF-stimulated migration. © 1994 Wiley-Liss, Inc.     

Stimulation of ultraviolet-induced apoptosis of human fibroblast UVr-1 cells by tyrosine kinase inhibitors

Damnacanthal is an anthraquinone compound isolated from the root of Morinda citrifolia and was reported to have a potent inhibitory activity towards tyrosine kinases such as Lck, Src, Lyn and EGF receptor. In the present study, we have examined the effects of damnacanthal on ultraviolet ray-induced apoptosis in ultraviolet-resistant human UVr-1 cells. When the cells were treated with damnacanthal prior to ultraviolet irradiation, DNA fragmentation was more pronounced as compared to the case of ultraviolet irradiation alone. The other tyrosine kinase inhibitors, herbimycin A and genistein, also caused similar effects on ultraviolet-induced apoptosis but to a lesser extent. Serine/threonine kinase inhibitors, K252a, staurosporine and GF109203X, rather suppressed the ultraviolet-induced DNA cleavage. Immunoblot analysis showed that pretreatment with damnacanthal followed by ultraviolet irradiation increased the levels of phosphorylated extracellular signal-regulated kinases and stress-activated protein kinases. However, the other tyrosine kinase inhibitors did not increase the phosphorylation of extracellular signal-regulated kinases but stimulated phosphorylation of stress-activated protein kinases. Consequently, the ultraviolet-induced concurrent increase in both phosphorylated extracellular signal-regulated kinases and stress-activated protein kinases after pretreatment with damnacanthal might be characteristically related to the stimulatory effect of damnacanthal on ultraviolet-induced apoptosis.     

Effect of genistein on the temporal coordination of cleavage and compaction in mouse preimplantation embryos

Initially, we investigated the effect of genistein, an inhibitor of protein tyrosine kinases, on compaction of the mouse embryo since tyrosine phosphorylation of the cadherin-catenins complex was suggested to down-regulate its adhesive function. Genistein prevented cleavage from the 2- to the 4-cell stage in a concentration-dependent manner. The next cleavage is inhibited at all concentrations used. Time course of intercellular flattening is however identical for both control 8-cell embryos and 4-cell arrested embryos. This confirms that compaction takes place according to a biological clock that does not depend on completion of the third cell cycle. Our results also suggest that, since, in contrast to genistein, protein kinases C modulators are known to cause a premature compaction, diacylglycerol-dependent kinases but not protein tyrosine kinases might be upregulators of compaction.