Biomedical subjects

S Nakashima

Publications and source records attributed to S Nakashima.

At least 163 records · Page 9Linked to original sources

PubMed1996

Effects of Clostridium difficile toxin A and toxin B on phospholipase D activation in human promyelocytic leukemic HL60 cells.

The possible involvement of Rho family GTP-binding proteins in the regulation of phospholipase D (PLD) activity has recently been demonstrated. In the present study, to further examine the role of Rho family proteins in PLD activation of human promyelocytic leukemic HL60 cells, we used toxin A and toxin B from the anaerobic bacterium Clostridium difficile, which was shown to glucosylate Rho family proteins and inhibit their interaction with effectors. Pretreatment of [3H]oleic acid-labeled HL60 cell lysates with either one of the toxins resulted in a remarkable inhibition of membrane PLD activity stimulated by guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). The magnitude of inhibition of PLD activity was correlated well with the extent of toxin A- or B-induced glucosylation of 22-kDa RhoA in HL60 cells, toxin B being more effective than toxin A. GTPgammaS-stimulated PLD activation measured with the exogenous substrate containing phosphatidylinositol 4,5-bisphosphate was also inhibited by toxin B. Toxin B had no effect on GTP-gammaS-induced translocation of RhoA from cytosol to membranes. Furthermore, the toxin B pretreatment also suppressed PLD activation induced by 4beta-phorbol 12-myristate 13-acetate in HL60 cell lysates. Thus, it was indicated that Rho family proteins play a key role in GTPgammaS- and 40-phorbol 12-myristate 13-acetate-induced PLD activity in HL60 cells. In addition, the results obtained here indicate that C. difficile toxins are a useful tool for researching the regulation of the Rho family protein-mediated PLD activation and also provide a clue toward understanding the pathogenic background of pseudomembranous colitis from the viewpoint of signal transduction.

ADP-Ribosylation Factors↗

PubMed1996

An autolysin ring associated with cell separation of Staphylococcus aureus.

atl is a newly discovered autolysin gene in Staphylococcus aureus. The gene product, ATL, is a unique, bifunctional protein that has an amidase domain and a glucosaminidase domain. It undergoes proteolytic processing to generate two extracellular peptidoglycan hydrolases, a 59-kDa endo-beta-N-acetylglucosaminidase and a 62-kDa N-acetylmuramyl-L-alanine amidase. It has been suggested that these enzymes are involved in the separation of daughter cells after cell division. We recently demonstrated that atl gene products are cell associated (unpublished data). The cell surface localization of the atl gene products was investigated by immunoelectron microscopy using anti-62-kDa N-acetylmuramyl-L-alanine amidase or anti-51-kDa endo-beta-N-acetylglucosaminidase immunoglobulin G. Protein A-gold particles reacting with the antigen-antibody complex were found to form a ring structure on the cell surface at the septal region for the next cell division site. Electron microscopic examination of an ultrathin section of the preembedded sample revealed preferential distribution of the gold particles at the presumptive sites for cell separation where the new septa had not been completed. The distribution of the gold particles on the surface of protoplast cells and the association of the gold particles with fibrous materials extending from the cells suggested that some atl gene products were associated with a cellular component extending from the cell membrane, such as lipoteichoic acid. The formation of a ring structure of atl gene products may be required for efficient partitioning of daughter cells after cell division.

Acetylglucosaminidase↗

PubMed1996

[Early and late results of surgical intervention for 32 active infective endocarditis patients in last 10 years].

Thirty-two active infectious endocarditis patients who underwent 36 surgical procedures (23 NVEs, 13 PVEs) in last 10 years were reviewed. Seven patients (19.4%) died early postoperatively, 3/23 (13%) in NVEs and 4/13 (31%) in PVEs, and the causes of death were LOS in 5, MOF in one and cerebral bleeding in one. NVE patients of double valve deterioration who developed cardiogenic shock had poor operative results, 3 death in 4 (75%) despite of circulatory assist. Aortic PVEs who underwent Danielson's translocation technique also showed 3 death in 4 (75%). Five in 25 survivors (20%) developed late death and 3 of them were related with reinfection of prosthetic valve. We concluded that surgical treatment for active IE provides reasonable results, although they are still challenging for double valve NVEs and aortic PVEs, for which aortic root replacement using homograft would be the procedure of choice.

Adolescent↗

PubMed1996

[Surgical treatment for recrudescent Stanford type A early closing dissection].

Two cases of recrudescent Stanford type A dissection were reported. They had non-opacified false channel on their initial CT and aortography. The first case was 65-year-old woman having a stable blood pressure and no chest pain after admission. However, recrudescent opacified false lumen was found at the mid-ascending aorta about three weeks later. She received ascending aortic replacement on 26th day after onset. The second case was 66-year-old woman having a unstable blood pressure and having periodic chest pain and back pain after admission. CT and angiography performed on the 41th day after onset revealed recrudescent descending aortic dissection and ulcer like projection at mid-ascending aorta. The ulcer like projection increased in size gradually. Ascending aorta replacement was performed on 110th day after onset. Two cases had a good post operative days. Some cases of Stanford type A early closing aortic dissection had recrudescent dissection later, even if they had a stable course after onset. Thus, careful follow up for long term is essential in these cases

Aged↗

PubMed1995

Spectroscopic and electrochemical studies on active-site transitions of the type 1 copper protein pseudoazurin from Achromobacter cycloclastes.

The single type 1 copper protein pseudoazurin from Achromobacter cycloclastes gives reversible electrochemical behavior at a (4-pyridyl)disulfide-modified gold electrode. Measurements carried out at 25.0 degrees C indicate a midpoint reduction potential of E 1/2 = 260 mV versus normal hydrogen electrode at pH 7.0 and a peak-to-peak separation of delta Ep = 59 mV. The diffusion coefficient and heterogeneous electron transfer rate constant are estimated to be 2.23 x 10(-6) cm2 s-1 and 3.7 x 10(-2) cm s-1, respectively. Also, controlled potential electrolysis indicates a 1-electron transfer process and a formal reduction potential of 259 mV versus normal hydrogen electrode for the Cu(II)/Cu(I) couple. The heterogeneous electron transfer rate constant determined at the (4-pyridyl)disulfide-modified gold electrode at pH 4.6 is 6.7 x 10(-3) cm s-1, consistent with a slower process at the positively charged electrode surface. At pH 11.3, UV-visible, EPR, and resonance Raman spectra indicate a conversion of the distorted tetrahedral copper geometry to a trigonal structure. The trigonal form has elongated axial bonding and an axial EPR spectrum. At pH 11.3, the reduction potential is further decreased, and Cu-S bands in resonance Raman spectra at 330-460 cm-1 are shifted to higher energy (approximately 10 cm-1), consistent with a stronger Cu-S bond.

Alcaligenes↗

PubMed1995

The mRNA overexpression of inflammatory enzymes, phospholipase A2 and cyclooxygenase, in the large bowel mucosa and neoplasms of F344 rats treated with naturally occurring carcinogen, 1-hydroxyanthraquinone.

Inflammation has been considered to be related to carcinogenesis. Previously, we demonstrated that 1-hydroxyanthraquinone (1-HA), a naturally occurring carcinogen, induced severe inflammation such as ulcerative colitis in colonic mucosa. We also showed that indomethacin inhibited the tumorigenicity of 1-HA. In this study, we examined the expressions of major enzymes in arachidonic acid cascade related to inflammation in the colon mucosa of rats treated with 1-HA. After the treatment of 1% 1-HA diet, colon lesions were observed and RNA was extracted from mucosa and neoplasms. The mRNA expressions of group II phospholipase A2, cyclooxygenase-2 and 5-lipoxygenase, were examined by using a reverse transcriptase polymerase chain reaction. The expressions of phospholipase A2 and cyclooxygenase were significantly increased in non-neoplastic mucosa in rats treated with 1-HA compared with those in control rats. The expressions in the neoplasms induced by 1-HA were also increased. Phospholipase A2, especially, was much higher in the neoplasms than in non-neoplastic mucosa. However, the expression of 5-lipoxygenase showed no change in the non-neoplastic mucosa and neoplasms of rats treated with 1-HA, compared with that in control rats. These findings suggest that the inflammation induced by 1-HA may be related to the metabolites through a cyclooxygenase pathway, which indicates a prostaglandin synthesis, but not through a lipoxygenase pathway, which indicates a leukotriene synthesis in arachidonic acid cascade.

Animals↗

PubMed1995

Implication of protein kinase C alpha in PAF-stimulated phospholipase D activation in Chinese hamster ovary (CHO) cells expressing PAF receptor.

Protein kinase C (PKC) isozyme(s) involved in regulation of platelet-activating factor (PAF)-induced phospholipase D (PLD) activation was investigated in CHO cells stably expressing cloned guinea-pig PAF receptor (WT-H cells). Three PKC isozymes, alpha, epsilon, and zeta, were identified by Western blotting, which displayed different kinetics of translocation from cytosol to membrane upon PAF stimulation. Cytosolic PKC alpha was rapidly translocated to membrane in response to PAF within 30 s and then returned to cytosol by 10 min. This kinetics was well correlated with PAF-induced transient PLD activation. Pretreatment of the cells with 100 nM 4 beta-phorbol 12-myristate 13-acetate (PMA) for 2 h resulted in down-regulation of PKC alpha, leaving PKC epsilon and zeta unchanged. Under the same conditions, PAF and PMA-mediated PLD activation were markedly reduced. These data suggest that PKC alpha is involved in the regulation of PAF-stimulated PLD activation in WT-H cells.

Animals↗

PubMed1995

Antigen-mediated phospholipase D activation in rat basophilic leukemia (RBL-2H3) cells: possible involvement of calcium/calmodulin.

The differential implication of protein kinase C (PKC) isozymes in antigen- or PMA-induced phospholipase D (PLD) activation was investigated in rat basophilic leukemia (RBL-2H3) cells. In [3H]oleic acid-labeled cells, both antigen (100 ng/ml) and phorbol 12-myristate 13-acetate (PMA) (100 nM) produced a specific product of PLD activation, [3H]phosphatidylbutanol (PBut) in the presence of butanol. Pretreatment of cells with a selective PKC inhibitor, Ro31-8425 (1-5 microM) inhibited PMA-stimulated PLD activity by 85%. In contrast, the antigen-stimulated PLD activity was much less sensitive to the inhibitor. RBL-2H3 cells express PKC alpha, beta, delta, epsilon and zeta isozymes and down-regulation of PKC by exposure to PMA (20 nM) for 1-2 h caused rapid decrease in PKC alpha and beta isozymes, leaving PKC delta, epsilon and zeta isozymes intact. Apparent decreases in the levels of PKC alpha and beta to about 50% were observed after adding 20 nM PMA for 1 h, when PMA-stimulated PLD activity was inhibited by up to 70%. Decrease in antigen-stimulated PLD activity was evident after 2 h PMA-treatment, when PKC alpha and beta decreased by nearly 70%. These results suggest that in the antigen-mediated PLD pathway PKC may be implicated but not play such a great role as PMA-stimulated pathway which is mediated through PKC alpha or beta. Then, we have examined the involvement of calcium/calmodulin (CaM) in PLD activation by antigen, since the antigen-stimulated PLD activation showed the absolute requirement for extracellular calcium. Preincubation of RBL-2H3 cells with a CaM antagonist W-7 (20 microM) inhibited the antigen-stimulated PLD activity by 90%, but W-5, a chlorine-deficient analogue of W-7 that only weakly interact with CaM, caused little inhibitory effect. Another non-specific CaM antagonist, trifluoperazine (TFP) also inhibited PLD activation. These results suggest that calcium/CaM may be involved in the antigen-stimulated PLD activation.

Animals↗

PubMed1995

Purification and characterization of lysophospholipase-transacylase (h-LPTA) from a highly virulent strain of Candida albicans.

A lysophospholipase-transacylase (h-LPTA) was purified to homogeneity from a clinical isolate of Candida albicans (C. albicans) that had high extracellular phospholipase activity (strain 16240). The purified enzyme was a glycoprotein with molecular mass of 84 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The specific activities of the enzyme were 117 mumol/min per mg protein for fatty acid release and 459 mumol/min per mg protein for phosphatidylcholine (PC) formation. An apparent Km of the hydrolase activity of the enzyme for 1-palmitoyl-sn-glycero-3-phosphocholine (1-palmitoyl-lyso-PC) was 60.6 microM. The enzyme had a pH optimum at 6.0. Transacylase activity of the enzyme was partially inhibited by palmitoylcarnitine (35% inhibition) and N-ethylmaleimide. In contrast, the hydrolase activity of the enzyme was stimulated by palmitoylcarnitine but was partially inhibited by N-ethylmaleimide. The enzyme exhibited broad specificity to lyso-phospholipids. The h-LPTA activity was not dependent on divalent cations (Ca2+ and Mg2+) and was not inhibited by addition of EDTA or EGTA. These results show that C. albicans strain 16240 with high extracellular phospholipase activity produced h-LPTA in large amount. This enzyme is biochemically distinct from the LPTA enzyme previously isolated from C. albicans 3125.

Acyltransferases↗

PubMed1995

Deletion and site-directed mutagenesis of EF-hand domain of phospholipase C-delta 1: effects on its activity.

In order to elucidate a role of a putative EF-hand motif (144-172) in phospholipase C-delta 1 (PLC-delta 1), deletion and point mutation of the enzyme were performed and the mutated cDNAs were expressed in CHO cells and E. coli AD202 strain. Deletion of amino acid residues of 141-236 or 173-236 resulted in abolition of PLC activity. However, the decreased PLC activity to 15-20% by deletion of the EF-hand motif (144-172) was still Ca(2+)-dependent. Furthermore, mutants, in which conserved Asp153, Asp157, Glu164 or all these acidic amino acids in the EF-hand motif were replaced with alanine residues, showed nearly the same PLC activity and Ca(2+)-dependency as those of wild-type. These results suggest that the region containing the EF-hand motif may not play a role in regulation of Ca(2+)-sensitivity of PLC-delta 1, but is important for its activity.

Alanine↗

PubMed1995

Activation of membrane-bound phospholipase D by protein kinase C in HL60 cells: synergistic action of a small GTP-binding protein RhoA.

Regulation of phospholipase D (PLD) activation by protein kinase C (PKC) was studied in membranes isolated from human promyelocytic leukemia HL60 cells. The activation of membrane-bound PLD by PKC partially purified from rat brain was most effectively induced with phorbol 12-myristate 13-acetate (PMA) and Ca2+ (1 microM) which caused translocation of PKC to membranes. Ro31-8425, a potent inhibitor of PKC, suppressed the catalytic activity of PKC in a concentration-dependent manner, with complete inhibition at 5 microM. However, the PKC-mediated PLD activation was not affected by Ro31-8425. It was thus suggested that membrane-bound PLD of HL60 cells was activated by PKC translocation but probably via a phosphorylation-independent mechanism. Furthermore, addition by guanosine 5'-3-O-(thio)trisphosphate (GTP gamma S) potentiated the PKC-mediated PLD activation and this potentiating effect was abolished by Rho GTPase dissociation inhibitor (RhoGDI). The suppressed PLD activation by RhoGDI was completely restored by addition of recombinant RhoA. These results indicate that the PKC-mediated PLD activation can be synergistically potentiated by RhoA in HL60 membranes.

Animals↗

PubMed1995

Endogenous cleavage of phospholipase C-beta 3 by agonist-induced activation of calpain in human platelets.

Two membrane-associated phosphoinositide-specific phospholipase Cs (mPI-PLC-1 and mPI-PLC-2) and a cytosolic enzyme (cPI-PLC) that were activated by brain G-protein beta gamma subunits have been isolated from human platelets. The truncation of mPI-PLC-1 that was mediated by mu-calpain induced much higher activation by beta gamma subunits (Banno, Y., Asano, T., and Nozawa, Y. (1994) FEBS Lett. 340, 185-188). On the basis of size and immunological cross-reactivity, mPI-PLC-1 (155 kDa) was PLC-beta 3, and mPI-PLC-2 (100 kDa) was its truncated form. The cPI-PLC (140 kDa) was recognized by the antibody selective for internal sequences of PLC-beta 3 but not by the antibody raised against its carboxyl terminus, indicating that it may be related to PLC-beta 3. Treatment of human platelets with A23187 and dibucaine, activators of calpain, caused cleavage of actin-binding protein and talin in a time-dependent manner. At the same time, decrease of PLC-beta 3 (155 and 140 kDa) and concomitant increase of the 100-kDa product of cleavage were observed on immunoblots with the antibody to internal sequences of PLC-beta 3. Furthermore, stimulation of platelets by natural agonists, thrombin and collagen, caused the cleavage of PLC-beta 3 (155 and 140 kDa) and an increase of 100 kDa PLC-beta 3 in a time- and dose-dependent manner. The cleavage of these PLC-beta 3 enzymes was completely blocked by calpain inhibitor, calpeptin, indicating that the PLC-beta 3 modification may be a consequence of platelet activation leading to activation of calpain. This is the first demonstration that PLC-beta 3 is indeed cleaved by calpain upon platelet activation by physiological agonists. The cleavage of PLC-beta 3 evoked by thrombin and collagen but not ADP was correlated with irreversible aggregation, suggesting that the PLC-beta 3 modification may play a role in secondary irreversible aggregation in agonist-stimulated human platelets.

Amino Acid Sequence↗

PubMed1995

Defective phospholipase D activation in Ki-ras-transformed NIH3T3 cells: evidence for downstream effector of PLC-gamma 1 in PDGF-mediated signal transduction.

Platelet-derived growth factor (PDGF), a potent mitogen for fibroblasts and many other cell types, was used to examine phosphatidylcholine-specific phospholipase D (PLD), phosphoinositide-specific phospholipase C (PI-PLC) and tyrosine phosphorylation in NIH3T3 fibroblast and its Ki-ras-transformed derivative, DT. When cells prelabeled with [3H] myristic acid were stimulated by 10 and 50 ng/ml of PDGF in presence of 0.3% butanol, formation of phosphatidylbutanol (PtdBut) was increased three to six fold in NIH3T3 fibroblasts whereas it was marginal in DT cells. Myo-[3H]inositol-labeled cells showed higher inositol phosphate production in nontransformed control fibroblasts, indicating higher phospholipase C activity compared to the transformed DT cells. PDGF caused increase in tyrosine phosphorylation of a group of proteins with 110-130 kDa, PLC-gamma 1 and PDGF receptor in NIH3T3 cells. There was no significant increase in tyrosine phosphorylation in both PDGF receptor and PLC-gamma 1 in DT cells. These results suggest that PLD acts as a downstream effector molecule of PLC-gamma 1 in the PDGF-mediated signal transduction pathway.

1-Butanol↗

PubMed1995

Effects of selective phosphodiesterase type IV inhibitor, rolipram, on signal transducing phospholipases in neutrophil: inhibition of phospholipases A2, D but not C.

The effects of a selective phosphodiesterase (PDE) type IV inhibitor, rolipram, on activation of neutrophil phospholipases in response to the chemotactic peptide formyl-methiony-leucyl-phenylalanine (fMLP) were investigated. fMLP caused liberation of arachidonic acid, a precursor of eicosanoids and in the presence of 0.3% butanol, production of phosphatidylbutanol, an indicator of phospholipase D activation. Rolipram inhibited arachidonic acid release and phosphatidylbutanol formation. The inhibition was considered to be mediated through a cAMP-dependent mechanism, probably protein kinase A, because selective inhibitors for protein kinase A, H-8 or H-89 overcame the action of rolipram. The concentration-dependent inhibitory profile for phospholipase D activation was similar to that for lysosomal enzyme release, providing additional evidence for the functional link of these two events. In contrast, rolipram was without effect on fMLP-induced inositol trisphosphate production. These results indicate that this selective PDE IV inhibitor had no effect on phosphatidylinositol-specific phospholipase C activation but effectively prevented activation of phospholipases A2 and D coupled to arachidonic acid liberation and lysosomal enzyme release, respectively.

Animals↗

PubMed1995

Alteration of bacteriolytic enzyme profile of Staphylococcus aureus during growth.

Profiles of cell-associated bacteriolytic activities and those in the culture supernatant of Staphylococcus aureus FDA209P at various stages of growth were analyzed using sodium dodecyl sulfate-polyacrylamide gels containing Micrococcus luteus or S. aureus. In the logarithmic growth phase, the cell-associated bacteriolytic activities extracted with Triton X-100 contained a number of bacteriolytic proteins, the profiles of which were similar to those we reported elsewhere (Sugai, M., Akiyama, T., Komatsuzawa, H., Miyake, Y., and Suginaka, H. (1990) J. Bacteriol., 172, 6494-6498). The proteins include P1, P2, P7, P9, PX, P13, P18 and other minor components. At the stationary growth phase, the bacteriolytic band-profile of the Triton X-100 extract changed dramatically. P1, P7 and P9 disappeared, and the other minor bands had markedly decreased band intensities. On the other hand, P2, PX, P13, and P18 retained their band intensities during the stationary growth phase. The band intensities of P7, P13, PX, and P18 increased in the supernatant during the logarithmic growth phase. These results indicated that the bacteriolytic band-profile changes during growth.

N-Acetylmuramoyl-L-alanine Amidase↗

PubMed1995

Roles of prostaglandin production and mitogen-activated protein kinase activation in hepatocyte growth factor-mediated rat hepatocyte proliferation.

Hepatocyte growth factor (HGF) and epidermal growth factor (EGF)-stimulated DNA synthesis in primary cultured rat hepatocytes. HGF-induced DNA synthesis was concentration-dependently inhibited by a cyclooxygenase inhibitor, indomethacin. BW755C, a dual inhibitor for cyclooxygenase and lipoxygenase activities, also inhibited hepatocyte growth. Prostaglandin E1 (PGE1), PGE2, and PGF2 alpha induced DNA synthesis even at such a low concentration as 5 nmol/L and potentiated [3H]thymidine incorporation induced by HGF in an additive manner. HGF caused arachidonic acid (AA) release and eicosanoid production. These events were detectable within 10 minutes after stimulation and lasted for at least 60 minutes. Furthermore, two proteins with approximately 40 kd were tyrosine phosphorylated by HGF. These proteins were identified as p42/p44 mitogen-activated protein (MAP) kinases by anti-MAP kinase immunoblots, which were known to activate cytosolic phospholipase A2 (cPLA2), a key enzyme in AA release. Activation of MAP kinases was detectable within 5 minutes after stimulation with HGF and lasted for at least 60 minutes. EGF-mediated DNA synthesis was also inhibited by the above cyclooxygenase inhibitors. EGF caused AA release and tyrosine phosphorylation of MAP kinases. These results suggest that HGF as well as EGF causes AA release, probably through activation of cPLA2 mediated by MAP kinases, and that PGs, metabolites of AA, might play a pivotal role in hepatocyte proliferation in an autocrine mechanism.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1995

[Effects of antiallergic drug, pemirolast potassium on phospholipase D activation in antigen-stimulated rat basophilic leukemia (RBL-2H3) cells].

An anti-allergic drug, permirolast potassium (TBX), inhibited antigen (Ag)-induced phospholipase D (PLD) activation in rat basophilic leukemia (RBL-2H3) cells. The concentration-dependent inhibitory profile for Ag-induced PLD activation was parallel to those for secretory response and inositol phosphate formation. In contrast, TBX had no effect on PLD activation caused by calcium ionophore A23187 or phorbol myristate acetate. These results suggest that TBX inhibits Ag-induced PLD activation by interfering with the signal transduction pathway upstream of Ca2+ mobilization and protein kinase C activation.

Animals↗

PubMed1995

Effects of an antiallergic drug, pemirolast potassium on tyrosine phosphorylation and map kinase activation in antigen-stimulated rat basophilic leukemia (RBL-2H3) cells.

Aggregation of high affinity IgE Fc receptors (Fc epsilon RI) on RBL-2H3 cells results in tyrosine phosphorylation of 33-, 42-, 44-, 72-, 80-, 90-, 125-kDa proteins. The 42 and 44 kDa proteins were identified as mitogen-activated protein (MAP) kinases with immunoblotting of anti-MAP kinase antibody. The effects of an antiallergic drug, pemirolast potassium (TBX) on Ag-induced protein tyrosine phosphorylation and MAP kinase activation were investigated. When RBL-2H3 cells were stimulated with Ag in the presence of TBX, tyrosine phosphorylation of three proteins (33, 42 and 44 kDa) was inhibited concentration-dependently (0.1-10 micrograms/ml). Inhibition of Ag-induced tyrosine phosphorylation of 33 kDa protein, which could be a beta subunit of Fc epsilon RI, suggests that TBX may prevent the activation of Fc epsilon RI. TBX suppressed activation of MAP kinases (42 and 44 kDa) in response to Ag as well as phorbol myristate acetate (100 nM) or calcium ionophore A23187 (500 nM), implying that the drug acts on signal transduction component(s) between the second messengers and MAP kinases. However, TBX had no effects on protein tyrosine phosphorylation and MAP kinase activation in MC3T3-E1 osteoblastic cells. These results indicate that TBX may affect Fc epsilon RI and also may act as a step distal of Ca2+ mobilization and protein kinase C activation leading to MAP kinase activation in RBL-2H3 cells.

Animals↗