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Biomedical subjects

I Kojima

Publications and source records attributed to I Kojima.

At least 73 records · Page 4Linked to original sources
PubMed1997

Effect of nitrogen source on biosynthesis of rapamycin by Streptomyces hygroscopicus.

Six non-amino acid nitrogen compounds were examined as nitrogen source for growth of Streptomyces hygroscopicus and biosynthesis of rapamycin. Of the nitrogen sources studied, ammonium sulfate was the best with respect to formation of rapamycin, and supported cell growth comparable to the organic nitrogen sources used in the control chemically defined medium, i.e., aspartate, arginine plus histidine. In the new chemically defined medium, which is buffered with 200 mM 2-(N-morpholino)ethanesulfonic acid to prevent decline of pH during fermentation, an ammonium sulfate concentration of 40 mM was optimal for biosynthesis of rapamycin. Rapamycin production increased by more than 30% on both volumetric and specific bases as compared to the previous medium containing the three amino acids as nitrogen source.

Ammonium Sulfate↗
PubMed1997

Reciprocal expression of mRNA for inhibin betaC and betaA subunits in hepatocytes.

Messenger RNA expression of activin betaC subunit in the liver was compared with that for betaA subunit before and after 70% hepatectomy. mRNA for betaC was abundantly expressed in the liver but decreased at 12 h and later after 70% hepatectomy, whereas that for betaA was increased 12 h after the hepatectomy. We also compared the expression of mRNA for betaA and betaC in cultured rat hepatocytes. mRNA for betaC subunit was abundantly expressed in the beginning of the culture but was reduced gradually after stimulation with epidermal growth factor. In contrast, mRNA for betaA subunit was undetectable before stimulation and was increased 24 to 48 h after stimulation with the mitogen. These results indicate that expression of mRNA for betaC and betaA is regulated differently. The role of activin C may be different from that of activin A in the liver.

Animals↗
PubMed1996

Small-Angle X-ray Diffraction of Muscle Using Undulator Radiation from the Tristan Main Ring at KEK.

Time-resolved X-ray diffraction of muscle has demanded ever-increasing flux into small sample volumes with low beam divergence. Results are reported of static and time-resolved small-angle X-ray diffraction studies on muscle fibers using a hard X-ray undulator installed in the Tristan main ring at KEK, Tsukuba, Japan, as an innovative source of synchrotron radiation more intense and better collimated than that available with the Photon Factory bending-magnet beamline. Static studies used the low divergence of the source to obtain detailed high-quality diffraction patterns of stable muscle states. The diffraction patterns from live skeletal muscles showed the numerous (over 100) meridional reflections. The well collimated beam from the undulator made it possible to clearly resolve, with an angular resolution of ca 700 nm, the closely spaced diffraction peaks arising from the two halves of the thick filaments centred on the M lines in a sarcomere, in addition, the diffraction peaks from the thin filaments on opposite sides of the Z bands could be resolved with an angular resolution of ca 1000 nm. The detailed structure of the meridional pattern defines the nature of the molecular packing in the thick and thin filaments. Time-resolved experiments using a focusing mirror aimed to prove cross-bridge states in striated muscle fibers by collecting X-ray diffraction data at a 0.185 ms time resolution from sinusoidally oscillating chemically skinned rabbit muscle fibers during active contraction and in rigor. When sinusoidal length changes at 500 Hz with a peak-to-peak amplitude of 0.6% of the muscle length were applied to a small fiber bundle, the tension showed a simple elastic response during the length oscillation. In the active muscle the intensity of the 14.5 nm myosin-based meridional reflection changed out of phase with the tension change during the oscillating length change. In contrast, in the rigor muscle it occurred in phase with the tension change. The high time-resolved experiments provide an insight into the coupling between conformational changes and force generation of the actomyosin cross-bridges. These studies provide a preview of the expected gains for muscle studies from the more widespread use of undulator radiation at third-generation synchrotron sources.

Journal Article↗
PubMed1996

A natural sulfated polysaccharide, calcium spirulan, isolated from Spirulina platensis: in vitro and ex vivo evaluation of anti-herpes simplex virus and anti-human immunodeficiency virus activities.

A sulfated polysaccharide named calcium spirulan (Ca-SP) has been isolated from a sea alga, Spirulina platensis, as an antiviral component. The anti-human immunodeficiency virus type 1 (HIV-1) and anti-herpes simplex virus type 1 (HSV-1) activities of Ca-SP were compared with those of dextran sulfate (DS) as a representative sulfated polysaccharide. Anti-HIV-1 activities of these agents were measured by three different assays: viability of acutely infected CD4-positive cells, or a cytopathology assay; determination of HIV-1 p24 antigen released into culture supernatants; and inhibition of HIV-induced syncytium formation. Anti-HSV-1 activity was assessed by plaque yield reduction. In addition, their effects on the blood coagulation processes and stability in the blood were evaluated. These data indicate that Ca-SP is a potent antiviral agent against both HIV-1 and HSV-1. Furthermore, Ca-SP is quite promising as an anti-HIV agent because even at low concentrations of Ca-SP an enhancement of virus-induced syncytium formation was not observed, as was observed in DS-treated cultures, Ca-SP had very low anticoagulant activity, and showed a much longer half-life in the blood of mice when compared with that of DS. Thus, Ca-SP can be a candidate agent for an anti-HIV therapeutic drug that might overcome the disadvantages observed in many sulfated polysaccharides. When the role of chelation of calcium ion with sulfate groups was examined by removing calcium or its replacement by sodium, the presence of calcium ion in the molecule was shown to be essential for the dose-dependent inhibition of cytopathic effect and syncytium formation induced by HIV-1.

Animals↗
PubMed1996

A synthetic peptide corresponding to the Rab4 hypervariable carboxyl-terminal domain inhibits insulin action on glucose transport in rat adipocytes.

The present study was conducted to examine the involvement of Rab4, a low molecular weight GTP-binding protein, in the action of insulin on glucose transport. A synthetic peptide corresponding to the Rab4 hypervariable carboxyl-terminal domain, Rab4-(191-210), was successfully transferred into rat adipocytes by electroporation and inhibited insulin-stimulated glucose transport by about 50% without affecting the basal transport activity. In contrast, synthetic peptides corresponding to the Rab3C and Rab3D carboxyl-terminal hypervariable domain had little effect on insulin action on glucose transport. The Rab4-(191-210) peptide also reduced insulin-induced GLUT4 translocation from the intracellular pool to the plasma membrane. Furthermore, the Rab4-(191-210) peptide reduced both insulin-induced glucose transport and GLUT4 translocation in the presence of a major histocompatibility complex class I antigen-derived peptide, D(k)-(62-85), which is a potent inhibitor of GLUT4 internalization, suggesting that the peptide inhibited exocytotic recruitment of GLUT4-containing vesicles. The Rab4-(191-210) peptide also inhibited GTP gamma S-stimulated glucose transport. In addition, insulin-stimulated glucose transport was inhibited by the addition of anti-Rab4 antibody. These results suggest that Rab4 protein plays a crucial role in insulin action on GLUT4 translocation, especially in exocytotic recruitment by the hormone of the glucose transporter to the plasma membrane from the intracellular retention pool.

3-O-Methylglucose↗
PubMed1996

Betacellulin and activin A coordinately convert amylase-secreting pancreatic AR42J cells into insulin-secreting cells.

Rat pancreatic AR42J cells possess exocrine and neuroendocrine properties. Activin A induces morphological changes and converts them into neuron-like cells. In activin-treated cells, mRNA for pancreatic polypeptide (PP) but not that for either insulin or glucagon was detected by reverse transcription-PCR. About 25% of the cells were stained by anti-PP antibody. When AR42J cells were incubated with betacellulin, a small portion of the cells were stained positively with antiinsulin and anti-PP antibodies. The effect of betacellulin was dose dependent, being maximal at 2 nM. Approximately 4% of the cells became insulin positive at this concentration, and mRNAs for insulin and PP were detected. When AR42J cells were incubated with a combination of betacellulin and activin A, approximately 10% of the cells became insulin positive. Morphologically, the insulin-positive cells were composed of two types of cells: neuron-like and round-shaped cells. Immunoreactive PP was found in the latter type of cells. The mRNAs for insulin, PP, glucose transporter 2, and glucokinase, but not glucagon, were detected. Depolarizing concentration of potassium, tolbutamide, carbachol, and glucagon-like peptide-1 stimulated the release of immunoreactive insulin. These results indicate that betacellulin and activin A convert amylase-secreting AR42J cells into cells secreting insulin. AR42J cells provide a model system to study the formation of pancreatic endocrine cells.

Activins↗
PubMed1996

Calcium as a second messenger of the action of transforming growth factor-beta on insulin secretion.

In MIN6 insulinoma cells, transforming growth factor-beta (TGF-beta) induced the oscillatory elevation of the cytoplasmic free calcium concentration, [Ca2+]c, in the presence of 5.5 mM glucose. The increase in [Ca2+]c induced by TGF-beta was totally dependent on calcium entry and attenuated by nifedipine or nickel chloride. In contrast, carbachol elevated [Ca2+]c in the presence of nickel chloride. When the plasma membrane was hyperpolarized by diazoxide, TGF-beta did not raise [Ca2+]c, whereas both carbachol and depolarizing concentration of potassium elevated [Ca2+]c under the same conditions. TGF-beta did not affect either the cellular cyclic AMP or inositol trisphosphate levels. In the presence of 5.5 mM glucose, TGF-beta induced a 3-fold increase in insulin secretion and the effect of TGF-beta was blocked by either nifedipine or nickel chloride. TGF-beta did not stimulate insulin secretion in the presence of 100 microM diazoxide, whereas both carbachol and 40 mM potassium chloride significantly increased insulin secretion. These results suggest that TGF-beta induces the oscillatory elevation of [Ca2+]c in MIN6 cells by stimulating calcium entry via voltage-dependent calcium channels. Calcium is an intracellular messenger of the action of TGF-beta on insulin secretion.

Calcium↗
PubMed1996

Norepinephrine reverses the effects of activin A on DNA synthesis and apoptosis in cultured rat hepatocytes.

Activin A, an autocrine factor produced by hepatocytes, inhibits mitogen-stimulated DNA synthesis and induces apoptotic death of cultured rat hepatocytes. Several lines of evidence indicate that norepinephrine (NE), as a comitogenic growth factor, alters the balance between growth stimulation and inhibition and acts as a trigger for the initiation of hepatocyte proliferation. In the present study, we examined whether NE modulated the effects of activin A on rat hepatocytes in primary culture. Activin A, at a concentration of 10(-9) mol/L, blocked the effect of epidermal growth factor (EGF) on DNA synthesis, that was assessed by measuring [3H] thymidine incorporation and nuclear labeling, almost completely, and NE reversed the inhibitory effect of activin A on DNA synthesis. This effect of NE was dose-dependent, being significant at concentrations of 10(-6) mol/L and above, but was overcome by higher concentrations of activin A, and was attenuated by prazosin, but not by yohimbine or propranolol. NE exerted its effect during the first 24 hours of culture, but was ineffective when added after 24 hours. EGF augmented the release of follistatin, an activin-binding protein known to block the action of activin A, by hepatocytes and NE did not affect the amount of follistatin they released. In addition to inhibiting DNA synthesis by hepatocytes cultured with EGF, activin A induced death of hepatocytes cultured in the absence of EGF. The nuclear morphology of cells cultured with activin A alone was strikingly changed compared with untreated control cells and marked identation of the nuclear membranes and moderate chromatin condensation were observed. Fragmentation of DNA was also observed, suggesting that activin A induced apoptosis, and activin-mediated cell death was prevented significantly by NE. These results indicate that NE, acting on alpha 1-adrenergic receptors, attenuates the effects of activin A on DNA synthesis by and apoptosis of cultured rat hepatocytes.

Activins↗
PubMed1996

Intravenous administration of follistatin: delivery to the liver and effect on liver regeneration after partial hepatectomy.

When 1 microgram 125I-follistatin was administered into a rat intravenously, radioactivity levels in serum decreased rapidly. Analysis with a biexponential equation showed that the initial half-life and the terminal half-life were 4.0 and 130.8 minutes, respectively. After 2 hours of infusion, approximately 9% of the follistatin infused remained in the liver, which was much more than that in kidney, spleen, pancreas, intestine, or lung. Autoradiography of the liver obtained at 24 hours of infusion revealed that numerous grains were located in parenchymal cells. Radioactivity of 125I-follistatin in the liver remained elevated until 72 hours and declined markedly thereafter. When a booster shot of 125I-follistatin was administered at 72 hours, radioactivity in the liver at 120 hours was markedly increased compared with that in rats that received a single shot of 125I-follistatin. We then examined the effect of intravenous infusion of follistatin on liver regeneration after hepatectomy of 70%. Immediately after the hepatectomy, either 1 microgram follistatin or saline was infused intravenously. In some rats, a booster shot was infused at 72 hours. After 120 hours of hepatectomy of 70%, remnant liver weight, liver regeneration rate, and DNA content were significantly (P < .05) higher in rats that received a booster shot of follistatin at 72 hours than those in control rats. These results indicate that follistatin administered intravenously accumulates in the liver and promotes liver regeneration after partial hepatectomy.

Animals↗
PubMed1996

Characterization of the activin receptor in cultured rat hepatocytes.

Activin A is an autocrine inhibitor of initiation of DNA synthesis in rat hepatocytes. The present study was conducted to characterize the cell-surface receptors for activin A in cultured rat hepatocytes by measuring 125I-activin A binding. Scatchard analysis of 125I-activin A binding indicated the existence of two classes of binding sites with apparent Kd values of 3 x 10(-10) mol/L and 3.5 x 10(-9) mol/L. Pretreatment of the cells with heparitinase reduced the number of low-affinity binding sites, whereas pretreatment with excess exogenous follistatin increased the number of low-affinity binding sites. Affinity cross-linking of 125I-activin A to hepatocytes revealed distinct protein complexes with molecular weights of approximately 48, 65, and 85 kd, which may represent cross-linked cell-bound follistatin, type I and type II activin receptors, respectively. Another band with a molecular weight of 180 kd was also found, which may represent the type III activin receptor. When hepatocytes were cultured with epidermal growth factor (EGF), both high- and low-affinity binding sites increased at 12 hours without altering their affinities. At 60 hours of the incubation with EGF, the high-affinity binding sites decreased while the number of low-affinity binding sites increased slightly. These results indicate that two classes of 125I-activin A binding sites exist in cultured hepatocytes: the high-affinity binding site may represent oligomeric complex of the type I and type II receptors, and at least part of the low-affinity binding site may represent cell-bound follistatin. The number of activin receptors in hepatocytes is increased after the stimulation with EGF.

Activin Receptors↗
PubMed1996

Calcium spirulan, an inhibitor of enveloped virus replication, from a blue-green alga Spirulina platensis.

Bioactivity-directed fractionation of a hot H2O extract from a blue-green alga Spirulina platensis led to the isolation of a novel sulfated polysaccharide named calcium spirulan (Ca-SP) as an antiviral principle. This polysaccharide was composed of rhamnose, ribose, mannose, fructose, galactose, xylose, glucose, glucuronic acid, galacturonic acid, sulfate, and calcium. Ca-SP was found to inhibit the replication of several enveloped viruses, including Herpes simplex virus type 1, human cytomegalovirus, measles virus, mumps virus, influenza A virus, and HIV-1. It was revealed that Ca-SP selectively inhibited the penetration of virus into host cells. Retention of molecular conformation by chelation of calcium ion with sulfate groups was suggested to be indispensable to its antiviral effect.

Antiviral Agents↗
PubMed1996

Nitric oxide: a modulator for the epidermal growth factor receptor expression in developing ovarian granulosa cells.

the present study was designed to assess the involvement of nitric oxide (NO) in the regulation of the epidermal growth factor (EGF) receptor during development of rat granulosa cells, which were prepared by puncturing ovaries of diethylstilbestrol-treated rats. The immature cells were cultured for 48 h with follicle-stimulating hormone (FSH) to be transformed into mature cells. A marked accumulation of guanosine 3',5' -cyclic monophosphate (cGMP) was observed during development. The accumulation of cGMP, but not of adenosine 3',5'-cyclic monophosphate (cAMP), was suppressed by specific inhibitors of NO synthase, L-NG-monomethyl-L-arginine (L-NMMA) and L-N(G)-nitro-L-arginine, and a selective inhibitor of the inducible NO synthase, aminoguanidine. The L-NMMA-induced suppression was partially reversed by addition of L-arginine to cultures but not D-arginine, indicating that NO formation is inhibited by competing with analogues of L-arginine for NO synthase. Treatment with 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide , an antagonist of NO, caused suppression in the increase of EGF binding sites, whereas exposure of the cells to sodium nitroprusside (SNP), an NO donor, caused elevation in EGF binding sites, with increasing extra- and intracellular cGMP levels. Analysis of the EGF receptor by affinity labeling with 125I-labeled EGF revealed that the intensity of the cross-linked receptor molecular with a molecular mass of 180 kDa was increased by exposure to SNP. The facilitatory effect of SNP on the EGF receptor was observed when the cAMP-dependent pathway was fully activated by FSH. However, the NO effect may be mediated by a cGMP-independent pathway, as 8-bromo-cGMP did not mimic the action of SNP. These results indicate that the L-arginine-NO system may contribute to the regulation of EGF receptor expression in developing granulosa cells stimulated by FSH.

Animals↗
PubMed1996

Formation of insulin-producing cells from pancreatic acinar AR42J cells by hepatocyte growth factor.

Pancreatic AR42J cells are derived from acinar cells and express both exocrine and neuroendocrine properties. We have recently shown that these cells convert into insulin-producing cells in vitro after treatment with activin A and betacellulin. Here, we investigated the effect of hepatocyte growth factor (HGF) in those cells. When AR42J cells were incubated with HGF, DNA synthesis was attenuated, and the amylase content was reduced in a concentration-dependent manner. HGF-treated cells extended processes, but bundle formation was not observed using an antibody against tubulin. Reverse both insulin and pancreatic polypeptide (PP) were expressed in HGF-treated, but not naive, AR42J cells. Immunocytochemical analysis indicated that approximately 3% of the HGF-treated cells were stained with antiinsulin antibody, and some were also stained with anti-PP antibody. When AR42J cells were exposed to a combination of activin A and HGF, cells extended longer processes, and over 10% of them were stained with antiinsulin antibody. In these cells, messenger RNAs for insulin, PP, glucose transporter 2, and glucokinase, but not those for glucagon or somatostatin, were expressed. A subclone of AR42J cells, AR42J-B13, was obtained. Most of the AR42J-B13 cells converted to insulin-producing cells after the incubation with activin A and HGF. Insulin secretion was augmented by tolbutamide, depolarizing concentrations of potassium, carbachol, and glucagon-like peptide-1 in these cells. These results indicate that HGF reduces the acinar cell-like property of AR42J cells and converts them into insulin-producing cells. The effect of HGF was markedly enhanced by activin A.

Activins↗
PubMed1996

Growth of differentiation: determination by FSH of the action of insulin-like growth factor-I in cultured rat granulosa cells.

Insulin-like growth factor-I (IGF-I) is a potent mitogen in many cell systems. In cultured rat granulosa cells, however, IGF-I is known to be an inducer of differentiation. The present study was conducted to identify the factor which determines the direction of IGF-I action: either DNA synthesis or LH receptor expression. When granulosa cells were incubated with IGF-I in the presence of various concentrations of follicle-stimulating hormone (FSH), DNA synthesis as assessed by [3H]thymidine incorporation was increased only in the presence of low doses of FSH. The stimulatory effect of FSH on DNA synthesis was observed in a very narrow range of FSH concentration between 2 and 10 ng/ml. At higher concentrations, FSH had little effect on DNA synthesis but instead induced expression of receptors for luteinizing hormone (LH), a marker of granulosa cell differentiation. At 5 ng/ml, FSH elicited maximal stimulation of DNA synthesis and simultaneously induced LH receptor expression to some extent. In these cells, DNA synthesis peaked at 36 h but expression of LH receptor occurred later than 36 h, peaking at 60 h. The ability of IGF-I to stimulate DNA synthesis was enhanced by the long term pretreatment with FSH: when FSH was added from the beginning and IGF-I was added after 36 h or later, IGF-I-mediated DNA synthesis was approximately twice as great, and was accompanied by a two-fold increase in the number of bromodeoxyuridine-labeled nuclei. Under these conditions, LH receptor expression was reduced to approximately 50%. Finally when cells were incubated for 12 h with or without FSH, washed extensively with the medium and then IGF-I was added, DNA synthesis was augmented only in FSH-primed cells. Forskolin, an activator of adenylate cyclase, reproduced the effect of FSH. These results indicate that, in the presence of FSH, IGF-I has the ability to induce both DNA synthesis and differentiation and that FSH determines the action of IGF-I on promotion of either growth or differentiation. Furthermore, priming with FSH renders granulosa cells responsive to IGF-I in terms of DNA synthesis.

Animals↗
PubMed1996

Two distinct signaling pathways activated by activin A in glucose-responsive pancreatic beta-cell lines.

Activin A stimulates insulin secretion in pancreatic beta-cells by a calcium-dependent mechanism. The present study was conducted to further characterize the effects of activin A in two glucose-responsive insulinoma cell lines, MIN6 and HIT-T15 cells. In HIT-T15 cells, activin A evoked an increase in cytoplasmic free calcium concentration, stimulated insulin secretion, maintained glucose responsiveness of the cells and inhibited DNA synthesis. However, activin A did not have any effect in MIN6 cells. Measurement of 125I-labeled activin A binding in MIN6 cells revealed that the number of binding sites was markedly reduced, suggesting that the refractoriness was due, at least partly, to the reduced numbers of the activin receptor. Stable transfectants of MIN6 cells that overexpressed the type II activin receptor were then developed. The transfected cells (MIN6-ActR cells) expressed ten times more 125I-labeled activin A-binding sites than parental cells and the apparent Kd was 1.15 nM, which was nearly identical to that in parental cells. Affinity cross-linking in MIN6-ActR cells showed that a 90 kDa type II receptor as well as a 52 kDa protein, presumably follistatin, was markedly labeled with 125I-labeled activin A. Although MIN6-ActR cells expressed significant numbers of activin receptors, activin A did not induce immediate calcium-dependent responses in these cells. In contrast, activin A was capable of inducing long-term effects in MIN6-ActR cells; thus, reduction of the glucose concentration in culture medium from 25 to 5.5 mM for 4 days resulted in a remarkable loss of insulin response to glucose stimulation but this decline in response to glucose was prevented by the addition of activin A during culture. In addition, activin A inhibited DNA synthesis in MIN6-ActR cells. Hence, although activin A did not induce calcium-dependent responses, it evoked some calcium-independent effects in MIN6-ActR cells. Taken together, activin A elicits various effects in beta-cells by both calcium-dependent and -independent mechanisms.

Activin Receptors↗
PubMed1996

Direct fermentative production of acyltylosins by genetically-engineered strains of Streptomyces fradiae.

A tylosin-producer, Streptomyces fradiae, was transformed with plasmids carrying genes from Streptomyces thermotolerans that are involved in acyl modification of macrolide antibiotics. A transformant with pMAB3, in which macrolide 4"-O-acyltransferase gene (acyB1) and its regulatory gene (acyB2) are subcloned, produced several types of 4"-O-acyltylosins. A transformant with pAB11 delta EH containing macrolide 3-O-acyltransferase gene (acyA) in addition to the above two genes produced 3-O-acetyltylosin and 3-O-acetyl-4"-O-acyltylosins. Among the products of the latter transformant, 3-O-acetyl-4"-O-isovaleryltylosin (AIV) was detected as a minor component. When L-leucine, a precursor of isovaleryl-CoA, was added to the medium at the late stage of the fermentation, AIV content among the total macrolides increased ten-fold and AIV became a main product. This fact suggests that a high level of endogenous isovaleryl-CoA may be essential for the selective production of AIV by S. fradiae carrying pAB11 delta EH.

Acylation↗
PubMed1996

Blockade of DNA synthesis induced by platelet-derived growth factor by tranilast, an inhibitor of calcium entry, in vascular smooth muscle cells.

The present study was conducted to establish a pharmacological method of controlling growth of vascular smooth muscle cells (VSMC) by blocking calcium entry. In cultured rat VSMC, 1 nM platelet-derived growth factor (PDGF) induced a biphasic elevation of cytoplasmic free calcium concentration, ([Ca2+]c). The second sustained phase of [Ca2+]c was dependent on extracellular calcium. At lower concentrations, PDGF induced oscillatory changes in [Ca2+]c, and reduction of extracellular calcium attenuated the oscillation. An antiallergic compound, tranilast, abolished the sustained phase of [Ca2+]c induced by 1 nM PDGF. Tranilast also inhibited the oscillatory changes in [Ca2+]c induced by 200 pM PDGF. In addition, PDGF-induced calcium influx in the late G1 phase, as assessed by measuring the initial uptake of 45Ca, was inhibited by tranilast in a concentration-dependent manner. Tranilast also inhibited PDGF-augmented DNA synthesis; the ID50 for the inhibition of DNA synthesis was nearly identical to that for calcium influx. Although tranilast blocked PDGF-induced calcium entry, it did not affect PDGF-mediated autophosphorylation of the PDGF receptor, activation of phosphatidylinositol 3-kinase, activation of Ras or mitogen-activated protein kinase. Similarly, PDGF-induced elevation of diacylglycerol was not affected by tranilast. These results suggest that the antiallergic drug tranilast inhibits PDGF-induced DNA synthesis by blocking PDGF-mediated calcium entry. Tranilast may be of use in controlling PDGF-induced DNA synthesis in VSMC.

Animals↗