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At least 865 records · Page 48Linked to original sources
PubMed1997

PDGF-BB decreases systolic blood pressure through an increase in macrovascular compliance in rats.

The cardiovascular roles of platelet-derived growth factor (PDGF) were examined in anesthetized rats by monitoring blood pressure and in isolated blood vessels and heart preparations. Intravenous injection of PDGF-BB lowered blood pressure. The decrease in systolic pressure was greater than that in diastolic pressure, so the pulse pressure decreased. PDGF-AA and -AB, other isoforms of PDGF, did not have any effect on blood pressure. Pretreatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, shortened duration of the hypotensive effect of PDGF-BB. The administration of L-arginine with L-NAME partially prevented the effect of L-NAME. PDGF-BB relaxed aortic rings precontracted with phenylephrine with a 50% effective concentration of 3 ng/ml. In contrast, in isolated mesenteric vascular preparations, the vasodilating activity of PDGF-BB was observed only at a high concentration (>12.5 ng/ml). In isolated heart preparations, PDGF-BB had no effect on the beat rate or contractile activity. These results suggest a new role of PDGF-BB that may contribute to the regulation in circulation through the increase in macrovascular compliance mediated by NO.

Animals↗
PubMed1998

Effect of PGE1, PGI2, and PGF2 alpha analogs on collagen gel compaction in vitro and interstitial pressure in vivo.

Acute inflammation in skin is accompanied by increased negativity of interstitial fluid pressure (PIF), which will increase capillary fluid filtration and thereby potentiate edema formation. A series of studies indicates that the connective tissue cells in rat dermis are involved in the control of PIF and mediate this response. The present study describes a novel effect of prostaglandin (PG) E1 isopropyl ester, carbaprostacyclin (PGI2 analog), and latanoprost (PGF2 alpha analog) on edema formation and PIF in parallel with their action on the fibroblast-populated collagen gel contraction assay. The prostaglandins were injected subdermally in pentobarbital-anesthetized rats. PIF was measured with a servo-controlled counterpressure system after circulatory arrest had been induced with saturated potassium chloride. Circulatory arrest was induced to limit edema formation that would raise interstitial fluid volume and thereby attenuate a possible increased negativity of PIF. PGE1 (0.91 mM) and carbaprostacyclin (1.28 mM) lowered PIF from a control value of -0.8 +/- 0.4 mmHg to -3.0 +/- 0.4 (P < 0.01) and -3.7 +/- 0.9 (P < 0.01) mmHg, respectively, within 45 min in a dose-dependent manner. Edema formation was measured in separate experiments. PGE1 and carbaprostacyclin significantly increased interstitial fluid volume (extravascular 51Cr-EDTA space) at concentrations as low as 0.1 and 1.1 microM, respectively. Latanoprost had no effect on PIF or edema formation. However, latanoprost reversed, in a dose-dependent manner, an increased negativity of PIF accompanying the anaphylactic reaction to dextran. In the gel contraction assay with human diploid fibroblasts (AG 1518), a corresponding specificity was observed where PGE1 and carbaprostacyclin effectively inhibited gel contraction although latanoprost had no effect. Thus the present data demonstrate a novel effect of prostaglandins and provide further evidence for active modulation of PIF via loose connective tissue cells.

Alprostadil↗
PubMed1998

PDGF-BB-induced DNA synthesis is delayed by angiotensin II in vascular smooth muscle cells.

The interaction of ANG II with platelet-derived growth factor (PDGF)-BB-induced DNA synthesis was studied in cultured rat aortic smooth muscle cells. PDGF-BB-induced DNA synthesis was delayed (approximately 6-8 h) by ANG II as shown by a time-course experiment. Losartan, an AT1-receptor antagonist, blocked the transient inhibitory effect of ANG II, whereas the AT2-receptor antagonist PD-123319 had no effect. Autocrine- or paracrine-acting transforming growth factor-beta 1 (TGF-beta 1), believed to be a mediator of ANG II-induced inhibitory effects, was not responsible for the delay of PDGF-BB-induced DNA synthesis, because a potent TGF-beta 1 neutralizing antibody could not reverse this effect of ANG II, nor was the delay of the PDGF-BB effect caused by inhibition of PDGF-beta-receptor phosphorylation as shown by Western blot analysis of immunoprecipitated PDGF-beta receptor. In conclusion, our results show that ANG II can exert a transient inhibitory effect on PDGF-BB-induced proliferation via the AT1 receptor.

Angiotensin II↗
PubMed1999

NOS gene transfer inhibits expression of cell cycle regulatory molecules in vascular smooth muscle cells.

The mechanisms of nitric oxide (NO)-mediated inhibition of vascular smooth muscle (VSM) cell proliferation are still obscure. Cyclins A and E in association with cyclin-dependent kinase 2 (cdk2) serve as positive regulators for mammalian cell cycle progression through the G1/S checkpoint of the cell cycle and subsequent cell proliferation. Therefore, we have tested the effect of adenovirus-mediated transfection of the endothelial nitric oxide synthase (eNOS) gene into guinea pig coronary VSM cells on platelet-derived growth factor (BB homodimer) (PDGF-BB)-stimulated cell proliferation and the expression of cell cycle regulatory molecules. Transfection of the eNOS gene (eNOS) into VSM cells significantly inhibited (P < 0.05) [3H]thymidine incorporation into the DNA in response to PDGF-BB stimulation compared with lacZ-transfected control cells. The eNOS transfer significantly inhibited (P < 0.05) PDGF-BB-induced proliferating cell nuclear antigen (PCNA) and cyclin A expression in VSM cells compared with cells transfected with the control vector. The time course of cyclin E expression in response to PDGF-BB stimulation was delayed in eNOS-transfected cells. Levels of cyclin-dependent kinase inhibitors p21 and p27 were not significantly affected by eNOS transfer. eNOS transfer did not decrease PDGF-beta receptor number, affinity, and autophosphorylation measured by radioreceptor assay and Western analysis. These results suggest that inhibition of PDGF-stimulated expression of cyclin A, cyclin E, and PCNA is the target of NO action. These findings could explain, at least in part, NO-mediated inhibition of VSM cell proliferation.

Adenoviridae↗
PubMed2003

Urokinase potentiates PDGF-induced chemotaxis of human airway smooth muscle cells.

We investigated the chemotactic action of PDGF and urokinase on human airway smooth muscle (HASM) cells in culture. Cells were put in collagen-coated transwells with 8-micro m perforations, incubated for 4 h with test compounds, then fixed, stained, and counted as migrated nuclei by microscopy. Cells from all culture conditions showed some basal migration (migration in the absence of stimuli during the assay), but cells preincubated for 24 h in 10% FBS or 20 ng/ml PDGF showed higher basal migration than cells quiesced in 1% FBS. PDGF(BB), PDGF(AA), and PDGF(AB) were all chemotactic when added during the assay. PDGF chemotaxis was blocked by the phosphatidyl 3'-kinase inhibitor LY-294002, the MEK inhibitor U-0126, PGE(2), formoterol, pertussis toxin, and the Rho kinase inhibitor Y-27632. Urokinase alone had no stimulatory effect on migration of quiescent cells but caused a dose-dependent potentiation of chemotaxis toward PDGF. Urokinase also potentiated the elevated basal migration of cells pretreated in 10% FBS or PDGF. This potentiating effect of urokinase appears to be novel. We conclude that PDGF and similar cytokines may be important factors in airway remodeling by redistribution of smooth muscle cells during inflammation and that urokinase may be important in potentiating the response.

Becaplermin↗
PubMed2005

A role for platelet-derived growth factor beta-receptor in a newborn rat model of endothelin-mediated pulmonary vascular remodeling.

Newborn rats exposed to 60% O2 for 14 days develop endothelin (ET)-1-dependent pulmonary hypertension with vascular remodeling, characterized by increased smooth muscle cell (SMC) proliferation and medial thickening of pulmonary resistance arteries. Using immunohistochemistry and Western blot analyses, we examined the effect of exposure to 60% O2 on expression in the lung of receptors for the platelet-derived growth factors (PDGF), which are implicated in the pathogenesis of arterial smooth muscle hyperplasia. We observed a marked O2-induced upregulation of PDGF-alpha and -beta receptors (PDGF-alphaR and -betaR) on arterial smooth muscle. This led us to examine pulmonary vascular PDGF receptor expression in 60% O2-exposed rats given SB-217242, a combined ET receptor antagonist, which we found prevented the O2-induced upregulation of PDGF-betaR, but not PDGF-alphaR, on arterial smooth muscle. PDGF-BB, a major PDGF-betaR ligand, was found to be a potent in vitro inducer of hyperplasia and DNA synthesis in cultured pulmonary artery SMC from infant rats. A critical role for PDGF-betaR ligands in arterial SMC proliferation was confirmed in vivo using a truncated soluble PDGF-betaR intervention, which attenuated SMC proliferation induced by exposure to 60% O2. Collectively, these data are consistent with a major role for PDGF-betaR-mediated SMC proliferation, acting downstream of increased ET-1 in a newborn rat model of 60% O2-induced pulmonary hypertension.

Animals↗
PubMed2004

Abrogation of apoptosis through PDGF-BB-induced sulfated glycosaminoglycan synthesis and secretion.

Platelet-derived growth factor (PDGF)-BB-stimulated glycosaminoglycan (GAG) synthesis/secretion in fetal lung fibroblasts is dependent on sequential activation of the PDGF beta-receptor, phosphatidylinositol 3-kinase (PI3K), the serine/threonine kinase Akt-1,2, and the GTPase Rab3D. Because the Akt pathway has been implicated in cell survival mechanisms, we investigated whether the pathway regulating GAG synthesis/secretion was antiapoptotic. PDGF-BB treatment protected fetal lung fibroblasts against serum starvation-induced apoptosis, whereas wortmannin, an inhibitor of PI3K, abrogated this protective effect. Transfection of constitutively active Akt into fetal lung fibroblasts also safeguarded the cells from apoptosis induced by serum starvation. To determine whether the antiapoptotic response was due, at least in part, to GAGs, we treated lung fibroblasts with beta-D-xyloside as well as with topically applied GAGs, specifically those produced by fetal lung fibroblasts. beta-D-xyloside increased GAG synthesis/secretion and diminished apoptosis. Application of sulfated GAGs, chondroitin sulfate, and heparan sulfate, but not nonsulfated hyaluronan, also resulted in diminished apoptosis. Moreover, topically applied sulfated GAGs increased Bcl-associated death promoter phosphorylation and diminished caspase-3 and -7 cleavage, indicating an antiapototic response. These data are compatible with the PDGF-BB-GAG signaling pathway regulating programmed fibroblast death in the fetal lung.

Animals↗
PubMed2002

Phosphatidylinositol 3-kinase but not tuberin is required for PDGF-induced cell migration.

The loss of function of the tumor suppressor gene TSC2 and its protein product tuberin promotes the development of benign lesions by stimulating cell growth, although the role of tuberin in regulating cell migration and metastasis has not been characterized. In addition, the role of phosphatidylinositol 3-kinase (PI 3-kinase), an important signaling event regulating cell migration, in modulating tuberin-deficient cell motility remains unknown. Using a tuberin-deficient rat smooth muscle cell line, ELT3, we demonstrate that platelet-derived growth factor (PDGF) stimulates cell migration by 3.2-fold, whereas vascular endothelial growth factor (VEGF), transforming growth factor (TGF)-alpha, and basic fibroblast growth factor (bFGF) increase migration by 2.1-, 2.1-, and 2.6-fold, respectively. Basal and PDGF-induced migration in tuberin-deficient ELT3, ELT4, and ERC15 cells was not significantly different from that of tuberin-positive transformed rat kidney epithelial 2, airway smooth muscle, and pulmonary arterial vascular smooth muscle cells. Expression of tuberin in tuberin-deficient ELT3 cells also had little effect on cell migration. In parallel experiments, the role of PI 3-kinase activation in ELT3 cell migration was investigated. LY-294002, a PI 3-kinase inhibitor, decreased PDGF-induced migration in a concentration-dependent manner with an IC(50) of approximately 5 microM. LY-294002 also abrogated ELT3 cell migration stimulated by bFGF and TGF-alpha but not by VEGF and phorbol 12-myristate 13-acetate. Furthermore, transient expression of constitutively active PI 3-kinase (p110*) was sufficient to induce ELT3 cell migration. However, the migration induced by p110* was less than that induced by growth factors, suggesting other signaling pathways are also critically important in modulating growth factor-induced cell migration. These data suggest that PI 3-kinase is required for growth factor-induced cell migration and loss of tuberin appears to have little effect on cell migration.

Animals↗
PubMed2002

Prostacyclin analogs inhibit fibroblast migration.

The controlled accumulation of fibroblasts to sites of inflammation is crucial to effective tissue repair after injury. Either inadequate or excessive accumulation of fibroblasts could result in abnormal tissue function. Prostacyclin (PGI(2)) is a potent mediator in the coagulation and inflammatory processes. The aim of this study was to investigate the effect of PGI(2) on chemotaxis of human fetal lung fibroblasts (HFL-1). Using the blind well chamber technique, we found that the PGI(2) analog carbaprostacyclin (10(-6) M) inhibited HFL-1 chemotaxis to human plasma fibronectin (20 microg/ml) 58.0 +/- 13.2% (P < 0.05) and to platelet-derived growth factor (PDGF)-BB (10 ng/ml) 48.7 +/- 4.6% (P < 0.05). Checkerboard analysis demonstrated that carbaprostacyclin inhibits both directed and undirected migration. The inhibitory effect of the carbaprostacyclin was concentration dependent and blocked by the cAMP-dependent protein kinase (PKA) inhibitor KT-5720, suggesting that a cAMP-PKA pathway may be involved in the process. Two other PGI(2) analogs, ciprostene and dehydro-15-cyclohexyl carbaprostacyclin (both 10(-6) M), significantly inhibited fibroblast migration to fibronectin. In summary, PGI(2) appears to inhibit fibroblast chemotaxis to fibronectin and PDGF-BB. Such an effect may contribute to the regulation of fibroblasts in wound healing and could contribute to the pathogenesis of diseases characterized by abnormal tissue repair remodeling.

Becaplermin↗
PubMed1996

PDGF isoform-induced proliferation and receptor expression in human cultured airway smooth muscle cells.

The effect of recombinant platelet-derived growth factor (PDGF) isoforms (PDGF-AA, -BB and -AB) on mitogenesis of human cultured airway smooth muscle (ASM) was examined using the MTT-reduction assay and [3H]thymidine incorporation. Results were correlated with expression of PDGF receptor (PDGFR)-alpha and -beta subunits in the absence and presence of fetal calf serum (FCS). When FCS was absent PDGF-AB and -BB were potent mitogens, whereas PDGF-AA was weakly mitogenic, evoking <20% of the maximum response induced by the B-chain isoforms. When FCS (2.5%) was present, all PDGF isoforms stimulated marked ASM proliferation with similar efficacy and potency. Cross-competition binding analysis in FCS-deprived cells revealed that ASM cells in culture express mainly PDGFR-beta. Preincubation with PDGF-AA or PDGFR-alpha neutralizing antiserum abolished PDGF-AA binding and decreased total receptor number by approximately 15%. The ratio of PDGFR-alpha to beta subunits was approximately 1:8, supported by intense immunofluorescence staining for PDGFR-beta and weak staining for PDGFR-alpha. In parallel studies, uptake of [3H]thymidine stimulated by PDGF-AA, but not PDGF-AB or -BB, was inhibited by PDGFR-alpha immobilization. Western immunoblot analysis confirmed expression of mature PDGFR-alpha and -beta subunits in ASM cells. FCS did not cause any detectable increase in PDGFR-alpha expression or in PDGF-AA binding. These data support a role for PDGFR-beta mediating ASM mitogenesis during FCS-free conditions, but in the presence of FCS, both PDGFR-alpha and -beta subunits are linked to mitogenesis. The enhanced mitogenicity of PDGF-AA in the presence of FCS was independent of any detectable upregulation of PDGFR-alpha, suggesting that the inability of PDGF-AA to promote mitogenesis in the absence of FCS is not simply due to relative numbers of PDGFR-alpha and PDGFR-beta.

Adult↗
PubMed1996

Role of phospholipase C and tyrosine kinase systems in growth response of human airway smooth muscle cells.

The primary culture of confluent human airway smooth muscle (ASM) cells were exposed up to 5 days to human recombinant interleukin (IL)-1 beta in the presence of indomethacin and 1% fetal bovine serum. The proliferation was assessed by a [3H]thymidine incorporation and direct cell count. We found that IL-1 beta significantly increased thymidine incorporation into and cell count of ASM cells in a concentration-dependent manner. Pretreatment of cells with specific polyclonal antibodies against platelet-derived growth factor (PDGF-BB homodimer) completely inhibited the IL-1 beta-induced increase in thymidine incorporation. The PDGF-BB, at the concentrations of 1.5 and 2.5 ng/ml, stimulated the proliferation of ASM cells. The proliferation action of IL-1 beta was potentiated when PDGF-BB was added into the medium in combination with IL-1 beta. Pretreatment of cells with genistein (0.37 microM), a specific tyrosine kinase inhibitor, attenuated the proliferative effect of IL-1 beta and PDGF-BB. To clarify whether these growth stimuli (IL-1 beta and PDGF-BB) activated phospholipase C (PLC), we examined the formation of phosphatidylinositols. We observed that both agents significantly increased phosphoinositide turnover. In contrast, genistein pretreatment (0.37 microM) prevented formation of inositol 1,4,5-trisphosphate (IP3), as induced by IL-1 beta and/or PDGF-BB. This study demonstrates that both IL-1 beta and PDGF-BB could induce proliferation of ASM cells through the activation of tyrosine kinase and PLC, which in turn stimulate the formation of IP3, a second messenger molecule.

Becaplermin↗
PubMed1996

Maximal PDGF-induced lung fibroblast chemotaxis requires PDGF receptor-alpha.

Alteration of the platelet-derived growth factor (PDGF) receptor system could be important in enhancing the mitogenic and chemotactic potential of lung fibroblasts during pulmonary fibrogenesis. We previously reported that interleukin-1 beta (IL-1 beta) upregulates the PDGF receptor-alpha (PDGFR-alpha) gene, and in this study we sought to establish the importance of the PDGFR-alpha relative to the PDGFR-beta in mediating a chemotactic response to PDGF-AA, -AB, and -BB. Pretreatment of fibroblasts for 24 h with IL-1 beta increased chemotaxis to all three PDGF isoforms. IL-1 beta pretreatment markedly increased the maximal number of 125I-labeled PDGF-AA binding sites but did not change the number of 125I-PDGF-AB or PDGF-BB sites. However, IL-1 beta increased 125I-PDGFR-AB affinity twofold. Neomycin (5 mM) was used as a PDGFR-alpha antagonist and completely blocked 125I-PDGF-AA binding and PDGF-AA-induced chemotaxis. The binding affinity of 125I-PDGF-AB and 125I-PDGF-BB was increased two-to threefold by neomycin, and chemotaxis to PDGF-AB and PDGF-BB was enhanced. These results define a role for the PDGFR-alpha as a regulatory receptor subtype that is necessary for PDGF isoforms to exert maximal chemotaxis.

Animals↗
PubMed1997

Pulmonary artery smooth muscle cells from chronically hypoxic neonatal calves retain fetal-like and acquire new growth properties.

Growth properties retained and acquired by immature pulmonary artery (PA) smooth muscle cells (SMC) in vivo after chronic exposure to hypoxia and the mechanisms that regulate hypoxia-induced change in proliferative phenotype are not known. We tested the hypothesis that PA SMC from neonatal calves exposed to hypoxia after birth would both retain fetal-like and acquire new growth characteristics and that these changes would be at least partially dependent on protein kinase C (PKC), a key proproliferative signal transduction pathway. Like fetal cells, PA SMC from hypoxic calves grew faster in the presence and absence of serum and were more responsive to insulin-like growth factor I and platelet-derived growth factor-BB than control neonatal and adult cells. PA SMC from hypoxic calves also acquired other growth properties (i.e., including increased hypoxic growth after PKC activation) that were new compared with those observed for fetal cells. The proliferative response to hypoxia was first detectable in the neonatal period and was further increased in cells from hypoxic calves. SMC from fetuses and hypoxic calves were more susceptible to the growth-inhibiting effects of PKC antagonists (dihydrosphingosine and calphostin C) than control neonatal and adult cells. To test if the Ca(2+)-dependent isozymes of PKC were uniquely important in the developmental and acquired growth changes observed, the antagonistic effect of the specific, but isozyme nonselective, PKC inhibitor Ro-81-8220 was then compared with GF-109203X, a structural analog with relative specificity for the Ca(2+)-dependent isozymes of PKC (alpha and beta in PA SMC). The faster growing PA SMC from bovine fetuses and hypoxia-exposed calves again demonstrated greater growth inhibition in response to both inhibitors. GF-109203X was equipotent to Ro-31-8220, and its antiproliferative effects were shown to not be due to an increase in apoptosis. Phorbol ester-induced PKC downregulation, another inhibitor strategy that selectively depletes bovine PA SMC of PKC-alpha, but not -beta, mimicked the antiproliferative effects of GF-109203X. Whole cellular PKC catalytic activity paralleled the pattern of peptide-induced growth and susceptibility to PKC inhibition. These results suggest that PA SMC from hypoxia-exposed neonatal calves retain enhanced fetal-like proliferative capacity and acquire new growth properties that are at least partially dependent on the Ca(2+)-regulated isozymes of PKC and in particular PKC-alpha.

Aging↗
PubMed1998

PDGF-induced glycosaminoglycan synthesis is mediated via phosphatidylinositol 3-kinase.

Platelet-derived growth factor (PDGF)-BB has been shown previously to increase glycosaminoglycan (GAG) synthesis but not DNA synthesis in freshly isolated fetal lung fibroblasts. In the present study, we found that PDGF-BB also enhanced 35SO4 incorporation into the small, soluble proteoglycan biglycan without affecting biglycan's core protein mRNA expression, suggesting that PDGF-BB mainly affects GAG chain elongation and/or sulfation. PDGF-BB-stimulated GAG synthesis was abrogated by tyrphostin 9, a PDGF receptor-associated tyrosine kinase inhibitor, implying that the stimulatory effect is mediated via the PDGF beta-receptor (PDGFR). The intracellular signal transduction pathways that mediate PDGF-BB-stimulated GAG synthesis in fetal lung fibroblasts were investigated. On ligand-induced tyrosine phosphorylation, PDGFR associated with phospholipase C (PLC)-gamma 1, Ras GTPase activating protein (RasGAP), and phosphatidylinositol 3-kinase (PI3K) but not with the Syp-growth factor receptor-bound protein 2-Son of Sevenless complex. Association of PDGFR with PLC-gamma 1 and RasGAP followed by their tyrosine phosphorylation failed, however, to activate PLC-gamma 1, protein kinase C (PKC), and Ras. Neither a PLC-gamma inhibitor, U-73122; a PKC inhibitor, calphostin C; nor a mitogen-activated protein kinase kinase inhibitor, PD-98059, inhibited PDGF-BB-induced GAG synthesis. In contrast, PDGF-BB stimulation triggered PDGFR-associated PI3K activity. Both PDGF-BB-induced PI3K activation and GAG synthesis were abolished by the PI3K inhibitors wortmannin and LY-294002. The results suggest that PI3K is a downstream mediator of PDGF-BB-stimulated GAG synthesis in fetal rat lung fibroblasts.

Animals↗
PubMed1999

Modulation of human airway smooth muscle proliferation by type 3 phosphodiesterase inhibition.

Elevation in cell cAMP content can inhibit mitogenic signaling in cultured human airway smooth muscle (HASM) cells. We studied the effects of the type 3-selective phosphodiesterase inhibitor siguazodan, the type 4-selective phosphodiesterase inhibitor rolipram, and the nonselective inhibitor 3-isobutyl-1-methylxanthine (IBMX) on proliferation of cultured HASM cells. At concentrations selective for the type 3 phosphodiesterase isoform, siguazodan inhibited both [3H]thymidine incorporation (IC50 2 microM) and the increase in cell number (10 microM; 64% reduction) induced by platelet-derived growth factor-BB (20 ng/ml). These effects were mimicked by IBMX. At concentrations selective for type 4 phosphodiesterase inhibition, rolipram was without effect. A 20-min exposure to siguazodan and rolipram did not increase whole cell cAMP levels. However, in HASM cells transfected with a cAMP-responsive luciferase reporter (p6CRE/Luc), increases in cAMP-driven luciferase expression were seen with siguazodan (3.9-fold) and IBMX (16.5-fold). These data suggest that inhibition of the type 3 phosphodiesterase isoform present in airway smooth muscle results in inhibition of mitogenic signaling, possibly through an increase in cAMP-driven gene expression.

1-Methyl-3-isobutylxanthine↗
PubMed2001

PDGF-BB-mediated activation of p42(MAPK) is independent of PDGF beta-receptor tyrosine phosphorylation.

Herein, we investigated the activity of mitogen-activated protein kinase (MAPK), a key component of downstream signaling events, which is activated subsequent to platelet-derived growth factor (PDGF)-BB stimulation. Specifically, p42(MAPK) activity peaked 60 min after addition of PDGF-BB, declined thereafter, and was determined not to be a direct or necessary component of glycosaminoglycan (GAG) synthesis. PDGF-BB also activated MAPK kinase 2 (MAPKK2) but had no effect on MAPKK1 and Raf-1 activity. Chemical inhibition of Janus kinase, phosphatidylinositol 3-kinase, Src kinase, or tyrosine phosphorylation inhibition of the PDGF beta-receptor (PDGFR-beta) did not abrogate PDGF-BB-induced p42(MAPK) activation or its threonine or tyrosine phosphorylation. A dominant negative cytoplasmic receptor for hyaluronan-mediated motility variant 4 (RHAMMv4), a regulator of MAPKK-MAPK interaction and activation, did not inhibit PDGF-BB-induced p42(MAPK) activation nor did a construct expressing PDGFR-beta with cytoplasmic tyrosines mutated to phenylalanine. However, overexpression of a dominant negative PDGFR-beta lacking the cytoplasmic signaling domain abrogated p42(MAPK) activity. These results suggest that PDGF-BB-mediated activation of p42(MAPK) requires the PDGFR-beta but is independent of its tyrosine phosphorylation.

Animals↗
PubMed2002

Tryptase's potent mitogenic effects in human airway smooth muscle cells are via nonproteolytic actions.

We reported previously that mast cell tryptase is a growth factor for dog tracheal smooth muscle cells. The goals of our current experiments were to determine if tryptase also is mitogenic in cultured human airway smooth muscle cells, to compare its strength as a growth factor with that of other mitogenic serine proteases, and to determine whether its proteolytic actions are required for mitogenesis. Highly purified preparations of human lung beta-tryptase (1-30 nM) caused dose-dependent increases in DNA synthesis in human airway smooth muscle cells. Maximum tryptase-induced increases in DNA synthesis far exceeded those occurring in response to coagulation cascade proteases, such as thrombin, factor Xa, or factor XII, or to other mast cell proteases, such as chymase or mastin. Irreversibly abolishing tryptase's catalytic activity did not alter its effects on increases in DNA synthesis. We conclude that beta-tryptase is a potent mitogenic serine protease in cultured human airway smooth muscle cells. However, its growth stimulatory effects in these cells occur predominantly via nonproteolytic actions.

Animals↗
PubMed2000

Evidence that platelet-derived growth factor may be a novel endogenous pyrogen in the central nervous system.

Platelet-derived growth factor (PDGF) exerts neurotrophic and neuromodulatory actions in the mammalian central nervous system (CNS). Like the cytokines, PDGF primarily signals through tyrosine phosphorylation-dependent pathways that activate multiple intracellular molecules including Janus family kinases. We previously showed that microinjection of PDGF-BB into the lateral ventricle induced a febrile response in rats that was reduced by pretreatment with Win 41662, a potent inhibitor of PDGF receptors (Pelá IR, Ferreira MES, Melo MCC, Silva CAA, and Valenzuela CF. Ann NY Acad Sci 856: 289-293, 1998). In this study, we further characterized the role of PDGF-BB in the febrile response in rats. Microinjection of PDGF-BB into the third ventricle produced a dose-dependent increase in colonic temperature that peaked 3-4 h postinjection. Win 41662 attenuated fever induced by intraperitoneal injection of bacterial lipopolysaccharide, suggesting that endogenous PDGF participates in the febrile response to this exogenous pyrogen. Importantly, febrile responses induced by tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 were unchanged by Win 41662. Both indomethacin and dexamethasone blocked the PDGF-BB-induced increase in colonic temperature, and, therefore, we postulate that PDGF-BB may act via prostaglandin- and/or inducible enzyme-dependent pathways. Thus our findings suggest that PDGF-BB is an endogenous CNS mediator of the febrile response in rats.

Animals↗