Platelet-derived Growth Factor Receptor Autophosphorylation Research Articles

Adiponectin Inhibits PDGF-induced Mesangial Cell Proliferation: Regulation of Mammalian Target of Rapamycin-mediated Survival Pathway by Adenosine 5-Monophosphate-activated Protein Kinase

An aberrant proliferation of mesangial cells (MCs) is one of the more important features of diabetic nephropathy (DN). Adiponectin, an adipocyte-derived hormone, has been associated with type 2 diabetes, a known cause of DN. Recent studies have suggested that adiponectin has a protective effect on the kidney. To elucidate the potential protective mechanism of adiponectin on kidney, we investigated the effects of adiponectin on platelet-derived growth factor (PDGF)-induced cell proliferation and intracellular signaling pathways in cultured Human MCs (HMCs). PDGF-induced HMC proliferation was significantly inhibited by the co-treatment of adiponectin. Adiponectin alone had no effect on HMC proliferation. The mammalian target of rapamycin (mTOR) and 40 S ribosomal S6 kinase 1 (S6K1) were activated by PDGF stimulation in HMCs. PDGF-induced mTOR and S6K1 phosphorylations were significantly attenuated by the co-treatment of adiponectin in HMC. Adiponectin alone had no effects on PDGF-receptor autophosphorylation by PDGF. We also confirmed that the inhibitory effect of adiponectin on PDGF-induced HMC proliferation was significantly suppressed by compound C, an adenosine 5'-monophosphate-activated protein kinase (AMPK) inhibitor. From these findings, it is implied that adiponectin could attenuate renal dysfunction associated with MC disorders through AMPK-mTOR signal pathway.

Masitinib demonstrates anti‐proliferative and pro‐apoptotic activity in primary and metastatic feline injection‐site sarcoma cells*

Dysregulation of platelet-derived growth factor receptor (PDGFR) may play a role in feline injection-site sarcoma (ISS) cell growth and viability. Masitinib, a tyrosine kinase inhibitor approved for treatment of canine mast cell tumours, is highly selective for the PDGFR signalling pathway and may offer a new therapeutic approach for this disease. The in vitro effects of masitinib on growth, apoptosis and PDGFR signalling in two novel ISS cell lines were investigated. PDGFR expression was confirmed by Western blot in cell lines derived from a primary ISS tumour (JB) and a corresponding, histologically confirmed ISS lung metastasis (JBLM). Masitinib inhibited cell growth and PDGFR phosphorylation in both cell lines. Higher drug concentrations were required to inhibit growth than to modulate ligand-induced autophosphorylation of PDGFR. These in vitro data suggest that masitinib displays activity against both primary and metastatic ISS cell line and may aid in the clinical management of ISS.

Chrysin restores PDGF-induced inhibition on protein tyrosine phosphatase and reduces PDGF signaling in cultured VSMCs

Previous studies have shown that an increased intake of dietary flavonoids is associated with a decreased risk of cardiovascular diseases (CVDs). PDGF is a major mitogen for vascular smooth muscle cell (VSMC) and participates in the pathogenesis of many CVDs. The study investigated whether the flavone chrysin affected PDGF functions in VSMCs and neointma formation in rat artery. We found that chrysin concentration-dependently inhibited PDGF-induced proliferation and chemotaxis and reduced PDGF signaling in VSMCs. Chrysin attenuated H2O2 signaling and PDGF-induced reactive oxygen species production and NADPH oxidase activation but did not interfere with PDGF binding to VSMCs. The further analyses revealed that chrysin relieved PDGF-induced inhibition on activity of protein tyrosine phosphatase (PTP) and reduced PDGF-induced oxidation of PTP cysteinyl active site. Moreover, it inhibited PDGF receptor autophosphorylation induced by low-dose vanadate (an inhibitor for PTP). The effect of chrysin, but not of the flavonoid (-)-epigallocatechin-3-gallate and antioxidant N-acetylcysteine, on PDGF signaling and PTP activity was reversed by depletion of intracellular glutathione (GSH), suggesting an involvement of chrysin on GSH/glutaredoxin system for PTP reactivation. Finally, to demonstrate the effectiveness of chrysin in vivo, we showed that oral administration of chrysin before and after angioplasty could reduce neointima formation in balloon-injured carotid artery in rats. In conclusion, we provide here evidence that chrysin can regulate intracellular PTP activity during PDGF signaling, inhibits PDGF-induced VSMC proliferation and chemotaxis, and reduces arterial intima hyperplasia in vivo.

The Resorcylic Acid Lactone Hypothemycin Selectively Inhibits the Mitogen-Activated Protein Kinase Kinase-Extracellular Signal-Regulated Kinase Pathway in Cells

The resorcylic acid lactone hypothemycin has been shown to inactivate protein kinases by binding to a cysteine conserved in 46 protein kinases, including mitogen-activated protein kinase kinase (MEK), extracellular signal-regulated kinase (ERK) and platelet-derived growth factor receptor (PDGFR). We assessed the selectivity of hypothemycin in cellular contexts. Hypothemycin normalized the morphology and inhibited anchorage-independent growth of Ki-ras transformed normal rat kidney (NRK) cells with selectivity and potency comparable to or greater than that of the MEK inhibitor U0126. In Ki-ras-transformed and phorbol 12-myristate 13-acetate (PMA)-treated NRK cells, hypothemycin blocked ERK activation but showed a minimal effect on autophosphorylation of protein kinase D1 (PKD1), another kinase containing the conserved cysteine. Hypothemycin potently inhibited PDGFR autophosphorylation and activation of the MEK-ERK pathway in platelet-derived growth factor (PDGF)-treated NRK cells. However, the phosphoinositide-3-kinase (PI3K) pathway was only modestly attenuated. Hypothemycin also inhibited growth factor- and anchorage-independent growth of human cancer cell lines with a constitutively active MEK-ERK pathway. Although hypothemycin has the potential to inactivate various protein kinases, the results indicate that in intracellular environments, hypothemycin can inhibit the MEK-ERK axis with sufficient selectivity to normalize transformed phenotypes of cells dependent on this pathway.

3′,4′‐Dihydroxyflavonol down‐regulates monocyte chemoattractant protein‐1 in smooth muscle: role of focal adhesion kinase and PDGF receptor signalling

We investigated the effects of a synthetic flavonol, 3',4'-dihydroxyflavonol (DiOHF) on the expression of monocyte chemoattractant protein-1 (MCP-1) in rat vascular smooth muscle cells. MCP-1 expression was assessed by quantitative real-time PCR and protein phosphorylation by immunoprecipitation and Western blots. DiOHF (1-30 micromol x L(-1)) concentration-dependently reduced MCP-1 expression in both quiescent cells and cells stimulated with platelet-derived growth factor (PDGF) or interleukin 1-beta. The effect of DiOHF was associated with a suppression of focal adhesion kinase (FAK)-mediated signalling. In vitro kinase assays demonstrated that DiOHF is a potent inhibitor of FAK kinase activity (EC(50)= 2.4 micromol x L(-1)). Expression of FAK-related non-kinase reduced basal MCP-1 expression, but not that induced by PDGF or interleukin 1-beta. DiOHF also inhibited autophosphorylation of PDGF receptors. The PDGF receptor inhibitor AG-1296 potently suppressed basal and PDGF-induced MCP-1 expression. Inhibition of extracellular signal-regulated kinase activation by DiOHF, either directly or indirectly, may also be involved in its effects on MCP-1 expression. DiOHF had no inhibitory effect on either p38 or nuclear factor-kappaB activation. Moreover, DiOHF inhibited smooth muscle cell spreading (a FAK-mediated response) and proliferation. This is the first report on a flavonoid compound (DiOHF) that is a potent FAK inhibitor. DiOHF also inhibits PDGF receptor autophosphorylation. These effects underlie the inhibitory action of DiOHF on MCP-1 expression in smooth muscle cells. Our results suggest that DiOHF might be a useful tool for dissection of the (patho)physiological roles of FAK signalling.

Inhibitory effects of adiponectin on platelet-derived growth factor-induced mesangial cell migration

Adiponectin, an adipocyte-derived hormone, has been involved in metabolic syndrome, a known risk factor for the development of chronic kidney disease (CKD). Recent studies have demonstrated that plasma adiponectin levels are elevated when kidney function declines in patients with CKD. Excessive mesangial cell (MC) turnover is one of the important features of CKD. The aim of the present study is to elucidate the effects of adiponectin on platelet-derived growth factor (PDGF)-induced cell migration and intracellular signaling pathways, in cultured rat MCs (RMCs). PDGF-induced RMC migration was significantly inhibited by the pretreatment of adiponectin. Adiponectin alone had no effect on RMC migration. Big mitogen-activated protein (MAP) kinase 1 (BMK1), p38 MAP kinase, and Akt were activated by PDGF stimulation in a time- and concentration-dependent manner in RMC. Adiponectin alone did not affect BMK1, p38 MAP kinase, and Akt phosphorylations in RMC. PDGF-induced BMK1 and p38 MAP kinase phosphorylations were significantly attenuated by the pretreatment of adiponectin in RMCs. On the other hand, the phosphorylation of Akt by PDGF was not diminished by the pretreatment of adiponectin. Adiponectin had no effects on PDGF-receptor autophosphorylation by PDGF. We also confirmed that PDGF-induced RMC migration was significantly suppressed by siBMK1 transfection or SB203580, a p38 MAP kinase inhibitor. From these findings, it is implied that the elevated plasma adiponectin levels in patients with CKD might play a compensatory role aimed at counteracting renal dysfunction related to MC disorders.

Atrial Remodeling and Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice. It can occur at any age but is very rare in children and becomes extremely common in the elderly, with a prevalence approaching 20% in patients >85 years of age.1 AF is associated with a wide range of potential complications and contributes significantly to population morbidity and mortality. Present therapeutic approaches to AF have major limitations, including limited efficacy and significant adverse effect liability. These limitations have inspired substantial efforts to improve our understanding of the mechanisms underlying AF, with the premise that improved mechanistic insights will lead to innovative and improved therapeutic approaches.2 Our understanding of AF pathophysiology has advanced significantly over the past 10 to 15 years through an increased awareness of the role of “atrial remodeling.” Any persistent change in atrial structure or function constitutes atrial remodeling. Many forms of atrial remodeling promote the occurrence or maintenance of AF by acting on the fundamental arrhythmia mechanisms illustrated in Figure 1. Both rapid ectopic firing and reentry can maintain AF. Reentry requires a suitable vulnerable substrate, as well as a trigger that acts on the substrate to initiate reentry. Ectopic firing contributes to reentry by providing triggers for reentry induction. Atrial remodeling has the potential to increase the likelihood of ectopic or reentrant activity through a multitude of potential mechanisms. This article reviews the types of atrial remodeling, their underlying pathophysiology, the molecular basis of their occurrence, and finally, their potential therapeutic significance. Figure 1. General schema representing AF mechanisms and the role of remodeling. The mechanisms underlying AF are portrayed schematically in Figure 2. AF can be maintained by rapid focal firing, which may itself be regular but result in fibrillatory activity because of wave breakup in portions of the atrium that …

Constitutive diffuse activation of phosphoinositide 3-kinase at the plasma membrane by v-Src suppresses the chemotactic response to PDGF by abrogating the polarity of PDGF receptor signalling

Cancer cells depend on chemotaxis for invasion and frequently overexpress and/or activate Src. We previously reported that v-Src accelerates motility by promoting phosphoinositide 3-kinase (PI3-K) signalling but abrogates chemotaxis. We here addressed the mechanism of the loss of chemotactic response to platelet-derived growth factor (PDGF) gradients in fibroblasts harbouring a thermosensitive v-Src kinase. At non-permissive temperature, PDGF receptor (PDGFR) signalling, assessed by phosphoY 751-specific antibodies (a docking site for PI3-K), was not detected without PDGF and showed a concentration-dependent PDGF response. Both immunolabeling of PI3-K (p110) and live cell imaging of its product (phosphatidylinositol 3,4,5 tris-phosphate) showed PI3-K recruitment and activation at lamellipodia polarized towards a PDGF gradient. Centrosomes and PDGFR- and Src-bearing endosomes were also oriented towards this gradient. Upon v-Src thermoactivation, (i) Y 751 phosphorylation was moderately induced without PDGF and synergistically increased with PDGF; (ii) PI3-K was recruited and activated all along the plasma membrane without PDGF and did not polarize in response to a PDGF gradient; and (iii) polarization of centrosomes and of PDGFR-bearing endosomes were also abrogated. Thus, PDGF can further increase PDGFR auto-phosphorylation despite strong Src kinase activity, but diffuse downstream activation of PI3-K by Src abrogates cell polarization and chemotaxis: “signalling requires silence”.

Functional Expression of IQGAP1 in Vasculature: Role in Reactive Oxygen Species‐dependent PDGF signaling and Vascular Migration

Vascular smooth muscle cell (VSMC) migration in response to platelet-derived growth factor (PDGF) is a key event in atherosclerosis and restenosis. Reactive oxygen species (ROS) derived from Rac1-dependent NADPH oxidase play an important role in PDGF receptor (PDGFR) signaling linked to VSMC migration. We previously identified IQGAP1 as a novel VEGF receptor binding protein expressed in endothelial cells. IQGAP1 controls cellular motility by interacting with actin and active Rac1; however, its role in VSMC remains unknown. Here we show that IQGAP1 expression is significantly increased after PDGF stimulation. Overexpression of IQGAP1 using adenovirus (Ad.IQGAP1) enhances PDGF-stimulated autophosphorylation of PDGFR, Rac1 binding to IQGAP1, ROS production and VSMC migration. Moreover, IQGAP1 promotes tyrosine phosphorylation of PLCgamma without affecting ERK1/2 phosphorylation. IQGAP1 siRNA inhibits PDGF-stimulated ROS production and VSMC migration. Wound assays reveal that IQGAP1 accumulates at the leading edge where it colocalizes with F-actin in actively migrating VSMCs. IQGAP1 expression is dramatically increased in the neointima in ApoE knockout mice with high fat-diet and mice with wire injury. In summary, IQGAP1 functions as a PDGFR-binding scaffold protein to organize ROS-dependent PDGF signaling, thereby promoting VSMC migration, which may contributes to formation of neointima in response to vascular injury.

Identification of Potent and Selective Inhibitors of PDGF Receptor Autophosphorylation

We report the structure-activity relationship of quinoline and quinazoline derivatives, which include urea, thiourea, urethane, and acylthiourea groups, as inhibitors of the platelet-derived growth factor (PDGF) receptor autophosphorylation. Our previous studies showed that the quinoline and quinazoline derivatives including urea, thiourea, and carbamate groups were highly potent compounds as the PDGF receptor autophosphorylation inhibitor, but these compounds did not exhibit receptor selectivity between the PDGF receptor and the c-kit receptor. As a result of further synthesis and biological evaluation, we have found that the quinoline and quinazoline-acylthiourea derivatives showed not only good inhibitory activity for the PDGF receptor but also receptor selectivity between the PDGF receptor and the c-kit receptor. Furthermore N-{4-[(6,7-dimethoxy-4-quinolyl)oxy]phenyl}-N'-(2-methylbenzoyl)thiourea exhibited potent oral efficacy in in vivo assay using the rat carotid balloon injury model. Therefore, the quinoline and quinazoline-acylthiourea derivatives may be expected to have potential as therapeutic agents for the treatment of restenosis.

Taurine suppresses platelet-derived growth factor (PDGF) BB-induced PDGF-β receptor phosphorylation by protein tyrosine phosphatase-mediated dephosphorylation in vascular smooth muscle cells

In atherosclerosis, abnormal vascular smooth muscle cell (VSMC) proliferation plays an important role to form fibroproliferative lesions and platelet-derived growth factor (PDGF)-BB is one of the most potent chemoattractants and proliferative factors for VSMCs. Taurine, sulfur-containing β-amino acid, has been considered to prevent the development of atherosclerosis, although the molecular mechanism remains obscure. Previously, we demonstrated that taurine significantly suppressed PDGF-BB-induced cell proliferation, DNA synthesis, immediate-early gene expressions and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in VSMCs. The present study was aimed at elucidating the precise molecular mechanism of taurine in PDGF-BB signaling pathway. We showed that taurine significantly suppressed PDGF-BB-induced phosphorylation of PDGF-β receptor and activation of its downstream signaling molecules such as Ras, MAPK/ERK kinase (MEK)1/2 and Akt. Because taurine did not attenuate phorbol 12-myristate 13-acetate (PMA)-induced PDGF-β receptor-independent ERK1/2 phosphorylation, we further investigated the suppressive mechanism of taurine in PDGF-β receptor level. Although taurine did not directly affect PDGF receptor autophosphorylation in vitro, taurine promoted PDGF-β receptor dephosphorylation and restored PDGF-BB-induced suppression of protein tyrosine phosphatase (PTPase) activity. Taken together, we propose that taurine could prevent or delay the progression of atherosclerosis by PTPase-mediated suppression of PDGF-β receptor phosphorylation, and by decreasing the activation of its downstream signaling molecules in VSMCs.

Synthesis and structure–activity relationship for new series of 4-Phenoxyquinoline derivatives as specific inhibitors of platelet-derived growth factor receptor tyrosine kinase

We discovered a new series of 4-phenoxyquinoline derivatives as potent and selective inhibitors of the platelet-derived growth factor receptor (PDGFr) tyrosine kinase. We researched the highly potent and selective inhibitors on the basis of both PDGFr and epidermal growth factor receptor (EGFr) inhibitory activity. First, we found a compound, Ki6783 (1), which inhibited PDGFr autophosphorylation at 0.13 μM, but it did not inhibit EGFr autophosphorylation at 100 μM. After extensive explorations, we found the two desired compounds, Ki6896 (2) and Ki6945 (3), which are substituted by benzoyl and benzamide at the 4-position of the phenoxy group on 4-phenoxyquinoline, respectively. These inhibitory activities were 0.31 and 0.050 μM, respectively, but neither of them inhibited EGFr autophosphorylation at 100 μM. We further investigated the profile of both compounds toward various tyrosine and serine/threonine kinases. The three compounds specifically inhibited PDGFr rather than the other kinases.

Gain-of-function mutations of platelet-derived growth factor receptor α gene in gastrointestinal stromal tumors

Background & Aims : Most gastrointestinal stromal tumors (GISTs) have gain-of-function mutations of c- kit receptor tyrosine kinase (KIT) gene, but some GISTs do not. We investigated the cause of GISTs without KIT mutations. Because GISTs apparently expressed platelet-derived growth factor receptor (PDGFR) α, we examined whether GISTs without KIT mutations had a mutation of PDGFR α. Methods : Whole coding region of PDGFR α complementary DNA (cDNA) was sequenced in GISTs with or without KIT mutations. Mutant PDGFR α cDNA was transfected into 293T human embryonic kidney cells, and autophosphorylation of PDGFR α was examined. Proliferation of Ba/F3 murine lymphoid cells stably transfected with mutant PDGFR α cDNA was estimated by tritium thymidine incorporation. Wild-type KIT cDNA was cotransfected with mutant PDGFR α cDNA, and immunoprecipitation by anti-KIT antibody was performed. Inhibitory effect of Imatinib mesylate on activated PDGFR α was examined. Results : We found 2 types of constitutively activated mutations of PDGFR α, Val-561 to Asp or Asp-842 to Val, in 5 of 8 GISTs without KIT mutations but not in 10 GISTs with KIT mutations. Stable transfection of each mutation induced autonomous proliferation of Ba/F3 cells. Constitutively activated mutant PDGFR α bound and activated the cotransfected wild-type KIT. The constitutive activation of PDGFR α with Val-561 to Asp was inhibited effectively by Imatinib mesylate but that of PDGFR α with Asp-842 to Val was inhibited only weakly, even at the concentration of 10 μmol/L. Conclusions : The gain-of-function mutations of PDGFR α appear to play an important role in development of GISTs without KIT mutations.

Eicosapentaenoic acid inhibits PDGF-induced mitogenesis and cyclin D1 expression via TGF-beta in mesangial cells.

Eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid derived from fish oil, is efficacious in glomerular diseases where mesangial proliferation is a key event. We examined the mechanisms of action of EPA on platelet-derived growth factor (PDGF)-stimulated rat mesangial cell mitogenesis. EPA dose-dependently inhibited PDGF-stimulated [(3)H]-thymidine incorporation. PDGF-induced PDGF receptor autophosphorylation, an initial event for PDGF signaling, was not affected by 2 micro g/ml EPA. Similarly, PDGF-stimulated activation of extracellular signal-regulated kinase (ERK) was not altered. On the other hand, EPA inhibited cyclin-dependent kinase 4 (CDK4) activation and cyclin D1 protein induction, a critical step for G1/S progression. TGF-beta secretion assessed by ELISA and bioassay was increased by EPA at 18 h. Coincubation with anti-TGF-beta antibody inhibited the EPA-induced suppression of [(3)H]-thymidine incorporation and cyclin D1 expression. SB203580, an inhibitor of p38, a downstream kinase of TGF-beta, did not affect EPA's growth inhibitory effect. These results demonstrate that EPA inhibits PDGF-stimulated mesangial cell mitogenesis and cyclin D1 expression via TGF-beta.

Effect of pirfenidone on rat hepatic stellate cell proliferation and collagen production

Background/Aims: Pirfenidone has been recently shown to reduce dimethynitrosamine-induced liver fibrosis in the rat, but no information are available on the effect of this drug on cultured hepatic stellate cells (HSC). Methods: HSC proliferation was evaluated by measuring bromodeoxyuridine incorporation; PDGF-receptor autophosphorylation, extracellular signal-regulated kinase (ERK1/2) and pp70 S6K activation were evaluated by western blot; protein kinase C activation was evaluated by western blot and by ELISA; type I collagen accumulation and α1(I) procollagen mRNA expression were evaluated by ELISA and northern blot, respectively. Results: Pirfenidone significantly inhibited PDGF-induced HSC proliferation, starting at a concentration of 1 μM, with a maximal effect at 1000 μM, without affecting HSC viability and without inducing apoptosis. The inhibition of PDGF-induced HSC proliferation was associated neither with variations in PDGF-receptor autophosphorylation, or with ERK1/2 and pp70 S6K activation. On the other hand, pirfenidone was able to inhibit PDGF-induced activation of the Na +/H + exchanger, which is involved in PDGF-induced HSC proliferation in HSC, with a maximal effect at 1000 μM and inhibited PDGF-induced protein kinase C activation. Pirfenidone 100 and 1000 μM inhibited type I collagen accumulation in the culture medium induced by transforming growth factor β1 by 54% and 92%, respectively, as well as TGF β1-induced α1(I) procollagen mRNA expression. Results: Pirfenidone could be a new candidate for antifibrotic therapy in chronic liver diseases.

Inhibitory effect of pentalenolactone on vascular smooth muscle cell proliferation

The effect of pentalenolactone, an inhibitor of glyceraldehyde-3-phosphate dehydrogenase, on rat vascular smooth muscle cell proliferation was studied. Addition of pentalenolactone together with serum to quiescent cells dose-dependently inhibited cell proliferation and DNA synthesis. This inhibition was not associated with cell death. When quiescent cells were stimulated with serum and then treated with pentalenolactone, the inhibitory effect on the DNA synthesis declined gradually. A similar result was obtained when PD 98059 (2′-amino-3′-methoxyflavone), an inhibitor of extracellular signal-regulated kinase1/2 (ERK1/2) kinase (MEK1/2), was added to the cells after serum stimulation. Pentalenolactone inhibited serum or protein kinase C activator (phorbol 12,13-dibutyrate)-induced phosphorylation of ERK1/2 and MEK1/2. In contrast, pentalenolactone had little effect on platelet-derived growth factor receptor autophosphorylation. Taken together, these results indicate that pentalenolactone inhibits vascular smooth muscle cell proliferation, and that this inhibition appears to be mediated by inhibition of the ERK1/2 cascade.

Interaction between 4-Hydroxy-2,3-alkenals and the Platelet-derived Growth Factor-β Receptor: REDUCED TYROSINE PHOSPHORYLATION AND DOWNSTREAM SIGNALING IN HEPATIC STELLATE CELLS

Hepatic stellate cells (HSC) undergo activation toward myofibroblast-like cells during early stages of liver injury associated with fibrogenesis. Platelet-derived growth factor (PDGF), particularly its BB isoform, has been identified as the most potent mitogen for HSC. 4-Hydroxy-2,3-nonenal and related 4-hydroxy-2, 3-alkenals (HAKs) have been suggested to modulate the process of HSC activation. In this study we investigated the relationship between HAKs and PDGF receptor activation in human HSC. By employing noncytotoxic concentrations (10(-6) m) of HAKs, we observed a significant inhibition of PDGF-BB-dependent DNA synthesis. HAKs inhibited relevant pathways of PDGF-BB-dependent mitogenic signaling, including autophosphorylation of PDGF receptor (PDGF-R) beta subunits and activation of phosphatidylinositol 3-kinase and extracellular regulated kinases 1/2. Inhibition of DNA synthesis was reversible, and recovery of PDGF-mediated mitogenic signaling occurred within 24-48 h and was associated with HAKs-induced up-regulation of PDGF-R beta gene expression. 4-Hydroxy-2,3-nonenal, used as a model HAK, inhibited the intrinsic tyrosine kinase activity associated with the PDGF-R beta subunit, whereas binding of PDGF to its receptor was unaffected. This study identifies a novel regulatory mechanism of reactive aldehydes on PDGF receptor signaling and biologic actions, which may be relevant in several pathophysiological conditions, including liver fibrosis.

Platelet-derived growth factor receptor association with Na(+)/H(+) exchanger regulatory factor potentiates receptor activity.

Platelet-derived growth factor (PDGF) is a potent mitogen for many cell types. The PDGF receptor (PDGFR) is a receptor tyrosine kinase that mediates the mitogenic effects of PDGF by binding to and/or phosphorylating a variety of intracellular signaling proteins upon PDGF-induced receptor dimerization. We show here that the Na(+)/H(+) exchanger regulatory factor (NHERF; also known as EBP50), a protein not previously known to interact with the PDGFR, binds to the PDGFR carboxyl terminus (PDGFR-CT) with high affinity via a PDZ (PSD-95/Dlg/Z0-1 homology) domain-mediated interaction and potentiates PDGFR autophosphorylation and extracellular signal-regulated kinase (ERK) activation in cells. A point-mutated version of the PDGFR, with the terminal leucine changed to alanine (L1106A), cannot bind NHERF in vitro and is markedly impaired relative to the wild-type receptor with regard to PDGF-induced autophosphorylation and activation of ERK in cells. NHERF potentiation of PDGFR signaling depends on the capacity of NHERF to oligomerize. NHERF oligomerizes in vitro when bound with PDGFR-CT, and a truncated version of the first NHERF PDZ domain that can bind PDGFR-CT but which does not oligomerize reduces PDGFR tyrosine kinase activity when transiently overexpressed in cells. PDGFR activity in cells can also be regulated in a NHERF-dependent fashion by stimulation of the beta(2)-adrenergic receptor, a known cellular binding partner for NHERF. These findings reveal that NHERF can directly bind to the PDGFR and potentiate PDGFR activity, thus elucidating both a novel mechanism by which PDGFR activity can be regulated and a new cellular role for the PDZ domain-containing adapter protein NHERF.

Pyrrolo[3,4- c]-β-carboline-diones as a novel class of inhibitors of the platelet-derived growth factor receptor kinase

Members of the structurally diverse family of β-carbolines have previously been shown to exhibit a wide range of biological activities. A novel synthetic strategy for generation of β-carbolines was developed, allowing imido-β-carbolines to be created in three steps from known compounds. The compounds were screened for inhibition of platelet-derived growth factor (PDGF)-stimulated tyrosine phosphorylation in Swiss 3T3 fibroblasts. A number of the newly synthesized β-carbolines with moderate to potent inhibitory activity were revealed. The most active derivative, 2,3-dihydro-8,9-dimethoxy-5-(2-methylphenyl)-1 H,6 H-pyrrolo[3,4- c]pyrido[3,4- b]indole-1,3-dione 2ee, inhibited purified PDGF receptor kinase and PDGF-receptor autophosphorylation in intact cells with IC 50 values of 0.4 and 2.6 μM, respectively. Dione 2ee also inhibited PDGF-stimulated DNA synthesis in Swiss 3T3 fibroblasts with an IC 50 of 3.2 μM. The compound had no effect on Src or epidermal growth factor (EGF) receptor kinase activity and a six–seven-fold higher IC 50 for inhibition of basic fibroblast growth factor (bFGF)-stimulated tyrosine phosphorylation or Kit/stem cell factor (SCF) receptor autophosphorylation, indicating a reasonable extent of kinase specificity. Thus, β-carbolines present a new lead of tyrosine kinase inhibitors with the capacity to selectively interfere with PDGF receptor signal transduction and PDGF-dependent cell growth.

Effect of pirfenidone, a novel antifibrotic agent, on PDGF-induced intracellular signaling in rat hepatic stellate cells

EFFECT OF PIRFENIDONE, A NOVEL ANTIFIBROTIC AGENT, ON PDGF-INDUCED INTRACELLULAR SIGNALING IN RAT HEPATIC STELLATE CELLS A. Di Sario, E. Bendia, G. Svegliati Baroni, S. Saccomanno 1, R. Ridolfi, U. Ugili t, L. Trozzi, A.M. Jezequel I, A. Benedetti Gastroenterology, University of Ancona, Ancona, Italy. 1Exp. Pathology, University of Ancona, Ancona, Italy. Pirfenidone (5 methyl-l-phonyl-2-(1H)-pyridone) is a potentially useful novel broad spectrum anfifibrotic agent which has been shown to inhibit fibroblast proliferation in response to nmneaetm growth factors, and to produce antitibrotic effects in a variety of nninml models. Aim of this study was to evaluate the effect o f pirfenidone on PDGF-mediated intracellular events in activated rat hepatic stellate cells (HSC). Incubation of HSC with PDGF-BB induced a six-fold increase in cell proliferation, evaluated by measuring bmmodeoxyur id i~ (BrdU) incorporation (12.4--t:I.2 vs 2.15±1.2 % BrdU positive cells in controls, P<0.001). The contemporaff incubation with pirfenidone, significantly inhibited PDGF-indueed HSC proliferation starting at a concentration of 1 pM (7.0~1.6; P<0.01), with a maximal effect at 1000 ~ (1.9-a:0.4; P<0.001). Measmement of LDH release in the culture medium, Uypan blue exclusion test and electron microscopy showed no cytotoxic effect of pirfenidone at coneenlrations that inhibited HSC proliferation (1, 10, 100, 500 and 1000 ldVl). The inhibition of P D G F i n d m ~ HSC proliferation was not associated with variations in PDGF-receptor autophosphorylation. Moreover, incubation with pirfenidoue did not inhibit PDGF-induced ERKI aml ERK2 activation, as well as pTOS6k (a downstream component of the PI-3 kinn.qe pathway) phosphorylation. On the contrary, piffenidone was able to inhibit PDGF-indueed activation of the Na+/H + exchange, which plays an important role in regadafing PDGF-induced HSC proliferation, with a maximal effect at I000 pM. These results suggest that l~fenidone could be a new candidate for antifibmtic thexa W in chronic liver diseases. Molecular and cell biology (gene expression, signalling, fibrosis)