Platelet-derived Growth Factor Receptor-β Research Articles

Functional analysis of platelet-derived growth factor receptor-β in neural stem/progenitor cells

Activation of neural stem/progenitor cells (NSPCs) is a potential therapeutic strategy of neurological disorders. In this study, NSPCs of subventricular zone were isolated and cultured from platelet-derived growth factor-β-receptor-knockout (PDGFR-β−/−) mice of postnatal day 1 (P1) and P28, and the roles of PDGFR-β were examined in these cells. In PDGFR-β-preserving control NSPCs, stem cell activities, such as numbers and diameters of secondary neurospheres, cell proliferation and survival rates, were significantly higher in P1 NSPCs than those in P28 NSPCs. In PDGFR-β−/− NSPCs, most of these parameters were decreased as compared with age-matched controls. Among them, the decrease of secondary neurosphere formation was most striking in P1 and P28 PDGFR-β−/− NSPCs and in P28 control NSPCs as compared with P1 control NSPCs. PCR-array and following quantitative real-time PCR (qRT-PCR) analyses demonstrated that expressions of fibroblast growth factor-2 (FGF2) and exons IV–IX of brain-derived neurotrophic factor (BDNF) were decreased, and noggin was increased in P1 PDGFR-β−/− as compared with P1 controls. Addition of BDNF rescued the number and diameter of secondary neurospheres in P1 PDGFR-β−/− NSPCs to similar levels as controls. The expressions of PDGFs and PDGFRs in control NSPCs were increased along with the differentiation-induction, where phosphorylated PDGFR-β was co-localized with neuronal and astrocyte differentiation markers. In controls, the neuronal differentiation was decreased, and the glial differentiation was increased from P1 to P28 NSPCs. Compared with P1 controls, neuronal differentiation was reduced in P1 PDGFR-β−/− NSPCs, whereas glial differentiation was comparable between the two genotypes. These results suggest that PDGFR-β signaling is important for the self-renewal and multipotency of NSPCs, particularly in neonatal NSPCs. BDNF, FGF2, and noggin may be involved in the effects of PDGFR-β signaling in these cells. Accordingly, the activation of PDGFR-β in NSPCs may be a novel therapeutic strategy of neurological diseases.

5‐Hydroxytryptamine type 7 receptor neuroprotection against NMDA‐induced excitotoxicity is PDGFβ receptor dependent

The serotonin (5-HT) type 7 receptor is expressed throughout the CNS including the hippocampus. Long-term (2-24 h) activation of 5-HT7 receptors regulates growth factor receptor expression, including the expression of platelet-derived growth factor (PDGF) β receptors. Direct activation of PDGFβ receptors in primary hippocampal and cortical neurons inhibits NMDA receptor activity and attenuates NMDA receptor-induced neurotoxicity. Our objective was to investigate whether the 5-HT7 receptor-induced increase in PDGFβ receptor expression would be similarly neuroprotective. We demonstrate that 5-HT7 receptor agonist treatment in primary hippocampal neurons also increases the expression of phospholipase C (PLC) γ, a downstream effector of PDGFβ receptors associated with the inhibition of NMDA receptor activity. To determine if the up-regulation of PDGFβ receptors is neuroprotective, primary hippocampal neurons were incubated with the 5-HT7 receptor agonist, LP 12, for 24 h. Indeed, LP 12 treatment prevented NMDA-induced neurotoxicity and this effect was dependent on PDGFβ receptor kinase activity. Treatment of primary neurons with LP 12 also differentially altered NMDA receptor subunit expression, reducing the expression of NR1 and NR2B, but not NR2A. These findings demonstrate the potential for providing growth factor receptor-dependent neuroprotective effects using small-molecule ligands of G protein-coupled receptors.

CXCL12 Promotes the Stabilization of Atherosclerotic Lesions Mediated by Smooth Muscle Progenitor Cells in Apoe -Deficient Mice

Unstable atherosclerotic lesions are prone to rupture, which leads to atherothrombosis. Chemokine (C-X-C motif) ligand 12 (CXCL12) promotes the mobilization and neointimal recruitment of smooth muscle progenitor cells (SPCs), and thereby mediates vascular repair. Moreover, treatment with SPCs stabilizes atherosclerotic lesions in mice. We investigated the role of CXCL12 in the treatment of unstable atherosclerotic lesions. Intravenous injection of CXCL12 selectively increased the level of Sca1(+)Lin platelet derived growth factor receptor-β(+) SPCs in the circulation as determined by flow cytometry. Macrophage-rich lesions were induced by partial ligation of the carotid artery in Apoe(-/-) mice. Repeated injection of CXCL12 reduced the macrophage content, increased the number of smooth muscle cells, increased the fibrous cap thickness, and increased the collagen content in these lesions. However, CXCL12 did not alter the lesion size or the luminal diameter of the carotid artery as determined by planimetry and micro-computed tomography, respectively. Recruitment of bone marrow-derived SPCs to the lesions was increased after treatment with CXCL12 in chimeric mice that expressed SM22-LacZ in bone marrow cells as determined by quantification of the number of lesional β-galactosidase-expressing cells. CXCL12 expression was upregulated in atherosclerotic arteries after CXCL12 treatment. Silencing of arterial CXCL12 expression during atherosclerosis promoted lesion formation and reduced the lesional smooth muscle cell content in CXCL12-treated mice. Systemic treatment with CXCL12 promotes a more stable atherosclerotic lesion phenotype and enhances the accumulation of SPCs in these lesions without promoting atherosclerosis. Thus, CXCL12-induced SPC mobilization appears a promising approach to treat unstable atherosclerosis.

Sponge-derived acetylenic alcohols, petrosiols, inhibit proliferation and migration of platelet-derived growth factor (PDGF)-induced vascular smooth muscle cells

Platelet-derived growth factor (PDGF) induces the proliferation and migration of vascular smooth muscle cells (VSMCs), leading to the development of various vascular disorders such as restenosis and atherosclerosis. Therefore, inhibitors of PDGF-induced cellular events would be candidate agents for treating these diseases. During the search for such inhibitors from marine sources, we isolated petrosiols A–D (1–4) and related compounds from the marine sponge Petrosia strongylata. These metabolites, which we previously reported as neurotrophic substances, showed an inhibitory effect on PDGF-induced DNA synthesis at IC50 values of 0.69–2.2μM. Petrosiol A (1) inhibited PDGF-induced cell proliferation without remarkable cytotoxicity and arrested cell cycle progression from the G0/G1 to S phase by inducing the downregulation of the expression of G1 checkpoint proteins cyclin D1, cyclin E, cyclin-dependent kinases (CDK)2, and CDK4 and the upregulation of the expression of p21 and p27. In addition, petrosiol A (1) inhibited the phosphorylation of PDGF receptor-β and its downstream proteins such as phospholipase C (PLC)-γ1, Akt, and extracellular signal-regulated kinase (ERK)1/2. These results suggest that 1 inhibited PDGF-induced VSMC proliferation by interrupting the phosphorylation of PDGF receptor-β followed by downstream signal transduction. Furthermore, petrosiol A (1) suppressed PDGF-induced actin filament dissociation and cell migration, suggesting that 1 and its derivatives may be used for the prevention and treatment of vascular diseases.

Emerging role of tyrosine phosphatase, TCPTP, in the organelles of the early secretory pathway

T-cell protein tyrosine phosphatase, TCPTP, is a ubiquitously expressed non-receptor type tyrosine phosphatase. There are two splice variants of TCPTP, TC48 and TC45, which differ in their sub-cellular localizations and functions. TC45 is a nuclear protein, which has both nuclear and cytoplasmic substrates, and is involved in many signaling events including endocytic recycling of platelet-derived growth factor β-receptor. TC48 is a predominantly endoplasmic reticulum (ER)-localizing protein, which dephosphorylates some of the substrates of TC45 at the ER. However, recently few specific substrates for TC48 have been identified. These include C3G (RapGEF1), syntaxin 17 and BCR-Abl. TC48 moves from the ER to post-ER compartments, the ER–Golgi intermediate compartment (ERGIC) and Golgi, and it is retrieved back to the ER. The retrieval of ER proteins from post-ER compartments is generally believed as a mechanism of targeting these proteins to the ER. However, it is possible that this shuttling of TC48 serves to regulate signaling in the early secretory pathway. For example, TC48 dephosphorylates phosphorylated C3G at the Golgi and inhibits neurite outgrowth. TC48 interacts with and dephosphorylates syntaxin 17, which is an ER and ERGIC-localizing protein involved in vesicle transport. A yeast two-hybrid screen identified several unique interacting partners of TC48 belonging to two groups — proteins involved in vesicle trafficking and proteins involved in cell adhesion. These interacting proteins could be substrates or regulators of TC48 function and localization. Thus, the role of TC48 seems to be more diverse, which is still to be explored.

Sunitinib, a Small-Molecule Receptor Tyrosine Kinase Inhibitor, Suppresses Neointimal Hyperplasia in Balloon-Injured Rat Carotid Artery

The migration and proliferation of vascular smooth muscle cells (VSMCs) induced by growth factors play a critical role in in-stent stenosis after percutaneous coronary intervention (PCI). The present study tested the hypothesis that sunitinib malate (sunitinib), a tyrosine kinase inhibitor of multiple receptors for growth factors, can reduce neointimal formation after arterial injury in vivo and sought to reveal the underlying mechanism in vitro. Male Wistar rats with balloon-injured carotid arteries were administered either sunitinib or a vehicle orally for 2 weeks. Sunitinib significantly inhibited neointimal hyperplasia relative to control by reducing active cell proliferation. In cultured human aortic smooth muscle cells (HASMCs), sunitinib significantly inhibited platelet-derived growth factor (PDGF)-induced increases of DNA synthesis, cell proliferation, and migration relative to controls as evaluated by [(3)H] thymidine incorporation, cell number, and the Boyden chamber assay, respectively. Immunoblot analyses showed that sunitinib suppressed phosphorylation of PDGF-BB inducible extracellular signal-regulated kinase and autophosphorylation of PDGF β-receptor, which are the key signaling steps involved in HASMC activation. These results indicate that sunitinib inhibits neointimal formation after arterial injury by suppressing VSMC proliferation and migration presumably through inactivation of PDGF signaling. As such, it may be a potential therapeutic agent, which targets arterial restenosis after PCI.

Dehydroglyasperin C, a component of liquorice, attenuates proliferation and migration induced by platelet-derived growth factor in human arterial smooth muscle cells

Liquorice is one of the botanicals used frequently as a traditional medicine in the West and in the East. Platelet-derived growth factor (PDGF)-BB is involved in the development of CVD by inducing abnormal proliferation and migration of vascular smooth muscle cells. In our preliminary study, dehydroglyasperin C (DGC), an active compound of liquorice, showed strong antioxidant activity. Since phytochemicals with antioxidant activities showed beneficial effects on chronic inflammatory diseases, the present study aimed to investigate the effects of DGC on PDGF-induced proliferation and migration of human aortic smooth muscle cells (HASMC). Treatment of HASMC with DGC for 24 h significantly decreased PDGF-induced cell number and DNA synthesis in a dose-dependent manner without any cytotoxicity, as demonstrated by the 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide test and thymidine incorporation. Upon cell cycle analysis, DGC blocked the PDGF-induced progression through the G0/G1 to S phase of the cell cycle, and down-regulated the expression of cyclin-dependent kinase (CDK); 2, cyclin E, CDK4 and cyclin D1. Furthermore, DGC significantly attenuated PDGF-stimulated phosphorylation of PDGF receptor-b, phospholipase C-g1, AKT and extracellular-regulated kinase 1/2, and DGC inhibited cell migration and the dissociation of actin filaments by PDGF. In a rat vascular balloon injury model, DGC suppressed an excessive reduction in luminal diameters and neointimal formation compared with the control group. These results demonstrate the mechanistic basis for the prevention of CVD and the potential therapeutic properties of DGC.

Necrotic renal epithelial cell inhibits renal interstitial fibroblast activation: role of protein tyrosine phosphatase 1B

Our recent studies showed that contents of necrotic renal proximal tubular cells (RPTC) from 2 × 10(6) cells/ml directly induced death of cultured renal interstitial fibroblasts. However, it remains unknown whether nonlethal number of necrotic RPTC would also alter the fate of renal interstitial fibroblasts. To address this issue, renal interstitial fibroblasts (NRK-49F) were exposed to necrotic RPTC supernatant (RPTC-Sup) obtained from 2 × 10(4) to 5 × 10(5) cells/ml. These concentrations of RPTC did not induce cell death, but led to inactivation of renal fibroblasts as indicated by reduced expression of α-smooth muscle actin and fibronectin, two hallmarks of activated fibroblasts. Concurrently, the same doses of necrotic RPTC-Sup suppressed phosphorylation of epidermal growth factor receptor (EGFR) and signal transducers and activators of transcription-3 (STAT3) in a time- and dose-dependent manner, but did not affect phosphorylation of platelet-derived growth factor receptor-β, AKT, and extracellular signal-regulated kinase 1/2. The presence of sodium orthovanadate, a general protein tyrosine phosphatase (PTP) inhibitor or TCS-401 (a selective PTP1B inhibitor), abrogated those effects of RPTC-Sup, whereas coincubation with the EGFR inhibitor (Gefitinib) or silencing of EGFR with siRNA preserved the ability of RPTC-Sup in suppressing renal fibroblast activation and STAT3 phosphorylation. Moreover, RPTC-Sup treatment induced PTP1B phosphorylation and its interaction with EGFR. Collectively, these results indicate that nonlethal necrotic RPTC-Sup can induce inactivation of renal interstitial fibroblasts, which occurs through a mechanism involved in PTP1B-mediated inhibition of EGFR signaling.

Bovine Papillomavirus Type 2 Infection and a Series of Mesenchymal Tumors of the Urinary Bladder in Cattle

This report describes the histopathology of two hundred and fifty-three mesenchymal tumors of the urinary bladder in cattle grazing on lands rich in bracken fern. Approximately 80% were hemangiomas and angiosarcomas. Hemangioma (capillary, cavernous, and large vessels) was the most frequent mesenchymal tumor and was more common than angiosarcoma. Although the appearance of endothelial cells can vary remarkably, epithelioid angiosarcomas, often containing multinucleated cells, were the most frequent malignant vascular tumors. Hemangiopericytoma and tumors of muscle and soft connective tissue origin, alone and/or in association with tumor-like lesions, were less frequently seen. Furthermore, forty-five cases of intravascular papillary endothelial hyperplasia (IPEH), a lesion not previously reported in the urinary bladder of cattle, were also described. Bovine papillomavirus type-2 DNA was amplified in tumor samples. Forty vascular tumors were investigated by dual-labeling immunofluorescence, and, for the first time, a coexpression of E5 and platelet-derived growth factor β receptor (PDGFβR) was shown to occur. The results show that the BPV-2 E5 oncoprotein binds to the activated form of the PDGFβ receptor thus playing an important role in mesenchymal as well as epithelial carcinogenesis of the urinary bladder. Furthermore, these findings demonstrate that BPV-2 infects both epithelial and mesenchymal cells.

5,8-Dimethoxy-2-Nonylamino-Naphthalene-1,4-Dione Inhibits Vascular Smooth Muscle Cell Proliferation by Blocking Autophosphorylation of PDGF-Receptor β

As the abnormal proliferation of vascular smooth muscle cells (VSMCs) plays a critical role in the development of atherosclerosis and vascular restenosis, a candidate drug with antiproliferative properties is needed. We investigated the antiproliferative action and underlying mechanism of a newly synthesized naphthoquinone derivative, 5,8-dimethoxy-2-nonylamino-naphthalene-1,4-dione (2-nonylamino-DMNQ), using VSMCs treated with platelet-derived growth factor (PDGF). 2-Nonylamino-DMNQ inhibited proliferation and cell number of VSMCs induced by PDGF, but not epidermal growth factor (EGF), in a concentration-dependent manner without any cytotoxicity. This derivative suppressed PDGF-induced [3H]-thymidine incorporation, cell cycle progression from G0/G1 to S phase, and the phosphorylation of phosphor-retinoblastoma protein (pRb) as well as the expression of cyclin E/D, cyclin-dependent kinase (CDK) 2/4, and proliferating cell nuclear antigen (PCNA). Importantly, 2-nonylamino-DMNQ inhibited the phosphorylation of PDGF receptorβ(PDGF-Rβ) enhanced by PDGF at Tyr579, Tyr716, Tyr751, and Tyr1021 residues. Subsequently, 2-nonylamino-DMNQ inhibited PDGF-induced phosphorylation of STAT3, ERK1/2, Akt, and PLCγ1. Therefore, our results indicate that 2-nonylamino-DMNQ inhibits PDGF-induced VSMC proliferation by blocking PDGF-Rβ autophosphorylation, and subsequently PDGF-Rβ-mediated downstream signaling pathways.

Peroxisome proliferator-activated receptor-γ interrupts angiogenic signal transduction via transrepression of platelet-derived growth factor-β receptor in hepatic stellate cells

Hepatic stellate cells (HSCs) are liver-specific pericytes that are recruited to vessels and secret pro-angiogenic cytokines, and thus actively involved in pathological vascularization during liver fibrosis. Peroxisome proliferator-activated receptor-γ (PPARγ) is a switch molecule controlling HSC activation. We investigated PPARγ regulation of angiogenic signal transduction and the molecular mechanisms involved in HSCs. Primary rat HSCs and liver sinusoidal endothelial cells (LSECs) were isolated and used in this study. Boyden chamber and tubulogenesis assays, identified that focal adhesion kinase (FAK)-RhoA signaling activated by platelet-derived growth factor (PDGF) was required for HSC motility and the associated vascularization. PDGF also stimulated vascular endothelial growth factor (VEGF) expression and HSC-driven vascularization through signals mediated by extracellular signal-regulated kinase (ERK) and mammalian target of rapamycin (mTOR). Gain- and loss-of-function analyses demonstrated that activation of PPARγ interrupted FAK-RhoA, ERK and mTOR cascades and inhibited HSC-based vascularization. Molecular evidence further revealed that PPARγ attenuation of HSC angiogenic properties was dependent on inhibition of PDGF-β receptor expression. We concluded that PPARγ inhibited angiogenic signal transduction through transrepression of PDGF-β receptor leading to reduced HSC motility, reduced VEGF expression, and thereby attenuated HSC-driven angiogenesis. PPARγ could be a molecular target for preventing vascular remolding in hepatic fibrosis.

Analysis of Activated Platelet-Derived Growth FactorβReceptor and Ras-MAP Kinase Pathway in Equine Sarcoid Fibroblasts

Equine sarcoids are skin tumours of fibroblastic origin affecting equids worldwide. Bovine papillomavirus type-1 (BPV-1) and, less commonly, type-2 are recognized as etiological factors of sarcoids. The transforming activity of BPV is related to the functions of its major oncoprotein E5 which binds to the platelet-derived growth factor β receptor (PDGFβR) causing its phosphorylation and activation. In this study, we demonstrate, by coimmunoprecipitation and immunoblotting, that in equine sarcoid derived cell lines PDGFβR is phosphorylated and binds downstream molecules related to Ras-mitogen-activated protein kinase-ERK pathway thus resulting in Ras activation. Imatinib mesylate is a tyrosine kinase receptors inhibitor which selectively inhibits the activation of PDGFβR in the treatment of several human and animal cancers. Here we show that imatinib inhibits receptor phosphorylation, and cell viability assays demonstrate that this drug decreases sarcoid fibroblasts viability in a dose-dependent manner. This study contributes to a better understanding of the molecular mechanisms involved in the pathology of sarcoids and paves the way to a new therapeutic approach for the treatment of this common equine skin neoplasm.

Mitogenesis of Vascular Smooth Muscle Cell Stimulated by Platelet-Derived Growth Factor-bb Is Inhibited by Blocking of Intracellular Signaling by Epigallocatechin-3-O-Gallate

Epigallocatechin gallate (EGCG) is known to exhibit antioxidant, antiproliferative, and antithrombogenic effects and reduce the risk of cardiovascular diseases. Key events in the development of cardiovascular disease are hypertrophy and hyperplasia according to vascular smooth muscle cell proliferation. In this study, we investigated whether EGCG can interfere with PDGF-bb stimulated proliferation, cell cycle distribution, and the gelatinolytic activity of MMP and signal transduction pathways on RAOSMC when it was treated in two different ways—cotreatment with PDGF-bb and pretreatment of EGCG before addition of PDGF-bb. Both cotreated and pretreated EGCG significantly inhibited PDGF-bb induced proliferation, cell cycle progression of the G0/G1 phase, and the gelatinolytic activity of MMP-2/9 on RAOSMC. Also, EGCG blocked PDGF receptor-β (PDGFR-β) phosphorylation on PDGF-bb stimulated RAOSMC under pretreatment with cells as well as cotreatment with PDGF-bb. The downstream signal transduction pathways of PDGFR-β, including p42/44 MAPK, p38 MAPK, and Akt phosphorylation, were also inhibited by EGCG in a pattern similar to PDGFR-β phosphorylation. These findings suggest that EGCG can inhibit PDGF-bb stimulated mitogenesis by indirectly and directly interrupting PDGF-bb signals and blocking the signaling pathway via PDGFR-β phosphorylation. Furthermore, EGCG may be used for treatment and prevention of cardiovascular disease through blocking of PDGF-bb signaling.

Inhibition of platelet-derived growth factor receptor tyrosine kinase and downstream signaling pathways by Compound C

AMP-activated protein kinase (AMPK) has been implicated in anti-proliferative actions in a range of cell systems. Recently, it was observed that Compound C, an inhibitor of AMPK, also reduced the cell viability in human diploid fibroblasts (HDFs). Compound C-induced growth arrest was associated with a decrease in the cell cycle regulatory proteins, such as proliferating cell nuclear antigen, phosphorylated pRB, cyclin-dependent protein kinases (Cdk 2 and 4), cyclins (D and E), and the Cdk inhibitors (p21, p16, and p27). Therefore, the present study examined the molecular mechanism of the antiproliferative effects of Compound C. Although Compound C inhibited serum-induced phosphorylation of Akt and its substrate, glycogen synthase kinase-3β, it did not affect the Akt activity in vitro. Compound C significantly inhibited the receptor tyrosine phosphorylation and the activity of downstream signaling molecules, such as p85 phosphoinositide 3-kinase, phospholipase C-γ1, and extracellular signal-regulated kinase 1/2, induced by platelet-derived growth factor (PDGF) but not by epidermal growth factor- and insulin-like growth factor. In vitro growth factor receptor tyrosine kinase activity profiling revealed the IC50 for PDGF receptor-β (PDGFRβ) to be 5.07μM, whereas the IC50 for the epidermal growth factor receptor and insulin-like growth factor receptor was ≥100μM. The inhibitory effect of Compound C on PDGFRβ and Akt was also observed in AMPKα1/α2-knockout mouse embryonic fibroblasts, indicating that its inhibitory effect is independent of the AMPK activity. The inhibitory effect of Compound C on cell proliferation and PDGFRβ tyrosine phosphorylation was also demonstrated in various PDGFR-expressing cells, including MRC-5, BEAS-2B, rat aortic vascular smooth muscle cells, and A172 glioblastoma cells. These results indicate that Compound C can be used as a potential antiproliferative agent for PDGF- or PDGFR-associated diseases, such as cancer, atherosclerosis, and fibrosis.

Fatal case of sorafenib-associated idiosyncratic hepatotoxicity in the adjuvant treatment of a patient with renal cell carcinoma

BackgroundSorafenib is an orally available kinase inhibitor with activity at Raf, PDGFβ and VEGF receptors that is licensed for the treatment of advanced renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). Current evidence-based post-nephrectomy management of individuals with localized RCC consists of surveillance-based follow up. The SORCE trial is designed to investigate whether treatment with adjuvant sorafenib can reduce recurrence rates in this cohort.Case presentationHere we report an idiosyncratic reaction to sorafenib resulting in fatal hepatotoxicity and associated renal failure in a 62 year-old man treated with sorafenib within the SORCE trial.ConclusionThis is the first reported case of sorafenib exposure associated fatal toxicity in the adjuvant setting and highlights the unpredictable adverse effects of novel adjuvant therapies.

Role of sorafenib in the treatment of advanced hepatocellular carcinoma: An update

Sorafenib is the first and only p.o. administrated drug currently approved to treat advanced hepatocellular carcinoma (HCC). However, concerns have been raised about sorafenib therapy, including acquired drug resistance. This review provides an overview of sorafenib in the treatment of HCC on the basis of data obtained in the laboratory and in clinical studies. Three underlying mechanisms have been found to support sorafenib therapy. First, sorafenib blocks HCC cell proliferation by inhibiting BRaf and Raf1/c-Raf serine/threonine kinase phosphorylation in the mitogen-activated protein kinase pathway. Second, sorafenib induces apoptosis by reducing elF4E phosphorylation and downregulating Mcl-1 levels in tumor cells. Third, sorafenib prevents tumor-associated angiogenesis by inactivating vascular endothelial growth factor receptors (VEGFR-2 and -3) and the platelet-derived growth factor receptor-β. Clinical trials have demonstrated the effectiveness and relative safety of sorafenib, and thus the drug is used in unresectable HCC. However, many patients may develop acquired resistance to sorafenib, so their response to sorafenib is eventually lost. Sorafenib may induce autophagy, which leads to apoptosis. However, autophagy can also cause drug resistance. Many studies have combined sorafenib with other treatments in an effort to increase its effects, reduce the necessary dose or overcome resistance. It is urgent to study the mechanisms underlying how sorafenib interacts with cellular molecules and other drugs to increase its efficacy and reduce resistance in HCC patients.

Cellular expression profile for interstitial cells of cajal in bladder - a cell often misidentified as myocyte or myofibroblast.

BackgroundInterstitial cells of Cajal (ICC) have been identified in urinary bladder of several species, but their presence in mice remains uncertain. Meanwhile, dozens of reports indicate that dysregulation of connexin 43 plays an important role in bladder overactivity, but its localization has not been clearly defined, with reports of expression in either the smooth muscle or in myofibroblasts. We recently identified a population of ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2) positive cells that resemble ICC and are distinct from smooth muscle, fibroblasts, myofibroblasts and neurons. Thus we sought to define more clearly the molecular signature of ICC and in doing so resolve some of these uncertainties.Principle findingsImmunofluorescent localization revealed that NTPDase2-positive cells lie closely adjacent to smooth muscle but are separate from them. NTPDase2 positive cells exhibited co-localization with the widely accepted ICC marker - c-kit. They were further shown to co-localize with other ICC markers CD34 and Ano1, but not with mast cell marker tryptase. Significantly, they show convincing co-localization with connexin 43, which was not present in smooth muscle. The identity of these cells as ICC was further confirmed by the presence of three mesenchymal markers – vimentin, desmin, and PDGFβ receptor, which indicates their mesenchymal origin. Finally, we observed for the first time, the presence of merlin/neurofibromin 2 in ICC. Normally considered a neuronal protein, the presence of merlin suggests ICC in bladder may have a role in neurotransmission.ConclusionsNTPDase2 positive cells in mice bladder are ICC, which can be defined by the presence of c-Kit, CD34, Ano1, NTPDase2, connexin 43, vimentin, desmin, PDGFβ receptor and merlin/NF2. These data establish a definitive molecular expression profile, which can be used to assist in explorations of their functional roles, and the presence of NTPDase2 suggests that purinergic signaling plays a role in regulation of ICC function.

Platelet‐derived growth factor‐BB increases expression of connexin 43 in an extracellular‐regulated protein kinase‐dependent manner in bladder smooth muscle cells

To investigate whether platelet-derived growth factor-BB induces the upregulation of connexin 43 in bladder smooth muscle cells and to examine the involved signaling pathway. Bladder smooth muscle cells were exposed to platelet-derived growth factor-BB in the presence or absence of p38 mitogen-activated protein kinase, c-jun amino-terminal kinase or extracellular-regulated protein kinase inhibitors. Transfection of bladder smooth muscle cells with specific small interference ribonucleic acid against platelet-derived growth factor receptor-β gene expression was also carried out to investigate whether platelet-derived growth factor receptor-β was involved in the signaling pathway. Expression of messenger ribonucleic acid and protein for connexin 43 was measured by real time polymerase chain reaction and western blot. The addition of platelet-derived growth factor-BB in cultured bladder smooth muscle cells caused the significant upregulation of connexin 43, and the activation of extracellular-regulated protein kinase, c-jun amino-terminal kinase and p38 mitogen-activated protein kinase compared with the control group. This action of platelet-derived growth factor-BB could be abolished by the pretreatment of bladder smooth muscle cells with the extracellular-regulated protein kinase inhibitor PD98059, whereas p38 mitogen-activated protein kinase and c-jun amino-terminal kinase inhibitors did not have any effect on this. Platelet-derived growth factor-BB could induce the activation of platelet-derived growth factor receptor-β. Transfection of bladder smooth muscle cells with small interference ribonucleic acid specific for platelet-derived growth factor receptor-β gene resulted in the potent suppression of gene expression and inhibition of extracellular-regulated protein kinase activation, as well as upregulation of connexin 43 induced by platelet-derived growth factor-BB. Platelet-derived growth factor-BB upregulates connexin 43 expression through the activation of extracellular-regulated protein kinase and platelet-derived growth factor receptor-β signaling pathways. This finding suggests that this signaling pathway might provide a potential target to manipulate detrusor overactivity.

PDGFR blockade is a rational and effective therapy for NPM-ALK–driven lymphomas

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkin's lymphoma found in children and young adults. ALCLs frequently carry a chromosomal translocation that results in expression of the oncoprotein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). The key molecular downstream events required for NPM-ALK-triggered lymphoma growth have been only partly unveiled. Here we show that the activator protein 1 family members JUN and JUNB promote lymphoma development and tumor dissemination through transcriptional regulation of platelet-derived growth factor receptor-β (PDGFRB) in a mouse model of NPM-ALK-triggered lymphomagenesis. Therapeutic inhibition of PDGFRB markedly prolonged survival of NPM-ALK transgenic mice and increased the efficacy of an ALK-specific inhibitor in transplanted NPM-ALK tumors. Notably, inhibition of PDGFRA and PDGFRB in a patient with refractory late-stage NPM-ALK(+) ALCL resulted in rapid, complete and sustained remission. Together, our data identify PDGFRB as a previously unknown JUN and JUNB target that could be a highly effective therapy for ALCL.

HBV promotes the proliferation of hepatic stellate cells via the PDGF-B/PDGFR-β signaling pathway in vitro

The activation of hepatic stellate cells (HSCs) is closely associated with liver fibrosis in chronic hepatitisB virus (HBV) infection. However, the molecular mechanisms leading to HSC activation remain unclear. It has been reported that the platelet-derived growth factor-B (PDGF-B)/PDGF receptor-β (PDGFR-β) signaling pathway is involved in this process. Thus, we investigated whether HBV and its protein contribute to HSC proliferation by the PDGF-B/PDGFR-β signaling pathway. HBV particles were purified from the supernatant of HepG2.2.15 cells by ultracentrifugation and the cell lines carrying HBV preS, e, c or x genes were obtained. After incubation with HBV particles or co-cultured with the cell lines expressed in the viral protein, the proliferation of LX-2 cells, an HSC cell line, were detected by flow cyto-metry and real-time PCR and the expression of molecules related to the PDGF-B/PDGFR-β signaling pathway were further measured. Our results indicated that HBV particles, c and x proteins promoted LX-2 proliferation and increased the mRNA levels of PDGF-B, PDGFR-β, collagen-I and α-smooth muscle actin (α-SMA), as well as the phosphorylation of PDGFR-β; however, the expression protein levels of PDGF-B and PDGFR-β remained unchanged. In conclusion, HBV particles and HBVc and x proteins promote HSC proliferation and fibrogenesis invitro and the PDGF-B/PDGFR-β signaling pathway is important in this process.