Platelet-derived Growth Factor B Signaling Research Articles

Neonatal stress disrupts the glymphatic system development and increases the susceptibility to Parkinson's disease in later life.

Neonatal stress disrupts brain development and increases the risk of neurological disorders later in life. However, the impact of neonatal stress on the development of the glymphatic system and susceptibility to Parkinson's disease (PD) remains largely unknown. Neonatal maternal deprivation (NMD) was performed on mice for 14 consecutive days to model chronic neonatal stress. Adeno-associated virus expressing A53T-α-synuclein (α-syn) was injected into the substantia nigra to establish PD model mice. Glymphatic activity was determined using invivo magnetic resonance imaging, exvivo fluorescence imaging and microplate assay. The transcription and expression of aquaporin-4 (AQP4) and other molecules were evaluated by qPCR, western blotting, and immunofluorescence. Animal's responses to NMD and α-syn overexpression were observed using behavioral tests. Glymphatic activity was impaired in adult NMD mice. AQP4 polarization and platelet-derived growth factor B (PDGF-B) signaling were reduced in the frontal cortex and hippocampus of both young and adult NMD mice. Furthermore, exogenous α-syn accumulation was increased and PD-like symptoms were aggravated in adult NMD mice. The results demonstrated that NMD could disrupt the development of the glymphatic system through PDGF-B signaling and increase the risk of PD later in life, indicating that alleviating neonatal stress could be beneficial in protecting the glymphatic system and reducing susceptibility to neurodegeneration.

Role of endothelial PDGFB in arterio-venous malformations pathogenesis

Arterial-venous malformations (AVMs) are direct connections between arteries and veins without an intervening capillary bed. Either familial inherited or sporadically occurring, localized pericytes (PCs) drop is among the AVMs’ hallmarks. Whether impaired PC coverage triggers AVMs or it is a secondary event is unclear. Here we evaluated the role of the master regulator of PC recruitment, Platelet derived growth factor B (PDGFB) in AVM pathogenesis. Using tamoxifen-inducible deletion of Pdgfb in endothelial cells (ECs), we show that disruption of EC Pdgfb-mediated PC recruitment and maintenance leads to capillary enlargement and organotypic AVM-like structures. These vascular lesions contain non-proliferative hyperplastic, hypertrophic and miss-oriented capillary ECs with an altered capillary EC fate identity. Mechanistically, we propose that PDGFB maintains capillary EC size and caliber to limit hemodynamic changes, thus restricting expression of Krüppel like factor 4 and activation of Bone morphogenic protein, Transforming growth factor β and NOTCH signaling in ECs. Furthermore, our study emphasizes that inducing or activating PDGFB signaling may be a viable therapeutic approach for treating vascular malformations.

PROX1 Inhibits PDGF-B Expression to Prevent Myxomatous Degeneration of Heart Valves.

Cardiac valve disease is observed in 2.5% of the general population and 10% of the elderly people. Effective pharmacological treatments are currently not available, and patients with severe cardiac valve disease require surgery. PROX1 (prospero-related homeobox transcription factor 1) and FOXC2 (Forkhead box C2 transcription factor) are transcription factors that are required for the development of lymphatic and venous valves. We found that PROX1 and FOXC2 are expressed in a subset of valvular endothelial cells (VECs) that are located on the downstream (fibrosa) side of cardiac valves. Whether PROX1 and FOXC2 regulate cardiac valve development and disease is not known. We used histology, electron microscopy, and echocardiography to investigate the structure and functioning of heart valves from Prox1ΔVEC mice in which Prox1 was conditionally deleted from VECs. Isolated valve endothelial cells and valve interstitial cells were used to identify the molecular mechanisms in vitro, which were tested in vivo by RNAScope, additional mouse models, and pharmacological approaches. The significance of our findings was tested by evaluation of human samples of mitral valve prolapse and aortic valve insufficiency. Histological analysis revealed that the aortic and mitral valves of Prox1ΔVEC mice become progressively thick and myxomatous. Echocardiography revealed that the aortic valves of Prox1ΔVEC mice are stenotic. FOXC2 was downregulated and PDGF-B (platelet-derived growth factor-B) was upregulated in the VECs of Prox1ΔVEC mice. Conditional knockdown of FOXC2 and conditional overexpression of PDGF-B in VECs recapitulated the phenotype of Prox1ΔVEC mice. PDGF-B was also increased in mice lacking FOXC2 and in human mitral valve prolapse and insufficient aortic valve samples. Pharmacological inhibition of PDGF-B signaling with imatinib partially ameliorated the valve defects of Prox1ΔVEC mice. PROX1 antagonizes PDGF-B signaling partially via FOXC2 to maintain the extracellular matrix composition and prevent myxomatous degeneration of cardiac valves.

MicroRNA-432-5p regulates sprouting and intussusceptive angiogenesis in osteosarcoma microenvironment by targeting PDGFB

Osteosarcoma (OS) is a type of bone tumor conferred with high metastatic potential. Attainable growth of tumors necessitates functional vasculature mediated by sprouting angiogenesis (SA) and intussusceptive angiogenesis (IA). However, the regulation of IA and SA is still unclear in OS. To understand the mechanisms adopted by OS to induce angiogenesis, initially, we assessed the expression profile of a set of miRNAs' in both OS cells (SaOS2 and MG63) and normal bone cells. Amongst them, miR-432-5p was found to be highly downregulated in OS. The functional role of miR-432-5p in OS was further analyzed using miR-432-5p mimic/inhibitor. Platelet-derived growth factor-B (PDGFB) was found to be a putative target of miR-432-5p and it was further confirmed that the PDGFB 3′UTR is directly targeted by miR-432-5p using the luciferase reporter gene system. PDGFB was found to be secreted by OS to regulate angiogenesis by targeting the cells in its microenvironment. The conditioned medium obtained from miR-432-5p mimic transfected MG63 and SaOS2 cells decreased cell viability, proliferation, migration, and aorta ring formation in endothelial cells. The miRNA mimic/inhibitor transfected MG63 and SaOS2 cells were placed on SA (day 6) and IA (day 9) phase of CAM development to analyze SA and IA mechanisms. It was found that miR-432-5p mimic transfection in OS promotes the transition of SA to IA which was documented by the angiogenic parameters and SA and IA-associated gene expression. Interestingly, this outcome was also supported by the zebrafish tumor xenograft model. Corroborating these results, it is clear that miR-432-5p expression in OS cells regulates SA and IA by targeting PDGFB genes. We conclude that targeting miR-432-5p/PDGFB signaling can be a potential therapeutic strategy to treat OS along with other existing strategies.MicroRNA-432-5p expression in osteosarcoma cells regulates sprouting and intussusceptive angiogenesis by targeting PDGFB genes. MicroRNA-432-5p/PDGFB signaling can be targeted to treat angiogenesis in osteosarcoma along with other strategies which will further strengthen the effectiveness of antiangiogenic therapy.

Aggravated pulmonary injury after subarachnoid hemorrhage in PDGF-Bret/ret mice

BackgroundRecent advances in surgical and neuroprotective strategies could effectively manage the pathophysiological progression of subarachnoid hemorrhage (SAH). However, pulmonary dysfunction frequently occurs in SAH patients with an increased risk of unsatisfactory outcomes. Based on the similar microvascular structures in the blood-air barrier and blood-brain barrier and possible brain-lung crosstalks, we believe that pericytes may be involved in both neurological and pulmonary dysfunction after SAH.MethodsIn our experiments, platelet-derived growth factor B (PDGF-B) retention motif knockout (PDGF-Bret/ret) mice and adeno-associated virus PDGF-B were employed to show the involvement of pericyte deficiency and PDGF-B expression. Neurological score, SAH grade, hematoxylin-eosin staining, and PaO2/FiO2 ratio analysis were performed to evaluate the neurological deficits and pulmonary functions in endovascular perforation SAH models at 24 h after surgery, as well as western blotting and immunofluorescence staining for underlying molecular expressions.ResultsWe found that neonatal PDGF-Bret/ret mice exhibited pulmonary atelectasis 12 h after birth. Further investigation showed a decrease in PaO2/FiO2 and lung-specific surfactant proteins in adult PDGF-Bret/ret mice. These dysfunctions were much worse than those in wild-type mice at 24 h after SAH. PDGF-B overexpression alleviated pulmonary dysfunction after SAH.ConclusionsThese results suggested pulmonary dysfunction after SAH and the pivotal role of PDGF-B signaling for the pathophysiological process and future therapeutic targets of pulmonary injury treatment after SAH. Further studies are needed for pathophysiological investigations and translational studies on pulmonary injuries after SAH.

Quantitative Proteomics of TRAMP Mice Combined with Bioinformatics Analysis Reveals That PDGF-B Regulatory Network Plays a Key Role in Prostate Cancer Progression.

Transgenic adenocarcinoma of the mouse prostate (TRAMP) mice is a widely used transgenic animal model of prostate cancer (PCa). We performed a label-free quantitative proteomics analysis combined with a bioinformatics analysis on the entire prostate protein extraction from TRAMP mice and compared it with WT littermates. From 2379 total identified proteins, we presented a modest mice prostate reference proteome containing 919 proteins. 61 proteins presented a significant expression difference between two groups. The integrative bioinformatics analysis predicted the overexpression of platelet-derived growth factor B (PDGF-B) in tumor tissues and supports the hypothesis of the PDGF-B signaling network as a key upstream regulator in PCa progression. Furthermore, we demonstrated that Crenolanib, a novel PDGF receptor inhibitor, inhibited PCa cell proliferation in a dose-dependent manner. Finally, we revealed the importance of PDGF-B regulatory network in PCa progression, which will assist us in understanding the role and mechanisms of PDGF-B in promoting cancer growth and provide valuable knowledge for future research on anti-PDGF therapy.

Cold Shock Proteins Mediate GN with Mesangioproliferation.

DNA binding protein A (DbpA) is a member of the human cold shock domain-containing protein superfamily, with known functions in cell proliferation, differentiation, and stress responses. DbpA mediates tight junction-associated activities in tubular epithelial cells, but the function of DbpA in mesangial cells is unknown. Here, we found DbpA protein expression restricted to vascular smooth muscle cells in healthy human kidney tissue but profound induction of DbpA protein expression within the glomerular mesangial compartment in mesangioproliferative nephritis. In vitro, depletion or overexpression of DbpA using lentiviral constructs led to inhibition or promotion, respectively, of mesangial cell proliferation. Because platelet-derived growth factor B (PDGF-B) signaling has a pivotal role in mesangial cell proliferation, we examined the regulatory effect of PDGF-B on DbpA. In vitro studies of human and rat mesangial cells confirmed a stimulatory effect of PDGF-B on DbpA transcript numbers and protein levels. Additional in vivo investigations showed DbpA upregulation in experimental rat anti-Thy1.1 nephritis and murine mesangioproliferative nephritis models. To interfere with PDGF-B signaling, we injected nephritic rats with PDGF-B neutralizing aptamers or the MEK/ERK inhibitor U0126. Both interventions markedly decreased DbpA protein expression. Conversely, continuous PDGF-B infusion in healthy rats induced DbpA expression predominantly within the mesangial compartment. Taken together, these results indicate that DbpA is a novel target of PDGF-B signaling and a key mediator of mesangial cell proliferation.

LHT7, a chemically modified heparin, inhibits multiple stages of angiogenesis by blocking VEGF, FGF2 and PDGF-B signaling pathways

Despite the therapeutic benefits of the angiogenesis inhibitors shown in the clinics, they have encountered an unexpected limitation by the occurrence of acquired resistance. Although the mechanism of the resistance is not clear so far, the upregulation of alternative angiogenic pathways and stabilization of endothelium by mural cells were reported to be responsible. Therefore, blocking multiple angiogenic pathways that are crucial in tumor angiogenesis has been highlighted to overcome such limitations. To develop an angiogenesis inhibitor that could block multiple angiogenic factors, heparin is an excellent lead compound since wide array of angiogenic factors are heparin-binding proteins. In previous study, we reported a heparin-derived angiogenesis inhibitor, LHT7, as a potent angiogenesis inhibitor and showed that it blocked VEGF signaling pathway. Here we show that LHT7 could block the fibroblast growth factor 2 (FGF2) and platelet-derived growth factor B (PDGF-B) in addition to VEGF. Simultaneous blockade of these angiogenic factors resulted in inhibition of multiple stages of the angiogenic process, including initial angiogenic response to maturation of the endothelium by pericyte coverage in vitro. In addition, the treatment of LHT7 in vivo did not show any sign of vascular normalization and directly led to decreased blood perfusion throughout the tumor. Our findings show that LHT7 could effectively inhibit tumor angiogenesis by blocking multiple stages of the angiogenesis, and could potentially be used to overcome the resistance.

Photoreceptor degeneration, structural remodeling and glial activation: A morphological study on a genetic mouse model for pericyte deficiency

Interaction between pericytes and endothelial cells via platelet-derived growth factor B (PDGF-B) signaling is critical for the development of the retinal microvasculature. The PDGF-B retention motif controls the spatial distribution range of the growth factor in the vicinity of its producing endothelial cells allowing its recognition by PDGF receptor beta-(PDGFR-β)-carrying pericytes; this promotes recruitment of pericytes to the vascular basement membrane. Impairment of the PDGF-B signaling mechanism causes development of vascular abnormalities, and in the retina this consequently leads to defects in the neurological circuitry. The vascular pathology in the pdgf-bret/ret (PDGF-B retention motif knockout) mouse retina has been previously reported; our study investigates the progressive neuronal defects and changes in the retinal morphology of this pericyte-deficient mouse model. Immunohistochemical analysis revealed retinal injuries to occur as early as postnatal day (P) 10 with substantial damage progressing from P15 and onward. Vascular abnormalities were apparent from P10, however, prominent neuronal defects were mostly observed from P15, beginning with the compromised integrity of the laminated retinal structure characterized by the presence of rosettes and focally distorted regions. Photoreceptor degeneration was observed by loss of both rod and cone cells, including the disassembly and altered structure of their synaptic terminals. Significant shortening of cone outer segments was observed from P10 and later stages; however, decrease in cone density was only observed at P28. Disorganization and dendrite remodeling of rod bipolar cells also added to the diminished neural and synaptic integrity. Moreover, in response to retinal injuries, Müller and microglial cells were observed to be in the reactive phenotype from P15 and onward. Such a sequence of events indicates that the pdgf-bret/ret mouse model displays a short time frame between P10 and P15, during which the retina shifts to a retinopathic phase by the development of prominently altered morphological features.

Overexpression of platelet-derived growth factor-B increases the growth, invasion, and angiogenesis of gastric carcinoma cells through protein kinase B

Platelet-derived growth factor-B (PDGF-B) promotes tumor metastasis by inducing tumor cell growth, invasion, and angiogenesis in several cancers. However, the roles of PDGF-B in gastric carcinoma are largely unknown. We established two gastric carcinoma cell lines, SGC7901 and BGC823, to stably overexpress PDGF-B by lentiviral vectors, and determined their growth, invasion and angiogenesis. Overexpression of PDGF-B significantly enhanced the cell proliferation, invasion and angiogenesis of both SGC7901 and BGC823 cells, accompanied with increased activation of AKT, which is a downstream target of PDGF signaling pathway. Consequently, an AKT kinase inhibitor abolished the PDGF-B overexpression-mediated up-regulation of growth, invasion and angiogenesis. These results indicate that PDGF-B signaling may promote the metastasis of gastric carcinoma through AKT signaling. Targeting the PDGF-B pathway may be an alternative strategy for the development of therapies for gastric cancers.

Clinicopathological significance of platelet-derived growth factor B, platelet-derived growth factor recpertor-β, and E-cadherin expression in gastric carcinoma

Aim of the studyPlatelet-derived growth factor B (PDGF-B), a vital growth factor which can induce angiogenesis and epithelial-mesenchymal transition (EMT), is important in the metastasis of many tumors. However, the roles of PDGF-B in gastric carcinoma are largely unknown. We investigated the correlation between PDGF-B, PDGFR-β and E-cadherin expression with the clinical features of gastric carcinoma patients to evaluate the relationship between PDGF-B signaling, E-cadherin and metastasis of gastric carcinoma, the correlation between PDGF-B and E-cadherin expression to assess the roles of PDGF-B signaling in metastasis of gastric carcinoma..Material and methodsWe detected expressions of PDGF-B, PDGFR-β and E-cadherin in gastric carcinoma tissues and normal gastric mucosa tissues of 64 patients with gastric carcinoma who had undergone surgical resection, and investigated their relationships with clinical features and the relationships between PDGF-B and E-cadherin expression in gastric carcinoma.ResultsIn surgical specimens, tumor cells expressed PDGF-B, and PDGFR-β was expressed by tumor stromal cells. E-cadherin was expressed by both tumor cells and normal gastric mucosa cells. Expressions of PDGF-B and PDGFR-β were increased in gastric carcinoma tissues (p < 0.05) and were positively correlated with the depth of cancer invasion, lymph node metastasis and TNM stage (p < 0.05). The expression of E-cadherin was reduced in gastric carcinoma tissues (p < 0.05) and was negatively correlated with the depth of cancer invasion, lymph node metastasis and TNM stage (p < 0.05). The correlation between PDGF-B and E-cadherin expression was negative (p < 0.05).ConclusionOur data indicate that either the overexpression of PDGF-B and PDGFR-β or the underexpression of E-cadherin is correlated with cancer progression and lymphogenous metastasis of gastric carcinoma. The PDGF-B signal pathway might induce EMT by down-regulating expression of E-cadherin to promote metastasis of gastric carcinoma.

Vaccination with Platelet-Derived Growth Factor B Kinoids Inhibits CCl4-Induced Hepatic Fibrosis in Mice

Platelet-derived growth factor B (PDGF-B) plays an essential role in hepatic fibrosis. Inhibition of the PDGF-B signaling in chronically injured livers might represent a potential therapeutic measure for hepatic fibrosis. In this study, we assessed the effects of vaccination against PDGF-B on CCl₄-induced liver fibrosis in BALB/c mice. The PDGF-B kinoid immunogens were prepared by cross-linking two PDGF-B-derived B-cell epitope peptides [PDGF-B¹⁶-(23-38) and PDGF-B¹⁶-(72-83)] to ovalbumin and keyhole limpet hemocyanin, respectively. Enzyme-linked immunosorbent assay, Western blotting, and NIH3T3 cell proliferation assay verified that immunization with the PDGF-B kinoids elicited the production of high levels of neutralizing anti-PDGF-B autoantibodies. The vaccination markedly alleviated CCl₄-induced hepatic fibrosis, as indicated by the lessened morphological alternations and reduced hydroxyproline contents in the mouse livers. Moreover, immunohistochemical staining for proliferating cell nuclear antigen, α-smooth muscle actin, and desmin demonstrated that neutralization of PDGF-B inhibited both the proliferation and the activation of hepatic stellate cells in the fibrotic mouse livers. Taken together, this study demonstrated that vaccination with PDGF-B kinoids significantly suppressed CCl₄-induced hepatic fibrosis in mice. Our results suggest that vaccination against PDGF-B might be developed into an effective, convenient, and safe therapeutic measure for the treatment of hepatic fibrosis.

PDGF in gliomas: more than just a growth factor?

Platelet-derived growth factor B (PDGF-B) is a growth factor promoting and regulating cell migration, proliferation, and differentiation, involved in both developmental processes and in maintaining tissue homeostasis under strict regulation. What are the implications of prolonged or uncontrolled growth factor signaling in vivo, and when does a growth factor such as PDGF-B become an oncogene? Under experimental conditions, PDGF-B induces proliferation and causes tumor induction. It is not known whether these tumors are strictly a PDGF-B-driven proliferation of cells or associated with secondary genetic events such as acquired mutations or methylation-mediated gene silencing promoting neoplasia. If PDGF-B-driven tumorigenesis was only cellular proliferation, associated changes in gene expression would thus be correlated with proliferation and not associated with secondary events involved in tumorigenesis and neoplastic transformation such as cycle delay, DNA damage response, and cell death. Changes in gene expression might be expected to be reversible, as is PDGF-B-driven proliferation under normal circumstances. Since PDGF signaling is involved in oligodendrocyte progenitor cell differentiation and maintenance, it is likely that PDGF-B stimulates proliferation of a pool of cells with that phenotype, and inhibition of PDGF-B signaling would result in reduced expression of oligodendrocyte-associated genes. More importantly, inhibition of PDGF signaling would be expected to result in reversion of genes induced by PDGF-B accompanied by a decrease in proliferation. However, if PDGF-B-driven tumorigenesis is more than simply a proliferation of cells, inhibition of PDGF signaling may not reverse gene expression or halt proliferation. These fundamental questions concerning PDGF-B as a potential oncogene have not been resolved.

Increased Vascular Delivery and Efficacy of Chemotherapy after Inhibition of Platelet-Derived Growth Factor-B

Inhibition of platelet-derived growth factor-B (PDGF-B) has multiple effects on tumors, including loss of pericytes, regression of some vessels, normalization of other vessels, and reduction of interstitial pressure. PDGF-B inhibition also increases the efficacy of cancer therapeutics, but the role on tumor vessel efficiency and drug delivery is unclear. We sought to determine whether inhibition of PDGF-B signaling can increase delivery and efficacy of cyclophosphamide in Lewis lung carcinomas or RIP-Tag2 tumors. PDGF-B blockade in Lewis lung carcinoma tumors by the DNA aptamer AX102 for 14 days increased the number of perfused tumor vessels marked by lectin in the bloodstream by 50%. AX102 also increased the width of sleeves of viable tumor cells around blood vessels by 66%, increased tumor cell proliferation by 90%, and increased intratumoral delivery of Hoechst 33342 by 78%. A low dose of cyclophosphamide (20 mg/kg) reduced tumor cell proliferation by 31% when combined with AX102 but not when given alone. Synergy of cyclophosphamide and AX102 on tumor cell proliferation also was found in RIP-Tag2 tumors. Similarly, the PDGF receptor signaling inhibitor imatinib increased delivery of cyclophosphamide and reduced tumor burden in RIP-Tag2 mice, without evidence of tumor cell sensitization to chemotherapy. Together, these findings indicate that inhibition of PDGF-B signaling promotes the delivery and efficacy of chemotherapeutic agents by increasing the efficiency of tumor blood vessels.

MicroRNA‐29, a key regulator of collagen expression in systemic sclerosis

To investigate the role of microRNA (miRNA) as posttranscriptional regulators of profibrotic genes in systemic sclerosis (SSc). MicroRNA, which target collagens, were identified by in silico analysis. Expression of miRNA-29 (miR-29) was determined by TaqMan real-time polymerase chain reaction analysis of skin biopsy and fibroblast samples from SSc patients and healthy controls as well as in the mouse model of bleomycin-induced skin fibrosis. Cells were transfected with precursor miRNA (pre-miRNA)/anti-miRNA of miR-29 using Lipofectamine. Collagen gene expression was also studied in luciferase reporter gene assays. For stimulation, recombinant transforming growth factor beta (TGFbeta), platelet-derived growth factor B (PDGF-B), or interleukin-4 (IL-4) was used. The effects of inhibiting PDGF-B and TGFbeta signaling on the levels of miR-29 were studied in vitro and in the bleomycin model. We found that miR-29a was strongly down-regulated in SSc fibroblasts and skin sections as compared with the healthy controls. Overexpression in SSc fibroblasts significantly decreased, and accordingly, knockdown in normal fibroblasts increased, the levels of messenger RNA and protein for type I and type III collagen. In the reporter gene assay, cotransfection with pre-miR-29a significantly decreased the relative luciferase activity, which suggests a direct regulation of collagen by miR-29a. TGFbeta, PDGF-B, or IL-4 reduced the levels of miR-29a in normal fibroblasts to those seen in SSc fibroblasts. Similar to human SSc, the expression of miR-29a was reduced in the bleomycin model of skin fibrosis. Inhibition of PDGF-B and TGFbeta pathways by treatment with imatinib restored the levels of miR-29a in vitro and in the bleomycin model in vivo. These data add the posttranscriptional regulation of collagens by miR-29a as a novel aspect to the fibrogenesis of SSc and suggest miR-29a as a potential therapeutic target.

Sox5 can suppress platelet-derived growth factor B-induced glioma development in Ink4a-deficient mice through induction of acute cellular senescence

SOX5 is a member of the high-mobility group superfamily of architectural non-histone proteins involved in gene regulation and maintenance of chromatin structure in a wide variety of developmental processes. Sox5 was identified as a brain tumor locus in a retroviral insertional mutagenesis screen of platelet-derived growth factor B (PDGFB)-induced mouse gliomas. Here we have investigated the role of Sox5 in PDGFB-induced gliomagenesis in mice. We show that Sox5 can suppress PDGFB-induced glioma development predominantly upon Ink4a-loss. In human glioma cell lines and tissues, we found very low levels of SOX5 compared with normal brain. Overexpression of Sox5 in human glioma cells led to a reduction in clone formation and inhibition of proliferation. Combined expression of Sox5 and PDGFB in primary brain cell cultures caused decreased proliferation and an increased number of senescent cells in the Ink4a-/- cells only. Protein analyses showed a reduction in the amount and activation of Akt and increased levels of p27(Kip1) upon Sox5 expression that was dominant to PDGFB signaling and specific to Ink4a-/- cells. Upon inhibition of p27(Kip1), the effects of Sox5 on proliferation and senescence could be reversed. Our data suggest a novel pathway, where Sox5 may suppress the oncogenic effects of PDGFB signaling during glioma development by regulating p27(Kip1) in a p19(Arf)-dependent manner, leading to acute cellular senescence.

Tumor Progression and Oncogene Addiction in a PDGF-B-Induced Model of Gliomagenesis

Platelet-derived growth factor B (PDGF-B) overexpression induces gliomas of different grades from murine embryonic neural progenitors. For the first time, we formally demonstrated that PDGF-B-induced neoplasms undergo progression from nontumorigenic low-grade tumors toward highly malignant forms. This result, showing that PDGF-B signaling alone is insufficient to confer malignancy to cells, entails the requirement for further molecular lesions in this process. Our results indicate that one of these lesions is represented by the down-regulation of the oncosuppressor Btg2. By in vivo transplantation assays, we further demonstrate that fully progressed tumors are PDGF-B-addicted because their tumor-propagating ability is lost when the PDGF-B transgene is silenced, whereas it is promptly reacquired after its reactivation. We provide evidence that this oncogene addiction is not caused by the need for PDGF-B as a mitogen but, rather, to the fact that PDGF-B is required to overcome cell-cell contact inhibition and to confer in vivo infiltrating potential on tumor cells.

Inhibition of Platelet-Derived Growth Factor B Signaling Enhances the Efficacy of Anti-Vascular Endothelial Growth Factor Therapy in Multiple Models of Ocular Neovascularization

'Vascular endothelial growth factor-A (VEGF-A) blockade has been recently validated as an effective strategy for the inhibition of new blood vessel growth in cancer and ocular pathologies. However, several studies have also shown that anti-VEGF therapy may not be as effective in the treatment of established unwanted blood vessels, suggesting they may become less dependent on VEGF-A for survival. The VEGF-A dependence of vessels may be related to the presence of vascular mural cells (pericytes or smooth muscle cells). Mural cell recruitment to the growing endothelial tube is regulated by platelet-derived growth factor-B (PDGF-B) signaling, and interference with this pathway causes disruption of endothelial cell-mural cell interactions and loss of mural cells. We have investigated the basis of blood vessel dependence on VEGF-A in models of corneal and choroidal neovascularization using a combination of reagents (an anti-VEGF aptamer and an anti-PDGFR-beta antibody) to inhibit both the VEGF-A and PDGF-B signaling pathways. We demonstrate that neovessels become refractory to VEGF-A deprivation over time. We also show that inhibition of both VEGF-A and PDGF-B signaling is more effective than blocking VEGF-A alone at causing vessel regression in multiple models of neovascular growth. These findings provide insight into blood vessel growth factor dependency and validate a combination therapy strategy for enhancing the current treatments for ocular angiogenic disease.

The oncogene PDGF-B provides a key switch from cell death to survival induced by TNF

Tumor necrosis factor (TNF) induces both cell death and survival signals. NF-kappaB, a transcription factor activated by TNF, is critical for controlling survival signals through trans-activation of downstream target genes. However, few NF-kappaB target survival genes have been identified with direct roles in oncogenesis. We report that platelet-derived growth factor B (PDGF-B), an oncogene and growth factor, is highly induced by TNF in fibroblasts in an NF-kappaB-dependent manner. PDGF-B can rescue NF-kappaB-deficient fibroblasts from TNF-mediated killing, and inhibition of PDGF-B signaling sensitizes wild-type cells to TNF-induced death. Interestingly, PDGF-B-transformed NIH-3T3 cells are even more highly sensitized to TNF-induced cell death with PDGF-B inhibition. Our results suggest that while normal cells contain multiple TNF-induced survival signals, tumor cells may favor a specific survival gene that is abnormally upregulated in order to evade death signals.