Platelet derived growth factor receptors (PDGFRs) play an important role in tumor pathogenesis, and they are frequently overexpressed in glioblastoma (GBM). the invasive capacity of PDGFR-depleted CSC as compared to parental cells correlated with the downmodulation of markers of epithelial-mesenchymal transition phenotype and angiogenesis. Surprisingly, we observed the induction of anti-apoptotic proteins and compensatory oncogenic signals such as EDN1, EDNRB, PRKCB1, PDGF-C and PDGF-D. To conclude, we hypothesize that the newly discovered PDGFR/Stat3/Rb1 regulatory axis might represent a potential therapeutic target for GBM treatment. studies to mouse models have implicated the role of the PDGF pathway in cellular invasion and tumor angiogenesis [6]. In fact, over-activity of PDGF signaling is associated with tumor development in brain, prostate, liver, lung, leukemia and colon cancers [7, 8]. Although anti-VEGF treatment has been the major therapeutic target in gliomas, other antiangiogenic agents such as anti-PDGFs or anti-FGFs are currently in 1211441-98-3 preclinical and clinical development [9]. PDGFR includes two receptors ( and ) and four ligands (PDGF-A, PDGF-B, PDGF-C and PDGF-D). The PDGFs bind to 1211441-98-3 the receptors with different affinities. Thus, PDGF-AA, -AB, -BB and -CC induce receptor homodimers, PDGF-BB and -DD receptor dimerization, and PDGF-AB, -BB, -CC and -DD receptor dimerization [5]. Ligand-induced dimerization favors autophosphorylation of specific tyrosine residues and subsequent activates downstream signal pathways: PI3K/Akt1/mTOR, Ras/MAPK, PLC-/PKC and STAT3. PDGFR binds and activates 1211441-98-3 signal transducers and activator of transcription (STATs). Phosphorylation of Y705 in Stat3 leads to dimerization, nuclear translocation, recognition of Stat3-specific DNA binding elements and up-regulation of various Stat3 downstream target genes, such as Bcl-xl, Bcl-2, Survivin, c-Myc and Cyclin D1. Stat3 regulates tumorigenesis and tumor inflammation and behaves in an oncogenic manner depending on the genetic background of the tumor [1]. In recent studies, Stat3 has been implicated in the self-renewal of neural stem cells and glial differentiation while restricting neuronal differentiation [8C13]. The PKC family consists of fifteen isozymes divided into three subfamilies: conventional (or classical), novel, and atypical. Conventional PKCs contain the isoforms , I, II, and . The PDGFR downstream target PKC plays an important role in migration, tumor growth, angiogenesis and drug resistance in GBM cells [14C16]. In 1992, PKC was suggested as marker of malignancy for gliomas, and more recently serum PKC serves as a biomarker for diagnosis of cancers [14, 15]. The invasion/migration of GBM cells induced by TPA, occurs through activation of PKC/ERK/NF-B-dependent MMP-9 expression [16]. A positive feedback loop between Wnt5A and phospho-PKC in promotion of epithelial-mesenchymal transition (EMT) in nasopharyngeal carcinoma 1211441-98-3 was disclosed [17]. In addition, PDGF receptors bind to other tyrosine kinase receptors, e.g. EGFR [18]. Retinoblastoma 1 (RB1) gene belongs CD271 to a family of three proteins, including also RBL1/p107 and RBL2/p130. Classically the tumor suppressive function of Rb proteins have been mainly attributed to their ability to arrest cell cycle by repressing E2F target genes. When Rb1 is in its active hypophosphorylated state, it represses E2F-mediated transcription by binding, blocks the E2F transactivation domain, and forms complexes with its (DPs transcription factors) partners at cell cycle gene promoters [19]. Conversely, Rb1 phosphorylation initiated by cyclin D-CDK4/6 in response to mitogenic signals, inactivates the Rb1 repressive function by dissociating the Rb1-E2F-DP complexes [19]. The Cancer Genome Atlas Research Network revealed in 2008 that the CycD1-CDK4/6-Rb1 pathway is among the top three most altered pathways in GBM, which makes this an appealing target for cancer therapy [20C22]. We and others recently demonstrated that inhibition of either PDGFR or PDGFR signaling induced apoptosis in glioblastoma stem cells [23, 7]. In the present study, we aimed to assess the effects of PDGFR depletion on stemness, invasion and differentiation in GBM CSC. Our findings reveal an inverse correlation between Stat3 1211441-98-3 Y705-phosphorylation and the hypophosphorylated Rb1 instructed by the PDGFR/PDGF-AA regulatory axis. Further, downmodulation of cell growth, invasion and the EMT phenotype are triggered by PDGFR depletion in GBM CSC. Surprisingly, we detected the activation of angiogenic and survival pathways as compared to parental cells, which supports a multimodal approach to treat GBM CSC. RESULTS Activation of PDGFR/PDGF-AA signaling regulates expression of downstream genes Egr1, Stat3 and Rb1 but not PKC in GBM CSC Cancer stem cells from GBM were isolated as described previously [23, 24]. We were able to collect either core- (c-CSC) or peritumor tissue-derived cancer stem cells (p-CSC) from several primary GBM samples; the two types of CSC had quite different tumorigenic potential and exclusive genetic anomalies [23, 24]. To demonstrate.