PDGFRα depletion attenuates glioblastoma stem cells features by modulation of STAT3, RB1 and multiple oncogenic signals

// Carlo Cenciarelli 1 , Hany E. Marei 2 , Armando Felsani 3 , Patrizia Casalbore 3 , Gigliola Sica 4 , Maria Ausiliatrice Puglisi 5 , Angus J.M. Cameron 6 , Alessandro Olivi 7 , Annunziato Mangiola 7 1 Institute of Translational Pharmacology, Department of Biomedical Sciences-National Research Council (IFT-CNR), Rome, Italy 2 Biomedical Research Center, Qatar University, Doha, Qatar 3 Institute of Cell Biology and Neurobiology, Dept. of Biomedical Sciences-National Research Council (IBCN-CNR), Rome, Italy 4 Institute of Histology and Embryology, Catholic University-School of Medicine, Rome, Italy 5 Department of Internal Medicine and Gastroenterology, Agostino Gemelli Hospital, Rome, Italy 6 Barts Cancer Institute, John Vane Science Centre, Queen Mary University of London, London, United Kingdom 7 Institute of Neurosurgery, Department of Head and Neck, Catholic University-School of Medicine, Rome, Italy Correspondence to: Carlo Cenciarelli, email: carlo.cenciarelli@ift.cnr.it Keywords: glioblastoma, cancer stem cells, PDGFRα, STAT3, RB1 Received: April 05, 2016      Accepted: June 09, 2016      Published: June 17, 2016 ABSTRACT Platelet derived growth factor receptors (PDGFRs) play an important role in tumor pathogenesis, and they are frequently overexpressed in glioblastoma (GBM). Earlier we have shown a higher protein expression of PDGFR isoforms (α and β) in peritumoral-tissue derived cancer stem cells (p-CSC) than in tumor core (c-CSC) of several GBM affected patients. In the current study, in order to assess the activity of PDGFRα/PDGF-AA signaling axis, we performed time course experiments to monitor the effects of exogenous PDGF-AA on the expression of downstream target genes in c-CSC vs p-CSC. Interestingly, in p-CSC we detected the upregulation of Y705-phosphorylated Stat3, concurrent with a decrement of Rb1 protein in its active state, within minutes of PDGF-AA addition. This finding prompted us to elucidate the role of PDGFRα in self-renewal, invasion and differentiation in p-CSC by using short hairpin RNA depletion of PDGFRα expression. Notably, in PDGFRα-depleted cells, protein analysis revealed attenuation of stemness-related and glial markers expression, alongside early activation of the neuronal marker MAP2a/b that correlated with the induction of tumor suppressor Rb1. The in vitro reduction of the invasive capacity of PDGFRα-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 PDGFRα/Stat3/Rb1 regulatory axis might represent a potential therapeutic target for GBM treatment.