Abstract 3124: Platelet-derived growth factor receptor α cooperates with loss of p16/INK4a and p19/ARF to enhance tumorigenesis through the PI3K- and SHP-2-mediated signaling in the brain

Glioblastomas are the most common and lethal cancer in the central nervous system. Comprehensive genetic studies showed that in high-grade gliomas, overexpression of platelet-derived growth factor receptor alpha (PDGFRα) ranks third among top amplified genes and frequently co-occurs with loss of tumor suppressor genes, p16/INK4a and p14/ARF (p19/ARF in mice), in these high-grade glioblastomas. However, the biological consequences of PDGFRα overexpression in INK4a/ARF-deficient glial cells and glioma cells remain elusive. Here we show that activation of PDGFRα signaling by overexpressing PDGFRα and/or PDGF-A transformed Ink4a/Arf-deficient mouse astrocytes in vitro and rendered these cells highly tumorigenic in the brain of mice. Consistently, in INK4a/ARF null but not wild-type human glioma cell lines that express endogenous PDGFRα, overexpression of PDGF-A significantly enhances glioma formation in the brain. Re-introduction of p16/INK4a into Ink4a/Arf-null astrocytes suppressed PDGFRα-induced cell transformation in vitro and glioma formation in the brain. Conversely, cellular depletion of endogenous p16/INK4a by RNA interference in human glioma cells markedly enhances colony formation in vitro when compared to the controls. Mechanistically, abrogation of intrinsic tyrosine kinase activity of PDGFRα or interruptions of signaling modules at PDGFRα (Y to F mutations at specific tyrosine residues) that lost binding capacity for PI3K or Shp-2, but not PLC gamma or c-Src, significantly diminished PDGFRα-induced glioma formation in the brain. In vitro, specific YF mutations or inhibitors of PI3K or Shp-2 attenuated Akt activation and PDGFRα-induced colony formation. Furthermore, inhibition of Shp-2 by its inhibitors and siRNAs disrupts the interaction of PI3K with PDGFRα that is critical for gliomagenesis of Ink4a/Arf null cells. In summary, our data suggests that activation of PDGFRα signaling, particularly through the PI3K and Shp-2 pathways, in INK4a/ARF deficient astrocytes and glioma cells induce gliomagenesis in the brain. Our findings provide critical insights into interactions of genetic lesions frequently found in clinical glioma specimens and will be useful for identification of new therapeutic targets for treatments of patients with malignant gliomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): A