title: RalA is overactivated in medulloblastoma.
abstract: Medulloblastoma (MDB) represents a major form of malignant brain tumors in the pediatric population. A vast spectrum of research on MDB has advanced our understanding of the underlying mechanism, however, a significant need still exists to develop novel therapeutics on the basis of gaining new knowledge about the characteristics of cell signaling networks involved. The Ras signaling pathway, one of the most important proto-oncogenic pathways involved in human cancers, has been shown to be involved in the development of neurological malignancies. We have studied an important effector down-stream of Ras, namely RalA (Ras-Like), for the first time and revealed overactivation of RalA in MDB. Affinity precipitation analysis of active RalA (RalA-GTP) in eight MDB cell lines (DAOY, RES256, RES262, UW228-1, UW426, UW473, D283 and D425) revealed that the majority contained elevated levels of active RalA (RalA-GTP) as compared with fetal cerebellar tissue as a normal control. Additionally, total RalA levels were shown to be elevated in 20 MDB patient samples as compared to normal brain tissue. The overall expression of RalA, however, was comparable in cancerous and normal samples. Other important effectors of RalA pathway including RalA binding protein-1 (RalBP1) and protein phosphatase A (PP2A) down-stream of Ral and Aurora kinase A (AKA) as an upstream RalA activator were also investigated in MDB. Considering the lack of specific inhibitors for RalA, we used gene specific silencing in order to inhibit RalA expression. Using a lentivirus expressing anti-RalA shRNA we successfully inhibited RalA expression in MDB and observed a significant reduction in proliferation and invasiveness. Similar results were observed using inhibitors of AKA and geranyl-geranyl transferase (non-specific inhibitors of RalA signaling) in terms of loss of in vivo tumorigenicity in heterotopic nude mouse model. Finally, once tested in cells expressing CD133 (a marker for MDB cancer stem cells), higher levels of RalA activation was observed. These data not only bring RalA to light as an important contributor to the malignant phenotype of MDB but introduces this pathway as a novel target in the treatment of this malignancy.
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.|Division of Hematology and Oncology, Children's Mercy Hospital and Clinics, Kansas City, MO, USA.
authors: Kevin F
authors: KF
authors: Ginn
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Ben
authors: B
authors: Fangman
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Kaoru
authors: K
authors: Terai
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Amanda
authors: A
authors: Wise
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Daniel
authors: D
authors: Ziazadeh
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Kushal
authors: K
authors: Shah
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Robyn
authors: R
authors: Gartrell
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Brandon
authors: B
authors: Ricke
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Kyle
authors: K
authors: Kimura
authors: Research Service (151), Kansas City Veteran Affairs Medical Center & Midwest Biomedical Research Foundation-Saint Luke's Marion Bloch Brain Tumor Research Program, 4801 E Linwood Blvd, F5-123, Kansas City, MO, 64128, USA.
authors: Sharad
authors: S
authors: Mathur
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA.
authors: Emma
authors: E
authors: Borrego-Diaz
authors: Molecular Medicine Laboratory, Department of Medicine, University of Kansas Medical School, Kansas City, KS, USA. faris.farassati@va.gov.|Research Service (151), Kansas City Veteran Affairs Medical Center & Midwest Biomedical Research Foundation-Saint Luke's Marion Bloch Brain Tumor Research Program, 4801 E Linwood Blvd, F5-123, Kansas City, MO, 64128, USA. faris.farassati@va.gov.
authors: Faris
authors: F
authors: Farassati
mesh_terms: D000818:Animals; D064096:Aurora Kinase A / Q000235:genetics / Q000378:metabolism; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002531:Cerebellum / Q000378:metabolism* / Q000473:pathology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005333:Fetus; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D008297:Male; D008527:Medulloblastoma / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014161:Transduction, Genetic; D020725:ral GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D034741:RNA, Small Interfering; D064096:Aurora Kinase A; D010749:Phosphoprotein Phosphatases; C492198:RALA protein, human; D020725:ral GTP-Binding Proteins
keywords: Aurora kinase; CD133; Cancer stem cells; Cell signaling; GGTI; Medulloblastoma; RalA; RalBP1; Ras; Therapy