title: RasGRP1 overexpression in T-ALL increases basal nucleotide exchange on Ras rendering the Ras/PI3K/Akt pathway responsive to protumorigenic cytokines.
abstract: Ras GTPases are activated by RasGEFs and inactivated by RasGAPs, which stimulate the hydrolysis of RasGTP to inactive RasGDP. GTPase-impairing somatic mutations in RAS genes, such as KRAS(G12D), are among the most common oncogenic events in metastatic cancer. A different type of cancer Ras signal, driven by overexpression of the RasGEF RasGRP1 (Ras guanine nucleotide-releasing protein 1), was recently implicated in pediatric T-cell acute lymphoblastic leukemia (T-ALL) patients and murine models, in which RasGRP1 T-ALLs expand in response to treatment with interleukins (ILs) 2, 7 and 9. Here, we demonstrate that IL-2/7/9 stimulation activates Erk and Akt pathways downstream of Ras in RasGRP1 T-ALL but not in normal thymocytes. In normal lymphocytes, RasGRP1 is recruited to the membrane by diacylglycerol (DAG) in a phospholipase C-γ (PLCγ)-dependent manner. Surprisingly, we find that leukemic RasGRP1-triggered Ras-Akt signals do not depend on acute activation of PLCγ to generate DAG but rely on baseline DAG levels instead. In agreement, using three distinct assays that measure different aspects of the RasGTP/GDP cycle, we established that overexpression of RasGRP1 in T-ALLs results in a constitutively high GTP-loading rate of Ras, which is constantly counterbalanced by hydrolysis of RasGTP. KRAS(G12D) T-ALLs do not show constitutive GTP loading of Ras. Thus, we reveal an entirely novel type of leukemogenic Ras signals that is based on a RasGRP1-driven increased in flux through the RasGTP/GDP cycle, which is mechanistically very different from KRAS(G12D) signals. Our studies highlight the dynamic balance between RasGEF and RasGAP in these T-ALLs and put forth a new model in which IL-2/7/9 decrease RasGAP activity.
authors.affiliation: Department of Anatomy, Roose University of California, San Francisco, San Francisco, CA, USA.
authors.forename: O
authors.initials: O
authors.lastname: Ksionda
authors.affiliation: Department of Anatomy, Roose University of California, San Francisco, San Francisco, CA, USA.|Department of Pediatrics, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: A A
authors.initials: AA
authors.lastname: Melton
authors.affiliation: Institute for Molecular Cell Biology, Center for Molecular Biomedicine, University Hospital, Friedrich-Schiller-University, Jena, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Bache
authors.affiliation: Department of Anatomy, Roose University of California, San Francisco, San Francisco, CA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Tenhagen
authors.affiliation: Department of Anatomy, Roose University of California, San Francisco, San Francisco, CA, USA.
authors.forename: J
authors.initials: J
authors.lastname: Bakker
authors.affiliation: Department of Pediatrics, University of New Mexico School of Medicine Albuquerque, NM, USA.
authors.forename: R
authors.initials: R
authors.lastname: Harvey
authors.affiliation: Department of Pediatrics, University of New Mexico School of Medicine Albuquerque, NM, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Winter
authors.affiliation: Institute for Molecular Cell Biology, Center for Molecular Biomedicine, University Hospital, Friedrich-Schiller-University, Jena, Germany.|Integrated Research and Treatment Center, Center for Sepsis Control and Care (CSCC), Jena University Hospital, Jena, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Rubio
authors.affiliation: Department of Anatomy, Roose University of California, San Francisco, San Francisco, CA, USA.
authors.forename: J P
authors.initials: JP
authors.lastname: Roose
mesh_terms: D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002648:Child; D016207:Cytokines / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D015851:Interleukin-7 / Q000494:pharmacology; D016906:Interleukin-9 / Q000494:pharmacology; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051966:Phospholipase C gamma / Q000378:metabolism; D054218:Precursor T-Cell Lymphoblastic Leukemia-Lymphoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018121:Receptors, Cytokine / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C011439:1,2-diacylglycerol; D016207:Cytokines; D004268:DNA-Binding Proteins; D004075:Diglycerides; D020662:Guanine Nucleotide Exchange Factors; D007376:Interleukin-2; D015851:Interleukin-7; D016906:Interleukin-9; C491790:RASGRP1 protein, human; D018121:Receptors, Cytokine; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051966:Phospholipase C gamma; D018631:ras Proteins