title: Depletion of guanine nucleotides with mycophenolic acid suppresses IgE receptor-mediated degranulation in rat basophilic leukemia cells.
abstract: In RBL-2H3 rat basophilic leukemia cells, Ag that crosslink IgE-receptor complexes stimulate the turnover of inositol phospholipids, the mobilization of Ca2+ from intra- and extracellular sources, the release of serotonin and other substances from granules and the transformation of the cell surface from a microvillous to a lamellar architecture. This study explores the role of GTP-binding proteins (G proteins) in the control of these biochemical and functional responses. We report that incubating RBL-2H3 cells for 4 h with 10 microM mycophenolic acid (MPA), an inhibitor of de novo GTP synthesis, reduces GTP levels by over 60% and causes an average reduction of 50% in Ag-stimulated serotonin release. This inhibition of secretion is associated with a 50% decrease in the rate of 45Ca2+ influx in MPA-treated cells. In contrast, Ag-stimulated inositol trisphosphate production is only slightly reduced, indicating that the phosphatidylinositol-specific phospholipase C can be activated by Ag in GTP-depleted cells. The membrane responses to IgE receptor cross-linking are unaffected by incubating cells with MPA. Exogenous guanine or guanosine protects the GTP pools in MPA-treated cells and permits normal ion transport and secretory responses to Ag; adenine does not. These results implicate a guanine nucleotide-binding protein in the control of IgE receptor-dependent signal transduction in RBL-2H3 cells. This protein may particularly control the Ca2+ influx pathway that is essential for secretion.
authors.affiliation: Department of Pathology, University of New Mexico, Albuquerque 87131.
authors.forename: B S
authors.initials: BS
authors.lastname: Wilson
authors.forename: G G
authors.initials: GG
authors.lastname: Deanin
authors.forename: J C
authors.initials: JC
authors.lastname: Standefer
authors.forename: D
authors.initials: D
authors.lastname: Vanderjagt
authors.forename: J M
authors.initials: JM
authors.lastname: Oliver
mesh_terms: D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology*; D001491:Basophils / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D006150:Guanine Nucleotides / Q000378:metabolism*; D006868:Hydrolysis; D007073:Immunoglobulin E / Q000378:metabolism*; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000378:metabolism; D007938:Leukemia; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism; D009173:Mycophenolic Acid / Q000494:pharmacology*; D051381:Rats; D011961:Receptors, Fc / Q000502:physiology*; D017455:Receptors, IgE
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D006150:Guanine Nucleotides; D007166:Immunosuppressive Agents; D007295:Inositol Phosphates; D011961:Receptors, Fc; D017455:Receptors, IgE; D007073:Immunoglobulin E; D009173:Mycophenolic Acid; D002118:Calcium