title: GTPase-deficient G alpha i2 oncogene gip2 inhibits adenylylcyclase and attenuates receptor-stimulated phospholipase A2 activity.
abstract: The GTPase activity of a G protein alpha subunit functions as a timer to control the lifetime of the activated conformation of the protein. Expression of the GTPase-deficient Gi2 alpha subunit oncogene, gip2 (alpha i2Q205L), in Chinese hamster ovary cells inhibited the stimulation of adenylylcyclase and altered the calcium regulation of the Gi2-phospholipase A2 (PLA2) effector complex. The phenotypic consequence of the activated alpha i2 mutant on hormonal stimulation of PLA2 varied depending on the cytoplasmic calcium transient elicited by different Gi2-linked receptors. The stimulation of PLA2 by thrombin, which mobilized calcium only from internal stores, was markedly attenuated in gip2-expressing cells. In contrast, the attenuation of the PLA2 response to ATP, a purinergic agonist which mobilizes calcium from both extracellular space and internal stores, was significantly less than that observed for thrombin. Ionomycin, a calcium ionophore, stimulated PLA2 activity in clones which expressed gip2 to a level similar to that observed in wild-type Chinese hamster ovary cells. Thus, the dominant GTPase-deficient gip2 polypeptide will constitutively inhibit adenylylcyclase but differentially modulate enzymes regulated by calcium and coupled to Gi2.
authors.affiliation: Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
authors.forename: J M
authors.initials: JM
authors.lastname: Lowndes
authors.forename: S K
authors.initials: SK
authors.lastname: Gupta
authors.forename: S
authors.initials: S
authors.lastname: Osawa
authors.forename: G L
authors.initials: GL
authors.lastname: Johnson
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000235:genetics*; D015759:Ionomycin / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D009857:Oncogenes; D010641:Phenotype; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D013917:Thrombin / Q000494:pharmacology; D014162:Transfection
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D001095:Arachidonic Acids; D016718:Arachidonic Acid; D015759:Ionomycin; D000255:Adenosine Triphosphate; D010741:Phospholipases A; D054467:Phospholipases A2; D013917:Thrombin; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium