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J. Biol. Chem. 277 (52): 50223-50225

© 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

Pertussis Toxin-insensitive Activation of the Heterotrimeric G-proteins Gi/Go by the NG108-15 G-protein Activator*

Catalina RibasDagger §, Aya Takesono, Motohiko Sato||, John D. Hildebrandt**, and Stephen M. Lanier||Dagger Dagger

From the Dagger  Centro de Biología Molecular, "Severo Ochoa" (CSIC-UAM), Universidad Autonoma de Madrid, Cantoblanco, 28049-Madrid, Spain, the ** Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina 29425, the || Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, and the  National Human Genome Research Institute, Bethesda, Maryland 20892

A ligand-independent activator of heterotrimeric brain G-protein was partially purified from detergent-solubilized extracts of the neuroblastoma-glioma cell hybrid NG108-15. The G-protein activator (NG108-15 G-protein activator (NG-GPA)) increased [35S]guanosine 5'-O-(thiotriphosphate) ([35S]GTPgamma S) to purified brain G-protein in a magnesium-dependent manner and promoted GDP dissociation from Galpha o. The NG-GPA also increased GTPgamma S binding to purified, recombinant Galpha i2, Galpha i3, and Galpha o, but minimally altered nucleotide binding to purified transducin. The NG-GPA increased GTPgamma S binding to membrane-bound G-proteins and inhibited basal, forskolin- and hormone-stimulated adenylyl cyclase activity in DDT1-MF-2 cell membranes. In contrast to G-protein coupled receptor-mediated activation of heterotrimeric G-proteins in DDT1-MF-2 cell membrane preparations, the action of the NG-GPA was not altered by treatment of the cells with pertussis toxin. ADP-ribosylation of purified brain G-protein also failed to alter the increase in GTPgamma S binding elicited by the NG-GPA. Thus, the NG-GPA acts in a manner distinct from that of a G-protein coupled receptor and other recently described receptor-independent activators of G-protein signaling. These data indicate the presence of unexpected regulatory domains on Gi/Go proteins and suggest the existence of pertussis toxin-insensitive modes of signal input to Gi/Go signaling systems.

* This work was supported by the National Institutes of Health Grants RO1-NS24821 and MH59931 (to S. M. L.) and DK37219 (to J. D. H.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

§ Recipient of a Medical University of South Carolina Health Sciences Foundation Research Fellowship, a Ministerio de Educación y Ciencia Postdoctoral Fellowship (Spain), and the Programa Ramón y Cajal (Ministerio de Ciencia y Tecnología).

Dagger Dagger To whom correspondence should be addressed: Dept. of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, 1901 Perdido St., New Orleans, LA 70112. Tel.: 504-568-4740; Fax: 504-568-2361; E-mail:

Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.

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