The small GTPase Rac1 is involved in regulating membrane ruffling, gene transcription, cell-cycle progression and cell transformation, and some of these events are blocked by inhibitors of phosphoinositide 3-kinase (PI 3-kinase). Moreover, Rac1 can be activated by several guanine nucleotide exchange factors, which facilitate the release of GDP. We therefore investigated the ability of PI 3-kinase lipid products to regulate Tiam1, a Rac1-specific exchange factor. Tiam1 bound to polyphosphorylated inositol lipids in the rank order PtdIns(3,4,5)P3 > PtdIns(3,4)P2 ≫ PtdIns(4,5)P2, and this binding could be attributed to the N-terminal pleckstrin-homology (N-PH) domain. Both PtdIns(3,4,5)P3 and PtdIns(3,4)P2 enhanced Tiam1 guanine nucleotide exchange activity in vitro, but PtdIns(4,5)P2 had no effect. Co-expression of a constitutively active PI 3-kinase with Tiam1 increased the amount of GTP-bound Rac1 in vivo, a response which required the N-PH domain of Tiam1. Ectopic expression of Tiam1 caused membrane ruffling in Swiss 3T3 cells that was characterized by wortmannin-sensitive and -insensitive components, which required the N-PH domain and the C-terminal PH domain of Tiam1 respectively. These results reveal novel facets of Tiam1-dependent regulation of Rac1 function.
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Research Article|
September 26 2000
Regulation of the Rac1-specific exchange factor Tiam1 involves both phosphoinositide 3-kinase-dependent and -independent components
Ian N. FLEMING;
Ian N. FLEMING
1
1Department of Biochemistry, Medical Sciences Institute, University of Dundee, Dundee DD1 5EH, Scotland, U.K.
1To whom correspondence should be addressed (e-mail I.N.Fleming@Dundee.ac.uk).
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Alexander GRAY;
Alexander GRAY
1Department of Biochemistry, Medical Sciences Institute, University of Dundee, Dundee DD1 5EH, Scotland, U.K.
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C. Peter DOWNES
C. Peter DOWNES
1Department of Biochemistry, Medical Sciences Institute, University of Dundee, Dundee DD1 5EH, Scotland, U.K.
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Publisher: Portland Press Ltd
Received:
May 25 2000
Revision Received:
July 11 2000
Accepted:
July 24 2000
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 2000
2000
Biochem J (2000) 351 (1): 173–182.
Article history
Received:
May 25 2000
Revision Received:
July 11 2000
Accepted:
July 24 2000
Citation
Ian N. FLEMING, Alexander GRAY, C. Peter DOWNES; Regulation of the Rac1-specific exchange factor Tiam1 involves both phosphoinositide 3-kinase-dependent and -independent components. Biochem J 1 October 2000; 351 (1): 173–182. doi: https://doi.org/10.1042/bj3510173
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