We have previously shown that addition of Ins(1,3,4,5)P4 to permeabilized L1210 cells increases the amount of Ca2+ mobilized by a submaximal concentration of Ins(2,4,5)P3, and we suggested that, in doing this, Ins(1,3,4,5)P4 is not working via an InsP3 receptor but indirectly via an InsP4 receptor [Loomis-Husselbee, Cullen, Dreikhausen, Irvine and Dawson (1996) Biochem. J. 314, 811–816]. Here we have investigated whether this effect might be mediated by GAP1IP4BP, recently identified as a putative receptor for Ins(1,3,4,5)P4. GAP1IP4BP is a protein that interacts with one or more monomeric G-proteins, so we sought evidence for involvement of monomeric G-proteins in the effects of Ins(1,3,4,5)P4 in permeabilized L1210 cells. Guanosine 5´-[γ-thio]triphosphate (GTP[S]) enhanced the effect of Ins(1,3,4,5)P4 on Ins(2,4,5)P3-stimulated Ca2+ mobilization, but had no effect on the action of Ins(2,4,5)P3 alone. A specific enhancement of only the action of Ins(1,3,4,5)P4 was also seen with GTP[S]-loaded R-Ras or Rap1a (two G-proteins known to interact with GAP1IP4BP), whereas H-Ras was inactive at similar concentrations. Guanosine 5´-[β-thio]diphosphate (GDP[S]) did not alter the action of either Ins(2,4,5)P3 or Ins(1,3,4,5)P4. Finally, the addition of exogenous GAP1IP4BP, purified from platelets, markedly enhanced the effect of Ins(1,3,4,5)P4, and again, the amount of Ca2+ mobilized by Ins(2,4,5)P3 alone was unaltered. We conclude that the increase in Ins(2,4,5)P3-stimulated Ca2+ mobilization by Ins(1,3,4,5)P4 may be mediated by GAP1IP4BP or a closely related protein (such as GAP1m), and if so, the action of the GAP1 is not solely to regulate GTP loading of a G-protein, but rather it acts with a G-protein to cause its effect.
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May 1998
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Research Article|
May 01 1998
Modulation of Ins(2,4,5)P3-stimulated Ca2+ mobilization by Ins(1,3,4,5)P4: enhancement by activated G-proteins, and evidence for the involvement of a GAP1 protein, a putative Ins(1,3,4,5)P4 receptor
Jefferson W. LOOMIS-HUSSELBEE;
Jefferson W. LOOMIS-HUSSELBEE
1
*School of Biology, University of East Anglia, Norwich NR4 7TJ, U.K.
†Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, U.K.
1To whom correspondence should be addressed (e-mail jwl21@cam.ac.uk).
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Christopher D. WALKER;
Christopher D. WALKER
*School of Biology, University of East Anglia, Norwich NR4 7TJ, U.K.
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Joanna R. BOTTOMLEY;
Joanna R. BOTTOMLEY
*School of Biology, University of East Anglia, Norwich NR4 7TJ, U.K.
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Peter J. CULLEN;
Peter J. CULLEN
‡Department of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TJ, U.K.
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Robin F. IRVINE;
Robin F. IRVINE
†Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, U.K.
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Alan P. DAWSON
Alan P. DAWSON
*School of Biology, University of East Anglia, Norwich NR4 7TJ, U.K.
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Publisher: Portland Press Ltd
Received:
December 15 1997
Revision Received:
February 27 1998
Accepted:
March 09 1998
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 1998
1998
Biochem J (1998) 331 (3): 947–952.
Article history
Received:
December 15 1997
Revision Received:
February 27 1998
Accepted:
March 09 1998
Citation
Jefferson W. LOOMIS-HUSSELBEE, Christopher D. WALKER, Joanna R. BOTTOMLEY, Peter J. CULLEN, Robin F. IRVINE, Alan P. DAWSON; Modulation of Ins(2,4,5)P3-stimulated Ca2+ mobilization by Ins(1,3,4,5)P4: enhancement by activated G-proteins, and evidence for the involvement of a GAP1 protein, a putative Ins(1,3,4,5)P4 receptor. Biochem J 1 May 1998; 331 (3): 947–952. doi: https://doi.org/10.1042/bj3310947
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