Biochem. J. (2006) 393
(235–243) (Printed in Great Britain)
Quantitative model of Ras–phosphoinositide 3-kinase signalling cross-talk based on co-operative molecular assembly
Harjeet KAUR1, Chang Shin PARK1, Jodee M. LEWIS and Jason M. HAUGH2
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695-7905, U.S.A.
In growth-factor-stimulated signal transduction, cell-surface receptors recruit PI3Ks (phosphoinositide 3-kinases) and Ras-specific GEFs (guanine nucleotide-exchange factors) to the plasma membrane, where they produce 3´-phosphorylated phosphoinositide lipids and Ras-GTP respectively. As a direct example of pathway networking, Ras-GTP also recruits and activates PI3Ks. To refine the mechanism of Ras–PI3K cross-talk and analyse its quantitative implications, we offer a theoretical model describing the assembly of complexes involving receptors, PI3K and Ras-GTP. While the model poses the possibility that a ternary receptor–PI3K–Ras complex forms in two steps, it also encompasses the possibility that receptor–PI3K and Ras–PI3K interactions are competitive. In support of this analysis, experiments with platelet-derived growth factor-stimulated fibroblasts revealed that Ras apparently enhances the affinity of PI3K for receptors; in the context of the model, this suggests that a ternary complex does indeed form, with the second step greatly enhanced through membrane localization and possibly allosteric effects. The apparent contribution of Ras to PI3K activation depends strongly on the quantities and binding affinities of the interacting molecules, which vary across different cell types and stimuli, and thus the model could be used to predict conditions under which PI3K signalling is sensitive to interventions targeting Ras.
Key words: mathematical modelling, phosphoinositide 3-kinase (PI3K), platelet-derived growth factor (PDGF), Ras, receptor tyrosine kinase, signal transduction.
Abbreviations used: ERK, extracellular-signal-regulated kinase; GEF, guanine nucleotide-exchange factor; GFP, green fluorescent protein; MKP, mitogen-activated protein kinase phosphatase; NDPK, nucleoside 5´-diphosphate kinase; N-WASP, neural Wiskott–Aldrich syndrome protein; PDGF, platelet-derived growth factor; PI3K, phosphoinositide 3-kinase; TIRF, total internal reflection fluorescence.
1These authors contributed equally to this work.
2To whom correspondence should be addressed (email jason_haugh@ncsu.edu).
Received 25 June 2005/12 August 2005; accepted 14 September 2005
Published as BJ Immediate Publication 14 September 2005, doi:10.1042/BJ20051022
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