Genome Informatics 13: 359–360 (2002)
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A Mathematical Modeling of Signal Transduction Cascade on Raf-Akt Cross-Talk Mariko Hatakeyama1
Shuhei Kimura1
Noriko Yumoto1
[email protected]
[email protected]
[email protected]
Mio Ichikawa1
Takuji Kawasaki2
Takashi Naka3
[email protected]
[email protected]
[email protected]
Akihiko
Konagaya1
[email protected] 1
2
3
Bioinformatics Group, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan Fuji Research Institute Corporation, 2-3 Kanda Nishikicho, Chiyoda-ku, Tokyo 1018443, Japan Department of Computer Science, Kyushu Sangyo University, 2-3-1 Matsukadai, Higashi-ku, Fukuoka 813-8503, Japan
Keywords: signal transduction, computer simulation, MAPK, Akt, cross-talk
1
Introduction
MAPK signaling cascade initiated by the activation of EGF receptor (EGFR) has been experimentally well studied and analyzed by mathematical modeling extensively [1, 3, 5]. Recently, several studies showed that some of growth hormone-stimulated membrane tyrosine kinase receptors interact with Shc adaptor protein and phosphatidylinositol 3’-kinase (PI3K), and consequently PI3K-activated Akt inhibits Raf-1 and the following ERK activity which locates at the downstream of Shc signaling [2, 4]. This inhibition of Raf-1 activity by Akt is called Raf-Akt cross-talk. Since these two Shc-Raf and PI3KAkt pathways exert opposite effects on cell proliferation and differentiation, a regulation balance of these two pathways is critical to define the cell fate. Based on the experimental proof reported to date, we developed a computational simulation model for a signal transduction cascade possessing Raf-Akt cross-talk to understand the regulation mechanism by analyzing the dynamics of kinase activities.
2
Methods
The model was described in Figure 1. Ligand-induced membrane tyrosine kinase receptor activates two distinct signaling cassettes, Shc-Ras-Raf-MEK-ERK pathway and PI3K-Akt pathway. For Shc signaling, we referred the EGFR simulation model [3] and gave minor modifications. An interaction scheme of PI3K-Akt and Raf-1 was constructed in our laboratory based on the several experimental results. Dephosphorylation of Raf-1, MEK and Akt are catalyzed by PP2A phosphatase. We described kinetics of protein-protein interactions in Mass action and enzymatic kinetics in MichaelisMenten equations. Known kinetic parameters were referred to the literatures and unavailable kinetics parameters were estimated by the parameter estimator by means of Genetic Algorithms. YAGNS was used for computer simulation.
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Hatakeyama et al. R Ligand
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Figure 1: Kinetic scheme of growth factor signaling possessing Raf-Akt cross-talk.
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Figure 2: Simulation results of receptor phosphorylation (A), MEK activation (B), ERK activation (C) and Akt activation (D). and bold solid line show 10 nM ligand, and thin line: 1 nM , , ligand, 4 and broken line: 0.1 nM ligand concentrations. 4 show experimental results from Western blot.
Results and Discussion
Simulation results showed ligand (10 nM)-induced transient receptor phosphorylation within 1 min, ERK activation at 5-10 min, and the rapid but sustained Akt activity for 30 min (Figure 2). When the different concentration of ligand (0.1-10 nM) was tested, these activation levels varied in dosedependent manner. These results are consistent with the experimental results. To simulate the effect of PI3K inhibitor on the kinetics of ERK and Akt activity, we set lower Vmax value for the enzymatic activity of PI3K. It caused higher activation in ERK and inhibition in Akt activities. This simulation result presents that our model well reflected the inhibition mechanism of ERK activity by PI3KAkt pathway. By simulating the effect of kinase inhibitors, we could show a possibility that action mechanisms of enzyme inhibitors can be evaluated by computer simulation.
References [1] Brightman, F.A. and Fell, D.A., Differential feedback regulation of the MAPK cascade underlies the quantitative differences in EGF and NGF signalling in PC12 cells, FEBS lett., 482:169–174, 2000. [2] Dhillon, A.S., Meikle, S., Yazici, Z., Eulitz, M., and Kolch, W., Regulation of Raf-1 activation and signaling by dephosphorylation, EMBO J., 21:64–71, 2002. [3] Kholodenko, B.N., Demin, O.V., Moehren, G., and Hoek, J.B., Quantification of short term signaling by the epidermal growth factor receptor, J. Biol. Chem., 274:30169–30181, 1999. [4] Moelling, K., Schad, K., Bosse, M., Zimmermann, S., and Schweneker, M., Regulation of Raf-Akt cross-talk, J. Biol. Chem., 277:31099–31106, 2002. [5] Schoeberl, B., Eichler-Jonsson, C., Gilles, E.D., and M¨ uler, G., Computational modeling of the dynamics of the MAP kinase cascade activated by surface and internalized EGF receptors, Nature Biotech., 20:370–375, 2002.
