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A Diffusion-Reaction Model of Signal Transduction by MAPK Cascades

The mitogen-activated protein kinase (MAPK) cascade is a highly conserved signaling module comprised of three sequentially activated protein kinases, which are rapidly phosphorylated near the membrane and dephosphorylated in the cytosol. It regulates various important biological processes including differentiation, proliferation, and synaptic plasticity. In this paper, a diffusion-reaction model is proposed to study this signal transduction pathway. It has been demonstrated before by quantitative analysis that the spatial separation of activation and deactivation of MAPK kinases will lead to a spatially precipitous gradient of active MAPKs, which may be useful to enhance local concentrations of MAPK-dedicated proteins, and hence promote signaling efficiency. On the other hand, this finding also poses a problem: how can signals concentrated near the membrane be effectively transmitted to the nucleus where necessary transcriptional programs have to be initiated? Several additional mechanisms like endocytic trafficking and MAPK dimerization may be responsible. The model is also extended to examine the possible contribution of phosphorylation-dependent MAPK homodimerization to the nuclear transport of MAPKs.