Serum concentration of the surrounding medium in percent, growth signal
Myc synthesis driven by growth signals (S)
This is the model described in the article: A bistable Rb-E2F switch underlies the restriction point Guang Yao, Tae Jun Lee, Seiichi Mori, Joseph R. Nevins, Lingchong You, Nat Cell Biol 2008 10:476-482; PMID: 18364697 ; DOI: 10.1038/ncb1711 . Abstract: The restriction point (R-point) marks the critical event when a mammalian cell commits to proliferation and becomes independent of growth stimulation. It is fundamental for normal differentiation and tissue homeostasis, and seems to be dysregulated in virtually all cancers. Although the R-point has been linked to various activities involved in the regulation of G1-S transition of the mammalian cell cycle, the underlying mechanism remains unclear. Using single-cell measurements, we show here that the Rb-E2F pathway functions as a bistable switch to convert graded serum inputs into all-or-none E2F responses. Once turned ON by sufficient serum stimulation, E2F can memorize and maintain this ON state independently of continuous serum stimulation. We further show that, at critical concentrations and duration of serum stimulation, bistable E2F activation correlates directly with the ability of a cell to traverse the R-point. This model reproduces the serum-pulse stimulation-protocol in Figure 3(b). To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information. In summary, you are entitled to use this encoded model in absolutely any manner you deem suitable, verbatim, or with modification, alone or embedded it in a larger context, redistribute it, commercially or not, in a restricted way or not. To cite BioModels Database, please use: Li C, Donizelli M, Rodriguez N, Dharuri H, Endler L, Chelliah V, Li L, He E, Henry A, Stefan MI, Snoep JL, Hucka M, Le Novere N, Laibe C (2010) BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. BMC Syst Biol., 4:92.
E2F synthesis by a synergy between Myc and E2F autocatalysis. Since neither Myc nor E2F forms a homodimer, we assumed no cooperativity in gene activation mediated by these factors, and used the Hill coefficient of 1.0. Using Hill coefficient greater than 1.0 will not change the qualitative behavior of system dynamics
E2F dissociation from Rb-E2F complex by CycD- and CycE-mediated phosphorylation
E2F titration by Rb via E2F-Rb complex formation