In-Silico Modeling of the Mitotic Spindle Assembly Checkpoint

Abstract

BackgroundThe Mitotic Spindle Assembly Checkpoint (MSAC) is an evolutionary conserved mechanism that ensures the correct segregation of chromosomes by restraining cell cycle progression from entering anaphase until all chromosomes have made proper bipolar attachments to the mitotic spindle. Its malfunction can lead to cancer.Principle FindingsWe have constructed and validated for the human MSAC mechanism an in silico dynamical model, integrating 11 proteins and complexes. The model incorporates the perspectives of three central control pathways, namely Mad1/Mad2 induced Cdc20 sequestering based on the Template Model, MCC formation, and APC inhibition. Originating from the biochemical reactions for the underlying molecular processes, non-linear ordinary differential equations for the concentrations of 11 proteins and complexes of the MSAC are derived. Most of the kinetic constants are taken from literature, the remaining four unknown parameters are derived by an evolutionary optimization procedure for an objective function describing the dynamics of the APC:Cdc20 complex. MCC:APC dissociation is described by two alternatives, namely the “Dissociation” and the “Convey” model variants. The attachment of the kinetochore to microtubuli is simulated by a switching parameter silencing those reactions which are stopped by the attachment. For both, the Dissociation and the Convey variants, we compare two different scenarios concerning the microtubule attachment dependent control of the dissociation reaction. Our model is validated by simulation of ten perturbation experiments.ConclusionOnly in the controlled case, our models show MSAC behaviour at meta- to anaphase transition in agreement with experimental observations. Our simulations revealed that for MSAC activation, Cdc20 is not fully sequestered; instead APC is inhibited by MCC binding.

Systems Biology Modeling of Five Pathways for Regulation and Potent Inhibition of the Anaphase-Promoting Complex (APC/C): Pivotal Roles for MCC and BubR1

“…How far partial inhibition of the APC by the SAC is tolerable by mitotic control is currently unclear. As many of the basic reactions described here and previously (Ibrahim et al, 2008a) and for the experimentally determined values, do not lead to complete Cdc20 sequestration, the studies described here have suggested that the MCC directly binds and completely blocks the APC/C. APC activation can then be a consequence of a MCC:APC complex modification or rearrangement (Ibrahim et al, 2008a shows the simulation where all pathways were included in one model.…”

“…In this model, if the kinetochore is unattached, u was set to u = 1, otherwise u = 0. Note that it is assumed that mass-action kinetics are used for all reactions (Ibrahim et al, 2008a;2008b). If other kinetics should be used, they have to be transformed to mass action kinetics.…”

“…From mathematical point of view, considering the complex as a species would not make any difference in this case as long as there is one form in our model. All previous mathematical models have considered the similar assumption to the template model (e.g., Ibrahim et al, 2008a;Lohel et al, 2009;Simonetta et al, 2009).…”

“…The SAC model was previously analyzed where MCC is the exclusive inhibitor of APC (Ibrahim et al, 2008a).This model is used in this study as a core part [Reactions (1)- (9)] to build on and compare with other model variants. First, this basic model was re-simulated with various MCC-APC binding rates (10 3 to 10 9 M -1 s -1 ).…”

“…They found that a diffusible signal can generally account for checkpoint operation. A more comprehensive model of the human SAC, including the Mad2 and BubR1 pathway, has been proposed by Ibrahim et al (2008a;2008b, 2009Ibrahim and Henze, 2014). A mathematical model for checkpoint activation based on the ''Mad2 template'' model by De Antoni et al (2005) is supported with in vitro experiments by Simonetta et al (2009).…”