Linking a mitotic oscillator to the extracellular environment: the importance of protein network structure and multisite phosphorylation
Vargo, Ryan Christopher
Doctor of Philosophy
This thesis work contributes the first vital steps in the development of a biologically based proliferation model to advance a bioartificial tissue regeneration model. Specifically, this work presents a mitotic oscillator model incorporating ATP, which was linked to extracellular glucose. This model is the first mitotic oscillator linked to the extracellular environment. Furthermore, this work is the first to connect extracellular glucose to mitosis with ATP. Taking a bottom-up approach, a base mitotic model was developed using the latest biology. The reaction network structure of mitosis is not fully understood, and the role of multisite phosphorylation is uncertain. Therefore, using bifurcation analysis and transient simulations, the effect of the mitotic reaction network structure and multisite phosphorylation on system behavior was analyzed by varying the MPF activation network structure, the number of positive feedback loops, and the number of phosphorylations on the positive feedback loop proteins. The results suggest that the MPF activation network has evolved to efficiently utilize cyclin B and to generate switch-like transitions into mitosis. The behavior of the mitotic oscillator model was affected by the order and number of multisite phosphorylations, which are essential to generate sharp switch-like transitions into mitosis. Addition of multiple positive feedback loops into the model enhanced the signal to initiate mitosis. Next, ATP was incorporated into the network. The model was then tuned to a relative ATP concentration, which is generic and therefore applicable to different cell lines. Multiple Wee1 networks were analyzed to elucidate the function of the two inhibition mechanisms, kinase inhibition and increased degradation. The results suggest that the inhibition mechanisms are redundant. Therefore, the model incorporates the Wee1 mechanism that allows the cell to maintain maximum control over the initiation of mitosis. To generalize the mitotic model, the parameter set was tuned for to a relative ATP concentration and fibroblast division times. Finally, the relative intracellular ATP model was linked to the extracellular glucose. The model developed in this thesis work is the first to use ATP as the link between mitosis and the extracellular glucose, and the first mitotic model connected to the extracellular environment.