Bistability, Stochasticity, and Oscillations in the Mitogen-Activated Protein Kinase Cascade

Department of Statistics and Operations Research, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7365, USA.
Biophysical Journal (Impact Factor: 3.97). 04/2006; 90(6):1961-78. DOI: 10.1529/biophysj.105.073874
Source: PubMed


Signaling pathways respond to stimuli in a variety of ways, depending on the magnitude of the input and the physiological status of the cell. For instance, yeast can respond to pheromone stimulation in either a binary or graded fashion. Here we present single cell transcription data indicating that a transient binary response in which all cells eventually become activated is typical. Stochastic modeling of the biochemical steps that regulate activation of the mitogen-activated protein kinase Fus3 reveals that this portion of the pathway can account for the graded-to-binary conversion. To test the validity of the model, genetic approaches are used to alter expression levels of Msg5 and Ste7, two of the proteins that negatively and positively regulate Fus3, respectively. Single cell measurements of the genetically altered cells are shown to be consistent with predictions of the model. Finally, computational modeling is used to investigate the effects of protein turnover on the response of the pathway. We demonstrate that the inclusion of protein turnover can lead to sustained oscillations of protein concentrations in the absence of feedback regulation. Thus, protein turnover can profoundly influence the output of a signaling pathway.

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Available from: Henrik G Dohlman
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    • "criptional in - duction using Hill kinetics . The Hill coeffi cient was taken to be 2 and the K m and V max values were free parameters determined by fi tting the models to experimental data . We did not include a term for degradation of Fus3 , because its half - life was measured to greater than 2 h and increased upon stimulation with pheromone ( Wang et al . , 2006 ) . The equation for the phosphorylated ( active ) Fus3 concentration , [ p - Fus3 ] , is given by stored at – 80°C . Alternatively , in Figure 5B , cells were collected in prechilled 50 - ml tubes containing trichloroacetic acid ( TCA ; 5% fi nal concentration ) . For preparation of extracts , cell pellets were thawed on ice and resusp"
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    • "We do not consider the effect of protein degradation either. Our model is however a first theoretical fully stochastic study of the MAPK cascade, modelled earlier, to our knowledge, only via rate equations [9] [16] [18] [23] [24] or stochastic simulations [25] [26]. "
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    • "In particular, the yeast Saccharomyces cerevisiae has served as an important eukaryotic model for cellular functions as fundamental as gene regulation and as complex as cell cycle orchestration (13–16). Models of gene regulation have been developed to elucidate sources of noise in gene expression and the effect of noise on fitness, to study the role of feedback in cellular networks, and have led to discoveries of novel network structure (6,17–29). "
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