Modeling Feedback Regulation of Cell Signaling

描述(申请人提供)：细胞对激素和神经递质的反应可以是二元的，也可以是分级的，它们通常是瞬时的。酵母中G蛋白介导的信息素反应是典型的。我们的中心假设是，为研究随机过程和动态系统而开发的数学技术可以解释细胞信号网络的复杂行为。这项建议的目的是了解反馈控制机制在酵母信息素反应途径中的作用。具体地说，我们将确定哪些反馈回路负责维持分级反应，哪些相互作用控制依赖于时间的动态反应，以及哪些相互作用对脱敏很重要。我们的方法是在整个途径的不同点激活酵母信息素信号，对转录反应进行定量分析，设计描述观察到的活性的计算模型，并通过实验测试每个模型的有效性。我们将考虑平均蛋白质浓度水平的确定性模型和考虑生化反应的随机性质的随机模型。这项建议有三个具体目标： 目的1：G蛋白激活后从分级反应转变为二元反应的基础是什么？我们将考虑三种能够产生二元响应的假设机制：随机切换、双稳态和临界减速。我们将通过分析单个细胞和细胞群体中G蛋白的激活来区分这些模型。 目的2：G蛋白下游的哪些途径组分调节A级到二元反应？我们将激活G蛋白下游的途径，并确定将分级反应转换为二元反应的其他下游机制。 目的3：信息素反应途径中各种反馈控制的生物学功能是什么？信息素诱导或抑制的蛋白质可能代表该途径的反馈调节因子。我们将鉴定这些蛋白质，并测试它们的表达改变对途径反应性的影响。 对酵母中信息素调节的综合计算和实验分析最终将导致改进包括人类在内的更复杂生物体中信号事件的预测模型。

DESCRIPTION (provided by applicant): Cellular responses to hormones and neurotransmitters can be either binary or graded, and they are usually transient. The G protein-mediated pheromone response in yeast is typical. Our central hypothesis is that mathematical techniques developed for studying stochastic processes and dynamical systems can explain the complex behaviors of cell signaling networks. The objective of this proposal is to understand the role of feedback control mechanisms used in the pheromone response pathway of yeast. Specifically, we will determine which feedback loops are responsible for maintaining the graded response, which interactions control the time-dependent dynamical response, and which interactions are important for desensitization. Our approach will be to activate the yeast pheromone signal at different points throughout the pathway, conduct a quantitative analysis of the transcription response, devise computational models that describe the observed activity, and test the validity of each model through experimentation. We will consider both deterministic models for the average protein concentration levels and stochastic models that take into account the random nature of biochemical reactions. There are three specific aims to this proposal: Aim 1: What is the basis for the conversion from a graded to binary response following G protein activation? We will consider three hypothetical mechanisms capable of producing a binary response: stochastic switching, bistability, and critical slowing down. We will distinguish between these models by analyzing G protein activation in individual cells and cell populations. Aim 2: Which pathway components downstream of the G protein moderate a graded to binary response? We will activate the pathway at points downstream of the G protein and identify additional downstream mechanisms for converting the graded response to a binary one. Aim 3: What is the biological function of the various feedback controls in the pheromone response pathway? Pheromone-induced or repressed proteins are likely to represent feedback regulators of the pathway. We will identify these proteins and test the consequence of altering their expression on pathway responsiveness. An integrated computational and experimental analysis of the pheromone regulation in yeast will eventually lead to improved predictive models of signaling events in more complex organisms including humans.