Starbuck C, Lauffenburger D A
Department of Chemical Engineering, University of Pennsylvania, Philadelphia 19104.
Biotechnol Prog. 1992 Mar-Apr;8(2):132-43. doi: 10.1021/bp00014a007.
We apply a mathematical model for receptor-mediated cell uptake and processing of epidermal growth factor (EGF) to analyze and predict proliferation responses to fibroblastic cells transfected with various forms of the EGF receptor (EGFR) to EGF. The underlying conceptual hypothesis is that the mitogenic signal generated by EGF/EGFR binding on the cell surface, via stimulation of receptor tyrosine kinase activity, is attenuated when the receptors are downregulated and growth factor is depleted by endocytic internalization and subsequent intracellular degradation. Hence, the cell proliferation rate ought to depend on receptor/ligand binding and trafficking parameters as well as on intrinsic receptor signal transduction properties. The goal of our modeling efforts is to formulate this hypothesis in quantitative terms. The mathematical model consists of kinetic equations for binding, internalization, degradation, and recycling of EGF and EGFR, along with an expression relating DNA synthesis rate to EGF/EGFR complex levels. Parameter values have been previously determined from independent binding and trafficking kinetic experiments on B82 fibroblasts transfected with wild-type and mutant EGFR. We show that this model can successfully interpret literature data for EGF-dependent growth of NR6 fibroblasts transfected with wild-type EGFR. Moreover, it successfully predicts the literature observation that NR6 cells transfected with a delta 973 truncation mutant EGFR, which is kinase-active but internalization-deficient, require an order of magnitude lower EGF concentration than cells with wild-type EGFR for half-maximal proliferation rate. This result demonstrates that it may be feasible to genetically engineer mammalian cell lines with reduced growth factor requirements by a rational, nonempirical approach. We explore by further model computations the possibility of exploiting other varieties of EGFR mutants to alter growth properties of fibroblastic cells, based on relationships between changes in the primary structure of the EGF receptor and the rates of specific receptor/ligand binding and trafficking processes. Our studies show that the ability to predict cell proliferation as a function of serum growth factors such as EGF could lead to the designed development of cells with optimized growth responses. This approach may also aid in elucidation of mechanisms underlying loss of normal cell proliferation control in malignant transformation, by demonstrating that receptor trafficking dynamics may in some cases play as important a role as intrinsic signal transduction in determining the overall resulting mitogenic response.
我们应用一个关于受体介导的表皮生长因子（EGF）细胞摄取和处理的数学模型，来分析和预测转染了各种形式表皮生长因子受体（EGFR）的成纤维细胞对EGF的增殖反应。潜在的概念假设是，当受体通过内吞作用内化和随后的细胞内降解而下调且生长因子耗尽时，EGF/EGFR在细胞表面结合所产生的有丝分裂信号（通过刺激受体酪氨酸激酶活性）会减弱。因此，细胞增殖速率应该取决于受体/配体结合和运输参数以及内在的受体信号转导特性。我们建模工作的目标是以定量方式阐述这一假设。该数学模型由EGF和EGFR的结合、内化、降解和再循环的动力学方程，以及将DNA合成速率与EGF/EGFR复合物水平相关联的表达式组成。参数值先前已通过对转染了野生型和突变型EGFR的B82成纤维细胞进行的独立结合和运输动力学实验确定。我们表明，该模型可以成功解释关于转染了野生型EGFR的NR6成纤维细胞的EGF依赖性生长的文献数据。此外，它成功预测了文献观察结果，即转染了δ973截短突变型EGFR（具有激酶活性但缺乏内化能力）的NR6细胞，在达到半数最大增殖速率时所需的EGF浓度比具有野生型EGFR的细胞低一个数量级。这一结果表明，通过合理的、非经验性的方法对哺乳动物细胞系进行基因工程改造以降低其生长因子需求可能是可行的。我们通过进一步的模型计算探讨了基于EGF受体一级结构变化与特定受体/配体结合及运输过程速率之间的关系，利用其他种类的EGFR突变体来改变成纤维细胞生长特性的可能性。我们的研究表明，预测细胞增殖作为血清生长因子（如EGF）的函数的能力可能会导致设计开发出具有优化生长反应的细胞。这种方法还可能有助于阐明恶性转化中正常细胞增殖控制丧失的潜在机制，通过证明受体运输动力学在某些情况下在决定整体有丝分裂反应中可能与内在信号转导起着同样重要的作用。
