Genentech, Inc., 1 DNA Way, South San Francisco, California 94080, USA.
Nature. 2010 Apr 1;464(7289):783-7. doi: 10.1038/nature08827. Epub 2010 Mar 7.
Epidermal growth factor receptor (EGFR) is a type I receptor tyrosine kinase, the deregulation of which has been implicated in a variety of human carcinomas. EGFR signalling is preceded by receptor dimerization, typically thought to result from a ligand-induced conformational change in the ectodomain that exposes a loop (dimerization arm) required for receptor association. Ligand binding may also trigger allosteric changes in the cytoplasmic domain of the receptor that is crucial for signalling. Despite these insights, ensemble-averaging approaches have not determined the precise mechanism of receptor activation in situ. Using quantum-dot-based optical tracking of single molecules combined with a novel time-dependent diffusivity analysis, here we present the dimerization dynamics of individual EGFRs on living cells. Before ligand addition, EGFRs spontaneously formed finite-lifetime dimers kinetically stabilized by their dimerization arms. The dimers were primed both for ligand binding and for signalling, such that after EGF addition they rapidly showed a very slow diffusivity state that correlated with activation. Although the kinetic stability of unliganded dimers was in principle sufficient for EGF-independent activation, ligand binding was still required for signalling. Interestingly, dimers were enriched in the cell periphery in an actin- and receptor-expression-dependent fashion, resulting in a peripheral enhancement of EGF-induced signalling that may enable polarized responses to growth factors.
表皮生长因子受体（EGFR）是一种 I 型受体酪氨酸激酶，其失调与多种人类癌有关。EGFR 信号转导之前是受体二聚化，通常认为这是配体诱导的细胞外结构域构象变化的结果，该构象变化暴露出受体缔合所需的环（二聚化臂）。配体结合也可能触发受体胞质结构域的变构变化，这对于信号转导至关重要。尽管有了这些见解，但总体平均方法尚未确定受体在原位激活的精确机制。本文使用基于量子点的单分子光学跟踪技术结合新型的时变扩散分析，展示了活细胞中单个 EGFR 的二聚化动力学。在添加配体之前，EGFR 自发形成有限寿命的二聚体，其通过二聚化臂动力学稳定。这些二聚体既可以与配体结合，也可以与信号转导结合，因此在添加 EGF 后，它们迅速显示出与激活相关的非常缓慢的扩散状态。尽管无配体二聚体的动力学稳定性原则上足以实现 EGF 独立激活，但配体结合仍然是信号转导所必需的。有趣的是，二聚体以肌动蛋白和受体表达依赖性的方式富集在细胞外周，导致 EGF 诱导的信号转导在外周增强，这可能使细胞对生长因子产生极化反应。
