Weddell Jared C, Imoukhuede Princess I
Department of Bioengineering, University of Illinois at Urbana-Champaign, 1304 W Springfield Ave., 3233 Digital Computer Laboratory, Urbana, IL 61801, USA.
Integr Biol (Camb). 2017 May 22;9(5):464-484. doi: 10.1039/c7ib00011a.
Recently, intracellular receptor signaling has been identified as a key component mediating cell responses for various receptor tyrosine kinases (RTKs). However, the extent each endocytic compartment (endocytic vesicle, early endosome, recycling endosome, late endosome, lysosome and nucleus) contributes to receptor signaling has not been quantified. Furthermore, our understanding of endocytosis and receptor signaling is complicated by cell- or receptor-specific endocytosis mechanisms. Therefore, towards understanding the differential endocytic compartment signaling roles, and identifying how to achieve signal transduction control for RTKs, we delineate how endocytosis regulates RTK signaling. We achieve this via a meta-analysis across eight RTKs, integrating computational modeling with experimentally derived cell (compartment volume, trafficking kinetics and pH) and ligand-receptor (ligand/receptor concentration and interaction kinetics) physiology. Our simulations predict the abundance of signaling from eight RTKs, identifying the following hierarchy in RTK signaling: PDGFRβ > IGFR1 > EGFR > PDGFRα > VEGFR1 > VEGFR2 > Tie2 > FGFR1. We find that endocytic vesicles are the primary cell signaling compartment; over 43% of total receptor signaling occurs within the endocytic vesicle compartment for these eight RTKs. Mechanistically, we found that high RTK signaling within endocytic vesicles may be attributed to their low volume (5.3 × 10 L) which facilitates an enriched ligand concentration (3.2 μM per ligand molecule within the endocytic vesicle). Under the analyzed physiological conditions, we identified extracellular ligand concentration as the most sensitive parameter to change; hence the most significant one to modify when regulating absolute compartment signaling. We also found that the late endosome and nucleus compartments are important contributors to receptor signaling, where 26% and 18%, respectively, of average receptor signaling occurs across the eight RTKs. Conversely, we found very low membrane-based receptor signaling, exhibiting <1% of the total receptor signaling for these eight RTKs. Moreover, we found that nuclear translocation, mechanistically, requires late endosomal transport; when we blocked receptor trafficking from late endosomes to the nucleus we found a 57% reduction in nuclear translocation. In summary, our research has elucidated the significance of endocytic vesicles, late endosomes and the nucleus in RTK signal propagation.
最近，细胞内受体信号传导已被确定为介导各种受体酪氨酸激酶（RTK）细胞反应的关键组成部分。然而，每个内吞区室（内吞囊泡、早期内体、循环内体、晚期内体、溶酶体和细胞核）对受体信号传导的贡献程度尚未量化。此外，细胞特异性或受体特异性内吞机制使我们对内吞作用和受体信号传导的理解变得复杂。因此，为了理解不同内吞区室的信号传导作用，并确定如何实现对RTK的信号转导控制，我们阐述了内吞作用如何调节RTK信号传导。我们通过对八种RTK进行荟萃分析来实现这一点，将计算模型与实验得出的细胞（区室体积、运输动力学和pH值）以及配体-受体（配体/受体浓度和相互作用动力学）生理学相结合。我们的模拟预测了八种RTK的信号传导丰度，确定了RTK信号传导中的以下层次结构：PDGFRβ > IGFR1 > EGFR > PDGFRα > VEGFR1 > VEGFR2 > Tie2 > FGFR1。我们发现内吞囊泡是主要的细胞信号传导区室；对于这八种RTK，超过43%的总受体信号传导发生在内吞囊泡区室内。从机制上讲，我们发现内吞囊泡内的高RTK信号传导可能归因于其小体积（5.3×10⁻¹⁵L），这有利于富集配体浓度（内吞囊泡内每个配体分子为3.2μM）。在分析的生理条件下，我们确定细胞外配体浓度是最敏感的可变参数；因此，在调节绝对区室信号传导时是最需要改变的重要参数。我们还发现晚期内体和细胞核区室是受体信号传导的重要贡献者，在这八种RTK中，平均分别有26%和18%的受体信号传导发生在这些区室。相反，我们发现基于膜的受体信号传导非常低，在这八种RTK中占总受体信号传导的比例不到1%。此外，我们发现从机制上讲，核转位需要晚期内体运输；当我们阻断受体从晚期内体向细胞核的运输时，我们发现核转位减少了57%。总之，我们的研究阐明了内吞囊泡、晚期内体和细胞核在RTK信号传播中的重要性。
