Departamento de Inmunología Clínica y Reumatología, Facultad de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Mol Biol Cell. 2010 Aug 15;21(16):2916-29. doi: 10.1091/mbc.E10-02-0167. Epub 2010 Jun 16.
Endocytosis modulates EGFR function by compartmentalizing and attenuating or enhancing its ligand-induced signaling. Here we show that it can also control the cell surface versus intracellular distribution of empty/inactive EGFR. Our previous observation that PKA inhibitors induce EGFR internalization prompted us to test phosphatidic acid (PA) generated by phospholipase D (PLD) as an endogenous down-regulator of PKA activity, which activates rolipram-sensitive type 4 phosphodiesterases (PDE4) that degrade cAMP. We found that inhibition of PA hydrolysis by propranolol, in the absence of ligand, provokes internalization of inactive (neither tyrosine-phosphorylated nor ubiquitinated) EGFR, accompanied by a transient increase in PA levels and PDE4s activity. This EGFR internalization is mimicked by PA micelles and is strongly counteracted by PLD2 silencing, rolipram or forskolin treatment, and PKA overexpression. Accelerated EGFR endocytosis seems to be mediated by clathrin-dependent and -independent pathways, leading to receptor accumulation in juxtanuclear recycling endosomes, also due to a decreased recycling. Internalized EGFR can remain intracellular without degradation for several hours or return rapidly to the cell surface upon discontinuation of the stimulus. This novel regulatory mechanism of EGFR, also novel function of signaling PA, can transmodulate receptor accessibility in response to heterologous stimuli.
内吞作用通过分隔和减弱或增强其配体诱导的信号来调节 EGFR 功能。在这里,我们表明它还可以控制空载/无活性 EGFR 的细胞表面与细胞内分布。我们之前的观察结果表明,PKA 抑制剂诱导 EGFR 内化,这促使我们测试由磷脂酶 D (PLD) 产生的磷脂酸 (PA) 作为 PKA 活性的内源性下调子,它激活依赖 rolipram 的 4 型磷酸二酯酶 (PDE4),从而降解 cAMP。我们发现,在没有配体的情况下,用普萘洛尔抑制 PA 水解会引发无活性 (既没有酪氨酸磷酸化也没有泛素化) EGFR 的内化,同时 PA 水平和 PDE4s 活性短暂增加。PA 胶束模拟这种 EGFR 内化,并且强烈拮抗 PLD2 沉默、rolipram 或 forskolin 处理以及 PKA 过表达。加速的 EGFR 内吞作用似乎通过网格蛋白依赖和非依赖途径介导,导致受体在核周再循环内体中积累,这也归因于再循环减少。内化的 EGFR 可以在没有降解的情况下在细胞内持续数小时,或者在刺激停止后迅速返回细胞表面。这种 EGFR 的新调节机制,也是信号 PA 的新功能,可以响应异源刺激来调节受体的可及性。