Plasma membrane receptors can be endocytosed through clathrin-dependent and clathrin-independent pathways. Here, we show that the epidermal growth factor (EGF) receptor (EGFR), when stimulated with low doses of EGF, is internalized almost exclusively through the clathrin pathway, and it is not ubiquitinated. At higher concentrations of ligand, however, a substantial fraction of the receptor is endocytosed through a clathrin-independent, lipid raft-dependent route, as the receptor becomes ubiquitinated. An ubiquitination-impaired EGFR mutant was internalized through the clathrin pathway, whereas an EGFR/ubiquitin chimera, that can signal solely through its ubiquitin (Ub) moiety, was internalized exclusively by the non-clathrin pathway. Non-clathrin internalization of ubiquitinated EGFR depends on its interaction with proteins harboring the Ub-interacting motif, as shown through the ablation of three Ub-interacting motif-containing proteins, eps15, eps15R, and epsin. Thus, eps15s and epsin perform an important function in coupling ubiquitinated cargo to clathrin-independent internalization.

中文翻译：

---

泛素化货物的网格蛋白非依赖性内吞作用。

质膜受体可以通过网格蛋白依赖性和网格蛋白依赖性途径被内吞。在这里，我们显示表皮生长因子（EGF）受体（EGFR）在用低剂量的EGF刺激时几乎完全通过网格蛋白途径内在化，并且没有泛素化。然而，在较高浓度的配体下，随着受体泛素化，大部分受体通过网格蛋白非依赖性，脂筏依赖性途径被内吞。泛素受损的EGFR突变体通过网格蛋白途径内在化，而仅通过泛素（Ub）部分发出信号的EGFR /泛素嵌合体仅通过非clathrin途径内在化。泛素化EGFR的非clathrin内在化取决于其与具有Ub相互作用基序的蛋白的相互作用，如通过消融三个包含Ub相互作用基序的蛋白eps15，eps15R和epsin所示。因此，eps15s和epsin在将泛素化的货物与网格蛋白无关的内在化过程中起着重要的作用。