Research Article

Reticulon 3–dependent ER-PM contact sites control EGFR nonclathrin endocytosis

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Science  12 May 2017:
Vol. 356, Issue 6338, pp. 617-624
DOI: 10.1126/science.aah6152

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ER-PM contacts in nonclathrin endocytosis

The epidermal growth factor receptor (EGFR) is internalized through both clathrin-mediated endocytosis and nonclathrin endocytosis (NCE). The two pathways act in concert to sustain EGFR signaling or its long-term attenuation. The mechanistic underpinnings of EGFR-NCE are unclear. Caldieri et al. used a variety of cell and molecular biology approaches to identify nine regulators of EGFR-NCE (see the Perspective by Tan and Anderson). They also identified an additional cargo of the pathway (CD147). One of the regulators of the pathway was the endoplasmic reticulum (ER)-resident protein reticulon 3 (RTN3). Unexpectedly, EGFR-NCE required the formation of specific contacts between the plasma membrane (PM) and the cortical ER, mediated by RTN3. ER-PM contact sites were required in the very early steps of the internalization process for the maturation of NCE tubular intermediates.

Science, this issue p. 617; see also p. 584

Abstract

The integration of endocytic routes is critical to regulate receptor signaling. A nonclathrin endocytic (NCE) pathway of the epidermal growth factor receptor (EGFR) is activated at high ligand concentrations and targets receptors to degradation, attenuating signaling. Here we performed an unbiased molecular characterization of EGFR-NCE. We identified NCE-specific regulators, including the endoplasmic reticulum (ER)–resident protein reticulon 3 (RTN3) and a specific cargo, CD147. RTN3 was critical for EGFR/CD147-NCE, promoting the creation of plasma membrane (PM)–ER contact sites that were required for the formation and/or maturation of NCE invaginations. Ca2+ release at these sites, triggered by inositol 1,4,5-trisphosphate (IP3)–dependent activation of ER Ca2+ channels, was needed for the completion of EGFR internalization. Thus, we identified a mechanism of EGFR endocytosis that relies on ER-PM contact sites and local Ca2+ signaling.

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