The epidermal growth factor (EGF) receptor (EGFR) controls many aspects of cell physiology. EGF binding to EGFR elicits the membrane recruitment and activation of phosphatidylinositol-3-kinase, leading to Akt phosphorylation and activation. Concomitantly, EGFR is recruited to clathrin-coated pits (CCPs), eventually leading to receptor endocytosis. Previous work uncovered that clathrin, but not receptor endocytosis, is required for EGF-stimulated Akt activation, and that some EGFR signals are enriched in CCPs. Here, we examine how CCPs control EGFR signaling. The signaling adaptor TOM1L1 and the Src-family kinase Fyn are enriched within a subset of CCPs with unique lifetimes and protein composition. Perturbation of TOM1L1 or Fyn impairs EGF-stimulated phosphorylation of Akt2 but not Akt1. EGF stimulation also triggered the TOM1L1- and Fyn-dependent recruitment of the phosphoinositide 5-phosphatase SHIP2 to CCPs. Thus, the recruitment of TOM1L1 and Fyn to a subset of CCPs underlies a role for these structures in the support of EGFR signaling leading to Akt activation.

No abstract

<p>The epidermal growth factor (EGF) receptor (EGFR) controls many aspects of cell physiology. EGF binding to EGFR elicits the membrane recruitment and activation of phosphatidylinositol-3-kinase, leading to Akt phosphorylation and activation. Concomitantly, EGFR is recruited to clathrin-coated pits (CCPs), eventually leading to receptor endocytosis. Previous work uncovered that clathrin, but not receptor endocytosis, is required for EGF-stimulated Akt activation, and that some EGFR signals are enriched in CCPs. Here, we examine how CCPs control EGFR signaling. The signaling adaptor TOM1L1 and the Src-family kinase Fyn are enriched within a subset of CCPs with unique lifetimes and protein composition. Perturbation of TOM1L1 or Fyn impairs EGF-stimulated phosphorylation of Akt2 but not Akt1. EGF stimulation also triggered the TOM1L1- and Fyn-dependent recruitment of the phosphoinositide 5-phosphatase SHIP2 to CCPs. Thus, the recruitment of TOM1L1 and Fyn to a subset of CCPs underlies a role for these structures in the support of EGFR signaling leading to Akt activation.</p>

<p>The epidermal growth factor (EGF) receptor (EGFR) controls many aspects of cell physiology. EGF binding to EGFR elicits the membrane recruitment and activation of phosphatidylinositol-3-kinase, leading to Akt phosphorylation and activation. Concomitantly, EGFR is recruited to clathrin-coated pits (CCPs), eventually leading to receptor endocytosis. Previous work uncovered that clathrin, but not receptor endocytosis, is required for EGF-stimulated Akt activation, and that some EGFR signals are enriched in CCPs. Here, we examine how CCPs control EGFR signaling. The signaling adaptor TOM1L1 and the Src-family kinase Fyn are enriched within a subset of CCPs with unique lifetimes and protein composition. Perturbation of TOM1L1 or Fyn impairs EGF-stimulated phosphorylation of Akt2 but not Akt1. EGF stimulation also triggered the TOM1L1- and Fyn-dependent recruitment of the phosphoinositide 5-phosphatase SHIP2 to CCPs. Thus, the recruitment of TOM1L1 and Fyn to a subset of CCPs underlies a role for these structures in the support of EGFR signaling leading to Akt activation.</p>

The Epidermal Growth Factor (EGF) Receptor (EGFR) is a receptor tyrosine kinase (RTK) that controls many key components of cell physiology, including proliferation, survival, and metabolism. When upregulated, EGFR drives tumor growth and progression in several types of cancer. EGF stimulation elicits EGFR phosphorylation and activation of phosphatidylinositol‐3‐kinase (PI3K), leading to Akt activation by its phosphorylation on T308 and S473. EGF‐stimulated Akt phosphorylation is dependent on clathrin coated pits (CCPs) at the plasma membrane, but not receptor endocytosis1. CCPs are 50‐100 nm protein assemblies that are well‐known endocytic portals and lead to eventual receptor downregulation. Importantly, we previously uncovered that CCPs are also required for Akt activation, likely by acting as protein and lipid scaffolds to coordinate signaling intermediates. One of the many proteins that are known to bind to clathrin directly is Activated Cdc42 Kinase 1 (Ack1), a non‐receptor tyrosine kinase implicated in oncogenic RTK signaling and tumor cell survival. Ack1 also interacts with EGFR and directly phosphorylates Akt at Y176, a regulatory site distinct from those required for canonical Akt activation. In addition to clathrin, Ack1 also interacts with a multitude of other proteins. How Ack1 regulates the PI3K/Akt signaling pathway, and how binding of Ack1 to clathrin controls this phenomenon, remains poorly defined. Here, we examine how Ack1 contributes to EGFR signaling. Using siRNA silencing of Ack1 and/or the related isoform Ack2, alone or in combination with inducible expression of fluorescent or mutant Ack constructs, we examined the role of Ack1 in EGFR signaling. Moreover, using various microscopy and image analysis techniques, we examined the mechanism of recruitment of Ack1 to CCPs. Our results indicate a critical role for Ack1 in EGFR signaling, in particular for the activation of PI3K‐Akt signaling. The improved understanding of the regulation and outcome of EGFR signals by proteins such as Ack1 and scaffolds such as clathrin‐coated pits, can lead to the development of novel cancer treatments.