title: EGF‑stimulated AKT activation is mediated by EGFR recycling via an early endocytic pathway in a gefitinib‑resistant human lung cancer cell line.
abstract: The receptor tyrosine kinase epidermal growth factor receptor (EGFR) and its ligand epidermal growth factor (EGF) are known to play important roles in malignant tumor cells, and the EGFR signaling pathway is one of the most important targets in various tumors, including non-small cell lung cancer (NSCLC). We reported recently that an aberration in certain steps of EGF-stimulated phosphorylated epidermal growth factor receptor (pEGFR) endocytic trafficking from the early endosomes to the late endosomes occurs in the gefitinib-resistant NSCLC cells, in which large amounts of sorting nexin 1 (SNX1) are colocalized with EGFR in the aggregated early endosomes where the internalized pEGFR is also accumulated of these cells. To further investigate the role of SNX1 in EGF‑stimulated pEGFR endocytosis, followed by downstream signaling leading to the activation of phosphatidylinositol 3-kinase (PI3K)--the serine/threonine kinase AKT pathway, we examined the effect of depletion of SNX1 knock-down expression by siRNA and an inhibition of targeting membrane recycling using monensin. Using immunofluorescence, we observed an efficient endocytic transport of pEGFR from early endosomes to late endosomes/lysosomes after EGF-stimulation in the cells transfected with siRNA‑SNX1, whereas the delayed endocytic delivery of pEGFR was evident in the siRNA-control-transfected cells. Furthermore, a large amount of endocytosed pEGFR was accumulated in the presence of monensin in the early endosomes of the SNX1 knock-down cells. In western blot analysis, EGF stimulation of both control and cells transfected with siRNA-SNX1 resulted in rapid phosphorylation of EGFR and enhanced AKT phosphorylation. Monensin-dependent inhibition of AKT phosphorylation was stronger in SNX1 knock-down cells than in controls. In contrast, however, monensin had no effect on AKT phosphorylation triggered by activation of the MET receptor tyrosine kinase. Collectively, we suggest that EGF-stimulated recycling of EGFR to the plasma membrane induces downstream signaling leading to AKT phosphorylation. Suppression of EGFR membrane recycling by SNX1 appears to be critical for the activation of EGFR/PI3K/AKT signaling pathway in human lung cancer cells.
authors: Division of Pharmaceutical Cell Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka 812‑8582, Japan.
authors: Yukio
authors: Y
authors: Nishimura
authors: Institute for Clinical Research, National Kyushu Cancer Center, Fukuoka 811‑1395, Japan.
authors: Soichi
authors: S
authors: Takiguchi
authors: Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo 101‑0062, Japan.
authors: Shigeru
authors: S
authors: Ito
authors: Department of Biology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Osaka 537‑8511, Japan.
authors: Kazuyuki
authors: K
authors: Itoh
mesh_terms: D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004705:Endocytosis / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000378:metabolism*; D000077156:Gefitinib; D055785:Gene Knockdown Techniques; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism* / Q000473:pathology; D008985:Monensin / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D058305:Sorting Nexins / Q000235:genetics / Q000378:metabolism*
chemical_list: D047428:Protein Kinase Inhibitors; D011799:Quinazolines; C513978:SNX1 protein, human; D058305:Sorting Nexins; D004815:Epidermal Growth Factor; D008985:Monensin; C512478:EGFR protein, human; D066246:ErbB Receptors; D051057:Proto-Oncogene Proteins c-akt; D000077156:Gefitinib