Abstract 4051: EGF receptor trafficking from the cell surface to the nucleus through the Golgi, ER, and nuclear envelope
Authors: Wang Ying-Nai , Yamaguchi Hirohito , Huo Longfei , Du Yi , Lee Hong-Jen , Lee Heng-Huan , Wang Hongmei , Hsu Jung-Mao , Hung Mien-Chie 
Published: August 2014

Abstract
Receptor tyrosine kinases (RTKs), including insulin-like growth factor 1 receptor, cMet, fibroblast growth factor receptor, vascular endothelial growth factor receptor, and the four members of the epidermal growth factor receptor (EGFR) family, have been shown to localize in the nucleus. Among these, both EGFR/ErbB-1 and ErbB-2 have been shown to be involved in transcriptional regulation, cell proliferation, DNA repair, DNA replication, and chemo- and radio-resistance. Recent studies have demonstrated that endocytosis and endosomal sorting are involved in the nuclear transport of cell surface RTKs, such as EGFR and ErbB-2. However, how full-length receptors embedded in the endosomal membrane pass through the nuclear pore complexes (NPCs) and function as non-membrane-bound receptors in the nucleus remains unclear. Here, we demonstrate that membrane-embedded vesicular trafficking is involved in the nuclear transport of EGFR. Confocal immunofluorescence reveals that in response to EGF, a portion of EGFR redistributes to the Golgi and the endoplasmic reticulum (ER), where its NH2-terminus resides within the lumen of Golgi/ER and COOH-terminus is exposed to the cytoplasm. Blockage of the Golgi-to-ER retrograde trafficking by brefeldin A or dominant mutants of the small GTPase ADP-ribosylation factor, which both resulted in the disassembly of the coat protein complex I (COPI) coat to the Golgi, inhibit EGFR transport to the ER and the nucleus. We further find that EGF-dependent nuclear transport of EGFR is regulated by retrograde trafficking from the Golgi to the ER involving an association of EGFR with γ-COP, one of the subunits of the COPI coatomer. Our findings experimentally provide a comprehensive pathway that nuclear transport of EGFR is regulated by COPI-mediated vesicular trafficking from the Golgi to the ER. Furthermore, we show that upon EGF treatment, the biotinylated cell surface EGFR is trafficked to the inner nuclear membrane (INM) by INTERNET (integral trafficking from the endoplasmic reticulum to the nuclear envelope transport) through the NPCs, remaining in a membrane-bound environment. We then find that importin β regulates EGFR nuclear transport to the INM in addition to the nucleus/nucleoplasm (NP). Unexpectedly, the well-known endoplasmic reticulum associated translocon Sec61β is found to reside in the INM and associate with EGFR. Knocking down Sec61β expression reduces EGFR level in the NP portion and accumulates it in the INM portion. Thus, the Sec61β translocon plays an unrecognized role in the release of the membrane-anchored EGFR from the lipid bilayer of the INM to the nucleus. The newly identified Sec61β function provides an alternative pathway for nuclear transport that can be utilized by membrane-embedded proteins such as full-length EGFR and may serve as a general mechanism for other cell surface receptors.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4051. doi:10.1158/1538-7445.AM2011-4051