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Signaling and Regulation

Increased Expression of Epidermal Growth Factor Receptor Induces Sequestration of Extracellular Signal-Related Kinases and Selective Attenuation of Specific Epidermal Growth Factor-Mediated Signal Transduction Pathways¹

¹ Departments of Neurology and ² Cancer Biology Program, Division of Hematology-Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA

Requests for reprints: Amyn A. Habib, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, Room 836, 77 Avenue Louis Pasteur, Boston, MA 02115. Phone: (617) 667-0837; Fax: (617) 667-0811. E-mail: ahabib{at}caregroup.harvard.edu

Increased expression of the epidermal growth factor receptor (EGFR) is common in cancer and correlates with neoplastic progression. Although the biology of this receptor has been the subject of intense investigation, surprisingly little is known about how increased expression of the wild-type EGFR affects downstream signal transduction in cells. We show that increasing the expression of the receptor results in dramatic shifts in signaling with attenuation of EGF-induced Ras, extracellular signal-related kinases (ERKs), and Akt activation, as well as amplification of STAT1 and STAT3 signaling. In this study, we focus on the mechanism of attenuated ERK signaling and present evidence suggesting that the mechanism of attenuated ERK signaling in EGFR-overexpressing cells is a sequestration of ERKs at the cell membrane in EGFR-containing complexes. Increased expression of the EGFR results in an aberrant localization of ERKs to the cell membrane. Furthermore, ERKs become associated with the EGFR in a physical complex in EGFR-overexpressing cells but not in control cells. The EGFR-ERK association is detected in unstimulated cells or on exposure to a low concentration of EGF; under these conditions, ERK activation is minimal. Exposure of these cells to saturating concentrations of EGF results in a decreased membrane localization of ERKs, a concomitant dissociation of ERKs from the EGFR, and restores ERK activation. A similar association can be detected between the EGFR and MEK1 in receptor-overexpressing cells, suggesting that multiple components of the ERK signaling pathway may become trapped in complexes with the EGFR. These findings can be demonstrated in cells transfected to express high levels of the EGFR as well as in cancer cells which naturally overexpress the EGFR and, thus, may be representative of altered EGFR signaling in human cancer.

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