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Filamin A Modulates Kinase Activation and Intracellular Trafficking of Epidermal Growth Factor Receptors in Human Melanoma Cells

Laboratories of Clinical Investigation (J.L.F., T.-N.Z., M.B.) and Immunology (M.P.O., A.T.W.) and Research Resources Branch (F.E.I., B.P.F., C.M.), National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224; Department of Dermatology (K.S.H.), University Hospital of Zürich, CH-8091 Zürich, Switzerland; MedStar Research Institute (S.K.), Hyattsville, Maryland 20783; and The Harry and Jeanette Weinberg Cancer Institute (J.H., G.E.), Franklin Square Hospital, Baltimore, Maryland 21237

Address all correspondence and requests for reprints to: Michel Bernier, Ph.D., Biomedical Research Center, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Suite 100, Room 09B135, Baltimore, Maryland 21224-6825. E-mail: bernierm{at}mail.nih.gov.

The actin-binding protein filamin A (FLNa) affects the intracellular trafficking of various classes of receptors and has a potential role in oncogenesis. However, it is unclear whether FLNa regulates the signaling capacity and/or down-regulation of the activated epidermal growth factor receptor (EGFR). Here it is shown that partial knockdown of FLNa gene expression blocked ligand-induced EGFR responses in metastatic human melanomas. To gain greater insights into the role of FLNa in EGFR activation and intracellular sorting, we used M2 melanoma cells that lack endogenous FLNa and a subclone in which human FLNa cDNA has been stably reintroduced (M2A7 cells). Both tyrosine phosphorylation and ubiquitination of EGFR were significantly lower in epidermal growth factor (EGF)-stimulated M2 cells when compared with M2A7 cells. Moreover, the lack of FLNa interfered with EGFR interaction with the ubiquitin ligase c-Cbl. M2 cells exhibited marked resistance to EGF-induced receptor degradation, which was very active in M2A7 cells. Despite comparable rates of EGF-mediated receptor endocytosis, internalized EGFR colocalized with the lysosomal marker lysosome-associated membrane protein-1 in M2A7 cells but not M2 cells, in which EGFR was found to be sequestered in large vesicles and subsequently accumulated in punctated perinuclear structures after EGF stimulation. These results suggest the requirement of FLNa for efficient EGFR kinase activation and the sorting of endocytosed receptors into the degradation pathway.