Retrograde Transport of Filopodial erbB1

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Science's STKE  23 Aug 2005:
Vol. 2005, Issue 298, pp. tw306
DOI: 10.1126/stke.2982005tw306

Lidke et al. used epidermal growth factor (EGF) conjugated to fluorescent quantum dots (EGF-QDs) to track individual ligand-bound erbB1 receptors and investigate in detail the retrograde transport on filopodia of activated erbB1 receptors (a process this group had recently reported). Using confocal microscopy to compare the localization of EGF-QD and activated erbB1 receptors (visualized through immunofluorescence detection of erbB1 phosphorylated on tyrosine-1068) on the filopodia of cultured human A431 cells, the authors found a direct correlation between EGF-QD binding and erbB1 activation. Pharmacological analysis indicated that the retrograde transport on filopodia of EGF-QD-erbB1 complexes depended on both activation of the erbB1 receptor tyrosine kinase and an intact actin cytoskeleton. Moreover, a comparison of EGF-QD-erbB1 transport and actin flow in the filopodia of HeLa cells that expressed enhanced green fluorescent protein (EGFP)-labeled actin indicated that both moved at the same rate. Receptor endocytosis occurred on the cell body, following retrograde transport, and not on the filopodia themselves. Isolated EGF-QD-erbB1 complexes obtained in the presence of very low concentrations of EGF-QD showed only diffusive movement; the addition of higher concentrations of unlabeled EGF under these conditions initiated retrograde transport, which suggests that monomeric EGF-QD-erbB1 complexes did not undergo retrograde transport. Visualization of low concentrations of EGF-QD of two different colors revealed that a switch in EGF-QD-erbB1 movement from diffusion to transport followed merging of the two colors, again suggesting that transport depended on EGF-erbB1 dimerization (or oligomerization). Thus, the authors suggest that filopodia may act as a sensory system to detect signaling molecules far from the cell body.

D. S. Lidke, K. A. Lidke, B. Rieger, T. M. Jovin, D. J. Arndt-Jovin, Reaching out for signals: Filopodia sense EGF and respond by directed retrograde transport of activated receptors. J. Cell Biol. 170, 619-626 (2005). [Abstract] [Full Text]