Double immunofluorescence microscopy reveals that epidermal growth factor (EGF) treatment of A431 cells results in more apparent co-localization of EGF receptor (EGFR) and actin filaments, as compared to control cells. This indicates that EGF induces actin polymerization as well as additional association of the EGFR with similar sites on the membrane-skeleton. We show that immunoprecipitation of the cytoskeleton-linked EGFR after fragmentation of the cytoskeleton results in specific co-precipitation of F-actin and a limited set of other unidentified proteins. Interestingly, EGF treatment of intact cells results in increased immunoprecipitation of cytoskeleton-associated EGFR as well as of F-actin, while actin does not co-precipitate with the non-ionic detergent-solubilized EGFR. These results demonstrate that the cytoskeleton-linked EGFR is associated with the actin microfilament system. EGF induces additional formation of protein complexes, containing the EGFR and F-actin and a limited set of other unidentified proteins. The increased co-precipitation of F-actin is most likely related to EGF-induced actin polymerization, which is specifically associated with the apical cortical microfilament system, as demonstrated by confocal laser scanning microscopy and a phallicidin-binding assay.

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