Association of p185neu with microfilaments via a large glycoprotein complex in mammary carcinoma microvilli. Evidence for a microfilament-associated signal transduction particle.

The protein product of the neu (proto)oncogene p185neu is an analog of the epidermal growth factor receptor. Immunoblot analyses of cell surface fractions (microvilli) from the ascites 13762 rat mammary adenocarcinoma indicate that these cells contain p185neu but not epidermal growth factor receptor. Phalloidin shift velocity sedimentation analysis indicated that essentially all of the microvillar p185 co-migrated with microvillar microfilament cores when extractions were performed under microfilament-stabilizing conditions. Fractionation studies of these microvilli indicated that the association of p185 with the microfilament core is mediated by its stable interaction with a previously described transmembrane complex (TMC), composed minimally of at least four glycoproteins, a 58-kDa cytoplasmic membrane protein, and actin (Carraway, C. A. C., Jung, G., and Carraway, K. L. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 430-434). A fraction of the p185 co-purifies with a large (> 2 x 10(6) kDa) complex of the TMC glycoproteins on gel filtration of microvilli, microfilament cores, or microvillar membranes in buffer containing 1 M KCl at pH 9.5, which are conditions required for the dissociation of actin from the complex. We propose that p185-containing TMC serves as a signal transduction particle at the surface of the 13762 cells and may be a prototype for similar microfilament-associated signal-transducing complexes in other cells.