THE CARBOXYL-TERMINUS OF EPIDERMAL GROWTH-FACTOR RECEPTOR ERBB-2 CHIMERAE IS INTERNALIZATION IMPAIRED/

The endocytosis of gp185erbB-2 was studied using chimeric receptors in which the intracellular domain of erbB-2, or subdomains thereof, was substituted for the corresponding regions of the epidermal growth fact or (EGF) receptor. Chimeric and wild-type EGF or erbB-2 receptors were expressed in mouse NIH3T3 or NR6 fibroblasts and in a human mammary a denocarcinoma cell line, MDAMB-134. The rate of EGF-induced internaliz ation for the chimera consisting of the extracellular EGF receptor dom ain and intracellular erbB-2 domain was reduced three- to fourfold com pared with the wild-type EGF receptor. The low rate of internalization of the chimeric receptor resulted in impaired down-regulation and deg radation of the receptor. Substitution of the carboxyl terminus of erh B-2 for the corresponding region of the EGF receptor caused a similar decrease of receptor endocytosis, whereas substitution of the erhB-2 t yrosine kinase domain did not affect internalization and down-regulati on. Since the tyrosine kinase of the internalization-defective chimeri c receptors could be activated by EGF, kinase activity and autophospho rylation of erhB-2 do not appear to be sufficient for a maximum rapid internalization of the chimeric receptors. These results suggest that the carboxyl terminus of erhB-2 either does not possess all the signal s required for the rapid internalization or contains an inhibitory sig nal for rapid internalization.