Selective cleavage of the heregulin receptor ErbB-4 by protein kinase C activation

The 180-kDa transmembrane tyrosine kinase ErbB-4 is a receptor for the growth factor heregulin, I-125-Heregulin binding to NIH 3T3 cells overexpressing the ErbB-4 receptor is rapidly decreased by 12-O-tetradecanoylphorbol-13-acetate (TPA) pretreatment. Immunologic analysis demonstrates that TPA treatment of cells induces the proteolytic cleavage of ErbB-4, producing an 80-kDa cytoplasmic domain fragment, which contains a low level of phosphotyrosine, and a 120-kDa ectodomain fragment, which is released into the extracellular medium, Cleavage of ErbB-4 was also enhanced by other protein kinase C activators, i,e, platelet-derived growth factor, ionomycin, and synthetic diacylglycerol, while protein kinase C inhibition or down-regulation suppressed the TPA stimulation of ErbB-4 degradation, TPA did not induce the degradation of related receptors (ErbB-1, ErbB-2, and ErbB-3) in the EGF receptor family, The phorbol ester-induced cleavage of ErbB-4 occurs within or close to the ectodomain, as the 80-kDa cytoplasmic domain fragment is recognized by antibody to the ErbB-4 carboxyl terminus and is membrane-associated, Coprecipitation experiments show that, while the 80-kDa ErbB-4 fragment is associated with the SH2-containing molecules PLC-gamma 1 and She, TPA did not induce the phosphorylation of these substrates in intact cells, In addition, kinase assays in vitro indicate that the 80-kDa fragment is not an active tyrosine kinase, These results show that protein kinase C negatively regulates heregulin signaling through the ErbB-4 receptor by the activation of a selective proteolytic mechanism.