Heregulin-dependent trafficking and cleavage of ErbB-4

Heregulin was shown to promote the proteolytic cleavage of its receptor, Er bB-4, in several cell lines. The growth factor also rapidly promoted the tr ansient translocation of ErbB-4 to a detergent-insoluble fraction, in which the receptor was hyper-tyrosine-phosphorylated compared with the receptor present in the detergent-soluble pool. However, an 80-kDa proteolytic fragm ent of ErbB-4 was found in the detergent soluble fraction, but not in the d etergent-insoluble fraction. Although the heregulin-induced cleavage of Erb B-4 produced a fragment of ErbB-4 very similar to that induced by 12-O-tetr adecanoylphorbol-13-acetate or pervanadate teach of which is blocked by met alloprotease inhibitors), the growth factor-induced cleavage was not sensit ive to these inhibitors under the same conditions. The heregulin-induced cl eavage of ErbB-4 could be blocked by conditions that prevent clathrin-coate d pit formation, suggesting that heregulin-mediated ErbB-4 cleavage occurs subsequent to internalization. When reagents that prevent acidification of endosomes were employed, heregulin-induced ErbB-4 cleavage was sensitive to metalloprotease inhibitors. The results imply that during ligand-dependent receptor trafficking, activated ErbB-4 receptors are subject to proteolyti c cleavage involving an intracellular metalloprotease.