Cathepsin-B fusion proteins misroute secretory protein partners such as the proprotein convertase PC2-7B2 complex toward the lysosomal degradation pathways

A general strategy is presented for the dominant negative reduction in the levels of heterodimeric soluble proteins within the secretory pathway throu gh fusion of one of its partners C-terminal to the lysosomal enzyme catheps in B (CB). Stable transfectants of CB-7B2 chimeras in AT20 cells result in a drastic reduction of the endogenous levels of its partner, the proprotein convertase PC2. This dominant negative suppressive effect requires active CB. It was partially reversed by NH4Cl, the cell-permeable CB inhibitor CA- 074Me, but not by the proteasome inhibitor Lactacystin, suggesting the pote ntial participation of the lysosomal/endosomal degradative pathway in this process. (C) 2000 Academic Press.