Abstract
1. A neurite outgrowth factor, neurocrescin (NC), which we previously identified from an extract of denervated skeletal muscle, was endoproteolytically processed in cell transfectants. In addition to the processing site identified in NC (DESD358/F) being similar to the optimal recognition sequence of group II caspases, DExD, cleavage site mutations confirmed the involvement of caspase(s) in NC processing. 2. However, both the recombinant NC and the synthetic octapeptide (YLDESDFG) were scarcely cleaved in vitro by caspase-3 or -7. Furthermore, transiently expressed NC was cleaved even in the caspase-3-deficient cell line, MCF-7 cells, and this efficiency was not altered by the transfectional expression of caspase-3. 3. Using the fluorescent substrate (Ac-DESD-AMC), the characteristic proteolytic activities, which cleaved it more effectively than caspase-3 and whose pH dependences were different from those of caspase-3, were endogenously identified in the muscle extract. These findings indicate the presence of proteolytic activities that are distinguishable from caspase-3.