SELECTIVE NUCLEAR TRANSPORT OF MU-CALPAIN

To study nuclear transport of purified calpains in an in vitro system, A431 cells were permeabilized with digitonin, and fluorescein-labeled calpains were introduced under conditions known to facilitate energy-dependent nuclear transport of proteins. Fluorescein-mu-calpain was transported into nuclei in an ATP-dependent fashion. The calpain-specific inhibitor protein, calpastatin, could not block mu-calpain translocation. Fluorescein-calpastatin and fluorescein-m-calpain were poorly transported at best. In the presence of rat liver cytosolic factors accumulation of nuclear mu-calpain was maximum at approximately 1 mu M Ca2+, and no transport was observed at 0.3 mu M Ca2+. Rat erythrocyte and HeLa cell extracts supported transport in the absence of Ca2+. (C) 1994 Academic Press, Inc.