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 tr ansported into nuclei in an ATP-dependent fashion. The calpain-specifi c inhibitor protein, calpastatin, could not block mu-calpain transloca tion. Fluorescein-calpastatin and fluorescein-m-calpain were poorly tr ansported at best. In the presence of rat liver cytosolic factors accu mulation 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) 19 94 Academic Press, Inc.