TRANSPORT OF PROTEIN-KINASE-C-ALPHA INTO THE NUCLEUS REQUIRES INTACT CYTOSKELETON WHILE THE TRANSPORT OF A PROTEIN CONTAINING A CANONICAL NUCLEAR-LOCALIZATION SIGNAL DOES NOT

Protein kinase C undergoes a redistribution from the cytosol into the nucleus upon various stimuli. Since protein kinase C does not contain any known nuclear localization signal, the exact pathway and mechanism of the translocation into the nucleus is not known. We used immunoflu orescence microscopy to investigate the role of the cytoskeleton in th is process, and to detect the subcellular distribution of protein kina se C alpha in NIH 3T3 fibroblasts. In these cells protein kinase C alp ha is translocated into the nucleus after stimulation with phorbol est er, We observed that cells treated with the cytoskeleton disrupting ag ents cytochalasin B or colchicine do not show the nuclear translocatio n of protein kinase C alpha after stimulation. In contrast, the nuclea r accumulation of a nuclear localization signal containing reporter pr otein in an in vitro nuclear transport assay is not affected by these drugs, This observation has been confirmed for intact cells by microin jection experiments: cells which have been incubated with cytochalasin B or colchicine prior to microinjection of the reporter protein show the same accumulation in the nucleus as untreated cells. Our data show that intact cytoskeleton plays an important role in the translocation of protein kinase C alpha into the nucleus but not in the nuclear imp ort of a karyophilic reporter protein.