D. Schmalz et al., NUCLEAR IMPORT OF PROTEIN-KINASE-C OCCURS BY A MECHANISM DISTINCT FROM THE MECHANISM USED BY PROTEINS WITH A CLASSICAL NUCLEAR-LOCALIZATIONSIGNAL, Journal of Cell Science, 111, 1998, pp. 1823-1830
Protein kinase C does not have any known nuclear localization signal b
ut, nevertheless, is redistributed from the cytoplasm to the nucleus u
pon various stimuli. In NIH 3T3 fibroblasts stimulation with phorbol e
ster leads to a translocation of protein kinase C alpha to the plasma
membrane and into the cell nucleus. We compared the mechanism of prote
in kinase C alpha's transport into the nucleus with the transport mech
anism of a protein with a classical nuclear localization signal at sev
eral steps. To this end, we co-microinjected fluorescently labeled bov
ine serum albumin to which a nuclear localization signal peptide was c
oupled, together with substances interfering with conventional nuclear
protein import. Thereafter, the distribution of both the nuclear loca
lization signal-bearing reporter protein and protein kinase C alpha wa
s analyzed in the same cells. We can show that, in contrast to the nuc
lear localization signal-dependent transport, the phorbol ester-induce
d transport of protein kinase C alpha is not affected by microinjectio
n of antibodies against the nuclear import factor p97/importin/karyoph
erin beta or microinjection of nonhydrolyzable GTP-analogs. This sugge
sts that nuclear import of protein kinase C alpha is independent of p9
7/importin/karyopherin beta and independent of GTP. At the nuclear por
e there are differences between the mechanisms too, since nuclear tran
sport of protein kinase C alpha cannot be inhibited by wheat germ aggl
utinin or an antibody against nuclear pore complex proteins. Together
these findings demonstrate that the nuclear import of protein kinase C
alpha occurs by a mechanism distinct from the one used by classical n
uclear localization signal-bearing proteins at several stages.