Effects of environmental stresses on the subcellular localization of PKN were investigated in NIH 3T3, BALB/c 3T3, and Rat-1 cells. The immunofluorescence of PKN resided prominently in the cytoplasmic region in nonstressed cells. When these cells were treated at 42 degrees C, there was a time-dependent decrease of the immunofluorescence of PKN in the cytoplasmic region that correlated with an increase within the nucleus as observed by confocal microscope. After incubation at 37 degrees C following beat shock, the immunofluorescence of PKN returned to the perinuclear and cytoplasmic regions from the nucleus. The nuclear translocation of PKN by heat shock was supported by the biochemical subcellular fractionation and immunoblotting. The nuclear localization of PKN was also observed when the cells were exposed to other stresses such as sodium arsenite and serum starvation. These results raise the possibility that there is a pathway mediating stress signals from the cytosol to the nucleus through PKN.