Phorbol ester-mediated association of protein kinase C to the nuclear fraction in NIH 3T3 cells

Abstract

Treatment of intact NIH 3T3 cells with 12-O-tetradecanoylphorbol-13-acetate (TPA) causes a rapid redistribution (stabilization) of protein kinase C to the particulate fraction. Part of the enzyme activity stabilized to the membrane fraction in response to TPA can be recovered associated with nuclear-cytoskeletal components. An apparently pure nuclear fraction prepared from NIH 3T3 cells was found to contain 25-30% of the total membrane-associated protein kinase C activity when isolated in the presence of Ca2+. In untreated control cells, most of this activity found with the nuclear fraction can be extracted by chelators. Phorbol ester (TPA) treatment of NIH 3T3 cells induces the tight association of protein kinase C to the nucleus; this tightly bound activity is not dissociable by chelators and can be recovered only by solubilization with detergent. Nuclei purified from untreated human promyelocytic leukemic HL-60 cells contain higher amounts of chelator-stable, detergent-extractable protein kinase C activity compared with control NIH 3T3 cells. However, TPA treatment of HL-60 cells does not enhance the amount of protein kinase C found tightly associated with the nuclear fraction. Immunohistochemical studies with polyclonal antibodies directed against protein kinase C further indicate that TPA treatment of NIH 3T3 cells does significantly enhance the amount of protein kinase C found tightly associated with the nucleus and cytoskeleton, whereas exposure of HL-60 cells to TPA does not appreciably alter the amount of protein kinase C observed to be associated with the nuclear fraction. The TPA-mediated association (activation) of protein kinase C to the nuclear and cytoskeletal fractions with NIH 3T3 cells is further supported by the enhanced phosphorylation of specific endogenous proteins noted when purified nuclei and cytoskeletal preparations are incubated with [gamma-32P]ATP. These results suggest that tumor promoters may induce association (activation) of protein kinase C with different subcellular components to alter the availability of endogenous substrates. This may result in differential responses by different cell types during exposure to tumor promoters.