TRANSLOCATION OF NUCLEOPHOSMIN FROM NUCLEOLI TO NUCLEOPLASM REQUIRES ATP

The movement of nucleophosmin from nucleoli to nucleoplasm in HeLa cells induced by cytotoxic drugs and detected by immunofluorescence is inhibited by concomitant treatment with antimycin A in glucose-free medium. Incubation of HeLa cells with antimycin A (300 nM; 30 min) and glucose-free medium resulted in an approximately 90% decrease in cellular ATP pools. To study the biochemical events involved in nucleophosmin translocation, we used an in vitro system consisting of Triton-permeabilized HeLA cells. Incubation of permeabilized cells with ATP (0.5 mM; 1 h) resulted in the translocation of nucleophosmin from nucleoli to nucleoplasm and cytoplasm. Similarly to drug-induced nucleophosmin translocation in whole cultured cells, there is no reduction (measured by e.l.i.s.a.) or degradation of nucleophosmin or change in the ratio of the high-molecular-mass form to the monomeric form (ascertained by Western blotting) during ATP treatment of permeabilized cells. Together, these results indicate a requirement for ATP for redistribution of nucleophosmin from nucleoli to nucleoplasm. Because this permeabilized cell model is simple and efficient and works effectively with exogenous factors, it should provide a powerful tool for investigating the biochemical features of nucleophosmin translocation from nucleoli to nucleoplasm.