Behavior of nucleolar proteins during the course of apoptosis in camptothecin-treated HL60 cells

By means of immunofluorescence and immunoelectron microscopy we have studie d the fate of different nucleolar components during the apoptotic process i n camptothecin-treated HL60 cells. We have found that RNA polymerase I disa ppeared while UBF was associated with previously described fibrogranular th readed bodies. In contrast fibrillarin. C23/nucleolin, and B23/nucleophosmi n remained detectable in granular material present amid micronuclei of late apoptotic cells. Double immunolabeling experiments showed colocalization o f both C23 and B23 with fibrillarin. Immunoblotting analysis showed that UB F was proteolytically degraded, whereas fibrillarin, C23/nucleolin and B23/ nucleophosmin were not. These results may help explain the presence of anti -nucleolar antibodies seen in various pathological disorders. (C) 2000 Wile y-Liss, Inc.