Alteration of the nucleolar localization of poly(ADP-ribose) polymerase upon treatment with transcription inhibitors.

The effect of RNA, DNA, and protein synthesis inhibitors on the subnuclear localization of poly(ADP-ribose) polymerase (PARP) was examined. Indirect immunofluorescence indicated that PARP was distributed throughout the nuclei but concentrated in nucleoli of MDBK, HeLa, and CHO cells. Treatment with the DNA synthesis inhibitor cytosine arabinoside or the protein synthesis inhibitor cycloheximide did not change the distribution of PARP. In contrast, incubation with the RNA-synthesis inhibitor 5,6-dichloro-1-beta-ribofuranosylbenzimidazole (DRB) caused PARP immunofluorescence to become evenly distributed throughout the nucleus. This phenomenon was observed after a 1-h incubation with a DRB concentration that inhibited [5,6-3H]uridine incorporation by 75%. Similar results were obtained with actinomycin D. Immunoblotting showed that the DRB treatment did not cause any changes in the integrity and content of PARP. Removal of DRB from the media allowed PARP to reaccumulate in nucleoli within 1 h, suggesting that the nucleolar localization of PARP is dependent upon active RNA synthesis.