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 subnucl ear localization of poly(ADP-ribose) polymerase (PARP) was examined. I ndirect immunofluorescence indicated that PARP was distributed through out the nuclei but concentrated in nucleoli of MDBK, HeLa, and CHO cel ls, Treatment with the DNA synthesis inhibitor cytosine arabinoside or the protein synthesis inhibitor cycloheximide did not change the dist ribution of PARP, In contrast, incubation with the RNA synthesis inhib itor 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 conce ntration that inhibited [5,6-H-3]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 conte nt 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. (C) 1996 Academic Press, Inc.