title: Rapid turnover of endogenous endonuclease activity in thymocytes: effects of inhibitors of macromolecular synthesis.
abstract: Previous work has shown that inhibitors of protein or mRNA synthesis block endonuclease activation in thymocytes undergoing programmed cell death. In the present study we used isolated nuclei to investigate the effects of cycloheximide and actinomycin D, inhibitors of protein and mRNA synthesis, respectively, on endogenous endonuclease activity in thymocytes. We observed a rapid loss of Ca2(+)-dependent endonuclease activity in nuclei isolated from thymocytes treated with these inhibitors. In contrast, pretreatment of cells with antipain and leupeptin, inhibitors of proteases, prevented the depletion of endonuclease activity in the nuclei, suggesting that proteolysis was involved. The effects of cycloheximide and actinomycin D were mimicked by incubating thymocytes with treatments known to exert their effects via activation of protein kinase C. Our results suggest that endonuclease activity in thymocyte nuclei undergoes rapid, spontaneous turnover. Agents interfering with macromolecular synthesis may therefore block DNA fragmentation in thymocytes by depleting nuclei of endogenous endonuclease activity.
authors.affiliation: Department of Toxicology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: D J
authors.initials: DJ
authors.lastname: McConkey
authors.forename: P
authors.initials: P
authors.lastname: Hartzell
authors.forename: S
authors.initials: S
authors.lastname: Orrenius
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D002467:Cell Nucleus / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D003208:Concanavalin A / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004720:Endonucleases / Q000378:metabolism*; D007375:Interleukin-1 / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D014176:Protein Biosynthesis; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains; D013950:Thymus Gland / Q000187:drug effects / Q000201:enzymology*
chemical_list: D007375:Interleukin-1; D007546:Isoquinolines; D010879:Piperazines; D011480:Protease Inhibitors; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D003208:Concanavalin A; D003609:Dactinomycin; D015240:Phorbol 12,13-Dibutyrate; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D003513:Cycloheximide; D004720:Endonucleases