title: Prevention of cisplatin-DNA adduct repair and potentiation of cisplatin-induced apoptosis in ovarian carcinoma cells by proteasome inhibitors.
abstract: Histones H2A and H2B are known to be reversibly post-translationally modified by ubiquitination. We previously observed in cultured tumor cells that proteasome inhibition stabilizes polyubiquitinated proteins, depletes unconjugated ubiquitin, and thereby promotes the deubiquitination of nucleosomal histones in chromatin. Provocative indirect evidence suggests that histone ubiquitination/deubiquitination cycles alter chromatin structure, which may limit accessibility of DNA repair proteins to damaged sites. In the present study, we focused on the relationship between the ubiquitination status of histone H2A, the structure of chromatin, and the efficiency of nucleotide excision repair (NER) of cisplatin-DNA adducts in human ovarian carcinoma cells exposed to the antitumor drug cisplatin. Pretreating cells with the proteasome inhibitor lactacystin (LC) or N-acetyl-leucyl-leucyl-norleucinal (ALLnL) induced deubiquitination of ubiquitinated histone H2A (uH2A) and concomitantly promoted chromatin condensation, increased the extent of cisplatin-DNA adducts, and diminished NER-dependent repair of cisplatin-DNA lesions, compared with control cells treated with cisplatin alone. Both proteasome inhibitors also prevented the increase in ERCC-1 mRNA expression that occurs in cells exposed to cisplatin. Cells treated with the combination of ALLnL and cisplatin underwent apoptosis, as indicated by caspase-dependent poly(ADP-ribose) polymerase (PARP) cleavage, more quickly than cells treated with either agent alone. Additionally, the combination of ALLnL and cisplatin potently increased p53 levels in cell lysates and stimulated the binding of p53 to chromatin. Together, these observations suggest that proteasome inhibition may be exploited therapeutically for its potential to sensitize ovarian tumor cells to cisplatin.
authors.affiliation: Tumor Cell Biology Section, Cell and Cancer Biology Department, Medicine Branch, National Cancer Institute, NIH, 20892, Bethesda, MD 20892, USA. edmim@boe-e.nih.gov
authors.forename: E G
authors.initials: EG
authors.lastname: Mimnaugh
authors.forename: M K
authors.initials: MK
authors.lastname: Yunmbam
authors.forename: Q
authors.initials: Q
authors.lastname: Li
authors.forename: P
authors.initials: P
authors.lastname: Bonvini
authors.forename: S G
authors.initials: SG
authors.lastname: Hwang
authors.forename: J
authors.initials: J
authors.lastname: Trepel
authors.forename: E
authors.initials: E
authors.lastname: Reed
authors.forename: L
authors.initials: L
authors.lastname: Neckers
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D002478:Cells, Cultured; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology*; D003546:Cysteine Endopeptidases; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004247:DNA / Q000737:chemistry / Q000187:drug effects; D018736:DNA Adducts; D004260:DNA Repair / Q000187:drug effects*; D004268:DNA-Binding Proteins; D004347:Drug Interactions; D004720:Endonucleases; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D006657:Histones / Q000378:metabolism; D006801:Humans; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D010051:Ovarian Neoplasms / Q000473:pathology; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D002843:Chromatin; D018736:DNA Adducts; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D006657:Histones; D009097:Multienzyme Complexes; D011506:Proteins; D012333:RNA, Messenger; D014452:Ubiquitins; C116500:acetyl-leucinal-nor-leucinal; C057270:cisplatin-DNA adduct; C067713:lactacystin; D004247:DNA; C499320:PARP1 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; C071447:ERCC1 protein, human; D004720:Endonucleases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D007930:Leucine; D002945:Cisplatin; D000111:Acetylcysteine