title: Effect of proteasome inhibition on toxicity and CYP3A23 induction in cultured rat hepatocytes: comparison with arsenite.
abstract: Previous work in our laboratory has shown that acute exposure of primary rat hepatocyte cultures to non-toxic concentrations of arsenite causes major decreases in the DEX-mediated induction of CYP3A23 protein, with minor decreases in CYP3A23 mRNA. To elucidate the mechanism for these effects of arsenite, the effects of arsenite and proteasome inhibition, separately and in combination, on induction of CYP3A23 protein were compared. The proteasome inhibitor, MG132, inhibited proteasome activity, but also decreased CYP3A23 mRNA and protein. Lactacystin, another proteasome inhibitor, decreased CYP3A23 protein without affecting CYP3A23 mRNA at a concentration that effectively inhibited proteasome activity. This result, suggesting that the action of lactacystin is similar to arsenite and was post-transcriptional, was confirmed by the finding that lactacystin decreased association of DEX-induced CYP3A23 mRNA with polyribosomes. Both MG132 and lactacystin inhibited total protein synthesis, but did not affect MTT reduction. Arsenite had no effect on ubiquitination of proteins, nor did arsenite significantly affect proteasomal activity. These results suggest that arsenite and lactacystin act by similar mechanisms to inhibit translation of CYP3A23.
authors.affiliation: Veterans Administration Medical Center, White River Junction, VT 05009, USA.
authors.forename: Trisha L
authors.initials: TL
authors.lastname: Noreault-Conti
authors.forename: Judith M
authors.initials: JM
authors.lastname: Jacobs
authors.forename: Heidi W
authors.initials: HW
authors.lastname: Trask
authors.forename: Steven A
authors.initials: SA
authors.lastname: Wrighton
authors.forename: Jacqueline F
authors.initials: JF
authors.lastname: Sinclair
authors.forename: Ralph C
authors.initials: RC
authors.lastname: Nichols
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000633:toxicity; D000818:Animals; D018053:Arsenites / Q000633:toxicity*; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000633:toxicity; D051544:Cytochrome P-450 CYP3A; D003907:Dexamethasone / Q000494:pharmacology; D004347:Drug Interactions; D022781:Hepatocytes / Q000187:drug effects* / Q000201:enzymology; D007976:Leupeptins / Q000633:toxicity; D008297:Male; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects; D061988:Proteasome Inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D018053:Arsenites; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D061988:Proteasome Inhibitors; D012333:RNA, Messenger; C067713:lactacystin; D003907:Dexamethasone; D001189:Aryl Hydrocarbon Hydroxylases; C465138:Cyp3a23-3a1 protein, rat; D051544:Cytochrome P-450 CYP3A; D046988:Proteasome Endopeptidase Complex; C015001:arsenite; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine