title: Lithium chloride inactivates the 20S proteasome from WEHI-3B D+ leukemia cells.
abstract: LiCl interacts synergistically with all-trans-retinoic acid, promoting the terminal differentiation of WEHI-3B D(+) cells, a phenomenon partially due to the ability of the monovalent lithium cation to inhibit the proteasome-dependent degradation of retinoic acid receptor alpha protein. In this report, the 20S proteasome was purified from WEHI-3B D(+) cells and the effects of LiCl on chymotrypsin-like (Chtl) activity and peptidyl-glutamyl peptide hydrolyzing (PGPH) activity were determined. LiCl functions to inactivate both proteasomal activities in a time-dependent manner, without affecting non-proteasomal proteases. The half-lives for inactivation of Chtl and PGPH hydrolyzing activities were approximately 23 and 36min, respectively, at 10mM LiCl. Both SDS and peptide substrate increased the rate of inactivation. Partial enzymatic activity was recovered after dialysis in the absence of SDS, indicating that the off-rate for lithium was extremely slow. The findings suggest that the inactivation of Chtl and PGPH activities by LiCl occurs through a proteasomal conformational change.
authors.affiliation: Department of Pharmacology and Developmental Therapeutics Program, Cancer Center, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Holtz
authors.forename: Anna M
authors.initials: AM
authors.lastname: Rice
authors.forename: Alan C
authors.initials: AC
authors.lastname: Sartorelli
mesh_terms: D000818:Animals; D002918:Chymotrypsin / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D007700:Kinetics; D007938:Leukemia / Q000201:enzymology*; D018021:Lithium Chloride / Q000494:pharmacology*; D009097:Multienzyme Complexes / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured
chemical_list: D015853:Cysteine Proteinase Inhibitors; D009097:Multienzyme Complexes; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D018021:Lithium Chloride