title: Rapamycin inhibits proteasome activator expression and proteasome activity.
abstract: Rapamycin (RAPA) is a potent immunosuppressive drug, and certain of its direct or indirect targets might be of vital importance to the regulation of an immune response. In this study, we used differential hybridization to search for human genes whose expression was sensitive to RAPA. Seven RAPA-sensitive genes were found and one of them encoded a protein with high homology to the alpha subunit of a proteasome activator (PA28 alpha). This gene was later found to code for the beta subunit of the proteasome activator (PA28 beta). Activated T and B cells had up-regulated PA28 beta expression at the mRNA level. Such up-regulation could be suppressed by RAPA, FK506, and cyclosporin A. RAPA and FK506 also repressed the up-regulated PA28 alpha messages in phytohemagglutinin (PHA)-stimulated T cells. At the protein level, RAPA inhibited PA28 alpha and PA28 beta in the activated T cells according to immunoblotting and confocal microscopy. Probably as a consequence, there was a fourfold increase of proteasome activities in the peripheral blood mononuclear cell lysate after the PHA activation. RAPA could inhibit the enhanced part of the proteasome activity. Considering the critical role played by the proteasome in degrading regulatory proteins, our data suggest that the proteasome activator is a relevant and important downstream target of rapamycin, and that the immune response could be modulated through the activity of the proteasome.
authors.affiliation: Laboratory of Transplantation Immunology, Louis-Charles Simard Research Center, Montreal, Canada.
authors.forename: X
authors.initials: X
authors.lastname: Wang
authors.forename: S
authors.initials: S
authors.lastname: Omura
authors.forename: L I
authors.initials: LI
authors.lastname: Szweda
authors.forename: Y
authors.initials: Y
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Bérard
authors.forename: J
authors.initials: J
authors.lastname: Seminaro
authors.forename: J
authors.initials: J
authors.lastname: Wu
mesh_terms: D003546:Cysteine Endopeptidases / Q000187:drug effects* / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000276:immunology; D006367:HeLa Cells; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors* / Q000187:drug effects* / Q000378:metabolism; D009124:Muscle Proteins; D009693:Nucleic Acid Hybridization; D009928:Organ Specificity / Q000276:immunology; D011090:Polyenes / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011506:Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects; D020123:Sirolimus; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D015853:Cysteine Proteinase Inhibitors; D009097:Multienzyme Complexes; D009124:Muscle Proteins; C085047:PSME1 protein, human; D011090:Polyenes; D011506:Proteins; D012333:RNA, Messenger; C088683:multicatalytic protease activator; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D020123:Sirolimus