title: How an inhibitor of the HIV-I protease modulates proteasome activity.
abstract: The human immunodeficiency virus, type I protease inhibitor Ritonavir has been used successfully in AIDS therapy for 4 years. Clinical observations suggested that Ritonavir may exert a direct effect on the immune system unrelated to inhibition of the human immunodeficiency virus, type I protease. In fact, Ritonavir inhibited the major histocompatibility complex class I restricted presentation of several viral antigens at therapeutically relevant concentrations (5 microM). In search of a molecular target we found that Ritonavir inhibited the chymotrypsin-like activity of the proteasome whereas the tryptic activity was enhanced. In this study we kinetically analyzed how Ritonavir modulates proteasome activity and what consequences this has on cellular functions of the proteasome. Ritonavir is a reversible effector of proteasome activity that protected the subunits MB-1 (X) and/or LMP7 from covalent active site modification with the vinyl sulfone inhibitor(125)I-NLVS, suggesting that they are the prime targets for competitive inhibition by Ritonavir. At low concentrations of Ritonavir (5 microM) cells were more sensitive to canavanine but proliferated normally whereas at higher concentrations (50 microM) protein degradation was affected, and the cell cycle was arrested in the G(1)/S phase. Ritonavir thus modulates antigen processing at concentrations at which vital cellular functions of the proteasome are not yet severely impeded. Proteasome modulators may hence qualify as therapeutics for the control of the cytotoxic immune response.
authors.affiliation: Research Department, Cantonal Hospital St. Gall, CH-9007 St. Gallen, Switzerland.
authors.forename: G
authors.initials: G
authors.lastname: Schmidtke
authors.forename: H G
authors.initials: HG
authors.lastname: Holzhütter
authors.forename: M
authors.initials: M
authors.lastname: Bogyo
authors.forename: N
authors.initials: N
authors.lastname: Kairies
authors.forename: M
authors.initials: M
authors.lastname: Groll
authors.forename: R
authors.initials: R
authors.lastname: de Giuli
authors.forename: S
authors.initials: S
authors.lastname: Emch
authors.forename: M
authors.initials: M
authors.lastname: Groettrup
mesh_terms: D000818:Animals; D001665:Binding Sites; D002172:Canavanine / Q000494:pharmacology; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D003587:Cytomegalovirus; D017320:HIV Protease Inhibitors / Q000737:chemistry / Q000494:pharmacology*; D015497:HIV-1 / Q000201:enzymology; D006801:Humans; D017874:Immediate-Early Proteins / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D009842:Oligopeptides / Q000493:pharmacokinetics; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D020836:Protein Structure, Quaternary; D019438:Ritonavir / Q000737:chemistry / Q000494:pharmacology*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013450:Sulfones / Q000493:pharmacokinetics; D014452:Ubiquitins / Q000378:metabolism
chemical_list: C402690:4-hydroxy-3-iodo-2-nitrophenyl-leucyl-leucyl-leucine vinyl sulfone; D017320:HIV Protease Inhibitors; D017874:Immediate-Early Proteins; D007457:Iodine Radioisotopes; D009097:Multienzyme Complexes; D009842:Oligopeptides; D013450:Sulfones; D014452:Ubiquitins; C052612:cytomegalovirus immediate early phosphoprotein pp89; D002172:Canavanine; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D019438:Ritonavir