title: In vivo and in vitro peripheral-type benzodiazepine receptor polymerization: functional significance in drug ligand and cholesterol binding.
abstract: Peripheral-type benzodiazepine receptor (PBR) is an 18 kDa high-affinity drug ligand and cholesterol binding protein involved in various cell functions. Antisera for distinct PBR areas identified immunoreactive proteins of 18, 40, and 56 kDa and occasionally 72, 90, and 110 kDa in testicular Leydig and breast cancer cells. These sizes may correspond to PBR polymers and correlated to the levels of reactive oxygen species. Treatment of Leydig cells with human chorionic gonadotropin rapidly induced free radical, PBR polymer, and steroid formation. UV photoirradiation generates ROS species, which increased the size of intramembraneous particles of recombinant PBR reconstituted into proteoliposomes consistent with polymer formation, determined both by SDS-PAGE and by freeze-fracture electron microscopy. Spectroscopic analysis revealed the formation of dityrosines as the covalent cross-linker between PBR monomers. Moreover, photoirradiation increased PK 11195 drug ligand binding and reduced cholesterol binding capacity of proteoliposomes. Further addition of PK 11195 drug ligand to polymers increased the rate of cholesterol binding. These data indicate that reactive oxygen species induce in vivo and in vitro the formation of covalent PBR polymers. We propose that the PBR polymer might be the functional unit responsible for ligand-activated cholesterol binding and that PBR polymerization is a dynamic process modulating the function of this receptor in cholesterol transport and other cell-specific PBR-mediated functions.
authors.affiliation: Division of Hormone Research, Department of Cell Biology, Georgetown University Medical Center, Washington, DC 20057, USA.
authors.forename: Franck
authors.initials: F
authors.lastname: Delavoie
authors.forename: Hua
authors.initials: H
authors.lastname: Li
authors.forename: Matthew
authors.initials: M
authors.lastname: Hardwick
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Robert
authors.forename: Christoforos
authors.initials: C
authors.lastname: Giatzakis
authors.forename: Gabriel
authors.initials: G
authors.lastname: Péranzi
authors.forename: Zhi-Xing
authors.initials: ZX
authors.lastname: Yao
authors.forename: Jean
authors.initials: J
authors.lastname: Maccario
authors.forename: Jean-Jacques
authors.initials: JJ
authors.lastname: Lacapère
authors.forename: Vassilios
authors.initials: V
authors.lastname: Papadopoulos
mesh_terms: D000818:Animals; D002784:Cholesterol / Q000378:metabolism*; D019281:Dimerization; D066298:In Vitro Techniques; D008024:Ligands; D051379:Mice; D011485:Protein Binding; D011510:Proteolipids / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D011963:Receptors, GABA-A / Q000032:analysis / Q000378:metabolism*; D013053:Spectrophotometry; D014466:Ultraviolet Rays
chemical_list: D008024:Ligands; D011510:Proteolipids; D017382:Reactive Oxygen Species; D011963:Receptors, GABA-A; C020485:proteoliposomes; D002784:Cholesterol