title: Ubiquitin ligase activity of Cul3-KLHL7 protein is attenuated by autosomal dominant retinitis pigmentosa causative mutation.
abstract: Substrate-specific protein degradation mediated by the ubiquitin proteasome system (UPS) is crucial for the proper function of the cell. Proteins are specifically recognized and ubiquitinated by the ubiquitin ligases (E3s) and are then degraded by the proteasome. BTB proteins act as the substrate recognition subunit that recruits their cognate substrates to the Cullin 3-based multisubunit E3s. Recently, it was reported that missense mutations in KLHL7, a BTB-Kelch protein, are related to autosomal dominant retinitis pigmentosa (adRP). However, the involvement of KLHL7 in the UPS and the outcome of the adRP causative mutations were unknown. In this study, we show that KLHL7 forms a dimer, assembles with Cul3 through its BTB and BACK domains, and exerts E3 activity. Lys-48-linked but not Lys-63-linked polyubiquitin chain co-localized with KLHL7, which increased upon proteasome inhibition suggesting that KLHL7 mediates protein degradation via UPS. An adRP-causative missense mutation in the BACK domain of KLHL7 attenuated only the Cul3 interaction but not dimerization. Nevertheless, the incorporation of the mutant as a heterodimer in the Cul3-KLHL7 complex diminished the E3 ligase activity. Together, our results suggest that KLHL7 constitutes a Cul3-based E3 and that the disease-causing mutation inhibits ligase activity in a dominant negative manner, which may lead to the inappropriate accumulation of the substrates targeted for proteasomal degradation.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan.
authors.forename: Yu
authors.initials: Y
authors.lastname: Kigoshi
authors.forename: Fuminori
authors.initials: F
authors.lastname: Tsuruta
authors.forename: Tomoki
authors.initials: T
authors.lastname: Chiba
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001324:Autoantigens / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D044842:Cullin Proteins / Q000378:metabolism*; D005799:Genes, Dominant / Q000235:genetics; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D008247:Lysosomes / Q000378:metabolism; D051379:Mice; D009154:Mutation / Q000235:genetics*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D012174:Retinitis Pigmentosa / Q000235:genetics*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D001324:Autoantigens; C503645:CUL3 protein, human; D044842:Cullin Proteins; C505353:KLHL7 protein, human; D061988:Proteasome Inhibitors; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex