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.

Selective Proteasomal Degradation of the B′β Subunit of Protein Phosphatase 2A by the E3 Ubiquitin Ligase Adaptor Kelch-like 15

“…GFP-KLHL15 recovered in FLAG-BЈ␤ immunoprecipitates migrated close to its predicted molecular weight, as well as a smear near the stacker/running gel interface. This suggests that KLHL15 undergoes autoubiquitylation, as was reported for other KLHL proteins (15,(33)(34)(35)(36).…”

A Genome-Wide Association Study of Chronic Obstructive Pulmonary Disease in Hispanics

“…(27) It appears to play a role in the proteasome-degradation pathway. (42) The second most significant SNP in our analysis (rs286499) is in an intron of DLG2, a gene that may stabilize nicotinic acetylcholine receptors at neuronal synapses. (34) These are the same types of synapses that are encoded by the COPD susceptibility gene CHRNA3, (4) which may also play a role in nicotine addiction.…”

Expanding the clinical spectrum of recessive truncating mutations ofKLHL7to a Bohring-Opitz-like phenotype

“…It has been shown that KLHL7 forms a homodimer, binds with two Cullin-RING ligase complexes (CUL3 and ROC1) with its BTB and BACK domains and recruits the substrates for polyubiquitination through the Kelch region 14. A potential target of KLHL7 is histone 2A, suggesting a role in chromatin remodelling.…”