WSB1/2 target chromatin-bound lysine-methylated RelA for proteasomal degradation and NF-κB termination

TL;DR

This study identifies WSB1/2 as E3 ligases that target methylated RelA for degradation, helping to terminate NF-κB signaling and reduce inflammation.

Contribution

WSB1/2 are newly identified E3 ligases that specifically recognize and ubiquitinate methylated RelA at chromatin.

Findings

WSB1/2 bind to methylated lysines K314 and K315 of RelA via their WDR domains.

Mutation of a conserved aspartic acid in WSB2 disrupts its interaction with methylated RelA.

WSB1/2 promote ubiquitination and degradation of methylated RelA, terminating NF-κB activity.

Abstract

Proteasome-mediated degradation of chromatin-bound NF-κB is critical in terminating the transcription of pro-inflammatory genes and can be triggered by Set9-mediated lysine methylation of the RelA subunit. However, the E3 ligase targeting methylated RelA remains unknown. Here, we find that two structurally similar substrate-recognizing components of Cullin-RING E3 ligases, WSB1 and WSB2, can recognize chromatin-bound methylated RelA for polyubiquitination and proteasomal degradation. We showed that WSB1/2 negatively regulated a subset of NF-κB target genes via associating with chromatin where they targeted methylated RelA for ubiquitination, facilitating the termination of NF-κB-dependent transcription. WSB1/2 specifically interacted with methylated lysines (K) 314 and 315 of RelA via their N-terminal WD-40 repeat (WDR) domains, thereby promoting ubiquitination of RelA. Computational modeling further revealed that a conserved aspartic acid (D) at position 158 within the WDR domain of WSB2 coordinates K314/K315 of RelA, with a higher affinity when either of the lysines is methylated. Mutation of D158 abolished WSB2’s ability to bind to and promote ubiquitination of methylated RelA. Together, our study identifies a novel function and the underlying mechanism for WSB1/2 in degrading chromatin-bound methylated RelA and preventing sustained NF-κB activation, providing potential new targets for therapeutic intervention of NF-κB-mediated inflammatory diseases.

Graphical Abstract

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