ADRM1/RPN13 attenuates cartilage extracellular matrix degradation via enhancing UCH37-mediated ALK5 deubiquitination

Ubiquitin Receptor RPN13-Mediated "Candidatus Liberibacter asiaticus" Virulence Effector Degradation to Positively Regulate Immunity

Ubiquitin-proteasome is a conserved mechanism that regulates cellular responses and disease resistance in plants. However, the regulation role of ubiquitin-proteasome in the pathogenicity of "Candidatus Liberibacter asiaticus" (CLas), the causal agent of citrus Huanglongbing, one of the most serious citrus diseases, remains poorly defined. In this study, we identified a CLas effector, SDE5640 (CLIBASIA_05640), which downregulates salicylic acid signaling pathway genes and partial 26S proteasome genes in SDE5640-transgenic citrus shoots. SDE5640 suppresses proteasome activity to promote bacterial infection. Intriguingly, RPN13, a known component of the proteasome, was first identified as a new ubiquitin receptor. Overexpression of NbRPN13 leads to the degradation of SDE5640 via the 26S proteasome system. We further revealed that SDE5640 can be ubiquitinated in planta and that NbRPN13 promotes the degradation of SDE5640 by binding to ubiquitinated SDE5640. Furthermore, transient coexpression of SDE5640 and CsRPN13 enhances citrus resistance against Xanthomonas. Together, these results demonstrate that RPN13 recognizes the ubiquitination site of SDE5640 and specifically degrades it using the ubiquitin-proteasome system, which provides evidence for the role of ubiquitin-proteasome in CLas-citrus interactions.

Novel insights into the role of ubiquitination in osteoarthritis

Ubiquitination (Ub) and deubiquitination are crucial post-translational modifications (PTMs) that precisely regulate protein degradation. Under the catalysis of a cascade of E1-E2-E3 ubiquitin enzymes, ubiquitination extensively regulates protein degradation exerting direct impact on various cellular processes, while deubiquitination opposes the effect of ubiquitination and prevents proteins from degradation. Notably, such dynamic modifications have been widely investigated to be implicated in cell cycle, transcriptional regulation, apoptosis and so on. Therefore, dysregulation of ubiquitination and deubiquitination could lead to certain diseases through abnormal protein accumulation and clearance. Increasing researches have revealed that the dysregulation of catalytic regulators of ubiquitination and deubiquitination triggers imbalance of cartilage homeostasis that promotes osteoarthritis (OA) progression. Hence, it is now believed that targeting on Ub enzymes and deubiquitinating enzymes (DUBs) would provide potential therapeutic pathways. In the following sections, we will summarize the biological role of Ub enzymes and DUBs in the development and progression of OA by focusing on the updating researches, with the aim of deepening our understanding of the underlying molecular mechanism of OA pathogenesis concerning ubiquitination and deubiquitination, so as to explore novel potential therapeutic targets of OA treatment.