Targeting Deubiquitinating Enzymes (DUBs) That Regulate Mitophagy via Direct or Indirect Interaction with Parkin

Mitophagy in acute central nervous system injuries: regulatory mechanisms and therapeutic potentials

Acute central nervous system injuries, including ischemic stroke, intracerebral hemorrhage, subarachnoid hemorrhage, traumatic brain injury, and spinal cord injury, are a major global health challenge. Identifying optimal therapies and improving the long-term neurological functions of patients with acute central nervous system injuries are urgent priorities. Mitochondria are susceptible to damage after acute central nervous system injury, and this leads to the release of toxic levels of reactive oxygen species, which induce cell death. Mitophagy, a selective form of autophagy, is crucial in eliminating redundant or damaged mitochondria during these events. Recent evidence has highlighted the significant role of mitophagy in acute central nervous system injuries. In this review, we provide a comprehensive overview of the process, classification, and related mechanisms of mitophagy. We also highlight the recent developments in research into the role of mitophagy in various acute central nervous system injuries and drug therapies that regulate mitophagy. In the final section of this review, we emphasize the potential for treating these disorders by focusing on mitophagy and suggest future research paths in this area.

USP14 inhibits mitophagy and promotes tumorigenesis and chemosensitivity through deubiquitinating BAG4 in microsatellite instability-high colorectal cancer

BACKGROUND

Mitophagy, essential for cellular homeostasis, is involved in eliminating damaged mitochondria and is associated with cancer progression and chemoresistance. The specific impact of mitophagy on microsatellite instability-high (MSI-H) colorectal cancer (CRC) is still under investigation. Ubiquitination, a post-translational modification, is essential for controlling protein stability, localization, and function. This study identifies USP14, a deubiquitinating enzyme, as a key regulator of mitophagy in MSI-H CRC.

METHODS

A deubiquitinating enzyme (DUBs) siRNA library screening identified USP14 as a key regulator of mitophagy. Tissue samples from patients were analyzed using immunohistochemistry and Western blot. USP14 knockdown cell lines were generated using lentiviral transfection. Protein interactions between USP14 and BAG4 were confirmed by co-immunoprecipitation, while quantitative PCR was used to measure gene expression. Mitochondrial proteins were extracted to analyze mitophagy, and flow cytometry was used to assess apoptosis. Finally, a mouse xenograft model was employed to study USP14's role in tumor growth and oxaliplatin sensitivity.

RESULTS

Screening reveals that USP14 inhibits mitophagy and CRC (MSI-H) show high USP14 expression which correlates with poor prognosis. Functional analyses reveal that knocking down USP14 reduces tumor growth, and increases sensitivity to oxaliplatin. Mechanically, USP14 inhibits mitophagy by K48-deubiquitinating and stabilizing BAG4 at K403, which prevents the recruitment of Parkin to damaged mitochondria. The significant clinical relevance of USP14, BAG4, and PRKN are proved in tumor tissues.

CONCLUSIONS

The study highlights the USP14/BAG4/PRKN axis as a critical pathway in CRC (MSI-H), suggesting that targeting USP14 could inhibit tumor progression and improve chemotherapeutic outcomes. These findings underscore the importance of ubiquitination and mitophagy in cancer biology, indicating a potential therapeutic target for MSI-H CRC.

PRKN-linked familial Parkinson's disease: cellular and molecular mechanisms of disease-linked variants

Parkinson's disease (PD) is a common and incurable neurodegenerative disorder that arises from the loss of dopaminergic neurons in the substantia nigra and is mainly characterized by progressive loss of motor function. Monogenic familial PD is associated with highly penetrant variants in specific genes, notably the PRKN gene, where homozygous or compound heterozygous loss-of-function variants predominate. PRKN encodes Parkin, an E3 ubiquitin-protein ligase important for protein ubiquitination and mitophagy of damaged mitochondria. Accordingly, Parkin plays a central role in mitochondrial quality control but is itself also subject to a strict protein quality control system that rapidly eliminates certain disease-linked Parkin variants. Here, we summarize the cellular and molecular functions of Parkin, highlighting the various mechanisms by which PRKN gene variants result in loss-of-function. We emphasize the importance of high-throughput assays and computational tools for the clinical classification of PRKN gene variants and how detailed insights into the pathogenic mechanisms of PRKN gene variants may impact the development of personalized therapeutics.

USP26 promotes colorectal cancer tumorigenesis by restraining PRKN-mediated mitophagy

Deubiquitinating enzymes (DUBs) are promising targets for cancer therapy because of their pivotal roles in various physiological and pathological processes. Among these, ubiquitin-specific peptidase 26 (USP26) is a protease with crucial regulatory functions. Our study sheds light on the upregulation of USP26 in colorectal cancer (CRC), in which its increased expression correlates with an unfavorable prognosis. Herein, we evidenced the role of USP26 in promoting CRC tumorigenesis in a parkin RBR E3 ubiquitin-protein ligase (PRKN) protein-dependent manner. Our investigation revealed that USP26 directly interacted with PRKN protein, facilitating its deubiquitination, and subsequently reducing its activity. Additionally, we identified the K129 site on PRKN as a specific target for USP26-mediated deubiquitination. Our research highlights that a K-to-R mutation at the site on PRKN diminishes its potential for activation and ability to mediate mitophagy. In summary, our findings underscore the significance of USP26-mediated deubiquitination in restraining the activation of the PRKN-mediated mitophagy pathway, ultimately driving CRC tumorigenesis. This study not only elucidated the multifaceted role of USP26 in CRC but also introduced a promising avenue for therapeutic exploration through the development of small molecule inhibitors targeting USP26. This strategy holds promise as a novel therapeutic approach for CRC.

VDR and deubiquitination control neuronal oxidative stress and microglial inflammation in Parkinson's disease

Close correlation between vitamin D (VitD) deficiency and Parkinson's Disease (PD) risk, VitD as an adjuvant treatment promising to improve PD progression. However, VitD excessive intake could induce hypercalcemia and renal damage. Therefore, upregulation of vitD receptor (VDR) is considered a compensatory strategy to overcome VitD insufficiency and alleviate PD symptoms. In this study, we discovered that VDR played antioxidative roles in dopaminergic neurons by decreasing reactive oxygen species (ROS) and maintaining mitochondrial membrane potential. Further, we newly identified VDR downstream events in C. elegans, including glutathione S-transferase (gst) and forkhead box transcription factor class O (daf-16) mediated oxidative stress resistance. VDR upregulation also mitigated microglial activation through inhibition of NLRP3/caspase-1-mediated inflammation and membrane permeabilization. These findings highlight the multifaceted protective effects of VDR in both neurons and microglia against the development of PD. Importantly, we discovered a novel deubiquitinase DUB3, whose N-terminal catalytic domain interacted with the C-terminal ligand-binding domain of VDR to reduce VDR ubiquitination. Identification of DUB3 as an essential player in the deubiquitinating mechanism of VDR provides valuable insights into VDR regulation and its potential as a therapeutic target for PD.