Ubiquitin-Specific Protease USP8 Regulates Endosome Maturation by Coordinating Rab5 and Rab7 GTPase Activation

Concepts de base

USP8 is recruited to Rab5-positive early endosomes through its interaction with the Rab5 guanine nucleotide exchange factor Rabex5, and this recruitment dissociates Rabex5 from endosomes while promoting the recruitment of the Rab7 guanine nucleotide exchange factor SAND-1/Mon1, thereby facilitating the transition from Rab5-positive early endosomes to Rab7-positive late endosomes and lysosomes.

Résumé

The study investigates the role of the ubiquitin-specific protease USP8 in the regulation of endosome maturation. The key findings are:

In USP8/USP-50 deficient cells, early endosomes (EEs) become enlarged while late endosomes/lysosomes are reduced in size. This is accompanied by the accumulation of abnormal vesicular structures containing abundant intraluminal vesicles (ILVs).

USP8/USP-50 is recruited to Rab5-positive EEs through its interaction with the Rab5 guanine nucleotide exchange factor (GEF) Rabex5. This recruitment dissociates Rabex5 from EEs and promotes the recruitment of the Rab7 GEF SAND-1/Mon1.

In the absence of USP8/USP-50, the level of active Rab5 is increased, while the Rab7 signal is decreased, leading to the accumulation of enlarged EEs and reduced late endosomes/lysosomes.

Overexpression of Rab7 can rescue the enlarged EE phenotype in USP8/USP-50 deficient cells, suggesting that USP8/USP-50 functions to promote the Rab5-to-Rab7 transition during endosome maturation.

The authors propose a model in which USP8/USP-50 recruitment to EEs, mediated by Rabex5, dissociates Rabex5 from the endosomes and facilitates the recruitment of the Rab7 GEF SAND-1/Mon1, thereby driving the maturation of EEs into late endosomes and lysosomes.

Stats

"The average size of those usp-50 mutant vesicles is significantly larger than wild type."
"In usp-50 mutants, the GFP::RAB-5 KI-labeled vesicles are significantly enlarged."
"The proportion of membrane-associated GFP::RAB-5 KI is also increased in usp-50 mutants."
"The total RAB-5 protein level is increased by usp-50 mutation."

Citations

"USP8 is recruited to Rab5-positive vesicles through Rabex5 and functions through both the endosomal dissociation of Rabex5 and recruitment of SAND-1/Mon1 to promote endosome maturation."
"In usp-50 mutants, the RABX-5 signal is enhanced, while the lysosome structures are reduced."
"Overexpressing rab-7 suppresses the enlarged early endosome phenotype of usp-50 mutants."

Idées clés tirées de

Spatiotemporal recruitment of the ubiquitin-specific protease USP8 directs endosome maturation

by Miao,Y., Du,... à www.biorxiv.org 01-11-2024

https://www.biorxiv.org/content/10.1101/2024.01.10.575034v2

Questions plus approfondies

How might the dysregulation of USP8-mediated endosome maturation contribute to the pathogenesis of USP8-related human diseases?

The dysregulation of USP8-mediated endosome maturation can have significant implications for the pathogenesis of USP8-related human diseases. USP8 plays a crucial role in the endosomal sorting of various transmembrane receptors, including growth factor receptor tyrosine kinases (RTKs). Dysfunctions in endosome maturation processes can lead to aberrant signaling cascades and impaired receptor trafficking, which are often associated with cancer progression and other diseases. For example, in cancer cells, dysregulated endosomal trafficking of RTKs can result in sustained activation of oncogenic signaling pathways, promoting cell proliferation, survival, and metastasis. Additionally, defects in endosome maturation can impact the turnover of cellular components, leading to the accumulation of toxic protein aggregates and impaired cellular homeostasis. Therefore, the disruption of USP8-mediated endosome maturation can contribute to the pathogenesis of USP8-related diseases by altering signaling pathways, protein turnover, and cellular homeostasis.

What other cellular pathways or processes might be impacted by the disruption of USP8 function in endosome maturation?

The disruption of USP8 function in endosome maturation can have broad implications for various cellular pathways and processes beyond receptor trafficking. Endosome maturation is intricately linked to multiple cellular functions, including membrane trafficking, protein degradation, and signal transduction. Therefore, the dysregulation of USP8-mediated endosome maturation can impact several key cellular pathways:

Protein Degradation Pathways: Endosome maturation plays a critical role in sorting ubiquitinated proteins for degradation in lysosomes. Disruption of USP8 function can affect the degradation of ubiquitinated cargos, leading to the accumulation of misfolded proteins and impaired proteostasis.

Signal Transduction: Endosomes serve as signaling platforms for various receptors, including RTKs. Alterations in endosome maturation processes can influence receptor signaling dynamics and downstream signaling cascades, impacting cell proliferation, differentiation, and survival.

Membrane Trafficking: Endosome maturation is essential for membrane trafficking and organelle biogenesis. Dysregulation of USP8-mediated endosome maturation can disrupt membrane dynamics, vesicle trafficking, and organelle homeostasis within the cell.

Autophagy: Endosomes are involved in the autophagy process, facilitating the degradation of damaged organelles and protein aggregates. Impaired endosome maturation due to USP8 dysfunction can affect autophagic flux and cellular quality control mechanisms.

Cellular Homeostasis: Proper endosome maturation is crucial for maintaining cellular homeostasis by regulating nutrient uptake, receptor turnover, and organelle function. Disruption of USP8 function in endosome maturation can perturb cellular homeostasis and contribute to disease pathogenesis.

Could the insights from this study on the role of USP8 in coordinating Rab5 and Rab7 activities be leveraged to develop novel therapeutic strategies for diseases associated with endolysosomal trafficking defects?

The insights from this study on the role of USP8 in coordinating Rab5 and Rab7 activities offer promising avenues for the development of novel therapeutic strategies for diseases associated with endolysosomal trafficking defects. Targeting the endolysosomal trafficking pathway, particularly the transition from Rab5 to Rab7-positive endosomes, holds great potential for therapeutic intervention in various diseases, including cancer and neurodegenerative disorders. Here are some potential therapeutic strategies based on the findings:

Targeting USP8: Modulating the activity of USP8, either through small molecule inhibitors or activators, could be a viable therapeutic approach to regulate endosome maturation and restore normal trafficking processes in diseases with endolysosomal defects.

Rab5 and Rab7 Modulators: Developing compounds that selectively target Rab5 or Rab7 activation could help restore the balance between early and late endosomal compartments, promoting efficient cargo sorting and degradation.

SAND-1/Mon1-Ccz1 Activators: Enhancing the recruitment and activation of SAND-1/Mon1-Ccz1 to promote Rab7-mediated endosome maturation could be a potential therapeutic strategy to correct endolysosomal trafficking defects.

Combination Therapies: Combinatorial approaches targeting multiple components of the endolysosomal trafficking pathway, including USP8, Rab5, Rab7, and SAND-1, may offer synergistic effects and improved therapeutic outcomes in diseases associated with endolysosomal defects.

By leveraging the insights from this study on the molecular mechanisms of endosome maturation and the coordination between Rab5 and Rab7 activities, novel therapeutic strategies can be developed to target endolysosomal trafficking pathways and address the pathogenesis of diseases linked to endolysosomal defects.