Ubiquitin Conjugation Probed by Inflammation in Myeloid-Derived Suppressor Cell Extracellular Vesicles

Area of Science:

• Immunology
• Proteomics
• Cell Biology

Background:

• Myeloid-derived suppressor cells (MDSC) play a crucial role in tumor-associated inflammation and immune suppression.
• Extracellular vesicles (EV) are key mediators of intercellular communication, particularly in the tumor microenvironment.
• Ubiquitination is a critical post-translational modification regulating protein function and stability.

Purpose of the Study:

• To investigate the ubiquitinated proteome within extracellular vesicles (EV) released by myeloid-derived suppressor cells (MDSC).
• To examine the impact of tumor-associated inflammation on the ubiquitination landscape of proteins carried by MDSC-derived EVs.
• To explore the functional implications of ubiquitinated proteins in MDSC biology and their potential role in tumor progression.

Main Methods:

• Proteomic analysis of extracellular vesicles (EV) isolated from myeloid-derived suppressor cells (MDSC) of tumor-bearing mice under varying inflammation conditions.
• Identification and characterization of ubiquitinated proteins and their attachment sites using mass spectrometry-based proteomics.
• Bioinformatic analysis, including spectral counting and pathway analysis, to assess ubiquitination patterns and functional associations.

Main Results:

• A significant proportion of identified proteins within MDSC-derived EVs were ubiquitinated proteoforms, with over three ubiquitin-attachment sites per protein on average.
• Key pro-inflammatory proteins (S100 A8, S100 A9), histones, and transcription regulators were found to be ubiquitinated.
• Ubiquitination of proteins within MDSC EVs occurred independently of the level of tumor-associated inflammation.
• Some ubiquitinated proteins were linked to MDSC migration, a process associated with immune suppression and tumor progression.
• MDSC EVs were found to contain enzymes necessary for ubiquitination, suggesting potential in situ protein modification.

Conclusions:

• MDSC-derived EVs are rich in ubiquitinated proteins, regardless of inflammation status.
• Ubiquitination within MDSC EVs may contribute to MDSC migration and subsequent immune suppression.
• MDSC EVs possess the machinery for in situ ubiquitination, highlighting a novel mechanism for protein modification and intercellular signaling.