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

Abstract

Ubiquitinated proteins carried by the extracellular vesicles (EV) released by myeloid-derived suppressor cells (MDSC) have been investigated using proteomic strategies to examine the effect of tumor-associated inflammation. EV were collected from MDSC directly following isolation from tumor-bearing mice with low and high inflammation. Among the 1092 proteins (high inflammation) and 925 proteins (low inflammation) identified, more than 50% were observed as ubiquitinated proteoforms. More than three ubiquitin-attachment sites were characterized per ubiquitinated protein, on average. Multiple ubiquitination sites were identified in the pro-inflammatory proteins S100 A8 and S100 A9, characteristic of MDSC and in histones and transcription regulators among other proteins. Spectral counting and pathway analysis suggest that ubiquitination occurs independently of inflammation. Some ubiquitinated proteins were shown to cause the migration of MDSC, which has been previously connected with immune suppression and tumor progression. Finally, MDSC EV are found collectively to carry all the enzymes required to catalyze ubiquitination, and the hypothesis is presented that a portion of the ubiquitinated proteins are produced in situ.

microRNAs Shape Myeloid Cell-Mediated Resistance to Cancer Immunotherapy

“…The MDSC chemotactics S100A8 and S100A9 are abundant in MDSC EVs and polarize macrophages into M2 phenotype (79). These pro-inflammatory proteins are characterized by multiple ubiquitination sites, and MDSC EVs were identified as carriers of enzymes catalyzing ubiquitination (80). Interestingly, EVs from TME-resident MDSC display a stronger immunosuppressive potential than those deriving from spleen or bone marrow MDSCs, suggesting the existence of different phenotypes and functions (81).…”

Regulatory Role of Immune Cell-Derived Extracellular Vesicles in Cancer: The Message Is in the Envelope

“…Recently, one of the areas of research in the immuno-oncology field has been focused on pharmacological inhibition of MDSC activity and combining these drugs with other known immunotherapeutic agents to improve therapeutic responses in cancer patients. A recent report suggested that common exosomal proteins (e.g., annexins, tetraspanins, cytoskeletal proteins, heat shock proteins) as well as several unique proteins are present in both MDSCs and MDSC-derived sEVs ( 143 , 144 ). These sEV-derived immune suppressive proteins participate in immune regulation in cancer-bearing hosts ( 143 , 144 ).…”

MicroRNA networks regulate the differentiation, expansion and suppression function of myeloid-derived suppressor cells in tumor microenvironment

“…Cancer cells secreted EVs, which were involved in the intercellular transfer of proteins, lipids, and genetic material (such as miRNAs). Those tumor-associated EVs represented an ideal candidate due to their ability to recirculate in body fluids during the process of MDSC generation from bone marrow in tumor microenvironment 29-31. In melanoma patients, some miRNAs (such as miR-99b, miR-100, miR-125a/-125b, miR-146a/-146b, miR-155, let-7e), which were highly detected in plasma as associated with EVs, mediated the generation and functional features of tumor M-MDSCs 8, 32, 33.…”