A Comprehensive Proteomics Analysis Reveals a Secretory Path- and Status-Dependent Signature of Exosomes Released from Tumor-Associated Macrophages

Exosomes are 30–120 nm-sized
membrane vesicles of endocytic
origin that are released into the extracellular environment and play
roles in cell–cell communication. Tumor-associated macrophages
(TAMs) are important constituents of the tumor microenvironment; thus,
it is critical to study the features and complex biological functions
of TAM-derived exosomes. Here, we constructed a TAM cell model from
a mouse macrophage cell line, Ana-1, and performed comparative proteomics
on exosomes, exosome-free media, and cells between TAMs and Ana-1.
Proteomic analysis between exosome and exosome-free fractions indicated
that the functions of exosome dominant proteins were mainly enriched
in RNA processing and proteolysis. TAM status dramatically affected
the abundances of 20S proteasome subunits and ribosomal proteins in
their exosomes. The 20S proteasome activity assay strongly indicated
that TAM exosomes possessed higher proteolytic activity. In addition,
Ana-1- and TAM-derived exosomes have different RNA profiles, which
may result from differential RNA processing proteins. Taken together,
our comprehensive proteomics study provides novel views for understanding
the complicated roles of macrophage-derived exosomes in the tumor
microenvironment.