T Cell Activation Induces Synthesis of CD47 Proteoglycan Isoforms and Their Release in Extracellular Vesicles.

Thrombospondin-1 potently inhibits T cell activation by engaging its cell surface receptor CD47. This inhibitory signal requires glycosaminoglycan modification of CD47. CD47 also regulates the composition of RNAs in extracellular vesicles released by T cells and their functional activities. Because CD47 is also present in extracellular vesicles, we examined the effect of T cell activation on CD47 glycoforms in T cells and extracellular vesicles released by these cells. Activation increased both heparan and chondroitin sulfate biosynthesis by globally inducing mRNA levels of the respective glycosaminoglycan synthases and sulfotransferases. T cell activation in the presence of thrombospondin-1 inhibited induction of these biosynthetic enzymes, but not in cells lacking CD47. Therefore, CD47 signaling controls its own post-translational modification by glycosaminoglycans that are required for thrombospondin-1 signaling. Activation of Jurkat T lymphoblasts and primary CD4 and CD8 T cells increased the release of proteoglycan isoforms of CD47 and amyloid precursor-like protein-2 associated with extracellular vesicles and smaller macromolecular complexes. However, cell surface levels of CD47 were minimally changed during activation. BJAB and RAJI B cell lines also produced CD47 extracellular vesicles and showed increased release of highly glycosylated CD47 following B cell receptor engagement. Therefore, T and B lymphocyte activation results in a selective increase in the synthesis and release of extracellular vesicles containing proteoglycan isoforms of CD47.