MicroRNA-4443 regulates mast cell activation by T cell-derived microvesicles

The mechanism by which mast cells (MCs) are activated in T cell-mediated inflammatory processes remains elusive. Recently, we have shown that microvesicles derived from activated T cells (mvT*s) can stimulate MCs to degranulate and release several cytokines.

The aim of this study was to characterize the contribution of microRNAs (miRs) delivered by microvesicles to MC activation.

miR profiling was performed with NanoString technology and validated by using real-time PCR. The biological role of mvT* miR was verified by overexpression of miRs in MCs using mimic or inhibitory molecules and analyzing the effect on their predicted targets.

mvT*s were found to downregulate the expression of the tyrosine phosphatase protein tyrosine phosphatase receptor type J (PTPRJ), a known extracellular signal-regulated kinase inhibitor. Bioinformatics analysis predicted that miR-4443 regulates the PTPRJ gene expression. Indeed, miR-4443, which was present in mvT*s, was also found to be overexpressed in human MCs stimulated with these MVs. α-Amanitin insensitivity confirmed that overexpression of miR-4443 was not due to transcriptional activation. The luciferase reporter assay indicated that the 3' untranslated region of PTPRJ was targeted by this miR. Transfection of MCs with mimic or inhibitor of miR-4443 resulted in decreased or enhanced PTPRJ expression, respectively. Furthermore, miR-4443 regulated extracellular signal-regulated kinase phosphorylation and IL-8 release in MCs activated by mvT*s.

These results support a scenario by which T cell-derived microvesicles act as intercellular carriers of functional miR-4443, which might exert heterotypic regulation of PTPRJ gene expression in MCs, leading to their activation in the context of T cell-mediated inflammatory processes.