Activation of the receptor KIT induces the secretion of exosome-like small extracellular vesicles.

The receptor tyrosine kinase (RTK) KIT and its ligand stem cell factor (SCF) are essential for human mast cell (huMC) survival and proliferation. HuMCs expressing oncogenic KIT variants secrete large numbers of extracellular vesicles (EVs). The role KIT plays in regulating EV secretion has not been examined. Here, we investigated the effects of stimulation or inhibition of KIT activity on the secretion of small EVs (sEVs). In huMCs expressing constitutively active KIT, the quantity and quality of secreted sEVs positively correlated with the activity status of KIT. SCF-mediated stimulation of KIT in huMCs or murine MCs, or of transiently expressed KIT in HeLa cells, enhanced the release of sEVs expressing exosome markers. In contrast, ligand-mediated stimulation of the RTK EGFR in HeLa cells did not affect sEV secretion. The release of sEVs induced by either constitutively active or ligand-activated KIT was remarkably decreased when cells were treated with KIT inhibitors, concomitant with reduced exosome markers in sEVs. Similarly, inhibition of oncogenic KIT signalling kinases like PI3K, and MAPK significantly reduced the secretion of sEVs. Thus, activation of KIT and its early signalling cascades stimulate the secretion of exosome-like sEVs in a regulated fashion, which may have implications for KIT-driven functions.