Mast cells are directly activated by cancer cell derived extracellular vesicles by a CD73 and adenosine dependent mechanism

Mast cells (MCs) are cells of the immune system that are best known for their involvement in allergic diseases. However, MCs are found in the tumor microenvironment (TME) and in most cases their number is correlated with poor prognosis. MCs are often found in the tumor periphery, rather than the tumor core, we explored the possibility that MCs could also be activated by cancer cell derived extracellular vesicles (EVs). To this goal, we exposed LAD-2 human MCs to EVs that we isolated from the conditioned media of Panc-1 human pancreatic ductal carcinoma cells, or H1299 human non-small cell lung carcinoma cells. We show that such EVs directly activate ERK1/2 signaling in the MCs. Further, we show that similarly to the MC activation by cancer cell contact, this activation involves autocrine formation of adenosine and signaling through the A3 adenosine receptor (A3R), as evident by the ability of adenosine 5`-(α , β -methylene) diphosphate (APCP), an inhibitor of the ecto enzyme CD73 that catalyzes adenosine formation, and MRS1220, a specific antagonist of the A3R, to inhibit EV-activated ERK1/2 signaling. We show that activation by either cell contact or EVs upregulates expression of angiogenic and tissue remodeling genes, including IL8, IL6, VEGF and amphiregulin. Our results suggest that MCs are directly activated in the TME by contact with either cancer cells or cancer cell-derived EVs, by a mechanism that is strictly dependent on CD73 and adenosine signaling through the A3R.