ADP-ribose/TRPM2-mediated Ca2+ signaling is essential for cytolytic degranulation and antitumor activity of natural killer cells.

ABSTRACT

Natural killer (NK) cells are essential for immunosurveillance against transformed cells. Transient receptor potential melastatin 2 (TRPM2) is a Ca(2+)-permeable cation channel gated by ADP-ribose (ADPR). However, the role of TRPM2-mediated Ca(2+) signaling in the antitumor response of NK cells has not been explored. Here, we show that ADPR-mediated Ca(2+) signaling is important for cytolytic granule polarization and degranulation but not involved in target cell recognition by NK cells. The key steps of this pathway are 1) the activation of intracellular CD38 by protein kinase A following the interaction of the NK cell with a tumor cell results in the production of ADPR, 2) ADPR targets TRPM2 channels on cytolytic granules, and 3) TRPM2-mediated Ca(2+) signaling induces cytolytic granule polarization and degranulation, resulting in antitumor activity. NK cells treated with 8-Br-ADPR, an ADPR antagonist, as well as NK cells from Cd38(-/-) mice showed reduced tumor-induced granule polarization, degranulation, granzyme B secretion, and cytotoxicity of NK cells. Furthermore, TRPM2-deficient NK cells showed an intrinsic defect in tumoricidal activity. These results highlight CD38, ADPR, and TRPM2 as key players in the specialized Ca(2+) signaling system involved in the antitumor activity of NK cells.