Figure 1. Critical role of TRPM2 for cytotoxicity of NK cells against tumor cells via Ca²⁺-dependent degranulation.

(a) Tumor cell-induced Ca²⁺ signals in NK cells from TRPM2^+/+ or TRPM2^−/− mice. Arrow indicates the time of addition of B16F10 tumor cells. Data are mean ± SEM of three independent experiments. *P < 0.001 vs basal; ^#P < 0.05. (b) Impairment of degranulation in TRPM2^−/− NK cells upon stimulation with B16F10 cells. TRPM2^+/+ or TRPM2^−/− NK cells were stimulated with target cells for 2 h at 37°C and then stained with FITC-conjugated anti-CD107a mAb and PE-conjugated anti-NK1.1 mAb. NK cells were gated on forward scatter/side scatter characteristics. (c) Reduced granzyme B release in tumor cell-stimulated TRPM2^−/− NK cells. The amount of granzyme B released into the media was measured by ELISA after incubation with NK cells and B16F10 cells for 30 min. (d) Decrease in cytolytic activity against B16F10 cells in TRPM2^−/− NK cells. TRPM2^+/+ or TRPM2^−/− NK cells were assessed for cytolytic activity against B16F10 target cells in a 4-h calcein-release assay. Data shown in b, c, and d are representative of three independent experiments. *P < 0.001. (e) B16F10 cells (1 × 10⁵) were injected into the flanks of TRPM2^+/+ and TRPM2^−/− mice (n = 10 per cohort), and tumor growth was monitored. *P < 0.001. (f) Kaplan-Meier plot of TRPM2^+/+ and TRPM2^−/− recipient mice after s.c. injection with B16F10 cells (1 × 10⁵) (n = 10 per cohort). (g) Antitumor effect of TRPM2^+/+ or TRPM2^−/− NK cells in the lung metastasis model of B16F10 cells. TRPM2^−/− mice (n = 4 per cohort) were injected i.v. with 1 × 10⁵ B16F10 melanoma cells. IL-2 activated NK cells (2 × 10⁶ cells) from TRPM2^+/+ or TRPM2^−/− mice were injected i.v. into B16F10-bearing TRPM2^−/− mice 2 d later. Lungs were harvested 14 d after and fixed with 4% paraformaldehyde, and metastatic nodules were counted. Representative images of lungs are shown. *P < 0.01.