Fig. 4.

TRAIL induces RyR-dependent calcium spike formation. (A) Total internal reflection fluorescence microscopy (TIRFM) time-lapse images of MDA-MB-231 expressing GCaMP6f after TRAIL incubation (100 ng/mL) in the presence or absence of Ry. (Scale bars: 5 μm.) (B) Quantification of Ca²⁺ oscillations in control, TRAIL, and TRAIL+Ry-treated cells. Boxes illustrate the time course where the Ca²⁺ oscillations induced by TRAIL shown in A occurred. (C) Quantification of Ca²⁺ oscillations in TRAIL + caspase-8 inhibitor (Z-IETD-FMK, 20 µM) -treated cells. (D) TRAIL and TfnR uptake in control cells (Ctrl) and cells pretreated with caspase-8 inhibitor 30 min before the uptake assay. Internalization rates were calculated relative to surface bound TRAIL or TfnR, respectively. All of the results are mean values ± SD (n = 3). Two-tailed Student’s t tests were used to assess statistical significance. *P < 0.05, **P < 0.005.