T-plastin expression in CTCL cells induces apoptosis resistance to etoposide and FK506 pretreatment potentiates CTCL cell apoptosis to conventional etoposide. HuT-78 cells or PBLs from SS patients were pretreated by 10μM FK506 (FK506) or not (control) for 1 hour, before exposed to etoposide (2 or 5μM) or not (basal) for 24 hours. Apoptosis was determined by percentage of cells exhibiting a loss of mitochondrial transmembrane potential (ΔΨm), as assessed by DiOC6 staining and flow cytometry analysis. (A) Top panel: Results are representative data from 1 experiment with HuT-78 cells. Bottom panel: Results are expressed as mean percentages of apoptotic cells (± SD) in response to etoposide (2 or 5μM) exposure from 3 independent experiments. **P < .01, ***P < .001, comparison of FK506-pretreated HuT-78 cells (gray) with nonpretreated HuT-78 cells (white) exposed to the same respective concentration of etoposide. (B) As in panel A with T-plastin–positive PBLs from patients with SS. Top panel: Results are presented for 1 representative SS patient. Bottom panel: Results are expressed as mean (± SEM) fold increase in apoptosis of FK506-treated cells (gray) and FK506 untreated cells (white) relative to respective apoptosis of cells not exposed to apoptosis (basal) and taken as 1 to allow patient comparison (n = 6). *P < .05, **P < .01, comparison of FK506-pretreated PBLs with nonpretreated PBLs exposed to the same respective concentration of etoposide. (C) As in panel B, with T-plastin–negative PBLs from patients with SS. (D) HuT-78 cells were transiently transfected with control siRNA (400nM), NFAT1 siRNA (200nM) and NFAT2 siRNA (400nM), as well as PLS3 siRNA (200μM) 24 hours before treatment with etoposide (2 or 5μM) or not (basal) for further 24 hours. Results are representative of 3 independent experiments.