JAK3A572V mutation causes constitutive JAK3 activity and IL-2–independent proliferation of NKTCL cells. JAK3A572V mutation causes constitutive JAK3 activity and IL-2–independent proliferation of NKTCL cells. A, NK-S1 cells were treated with 100 nmol/L JAK3 siRNA (si-JAK3) or control siRNA (si-Ctrl) for 24 hours before being subjected to proliferation assays up to 72 hours (right). In parallel, these cells were harvested, and protein extracts were subjected to Western blotting with antibodies against phosphorylated JAK3 (p-JAK3), phosphorylated STAT5 (p-STAT5), JAK3, STAT5, or β-actin as a normalization control. B, KHYG-1 cells were transiently transfected with wild-type JAK3 (JAK3 WT) or mutated JAK3 expression vectors (i.e., JAK3A572V). The relative p-JAK3, p-STAT5, JAK3, and STAT5 levels in these cells were detected by Western blotting (top), and proliferation assays using these cells were conducted for 48 hours with or without IL-2 (bottom). All results are expressed as mean ± SEM of 3 independent experiments. *, P < 0.05 compared with vehicle control (vehicle). Ghee Chong Koo et al. Cancer Discovery 2012;2:591-597 ©2012 by American Association for Cancer Research