Bcl-2 overexpression completely blocks NO-induced apoptosis in Jurkat leukemic cells. Cells transfected with neomycin vector only (J-Neo) or with bcl-2 expressing vector (J-Bcl-2) were incubated with NO donor GTN at different concentrations for 24 hours. Percentage of apoptotic cells was measured by the DNA-release assay using treatment with a hypotonic PI solution at 4°C overnight in the dark followed by flow cytometric analysis. Each bar represents the mean ± SD of three independent experiments.