Induction of caspase activity in HTLV-1–transformed cells treated with shRNA specific for HIAP-1. The HTLV-1–transformed T-cell lines (MT-2 and C91-PL) and HTLV-1–negative control cells (HuT-78) were infected with lentiviruses containing shRNAs specific for HIAP-1 (siHIAP), nonsense shRNAs (sinon), empty lentiviruses (vector), and were mock-infected. In these cultures the activity of caspases 3/7 was determined by means of a substrate that releases aminoluciferin upon cleavage by these caspases. Aminoluciferin, which is proportional to the amount of active caspases 3/7, was measured in a luciferase reaction. The relative caspases 3/7 activity in cells was calculated as multiple of the empty vector control. As an apoptosis control, uninfected cells were treated with 1 μg/mL etoposide (etop.) for 24 hours. ▦ indicates unselected cultures; ▪, cultures treated with blasticidin.