Immunoblot analysis for caspases and PARP in myeloma cells exhibiting differential sensitivities to TRAIL.

MM.1S, ARH-77, and IM-9 cells were treated with TRAIL (300 ng/mL) for 0.5, 1, and 5 hours. Rapid cleavage of caspase-8, caspase-3, and PARP was observed in the TRAIL-sensitive MM.1S cells. Due to lower caspase-8 protein levels in TRAIL-resistant cells, longer exposures were used to ensure adequate visualization of the bands. Caspase-10 was not cleaved, excluding it as an apical caspase in the TRAIL pathway for MM. In the moderately TRAIL-resistant ARH-77 cells, cleavage of caspases and PARP was significantly inhibited, though eventually low-level cleavage of caspase-3 (on longer exposure of the film) and PARP was seen at 5 hours of treatment. No cleavage of any caspases or PARP was detected in highly TRAIL-resistant IM-9 cells.