UV light–induced activation of caspases and apoptosis in leukemic cells.

(A) UV light–induced procaspase-9 activation. Increased activity of caspase-9 in Apaf-1–transfected cells was compared with their wild type (*P < .0001; **P < .001). Processing of procaspase-9 was confirmed by immunoblotting. Caspase-9 precursors are indicated by an asterisk, and the processed caspase-9 is indicated by an arrowhead. (B) UV light–induced procaspase-3 activation. *P < .0001; **P < .01. Processing of procaspase-3 protein was indicated by immunoblotting. Caspase-9 precursors are indicated by an asterisk, and β-actin is indicated by an arrow. (C) UV light–induced apoptosis. Apaf-1–transfected cells were statistically significantly more sensitive than wild-type cells (*P < .0001).