Decreased expression of procaspase-2L prevents anti-Fas Ab–induced c-FLIP cleavage.

Kinetics of c-FLIP expression was monitored in U937/neo and U937/AS3 cells by Western blot analysis with 2 different Abs at the indicated times after anti-Fas Ab treatment. (A) Anti–c-FLIP polyclonal Ab from Upstate Biotechnology detected the 55-kd native protein. (B) Anti–c-FLIP polyclonal Ab from Pharmingen also detected a faint 12-kd band corresponding to a cleavage product.