Figure 4. CDK5 activity is required to activate the TAT-NBI1 treatment-induced recovery program. LLC–PK1 cells were transfected with a mock vector or with dominant-negative Cdk5 (DNcdk5) (A) or WtCDK5 (B). After 24 h of transfection, cells were treated as indicated in Figure 1, and the caspase-3/7 activity of cytosolic cell extracts was measured under the conditions described above. The cellular extracts of the LLC–PK1 cells were analyzed by western blot for the overexpression of CDK5 (right-hand panels).