CASP3 and infection: On the other hand, VRSA infection obviously triggered higher expression of the precursor (37 kDa) and cleaved forms (22 and 10 kDa) of caspase-9, thereafter leading to higher expression levels of pro-caspase-3 (35 kDa) and cleaved caspase-3 (20 and 11 kDa), which is the effector caspase, in A549-5.20 cells than in scrambled control cells (Figure 4).