Granzyme B induces apoptosis and cyclin A-associated cyclin-dependent kinase activity in all stages of the cell cycle.

Granzyme B rapidly induces apoptosis in the presence of the pore-forming protein perforin. We have examined the cell cycle restriction of this apoptosis by separating Jurkat cells into fractions representing different stages of the cell cycle by centrifugal elutriation. Cells were susceptible to apoptosis from G1 through to G2/M, with no significant resistance detected at any stage. Similarly, cells arrested at G1/S or G2/M with either hydroxyurea or nocodazole were slightly more sensitive than asynchronously growing cells. Granzyme B induces Cdc2 kinase activity and requires its induction for apoptosis. Cyclin-dependent kinase (CDK) activity is regulated by phosphorylation and association with cyclins that also control subcellular localization of the CDK/cyclin complexes. Cdc2 associates with both cyclin A, which is synthesized at G1 and S, and cyclin B, which is produced later during S and G2 before G2/M transition. We find that the CDK activity induced by granzyme B is associated primarily with cyclin A in both asynchronous and G1/S-arrested cells, while cyclin B-associated kinase activity is minimal. Because cyclin A is also able to associate with Cdk2, a kinase that is important for G1/S transition, we examined the activation of this CDK during granzyme B-induced apoptosis and find that Cdk2 is induced as rapidly as Cdc2. In conclusion, we have identified a lack of cell cycle restriction of granzyme B-induced apoptosis and the rapid activation of both cyclin A/Cdc2 and cyclin A/Cdk2 kinase activity.