[Caspase-3 plays a required role in PC12 cell apoptotic death induced by roscovitine]

Roscovitine is a specific inhibitor of cyclin-dependent kinases (cdks) cdc2/cyclin B, cdk2/cyclin A, cdk2/cyclin E and cdk5/p35. The studies on the enzyme inhibitory properties and cellular effects of roscovitine revealed that it arrests cells in G(2)/M and G(1)/S phase, inhibits the proliferation of mammalian cells and induces cell death. However, the characteristics of cell death and exact mechanism by which this cdk inhibitor kills transformed cells are unknown. We previously investigated that the roscovitine induces apoptotic death of mitotic PC12 cells. The present study was to identify whether the roscovitine-induced death is related with the specific elements of caspases in pathway of apoptosis. The morphological data of caspase-3 immunofluorocytochemistry double staining with hoechst 33342 indicated that apoptotic nuclei were identified as nuclei with chromatin condensation and nuclear fragmentation, and that caspase-3 active p17 subunit co-existed in PC12 cells treated with roscovitine 50 micromol/L for 4 h. The number of the caspase-3 positive cells increased significantly to about 42%, as compared with the normal control (P<0.001). The data of MTT assay showed that the number of viable cells treated by roscovitine (50 micromol/L) alone for 12 h was 29.03%, of the untreated controls. Both a broad-spectrum caspase inhibitor Z-VAD-FMK (50 mumol/L) and a specific caspase-3 inhibitor Z-DEVD-FMK (100 micromol/L) increased viable PC12 cells to 45.16%, (Z-DEVD-FMK) and 58.06%, (Z-VAD-FMK), respectively, in the presence of roscovitine. Non-erythroid a-spectrin is a cytoskeleted protein that is a substrate of caspase-3 cysteine proteases. To confirm the activity of caspase-3 that produced in roscovitine (50 micromol/L for 12 h)-induced PC12 cell death, activated caspase-3 specific 120 kDa spectrin breakdown products (SBDP) were detected by Western bloting using the mouse anti-non-erythroid a-spectrin monoclonal antibody. The mean relative density of bands corresponding to caspase-3 specific SBDP levels were significantly increased in the cytosolic fractions treated with roscovitine, as compared to the normal control (P<0.001). These results indicate that caspase signals, especially caspase-3 signal are necessary for the progression of proliferating PC12 cell apoptotic death evoked by roscovintine.