Regulation and deregulation of G2 checkpoint proteins with cisplatin

Background. The G2 checkpoint has a key role in the response to DNA damage. G2 arrest following DNA damage is associated with inactivation of the prot ein kinase cyclin B-cdc2. The role of changes in protein expression in enzy me inhibition is controversial. Methods. Expression of cyclin B1, cdc2, cdc 25c, total protein and DNA content were examined by flow cytometry in two l ung cancer cell lines. Changes in protein expression were compared to cell cycle matched controls under conditions associated with and without G2 arre st Results. Total protein increased with G2 arrest and decreased with cell death. Changes in cdc2, cdc25c and p16 paralleled changes in total protein. A larger increase in cyclin B1 was seen which was due to cell cycle redist ribution. Deregulation of cyclin B1 was seen with a sublethal dose of cispl atin. Conclusions. Our results do not support the model that changes in exp ression of cyclin B1 or other checkpoint proteins mediate G2 arrest after c isplatin.