ACTIVATION OF CYCLIN A-DEPENDENT KINASES ASSOCIATED WITH WAF1 DEGRADATION DURING RADIATION-INDUCED APOPTOSIS

We describe here the further characterisation of the radiation respons e of a pair of isogenic Burkitt's lymphoma cell lines which differ sig nificantly in their susceptibility to radiation induced apoptosis. In both cases a marked inhibition of cyclin A-dependent kinase activity w as observed at 4 h post-irradiation which recovered to normal levels i n the susceptible line by 12 h but remained inhibited in the resistant cell line. Under these conditions the cellular abundance of p58(cycli nA) and p33(cdk2) did not significantly change in the two cell types a nd there was no evidence for phosphorylation changes in p33(cdk2) whic h might account for the activity differences. In parallel with the cha nges in activity, p21(WAF1) increased initially in both cell lines, de clined in the sensitive cell line as the activity recovered but remain ed high in the resistant cell line. This appears to be explained by a more rapid turn-over of p21(WAF1) in the sensitive cell line and an in creased association of p21(WAF1) with cyclin kinase as determined by i mmunoprecipitation. These results implicate p21(WAF1) in the regulatio n of cyclin-dependent kinases during radiation-induced apoptosis, with persistence of induced p21(WAF1) being associated with a more resista nt phenotype.