Involvement of retinoblastoma family members and E2F/DP complexes in the death of neurons evoked by DNA damage

Neuronal death evoked by DNA damage requires cyclin-dependent kinase 4 (Cdk 4) and 6 activity and is accompanied by elevation of cyclin D1-associated k inase activity. Because Cdk4/6 phosphorylates retinoblastoma protein (pRb) family members that then modulate the transcriptional activity of E2F/DP1 c omplexes, we examined the involvement of these components in DNA damage-evo ked neuronal death. Camptothecin induced rapid pRb and p107 phosphorylation at a Cdk4/6 phosphorylation site followed by selective loss of Rb and p107 . The CDK inhibitor flavopiridol suppressed pRb and p107 phosphorylation an d loss, implicating CDK activity in these events. Moreover, the loss of pRb and p107 appeared to be mediated by caspases because it was blocked by gen eral caspase inhibitors. The role of phosphorylation and pRb and p107 loss in the death pathway was indicated by observations that virally mediated ex pression of pRb mutated at sites of phosphorylation, including the Cdk4/6 s ite, inhibited death. Finally, expression of dominant-negative versions of DP1, known to compromise E2F transcriptional activity, protects cortical ne urons from death induced by camptothecin and sympathetic neurons from death evoked by UV treatment. Taken together, these results implicate the CDK-pR b/E2F/DP pathway as a required element in the neuronal death evoked by DNA damage.