The mechanism of Ara-C-induced apoptosis of differentiating cerebellar granule neurons

Neurotoxicity is one of the side-effects of the therapeutically useful anti tumour agent, Ara-C (or 1-beta-D-arabinofuranosyl-cytosine, cytarabine). Th is agent is also reported to induce cell death of cultured neurons. In this study, we show that Ara-C-induced death of differentiating rat cerebellar granule neurons is prevented by cycloheximide at concentrations correspondi ng to its action in preventing protein synthesis. The death is accompanied by cleavage of the caspase substrate poly ADP ribose polymerase (PARP) and c-Abl-dependent activation of the stress-activated protein kinases c-Jun N- terminal kinase and p38. However, c-Jun levels do not rise and the activati on of the stress-activated protein kinases is not required for this form of neuronal death. Cyclin-dependent kinase (cdk) activity and inappropriate c ell-cycle re-entry have been implicated in some forms of death in different iated neurons. Here we show that Ara-C-induced death of cerebellar granule neurons is prevented by an inhibitor of cdk4, whereas inhibition of cdk1, - 2 and -5 mimics the death, and non-cdk4/6 cdks are inhibited by Ara-C treat ment. Cdk1 and -2 are dramatically downregulated during neuronal differenti ation, and neither Ara-C nor inhibition of these cdks induces death in matu re neurons. This mechanism could also play a significant role in the neurot oxicity associated with the therapeutic use of Ara-C, as cdk levels can be upregulated in stressed neurons of adult brain. We propose that the balance between cdk4/6 and cdk1/2/5 activity may determine the survival of early d ifferentiating neurons, and that DNA-damaging agents may induce neuronal de ath by inhibiting cdk1/2/5 under conditions which require these activities for survival.