Recent evidence suggests that unscheduled cell cycle activity leads to neuronal cell death. 3-Nitropropionic acid (3-NP) is an irreversible inhibitor of succinate dehydrogenase, and induces cell death in both striatum and cerebral cortex. Here we analyzed the involvement of aberrant cell cycle progression in 3-NP-induced cell death in these brain regions. 3-NP reduced level of cyclin-dependent kinase (CDK) inhibitor p27 in striatum, but not in cerebral cortex. 3-NP also induced phosphorylation of retinoblastoma protein, a marker of cell cycle progression at late G1 phase, only in striatum. Pharmacological experiments revealed that CDK activity and N-methyl-D-aspartate (NMDA) receptor were cooperatively involved in cell death by 3-NP in striatal neurons, while only NMDA receptor was involved in 3-NP-induced neurotoxicity in cortical neurons. Death of striatal neurons was preceded by elevation of somatic Ca²⁺ and activation of calpain, a Ca²⁺-dependent protease. Both striatal p27 down-regulation and cell death provoked by 3-NP were dependent on calpain activity. Moreover, transfection of p27 small interfering RNA reduced striatal cell viability. In cortical neurons, however, there was no change in somatic Ca²⁺ and calpain activity by 3-NP, and calpain inhibitors were not protective. These results suggest that 3-NP induces aberrant cell cycle progression and neuronal cell death via p27 down-regulation by calpain in striatum, but not in cerebral cortex. This is the first report for differential involvement of cell cycle reactivation in different brain regions and lightens the mechanism for region-selective vulnerability in human disease including Huntington disease.