Mutations in parkin,a ubiquitin ligase,cause early-onset familial Parkinsons disease.There are many reports on the functions of parkin,but the precise mechanism of parkin/PARK2 effects in Parkinsons disease remains unknown.The purposes of this study were to investigate the cellular features of parkin wild type and mutants in cells,and their relation to mitochondrial function and cell viability.We constructed a parkin plasmid in a Tet-off system and established stable,parkin over-expressing cell lines.We observed parkin cellular distribution and function by immunofluorescence and immunoblotting.Cell viability and degeneration were analyzed by LDH,WST-1,and TUNEL assays.The results showed that (1) wild type parkin is nearly dispersed in the cytoplasm,while the mutants take the shape of small granular structures that form perinudear inclusions,causing mitochondrial dysfunction; and (2) parkin mutants enhance cellular toxicity,reduce cell viability,and promote cell degeneration.These data suggest that disease-causing mutations in parkin impair mitochondrial function and enhance cellular toxicity.