title: Caspase-3-mediated cleavage of Cdc6 induces nuclear localization of p49-truncated Cdc6 and apoptosis.
abstract: We show that Cdc6, an essential initiation factor for DNA replication, undergoes caspase-3-mediated cleavage in the early stages of apoptosis in HeLa cells and SK-HEP-1 cells induced by etoposide, paclitaxel, ginsenoside Rh2, or tumor necrosis factor-related apoptosis-inducing ligand. The cleavage occurs at the SEVD442/G motif and generates an N-terminal truncated Cdc6 fragment (p49-tCdc6) that lacks the carboxy-terminal nuclear export sequence. Cdc6 is known to be phosphorylated by cyclin A-cyclin dependent kinase 2 (Cdk2), an event that promotes its exit from the nucleus and probably blocks it from initiating inappropriate DNA replication. In contrast, p49-tCdc6 translocation to the cytoplasm is markedly reduced under the up-regulated conditions of Cdk2 activity, which is possibly due to the loss of nuclear export sequence. Thus, truncation of Cdc6 results in an increased nuclear retention of p49-tCdc6 that could act as a dominant negative inhibitor of DNA replication and its accumulation in the nucleus could promote apoptosis. Supporting this is that the ectopic expression of p49-tCdc6 not only promotes apoptosis of etoposide-induced HeLa cells but also induces apoptosis in untreated cells. Thus, the caspase-mediated cleavage of Cdc6 creates a truncated Cdc6 fragment that is retained in the nucleus and induces apoptosis.
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D020816:Amino Acid Motifs; D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D042846:CDC2-CDC28 Kinases / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D004261:DNA Replication; D005047:Etoposide / Q000494:pharmacology; D005434:Flow Cytometry; D036145:Ginsenosides / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D008562:Membrane Glycoproteins / Q000494:pharmacology; D019913:Nuclear Localization Signals / Q000378:metabolism*; D017239:Paclitaxel / Q000494:pharmacology; D010766:Phosphorylation; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D017304:Annexin A5; D051017:Apoptosis Regulatory Proteins; D036145:Ginsenosides; D008562:Membrane Glycoproteins; D019913:Nuclear Localization Signals; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D005047:Etoposide; C055305:ginsenoside Rh2; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D017239:Paclitaxel