title: Generation of an indestructible cyclin B1 by caspase-6-dependent cleavage during mitotic catastrophe.
abstract: Overriding the G(2) DNA damage checkpoint permits precocious entry into mitosis that ultimately leads to mitotic catastrophe. Mitotic catastrophe is manifested by an unscheduled activation of CDK1, caspase activation and apoptotic cell death. We found that although cyclin B1 was required for mitotic catastrophe, it was cleaved into a approximately 35 kDa protein by a caspase-dependent mechanism during the process. Cyclin B1 cleavage occurred after Asp123 in the motif ILVD(123) downward arrow, and mutation of this motif attenuated the cleavage. Cleavage was abolished by a pan-caspase inhibitor as well as by specific inhibitors for the effector caspase-6 and the initiator caspase-8. Cleavage created a truncated cyclin B1 lacking part of the NH(2)-terminal regulatory domain that included the destruction box sequence. Although cleavage of cyclin B1 itself was not absolutely required for mitotic catastrophe, expression of the truncated product enhanced cell death. In support of this, ectopic expression of this truncated cyclin B1 was not only sufficient to induce mitotic block and apoptosis but also enhanced mitotic catastrophe induced by ionizing radiation and caffeine. These data underscore a possible linkage between mitotic and apoptotic functions by caspase-dependent processing of mitotic activators.
authors.affiliation: Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong.
authors.forename: Y W
authors.initials: YW
authors.lastname: Chan
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: R Y C
authors.initials: RY
authors.lastname: Poon
mesh_terms: D020816:Amino Acid Motifs; D019943:Amino Acid Substitution; D017209:Apoptosis / Q000502:physiology*; D002110:Caffeine / Q000494:pharmacology; D053178:Caspase 6 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism; D061945:Caspase Inhibitors; D019926:Cyclin B / Q000737:chemistry / Q000378:metabolism*; D056744:Cyclin B1; D004249:DNA Damage; D004317:Doxorubicin / Q000494:pharmacology; D005260:Female; D016195:G2 Phase / Q000502:physiology; D006367:HeLa Cells / Q000187:drug effects / Q000378:metabolism / Q000528:radiation effects; D006801:Humans; D008938:Mitosis / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016297:Mutagenesis, Site-Directed; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D015739:Nocodazole / Q000494:pharmacology; D011064:Poly Adenosine Diphosphate Ribose / Q000378:metabolism; D025941:Protein Interaction Mapping; D013379:Substrate Specificity
chemical_list: C534699:CCNB1 protein, human; D061945:Caspase Inhibitors; D019926:Cyclin B; D056744:Cyclin B1; D009363:Neoplasm Proteins; D011064:Poly Adenosine Diphosphate Ribose; D002110:Caffeine; D004317:Doxorubicin; C505514:CASP6 protein, human; D053178:Caspase 6; D053453:Caspase 9; D015739:Nocodazole