Cleavage and degradation of Claspin during apoptosis by caspases and the proteasome.
Apoptosis plays a crucial role in development and tissue homeostasis. Some key survival pathways, such as DNA damage checkpoints and DNA repair, have been described to be inactivated during apoptosis. Here, we describe the processing of the human checkpoint protein Claspin during apoptosis. We observed cleavage of Claspin into multiple fragments in vivo. In vitro cleavage with caspases 3 and 7 of various fragments of the protein, revealed cut sites near the N- and C-termini of the protein. Using mass spectrometry, we identified a novel caspase cleavage site in Claspin at Asp25. Importantly, in addition to cleavage by caspases, we observed a proteasome-dependent degradation of Claspin under apoptotic conditions, resulting in a reduction of the levels of both full-length Claspin and its cleavage products. This degradation was not dependent upon the DSGxxS phosphodegron motif required for SCF(beta-TrCP)-mediated ubiquitination of Claspin. Finally, downregulation of Claspin protein levels by short interfering RNA resulted in an increase in apoptotic induction both in the presence and absence of DNA damage. We conclude that Claspin has antiapoptotic activity and is degraded by two different pathways during apoptosis. The resulting disappearance of Claspin from the cells further promotes apoptosis.
Semple
J I
JI
Unidad de Investigación, Hospital Universitario de Canarias. Ofra s/n, La Cuesta, 38320 La Laguna, Tenerife, Spain. semple.j@gmail.com
Smits
V A J
VA
Fernaud
J-R
JR
Mamely
I
I
Freire
R
R
D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D017209:Apoptosis / Q000502:physiology*; D064007:Ataxia Telangiectasia Mutated Proteins; D001483:Base Sequence; D001665:Binding Sites; D053148:Caspase 3 / Q000378:metabolism; D053179:Caspase 7 / Q000378:metabolism; D020169:Caspases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D000071877:Checkpoint Kinase 1; D004249:DNA Damage; D018922:HL-60 Cells; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008954:Models, Biological; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C488158:CLSPN protein, human; D018797:Cell Cycle Proteins; D010446:Peptide Fragments; D034741:RNA, Small Interfering; D011994:Recombinant Proteins; D011494:Protein Kinases; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D046988:Proteasome Endopeptidase Complex