title: BRCA1 phosphorylation regulates caspase-3 activation in UV-induced apoptosis.
abstract: Apoptosis is implemented by death machinery that involves the caspase family of proteins, under the condition of a variety of stresses. Previous studies have shown that mouse embryonic stem cells deficient for caspase-3 are resistant to UV-induced apoptosis and that the active form of caspase-3 translocates to the nucleus. It has also been shown that the breast cancer tumor suppressor, BRCA1, is phosphorylated on Ser1423 and Ser1524 by the ataxia telangiectasia mutated-related kinase (ATR) after UV damage. Here, we show that activation of caspase-3 by UV is abrogated in BRCA1-mutated SNU251 and HCC1937 cells but was restored by reexpressing wild-type (wt) BRCA1, but not phosphorylation-deficient BRCA1Ser1423Ala/Ser1524Ala (BRCA1(S1423/1524A)). In SNU251 cells expressing BRCA1(S1423/1524A), the inhibitory interaction between X-linked inhibitor of apoptosis protein (XIAP) and caspase-9 remains intact after UV, compared with cells expressing wt BRCA1. We determined that XIAP and BRCA1 interact and upon phosphorylation this complex is disrupted. Nuclear translocation of active caspase-3 is detected only when wt BRCA1 is reexpressed. Consistent with this, Rad21, a known substrate of caspase-3, is cleaved only when wt BRCA1 is expressed in vivo. These results propose a model that inhibition of BRCA1 phosphorylation leads to the abrogation of a specific form of apoptosis that is mediated by caspase-3.
authors.affiliation: Department of Oncological Sciences, Mount Sinai School of Medicine, New York University, New York, New York 10029, USA.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Martin
authors.forename: Toru
authors.initials: T
authors.lastname: Ouchi
mesh_terms: D017209:Apoptosis / Q000502:physiology / Q000528:radiation effects*; D019313:BRCA1 Protein / Q000378:metabolism*; D053148:Caspase 3; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D042361:Mammary Glands, Human / Q000166:cytology / Q000201:enzymology / Q000528:radiation effects; D010766:Phosphorylation; D014466:Ultraviolet Rays; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism
chemical_list: D019313:BRCA1 Protein; D061945:Caspase Inhibitors; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases