title: Cytosolic Ku70 regulates Bax-mediated cell death.
abstract: The first known function of Ku70 is as a DNA repair factor in the nucleus. Using neuronal neuroblastoma cells as a model, we have established that cytosolic Ku70 binds to the pro-apoptotic protein Bax in the cytosol and blocks Bax's cell death activity. Ku70-Bax binding is regulated by Ku70 acetylation in that when Ku70 is acetylated Bax dissociates from Ku70, triggering cell death. We propose that Ku70 may act as a survival factor in these cells such that Ku70 depletion triggers Bax-dependent cell death. Here, we addressed two fundamental questions about this model: (1) Does all Bax, which is a cytosolic protein, bind to all cytosolic Ku70? and (2) Is Ku70 a survival factor in cells types other than neuronal neuroblastoma cells? We show here that, in neuronal neuroblastoma cells, only a small fraction of Ku70 binds to a small fraction of Bax; most Bax is monomeric. Interestingly, there is no free or monomeric Ku70 in the cytosol; most cytosolic Ku70 is in complex with other factors forming several high molecular weight complexes. A fraction of cytosolic Ku70 also binds to cytosolic Ku80, Ku70's binding partner in the nucleus. Ku70 may not be a survival factor in some cell types (Ku70-depletion less sensitive) because Ku70 depletion does not affect survival of these cells. These results indicate that, in addition to Ku70 acetylation, other factors may be involved in regulating Ku70-Bax binding in the Ku70-depletion less sensitive cells because Ku70 acetylation in these cells is not sufficient to dissociate Bax from Ku70 or to activate Bax.
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Manila
authors.initials: M
authors.lastname: Hada
authors.affiliation: General Surgery, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Chitra
authors.initials: C
authors.lastname: Subramanian
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA.
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Andrews
authors.affiliation: Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI, USA. rkwok@umich.edu.|Obstetrics and Gynecology, University of Michigan Medical School, 1150 West Medical Center Drive, Ann Arbor, MI, 48109, USA. rkwok@umich.edu.
authors.forename: Roland P S
authors.initials: RP
authors.lastname: Kwok
mesh_terms: D000107:Acetylation; D017209:Apoptosis; D015153:Blotting, Western; D049109:Cell Proliferation; D003600:Cytosol / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D047468:Immunoprecipitation; D000072200:Ku Autoantigen / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology*; D010051:Ovarian Neoplasms / Q000378:metabolism / Q000473:pathology*; D034741:RNA, Small Interfering / Q000235:genetics; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein / Q000378:metabolism*
chemical_list: C494826:BAX protein, human; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D000072200:Ku Autoantigen
keywords: apoptosis; histone deacetylase