Role of Ku70 in deubiquitination of Mcl-1 and suppression of apoptosis

• Published in: Cell death and differentiation 2014-07, Vol.21 (7), p.1160-1169
• Main Authors: Wang, B, Xie, M, Li, R, Owonikoko, T K, Ramalingam, S S, Khuri, F R, Curran, W J, Wang, Y, Deng, X
• Format: Article
• Language: English
• Subjects: 631/80/474/582; 631/80/82/23; Animals; Antigens, Nuclear - physiology; Antineoplastic Agents - pharmacology; Apoptosis; Biochemistry; Biomedical and Life Sciences; Biphenyl Compounds - pharmacology; Cancer therapies; Cell Biology; Cell Cycle Analysis; Cell death; Cell Survival; DNA-Binding Proteins - physiology; Endoplasmic reticulum; Enzymes; Half-Life; HCT116 Cells; HEK293 Cells; Humans; Kinases; Ku Autoantigen; Life Sciences; Lung cancer; Mice; Mice, Nude; Myeloid Cell Leukemia Sequence 1 Protein - metabolism; Nitrophenols - pharmacology; Oncology; Original Paper; Phosphorylation; Piperazines - pharmacology; Protein Interaction Domains and Motifs; Protein Stability; Protein Transport; Proteins; Radiation; Staurosporine - pharmacology; Stem Cells; Sulfonamides - pharmacology; Ubiquitination; Xenograft Model Antitumor Assays; Yeast
• ISSN: 1350-9047; 1476-5403
• DOI: 10.1038/cdd.2014.42

Mcl-1 is a unique antiapoptotic Bcl2 family member with a short half-life due to its rapid turnover through ubiquitination. We discovered that Ku70, a DNA double-strand break repair protein, functions as a deubiquitinase to stabilize Mcl-1. Ku70 knockout in mouse embryonic fibroblast (MEF) cells or depletion from human lung cancer H1299 cells leads to the accumulation of polyubiquitinated Mcl-1 and a reduction in its half-life and protein expression. Conversely, expression of exogenous Ku70 in Ku70 −/− MEF cells restores Mcl-1 expression. Subcellular fractionation indicates that Ku70 extensively colocalizes with Mcl-1 in mitochondria, endoplasmic reticulum and nucleus in H1299 cells. Ku70 directly interacts with Mcl-1 via its C terminus (that is, aa 536–609), which is required and sufficient for deubiquitination and stabilization of Mcl-1, leading to suppression of apoptosis. Purified Ku70 protein directly deubiquitinates Mcl-1 by removing K48-linked polyubiquitin chains. Ku70 knockdown not only promotes Mcl-1 turnover but also enhances antitumor efficacy of the BH3-mimetic ABT-737 in human lung cancer xenografts. These findings identify Ku70 as a novel Mcl-1 deubiquitinase that could be a potential target for cancer therapy by manipulating Mcl-1 deubiquitination.