Targeting Mcl-1 enhances DNA replication stress sensitivity to cancer therapy
Guo Chen, … , Paul W. Doetsch, Xingming Deng
Guo Chen, … , Paul W. Doetsch, Xingming Deng
Published December 11, 2017
Citation Information: J Clin Invest. 2018;128(1):500-516. https://doi.org/10.1172/JCI92742.
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Research Article Cell biology

Targeting Mcl-1 enhances DNA replication stress sensitivity to cancer therapy

Abstract

DNA double-strand breaks (DSBs) are mainly repaired either by homologous recombination (HR) or by nonhomologous end-joining (NHEJ) pathways. Here, we showed that myeloid cell leukemia sequence 1 (Mcl-1) acts as a functional switch in selecting between HR and NHEJ pathways. Mcl-1 was cell cycle–regulated during HR, with its expression peaking in S/G2 phase. While endogenous Mcl-1 depletion reduced HR and enhanced NHEJ, Mcl-1 overexpression resulted in a net increase in HR over NHEJ. Mcl-1 directly interacted with the dimeric Ku protein complex via its Bcl-2 homology 1 and 3 (BH1 and BH3) domains, which are required for Mcl-1 to inhibit Ku-mediated NHEJ. Mcl-1 also promoted DNA resection mediated by the Mre11 complex and HR-dependent DSB repair. Using the Mcl-1 BH1 domain as a docking site, we identified a small molecule, MI-223, that directly bound to BH1 and blocked Mcl-1–stimulated HR DNA repair, leading to sensitization of cancer cells to hydroxyurea- or olaparib-induced DNA replication stress. Combined treatment with MI-223 and hydroxyurea or olaparib exhibited a strong synergy against lung cancer in vivo. This mechanism-driven combination of agents provides a highly attractive therapeutic strategy to improve lung cancer outcomes.

Authors

Guo Chen, Andrew T. Magis, Ke Xu, Dongkyoo Park, David S. Yu, Taofeek K. Owonikoko, Gabriel L. Sica, Sarah W. Satola, Suresh S. Ramalingam, Walter J. Curran, Paul W. Doetsch, Xingming Deng

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Figure 7

BH1 and BH3 domains are required for Mcl-1 promotion of HR-dependent DSB repair and clonogenic survival.

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BH1 and BH3 domains are required for Mcl-1 promotion of HR-dependent DSB...
(A) FLAG-tagged WT or individual Mcl-1 deletion mutants were transfected into Mcl1–/– MEFs. Mcl-1 expression was analyzed by Western blot using FLAG antibody. (B) Mcl1–/– MEFs expressing exogenous WT or individual Mcl-1 deletion mutants were treated with 0.2 mM Hu for 24 hours. After washing, cells were cultured in normal medium for another 24 hours. DSBs were analyzed by immunofluorescence using γ-H2AX antibody. Scale bar: 25 μm. The percentage of γ-H2AX–positive cells (left panel) and the number of γ-H2AX foci per cell (right panel) were determined by counting of at least 100 cells from each sample. Data represent the mean ± SD, n = 3 per group. ***P < 0.001, by 2-tailed t test. (C) Mcl1–/– MEFs expressing exogenous WT or individual Mcl-1 deletion mutants were treated with 0.2 mM Hu for 24 hours. After washing, cells were cultured in normal medium, followed by colony formation analysis. EV, empty vector. Data represent the mean ± SD, n = 3 per group. **P < 0.01, by 2-tailed t test.