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 4

Depletion of Mcl-1 downregulates HR and upregulates NHEJ.

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Depletion of Mcl-1 downregulates HR and upregulates NHEJ. (A) Schematic ...
(A) Schematic diagram of HR and NHEJ reporter systems. HR reporter is composed of 2 defective GFP genes that can be rescued only by HR, resulting in GFP fluorescence. In the NHEJ reporter, GFP is interrupted by an adenoviral exon (Ad2) and can be restored upon HindIII digestion and NHEJ repair. (B) HR activity was compared in WT and Mcl1–/– MEFs. Data represent the mean ± SD, n = 3 per group. **P < 0.01, by 2-tailed t test. (C) Mcl-1 was knocked down using Mcl-1 siRNA from U2OS DR-GFP cells, followed by analysis of HR activity. Data represent the mean ± SD, n = 3 per group. **P < 0.01, by 2-tailed t test. (D) NHEJ activity was compared in WT and Mcl1–/– MEFs. Data represent the mean ± SD, n = 3 per group. *P < 0.05, by 2-tailed t test.