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 6

Mcl-1 promotes DNA resection in cell-free system and in cells.

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Mcl-1 promotes DNA resection in cell-free system and in cells. (A and B)...
(A and B) 5′-End-labeled forked DNA substrate was incubated with MR complex in the absence or presence of Ku and/or increasing concentrations of WT Mcl-1 protein (A) or individual Mcl-1 deletion mutant proteins (B). Resected DNA product was run on 16% urea-PAGE gel and analyzed by phosphoimager. (C) MEF WT and MEF Mcl1–/– cells were treated with Hu (0.2 mM) for 24 hours or CPT (1 μM) for 1 hour or exposed to IR (5 Gy), followed by immunostaining with anti-RPA2 antibody. Data represent the mean ± SD, n = 3 per group. **P < 0.01, by 2-tailed t test. Scale bar: 25 μm. (D) RPA2 phosphorylation at Ser4 and Ser8 was analyzed by Western blot using the S4/S8 dual-site phosphospecific RPA2 antibody following exposure of MEF WT or MEF Mcl1–/– cells to IR (5 Gy), Hu (0.2 mM) for 24 hours, or CPT (1 μM) for 1 hour.