Targeting MTAP increases PARP inhibitor susceptibility in triple-negative breast cancer through a feed-forward loop
Xiangyu Zeng, Fei Zhao, Xinyi Tu, Yong Zhang, Wen Yang, Jing Hou, Qi Jiang, Shouhai Zhu, Zheming Wu, Yalan Hao, Lingxin Zhang, Richard M. Weinshilboum, Kaixiong Tao, Liewei Wang, Zhenkun Lou
Xiangyu Zeng, Fei Zhao, Xinyi Tu, Yong Zhang, Wen Yang, Jing Hou, Qi Jiang, Shouhai Zhu, Zheming Wu, Yalan Hao, Lingxin Zhang, Richard M. Weinshilboum, Kaixiong Tao, Liewei Wang, Zhenkun Lou
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Research Article Oncology

Targeting MTAP increases PARP inhibitor susceptibility in triple-negative breast cancer through a feed-forward loop

Abstract

Triple-negative breast cancer (TNBC) represents the most malignant subtype of breast cancer. The clinical application of PARP inhibitors (PARPi) is limited by the low frequency of BRCA1/2 mutations in TNBC. Here, we identified that MTAP deletion sensitized genotoxic agents in our clinical cohort of metastatic TNBC. Further study demonstrated that MTAP deficiency or inhibition rendered TNBC susceptibility to chemotherapeutic agents, particularly PARPi. Mechanistically, targeting MTAP that synergized with PARPi by disrupting the METTL16-MAT2A axis involved in methionine metabolism and depleting in vivo s-adenosylmethionine (SAM) levels. Exhausted SAM in turn impaired PARPi-induced DNA damage repair through attenuation of MRE11 recruitment and end resection by diminishing MRE11 methylation. Notably, brain metastatic TNBC markedly benefited from a lower dose of PARPi and MTAP deficiency/inhibition synergy due to the inherently limited methionine environment in the brain. Collectively, our findings revealed a feed-forward loop between methionine metabolism and DNA repair through SAM, highlighting a therapeutic strategy of PARPi combined with MTAP deficiency/inhibition for TNBC.

Authors

Xiangyu Zeng, Fei Zhao, Xinyi Tu, Yong Zhang, Wen Yang, Jing Hou, Qi Jiang, Shouhai Zhu, Zheming Wu, Yalan Hao, Lingxin Zhang, Richard M. Weinshilboum, Kaixiong Tao, Liewei Wang, Zhenkun Lou

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Figure 3

PARPi regulates MAT2A intron retention by mediating METTL16 phosphorylation within Ser419.

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PARPi regulates MAT2A intron retention by mediating METTL16 phosphorylat...
(A and B) Representative Western blots (A) and quantitation (B) showing levels of MAT2A and METTL16 in HCC70 cells expressing control or METTL16 sgRNAs with or without cycloleucine (20 mM) treatment. (C) Schematic representation of RT-qPCR assay primers designed for total, intron retention (RI), or mature MAT2A mRNA. (D) RT-qPCR analysis of total, intron retention, and mature MAT2A mRNA levels in HCC70 cells with or without METTL16 KO treated with vehicle or cycloleucine (20 mM). (E–H) Representative Western blots and quantitation showing levels of MAT2A and METTL16 in HCC70 cells treated with the indicated dose of olaparib for 24 hours (E and F) or the indicated time period of olaparib at 5 μM (G and H). (I) RT-qPCR analysis of total, intron retention, and mature MAT2A mRNA levels in HCC70 cells treated with olaparib (5 μM), or cycloleucine (20 mM), or their combination. (J and K) Representative Western blots (J) and quantitation (K) showing levels of MAT2A and METTL16 in HCC70 cells expressing the indicated vectors treated with olaparib (5 μM), cycloleucine (20 mM), or their combination. (L) Schematic representation of PARPi downregulation of MAT2A expression by attenuation of its mRNA splicing through METTL16 conformational change induced by phosphorylation within Ser419. (A, E, G, and J) The experiment was repeated 3 times, and representative blots are presented. (B, D, F, H, I, and K) Data are shown as the mean ± SD from 3 independent experiments. P values are indicated. Significance was determined using (B, D, F, H, I, and K) 1-way ANOVA test.