Theranostics 2020; 10(20):9050-9065. doi:10.7150/thno.47897

Research Paper

Deubiquitinase USP7-mediated MCL-1 up-regulation enhances Arsenic and Benzo(a)pyrene co-exposure-induced Cancer Stem Cell-like property and Tumorigenesis

Ping Yang1,2, Jie Xie1,3, Yunfei Li1, Hsuan-Pei Lin1, William Fenske1, Marco Clementino1, Yiguo Jiang2, Chengfeng Yang1, Zhishan Wang1✉

1. Department of Toxicology and Cancer Biology, University of Kentucky College of Medicine, Lexington, Kentucky, USA.
2. School of Public Health, Guangzhou Medical University, Guangzhou, Guangdong, P.R. China.
3. School of Health Sciences, Wuhan University, Wuhan, Hubei, P.R. China.

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Yang P, Xie J, Li Y, Lin HP, Fenske W, Clementino M, Jiang Y, Yang C, Wang Z. Deubiquitinase USP7-mediated MCL-1 up-regulation enhances Arsenic and Benzo(a)pyrene co-exposure-induced Cancer Stem Cell-like property and Tumorigenesis. Theranostics 2020; 10(20):9050-9065. doi:10.7150/thno.47897. Available from

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Rationale: MCL-1 is up-regulated in cancer and a target for cancer treatment. How MCL-1 is up-regulated and whether MCL-1 up-regulation plays a role in tumorigenic process is not well-known. Arsenic and benzo(a)pyrene (BaP) are well-recognized lung carcinogens and we recently reported that arsenic and BaP co-exposure acts synergistically in inducing cancer stem cell (CSC)-like property and lung tumorigenesis. This study was performed to further investigate the underlying mechanism focusing on the role of MCL-1.

Methods: The spheroid formation assay and nude mouse tumorigenesis assay were used to determine the CSC-like property and tumorigenicity of arsenic plus BaP co-exposure-transformed human bronchial epithelial BEAS-2B cells, respectively. Biochemical, pharmacological and genetic approaches were used to manipulate gene expressions, dissect signaling pathways and determine protein-protein interactions. Both loss-of-function and gain-of-function approaches were used to validate the role of MCL-1 in arsenic plus BaP co-exposure-enhanced CSC-like property and tumorigenicity.

Results: Arsenic plus BaP co-exposure-transformed cells express significantly higher protein levels of MCL-1 than the passage-matched control, arsenic or BaP exposure alone-transformed cells. Knocking down MCL-1 levels in arsenic plus BaP co-exposure-transformed cells significantly reduced their apoptosis resistance, CSC-like property and tumorigenicity in mice. Mechanistic studies revealed that arsenic plus BaP co-exposure up-regulates MCL-1 protein levels by synergistically activating the PI3K/Akt/mTOR pathway to increase the level of a deubiquitinase USP7, which in turn reduces the level of MCL-1 protein ubiquitination and prevents its subsequent proteasome degradation.

Conclusions: The deubiquitinase USP7-mediated MCL-1 up-regulation enhances arsenic and BaP co-exposure-induced CSC-like property and tumorigenesis, providing the first evidence demonstrating that USP7 stabilizes MCL-1 protein during the tumorigenic process.

Keywords: USP7, MCL-1, arsenic, benzo(a)pyrene, cancer stem cell-like property