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Geng C, Kaochar S, Li M, Rajapakshe K, Fiskus W, Dong J, Foley C, Dong B, Zhang L, Kwon OJ, Shah SS, Bolaki M, Xin L, Ittmann M, O'Malley BW, Coarfa C, Mitsiades N. SPOP regulates prostate epithelial cell proliferation and promotes ubiquitination and turnover of c-MYC oncoprotein. Oncogene 2017; 36:4767-4777. [PMID: 28414305 PMCID: PMC5887163 DOI: 10.1038/onc.2017.80] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 01/16/2017] [Accepted: 02/26/2017] [Indexed: 12/13/2022]
Abstract
The E3 ubiquitin ligase adaptor speckle-type POZ protein (SPOP) is frequently dysregulated in prostate adenocarcinoma (PC), via either somatic mutations or mRNA downregulation, suggesting an important tumor suppressor function. To examine its physiologic role in the prostate epithelium in vivo, we generated mice with prostate-specific biallelic ablation of Spop. These mice exhibited increased prostate mass, prostate epithelial cell proliferation, and expression of c-MYC protein compared to littermate controls, and eventually developed prostatic intraepithelial neoplasia (PIN). We found that SPOPWT can physically interact with c-MYC protein and, upon exogenous expression in vitro, can promote c-MYC ubiquitination and degradation. This effect was attenuated in PC cells by introducing PC-associated SPOP mutants or upon knockdown of SPOP via short-hairpin-RNA, suggesting that SPOP inactivation directly increases c-MYC protein levels. Gene set enrichment analysis revealed enrichment of Myc-induced genes in transcriptomic signatures associated with SPOPMT. Likewise, we observed strong inverse correlation between c-MYC activity and SPOP mRNA levels in two independent PC patient cohorts. The core SPOPMT;MYCHigh transcriptomic response, defined by the overlap between the SPOPMT and c-MYC transcriptomic programs, was also associated with inferior clinical outcome in human PCs. Finally, the organoid-forming capacity of Spop-null murine prostate cells was more sensitive to c-MYC inhibition than that of Spop-WT cells, suggesting that c-MYC upregulation functionally contributes to the proliferative phenotype of Spop knock-out prostates. Taken together, our data highlight SPOP as an important regulator of luminal epithelial cell proliferation and c-MYC expression in prostate physiology, identify c-MYC as a novel bona fide SPOP substrate, and help explain the frequent inactivation of SPOP in human PC. We propose SPOPMT–induced stabilization of c-MYC protein as a novel mechanism that can increase total c-MYC levels in PC cells, in addition to amplification of c-MYC locus.
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Affiliation(s)
- C Geng
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - S Kaochar
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - M Li
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - K Rajapakshe
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - W Fiskus
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - J Dong
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - C Foley
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - B Dong
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - L Zhang
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - O-J Kwon
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - S S Shah
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - M Bolaki
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - L Xin
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Dan L Duncan Cancer Center, Houston, TX, USA
| | - M Ittmann
- Dan L Duncan Cancer Center, Houston, TX, USA.,Department of Pathology and Immunology and Michael E. DeBakey Veterans Affairs Medical Center, Houston, TX, USA
| | - B W O'Malley
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA
| | - C Coarfa
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Dan L Duncan Cancer Center, Houston, TX, USA
| | - N Mitsiades
- Department of Medicine, Baylor College of Medicine, Houston, TX, USA.,Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX, USA.,Dan L Duncan Cancer Center, Houston, TX, USA.,Center for Drug Discovery, Baylor College of Medicine, Houston, TX, USA
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