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SKP2 loss destabilizes EZH2 by promoting TRAF6-mediated ubiquitination to suppress prostate cancer

Oncogene volume 36, pages 1364–1373 (2017)Cite this article

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Abstract

EZH2 is crucial for the progression of prostate cancer (PCa) and castration-resistant prostate cancer (CRPC) through upregulation and activation of progenitor genes, as well as androgen receptor (AR)-target genes. However, the mechanisms by which EZH2 is regulated in PCa and CRPC remain elusive. Here we report that EZH2 is post-transcriptionally regulated by SKP2 in vitro in cultured cells and in vivo in mouse models. We observed aberrant upregulation of Skp2, Ezh2 and histone H3 lysine 27 trimethylation (H3K27me3) in both Pten null mouse embryonic fibroblasts (MEFs) and Pten null mouse prostate tissues. Loss of Skp2 resulted in a striking decrease of Ezh2 levels in Pten/Trp53 double-null MEFs and in prostate tumors of Pten/Trp53 double-null mutant mice. SKP2 knockdown decreased EZH2 levels in human PCa cells through upregulation of TRAF6-mediated and lysine(K) 63-linked ubiquitination of EZH2 for degradation. Ectopic expression of TRAF6 promoted the K63-linked ubiquitination of EZH2 to decrease EZH2 and H3K27me3 levels in PCa cells. In contrast, TRAF6 knockdown resulted in a reduced EZH2 ubiquitination with an increase of EZH2 and H3K27me3 levels in PCa cells. Furthermore, the catalytically dead mutant TRAF6 C70A abolished the TRAF6-mediated polyubiquitination of recombinant human EZH2 in vitro. Most importantly, a concurrent elevation of Skp2 and Ezh2 was found in CRPC tumors of Pten/Trp53 mutant mice, and expression levels of SKP2 and EZH2 were positively correlated in human PCa specimens. Taken together, our findings revealed a novel mechanism on EZH2 ubiquitination and an important signaling network of SKP2-TRAF6-EZH2/H3K27me3, and targeting SKP2-EZH2 pathway may be a promising therapeutic strategy for CRPC treatment.

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Acknowledgements

We would like to thank Dr Jae-Il Park for Flag-EZH2 plasmid, Dr Paul Bates and Dr Zhaocai (Joe) Zhou for Myc-TRAF6 and Myc-TRAF6-C70A plasmids, Dr Edward W. Harhaj for ubiquitin and ubiquitin mutant plasmids, and Dr Hui-Kuan Lin for GST, GST-TRAF6 and GST-TRAF6-C70A plasmids. HA-tagged EZH2 is a gift from Kristian Helin (Addgene plasmid # 24230).54 This work was supported in part by NIH grants MD004038, DK055748, CA163069, MD007593 and UL1TR000445-06. Human tissue staining, microscopy experiments and data analysis were performed through the Human Tissue & Pathology Core and Morphology Core of Meharry Medical College, supported in part by NIH grants MD007593, MD007586, DA036420 and S10RR0254970.

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Authors and Affiliations

  1. Department of Biochemistry and Cancer Biology, Meharry Medical College, Nashville, TN, USA

    W Lu, S Liu, B Li, S E Adunyah & Z Chen

  2. Department of Biology, School of Science and Technology, Nazarbayev University, Astana, Republic of Kazakhstan

    Y Xie

  3. Department of Pathology, Anatomy and Cell Biology, Meharry Medical College, Nashville, TN, USA

    M G Izban & B R Ballard

  4. Department of Surgery, Meharry Medical College, Nashville, TN, USA

    S A Sathyanarayana

  5. Department of Urologic Surgery, Vanderbilt University School of Medicine, Nashville, TN, USA

    R J Matusik

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Lu, W., Liu, S., Li, B. et al. SKP2 loss destabilizes EZH2 by promoting TRAF6-mediated ubiquitination to suppress prostate cancer. Oncogene 36, 1364–1373 (2017). https://doi.org/10.1038/onc.2016.300

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