Inhibition of proteasome deubiquitinating activity as a new cancer therapy

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Ubiquitin-tagged substrates are degraded by the 26S proteasome, which is a multisubunit complex comprising a proteolytic 20S core particle capped by 19S regulatory particles1,2. The approval of bortezomib for the treatment of multiple myeloma validated the 20S core particle as an anticancer drug target3. Here we describe the small molecule b-AP15 as a previously unidentified class of proteasome inhibitor that abrogates the deubiquitinating activity of the 19S regulatory particle. b-AP15 inhibited the activity of two 19S regulatory-particle–associated deubiquitinases, ubiquitin C-terminal hydrolase 5 (UCHL5) and ubiquitin-specific peptidase 14 (USP14), resulting in accumulation of polyubiquitin. b-AP15 induced tumor cell apoptosis that was insensitive to TP53 status and overexpression of the apoptosis inhibitor BCL2. We show that treatment with b-AP15 inhibited tumor progression in four different in vivo solid tumor models and inhibited organ infiltration in an acute myeloid leukemia model. Our results show that the deubiquitinating activity of the 19S regulatory particle is a new anticancer drug target.

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Figure 1: b-AP15 inhibits the UPS.
Figure 2: b-AP15 inhibits deubiquitination by the 19S regulatory particle (RP).
Figure 3: b-AP15 inhibits the 19S regulatory particle (RP) deubiquitinases UCHL5 and USP14.
Figure 4: b-AP15 inhibits tumor growth in vivo.

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We thank M. Glickman (Department of Biology, Technion-Israel Institute of Technology) for providing the Ub-GFP constructs, N. Dantuma (Department of Cell and Molecular Biology, Karolinska Institutet) for providing the MelJuSo Ub-YFP reporter cell line, B. Vogelstein (Sidney Kimmel Comprehensive Cancer Center, John Hopkins University) for providing the HCT-116 cell lines with targeted disruptions, L. Perup Segerström for technical advice, Uppsala Array Platform and L. Gatti for drug formulation. We thank Cancerfonden, Radiumhemmets forskningsfonder, Vetenskapsrådet, Strategiska forskningsstiftelsen, Vinnova, European Union CHEMORES, Frame Program 6 (LSHC-CT-2007-037665), Lions Cancerforskningsfond and Swedish Children Cancer Society for support.

Author information

All authors were involved in designing experiments and interpreting data. P.D. and S.B. carried out most of the experiments and contributed equally to this work. P.D. and S.L. wrote the manuscript. M.H.O. performed the immunohistochemisty. M.F. and R.L. performed the CMAP analysis and in vitro cytotoxicity analysis. K.L. performed deubiquitinase labeling. M.D.C. and P.P. performed the in vivo study on colon carcinoma xenografts. B.S. and M.H. performed the in vivo study and staining on the AML model.

Correspondence to Stig Linder.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–10, Supplementary Tables 1 and 2 and Supplementary Methods (PDF 3893 kb)

Supplementary Data

CMAP data of b-AP15 treated cells (XLS 964 kb)

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