EZH2, the catalytic subunit of the Polycomb repressive complex 2 (PRC2), silences gene transcription by methylating histone H3 at lysine 27. EZH2 is mutated or highly expressed in many types of cancer, including lymphoma, melanoma, prostate cancer, ovarian cancer, and breast cancer. Although EZH2 enzymatic inhibitors have recently shown antitumor effects in EZH2-mutated lymphoma and ARID1A-mutated ovarian cancer, many cancers do not respond, because EZH2 can promote cancer independently of its histone methyltransferase activity. We propose that an alternative strategy to treating EZH2-dependent tumors is to destroy EZH2 protein by targeting its deubiquitinase. By screening a human deubiquiti...

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EZH2, the catalytic subunit of the Polycomb repressive complex 2 (PRC2), silences gene transcription by methylating histone H3 at lysine 27. EZH2 is mutated or highly expressed in many types of cancer, including lymphoma, melanoma, prostate cancer, ovarian cancer, and breast cancer. Although EZH2 enzymatic inhibitors have recently shown antitumor effects in EZH2-mutated lymphoma and ARID1A-mutated ovarian cancer, many cancers do not respond, because EZH2 can promote cancer independently of its histone methyltransferase activity. We propose that an alternative strategy to treating EZH2-dependent tumors is to destroy EZH2 protein by targeting its deubiquitinase. By screening a human deubiquitinase library, we identified ZRANB1 as the deubiquitinase of EZH2. ZRANB1 binds, deubiquitinates, and stabilizes EZH2. Depletion of ZRANB1 in breast cancer cells resulted in destabilization of EZH2, inhibition of cell proliferation and migration, and induction of cell death, but had no effect on EZH2 or viability in normal mammary epithelial cells with no detectable ZRANB1 protein. Intriguingly, delivery of ZRANB1 siRNA via nanoliposomes led to marked antitumor and antimetastatic effects in a breast cancer model. Moreover, we found that a small-molecule inhibitor of ZRANB1 destabilized EZH2 and inhibited cell viability in a ZRANB1-dependent manner. In patients with breast cancer, ZRANB1 protein levels correlated with EZH2 protein levels and poor survival. These data suggest the therapeutic potential for targeting the EZH2 deubiquitinase ZRANB1. In future studies, we will pursue the following Specific Aims: 1) study the mechanism by which ZRANB1 regulates EZH2, PRC2, and downstream pathways; 2) determine whether ZRANB1 functions as a cancer-promoting deubiquitinase by stabilizing EZH2; and 3) investigate whether ZRANB1 is a therapeutically relevant anticancer target. If successful, this study will provide a novel and more effective strategy to treating EZH2-dependent tumors.

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