The Deubiquitin Enzyme USP28 Maintains the Viability of Triple Negative Breast Cancer Cells through Stabilizing the RecQ Family Helicases

Abstract Background: Triple-negative breast cancer lacks significant expression of estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. It is the more aggressive and malignant kind of breast cancers and is currently without any effective targeted therapies. Methods: We have screened for genes in the ubiquitin-proteasome system that are essential for the proliferation and survival of TNBC cells via CRISPR/Cas9-mediated gene editing. Growth of TNBC cells were assayed using cell and tumor xenograft models to validate the vital role of USP28. We employed cell biology and biochemical methods to uncover the mechanisms underlying the requirement of USP28 for the proliferation of TNBC cells. Results: USP28, a deubiquitin enzyme, is an essential gene for TNBC cells in vitro and in vivo. Compromising the function of USP28 causes TNBC cells to arrest in S/G2 phases with DNA damage checkpoint activation. We show that RecQ family helicases are regulated by USP28, which is more important in TNBC cells than in other breast cancer cells. We further showed that a small molecule inhibitor of USP28 displayed anti-tumor activities against xenografts derived from TNBC cells. Conclusion: Our data establish a critical role played by USP28 in supporting the proliferation and viability of triple negative breast cancer cells through stabilizing RecQ family helicases and support USP28 as a therapeutic target for TNBC.