The Deubiquitinase USP28 Stabilizes Expression of RecQ Family Helicases and Maintains the Viability of Triple Negative Breast Cancer Cells.

Abstract Triple-negative breast cancer lacks significant expression of the estrogen receptor, the progesterone receptor, and of human epidermal growth factor receptor. It is the most aggressive and malignant of all breast cancers, and for which there are currently no effective targeted therapies. We have shown previously that the RecQ helicase family member RECQL5 is essential for the proliferation and survival of TNBC cells; however, the mechanism of its involvement in cell viability has not been shown. Here we report that the expression of RecQ family helicases, including RECQL5, are regulated by the deubiquitinase USP28. We found using genetic depletion or a small molecule inhibitor that like RECQL5, USP28 is also essential for TNBC cells to proliferate in vitro and in vivo. Compromising the function of USP28 by shRNA knockdown or the inhibitor caused TNBC cells to arrest in S/G2 phases, concurrent with DNA damage checkpoint activation. We further showed that the small molecule inhibitor of USP28 displayed anti-tumor activity against xenografts derived from TNBC cells. Our results suggest that USP28 could be a potential therapeutic target for triple negative breast cancer.