E3 Ubiquitin Ligase UBR5 Drives the Growth and Metastasis of Triple-Negative Breast Cancer.

Patients with triple-negative breast cancers (TNBC) are at high risk for recurrence and metastasis at an early time despite standard treatment, underscoring the need for novel therapeutic modalities. Here, we report for the first time a distinctive and profound role of the E3 ubiquitin ligase UBR5 in the growth and metastasis of TNBC. An analysis of primary TNBC specimen by whole-exon sequencing revealed strong gene amplifications of UBR5 associated with the disease. UBR5 overexpression in TNBC tissues was confirmed at mRNA and protein levels. CRISPR/Cas9-mediated deletion of ubr5 in an experimental murine mammary carcinoma model of TNBC dramatically abrogated tumor growth and metastasis in vivo, which could be reversed completely via reconstitution with wild-type UBR5 but not a catalytically inactive mutant. Loss of UBR5 caused an impairment in angiogenesis within the tumor, associated with increased apoptosis, necrosis, and growth arrest. Absence of UBR5 in the tumor triggered aberrant epithelial-to-mesenchymal transition, principally via abrogated expression of E-cadherin, which resulted in severely reduced tumor metastasis to secondary organs. Use of NOD/SCID mice revealed that tumor-derived UBR5 facilitated tumor growth in a manner completely dependent upon immune cells in the microenvironment, whereas it promoted metastasis in a tumor cell-autonomous fashion. Our findings unveil UBR5 as a novel and critical regulator of tumor growth, metastasis, and immune response and highlight the potential for UBR5 as an effective therapeutic target for the treatment of highly aggressive breast and ovarian cancers that fail conventional therapy. Cancer Res; 77(8); 2090-101. ©2017 AACR. ©2017 American Association for Cancer Research.