Functional Roles of the E3 Ubiquitin Ligase UBR5 in Cancer.

The Ubiquitin-Proteasome System (UPS) is an important regulator of cell signaling and proteostasis, which are essential to a variety of cellular processes. The UPS is disrupted in many diseases including cancer, and targeting the UPS for cancer therapy is gaining wide interest. E3 ubiquitin ligases occupy a key position in the hierarchical UPS enzymatic cascade, largely responsible for determining substrate specificity and ubiquitin (Ub) chain topology. The E3 ligase UBR5 (aka EDD1) is emerging as a key regulator of the UPS in cancer and development. UBR5 expression is deregulated in many cancer types and UBR5 is frequently mutated in mantle cell lymphoma. UBR5 is highly conserved in metazoans, has unique structural features, and has been implicated in regulation of DNA damage response, metabolism, transcription, and apoptosis. Hence, UBR5 is a key regulator of cell signaling relevant to broad areas of cancer biology. However, the mechanism by which UBR5 may contribute to tumor initiation and progression remains poorly defined. This review synthesizes emerging insights from genetics, biochemistry, and cell biology to inform our understanding of UBR5 in cancer. These molecular insights indicate a role for UBR5 in integrating/coordinating various cellular signaling pathways. Finally, we discuss outstanding questions in UBR5 biology and highlight the need to systematically characterize substrates, and address limitations in current animal models, to better define the role of UBR5 in cancer. ©2015 American Association for Cancer Research.