Imaging-Based Screening of Deubiquitinating Proteases Identifies Otubain-1 as a Stabilizer of c-MYC

SIMPLE SUMMARY: The transcription factor c-MYC drives growth and proliferation in most cancers. The c-MYC protein is short-lived and rapidly degraded. However, deubiquitinating enzymes can counteract its degradation and increase the levels of this oncogenic protein. We altered the expression of 41 individual deubiquitinases and measured the abundance of c-MYC. We discovered that the deubiquitinating enzyme OTUB1 slows the degradation of the transcription factor c-MYC and increases its abundance in the nucleus. Further, patients with high expression of OTUB1 show poor clinical outcomes in the c-MYC-dependent cancer multiple myeloma. Finally, elevating OTUB1 expression in multiple myeloma cells stimulates more aggressive growth. Thus, inhibition of OTUB1 may blunt c-MYC activity, making it a promising target for cancer treatment. ABSTRACT: The ubiquitin–proteasome pathway precisely controls the turnover of transcription factors in the nucleus, playing an important role in maintaining appropriate quantities of these regulatory proteins. The transcription factor c-MYC is essential for normal development and is a critical cancer driver. Despite being highly expressed in several tissues and malignancies, the c-MYC protein is also continuously targeted by the ubiquitin–proteasome pathway, which can either facilitate or inhibit c-MYC degradation. Deubiquitinating proteases can remove ubiquitin chains from target proteins and rescue them from proteasomal digestion. This study sought to determine novel elements of the ubiquitin–proteasome pathway that regulate c-MYC levels. We performed an overexpression screen with 41 human proteases to identify which deubiquitinases stabilize c-MYC. We discovered that the highly expressed Otubain-1 (OTUB1) protease increases c-MYC protein levels. Confirming its role in enhancing c-MYC activity, we found that elevated OTUB1 correlates with inferior clinical outcomes in the c-MYC-dependent cancer multiple myeloma, and overexpression of OTUB1 accelerates the growth of myeloma cells. In summary, our study identifies OTUB1 as a novel amplifier of the proto-oncogene c-MYC.