UCH-L1 bypasses mTOR to promote protein biosynthesis and is required for MYC-driven lymphomagenesis in mice

Abstract

<jats:title>Abstract</jats:title> <jats:p>The mechanistic target of rapamycin (mTOR) is a central regulator of cellular proliferation and metabolism. Depending on its binding partners, mTOR is at the core of 2 complexes that either promote protein biosynthesis (mTOR complex 1; mTORC1) or provide survival and proliferation signals (mTORC2). Protein biosynthesis downstream of mTORC1 plays an important role in MYC-driven oncogenesis with translation inhibitors garnering increasing therapeutic attention. The germinal center B-cell oncogene UCHL1 encodes a deubiquitinating enzyme that regulates the balance between mTOR complexes by disrupting mTORC1 and promoting mTORC2 assembly. While supporting mTORC2-dependent growth and survival signals may contribute to its role in cancer, the suppression of mTORC1 activity is enigmatic, as its phosphorylation of its substrate 4EBP1 promotes protein biosynthesis. To address this, we used proximity-based proteomics to identify molecular complexes with which UCH-L1 associates in malignant B cells. We identified a novel association of UCH-L1 with the translation initiation complex eIF4F, the target of 4EBP1. UCH-L1 associates with and promotes the assembly of eIF4F and stimulates protein synthesis through a mechanism that requires its catalytic activity. Because of the importance of mTOR in MYC-driven oncogenesis, we used novel mutant Uchl1 transgenic mice and found that catalytic activity is required for its acceleration of lymphoma in the Eμ-myc model. Further, we demonstrate that mice lacking UCH-L1 are resistant to MYC-induced lymphomas. We conclude that UCH-L1 bypasses the need for mTORC1-dependent protein synthesis by directly promoting translation initiation, and that this mechanism may be essential for MYC in B-cell malignancy.</jats:p>

Ubiquitin C‐Terminal Hydrolase L1: Biochemical and Cellular Characterization of a Covalent Cyanopyrrolidine‐Based Inhibitor

“…Three cell lines were selected to evaluate the efficacy of compound 1 based on their sensitivity to genetic depletion of UCHL1: SW1271 (small‐cell lung cancer line), KMS11, and KMS12 (myeloma cell lines). SW1271 and KMS11 cells have high levels of UCHL1 expression and are sensitive to shRNA depletion of UCHL1, as determined by the project Achilles score . In contrast, KMS12 cells have low levels of UCHL1 and are not dependent on the DUB for proliferation (Figure A) .…”

“…UCHL1 levels of expression and enzymatic activity are correlated with increased metastatic behavior in various cancers, including small‐cell lung cancer, myeloma, and lymphoma –. Three cell lines were selected to evaluate the efficacy of compound 1 based on their sensitivity to genetic depletion of UCHL1: SW1271 (small‐cell lung cancer line), KMS11, and KMS12 (myeloma cell lines).…”

“…SW1271 and KMS11 cells have high levels of UCHL1 expression and are sensitive to shRNA depletion of UCHL1, as determined by the project Achilles score . In contrast, KMS12 cells have low levels of UCHL1 and are not dependent on the DUB for proliferation (Figure A) . Thus, we sought to evaluate differential cell growth in these cell lines upon pharmacological inhibition of UCHL1.…”

DUBbing Down Translation: The Functional Interaction of Deubiquitinases with the Translational Machinery

“…Importantly, upon overexpression of UCHL-1, but not its inactive mutant, the recruitment of the eIF4F complex protein on the cap was enhanced, positioning UCHL-1 as a DUB involved in promoting the translational initiation complex. The protein seems to play a role in the regulation of translation initiation but its substrate(s) on the translational complex are still unknown (92). Because many of these studies were performed with an ectopically expressed protein, analysis of the endogenous UCHL-1 on the translational machinery will be essential to understand the physiology as well as the rewired pathologic signaling in promoting tumors.…”

“…The impact of the protein can be appreciated by the observation that transgenic expression in B cells was sufficient to drive spontaneous B-cell malignancies, which were further accelerated in disease models such as Em-Myc (91,95). Indeed, transcriptomic analysis of UCHL-1-driven B-cell lymphoma from Em-MYC and PI3Koverexpressing mice models show a high degree of similarity in gene-expression patterns (92). Further, UCHL-1 downregulated mTOR activity but promotes Akt activity by deregulating PHLPP1 expression (95).…”