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Cancer Res. 2020 Feb 6. pii: canres.1647.2019. doi: 10.1158/0008-5472.CAN-19-1647. [Epub ahead of print]

UBR5 is co-amplified with MYC in breast tumors and encodes an ubiquitin ligase that limits MYC-dependent apoptosis.

Author information

1
Turku Centre for Biotechnology and Department of Pathology (UTU), University of Turku and Åbo Akademi University.
2
Faculty of Biological and Environmental Sciences/Institute of Biotechnology, University of Helsinki.
3
Theodor Boveri Institute and Comprehensive Cancer Center Mainfranken, Biocenter, University of Würzburg.
4
Faculty of Science and Engineering, Abo Akademi.
5
Institute for Molecular Medicine Finland (FIMM), University of Helsinki.
6
Institute for Molecular Medicine Finland, University of Helsinki.
7
Pathology, University of Turku.
8
Turku Bioscience, University of Turku.
9
Department of Medical Oncology, Dana-Farber Cancer Institute.
10
Institute of Biomedicine, Department of Pathology, University of Turku.
11
University of Turku.
12
Turku BioImaging, University of Turku and Åbo Akademi University.
13
Translational Cancer Biology Research Program and Institute of Biomedicine, University of Helsinki.
14
Institute of Biomedicine, Department of Cell Biology and Anatomy, University of Turku.
15
Cell Biology, Åbo Akademi University.
16
Faculty of Biological and Environmental Sciences & Institute of Biotechnology, University of Helsinki.
17
Turku Bioscience Centre, University of Turku jukwes@utu.fi.

Abstract

For maximal oncogenic activity, cellular MYC protein levels need to be tightly controlled so that they do not induce apoptosis. Here, we show how ubiquitin ligase UBR5 functions as a molecular rheostat to prevent excess accumulation of MYC protein. UBR5 ubiquitinates MYC, and its effects on MYC protein stability are independent of FBXW7. Silencing of endogenous UBR5 induced MYC protein expression and regulated MYC target genes. Consistent with the tumor suppressor function of UBR5 (Hyd) in Drosophila, Hyd suppressed dMyc-dependent overgrowth of wing imaginal discs. In contrast, in cancer cells UBR5 suppressed MYC-dependent priming to therapy-induced apoptosis. Of direct cancer relevance, MYC and UBR5 genes were co-amplified in MYC-driven human cancers. Functionally, UBR5 suppressed MYC-mediated apoptosis in p53-mutant breast cancer cells with UBR5/MYC co-amplification. Further, single-cell immunofluorescence analysis demonstrated reciprocal expression of UBR5 and MYC in human basal-type breast cancer tissues. In summary, UBR5 is a novel MYC ubiquitin ligase and an endogenous rheostat for MYC activity. In MYC amplified, and p53-mutant breast cancer cells, UBR5 has an important role in suppressing MYC-mediated apoptosis priming and in protection from drug-induced apoptosis.

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