c-Myc is targeted to the proteasome for degradation in a SUMOylation-dependent manner, regulated by PIAS1, SENP7 and RNF4.
c-Myc is the most frequently overexpressed oncogene in tumors, including breast cancer, colon cancer and lung cancer. Post-translational modifications comprising phosphorylation, acetylation and ubiquitylation regulate the activity of c-Myc. Recently, it was shown that c-Myc-driven tumors are strongly dependent on the SUMO pathway. Currently, the relevant SUMO target proteins in ... this pathway are unknown. Here we show that c-Myc is a target protein for SUMOylation, and that SUMOylated c-Myc is subsequently ubiquitylated and degraded by the proteasome. SUMO chains appeared to be dispensable for this process, polymerization-deficient SUMO mutants supported proteolysis of SUMOylated c-Myc. These results indicate that multiple SUMO monomers conjugated to c-Myc could be sufficient to direct SUMOylated c-Myc to the ubiquitin-proteasome pathway. Knocking down the SUMO-targeted ubiquitin ligase RNF4 enhanced the levels of SUMOylated c-Myc, indicating that RNF4 could recognize a multi-SUMOylated protein as a substrate in addition to poly-SUMOylated proteins. Knocking down the SUMO E3 ligase PIAS1 resulted in reduced c-Myc SUMOylation and increased c-Myc transcriptional activity, indicating that PIAS1 mediates c-Myc SUMOylation. Increased SUMOylation of c-Myc was noted upon knockdown of the SUMO protease SENP7, indicating that it also could regulate a multi-SUMOylated protein in addition to poly-SUMOylated proteins. C-Myc lacks KxE-type SUMOylation consensus motifs. We used mass spectrometry to identify 10 SUMO acceptor lysines: K52, K148, K157, K317, K323, K326, K389, K392, K398 and K430. Intriguingly, mutating all 10 SUMO acceptor lysines did not reduce c-Myc SUMOylation, suggesting that SUMO acceptor lysines in c-Myc act promiscuously. Our results provide novel insight into the complexity of c-Myc post-translational regulation.
Mesh Terms:
Amino Acid Motifs, Cell Line, Tumor, Cell Nucleus, Cytoplasm, Endopeptidases, Gene Expression Regulation, Neoplastic, HeLa Cells, Humans, Lysine, Mass Spectrometry, Nuclear Proteins, Phosphorylation, Proteasome Endopeptidase Complex, Protein Inhibitors of Activated STAT, Protein Processing, Post-Translational, Protein Transport, Proteolysis, Proto-Oncogene Proteins c-myc, Small Ubiquitin-Related Modifier Proteins, Sumoylation, Transcription Factors, Ubiquitination
Amino Acid Motifs, Cell Line, Tumor, Cell Nucleus, Cytoplasm, Endopeptidases, Gene Expression Regulation, Neoplastic, HeLa Cells, Humans, Lysine, Mass Spectrometry, Nuclear Proteins, Phosphorylation, Proteasome Endopeptidase Complex, Protein Inhibitors of Activated STAT, Protein Processing, Post-Translational, Protein Transport, Proteolysis, Proto-Oncogene Proteins c-myc, Small Ubiquitin-Related Modifier Proteins, Sumoylation, Transcription Factors, Ubiquitination
Cell Cycle
Date: Apr. 22, 2015
PubMed ID: 25895136
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