MYC dephosphorylation by the PP1/PNUTS phosphatase complex regulates chromatin binding and protein stability

  • Nat Commun. 2018 Aug 29;9(1):3502. doi: 10.1038/s41467-018-05660-0.
Dharmendra Dingar  1 ,  William B Tu  1  2 ,  Diana Resetca  1  2 ,  Corey Lourenco  1  2 ,  Aaliya Tamachi  1 ,  Jason De Melo  1 ,  Kathleen E Houlahan  2  3 ,  Manpreet Kalkat  1  2 ,  Pak-Kei Chan  1 ,  Paul C Boutros  2  3  4 ,  Brian Raught  1  2 ,  Linda Z Penn  5  6
Affiliations
  • 1. Princess Margaret Cancer Centre, University Health Network, Toronto, M5G 1L7, ON, Canada.
  • 2. Department of Medical Biophysics, University of Toronto, Toronto, M5G 1L7, Canada.
  • 3. Ontario Institute for Cancer Research, Toronto, ON Canada M5G 0A3, Canada.
  • 4. Department of Pharmacology and Toxicology, University of Toronto, Toronto, Canada M5S 1A8, Canada.
  • 5. Princess Margaret Cancer Centre, University Health Network, Toronto, M5G 1L7, ON, Canada. [email protected].
  • 6. Department of Medical Biophysics, University of Toronto, Toronto, M5G 1L7, Canada. [email protected].
PMID: 30158517 DOI: 10.1038/s41467-018-05660-0
Abstract

The c-Myc (MYC) oncoprotein is deregulated in over 50% of cancers, yet regulatory mechanisms controlling MYC remain unclear. To this end, we interrogated the MYC interactome using BioID mass spectrometry (MS) and identified PP1 (protein Phosphatase 1) and its regulatory subunit PNUTS (protein phosphatase-1 nuclear-targeting subunit) as MYC interactors. We demonstrate that endogenous MYC and PNUTS interact across multiple cell types and that they co-occupy MYC target gene promoters. Inhibiting PP1 by RNAi or pharmacological inhibition results in MYC hyperphosphorylation at multiple serine and threonine residues, leading to a decrease in MYC protein levels due to proteasomal degradation through the canonical SCFFBXW7 pathway. MYC hyperphosphorylation can be rescued specifically with exogenous PP1, but not Other phosphatases. Hyperphosphorylated MYC retained interaction with its transcriptional partner MAX, but binding to chromatin is significantly compromised. Our work demonstrates that PP1/PNUTS stabilizes chromatin-bound MYC in proliferating cells.