SCP1 regulates c-Myc stability and functions through dephosphorylating c-Myc Ser62

Serine 62 (Ser62) phosphorylation affects the c-Myc protein stability in cancer cells. However, the mechanism for dephosphorylating c-Myc is not well understood. In this study, we identified carboxyl-terminal domain RNA polymerase II polypeptide A small phosphatase 1 (SCP1) as a novel phosphatase specifically dephosphorylating c-Myc Ser62. Ectopically expressed SCP1 strongly dephosphorylated c-Myc Ser62, destabilized c-Myc protein and suppressed c-Myc transcriptional activity. Knockdown of SCP1 increased the c-Myc protein levels in liver cancer cells. SCP1 interacted with c-Myc both in vivo and in vitro. In addition, Ser245 at the C-terminus of SCP1 was essential for its phosphatase activity towards c-Myc. Functionally, SCP1 negatively regulated the cancer cell proliferation. Collectively, our findings indicate that SCP1 is a potential tumor suppressor for liver cancers through dephosphorylating c-Myc Ser62.

[1]  Charles Y. Lin,et al.  Transcriptional Amplification in Tumor Cells with Elevated c-Myc , 2012, Cell.

[2]  R. Davis,et al.  Transactivation of gene expression by Myc is inhibited by mutation at the phosphorylation sites Thr-58 and Ser-62. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[3]  R. Colbran,et al.  Cloning and characterization of B delta, a novel regulatory subunit of protein phosphatase 2A. , 1999, FEBS letters.

[4]  S. Mathivanan,et al.  A curated compendium of phosphorylation motifs , 2007, Nature Biotechnology.

[5]  Y Taya,et al.  Multiple Ras-dependent phosphorylation pathways regulate Myc protein stability. , 2000, Genes & development.

[6]  M. Buendia,et al.  Activation of c-myc by woodchuck hepatitis virus insertion in hepatocellular carcinoma , 1988, Cell.

[7]  B. Clurman,et al.  The Fbw7 tumor suppressor regulates glycogen synthase kinase 3 phosphorylation-dependent c-Myc protein degradation , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[8]  D. Litchfield,et al.  Subtype-specific regulation of equilibrative nucleoside transporters by protein kinase CK2. , 2005, The Biochemical journal.

[9]  Kathryn A. O’Donnell,et al.  c-Myc-regulated microRNAs modulate E2F1 expression , 2005, Nature.

[10]  Chi V Dang,et al.  MYC on the Path to Cancer , 2012, Cell.

[11]  R. Eisenman,et al.  Post-translational control of Myc function during differentiation , 2011, Cell cycle.

[12]  Xin-Hua Feng,et al.  Small C-terminal Domain Phosphatases Dephosphorylate the Regulatory Linker Regions of Smad2 and Smad3 to Enhance Transforming Growth Factor-β Signaling* , 2006, Journal of Biological Chemistry.

[13]  S. Pfaff,et al.  Small CTD Phosphatases Function in Silencing Neuronal Gene Expression , 2005, Science.

[14]  H. Chen,et al.  A positive feedback loop between EBP2 and c-Myc regulates rDNA transcription, cell proliferation, and tumorigenesis , 2014, Cell Death and Disease.

[15]  S. Kim,et al.  Skp2 regulates Myc protein stability and activity. , 2003, Molecular cell.

[16]  Yigong Shi.  Serine/Threonine Phosphatases: Mechanism through Structure , 2009, Cell.

[17]  K. Nakayama,et al.  Phosphorylation‐dependent degradation of c‐Myc is mediated by the F‐box protein Fbw7 , 2004, The EMBO journal.

[18]  D. Seldin,et al.  Endogenous Protein Kinase CK2 Participates in Wnt Signaling in Mammary Epithelial Cells* , 2000, The Journal of Biological Chemistry.

[19]  B. Zhou,et al.  Small C-terminal Domain Phosphatase Enhances Snail Activity through Dephosphorylation* , 2009, Journal of Biological Chemistry.

[20]  Xin-Hua Feng,et al.  Direct interaction of c-Myc with Smad2 and Smad3 to inhibit TGF-beta-mediated induction of the CDK inhibitor p15(Ink4B). , 2002, Molecular cell.

[21]  R. Sears.  The Life Cycle of C-Myc: From Synthesis to Degradation , 2004, Cell cycle.

[22]  L. Zender,et al.  Deregulated MYC expression induces dependence upon AMPK-related kinase 5 , 2012, Nature.

[23]  Xia Lin,et al.  Direct Interaction of c-Myc with Smad2 and Smad3 to Inhibit TGF-β-Mediated Induction of the CDK Inhibitor p15(Ink4B). , 2016, Molecular cell.

[24]  Joseph R. Nevins,et al.  A signalling pathway controlling c-Myc degradation that impacts oncogenic transformation of human cells , 2004, Nature Cell Biology.

[25]  R. Sears,et al.  MYC degradation. , 2014, Cold Spring Harbor perspectives in medicine.

[26]  R. Sears,et al.  Protein Phosphatase 2A Regulatory Subunit B56α Associates with c-Myc and Negatively Regulates c-Myc Accumulation , 2006, Molecular and Cellular Biology.

[27]  R. Colbran,et al.  Cloning and characterization of Bδ, a novel regulatory subunit of protein phosphatase 2A , 1999 .

[28]  Colin J. Daniel,et al.  Mechanistic insight into Myc stabilization in breast cancer involving aberrant Axin1 expression , 2011, Proceedings of the National Academy of Sciences.

[29]  R. Eisenman,et al.  Regulation of c-Myc Protein Abundance by a Protein Phosphatase 2A-Glycogen Synthase Kinase 3β-Negative Feedback Pathway. , 2012, Genes & cancer.

[30]  Qiang Yu,et al.  B55β-associated PP2A complex controls PDK1-directed myc signaling and modulates rapamycin sensitivity in colorectal cancer. , 2010, Cancer cell.

[31]  J. Dixon,et al.  Structural and functional analysis of the phosphoryl transfer reaction mediated by the human small C‐terminal domain phosphatase, Scp1 , 2010, Protein science : a publication of the Protein Society.

[32]  Yu Xue,et al.  GPS: a comprehensive www server for phosphorylation sites prediction , 2005, Nucleic Acids Res..

[33]  D. Green,et al.  c-Myc Is a Universal Amplifier of Expressed Genes in Lymphocytes and Embryonic Stem Cells , 2012, Cell.

[34]  Shuangxi Li,et al.  The Fbw7/Human CDC4 Tumor Suppressor Targets Proproliferative Factor KLF5 for Ubiquitination and Degradation through Multiple Phosphodegron Motifs* , 2010, The Journal of Biological Chemistry.

[35]  Xiao Zhen Zhou,et al.  Pin1 modulates the dephosphorylation of the RNA polymerase II C‐terminal domain by yeast Fcp1 , 2002, FEBS letters.

[36]  L. Penn,et al.  Reflecting on 25 years with MYC , 2008, Nature Reviews Cancer.

[37]  Colin J. Daniel,et al.  Pin1 Regulates the Dynamics of c-Myc DNA Binding To Facilitate Target Gene Regulation and Oncogenesis , 2013, Molecular and Cellular Biology.

[38]  D. Gillespie,et al.  Gene-regulatory properties of Myc helix-loop-helix/leucine zipper mutants: Max-dependent DNA binding and transcriptional activation in yeast correlates with transforming capacity. , 1993, Oncogene.

[39]  P. Pandolfi,et al.  Deciphering the transcriptional complex critical for RhoA gene expression and cancer metastasis , 2010, Nature Cell Biology.

[40]  B. Amati.  Myc degradation: Dancing with ubiquitin ligases , 2004, Proceedings of the National Academy of Sciences of the United States of America.

[41]  Yigong Shi,et al.  PPM1A Functions as a Smad Phosphatase to Terminate TGFβ Signaling , 2016, Cell.

[42]  Yan Zhang,et al.  Determinants for dephosphorylation of the RNA polymerase II C‐terminal domain by Scp1 , 2006, Molecular cell.

[43]  Colin J. Daniel,et al.  The Axin1 scaffold protein promotes formation of a degradation complex for c‐Myc , 2009, The EMBO journal.

[44]  P. Lin,et al.  A Novel RNA Polymerase II C-terminal Domain Phosphatase That Preferentially Dephosphorylates Serine 5* , 2003, Journal of Biological Chemistry.

[45]  M. Troxell,et al.  Phosphorylation regulates c-Myc's oncogenic activity in the mammary gland. , 2011, Cancer research.

[46]  D. Barford.  Molecular mechanisms of the protein serine/threonine phosphatases. , 1996, Trends in biochemical sciences.

[47]  Colin J. Daniel,et al.  Targeting c-MYC by antagonizing PP2A inhibitors in breast cancer , 2014, Proceedings of the National Academy of Sciences.