Hong Ma

University of Southern California, Los Angeles, California, United States

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Publications (3)12.85 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Both p300 and β-catenin are transcriptional activators and phosphoproteins, and play a central role in Wnt/β-catenin-dependent transcriptional regulation. The minimum β-catenin binding domain of p300 has been mapped to the N-terminus 1-111 amino acids. Here, we performed phosphoproteomic analysis for the critical binding region using LC-MS/MS approach to investigate potential phosphosites that may affect the binding affinity. By implementing TiO(2)-based phosphopeptide affinity purification followed by LC-MS/MS analysis with both collision-induced dissociation (CID) and electron transfer dissociation (ETD) methods, two unique phosphosites Ser12 and Ser89 were identified, of which, phosphorylation at Ser12 is novel. Functional studies aided by site-directed mutagenesis, co-immunoprecipitation and mammalian two-hybrid assay have concluded that phosphorylation at Ser12 critically mediates the binding ability of p300 with β-catenin. Further studies utilizing specific MAPK inhibitors suggest that the p38 MAPK activation is the upstream signal required for Ser12 phosphorylation. The transcriptional roles of p300/β-catenin complex in myoblast differentiation are discussed.
    Journal of proteomics 03/2012; 75(9):2601-10. · 5.07 Impact Factor
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    ABSTRACT: In the Wnt/β-catenin pathway, p300/CBP (CREB-binding protein) is recruited by nuclear β-catenin to regulate a wide array of T-cell factor (TCF)-dependent gene expression. Previous studies have indicated that CBP/β-catenin complex-mediated transcription is critical for cell proliferation. Both CBP and β-catenin are phosphoproteins. The interaction domain has been mapped to the N-terminal region of CBP (amino acids 1-111) and the C-terminal region of β-catenin, but it is unclear whether phosphorylation on specific residues of these regions is required for the interaction. To address this unmet challenge, phosphoproteomic profile of the critical N-terminus of CBP was determined by utilizing TiO(2) affinity chromatography followed by LC-MS/MS analysis. Two unique and novel phosphorylation sites Ser77 and Ser92 were identified. Further studies aided by site-directed mutagenesis, immunoprecipitation and mammalian two-hybrid assay have concluded that the phosphorylation of a Proline-directed Ser92 residue modulates the selective binding ability of CBP with β-catenin. The specific Mitogen-activated protein kinase inhibitor PD98059, which promotes cell cycle G1 arrest, concomitantly inhibits the interaction, and the evidences suggest that the MEK/ERK (extracellular signal-regulated kinase) cascade activation is the upstream signal required for Ser92 phosphorylation, leading to enhancement of the interaction of CBP with β-catenin.
    Proteomics 09/2011; 11(17):3444-51. · 4.43 Impact Factor
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    ABSTRACT: An effective new platform for phosphosite mapping and subsequent functional screening was developed to analyze the targeted protein-protein interactions of p300 and CBP with β-catenin. Two novel functional phosphosites, Ser12 of p300 and Ser92 of CBP, were revealed to modulate p300/β-catenin and CBP/β-catenin interactions, respectively.
    Molecular BioSystems 06/2011; 7(6):1838-41. · 3.35 Impact Factor

Publication Stats

11 Citations
12.85 Total Impact Points


  • 2011–2012
    • University of Southern California
      • Keck School of Medicine
      Los Angeles, California, United States
    • Children's Hospital Los Angeles
      Los Angeles, California, United States