Professional Education


  • Master of Science, National Taiwan University (2014)
  • Doctor of Philosophy, University of Wisconsin Madison (2020)
  • Bachelor of Science, National Yang-Ming University (2014)
  • Ph.D., University of Wisconsin-Madison, Biophysics (2020)
  • M.S., National Taiwan University, Biochemistry (2014)
  • B.S., National Yang-Ming University, Biology (2012)

Stanford Advisors


All Publications


  • Roles of constitutive and signal-dependent protein phosphatase 2A docking motifs in burst attenuation of the cyclic AMP response element-binding protein JOURNAL OF BIOLOGICAL CHEMISTRY Kim, S., Wu, C., Jia, W., Xing, Y., Tibbetts, R. S. 2021; 297 (1): 100908

    Abstract

    The cAMP response element-binding protein (CREB) is an important regulator of cell growth, metabolism, and synaptic plasticity. CREB is activated through phosphorylation of an evolutionarily conserved Ser residue (S133) within its intrinsically disordered kinase-inducible domain (KID). Phosphorylation of S133 in response to cAMP, Ca2+, and other stimuli triggers an association of the KID with the KID-interacting (KIX) domain of the CREB-binding protein (CBP), a histone acetyl transferase (HAT) that promotes transcriptional activation. Here we addressed the mechanisms of CREB attenuation following bursts in CREB phosphorylation. We show that phosphorylation of S133 is reversed by protein phosphatase 2A (PP2A), which is recruited to CREB through its B56 regulatory subunits. We found that a B56-binding site located at the carboxyl-terminal boundary of the KID (BS2) mediates high-affinity B56 binding, while a second binding site (BS1) located near the amino terminus of the KID mediates low affinity binding enhanced by phosphorylation of adjacent casein kinase (CK) phosphosites. Mutations that diminished B56 binding to BS2 elevated both basal and stimulus-induced phosphorylation of S133, increased CBP interaction with CREB, and potentiated the expression of CREB-dependent reporter genes. Cells from mice harboring a homozygous CrebE153D mutation that disrupts BS2 exhibited increased S133 phosphorylation stoichiometry and elevated transcriptional bursts to cAMP. These findings provide insights into substrate targeting by PP2A holoenzymes and establish a new mechanism of CREB attenuation that has implications for understanding CREB signaling in cell growth, metabolism, synaptic plasticity, and other physiologic contexts.

    View details for DOI 10.1016/j.jbc.2021.100908

    View details for Web of Science ID 000678068400095

    View details for PubMedID 34171357

    View details for PubMedCentralID PMC8294589

  • Methylation-regulated decommissioning of multimeric PP2A complexes NATURE COMMUNICATIONS Wu, C., Zheng, A., Jiang, L., Rowse, M., Stanevich, V., Chen, H., Li, Y., Satyshur, K. A., Johnson, B., Gu, T., Liu, Z., Xing, Y. 2017; 8: 2272

    Abstract

    Dynamic assembly/disassembly of signaling complexes are crucial for cellular functions. Specialized latency and activation chaperones control the biogenesis of protein phosphatase 2A (PP2A) holoenzymes that contain a common scaffold and catalytic subunits and a variable regulatory subunit. Here we show that the butterfly-shaped TIPRL (TOR signaling pathway regulator) makes highly integrative multibranching contacts with the PP2A catalytic subunit, selective for the unmethylated tail and perturbing/inactivating the phosphatase active site. TIPRL also makes unusual wobble contacts with the scaffold subunit, allowing TIPRL, but not the overlapping regulatory subunits, to tolerate disease-associated PP2A mutations, resulting in reduced holoenzyme assembly and enhanced inactivation of mutant PP2A. Strikingly, TIPRL and the latency chaperone, α4, coordinate to disassemble active holoenzymes into latent PP2A, strictly controlled by methylation. Our study reveals a mechanism for methylation-responsive inactivation and holoenzyme disassembly, illustrating the complexity of regulation/signaling, dynamic complex disassembly, and disease mutations in cancer and intellectual disability.

    View details for DOI 10.1038/s41467-017-02405-3

    View details for Web of Science ID 000418570600017

    View details for PubMedID 29273778

    View details for PubMedCentralID PMC5741625

  • PP2A-B ' holoenzyme substrate recognition, regulation and role in cytokinesis CELL DISCOVERY Wu, C., Chen, H., Guo, F., Yadav, V. K., Mcilwain, S. J., Rowse, M., Choudhary, A., Lin, Z., Li, Y., Gu, T., Zheng, A., Xu, Q., Lee, W., Resch, E., Johnson, B., Day, J., Ge, Y., Ong, I. M., Burkard, M. E., Ivarsson, Y., Xing, Y. 2017; 3: 17027

    Abstract

    Protein phosphatase 2A (PP2A) is a major Ser/Thr phosphatase; it forms diverse heterotrimeric holoenzymes that counteract kinase actions. Using a peptidome that tiles the disordered regions of the human proteome, we identified proteins containing [LMFI]xx[ILV]xEx motifs that serve as interaction sites for B'-family PP2A regulatory subunits and holoenzymes. The B'-binding motifs have important roles in substrate recognition and in competitive inhibition of substrate binding. With more than 100 novel ligands identified, we confirmed that the recently identified LxxIxEx B'α-binding motifs serve as common binding sites for B' subunits with minor variations, and that S/T phosphorylation or D/E residues at positions 2, 7, 8 and 9 of the motifs reinforce interactions. Hundreds of proteins in the human proteome harbor intrinsic or phosphorylation-responsive B'-interaction motifs, and localize at distinct cellular organelles, such as midbody, predicting kinase-facilitated recruitment of PP2A-B' holoenzymes for tight spatiotemporal control of phosphorylation at mitosis and cytokinesis. Moroever, Polo-like kinase 1-mediated phosphorylation of Cyk4/RACGAP1, a centralspindlin component at the midbody, facilitates binding of both RhoA guanine nucleotide exchange factor (epithelial cell transforming sequence 2 (Ect2)) and PP2A-B' that in turn dephosphorylates Cyk4 and disrupts Ect2 binding. This feedback signaling loop precisely controls RhoA activation and specifies a restricted region for cleavage furrow ingression. Our results provide a framework for further investigation of diverse signaling circuits formed by PP2A-B' holoenzymes in various cellular processes.

    View details for DOI 10.1038/celldisc.2017.27

    View details for Web of Science ID 000414925200001

    View details for PubMedID 28884018

    View details for PubMedCentralID PMC5586252

  • Structure of a Highly Active Cephalopod S-crystallin Mutant: New Molecular Evidence for Evolution from an Active Enzyme into Lens-Refractive Protein SCIENTIFIC REPORTS Tan, W., Cheng, S., Liu, Y., Wu, C., Lin, M., Chen, C., Lin, C., Chou, C. 2016; 6: 31176

    Abstract

    Crystallins are found widely in animal lenses and have important functions due to their refractive properties. In the coleoid cephalopods, a lens with a graded refractive index provides good vision and is required for survival. Cephalopod S-crystallin is thought to have evolved from glutathione S-transferase (GST) with various homologs differentially expressed in the lens. However, there is no direct structural information that helps to delineate the mechanisms by which S-crystallin could have evolved. Here we report the structural and biochemical characterization of novel S-crystallin-glutathione complex. The 2.35-Å crystal structure of a S-crystallin mutant from Octopus vulgaris reveals an active-site architecture that is different from that of GST. S-crystallin has a preference for glutathione binding, although almost lost its GST enzymatic activity. We've also identified four historical mutations that are able to produce a "GST-like" S-crystallin that has regained activity. This protein recapitulates the evolution of S-crystallin from GST. Protein stability studies suggest that S-crystallin is stabilized by glutathione binding to prevent its aggregation; this contrasts with GST-σ, which do not possess this protection. We suggest that a tradeoff between enzyme activity and the stability of the lens protein might have been one of the major driving force behind lens evolution.

    View details for DOI 10.1038/srep31176

    View details for Web of Science ID 000392101500001

    View details for PubMedID 27499004

    View details for PubMedCentralID PMC4976375

  • Mechanism for controlling the monomer-dimer conversion of SARS coronavirus main protease ACTA CRYSTALLOGRAPHICA SECTION D-STRUCTURAL BIOLOGY Wu, C., Cheng, S., Chen, S., Li, J., Fang, Y., Chen, Y., Chou, C. 2013; 69: 747-755

    Abstract

    The Severe acute respiratory syndrome coronavirus (SARS-CoV) main protease (M(pro)) cleaves two virion polyproteins (pp1a and pp1ab); this essential process represents an attractive target for the development of anti-SARS drugs. The functional unit of M(pro) is a homodimer and each subunit contains a His41/Cys145 catalytic dyad. Large amounts of biochemical and structural information are available on M(pro); nevertheless, the mechanism by which monomeric M(pro) is converted into a dimer during maturation still remains poorly understood. Previous studies have suggested that a C-terminal residue, Arg298, interacts with Ser123 of the other monomer in the dimer, and mutation of Arg298 results in a monomeric structure with a collapsed substrate-binding pocket. Interestingly, the R298A mutant of M(pro) shows a reversible substrate-induced dimerization that is essential for catalysis. Here, the conformational change that occurs during substrate-induced dimerization is delineated by X-ray crystallography. A dimer with a mutual orientation of the monomers that differs from that of the wild-type protease is present in the asymmetric unit. The presence of a complete substrate-binding pocket and oxyanion hole in both protomers suggests that they are both catalytically active, while the two domain IIIs show minor reorganization. This structural information offers valuable insights into the molecular mechanism associated with substrate-induced dimerization and has important implications with respect to the maturation of the enzyme.

    View details for DOI 10.1107/S0907444913001315

    View details for Web of Science ID 000318240200008

    View details for PubMedID 23633583

    View details for PubMedCentralID PMC7161611