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Nature Structural & Molecular Biology Oct 2022SHOC2 acts as a strong synthetic lethal interactor with MEK inhibitors in multiple KRAS cancer cell lines. SHOC2 forms a heterotrimeric complex with MRAS and PP1C that...
SHOC2 acts as a strong synthetic lethal interactor with MEK inhibitors in multiple KRAS cancer cell lines. SHOC2 forms a heterotrimeric complex with MRAS and PP1C that is essential for regulating RAF and MAPK-pathway activation by dephosphorylating a specific phosphoserine on RAF kinases. Here we present the high-resolution crystal structure of the SHOC2-MRAS-PP1C (SMP) complex and apo-SHOC2. Our structures reveal that SHOC2, MRAS, and PP1C form a stable ternary complex in which all three proteins synergistically interact with each other. Our results show that dephosphorylation of RAF substrates by PP1C is enhanced upon interacting with SHOC2 and MRAS. The SMP complex forms only when MRAS is in an active state and is dependent on SHOC2 functioning as a scaffolding protein in the complex by bringing PP1C and MRAS together. Our results provide structural insights into the role of the SMP complex in RAF activation and how mutations found in Noonan syndrome enhance complex formation, and reveal new avenues for therapeutic interventions.
Topics: Humans; Intracellular Signaling Peptides and Proteins; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase Kinases; Noonan Syndrome; Phosphoserine; Protein Phosphatase 1; Proto-Oncogene Proteins p21(ras); raf Kinases; ras Proteins
PubMed: 36175670
DOI: 10.1038/s41594-022-00841-4 -
The FEBS Journal Feb 2021Protein phosphorylation is a major reversible post-translational modification. Protein phosphatases function as 'critical regulators' in signaling networks through... (Review)
Review
Protein phosphorylation is a major reversible post-translational modification. Protein phosphatases function as 'critical regulators' in signaling networks through dephosphorylation of proteins, which have been phosphorylated by protein kinases. A large understanding of their working has been sourced from animal systems rather than the plant or the prokaryotic systems. The eukaryotic protein phosphatases include phosphoprotein phosphatases (PPP), metallo-dependent protein phosphatases (PPM), protein tyrosine (Tyr) phosphatases (PTP), and aspartate (Asp)-dependent phosphatases. The PPP and PPM families are serine(Ser)/threonine(Thr)-specific phosphatases (STPs), while PTP family is Tyr specific. Dual-specificity phosphatases (DsPTPs/DSPs) dephosphorylate Ser, Thr, and Tyr residues. PTPs lack sequence homology with STPs, indicating a difference in catalytic mechanisms, while the PPP and PPM families share a similar structural fold indicating a common catalytic mechanism. The catalytic cysteine (Cys) residue in the conserved HCX R active site motif of the PTPs acts as a nucleophile during hydrolysis. The PPP members require metal ions, which coordinate the phosphate group of the substrate, followed by a nucleophilic attack by a water molecule and hydrolysis. The variable holoenzyme assembly of protein phosphatase(s) and the overlap with other post-translational modifications like acetylation and ubiquitination add to their complexity. Though their functional characterization is extensively reported in plants, the mechanistic nature of their action is still being explored by researchers. In this review, we exclusively overview the plant protein phosphatases with an emphasis on their mechanistic action as well as structural characteristics.
Topics: Biocatalysis; Catalytic Domain; Models, Molecular; Phosphoprotein Phosphatases; Phosphorylation; Plant Proteins; Protein Domains; Protein Subunits; Signal Transduction; Substrate Specificity
PubMed: 32542989
DOI: 10.1111/febs.15454 -
Nature Communications Nov 2022Activation of client protein kinases by the HSP90 molecular chaperone system is affected by phosphorylation at multiple sites on HSP90, the kinase-specific co-chaperone...
Activation of client protein kinases by the HSP90 molecular chaperone system is affected by phosphorylation at multiple sites on HSP90, the kinase-specific co-chaperone CDC37, and the kinase client itself. Removal of regulatory phosphorylation from client kinases and their release from the HSP90-CDC37 system depends on the Ser/Thr phosphatase PP5, which associates with HSP90 via its N-terminal TPR domain. Here, we present the cryoEM structure of the oncogenic protein kinase client BRAF bound to HSP90-CDC37, showing how the V600E mutation favours BRAF association with HSP90-CDC37. Structures of HSP90-CDC37-BRAF complexes with PP5 in autoinhibited and activated conformations, together with proteomic analysis of its phosphatase activity on BRAF and CRAF, reveal how PP5 is activated by recruitment to HSP90 complexes. PP5 comprehensively dephosphorylates client proteins, removing interaction sites for regulatory partners such as 14-3-3 proteins and thus performing a 'factory reset' of the kinase prior to release.
Topics: Humans; Cell Cycle Proteins; Chaperonins; HSP90 Heat-Shock Proteins; Molecular Chaperones; Phosphoric Monoester Hydrolases; Proteomics; Proto-Oncogene Proteins B-raf
PubMed: 36446791
DOI: 10.1038/s41467-022-35143-2 -
The Journal of Biological Chemistry Apr 2024FOXO1 is a transcription factor and potential tumor suppressor that is negatively regulated downstream of PI3K-PKB/AKT signaling. Paradoxically, FOXO also promotes tumor...
FOXO1 is a transcription factor and potential tumor suppressor that is negatively regulated downstream of PI3K-PKB/AKT signaling. Paradoxically, FOXO also promotes tumor growth, but the detailed mechanisms behind this role of FOXO are not fully understood. In this study, we revealed a molecular cascade by which the Thr24 residue of FOXO1 is phosphorylated by AKT and is dephosphorylated by calcineurin, which is a Ca-dependent protein phosphatase. Curiously, single nucleotide somatic mutations of FOXO1 in cancer occur frequently at and near Thr24. Using a calcineurin inhibitor and shRNA directed against calcineurin, we revealed that calcineurin-mediated dephosphorylation of Thr24 regulates FOXO1 protein stability. We also found that FOXO1 binds to the promoter region of MDM2 and activates transcription, which in turn promotes MDM2-mediated ubiquitination and degradation of p53. FOXO3a and FOXO4 are shown to control p53 activity; however, the significance of FOXO1 in p53 regulation remains largely unknown. Supporting this notion, FOXO1 depletion increased p53 and p21 protein levels in association with the inhibition of cell proliferation. Taken together, these results indicate that FOXO1 is stabilized by calcineurin-mediated dephosphorylation and that FOXO1 supports cancer cell proliferation by promoting MDM2 transcription and subsequent p53 degradation.
Topics: Proto-Oncogene Proteins c-mdm2; Humans; Tumor Suppressor Protein p53; Forkhead Box Protein O1; Calcineurin; Proteolysis; Phosphorylation; Cell Proliferation; Ubiquitination; Cell Line, Tumor; Neoplasms; Forkhead Transcription Factors; Proto-Oncogene Proteins c-akt; Protein Stability
PubMed: 38519029
DOI: 10.1016/j.jbc.2024.107209 -
International Journal of Molecular... Apr 2021More than 70% of eukaryotic proteins are regulated by phosphorylation. However, the mechanism of dephosphorylation that counteracts phosphorylation is less studied.... (Review)
Review
More than 70% of eukaryotic proteins are regulated by phosphorylation. However, the mechanism of dephosphorylation that counteracts phosphorylation is less studied. Phosphatases are classified into 104 distinct groups based on substrate-specific features and the sequence homologies in their catalytic domains. Among them, dual-specificity phosphatases (DUSPs) that dephosphorylate both phosphoserine/threonine and phosphotyrosine are important for cellular homeostasis. Ssu72 is a newly studied phosphatase with dual specificity that can dephosphorylate both phosphoserine/threonine and phosphotyrosine. It is important for cell-growth signaling, metabolism, and immune activation. Ssu72 was initially identified as a phosphatase for the Ser5 and Ser7 residues of the C-terminal domain of RNA polymerase II. It prefers the configuration of the serine-proline motif within its substrate and regulates Pin1, different from other phosphatases. It has recently been reported that Ssu72 can regulate sister chromatid cohesion and the separation of duplicated chromosomes during the cell cycle. Furthermore, Ssu72 appears to be involved in the regulation of T cell receptor signaling, telomere regulation, and even hepatocyte homeostasis in response to a variety of stress and damage signals. In this review, we aim to summarize various functions of the Ssu72 phosphatase, their implications in diseases, and potential therapeutic indications.
Topics: Animals; Chromatids; Chromosomes, Human; Humans; NIMA-Interacting Peptidylprolyl Isomerase; Phosphoprotein Phosphatases; Protein Domains; RNA Polymerase II; Receptors, Antigen, T-Cell; Signal Transduction
PubMed: 33917542
DOI: 10.3390/ijms22073791 -
Open Biology Jul 2023Mitotic exit requires the dephosphorylation of many proteins whose phosphorylation was needed for mitosis. Protein phosphatase 2A with its B55 regulatory subunit...
Mitotic exit requires the dephosphorylation of many proteins whose phosphorylation was needed for mitosis. Protein phosphatase 2A with its B55 regulatory subunit (PP2A-B55) promotes this transition. However, the events and substrates that it regulates are incompletely understood. We used proteomic approaches in to identify proteins that interact with and are dephosphorylated by PP2A-B55. Among several candidates, we identified emerin (otefin in ). Emerin resides in the inner nuclear membrane and interacts with the DNA-binding protein barrier-to-autointegration factor (BAF) via a LEM domain. We found that the phosphorylation of emerin at Ser50 and Ser54 near its LEM domain negatively regulates its association with BAF, lamin and additional emerin in mitosis. We show that dephosphorylation of emerin at these sites by PP2A-B55 determines the timing of nuclear envelope reformation. Genetic experiments indicate that this regulation is required during embryonic development. Phosphoregulation of the emerin-BAF complex formation by PP2A-B55 appears as a key event of mitotic exit that is likely conserved across species.
Topics: Animals; Drosophila; Nuclear Envelope; Protein Phosphatase 2; Proteomics; Mitosis
PubMed: 37463656
DOI: 10.1098/rsob.230104 -
Autophagy Feb 2021Histone deacetylases (HDACs) are important for global gene expression and contribute to numerous physiological events. Deacetylase Rpd3 in yeast and its conserved...
Histone deacetylases (HDACs) are important for global gene expression and contribute to numerous physiological events. Deacetylase Rpd3 in yeast and its conserved homolog HDAC1 in mammals oppositely regulate autophagy; however, how Rpd3/HDAC1 is regulated to mediate autophagy remains unclear. Here, we showed autophagy occurrence in silkworm () required BmRpd3, wherein steroid hormone 20-hydroxyecdysone (20E) signaling regulated its protein level and nuclear localization negatively. Inhibition of MTOR led to dephosphorylation and nucleo-cytoplasmic translocation of BmRpd3/HsHDAC1. Besides, cholesterol, 20E, and 27-hydroxycholesterol could all induce massive dephosphorylation and cytoplasmic localization of BmRpd3/HsHDAC1, and thus autophagy by affecting MTORC1 activity. In addition, three phosphorylation sites (Ser392, Ser421, and Ser423) identified in BmRpd3 were conserved in HsHDAC1. Single or triple phosphorylation-site mutation attenuated the phosphorylation levels of BmRpd3/HsHDAC1, leading to their cytoplasmic localization and autophagy activation. In general, cholesterol derivatives, especially hydroxylated cholesterol, caused dephosphorylation and nucleo-cytoplasmic shuttling of BmRpd3/HsHDAC1 through inhibition of MTOR signaling to facilitate autophagy in and mammals. These findings improve our understandings of BmRpd3/HsHDAC1-mediated autophagy induced by cholesterol derivatives and shed light on their potential as a therapeutic target for neurodegenerative diseases and autophagy-related studies. 20E: 20-hydroxyecdysone; 27-OH: 27-hydroxycholesterol; ACTB: actin beta; AMPK: AMP-activated protein kinase; Atg: autophagy-related; BmSqstm1: sequestosome 1; CQ: chloroquine; HDAC: histone deacetylase; LMNB: Lamin B1; MTOR: mechanistic target of rapamycin kinase; PE: phosphatidylethanolamine; SQSTM1/p62: sequestosome 1; TUBA1A: tubulin alpha 1a.
Topics: AMP-Activated Protein Kinases; Animals; Autophagy; Cholesterol; Histone Deacetylases; Lysosomes; Mechanistic Target of Rapamycin Complex 1; Phosphorylation; Signal Transduction; Up-Regulation
PubMed: 32013726
DOI: 10.1080/15548627.2020.1725376 -
Journal of Clinical Medicine Oct 2021Calcineurin inhibitors (CNIs) are drugs that inhibit calcineurin, a key phosphatase that dephosphorylates a transcription factor called the nuclear factor of activated T... (Review)
Review
Calcineurin inhibitors (CNIs) are drugs that inhibit calcineurin, a key phosphatase that dephosphorylates a transcription factor called the nuclear factor of activated T cells (NFAT), allowing its translocation into the nucleus of quiescent T cells. In the nucleus, NFAT activates interleukin 2, which stimulates the proliferation and differentiation of T-cells. CNIs can also stabilize the actin cytoskeleton of podocytes reducing proteinuria. Thanks to these characteristics, CNIs have been often used in the treatment of autoimmune diseases. However, the therapeutic index of CNIs is narrow, and their interactions with other drugs can increase toxicity or reduce efficacy. In lupus nephritis, cyclosporine and tacrolimus have been used both in induction and maintenance therapies. Observational studies and randomized controlled trials showed that both cyclosporine and tacrolimus can increase efficacy. Tolerance is satisfactory if low doses are used and the patient is carefully monitored. More recently, a new CNI, called voclosporin (VCS), has been approved by the Food and Drug Administration for use in lupus nephritis. VCS offers potential advantages over other CNIs. In two large multiethnic trials, VCS was not associated with adverse renal and metabolic events and obtained positive results despite a novel and rapid corticosteroid tapering regime.
PubMed: 34768354
DOI: 10.3390/jcm10214832 -
Science Advances Mar 2024We recently developed a heterobifunctional approach [phosphorylation targeting chimeras (PhosTACs)] to achieve the targeted protein dephosphorylation (TPDephos). Here,...
We recently developed a heterobifunctional approach [phosphorylation targeting chimeras (PhosTACs)] to achieve the targeted protein dephosphorylation (TPDephos). Here, we envisioned combining the inhibitory effects of receptor tyrosine kinase inhibitors (RTKIs) and the active dephosphorylation by phosphatases to achieve dual inhibition of kinases. We report an example of tyrosine phosphatase-based TPDephos and the effective epidermal growth factor receptor (EGFR) tyrosine dephosphorylation. We also used phosphoproteomic approaches to study the signaling transductions affected by PhosTAC-related molecules at the proteome-wide level. This work demonstrated the differential signaling pathways inhibited by PhosTAC compared with the TKI, gefitinib. Moreover, a covalent PhosTAC selective for mutated EGFR was developed and showed its inhibitory potential for dysregulated EGFR. Last, EGFR PhosTACs, consistent with EGFR dephosphorylation profiles, induced apoptosis and inhibited cancer cell viability during prolonged PhosTAC treatment. PhosTACs showcased their potential of modulating RTKs activity, expanding the scope of bifunctional molecule utility.
Topics: Apoptosis; Cell Line, Tumor; ErbB Receptors; Phosphorylation; Signal Transduction; Tyrosine; Tyrosine Kinase Inhibitors; Humans; Proteolysis Targeting Chimera
PubMed: 38536914
DOI: 10.1126/sciadv.adj7251 -
Cell Host & Microbe Dec 2022A recent study in Science found Mycobacterium tuberculosis inhibits pyroptosis of the host cell by secreting a phosphatase (PtpB). PtpB targets the plasma membrane to...
A recent study in Science found Mycobacterium tuberculosis inhibits pyroptosis of the host cell by secreting a phosphatase (PtpB). PtpB targets the plasma membrane to dephosphorylate PI4P and PI(4,5)P, inhibiting recruitment of the pore-forming gasdermin D N-terminal fragment. Pyroptosis inhibition contributes to virulence, as ptpB-deficient Mtb is attenuated in mice.
Topics: Mice; Animals; Pyroptosis; Phosphate-Binding Proteins; Intracellular Signaling Peptides and Proteins; Cell Membrane; Mycobacterium tuberculosis
PubMed: 36521438
DOI: 10.1016/j.chom.2022.11.010