Serine 15 Phosphorylation of p53 Directs Its Interaction with B56 and the Tumor Suppressor Activity of B56 -Specific Protein Phosphatase 2A

Department of Biochemistry, University of California, Riverside, CA 92521, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 02/2008; 28(1):448-56. DOI: 10.1128/MCB.00983-07
Source: PubMed


Earlier studies have demonstrated a functional link between B56γ-specific protein phosphatase 2A (B56γ-PP2A) and p53 tumor
suppressor activity. Upon DNA damage, a complex including B56γ-PP2A and p53 is formed which leads to Thr55 dephosphorylation
of p53, induction of the p53 transcriptional target p21, and the inhibition of cell proliferation. Although an enhanced interaction
between p53 and B56γ is observed after DNA damage, the underlying mechanism and its significance in PP2A tumor-suppressive
function remain unclear. In this study, we show that the increased interaction between B56γ and p53 after DNA damage requires
ATM-dependent phosphorylation of p53 at Ser15. In addition, we demonstrate that the B56γ3-induced inhibition of cell proliferation,
induction of cell cycle arrest in G1, and blockage of anchorage-independent growth are also dependent on Ser15 phosphorylation of p53 and p53-B56γ interaction.
Taken together, our results provide a mechanistic link between Ser15 phosphorylation-mediated p53-B56γ interaction and the
modulation of p53 tumor suppressor activity by PP2A. We also show an important link between ATM activity and the tumor-suppressive
function of B56γ-PP2A.

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    • "In regard to a specific binding domain, they all have the same amino acids from 391 to 402, which constitute a domain required for interaction with p53 [49]. Indeed, PP2A-B56γ1, γ2 nd γ3 have been reported to dephosphorylate p53 protein at Ser15 [48], [49], [74]. Similarly, all the γvariants could be plausible to bind to ERK as the present study showed that B56γ1 bound to and phosphorylated ERK. "
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    ABSTRACT: Extracellular signal-regulated kinase (ERK) signalling plays a central role in various biological processes, including cell migration, but it remains unknown what factors directly regulate the strength and duration of ERK activation. We found that, among the B56 family of protein phosphatase 2A (PP2A) regulatory subunits, B56γ1 suppressed EGF-induced cell migration on collagen, bound to phosphorylated-ERK, and dephosphorylated ERK, whereas B56α1 and B56β1 did not. B56γ1 was immunolocalized in nuclei. The IER3 protein was immediately highly expressed in response to costimulation of cells with EGF and collagen. Knockdown of IER3 inhibited cell migration and enhanced dephosphorylation of ERK. Analysis of the time course of PP2A-B56γ1 activity following the costimulation showed an immediate loss of phosphatase activity, followed by a rapid increase in activity, and this activity then remained at a stable level that was lower than the original level. Our results indicate that the strength and duration of the nuclear ERK activation signal that is initially induced by ERK kinase (MEK) are determined at least in part by modulation of the phosphatase activity of PP2A-B56γ1 through two independent pathways.
    Full-text · Article · Dec 2013 · PLoS ONE
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    • "PPP2R5C plays a crucial role in cell proliferation, differentiation, and transformation based on its induction of the dephosphorylation of p53 at various residues [19] and may be responsible for the tumor-suppressive function of PP2A [18]. To confirm the role of PPP2R5C down-regulation on the inhibition of CML cells, particularly TKI-resistant CML cells, we used two PPP2R5C siRNAs that target different exon sequences to analyze their effect on the inhibition of proliferation and apoptosis induction in CML cells. "
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    ABSTRACT: Despite the success of imatinib and other tyrosine kinase inhibitors (TKIs), chronic myeloid leukemia (CML) remains largely incurable, and a number of CML patients die due to Abl mutation-related drug resistance and blast crisis. The aim of this study was to evaluate proliferation inhibition and apoptosis induction by down-regulating PPP2R5C gene expression in the imatinib-sensitive and imatinib-resistant CML cell lines K562, K562R (imatinib resistant without an Abl gene mutation), 32D-Bcr-Abl WT (imatinib-sensitive murine CML cell line with a wild type abl gene) and 32D-Bcr-Abl T315I (imatinib resistant with a T315I Abl gene mutation) and primary cells from CML patients by RNA interference. PPP2R5C siRNAs numbered 799 and 991 were obtained by chemosynthesis. Non-silencing siRNA scrambled control (SC)-treated, mock-transfected, and untreated cells were used as controls. The PPP2R5C mRNA and protein expression levels in treated CML cells were analyzed by quantitative real-time PCR and Western blotting, and in vitro cell proliferation was assayed with the cell counting kit-8 method. The morphology and percentage of apoptosis were revealed by Hoechst 33258 staining and flow cytometry (FCM). The results demonstrated that both siRNAs had the best silencing results after nucleofection in all four cell lines and primary cells. A reduction in PPP2R5C mRNA and protein levels was observed in the treated cells. The proliferation rate of the PPP2R5C-siRNA-treated CML cell lines was significantly decreased at 72 h, and apoptosis was significantly increased. Significantly higher proliferation inhibition and apoptosis induction were found in K562R cells treated with PPP2R5C-siRNA799 than K562 cells. In conclusion, the suppression of PPP2R5C by RNA interference could inhibit proliferation and effectively induce apoptosis in CML cells that were either imatinib sensitive or resistant. Down-regulating PPP2R5C gene expression might be considered as a new therapeutic target strategy for CML, particularly for imatinib-resistant CML.
    Full-text · Article · Sep 2013 · Journal of Hematology & Oncology
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    • "The ranks of the relative conservation score of these 5 sites were 2, 3, 5, 6 and 19, respectively. p53 serine 15 phosphorylation could direct its interaction with B56γ and the tumor suppressor activity of B56γ-specific protein phosphatase 2A (Shouse et al., 2008). p53 serine 46 could be phosphorylated by HIPK2 upon UV irradiation, which could regulate p53 apoptotic activity and is required for acetylation by CREBBP (D'Orazi et al., 2002; Hofmann et al., 2002; Chang et al., 2005; Lee et al., 2009). "
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    ABSTRACT: Protein phosphorylation is a ubiquitous protein post-translational modification, which plays an important role in cellular signaling systems underlying various physiological and pathological processes. Current in silico methods mainly focused on the prediction of phosphorylation sites, but rare methods considered whether a phosphorylation site is functional or not. Since functional phosphorylation sites are more valuable for further experimental research and a proportion of phosphorylation sites have no direct functional effects, the prediction of functional phosphorylation sites is quite necessary for this research area. Previous studies have shown that functional phosphorylation sites are more conserved than non-functional phosphorylation sites in evolution. Thus, in our method, we developed a web server by integrating existing phosphorylation site prediction methods, as well as both absolute and relative evolutionary conservation scores to predict the most likely functional phosphorylation sites. Using our method, we predicted the most likely functional sites of the human, rat and mouse proteomes and built a database for the predicted sites. By the analysis of overall prediction results, we demonstrated that protein phosphorylation plays an important role in all the enriched KEGG pathways. By the analysis of protein-specific prediction results, we demonstrated the usefulness of our method for individual protein studies. Our method would help to characterize the most likely functional phosphorylation sites for further studies in this research area.
    Preview · Article · Jul 2012 · Protein & Cell
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