KSR2 Is a Calcineurin Substrate that Promotes ERK Cascade Activation in Response to Calcium Signals

Laboratory of Cell and Developmental Signaling, SAIC-Frederick, Inc., National Cancer Institute at Frederick, Frederick, MD 21702, USA.
Molecular cell (Impact Factor: 14.02). 07/2009; 34(6):652-62. DOI: 10.1016/j.molcel.2009.06.001
Source: PubMed

ABSTRACT Protein scaffolds have emerged as important regulators of MAPK cascades, facilitating kinase activation and providing crucial spatio/temporal control to their signaling outputs. Using a proteomics approach to compare the binding partners of the two mammalian KSR scaffolds, we find that both KSR1 and KSR2 interact with the kinase components of the ERK cascade and have a common function in promoting RTK-mediated ERK signaling. Strikingly, we find that the protein phosphatase calcineurin selectively interacts with KSR2 and that KSR2 uniquely contributes to Ca2+-mediated ERK signaling. Calcineurin dephosphorylates KSR2 on specific sites in response to Ca2+ signals, thus regulating KSR2 localization and activity. Moreover, we find that depletion of endogenous KSR2 impairs Ca2+-mediated ERK activation and ERK-dependent signaling responses in INS1 pancreatic beta-cells and NG108 neuroblastoma cells. These findings identify KSR2 as a Ca2+-regulated ERK scaffold and reveal a new mechanism whereby Ca2+ impacts Ras to ERK pathway signaling.

Download full-text


Available from: Daniel Ritt, Sep 28, 2015
28 Reads
  • Source
    • "Inhibition of intracellular calcium resulted in a complete inhibition of PGE2 induced Erk1/2 and p38 phosphorylation at BAPTA concentrations greater than 25 µM (Fig. 6A, data not shown). Erk 1/2 could be activated by intracellular calcium through several pathways including calcineurin and calmodulin dependent kinase II (CamKII) [22]–[24]. However, we found that activity of calcineurin in WT and EP3 −/− cells significantly decreased after PGE2 stimulation. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Increased mast cell numbers are observed at sites of allergic inflammation and restoration of normal mast cell numbers is critical to the resolution of these responses. Early studies showed that cytokines protect mast cells from apoptosis, suggesting a simple model in which diminished cytokine levels during resolution leads to cell death. The report that prostaglandins can contribute both to recruitment and to the resolution of inflammation together with the demonstration that mast cells express all four PGE2 receptors raises the question of whether a single PGE2 receptor mediates the ability of PGE2 to regulate mast cell survival and apoptosis. We report here that PGE2 through the EP3 receptor promotes cell death of mast cells initiated by cytokine withdrawal. Furthermore, the ability of PGE2 to limit reconstitution of tissues with cultured mast cells is lost in cell lacking the EP3 receptor. Apoptosis is accompanied by higher dissipation of mitochondrial potential (ΔΨm), increased caspase-3 activation, chromatin condensation, and low molecular weight DNA cleavage. PGE2 augmented cell death is dependent on an increase in intracellular calcium release, calmodulin dependent kinase II and MAPK activation. Synergy between the EP3 pathway and the intrinsic mitochondrial apoptotic pathway results in increased Bim expression and higher sensitivity of mast cells to cytokine deprivation. This supports a model in which PGE2 can contribute to the resolution of inflammation in part by augmenting the removal of inflammatory cells in this case, mast cells.
    PLoS ONE 07/2014; 9(7):e102948. DOI:10.1371/journal.pone.0102948 · 3.23 Impact Factor
  • Source
    • "These observations reveal ksr2 À/À mice as a useful model for understanding physiological pathways contributing to human obesity and for revealing novel biochemical mechanisms that link obesity to insulin resistance. KSR2 is a scaffold protein in the Raf/MEK/ERK signaling cascade, where it functions along with its paralog, KSR1, to coordinate the interaction of these molecules to facilitate signal transduction and regulate the intensity and duration of ERK signaling (Dougherty et al. 2009). KSR2 also interacts with and promotes activation of the primary regulator of cellular energy homeostasis, AMPK (Costanzo-Garvey et al. 2009; Fernandez et al. 2012). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Disruption of KSR2 in humans and mice decreases metabolic rate and induces obesity, coincident with dysregulation of glucose homeostasis. Relative to wild-type mice, ksr2−/− mice are small prior to weaning with normal glucose tolerance at 6 weeks of age, but demonstrate excess adiposity by 9 weeks and glucose intolerance by 12–14 weeks. Defects in AICAR tolerance, a measure of whole-body AMPK activation, are detectable only when ksr2−/− mice are obese. Food restriction prevents the obesity of adult ksr2−/− mice and normalizes glucose and AICAR sensitivity. Obesity and glucose intolerance return when ad lib feeding is restored to the diet-restricted mice, indicating that glucose dysregulation is secondary to obesity in ksr2−/− mice. The phenotype of C57BL/6 ksr2−/− mice, including obesity and obesity-related dysregulation of glucose homeostasis, recapitulates that of humans with KSR2 mutations, demonstrating the applicability of the C57BL/6 ksr2−/− mouse model to the study of the pathogenesis of human disease. These data implicate KSR2 as a physiological regulator of glucose metabolism during development affecting energy sensing, insulin signaling, and lipid storage, and demonstrate the value of the C57BL/6 ksr2−/− mouse model as a unique and relevant model system in which to develop and test therapeutic targets for the prevention and treatment of obesity, type 2 diabetes, and obesity-related metabolic disorders.
    07/2014; 2(7). DOI:10.14814/phy2.12053
  • Source
    • "Previous work in our laboratory showed that kinase suppressor of Ras 1 (KSR1), a scaffold protein for Raf, MEK and ERK [18], plays a critical role in the optimal activation of ERK in T cells [16], [17], [19]. Furthermore, KSR1 is known to associate with mTOR, Raptor and Rictor in cycling 293T cells [20]. Thus, KSR1 might regulate mTOR activation in T cells, both by controlling ERK activation and by bringing together members of the ERK and the mTOR pathway. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The mammalian target of rapamycin (mTOR) kinase is a critical regulator of the differentiation of helper and regulatory CD4+ T cells, as well as memory CD8+ T cells. In this study, we investigated the role of the ERK signaling pathway in regulating mTOR activation in T cells. We showed that activation of ERK following TCR engagement is required for sustained mTOR complex 1 (mTORC1) activation. Absence of kinase suppressor of Ras 1 (KSR1), a scaffold protein of the ERK signaling pathway, or inhibition of ERK resulted in decreased mTORC1 activity following T cell activation. However, KSR1-deficient mice displayed normal regulatory CD4+ T cell development, as well as normal memory CD8+ T cell responses to LCMV and Listeria monocytogenes infection. These data indicate that despite its role in mTORC1 activation, KSR1 is not required in vivo for mTOR-dependent T cell differentiation.
    PLoS ONE 02/2013; 8(2):e57137. DOI:10.1371/journal.pone.0057137 · 3.23 Impact Factor
Show more