Article

TOR Complex 2 Integrates Cell Movement during Chemotaxis and Signal Relay in Dictyostelium

Section of Cell and Developmental Biology, Division of Biological Sciences and Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093-0380, USA.
Molecular Biology of the Cell (Impact Factor: 4.47). 11/2005; 16(10):4572-83. DOI: 10.1091/mbc.E05-04-0342
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ABSTRACT

Dictyostelium cells form a multicellular organism through the aggregation of independent cells. This process requires both chemotaxis and signal relay in which the chemoattractant cAMP activates adenylyl cyclase through the G protein-coupled cAMP receptor cAR1. cAMP is produced and secreted and it activates receptors on neighboring cells, thereby relaying the chemoattractant signal to distant cells. Using coimmunoprecipitation and mass spectrometric analyses, we have identified a TOR-containing complex in Dictyostelium that is related to the TORC2 complex of Saccharomyces cerevisiae and regulates both chemotaxis and signal relay. We demonstrate that mutations in Dictyostelium LST8, RIP3, and Pia, orthologues of the yeast TORC2 components LST8, AVO1, and AVO3, exhibit a common set of phenotypes including reduced cell polarity, chemotaxis speed and directionality, phosphorylation of Akt/PKB and the related PKBR1, and activation of adenylyl cyclase. Further, we provide evidence for a role of Ras in the regulation of TORC2. We propose that, through the regulation of chemotaxis and signal relay, TORC2 plays an essential role in controlling aggregation by coordinating the two essential arms of the developmental pathway that leads to multicellularity in Dictyostelium.

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Available from: Koichi Okumura
    • "The mTORC2 complex, in contrast, is less well characterized. Evidence from D. melanogaster, Dictyostelium discoideum, and human cells suggest that mTORC2 responds to insulin and Ras signaling (Lee et al. 2005; Sarbassov et al. 2005; Charest et al. 2010), but its precise mechanism of activation remains elusive. mTORC2 regulates the activity of several substrates involved in cytoskeleton reorganization and cell polarity, but "
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    ABSTRACT: The mechanisms underlying biological aging have been extensively studied in the past 20 years with the avail of mainly four model organisms: the budding yeast Saccharomyces cerevisiae, the nematode Caenorhabditis elegans, the fruitfly Drosophila melanogaster, and the domestic mouse Mus musculus. Extensive research in these four model organisms has identified a few conserved genetic pathways that affect longevity as well as metabolism and development. Here, we review how the mechanistic target of rapamycin (mTOR), sirtuins, adenosine monophosphate-activated protein kinase (AMPK), growth hormone/insulin-like growth factor 1 (IGF-1), and mitochondrial stress-signaling pathways influence aging and life span in the aforementioned models and their possible implications for delaying aging in humans. We also draw some connections between these biochemical pathways and comment on what new developments aging research will likely bring in the near future. © 2015 Cold Spring Harbor Laboratory Press; all rights reserved.
    No preview · Article · Nov 2015 · Cold Spring Harbor Perspectives in Medicine
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    • "Pia is a component of the target of rapamycin complex 2 (TORC2) [40]. TORC2 plays roles in activation of ACA and PKB [40]–[43]. By reconstitution experiments using cells lacking both CRAC and Pia, it has shown that both CRAC and Pia are absolutely required for ACA activity [35]. "
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    ABSTRACT: Background In our previous study we found that the expression of stlA showed peaks both in the early and last stages of development and that a product of SteelyA, 4-methyl-5-pentylbenzene-1,3-diol (MPBD), controlled Dictyostelium spore maturation during the latter. In this study we focused on the role of SteelyA in early stage development. Principal Findings Our stlA null mutant showed aggregation delay and abnormally small aggregation territories. Chemotaxis analysis revealed defective cAMP chemotaxis in the stlA null mutant. cAMP chemotaxis was restored by MPBD addition during early stage development. Assay for cAMP relay response revealed that the stlA null mutant had lower cAMP accumulation during aggregation, suggesting lower ACA activity than the wild type strain. Exogenous cAMP pulses rescued the aggregation defect of the stlA null strain in the absence of MPBD. Expression analysis of cAMP signalling genes revealed lower expression levels in the stlA null mutant during aggregation. Conclusion Our data indicate a regulatory function by SteelyA on cAMP signalling during aggregation and show that SteelyA is indispensable for full activation of ACA.
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    • "Cyclic-AMP–induced blebbing depends on the single G protein encoded in the genome (Wu et al., 1995), but surprisingly, elimination of many proteins considered central to chemotaxis has no effect (Fig. S1 and Table S1). These include components of the TORC2 complex (Lee et al., 2005), the AKT homologue PKB (Meili et al., 1999; see later), the phospholipases PLA2 (Chen et al., 2007) and PLC (Kortholt et al., 2007), and the MAP kinase ERK2 (Segall et al., 1995). Calcium signaling is important for blebbing in zebrafish germ cells (Blaser et al., 2006), but eliminating chemotactic calcium signaling in Dictyostelium by knockout of the presumed IP 3 receptor, IplA (Traynor et al., 2000), has no discernable effect on blebbing. "
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