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
Source: PubMed


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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    • "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.
    PLoS ONE 09/2014; 9(9):e106634. DOI:10.1371/journal.pone.0106634 · 3.23 Impact Factor
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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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    ABSTRACT: Blebs and F-actin-driven pseudopods are alternative ways of extending the leading edge of migrating cells. We show that Dictyostelium cells switch from using predominantly pseudopods to blebs when migrating under agarose overlays of increasing stiffness. Blebs expand faster than pseudopods leaving behind F-actin scars, but are less persistent. Blebbing cells are strongly chemotactic to cyclic-AMP, producing nearly all of their blebs up-gradient. When cells re-orientate to a needle releasing cyclic-AMP, they stereotypically produce first microspikes, then blebs and pseudopods only later. Genetically, blebbing requires myosin-II and increases when actin polymerization or cortical function is impaired. Cyclic-AMP induces transient blebbing independently of much of the known chemotactic signal transduction machinery, but involving PI3-kinase and downstream PH domain proteins, CRAC and PhdA. Impairment of this PI3-kinase pathway results in slow movement under agarose and cells that produce few blebs, though actin polymerization appears unaffected. We propose that mechanical resistance induces bleb-driven movement in Dictyostelium, which is chemotactic and controlled through PI3-kinase.
    The Journal of Cell Biology 03/2014; 204(6). DOI:10.1083/jcb.201306147 · 9.83 Impact Factor
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    • "ce of PDK1 from PI3K and TORC1 regulation ( Kamimura and Devreotes , 2010 ; Liao et al . , 2010 ) further demonstrate that AKT , or the related kinase PKBR1 , do not function as downstream targets of either TORC2 or TORC1 in control of phagocytosis . Although during development there is a dependency of actin polarization on a TORC2 – AKT pathway ( Lee et al . , 2005 ) , during growth these components are unlinked for phagocytic uptake ."
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    ABSTRACT: The TOR protein kinase functions in two distinct complexes, TOR complex 1 (TORC1) and 2 (TORC2). TORC1 is required for growth in response to growth factors, nutrients and the cellular energy state; TORC2 regulates AKT signaling, which can modulate cytoskeletal polarization. In its ecological niche, Dictyostelium engulf bacteria and yeast for nutrient capture. Despite the essential role of TORC1 in control of cellular growth, we show that nutrient particle capture (phagocytosis) in Dictyostelium is independent of TORC1-mediated nutrient sensing and growth regulation. However, loss of Dictyostelium TORC2 components Rictor/Pia, SIN1/RIP3 and Lst8 promotes nutrient particle uptake; inactivation of TORC2 leads to increased efficiency and speed of phagocytosis. In contrast to phagocytosis, we show that macropinocytosis, an AKT-dependent process for cellular uptake of fluid phase nutrients, is not regulated by either of the TOR complexes. The integrated and balanced regulation of TORC1 and TORC2 might be crucial in Dictyostelium to coordinate growth and energy needs with other essential TOR-regulated processes.
    Journal of Cell Science 02/2012; 125(Pt 1):37-48. DOI:10.1242/jcs.077040 · 5.43 Impact Factor
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