The exocyst is a Ral effector complex

Moskalenko, Serge A.; Henry, Dale O.; Rossé, Carine; Mirey, Gladys; Camonis, Jacques; White, Michael A.

doi:10.1038/ncb728

Cited by 393 publications

(428 citation statements)

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“…Moreover, Exo70 primarily functions at the early stages of the yeast cell cycle, suggesting a temporal control of Exo70 function (He et al, 2007). In mammalian cells, growth factor signaling involving small GTPases may mediate the subunits assembly, translocation of the exocyst from intracellular compartments to, or activation of the exocyst at, the PM (Sugihara et al, 2002;Moskalenko et al, 2002Moskalenko et al, , 2003Inoue et al, 2003;Takaya et al, 2004;Zuo et al, 2006). Future work will be focused on the identification and characterization of proteins that temporally and/or spatially regulate Exo70 and other exocyst components using different eukaryotic systems.…”

Section: Discussionmentioning

confidence: 99%

Phosphatidylinositol 4,5-Bisphosphate Mediates the Targeting of the Exocyst to the Plasma Membrane for Exocytosis in Mammalian Cells

Liu

Zuo

Peng

et al. 2007

MBoC

193

248

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The exocyst is an evolutionarily conserved octameric protein complex that tethers post-Golgi secretory vesicles at the plasma membrane for exocytosis. To elucidate the mechanism of vesicle tethering, it is important to understand how the exocyst physically associates with the plasma membrane (PM). In this study, we report that the mammalian exocyst subunit Exo70 associates with the PM through its direct interaction with phosphatidylinositol 4,5-bisphosphate (PI(4,5)P 2 ). Furthermore, we have identified key conserved residues at the C-terminus of Exo70 that are crucial for the interaction of Exo70 with PI(4,5)P 2 . Disrupting Exo70-PI(4,5)P 2 interaction abolished the membrane association of Exo70. We have also found that wild-type Exo70 but not the PI(4,5)P 2 -binding-deficient Exo70 mutant is capable of recruiting other exocyst components to the PM. Using the ts045 vesicular stomatitis virus glycoprotein trafficking assay, we demonstrate that Exo70-PI(4,5)P 2 interaction is critical for the docking and fusion of post-Golgi secretory vesicles, but not for their transport to the PM. INTRODUCTIONExocytosis is important for a variety of cellular functions, ranging from the release of hormones to the incorporation of membrane proteins for cell growth and morphogenesis. The late stage of exocytosis is a multistep process that includes directional transport, tethering, docking, and fusion of postGolgi secretory vesicles with the plasma membrane (PM). The tethering step, defined as the initial contact of secretory vesicles with the PM before SNARE-mediated docking and fusion (Pfeffer, 1999;Guo et al., 2000;Waters and Hughson, 2000;Whyte and Munro, 2002), is mediated by the exocyst, an evolutionarily conserved octameric complex composed of Sec3, Sec5, Sec6, Sec8, Sec10, Sec15, Exo70, and Exo84 (for review, see Guo et al., 2000;Hsu et al., 2004;Munson and Novick, 2006;Wang and Hsu, 2006). In budding yeast, the exocyst components localize to the growing end of the daughter cell ("bud"), where active exocytosis and membrane addition take place (TerBush and Novick, 1995;Finger et al., 1998, Guo et al., 1999. This localization pattern contrasts that of the membrane fusion machine, the t-SNAREs, which are evenly distributed along both the mother and daughter cell membrane (Brennwald et al., 1994). In mammalian cells, the exocyst components were found in the cytosol, recycling endosomes and trans-Golgi network Fö lsch et al., 2003;Ang et al., 2004;Langevin et al., 2005). However, they are recruited to the PM during a number of cellular processes. For example, in epithelial cells, the exocyst is recruited to the adherens junction region upon cell-cell contact, where it mediates protein and membrane addition at the basolateral domain (Grindstaff et al., 1998;Yeaman et al., 2001); in developing neurons, the exocyst is localized to the growing neurites, where it mediates membrane expansion (Hazuka et al., 1999;Vega and Hsu, 2001); during cell migration, the exocyst is recruited to the leading edges of the PM (Rosse et al., 2006;...

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Section: Discussionmentioning

confidence: 99%

Phosphatidylinositol 4,5-Bisphosphate Mediates the Targeting of the Exocyst to the Plasma Membrane for Exocytosis in Mammalian Cells

Liu

Zuo

Peng

et al. 2007

MBoC

193

248

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“…Sec5 and Exo84 are members of the exocyst complex and are responsible for targeting various secretory vesicles to specific regions of the cellular membrane [39,40] . This regulation of vesicular trafficking controls various complex cellular functions such as polarized membrane formation, cytokinesis, tight junction formation, and tumor cell invasion [41][42][43][44] .…”

Section: Ras Mutation and Cancer Therapeuticsmentioning

confidence: 99%

The RAS-RAL axis in cancer: evidence for mutation-specific selectivity in non-small cell lung cancer

Guin

Theodorescu

2015

Acta Pharmacol Sin

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Activating RAS mutations are common in human tumors. These mutations are often markers for resistance to therapy and subsequent poor prognosis. So far, targeting the RAF-MEK-ERK and PI3K-AKT signaling pathways downstream of RAS is the only promising approach in the treatment of cancer patients harboring RAS mutations. RAL GTPase, another downstream effector of RAS, is also considered as a therapeutic option for the treatment of RAS-mutant cancers. The RAL GTPase family comprises RALA and RALB, which can have either divergent or similar functions in different tumor models. Recent studies on non-small cell lung cancer (NSCLC) have showed that different RAS mutations selectively activate specific effector pathways. This observation requires broader validation in other tumor tissue types, but if true, will provide a new approach to the treatment of RAS-mutant cancer patients by targeting specific downstream RAS effectors according to the type of RAS mutation. It also suggests that RAL GTPase inhibition will be an important treatment strategy for tumors harboring RAS glycine to cysteine (G12C) or glycien to valine (G12V) mutations, which are commonly found in NSCLC and pancreatic cancer. Review RAS GTPase overviewRAS is the most extensively studied GTPase [1] . It is known to regulate various cellular functions, including proliferation, survival, growth, migration, differentiation and cytoskeletal dynamics [2][3][4] (Figure 1). Not coincidentally, increased activities of all of these processes are required by tumor cells to promote tumor growth. Activating oncogenic RAS mutations lead to treatment resistance in various tumor models and poor patient outcomes [3,[5][6][7][8][9] . Three human RAS genes have been identified: HRAS, KRAS, and NRAS [1,2] . These encode the related proteins HRAS, KRAS and NRAS, respectively, of 189 amino acids in length [1,4] . KRAS exists as two isoforms, 4A and 4B, which are generated by alternative exon splicing [10] . These different RAS genes are well known to have differential cellular specificities and intrinsic transforming potentials [3,4,10] .In normal cells, RAS proteins act as molecular switches for critical cellular functions. RAS proteins are activated by upstream receptors such as receptor tyrosine kinases * To whom correspondence should be addressed. E-mail dan.theodorescu@ucdenver.edu Received 2014-08-07 Accepted 2014-10-30 Figure 1. RAS GTPase activation and downstream signaling. The cartoon shows the mechanism of RAS GTPase activation by upstream stimuli and numerous downstream effectors stimulated by activated RAS. RAS regulates critical cellular functions through these effectors. Constitutive RAS activation due to mutations leads to protumorigenic signaling through these effectors.

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“…In their active GTPbound states, RalA and RalB interact with a set of effectors that mediate their functions in cells. These include RalBP1 (RLIP) (4,15,23), the exocyst complex (3,22,24), and Zonab (12). Despite these similarities, RalA and RalB appear to play quite distinct roles in cells.…”

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confidence: 99%

RalGDS Couples Growth Factor Signaling to Akt Activation

Hao

Wong

Feig

2008

Molecular and Cellular Biology

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The Akt kinase is a key regulator of cell proliferation and survival. It is activated in part by PDK1-induced phosphorylation. Here we show that RalGDS, a Ras effector protein that activates Ral GTPases, has a second function that promotes Akt phosphorylation by PDK1 by bringing these two kinases together. In support of this conclusion is our finding that suppression of RalGDS expression in cells inhibits both epidermal growth factor and insulin-induced phosphorylation of Akt. Moreover, while PDK1 complexes with N-GDS, Akt complexes with the central region of RalGDS through an intermediary, JIP1. The biological significance of this newly discovered RalGDS function is highlighted by the observation that an N-terminally deleted mutant of RalGDS that retains the ability to activate Ral proteins but loses the ability to activate Akt also fails to promote cell proliferation. Thus, RalGDS forms a nexus that transduces growth factor signaling to both Ral GTPase and Akt-mediated signaling cascades.The Akt kinase is a key mediator of the actions of many growth factors and hormones (10). Its effects on cells include regulation of metabolism, gene transcription, cell proliferation, angiogenesis, and apoptosis. Loss or gain of Akt activity contributes to a variety of diseases, including diabetes and cancer. Akt influences these processes by phosphorylating a broad spectrum of substrates, including MDM2, FOXO transcription factors, p27 kip1 , Bad, and GSK3. The three Akt isoforms, Akt1 to -3, belong to the AGC family of kinases, all of which are activated by the PDK1 kinase (for review, see reference 20). The accepted mode of Akt activation involves ligand-induced activation of phosphatidylinositol 3-kinase (PI3-kinase), which leads to the production of PIP2 and PIP3. These phospholipids interact with the PH domain of Akt to target the protein to PDK1 in the plasma membrane, where PDK1 phosphorylates Akt on threonine 308 (2). How specific PDK1 substrates are chosen for activation in response to specific stimuli is poorly understood. A secondary activation event occurs through phosphorylation of Akt at serine 473. Multiple kinases have been reported to be responsible for this event, the most recent of which is the rictor/mTor complex (29).RalGDS is one of a family of guanine nucleotide exchange factors (GEFs) that activate Ral-GTPases in cells by promoting their switch from GDP-bound to GTP-bound states. A subset of these GEFs, including RalGDS, Rlf, Rgl, and Rgl3, are downstream effectors of Ras proteins, as active Ras binds to their C termini and targets them to Ral in cells (25). Recent studies on human cells and in knockout mice have highlighted the importance of this effector pathway in the Ras-mediated oncogenesis. For example, Ral exchange factors can replace Ras in assays designed to test the minimal number of genes that are required to transform primary human cells to a tumorigenic state (14, 26), while a RalGDS knockout suppresses tumor formation in a Ras-mediated tumor model (13).Activation of RalGDS in cells also ...

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The exocyst is a Ral effector complex

Cited by 393 publications

References 44 publications

Phosphatidylinositol 4,5-Bisphosphate Mediates the Targeting of the Exocyst to the Plasma Membrane for Exocytosis in Mammalian Cells

Phosphatidylinositol 4,5-Bisphosphate Mediates the Targeting of the Exocyst to the Plasma Membrane for Exocytosis in Mammalian Cells

The RAS-RAL axis in cancer: evidence for mutation-specific selectivity in non-small cell lung cancer

RalGDS Couples Growth Factor Signaling to Akt Activation

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