1: cAR1-mediated spatiotemporal dynamics of Ras signaling. To reveal the inhibitory mechanism, we monitored spatiotemporal activation of Ras by observing the membrane translocation of a fluorescent probe, active Ras Binding Domain fused to GFP (RBD-GFP) in response to a cAMP gradient. The Ras-activation dynamics we observed indicate that a negative regulator, possibly a RasGAP, is gradually recruited to the membrane and promotes Ras inactivation. In mammalian cells, a RasGAP containing a phospholipid-binding domain has been shown to translocate to the plasma membrane's inner face, deactivate Ras, and thereby inhibit PI3K. We proposed that a similar phospholipid-bound RasGAP is likely to be an important inhibitor in cAR1-mediated chemosensing in D. discoideum. To test this hypothesis, we are studying the roles of RasGAP in chemosensing in D. discoideum. 2: A novel Gbg effector, ElmoE, transduces GPCR signaling to the actin network during chemotaxis. Activation of G-protein-coupled receptors (GPCRs) leads to the dissociation of heterotrimeric G-proteins into Ga and Gbg subunits, which go on to regulate various effectors involved in a panoply of cellular responses. During chemotaxis, Gbg subunits regulate actin assembly and migration, but the protein(s) linking Gbg to the actin cytoskeleton remains unknown. Here, we identified a new Gbg effector, ElmoE in Dictyostelium, and demonstrated that it is required for GPCR-mediated chemotaxis. Remarkably, ElmoE interacts with Gbg and Dock-like proteins to activate the small GTPase Rac, in a GPCR-dependent manner, and also associates with Arp2/3 complex and F-actin. Thus, ElmoE serves as the first direct link between chemoattractant GPCRs, G-proteins and the actin cytoskeleton. The pathway, consisting of GPCR, Gbg, Elmo/Dock, Rac, and Arp2/3, spatially guides the growth of dendritic actin networks in pseudopods of eukaryotic cells during chemotaxis (Yan et al Dev. Cell 2012).

Project Start
Project End
Budget Start
Budget End
Support Year
11
Fiscal Year
2012
Total Cost
$505,084
Indirect Cost
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State
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Pan, Miao; Xu, Xuehua; Chen, Yong et al. (2016) Identification of a Chemoattractant G-Protein-Coupled Receptor for Folic Acid that Controls Both Chemotaxis and Phagocytosis. Dev Cell 36:428-39
Cao, Xiumei; Yan, Jianshe; Shu, Shi et al. (2014) Arrestins function in cAR1 GPCR-mediated signaling and cAR1 internalization in the development of D. discoideum. Mol Biol Cell :
Jin, Tian (2013) Gradient sensing during chemotaxis. Curr Opin Cell Biol 25:532-7
Kataria, Rama; Xu, Xuehua; Fusetti, Fabrizia et al. (2013) Dictyostelium Ric8 is a nonreceptor guanine exchange factor for heterotrimeric G proteins and is important for development and chemotaxis. Proc Natl Acad Sci U S A 110:6424-9
Xu, Xuehua; Jin, Tian (2012) A shortcut from GPCR signaling to Rac-mediated actin cytoskeleton through an ELMO/DOCK complex. Small GTPases 3:183-5
Yan, Jianshe; Jin, Tian (2012) Signaling network from GPCR to the actin cytoskeleton during chemotaxis. Bioarchitecture 2:15-18
Yan, Jianshe; Mihaylov, Vassil; Xu, Xuehua et al. (2012) A Gýýýý effector, ElmoE, transduces GPCR signaling to the actin network during chemotaxis. Dev Cell 22:92-103
Jin, Tian (2011) GPCR-controlled chemotaxis in Dictyostelium discoideum. Wiley Interdiscip Rev Syst Biol Med 3:717-27
Yan, Jianshe; Hereld, Dale; Jin, Tian (2010) Chemotaxis: new role for Ras revealed. Protein Cell 1:879-80
Brzostowski, Joseph A; Fey, Petra; Yan, Jianshe et al. (2009) The Elmo family forms an ancient group of actin-regulating proteins. Commun Integr Biol 2:337-40

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