We are investigating the following questions: 1. how a GPCR chemosensing network regulates the polarized reorganization of the actin cytoskeleton required for protrusion of the cell's front and retraction of its back during chemotaxis. 2. What are the molecular mechanisms underlying phagosome maturation process during phagocytosis? 1. In recent years, the Elmo (Engulfment and Motility) protein family has been implicated in actin cytoskeleton reorganization during both phagocytosis and chemotaxis. ELMO was first discovered as an essential component involved in engulfment of dead cells in C. elegans. DOCK180 and ELMO form a complex that functions as a bipartite GEF to optimally activate Rac and promote actin cytoskeleton rearrangement. DOCK-ELMO complexes also receive signals from GPCRs, integrins and tyrosine kinases to activate Rac, leading to cell migration. However, how GPCRs and other receptors activate DOCK-ELMO has not been determined in any system. As both DOCK and ELMO are evolutionarily conserved, we have been using D. discoideum, as a model system to study the functions of ELMO (A-F) proteins in GPCR-mediated signaling network leading to chemotaxis. We have identified six Elmo homologs in D. discoideum, and have reported that ElmoA functions to maintain cell polarization by preventing excessive actin polymerization around the cell periphery during phagocytosis and chemotaxis. We have been investigating the roles of ELMO-E in chemotaxis. We performed gene disruption, replacement, and over-expression experiments. We found that cells lacking ELMO-E display chemotaxis defect. Visualization of YFP tagged ELMO-E by confocal microscopy revealed ELMO-E translocates to regions of newly forming actin filaments, colocalizing at the leading edge of dominant pseudopod in chemotaxing cells. ELMO-E transiently translocates to membrane under cAMP stimulation by the facility of actin polymerization. This translocation is PI3K independent. More interestingly, we found that ELMO-E interacts with G protein beta subunit and may associate with Rac family proteins as well. Taken together, we propose that ELMO-E protein may be the missing connection between the GPCR/G-protein, the chemoattractant sensing machinery, and the actin cytoskeleton, the machinery of cell movement. 2. Phagocytosis is crucial for host defense against microbial pathogens and for obtaining nutrients in Dictyostelium discoideum. Phagocytosed particles are delivered from phagosomes to lysosomes for degradation, but the molecular mechanism regulating phagosome maturation remains unclear. Using D. discoideum as a model system, we plan to reveal important components involved in phagosome maturation. We have identified 3 novel vesicle-associated receptor tyrosine kinases, VSK1-3, in D. discoideum. Our previous study suggests that localized VSK3 tyrosine kinase signaling on the surface of endosome/lysosomes represents a new control mechanism for phagosome maturation. We are identifying targets of VSK 2 and 3. This study will provide a foundation for understanding the molecular mechanism of VSK signaling that regulate phagosome maturation.

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Schwebs, David J; Pan, Miao; Adhikari, Nirakar et al. (2018) Dictyostelium Erk2 is an atypical MAPK required for chemotaxis. Cell Signal 46:154-165
Pan, Miao; Neilson, Matthew P; Grunfeld, Alexander M et al. (2018) A G-protein-coupled chemoattractant receptor recognizes lipopolysaccharide for bacterial phagocytosis. PLoS Biol 16:e2005754
Gera, Nidhi; Swanson, Kenneth D; Jin, Tian (2017) ?-Arrestin 1-dependent regulation of Rap2 is required for fMLP-stimulated chemotaxis in neutrophil-like HL-60 cells. J Leukoc Biol 101:239-251
Xu, Xuehua; Wen, Xi; Veltman, Douwe M et al. (2017) GPCR-controlled membrane recruitment of negative regulator C2GAP1 locally inhibits Ras signaling for adaptation and long-range chemotaxis. Proc Natl Acad Sci U S A 114:E10092-E10101
Xu, Xuehua; Jin, Tian (2017) ELMO proteins transduce G protein-coupled receptor signal to control reorganization of actin cytoskeleton in chemotaxis of eukaryotic cells. Small GTPases :1-9
Wang, Gang; Cao, Luyang; Liu, Xiaowen et al. (2016) Oxidant Sensing by TRPM2 Inhibits Neutrophil Migration and Mitigates Inflammation. Dev Cell 38:453-62
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
Wen, Xi; Jin, Tian; Xu, Xuehua (2016) Imaging G Protein-coupled Receptor-mediated Chemotaxis and its Signaling Events in Neutrophil-like HL60 Cells. J Vis Exp :
Cao, Xiumei; Yan, Jianshe; Shu, Shi et al. (2014) Arrestins function in cAR1 GPCR-mediated signaling and cAR1 internalization in the development of Dictyostelium discoideum. Mol Biol Cell 25:3210-21
Jin, Tian (2013) Gradient sensing during chemotaxis. Curr Opin Cell Biol 25:532-7

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