title: Involvement of the cytoskeleton in controlling leading-edge function during chemotaxis.
abstract: In response to directional stimulation by a chemoattractant, cells rapidly activate a series of signaling pathways at the site closest to the chemoattractant source that leads to F-actin polymerization, pseudopod formation, and directional movement up the gradient. Ras proteins are major regulators of chemotaxis in Dictyostelium; they are activated at the leading edge, are required for chemoattractant-mediated activation of PI3K and TORC2, and are one of the most rapid responders, with activity peaking at approximately 3 s after stimulation. We demonstrate that in myosin II (MyoII) null cells, Ras activation is highly extended and is not restricted to the site closest to the chemoattractant source. This causes elevated, extended, and spatially misregulated activation of PI3K and TORC2 and their effectors Akt/PKB and PKBR1, as well as elevated F-actin polymerization. We further demonstrate that disruption of specific IQGAP/cortexillin complexes, which also regulate cortical mechanics, causes extended activation of PI3K and Akt/PKB but not Ras activation. Our findings suggest that MyoII and IQGAP/cortexillin play key roles in spatially and temporally regulating leading-edge activity and, through this, the ability of cells to restrict the site of pseudopod formation.
authors.affiliation: Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093-0380, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Lee
authors.forename: Zhouxin
authors.initials: Z
authors.lastname: Shen
authors.forename: Douglas N
authors.initials: DN
authors.lastname: Robinson
authors.forename: Steven
authors.initials: S
authors.lastname: Briggs
authors.forename: Richard A
authors.initials: RA
authors.lastname: Firtel
mesh_terms: D000818:Animals; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism*; D004023:Dictyostelium / Q000166:cytology / Q000378:metabolism; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism; D024462:Myosin Type II / Q000235:genetics / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D011554:Pseudopodia / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D020703:ras GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C101203:IQ motif containing GTPase activating protein 1; D008840:Microfilament Proteins; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; C101109:ctxA protein, Dictyostelium discoideum; C101110:ctxB protein, Dictyostelium discoideum; D020703:ras GTPase-Activating Proteins; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D024462:Myosin Type II; D020830:rac1 GTP-Binding Protein; D018631:ras Proteins