Rac regulation of chemotaxis and morphogenesis in Dictyostelium.
Chemotaxis requires localized F-actin polymerization at the site of the plasma membrane closest to the chemoattractant source, a process controlled by Rac/Cdc42 GTPases. We identify Dictyostelium RacB as an essential mediator of this process. RacB is activated upon chemoattractant stimulation, exhibiting biphasic kinetics paralleling F-actin polymerization. racB null cells have strong chemotaxis and morphogenesis defects and a severely reduced chemoattractant-mediated F-actin polymerization and PAKc activation. RacB activation is partly controlled by the PI3K pathway. pi3k1/2 null cells and wild-type cells treated with LY294002 exhibit a significantly reduced second peak of RacB activation, which is linked to pseudopod extension, whereas a PTEN hypomorph exhibits elevated RacB activation. We identify a RacGEF, RacGEF1, which has specificity for RacB in vitro. racgef1 null cells exhibit reduced RacB activation and cells expressing mutant RacGEF1 proteins display chemotaxis and morphogenesis defects. RacGEF1 localizes to sites of F-actin polymerization. Inhibition of this localization reduces RacB activation, suggesting a feedback loop from RacB via F-actin polymerization to RacGEF1. Our findings provide a critical linkage between chemoattractant stimulation, F-actin polymerization, and chemotaxis in Dictyostelium.
Section of Cell and Developmental Biology, Division of Biological Sciences, Center for Molecular Genetics, University of California, San Diego, La Jolla, CA 92093-0380, USA.
Kyung Chan
KC
Park
Francisco
F
Rivero
Ruedi
R
Meili
Susan
S
Lee
Fabio
F
Apone
Richard A
RA
Firtel
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D048430:Cell Shape; D002630:Chemotactic Factors / Q000378:metabolism; D002633:Chemotaxis / Q000502:physiology*; D004023:Dictyostelium / Q000166:cytology* / Q000502:physiology*; D004789:Enzyme Activation; D008969:Molecular Sequence Data; D009024:Morphogenesis; D024462:Myosin Type II / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D020744:rac GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D000199:Actins; D002630:Chemotactic Factors; D015800:Protozoan Proteins; D019869:Phosphatidylinositol 3-Kinases; D024462:Myosin Type II; D020744:rac GTP-Binding Proteins