Dataset Information

Rac regulation of chemotaxis and morphogenesis in Dictyostelium.

ABSTRACT: 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.

SUBMITTER: Park KC

PROVIDER: S-EPMC524383 | biostudies-literature | 2004 Oct

REPOSITORIES: biostudies-literature

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Rac regulation of chemotaxis and morphogenesis in Dictyostelium.

Park Kyung Chan KC Rivero Francisco F Meili Ruedi R Lee Susan S Apone Fabio F Firtel Richard A RA

The EMBO journal 20041007 21

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 ...[more]

PMID: 15470506

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Project description:BACKGROUND: Ras proteins are guanine-nucleotide-binding enzymes that couple cell surface receptors to intracellular signaling pathways controlling cell proliferation and differentiation, both in lower and higher eukaryotes. They act as molecular switches by cycling between active GTP and inactive GDP-bound states, through the action of two classes of regulatory proteins: a) guanine nucleotide exchange factor (GEFs) and b) GTP-ase activating proteins (GAPs). Genome wide analysis of the lower eukaryote Dictyostelium discoideum revealed a surprisingly large number of Ras Guanine Nucleotide Exchange Factors (RasGEFs). RasGEFs promote the activation of Ras proteins by catalyzing the exchange of GDP for GTP, thus conferring to RasGEFs the role of main activator of Ras proteins. Up to date only four RasGEFs, which are all non-redundant either for growth or development, have been characterized in Dictyostelium. We report here the identification and characterization of a fifth non-redundant GEF, RasGEFM. RESULTS: RasGEFM is a multi-domain protein containing six poly-proline stretches, a DEP, RasGEFN and RasGEF catalytic domain. The rasGEFM gene is differentially expressed during growth and development. Inactivation of the gene results in cells that form small, flat aggregates and fail to develop further. Expression of genes required for aggregation is delayed. Chemotaxis towards cAMP is impaired in the mutant, due to inability to inhibit lateral pseudopods. Endogenous cAMP accumulates during early development to a much lower extent than in wild type cells. Adenylyl cyclase activation in response to cAMP pulses is strongly reduced, by contrast guanylyl cyclase is stimulated to higher levels than in the wild type. The actin polymerization response to cAMP is also altered in the mutant. Cyclic AMP pulsing for several hours partially rescues the mutant. In vitro experiments suggest that RasGEFM acts downstream of the cAMP receptor but upstream of the G protein. CONCLUSION: The data indicate that RasGEFM is involved in the establishment of the cAMP relay system. We propose that RasGEFM is a component of a Ras regulated pathway, which integrate signals acting as positive regulator for adenylyl cyclase and negative regulator for guanylyl cyclase. Altered guanylyl cyclase, combined with defective regulation of actin polymerization, results in altered chemotaxis.

Dataset Information

Rac regulation of chemotaxis and morphogenesis in Dictyostelium.

Publications

Rac regulation of chemotaxis and morphogenesis in Dictyostelium.

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