title: Negative feedback regulation of Rac in leukocytes from mice expressing a constitutively active phosphatidylinositol 3-kinase gamma.
abstract: Polarization of chemotaxing cells depends on positive feedback loops that amplify shallow gradients of chemoattractants into sharp intracellular responses. In particular, reciprocal activation of phosphatidylinositol 3-kinases (PI3Ks) and small GTPases like Rac leads to accumulation, at the leading edge, of the PI3K product phosphatidylinositol 3,4,5-trisphosphate (PIP3). Mice carrying a "knockin" allele of the G protein-coupled receptor (GPCR)-activated PI3Kgamma, encoding a plasma membrane-targeted protein appeared normal, but their leukocytes showed GPCR-uncoupled PIP3 accumulation. In vivo, the mutation increased proliferation and decreased apoptosis, leading to leukocytosis and delayed resolution of inflammation in wound healing. Mutant leukocytes showed significantly impaired directional cell migration in response to chemoattractants. Stimulated mutant macrophages did not polarize PIP3 and showed a shortened Rac activation because of enhanced PI3K-dependent activation of RacGAPs. Together with the finding that chemoattractants stimulate a PIP3-dependent GAP activation in wild-type macrophages, these results identify a molecular mechanism involving PI3K- and RacGAP-dependent negative control of Rac that limits and fine-tunes feedback loops promoting cell polarization and directional motility.
authors.affiliation: Dipartimento di Genetica, Biologia e Biochimica, Molecular Biotechnology Center, University of Torino, Via Nizza 52, 10126 Torino, Italy.
authors.forename: Carlotta
authors.initials: C
authors.lastname: Costa
authors.forename: Laura
authors.initials: L
authors.lastname: Barberis
authors.forename: Chiara
authors.initials: C
authors.lastname: Ambrogio
authors.forename: Andrea D
authors.initials: AD
authors.lastname: Manazza
authors.forename: Enrico
authors.initials: E
authors.lastname: Patrucco
authors.forename: Ornella
authors.initials: O
authors.lastname: Azzolino
authors.forename: Paul O
authors.initials: PO
authors.lastname: Neilsen
authors.forename: Elisa
authors.initials: E
authors.lastname: Ciraolo
authors.forename: Fiorella
authors.initials: F
authors.lastname: Altruda
authors.forename: Glenn D
authors.initials: GD
authors.lastname: Prestwich
authors.forename: Roberto
authors.initials: R
authors.lastname: Chiarle
authors.forename: Matthias
authors.initials: M
authors.lastname: Wymann
authors.forename: Anne
authors.initials: A
authors.lastname: Ridley
authors.forename: Emilio
authors.initials: E
authors.lastname: Hirsch
mesh_terms: D000818:Animals; D049109:Cell Proliferation; D002478:Cells, Cultured; D002633:Chemotaxis; D058544:Class Ib Phosphatidylinositol 3-Kinase; D015971:Gene Expression Regulation, Enzymologic; D007527:Isoenzymes / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D007962:Leukocytes / Q000166:cytology / Q000201:enzymology*; D051379:Mice; D008822:Mice, Transgenic; D019869:Phosphatidylinositol 3-Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D058544:Class Ib Phosphatidylinositol 3-Kinase; C546764:Pik3cg protein, mouse; D020744:rac GTP-Binding Proteins