title: Phosphoinositide 3-kinase activates Rac by entering in a complex with Eps8, Abi1, and Sos-1.
abstract: Class I phosphoinositide 3-kinases (PI3Ks) are implicated in many cellular responses controlled by receptor tyrosine kinases (RTKs), including actin cytoskeletal remodeling. Within this pathway, Rac is a key downstream target/effector of PI3K. However, how the signal is routed from PI3K to Rac is unclear. One possible candidate for this function is the Rac-activating complex Eps8-Abi1-Sos-1, which possesses Rac-specific guanine nucleotide exchange factor (GEF) activity. Here, we show that Abi1 (also known as E3b1) recruits PI3K, via p85, into a multimolecular signaling complex that includes Eps8 and Sos-1. The recruitment of p85 to the Eps8-Abi1-Sos-1 complex and phosphatidylinositol 3, 4, 5 phosphate (PIP3), the catalytic product of PI3K, concur to unmask its Rac-GEF activity in vitro. Moreover, they are indispensable for the activation of Rac and Rac-dependent actin remodeling in vivo. On growth factor stimulation, endogenous p85 and Abi1 consistently colocalize into membrane ruffles, and cells lacking p85 fail to support Abi1-dependent Rac activation. Our results define a mechanism whereby propagation of signals, originating from RTKs or Ras and leading to actin reorganization, is controlled by direct physical interaction between PI3K and a Rac-specific GEF complex.
authors.affiliation: Department of Experimental Oncology, European Institute of Oncology, 20141 Milan, Italy.
authors.forename: Metello
authors.initials: M
authors.lastname: Innocenti
authors.forename: Emanuela
authors.initials: E
authors.lastname: Frittoli
authors.forename: Isabella
authors.initials: I
authors.lastname: Ponzanelli
authors.forename: John R
authors.initials: JR
authors.lastname: Falck
authors.forename: Saskia M
authors.initials: SM
authors.lastname: Brachmann
authors.forename: Pier Paolo
authors.initials: PP
authors.lastname: Di Fiore
authors.forename: Giorgio
authors.initials: G
authors.lastname: Scita
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D000818:Animals; D029681:Arabidopsis Proteins; D019556:COS Cells; D002851:Chromatography, High Pressure Liquid; D003598:Cytoskeletal Proteins; D004789:Enzyme Activation; D005347:Fibroblasts / Q000378:metabolism; D005822:Genetic Vectors; D005982:Glutathione Transferase / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000378:metabolism*; D020837:SOS1 Protein / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D029681:Arabidopsis Proteins; D003598:Cytoskeletal Proteins; C083430:Eps8 protein, mouse; D011506:Proteins; D020837:SOS1 Protein; D005982:Glutathione Transferase; D019869:Phosphatidylinositol 3-Kinases; C087434:ABI1 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases; D020744:rac GTP-Binding Proteins