title: The Ras/Rac guanine nucleotide exchange factor mammalian Son-of-sevenless interacts with PACSIN 1/syndapin I, a regulator of endocytosis and the actin cytoskeleton.
abstract: Mammalian Son-of-sevenless (mSos) functions as a guanine nucleotide exchange factor for Ras and Rac, thus regulating signaling to mitogen-activated protein kinases and actin dynamics. In the current study, we have identified a new mSos-binding protein of 50 kDa (p50) that interacts with the mSos1 proline-rich domain. Mass spectrometry analysis and immunodepletion studies reveal p50 as PACSIN 1/syndapin I, a Src homology 3 domain-containing protein functioning in endocytosis and regulation of actin dynamics. In addition to PACSIN 1, which is neuron-specific, mSos also interacts with PACSIN 2, which is expressed in neuronal and nonneuronal tissues. PACSIN 2 shows enhanced binding to the mSos proline-rich domain in pull-down assays from brain extracts as compared with lung extracts, suggesting a tissue-specific regulation of the interaction. Proline to leucine mutations within the Src homology 3 domains of PACSIN 1 and 2 abolish their binding to mSos, demonstrating the specificity of the interactions. In situ, PACSIN 1 and mSos1 are co-expressed in growth cones and actin-rich filopodia in hippocampal and dorsal root ganglion neurons, and the two proteins co-immunoprecipitate from brain extracts. Moreover, epidermal growth factor treatment of COS-7 cells causes co-localization of PACSIN 1 and mSos1 in actin-rich membrane ruffles, and their interaction is regulated through epidermal growth factor-stimulated mSos1 phosphorylation. These data suggest that PACSINs may function with mSos1 in regulation of actin dynamics.
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal H3A 2B4, Quebec, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Wasiak
authors.forename: C C
authors.initials: CC
authors.lastname: Quinn
authors.forename: B
authors.initials: B
authors.lastname: Ritter
authors.forename: E
authors.initials: E
authors.lastname: de Heuvel
authors.forename: D
authors.initials: D
authors.lastname: Baranes
authors.forename: M
authors.initials: M
authors.lastname: Plomann
authors.forename: P S
authors.initials: PS
authors.lastname: McPherson
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D003599:Cytoskeleton / Q000378:metabolism; D004705:Endocytosis; D051381:Rats; D015398:Signal Transduction; D020664:Son of Sevenless Proteins / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; C117738:Pacsin1 protein, rat; D020664:Son of Sevenless Proteins; D020744:rac GTP-Binding Proteins; D018631:ras Proteins