title: Lsb1 is a negative regulator of las17 dependent actin polymerization involved in endocytosis.
abstract: The spatial and temporal regulation of actin polymerization is crucial for various cellular processes. Members of the Wiskott-Aldrich syndrome protein (WASP) family activate the Arp2/3-complex leading to actin polymerization. The yeast Saccharomyces cerevisiae contains only one WASP homolog, Las17, that requires additional factors for its regulation. Lsb1 and Lsb2/Pin3 are two yeast homologous proteins bearing an SH3 domain that were identified as Las17-binding proteins. Lsb2/Pin3 that promotes prion induction was suggested to link this prion formation to the actin cytoskeleton. However, the cellular role of Lsb1 and the molecular function of both Lsb1 and Lsb2 remain unknown. In this study, we show that Lsb1 and/or Lsb2 full-length proteins inhibit Las17-mediated actin polymerization in vitro, Lsb2 being a less potent inhibitor of Las17 activity compared to Lsb1. Addition of Lsb1 or Lsb2 to the corresponding full-length Lsb1/2 further inhibits Las17 activity. Lsb1 and Lsb2 form homo- and hetero-oligomeric complexes suggesting that these two proteins could regulate Las17 activity via dimerization or cooperative binding. In vivo, overexpressed Lsb1 and Lsb2 proteins cluster Las17-CFP in few cytoplasmic punctate structures that are also positive for other Arp2/3-dependent actin polymerization effectors like Sla1 or Abp1. But, only Lsb1 overexpression blocks the internalization step of receptor-mediated endocytosis. This shows a specific function of Lsb1 in endocytosis.
authors.affiliation: Department of Molecular and Cellular Genetics, UMR7156, Université de Strasbourg and CNRS, Strasbourg, France.
authors.forename: Matthias
authors.initials: M
authors.lastname: Spiess
authors.forename: Johan-Owen
authors.initials: JO
authors.lastname: de Craene
authors.forename: Alphée
authors.initials: A
authors.lastname: Michelot
authors.forename: Bruno
authors.initials: B
authors.lastname: Rinaldi
authors.forename: Aline
authors.initials: A
authors.lastname: Huber
authors.forename: David G
authors.initials: DG
authors.lastname: Drubin
authors.forename: Barbara
authors.initials: B
authors.lastname: Winsor
authors.forename: Sylvie
authors.initials: S
authors.lastname: Friant
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000737:chemistry*; D026923:Amino Acid Transport Systems, Basic / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004705:Endocytosis; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D021381:Protein Transport; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism*
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D026923:Amino Acid Transport Systems, Basic; C502212:CAN1 protein, S cerevisiae; D002352:Carrier Proteins; C480361:LAS17 protein, S cerevisiae; C583844:Lsb1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D051316:Wiskott-Aldrich Syndrome Protein