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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Actin-Related Protein 2-3 Complex / metabolism
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Actins / chemistry*
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Amino Acid Transport Systems, Basic / metabolism
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Carrier Proteins / chemistry
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Carrier Proteins / metabolism*
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Endocytosis*
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Protein Multimerization*
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Protein Structure, Quaternary
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Protein Transport
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Saccharomyces cerevisiae / cytology*
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Saccharomyces cerevisiae / metabolism*
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Saccharomyces cerevisiae Proteins / chemistry
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Saccharomyces cerevisiae Proteins / metabolism*
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Wiskott-Aldrich Syndrome Protein / metabolism*
Substances
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Actin-Related Protein 2-3 Complex
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Actins
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Amino Acid Transport Systems, Basic
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CAN1 protein, S cerevisiae
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Carrier Proteins
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LAS17 protein, S cerevisiae
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Lsb1 protein, S cerevisiae
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Saccharomyces cerevisiae Proteins
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Wiskott-Aldrich Syndrome Protein
Grants and funding
This work was supported by the Marie Curie Research Training Network “Penelope” (MRTN-CT-2006-036076 to BW and MS), the Agence National de la Recherche (ANR-07-PCV-0035 to BW and ANR-07-BLAN-0065 to SF), the CNRS (ATIP-CNRS 05-00932 and ATIP-Plus 2008-3098 to SF), the Fondation Recherche Médicale (FRM INE20051105238 and FRM-Comité Alsace 2006CX67-1 to SF and FRM Postdoctoral fellowship to J-ODC), the Association pour la Recherche sur le Cancer (ARC JR/MLD/MDV-CR306/7901 to SF) and the National Institutes of Health (NIH) grant GM 1 R01 42759 to DGD. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.