A Novel Dynamin-associating Molecule, Formin-binding Protein 17, Induces Tubular Membrane Invaginations and Participates in Endocytosis

Actin reorganization is important for regulation of neuronal morphology. Neural Wiskott-Aldrich syndrome protein (N-WASP) is an important regulator of actin polymerization and also known to be strongly expressed in brain. Recently, Toca-1 (transducer of Cdc42-dependent actin assembly) has been shown to be required for Cdc42 to activate N-WASP from biochemical experiments. Toca-1 has three functional domains: an F-BAR/EFC domain at the N terminus, an HR1 at the center, and an SH3 domain at the C terminus. The F-BAR/EFC domain induces tubular invagination of plasma membrane, while Toca-1 binds both N-WASP and Cdc42 through the SH3 domain and the HR1, respectively. However, the physiological role of Toca-1 is completely unknown. Here we have investigated the neural function of Toca-1. Toca-1 is strongly expressed in neurons including hippocampal neurons in developing brain at early times. Knockdown of Toca-1 in PC12 cells significantly enhances neurite elongation. Consistently, overexpression of Toca-1 suppresses neurite elongation through the F-BAR/EFC domain with a membrane invaginating property, suggesting an implication of membrane trafficking in the neural function of Toca-1. In addition, knockdown of N-WASP, to our surprise, also enhances neurite elongation in PC12 cells, which is in clear contrast to the previous report that dominant negative mutants of N-WASP suppress neurite extension in PC12 cells. On the other hand, knockdown of Toca-1 in cultured rat hippocampal neurons enhances axon branching a little but not axon elongation, while knockdown of N-WASP enhances both axon elongation and branching. These results suggest that a vesicle trafficking regulator Toca-1 regulates different aspects of neuronal morphology from N-WASP.Actin reorganization is important for regulating morphology of various cells including neurons (1). Neurons extend axons during the early phase of neural development. In this process, growth cones at the growing tips of axons play a critical role by detecting the guidance cues and mediating motility. Neurons then form synaptic connections and form a complex neural network to function properly. Rho family GTPases are implicated in morphological changes of various cells by reorganizing actin cytoskeleton (1). Among them, Rho, Rac, and Cdc42 have been extensively investigated. In neurons, Rac and Cdc42 stimulate neurite extension, whereas Rho triggers growth cone collapse and neurite retraction.Wiskott-Aldrich syndrome protein (WASP) 3 family members play essential roles in actin polymerization and have been much studied as a link between Rho family and actin cytoskeleton (2). WASP family members are characterized by their C-terminal VCA region (for verprolin homology (V) region, cofilin-homology (C) region, and acidic (A) region). They bind to both G-actin through the V region and Arp2/3 complex through the CA region, and activate Arp2/3 complex. The activated Arp2/3 complex nucleates de novo actin filaments and forms branched actin filament network. Five WASP family members have been d...

Section: Overexpressed Toca-1 Suppresses Neurite Elongation Of Pc12 Csupporting

confidence: 70%

Section: Overexpressed Toca-1 Suppresses Neurite Elongation Of Pc12 Cmentioning

confidence: 99%

mentioning

confidence: 99%

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Regulation of Neuronal Morphology by Toca-1, an F-BAR/EFC Protein That Induces Plasma Membrane Invagination

Kakimoto¹,

Katoh

Negishi

2006

“…In particular, FBP17 (formin-binding protein 17) has been shown to interact with dynamin and to regulate endocytosis by forming vesicotubular structures (31). PSTPIP, on the other hand, is involved in actin polymerization (32), a process known to be important for endocytosis (33).…”

Section: Discussionmentioning

confidence: 99%

Binding of the Intracellular Fas Ligand (FasL) Domain to the Adaptor Protein PSTPIP Results in a Cytoplasmic Localization of FasL

Baum

Kirkin

Fernández

et al. 2005

The tumor necrosis factor family member Fas ligand (FasL) induces apoptosis in Fas receptor-expressing target cells and is an important cytotoxic effector molecule used by CTL-and NK-cells. In these hematopoietic cells, newly synthesized FasL is stored in specialized secretory lysosomes and only delivered to the cell surface upon activation and target cell recognition. FasL contains an 80-amino acid-long cytoplasmic tail, which includes a proline-rich domain as a bona fide Src homology 3 domain-binding site. This proline-rich domain has been implicated in FasL sorting to secretory lysosomes, and it may also be important for reverse signaling via FasL, which has been described to influence T-cell activation. Here we report the identification of the Src homology 3 domaincontaining adaptor protein PSTPIP as a FasL-interacting partner, which binds to the proline-rich domain. PSTPIP co-expression leads to an increased intracellular localization of Fas ligand, thereby regulating extracellular availability and cytotoxic activity of the molecule. In addition, we demonstrate recruitment of the tyrosine phosphatase PTP-PEST by PSTPIP into FasL⅐PSTPIP⅐PTP-PEST complexes which may contribute to FasL reverse signaling.Fas ligand (FasL 3 ; CD95/APO-1 ligand, CD178, TNFSF6) is a 281-amino acid (aa)-long type II transmembrane molecule belonging to the large TNF family of proteins that bind to and activate members of the TNF receptor family (1, 2). FasL and its corresponding receptor Fas (CD95/APO-1) both interact as oligomers (3), and the activated Fas receptor complex initiates a proapoptotic death signal in the receptorbearing cell (4, 5).Although mainly known for its death-promoting activity, FasL has also been studied in the context of further nonapoptotic functions (1, 2, 6). Such experiments are motivated by the special structure of this type II transmembrane protein. In addition to its hydrophobic transmembrane domain, which anchors the molecule within the plasma membrane, and to its extracellular ectodomain, responsible for binding to its receptor, the FasL protein possesses an 80-aa-long N-terminal intracellular part that is responsible for the transduction of (extracellular) signals into FasL-bearing cells and/or that may fulfill regulatory functions. Such a "reverse signaling" has been described in mouse T-cells, which display an altered proliferative behavior upon triggering of their FasL surface molecules (7-9). Results obtained with mouse Sertoli cells, in which FasL engagement leads to mitogen-activated protein kinase activation, as measured by an increase in Erk phosphorylation, also imply stimulatory FasL reverse signaling (10).The importance of the intracellular domain for FasL function and regulation is underlined by its high homology among different species (7,11,12). Several signaling motives within the FasL intracellular domain are highly conserved, including a tandem casein kinase I phosphorylation site (aa 17-21 (11)), a phosphorylatable tyrosine at position 7, a proline-rich region (aa 40 -70) with bona...

“…F-BAR or EFC domains (9,13) were identified from a group of proteins known as Pombe Cds15 homology proteins (25,26) that are involved in various actin-related processes, including clathrin-mediated endocytosis. F-BAR domains, like N-BAR domains, bind anionic lipids and induce vesicle tubulation in vitro (16,27) and cause tubulation of plasma membrane when overexpressed in mammalian cells (16,27,28). Crystal structures of F-BAR domains of FBP17 and CIP4 showed that they also form a crescent-like dimer but that their intrinsic curvature is smaller than that of dAmp-BAR (29).…”

mentioning

confidence: 99%

Phosphatidylinositol 4,5-Bisphosphate (PtdIns(4,5)P2) Specifically Induces Membrane Penetration and Deformation by Bin/Amphiphysin/Rvs (BAR) Domains

Yoon¹,

Zhang²,

Cho

2012

Background:The roles of anionic lipids in the actions of N-BAR domains are not fully understood. Results: PtdIns(4,5)P 2 specifically induces membrane penetration and self-association of N-BAR domains. Conclusion: PtdIns(4,5)P 2 is an important regulator of the membrane deforming activity of N-BAR domains. Significance: This study provides new insight into how PtdIns(4,5)P 2 in the plasma membrane regulates the endocytic function of N-BAR domain proteins.