WIP, a protein associated with Wiskott–Aldrich syndrome protein, induces actin polymerization and redistribution in lymphoid cells

Abstract

Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency caused by mutations that affect the WAS protein (WASP) and characterized by cytoskeletal abnormalities in hematopoietic cells. By using the yeast two-hybrid system we have identified a proline-rich WASPinteracting protein (WIP), which coimmunoprecipitated with WASP from lymphocytes. WIP binds to WASP at a site distinct from the Cdc42 binding site and has actin as well as profilin binding motifs. Expression of WIP in human B cells, but not of a WIP truncation mutant that lacks the actin binding motif, increased polymerized actin content and induced the appearance of actin-containing cerebriform projections on the cell surface. These results suggest that WIP plays a role in cortical actin assembly that may be important for lymphocyte function.Wiskott-Aldrich syndrome (WAS) is characterized by thrombocytopenia, eczema, impaired immunity, and a predisposition to develop lymphomas and leukemias (1). The size of platelets and lymphocytes is reduced in WAS, and scanning electron microscopy of T lymphocytes shows a relatively smooth surface with decrease in the number and size of microvilli, suggesting a defect in cytoskeletal architecture (2). The WAS gene is located on Xp11.22-Xp11.23 and encodes a 502-aa-long proline-rich protein (WASP) (3). WASP contains an N-terminal pleckstrin homology domain, which partially overlaps with a WASP homology (WH) domain, WH1, found in several proteins involved in the maintenance of cytoskeletal integrity that include Ena, Mena, Evl, and VASP (4). The WH1 domain in WASP is followed by a GTPase binding domain (GBD͞CRIB) (5), a number of proline-rich stretches, a second WH domain (WH2), a short verprolin homology sequence, a cofilin homology sequence, and an acidic C-terminal region. Recently, a protein homologous to WASP was cloned from bovine brain and was termed N-WASP (6). N-WASP has a domain organization similar to that of WASP, and is widely expressed, in contrast to WASP, which is expressed only in hematopoietic cells.WASP binds via its GBD to the small molecular weight GTPase Cdc42 and weakly to Rac but not to Rho (7-9). Cdc42, Rac, and Rho regulate cytoskeletal organization (10). Overexpression of WASP induces the formation of actin-containing clusters (9). This formation is inhibited by dominant negative mutants of Cdc42, but not of Rac or Rho (9). These findings suggest that WASP may provide a link between Cdc42, Rac, and the cytoskeleton.WASP interacts with components of signal transduction pathways via their Src homology 3 (SH3) domains, which recognize the proline-rich domain in WASP (11). WASP associates with the adaptor protein Nck (12). Nck can be recruited via its SH2 domain to tyrosine phosphorylated receptors (13). WASP also binds in vivo to fyn (12,14) and in vitro to the src kinase fgr, to the tyrosine kinases btk, itk, and Abl and to the p85 subunit of PLC-␥ (14-16).In an attempt to better understand the function of WASP, we cloned, by using the yeast two-hybrid system, a novel human gene whose...

Adapter proteins SLP-76 and BLNK both are expressed by murine macrophages and are linked to signaling via Fcγ receptors I and II/III

“…1C Lower). This coprecipitation was specific: PLC-␥2 was not detected in Western blots of immunoprecipitates of the Wiskott-Aldrich syndrome protein-interacting protein (27) (not shown).…”

Cellular functions of WASP family proteins at a glance

“…Upon DNA damage, there is enhanced cytoplasmic actin polymerization, which sequesters monomeric actin into F-actin. This effectively decreases the binding of G-actin to the WH2 domains, thereby exposing the NLS; this then results in importin binding, JMY nuclear accumulation and p53-dependent gene expression (Zuchero et al, 2012 Fuente et al, 2007;Ramesh et al, 1997) and is required to stabilize WASP. Direct binding to the GTPase-binding domain (GBD) of WASP by the GTP-bound form of Cdc42, a member of the Rho GTPase family, relieves an autoinhibitory fold (Kim et al, 2000).…”

Requirement for a Complex of Wiskott-Aldrich Syndrome Protein (WASP) with WASP Interacting Protein in Podosome Formation in Macrophages

“…Three mammalian verprolins have been identified as proteins binding to the WASP N-terminal region (residues 1-170): the WASP interacting protein (WIP) (9), CR16 (10), and the WIP and CR16 homologous protein (WICH) (11) or WIP-related protein (WIRE) (12). Two independent groups identified WICH/WIRE simultaneously.…”