WIP null mice display a progressive immunological disorder that resembles Wiskott-Aldrich syndrome

The Wiskott-Aldrich syndrome (WAS) is an X-linked immunodeficiency syndrome caused by mutations in the WAS protein (WASP). This participates in signalling and cytoskeletal homoeostasis, and some of its activities are regulated by its binding to the WASP interacting protein (WIP). WIP deficiency, however, has not yet been shown to be of pathological significance in humans. Here we show that, in WIP null (WIP(-/-)) mice, it produces haematological alterations and anatomical abnormalities in several organs, most probably as a consequence of autoimmune attacks. Granulocytosis and severe lymphopenia are associated with a proportional increase in segmented cells and fewer bone marrow erythrocytes and lymphocytes. Splenomegaly is accompanied by an increase of haematopoietic tissue and red pulp, reduction of the white pulp, and fewer B (B220(+)) lymphocytes (also apparent in the lymph nodes and Peyer's patches). Ulcerative colitis, interstitial pneumonitis, glomerular nephropathy with IgA deposits, autoantibodies, and joint inflammation are also evident. These progressive immunological disorders closely mimic those seen in WAS. WIP deficiency may thus be implicated in some cases in which mutations in the gene encoding WASP are not detected.

WIP regulates N-WASP-mediated actin polymerization and filopodium formation

Induction of filopodia is dependent on activation of the small GTPase Cdc42 and on neural Wiskott-Aldrich-syndrome protein (N-WASP). Here we show that WASP-interacting protein (WIP) interacts directly with N-WASP and actin. WIP retards N-WASP/Cdc42-activated actin polymerization mediated by the Arp2/3 complex, and stabilizes actin filaments. Microinjection of WIP into NIH 3T3 fibroblasts induces filopodia; this is inhibited by microinjection of anti-N-WASP antibody. Microinjection of anti-WIP antibody inhibits induction of filopodia by bradykinin, by an active Cdc42 mutant (Cdc42(V12)) and by N-WASP. Our results indicate that WIP and N-WASP may act as a functional unit in filopodium formation, which is consistent with their role in actin-tail formation in cells infected with vaccinia virus or Shigella.

Waltzing with WASP

Wiskott-Aldrich syndrome (WAS) is an inherited immune deficiency that is marked by eczema, bleeding and recurrent infections. The lymphocytes and platelets of WAS patients display cytoskeletal abnormalities, and their T lymphocytes show a diminished proliferative response to stimulation through the T-cell receptor-CD3 complex (TCR-CD3). The product of the WAS gene, WAS protein (WASP), binds to the small GTPase Cdc42. Small GTPases of the Rho family are crucial for the regulation of the actin-based cytoskeleton. WASP and its relative NWASP might play an important role in regulating the actin cytoskeleton. Since both WASP and NWASP have the potential to bind to multiple proteins, they might serve as a hub to coordinate the redistribution of many cellular signals to the actin cytoskeleton. In this review, the authors discuss the possible role of WASP/NWASP and of the newly described protein WIP, which interacts with WASP and NWASP, in coupling signals from the T-cell receptor to the actin-based cytoskeleton.

Structure and intracellular assembly of the transmissible gastroenteritis coronavirus

Coronaviruses have been described as pleomorphic, round particles with a helical nucleocapsid as the unique internal structure under the virion envelope. Our studies on the organization of the transmissible gastroenteritis coronavirus (TGEV) have shown that the structure of these viruses is more complex. Different electron microscopy techniques, including cryomicroscopy of vitrified viruses, revealed the existence of an internal core, most probably icosahedral, in TGEV virions. Disruption of these cores induced the release of elongated ribonucleoprotein complexes. Ultrastructural analysis of freeze-substituted TGEV-infected swine testis (ST) cells showed characteristic intracellular budding profiles as well as two types of virions. While large virions with an electron-dense internal periphery are seen at perinuclear regions, smaller viral particles exhibiting compact internal cores of poligonal contours are more abundant in areas closer to the plasma membrane of the cell. These data strongly suggest that maturation events following the budding process are responsible for the formation of the internal core shell, the new structural element that we have recently described in extracellular infectious TGEV virions.

The Wiskott-Aldrich syndrome protein-interacting protein (WIP) binds to the adaptor protein Nck

Nck is a ubiquitous adaptor molecule composed of three Src homology 3 (SH3) domains followed by a single SH2 domain. Nck links, via its SH2 domain, tyrosine-phosphorylated receptors to effector proteins that contain SH3-binding proline-rich sequences. In this report, we demonstrate that recombinant Nck precipitates endogenous WIP, a novel proline-rich protein that interacts with the Wiskott-Aldrich syndrome protein (WASP), from BJAB cell lysates. Nck binds through its second SH3 domain to WIP, and Nck binds to WIP at a site (amino acids 321-415) that differs from the WASP-binding site (amino acids 416-488). WIP has been shown to associate with the actin polymerization regulatory protein profilin and to induce actin polymerization and cytoskeletal reorganization in lymphoid cells. We demonstrate the presence of profilin in Nck precipitates suggesting that Nck may couple extracellular signals to the cytoskeleton via its interaction with WIP and profilin.

WIP, a protein associated with wiskott-aldrich syndrome protein, induces actin polymerization and redistribution in lymphoid cells

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 WASP-interacting 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.

Cooperation between transmissible gastroenteritis coronavirus (TGEV) structural proteins in the in vitro induction of virus-specific antibodies

Following infection of haplotype defined NIH-miniswine with virulent transmissible gastroenteritis coronavirus (TGEV), isolated mesenteric lymph node CD4+ T-cells mounted a specific proliferative response against infectious or inactivated purified virus in secondary in vitro stimulation. A specific, dose-dependent response to the three major recombinant viral proteins: spike (S), membrane (M), and nucleoprotein (N), purified by affinity chromatography, was characterized. Induction of in vitro antibody synthesis was analyzed. The purified recombinant viral proteins induced the in vitro synthesis of neutralizing TGEV-specific antibodies when porcine TGEV-immune cells were stimulated with each of the combinations made with two of the major structural proteins: S + N, S + M, and to a minor extent with M + N, but not by the individual proteins. S-protein was dissociated from purified virus using NP-40 detergent and then micellar S-protein oligomers (S-rosettes) were formed by removing the detergent. These occurred preferentially by the association of more than 10 S-protein trimmers. These S-rosettes in collaboration with either N or M-proteins elicited TGEV-specific antibodies with titers up to 84 and 60%, respectively, of those induced by the whole virus. N-protein could be partially substituted by a 15-mer peptide that represents a T helper epitope previously identified in N-protein (Antón et al. (1995)). These results indicate that the induction of high levels of TGEV-specific antibodies requires stimulation by at least two viral proteins, and that optimum responses are induced by a combination of S-rosettes and the nucleoprotein.

The transmissible gastroenteritis coronavirus contains a spherical core shell consisting of M and N proteins

Coronaviruses are enveloped RNA viruses involved in a variety of pathologies that affect animals and humans. Existing structural models of these viruses propose a helical nucleocapsid under the virion envelope as the unique internal structure. In the present work, we have analyzed the structure of the transmissible gastroenteritis coronavirus. The definition of its organization supports a new structural model for coronaviruses, since a spherical, probably icosahedral, internal core has been characterized. Disruption of these cores induces the release of N-protein-containing helical nucleocapsids. Immunogold mapping and protein analysis of purified cores showed that they consist of M and N proteins, M being the main core shell component. This surprising finding, together with the fact that M protein molecules are also located in the virion envelope, indicates that a reconsideration of the assembly and maturation of coronaviruses, as well as a study of potential M-protein subclasses, is needed.

A transmissible gastroenteritis coronavirus nucleoprotein epitope elicits T helper cells that collaborate in the in vitro antibody synthesis to the three major structural viral proteins

Four strong T cell epitopes have been identified studying the blastogenic response of lymphocytes from haplotype-defined transmissible gastroenteritis virus (TGEV) immune miniswine to sixty-one 15-mer synthetic peptides. Three of these epitopes are located on the nucleoprotein (N46, amino acids 46 to 60; N272, amino acids 272 to 286; and N321, amino acids 321 to 335), and one on the membrane protein (M196, amino acids 196 to 210). N321 peptide induced the highest T cell response and was recognized by immune miniswine lymphocytes with haplotypes dd, aa, and cc. T lymphocytes from peptide N321-immune miniswine reconstituted the in vitro synthesis of TGEV-specific antibodies by complementing CD4- TGEV-immune cells. This response was directed at least against the three major structural proteins. The synthesized antibodies specific for S protein preferentially recognized discontinuous epitopes and neutralized TGEV infectivity. These results show that peptide N321 defines a functional T helper epitope eliciting T cells capable of collaborating with B cells specific for different proteins of TGEV.

Membrane protein molecules of transmissible gastroenteritis coronavirus also expose the carboxy-terminal region on the external surface of the virion

The binding domains of four monoclonal antibodies (MAbs) specific for the M protein of the PUR46-MAD strain of transmissible gastroenteritis coronavirus (TGEV) have been located in the 46 carboxy-terminal amino acids of the protein by studying the binding of MAbs to recombinant M protein fragments. Immunoelectron microscopy using these MAbs demonstrated that in a significant proportion of the M protein molecules, the carboxy terminus is exposed on the external surface both in purified viruses and in nascent TGEV virions that recently exited infected swine testis cells. The same MAbs specifically neutralized the infectivity of the PUR46-MAD strain, indicating that the C-terminal domain of M protein is exposed on infectious viruses. This topology of TGEV M protein probably coexists with the structure currently described for the M protein of coronaviruses, which consists of an exposed amino terminus and an intravirion carboxy-terminal domain. The presence of a detectable number of M protein molecules with their carboxy termini exposed on the surface of the virion has relevance for viral function, since it has been shown that the carboxy terminus of M protein is immunodominant and that antibodies specific for this domain both neutralize TGEV and mediate the complement-dependent lysis of TGEV-infected cells.

Antigen selection and presentation to protect against transmissible gastroenteritis coronavirus

The antigenic structure of the S glycoprotein of transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV) has been determined and correlated with the physical structure. Four antigenic sites have been defined (A, B, C, and D). The sites involved in the neutralization of TGEV are: A, D, and B, sites A and D being antigenically dominant for TGEV neutralization in vitro. These two sites have specific properties of interest: site A is highly conserved and is present in coronaviruses of three animal species, and site D can be represented by synthetic peptides. Both sites might be relevant in protection in vivo. PRCV does not have sites B and C, due to a genomic deletion. Complex antigenic sites, i.e., conformation and glycosylation dependent sites, have been represented by simple mimotopes selected from a library expressing recombinant peptides with random sequences, or by anti-idiotypic internal image monoclonal antibodies. An epidemiological tree relating the TGEVs and PRCVs has been proposed. The estimated mutation fixation rate of 7 +/- 2 x 10(-4) substitutions per nucleotide and year indicates that TGEV related coronaviruses show similar variability to other RNA viruses. In order to induce secretory immunity, different segments of the S gene have been expressed using a virulent forms of Salmonella typhimurium and adenovirus. These vectors, with a tropism for Peyer's patches may be ideal candidates in protection against TGEV.

A conserved coronavirus epitope, critical in virus neutralization, mimicked by internal-image monoclonal anti-idiotypic antibodies

Monoclonal antibody (MAb) 6A.C3 neutralizes transmissible gastroenteritis coronavirus (TGEV) and is specific for a conserved epitope within subsite Ac of the spike (S) glycoprotein of TGEV. Six hybridomas secreting anti-idiotypic (Ab2) MAbs specific for MAb 6A.C3 (Ab1) have been selected. All six MAbs inhibited the binding of Ab1 to TGEV and specifically cross-linked MAb1-6A.C3. Four of these hybridomas secreted gamma-type anti-idiotypic MAbs. The other two Ab2s (MAbs 9A.G3 and 9C.E11) were recognized by TGEV-specific antiserum induced in two species. This binding was inhibited by viruses of the TGEV group but not by serologically unrelated coronaviruses. These results indicate that MAb2-9A.G3 and MAb2-9C.E11 mimic an antigenic determinant present on the TGEV surface, and they were classified as beta-type ("internal-image") MAbs. TGEV-binding Ab3 antiserum was induced in 100% of mice immunized with the two beta-type MAb2s and in 25 to 50% of mice immunized with gamma-type MAb2. Both beta- and gamma-type Ab2s induced neutralizing Ab3 antibodies in mice that were mainly directed to antigenic subsite Ac of the S protein.