Roles of Src-like adaptor protein 2 (SLAP-2) in GPVI-mediated platelet activation SLAP-2 and GPVI signaling

BACKGROUND: Glycoprotein VI (GPVI) /Fc receptor gamma (FcRγ)-chain complex is one of the collagen receptors in platelets and responsible for the majority of the intracellular signaling events through a similar pathway to immune receptors. Src-like adaptor protein 2 (SLAP-2) is a recently characterized adaptor protein predominantly expressed in hematopoietic cells. In T cells, SLAP-2 was reported to associate with several tyrosine phosphorylated proteins, and function as a negative regulator of signaling downstream of T cell antigen receptor by virtue of its interaction with the ubiquitin ligase c-Cbl. But the data regarding the presence and role of SLAP-2 proteins in platelets is limited. OBJECTIVES: We describe the characterization of SLAP-2 in human platelets. METHODS: Human platelets were analyzed by Western blot analysis, immunoprecipitation, and pull down assay, etc. RESULTS: Immunoprecipitation revealed the presence of two forms of SLAP-2 with approximately 28kD and 25kD, and following stimulation of GPVI, the additional form with approximately 32kD apppeared. We have found that upon GPVI activation, SLAP-2 translocated from the Triton X-100-soluble fraction to the Triton X-100-insoluble cytoskeleton fraction, with concomitant association with Syk, c-Cbl, and LAT. CONCLUSIONS: SLAP-2 appears to play a role in regulating signaling pathways by bringing important signaling molecules such as c-Cbl and Syk into proximity of cytoskeletal substrates. In platelets, SLAP-2 may have function as a negative regulator of GPVI-mediated signaling by interacting with c-Cbl, being similar to that reported in T cells.status: publishe

New approaches for antithrombotic antiplatelet therapies

Cardiovascular diseases are one of the major causes of mortality in the western world. As platelet dependent thrombosis is of central importance in their pathophysiology, several successful strategies, targeting a specific platelet function or interaction, have been developed to prevent or treat these disorders. However, as the current antiplatelet strategies are limited in efficacy and safety, and often influence normal haemostatic functions, new compounds are being developed with improved characteristics.status: publishe

Monoclonal antibody IAC-1 is specific for activated alpha2beta1 and binds to amino acids 199 to 201 of the integrin alpha2 I-domain

In this study we describe the first monoclonal antibody, integrin activated conformation-1 (IAC-1), to recognize the active form of the platelet-collagen receptor, the integrin alpha(2)beta(1). IAC-1 has the following properties: (1) IAC-1 fails to bind to resting platelets but readily interacts with platelets stimulated by the glycoprotein VI-specific agonist, convulxin, and by other agonists; (2) similar concentration response relationships for binding of IAC-1 and soluble collagen were observed in convulxin-stimulated platelets; (3) the epitope for IAC-1 is T199Y200K201, which is located at the opposite site of the metal ion-dependent adhesion site in a region not involved in the I-domain "shifts" that occur upon ligand binding; (4) IAC-1 strongly binds to recombinant alpha(2) I-domain, therefore suggesting that the neo-epitope appears to be exposed by an "unmasking" of I-domain-covering regions upon activation; (5) IAC-1 binds to platelets during adhesion to collagen under shear conditions, demonstrating activation of alpha(2)beta(1); (6) as IAC-1 does not interfere with platelet-collagen binding, it defines a new class of antibodies that is distinct from those belonging to the "cation- and ligand-induced binding sites" (CLIBSs) and the "ligand mimetic" group. These characteristics make IAC-1 a very powerful tool to study alpha(2)beta(1) activation under dynamic and physiologically relevant conditions.Centrum voor Moleculaire en vasculaire biologie. Interdisciplinair Research centrum Campus Kortrijk (IRC) Subfaculteit Wetenschappen Campus Kortrijk.status: publishe

Successful haploidentical stem cell transplantation with prophylactic administration of liposomal amphotericin B after invasive pulmonary zygomycosis

A 54-year-old woman with acute myeloid leukemia (AML) achieved complete remission by induction chemotherapy, but developed zygomycosis after consolidation therapy. As zygomycosis could not be cured by liposomal amphotericin B and micafungin, left lower lobectomy was performed. As AML relapsed 7 months after onset, she received haploidentical stem cell transplantation under administration of liposomal amphotericin B. Despite experiencing severe acute graft-versus-host disease, she remains alive with no relapse of either zygomycosis or AML. Keywords: Zygomycosis, Acute myeloid leukemia, Liposomal amphotericin B, Stem cell transplantatio