Impaired NK-cell migration in WAS/XLT patients: role of Cdc42/WASp pathway in the control of chemokine-induced β2 integrin high-affinity state

Abstract

IntroductionThe Wiskott-Aldrich syndrome protein (WASp) is a multidomain member of the WASp/suppressor of cAMP receptor/WASP family verprolin-homologous protein family whose expression is restricted to hematopoietic cells. WASp has been identified as one of the main regulators of actin cytoskeletal dynamics. 1,2 WASp was initially discovered as the product of the gene whose mutations are responsible for the Wiskott-Aldrich syndrome (WAS), a rare X-linked recessive primary immunodeficiency characterized by eczema, thrombocytopenia, and impaired cellular and humoral immunity. [3][4][5][6] This syndrome is highly heterogeneous in terms of clinical severity with some cases showing an attenuated clinical and immunologic phenotype referred to as X-linked thrombocytopenia (XLT). Most of the patients with XLT have missense mutations in exons 1 and 2 of the WASP gene, leading to decreased but detectable levels of protein expression. In contrast, WASP mutations that lead to total absence of WASp are usually associated with a more severe clinical phenotype.In resting cells, WASp is found in a closed, autoinhibited form in which the guanosine triphosphate (GTPase) binding domain is bound to the carboxyl-terminal verprolin homology, cofilin homology, acidic region. 1,2,7 After cell activation, WASp interacts with the GTP-bound form of the small Rho GTPase Cdc42 by its GTPase binding domain; this association results in a conformational change that allows WASp interaction with the Arp2/3 complex, thus initiating actin polymerization. WASp also contains a proline-rich region that is responsible for its association with several tyrosine kinases and adaptor proteins. Moreover, the N-terminal located at ENA-Vasp homology 1 domain binds to the WASp-interacting protein, known to modulate WASp functions. The ability of WASp to interact with and activate the Arp2/3 complex is regulated in a cooperative manner by the GTP-bound form of Cdc42 and the phosphatidylinositol 4,5 bisphosphate. Moreover, it has been reported that WASp functional activation is also enhanced by its tyrosine phosphorylation after ligation of immune or adhesion receptors. [8][9][10][11] Because of its ability to induce cytoskeletal remodeling, WASp has been implicated in the regulation of many cellular functions, including T-cell activation and proliferation, phagocytosis, cell migration, and chemotaxis. 1,2 Moreover, we and others have reported that patients with WAS or XLT phenotype are impaired in both natural and CD16-mediated natural killer (NK)-cell cytotoxicity as a result of disturbed cytoskeletal reorganization. 12,13 NK cells are a CD3 Ϫ CD16 ϩ CD56 ϩ lymphocyte subpopulation that plays an important role in the early phase of immune responses against viruses, parasites, and microbial pathogens by exhibiting cytotoxic functions and secreting a number of cytokines and chemokines. 14,15 NK cells are mainly found in the peripheral blood, but they are also present in several lymphoid and nonlymphoid organs such as spleen, lymph nodes, tonsils, liver, lungs, i...

Wiskott‐Aldrich syndrome protein (WASp) and N‐WASp are involved in the regulation of NK‐cell migration upon NKG2D activation

“…Under control conditions, cells transfected with siRNA for WASp showed a dramatic reduction in CXCL12-induced chemotaxis (*p < 0.05; Fig. 5B), in agreement with Stabile et al [28]. However, activation of NKG2D in transfected cells did not impair cell migration compared with cells transfected with scrambled siRNA (2% of inhibition), indicating that both N-WASp and WASp proteins are involved in the regulation of NK-cell migration upon NKG2D stimulation.…”

“…Knocking down N-WASp expression with siRNA partially reverted NKG2D effect on cell migration in keeping with wiskostatin effect. Regarding WASp, the inhibition of its expression led to a defect in NK-cell motility in IgG-treated cells, as described recently [28] and NKG2D activation failed to decrease migration rates. These results indicate that both proteins, N-WASp and WASp, act downstream Cdc42 for the regulation of NK-cell migration in our experimental conditions.…”

Syk Regulates Multiple Signaling Pathways Leading to CX3CL1 Chemotaxis in Macrophages

“…Interestingly, the Src kinase Hck can phosphorylate WASP at tyrosine 291 and this phosphorylation results in enhanced actin polymerization in vitro (40), suggesting that Hck may be responsible for the phosphorylation of WASP. However, WASP can associate with both the Src kinase Fyn and with focal adhesion kinase Pyk-2 following the triggering of chemokine receptors on NK cells (18). Further studies are required to identify the specific tyrosine kinase required for WASP phosphorylation during CX3CL1chemotaxis.…”

“…Also, Syk was rapidly activated and required for proper formation of membrane protrusions and cell chemotaxis in response to CX3CL1 in RAW/LR5 monocyte/macrophage cells (17). Furthermore, Stabile et al (18) show that Wiskott-Aldrich syndrome protein (WASP) 3 was associated with Fyn and Pyk-2 tyrosine kinases and that Cdc42 and WASP could play a crucial role in the regulation of natural killer cell migration by CX3CL1. These observations indicate that chemotaxis toward CX3CL1 could be regulated by the coordinate action of both Cdc42/WASP and tyrosine kinases.…”

Wiskott-Aldrich syndrome protein-deficient hematopoietic cells can be efficiently mobilized by granulocyte colony-stimulating factor

“…14 WASp is an important regulator of chemokine responses in lymphocytes in particular through a chemokine-induced inside-out signaling pathway involving cdc42/WASp activation. [15][16][17][18] WASp deficiency causes a marked defect in localization and trafficking of phagocytes and lymphocytes, including B cells, affecting their function. 18,19 The Wiskott-Aldrich syndrome protein is an essential cytoskeleton regulator found in cells of the hematopoietic lineage and controls the motility of leukocytes.…”