The integrin α6β1 modulation of PI3K and Cdc42 activities induces dynamic filopodium formation in human platelets
ABSTRACT Platelets are an ideal model for studying a rapid morphological change in response to various signal transduction systems. Morphological changes via the activation of integrin alphaIIbbeta3 in platelets have been investigated intensively. In contrast, activation via integrin alpha6beta1 is less well studied. Here, we provide the first biochemical evidence that integrins alpha6beta1 and alphaIIbbeta3 of platelets are associated with different membrane proteins. We also demonstrate that platelets activated by integrin alpha6beta1 show dynamic change by actively forming filopodia and never fully spreading over a period of more than an hour. In addition, platelets activated by integrin alpha6beta1 are different from those activated by integrin alphaIIbbeta3 in terms of cell-substrate contact and in their distribution pattern of actin, Arp2/3 and various phosphotyrosine proteins. The morphological appearance of platelets produced through integrin alpha6beta1 activation is highly dependent on PI3 kinase (PI3K) but less dependent on Src kinase. Suppression of PI3K activity in integrin alpha6beta1 activated platelets induces an increase in Cdc42 activity and more filopodium formation. However, both Cdc42 and PI3K activity are higher in platelets activated by integrin alpha6beta1 than in those activated by integrin alphaIIbbeta3. Taken together, this study demonstrates that the signals induced by integrin alpha6beta1 modulate at the level of PI3K and Cdc42 activity to allow platelets to actively form filopodia.
- SourceAvailable from: Naheda Alkazemi
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- "We also found WNT-3a to increase Cdc42 and Rac1-GTP levels during platelet activation. Since Cdc42 is thought to be required for filopodia growth , this may offer an explanation for the rapid, transient filopodia formation observed during platelet spreading. However, recent studies suggest that filopodia formation can also occur independantly of Cdc42 . "
ABSTRACT: Here we provide evidence that WNT-3a modulates platelet function by regulating the activity of four key GTPase proteins: Rap1, Cdc42, Rac1 and RhoA. We observe WNT-3a to differentially regulate small GTPase activity in platelets, promoting the GDP-bound form of Rap1b to inhibit integrin-α(IIb)β(3) adhesion, while concomitantly increasing Cdc42 and Rac1-GTP levels thereby disrupting normal platelet spreading. We demonstrate that Daam-1 interacts with Dishevelled upon platelet activation, which correlates with increased RhoA-GTP levels. Upon pre-treatment with WNT-3a, this complex disassociates, concurrent with a reduction in RhoA-GTP. Together these data implicate WNT-3a as a novel upstream regulator of small GTPase activity in platelets.FEBS letters 06/2012; 586(16):2267-72. DOI:10.1016/j.febslet.2012.05.060 · 3.34 Impact Factor
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- "Like other members of the Rho GTPase family, Cdc42 influences a large array of cellular activities. Its downstream effectors include a large number of kinases which activate many signaling pathways   as well as nonkinase proteins, such as neuronal Wiskott-Aldrich Syndrome protein (N-WASP)  which promotes actin nucleation. The evolutionarily conserved polarity proteins are localized into different regions of a cell to act as scaffolds for the recruitment of other protein complexes (reviewed in ). "
ABSTRACT: Polarity refers to the asymmetric distribution of different cellular components within a cell and is central to many cell functions. In T-cells, polarity regulates the activation, migration, and effector function of cytotoxic T-cells (CTLs) during an immune response. The regulation of asymmetric cell division by polarity proteins may also dictate CTL effector and memory differentiation following antigen presentation. Small GTPases, along with their associated polarity and adaptor proteins, are critical for mediating the polarity changes necessary for T-cell activation and function, and in turn, are regulated by guanine exchange factors (GEFS) and GTPase activating proteins (GAPS). For example, a novel GEF, dedicator of cytokinesis 8 (DOCK8) was recently identified as a regulator of immune cell function and mutations in DOCK8 have been detected in patients with severe combined immunodeficiency. Both B and T-cells from DOCK8 mutant mice form defective immunological synapses and have abnormal functions, in addition to impaired immune memory development. This paper will discuss the interplay between polarity proteins and GTPases, and their role in T-cell function.Clinical and Developmental Immunology 02/2012; 2012:417485. DOI:10.1155/2012/417485 · 2.93 Impact Factor
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- "This would be observed especially when PI3K is required upstream of RhoA activation. Our previous studies have shown that RhoA plays a critical role during phagoctyic uptake of HSV-1 by primary human CF (Clement et al., 2006) and likewise, it has been suggested that PI3K is involved in integrinmediated signalling pathway that leads to the induction of filopodia (Chang et al., 2005). As shown in Fig. 3(c), pretreatment of human CF with the PI3K inhibitor significantly reduced RhoA activation, which may also be a reason why HSV-1 activity is adversely affected by the inhibitor. "
ABSTRACT: Early interactions of herpes simplex virus type-1 (HSV-1) with cells lead to cytoskeletal changes facilitating filopodia formation and membrane fusion. Here, we demonstrate that phosphoinositide 3 kinase (PI3K) signalling may affect multiple steps during HSV-1 entry. An inhibitor of PI3K (LY294002) blocked HSV-1 entry and the blockage was cell-type- and gD receptor-independent. Entry inhibition was also observed with primary cultures of the human corneal fibroblasts and unrelated β- and γ-herpesviruses. Immunofluorescence analysis demonstrated that LY294002 negatively affected HSV-1-induced filopodia formation. Similar effects of the inhibitor were seen on HSV-1 glycoprotein-induced cell-to-cell fusion. Cells expressing HSV-1 glycoproteins (gB, gD, gH and gL) showed significantly less fusion with target cells in the presence of the inhibitor. Expression of a dominant-negative PI3K mutant negatively affected both entry and fusion. We also show that inhibition of PI3K signalling also affected RhoA activation required for HSV-1 entry into certain cell types.Journal of General Virology 12/2010; 91(Pt 12):3002-9. DOI:10.1099/vir.0.024166-0 · 3.53 Impact Factor