Regulating Vav1 phosphorylation by the SHP-1 tyrosine phosphatase is a fine-tuning mechanism for the negative regulation of DISC formation and Fas-mediated cell death signaling

Abstract

The actin cytoskeleton association is required for caspase 8-independent Fas/CD95 receptor internalization, a critical step for an optimal death-inducing signaling complex formation along the endocytic pathway, leading to efficient activation of the caspase cascade and, ultimately, cell death. However, the way in which this initiation phase of Fas receptor signaling is regulated is still unknown. We report herein that, in B cells, upon Fas engagement, the tyrosine phosphatase SHP-1-regulated Vav dephosphorylation, by downmodulating the Fas-ezrin-actin linkage is a fine-tune switch-off mechanism that the cell uses as a way to terminate the receptor internalization, controlling therefore the time and extent of the DISC formation and cell death.

Lyn-mediated SHP-1 recruitment to CD5 contributes to resistance to apoptosis of B-cell chronic lymphocytic leukemia cells

“…41,44 It has been shown that dephosphorylation of Vav1 blocks lymphocyte activation, 45 which underscores the role of the inhibitory signaling pathway mediated by inhibitory co-receptors/SHP-1, and has recently been proposed as a key event inhibiting Fas-induced cell death. 46 In agreement with these data, our results are compatible with the hypothesis that the phosphorylation status of specific protein targets, among which Vav1, determined by the axis Lyn-CD5-SHP-1 may have a role in the maintenance of the leukemic phenotype by counteracting apoptosis, as demonstrated by the substantial drop in cell viability due to the use of PTP-I-I or SHP-1 knockdown. Notably, genetic and pharmacological inhibition of SHP-1 triggers apoptosis through a caspase-independent mechanism despite Mcl-1 downmodulation (Figures 7 and 8), leaving expression and activity of Lyn and Syk unaltered (Figures 5c and 6d).…”

Impact of TNF-R1 and CD95 Internalization on Apoptotic and Antiapoptotic Signaling

“…However, several other studies have indicated a constitutive and inducible association of CD95 with lipid rafts (Henkler et al 2005 ;Siegel et al 2004 ;Grassme et al 2001 ;Hueber et al 2002 ;Scheel-Toellner et al 2002 ;Muppidi et al 2004 ;Eramo et al 2004 ;Miyaji et al 2005 ;Nakayama et al 2006 ;Legembre et al 2005 ;Chakrabandhu et al 2007 ;Koncz et al 2007) . It was indeed thought that CD95 preassociation, lipid raft translocation, SPOT formation, DISC recruitment, and initiation of apoptosis signaling from lipid rafts are restricted to type I cells Eramo et al 2004 ;Nakayama et al 2006) .…”

“…The connection between CD95 and actin filaments is mediated through the association of CD95 with ezrin, a membrane cytoskeletal crosslinker protein Parlato et al 2000) . Ezrin/actin cytoskeleton rearrangements were proposed to be regulated by the SH2-domain-containing tyrosine phosphatase SHP1 (Koncz et al 2007) . According to Algeciras-Schimnich et al (2002) , FADD-and caspase-8 recruitment preceded CD95 internalization in lymphoblasts and T cells, pointing toward the regulatory role of caspase-8 in CD95 internalization.…”

Vav Protein Guanine Nucleotide Exchange Factor Regulates CD36 Protein-mediated Macrophage Foam Cell Formation via Calcium and Dynamin-dependent Processes

“…Alexa Fluor-coupled secondary antibodies were then applied and cells were analyzed by fluorescence microscopy. (31) have been shown to participate in Vav activation in other systems, we examined the effect of selective pharmacologic inhibitors of these processes on CD36-mediated macrophage Vav activation. MPM pretreated with BAPTA/AM to chelate intracellular calcium, methyl-␤-cyclodextrin to disrupt lipid rafts, cytochalasin-D to inhibit actin polymerization, or sodium orthovanadate to inhibit phosphatases were exposed to NO 2 LDL (a highly specific ligand for CD36), and Vav phosphorylation was assayed by IP/IB.…”