Vav Signaling Research Articles

Presynaptic structural and functional plasticity are coupled by convergent Rap1 signaling.

Dynamic presynaptic actin remodeling drives structural and functional plasticity at synapses, but the underlying mechanisms remain largely unknown. Previous work has shown that actin regulation via Rac1 guanine exchange factor (GEF) Vav signaling restrains synaptic growth via bone morphogenetic protein (BMP)-induced receptor macropinocytosis and mediates synaptic potentiation via mobilization of reserve pool vesicles in presynaptic boutons. Here, we find that Gef26/PDZ-GEF and small GTPase Rap1 signaling couples the BMP-induced activation of Abelson kinase to this Vav-mediated macropinocytosis. Moreover, we find that adenylate cyclase Rutabaga (Rut) signaling via exchange protein activated by cAMP (Epac) drives the mobilization of reserve pool vesicles during post-tetanic potentiation (PTP). We discover that Rap1 couples activation of Rut-cAMP-Epac signaling to Vav-mediated synaptic potentiation. These findings indicate that Rap1 acts as an essential, convergent node for Abelson kinase and cAMP signaling to mediate BMP-induced structural plasticity and activity-induced functional plasticity via Vav-dependent regulation of the presynaptic actin cytoskeleton.

Vav proteins do not influence dengue virus replication but are associated with induction of phospho-ERK, IL-6, and viperin mRNA following DENV infection in vitro.

Dengue disease is characterized by an inflammatory-mediated immunopathology, with elevated levels of circulating factors including TNF-α and IL-6. If the damaging inflammatory pathways could be blocked without loss of antiviral responses or exacerbating viral replication, then this would be of potential therapeutic benefit. The study here has investigated the Vav guanine exchange factors as a potential alternative signaling pathway that may drive dengue virus (DENV)-induced inflammatory responses, with a focus on Vav1 and 2. While Vav proteins were positively associated with mRNA for inflammatory cytokines, blocking Vav signaling didn't affect DENV replication but prevented DENV-induction of p-ERK and enhanced IL-6 (inflammatory) and viperin (antiviral) mRNA. These initial data suggest that Vav proteins could be a target that does not compromise control of viral replication and should be investigated further for broader impact on host inflammatory responses, in settings such as antibody-dependent enhancement of infection and in different cell types.

Vav independently regulates synaptic growth and plasticity through distinct actin-based processes.

Modulation of presynaptic actin dynamics is fundamental to synaptic growth and functional plasticity; yet the underlying molecular and cellular mechanisms remain largely unknown. At Drosophila NMJs, the presynaptic Rac1-SCAR pathway mediates BMP-induced receptor macropinocytosis to inhibit BMP growth signaling. Here, we show that the Rho-type GEF Vav acts upstream of Rac1 to inhibit synaptic growth through macropinocytosis. We also present evidence that Vav-Rac1-SCAR signaling has additional roles in tetanus-induced synaptic plasticity. Presynaptic inactivation of Vav signaling pathway components, but not regulators of macropinocytosis, impairs post-tetanic potentiation (PTP) and enhances synaptic depression depending on external Ca2+ concentration. Interfering with the Vav-Rac1-SCAR pathway also impairs mobilization of reserve pool (RP) vesicles required for tetanus-induced synaptic plasticity. Finally, treatment with an F-actin-stabilizing drug completely restores RP mobilization and plasticity defects in Vav mutants. We propose that actin-regulatory Vav-Rac1-SCAR signaling independently regulates structural and functional presynaptic plasticity by driving macropinocytosis and RP mobilization, respectively.

Cancer‐associated mutations in VAV1 trigger variegated signaling outputs and T‐cell lymphomagenesis

Mutations in VAV1, a gene that encodes a multifunctional protein important for lymphocytes, are found at different frequencies in peripheral T‐cell lymphoma (PTCL), non‐small cell lung cancer, and other tumors. However, their pathobiological significance remains unsettled. After cataloguing 51 cancer‐associated VAV1 mutations, we show here that they can be classified in five subtypes according to functional impact on the three main VAV1 signaling branches, GEF‐dependent activation of RAC1, GEF‐independent adaptor‐like, and tumor suppressor functions. These mutations target new and previously established regulatory layers of the protein, leading to quantitative and qualitative changes in VAV1 signaling output. We also demonstrate that the most frequent VAV1 mutant subtype drives PTCL formation in mice. This process requires the concurrent engagement of two downstream signaling branches that promote the chronic activation and transformation of follicular helper T cells. Collectively, these data reveal the genetic constraints associated with the lymphomagenic potential of VAV1 mutant subsets, similarities with other PTCL driver genes, and potential therapeutic vulnerabilities.

VAV1 Gene Polymorphism is Associated With Kidney Allograft Rejection

VAV1 is an intracellular signal transduction protein that plays a significant role in signal transduction in T cells. Several studies suggest that VAV1 signaling plays significant roles in allograft rejection. The aim of this study was to examine the association between VAV1 gene polymorphisms and renal allograft function. The study included 270 patients after allograft renal transplantation. We examined the associations between VAV1 gene polymorphisms and complications after transplantation, such as delayed graft function, acute rejection, and chronic allograft dysfunction. There were no statistically significant associations between VAV1 genotypes and delayed graft function and chronic allograft dysfunction. Among patients with acute allograft rejection, we observed decreased frequencies of VAV1 rs2546133 TT and CT genotypes (P=.03) and T allele (P=.02), as well as VAV1 rs2617822 GG and AG genotypes (P=.05) and G allele (P=0.04). In the multivariate regression analysis, the higher number of VAV1 rs2546133 T alleles showed a protective effect against the acute rejection in kidney allograft recipients. The results of our study suggest that polymorphisms in the VAV1 gene are associated with kidney allograft rejection.

Siglec-E retards atherosclerosis by inhibiting CD36-mediated foam cell formation

BackgroundThe accumulation of lipid-laden macrophages, foam cells, within sub-endothelial intima is a key feature of early atherosclerosis. Siglec-E, a mouse orthologue of human Siglec-9, is a sialic acid binding lectin predominantly expressed on the surface of myeloid cells to transduce inhibitory signal via recruitment of SH2-domain containing protein tyrosine phosphatase SHP-1/2 upon binding to its sialoglycan ligands. Whether Siglec-E expression on macrophages impacts foam cell formation and atherosclerosis remains to be established.MethodsApoE-deficient (apoE−/−) and apoE/Siglec-E-double deficient (apoE−/−/Siglec-E−/−) mice were placed on high fat diet for 3 months and their lipid profiles and severities of atherosclerosis were assessed. Modified low-density lipoprotein (LDL) uptake and foam cell formation in wild type (WT) and Siglec-E−/−- peritoneal macrophages were examined in vitro. Potential Siglec-E-interacting proteins were identified by proximity labeling in conjunction with proteomic analysis and confirmed by coimmunoprecipitation experiment. Impacts of Siglec-E expression and cell surface sialic acid status on oxidized LDL uptake and signaling involved were examined by biochemical assays.ResultsHere we show that genetic deletion of Siglec-E accelerated atherosclerosis without affecting lipid profile in apoE−/− mice. Siglec-E deficiency promotes foam cell formation by enhancing acetylated and oxidized LDL uptake without affecting cholesterol efflux in macrophages in vitro. By performing proximity labeling and proteomic analysis, we identified scavenger receptor CD36 as a cell surface protein interacting with Siglec-E. Further experiments performed in HEK293T cells transiently overexpressing Siglec-E and CD36 and peritoneal macrophages demonstrated that depletion of cell surface sialic acids by treatment with sialyltransferase inhibitor or sialidase did not affect interaction between Siglec-E and CD36 but retarded Siglec-E-mediated inhibition on oxidized LDL uptake. Subsequent experiments revealed that oxidized LDL induced transient Siglec-E tyrosine phosphorylation and recruitment of SHP-1 phosphatase in macrophages. VAV, a downstream effector implicated in CD36-mediated oxidized LDL uptake, was shown to interact with SHP-1 following oxidized LDL treatment. Moreover, oxidized LDL-induced VAV phosphorylation was substantially lower in WT macrophages comparing to Siglec-E−/− counterparts.ConclusionsThese data support the protective role of Siglec-E in atherosclerosis. Mechanistically, Siglec-E interacts with CD36 to suppress downstream VAV signaling involved in modified LDL uptake.

CD28 regulates T cell metabolic reprogramming through ARS2-dependent effects on alternative splicing

Abstract An adaptive immune response requires activation of naïve T cells via T cell receptor (TCR) ligation and engagement of costimulatory molecules such as CD28, which enables cell growth, rapid proliferation, and effector differentiation. To accomplish such bioenergetically demanding processes, T cells must dynamically regulate their metabolism upon activation. After initial TCR triggering of aerobic glycolysis, CD28 co-stimulation maintains uptake and catabolism of glucose required for CD8+ T cells to attain full effector status. Despite evidence that CD28 signaling through the PI3-kinase pathway induces glucose uptake via increased GLUT1 surface expression, knockin T cells expressing PI3-kinase signaling-deficient CD28 are functional in vivo and displayed only transient defects in glycolysis. In contrast, knockin T cells expressing Grb2/Vav signaling-deficient CD28 lacked in vivo function and displayed sustained defects in glycolysis. Here we identify a novel link between CD28-Grb2/Vav signaling and T cell glycolytic reprogramming through the RNA binding protein ARS2, a protein central to co-transcriptional processing of nascent RNA polymerase II transcripts. Data show that ARS2 is a critical downstream mediator of CD28-Grb2/Vav signaling that supports alternative splicing (AS) of the rate-limiting glycolytic enzyme pyruvate kinase M from the M1 to M2 isoform. Mechanistically, ARS2 binds known Pkm splicing factors and promotes their interaction with Pkm mRNA. Consistent with this, ARS2 knockout T cells displayed reduced Pkm2 AS, defective glycolytic reprogramming and lacked the ability to control in vivo tumor growth, suggesting a novel mechanism by which co-stimulation drives T cell metabolic reprogramming.

Lysine Acetylation Reshapes the Downstream Signaling Landscape of Vav1 in Lymphocytes.

Vav1 works both as a catalytic Rho GTPase activator and an adaptor molecule. These functions, which are critical for T cell development and antigenic responses, are tyrosine phosphorylation-dependent. However, it is not known whether other posttranslational modifications can contribute to the regulation of the biological activity of this protein. Here, we show that Vav1 becomes acetylated on lysine residues in a stimulation- and SH2 domain-dependent manner. Using a collection of both acetylation- and deacetylation-mimicking mutants, we show that the acetylation of four lysine residues (Lys222, Lys252, Lys587, and Lys716) leads to the downmodulation of the adaptor function of Vav1 that triggers the stimulation of the nuclear factor of activated T cells (NFAT). These sites belong to two functional subclasses according to mechanistic criteria. We have also unveiled additional acetylation sites potentially involved in either the stimulation (Lys782) or the downmodulation (Lys335, Lys374) of specific Vav1-dependent downstream responses. Collectively, these results indicate that Nε-lysine acetylation can play variegated roles in the regulation of Vav1 signaling. Unlike the case of the tyrosine phosphorylation step, this new regulatory layer is not conserved in other Vav family paralogs.

Phosphatidylinositol Monophosphates Regulate Optimal Vav1 Signaling Output

Phosphatidylinositol–5 phosphate (PI5P) and other mono-phosphoinositides (mono-PIs) play second messenger roles in both physiological and pathological conditions. Despite this, their intracellular targets and mechanisms of action remain poorly characterized. Here, we show that Vav1, a protein that exhibits both Rac1 GDP/GTP exchange and adaptor activities, is positively modulated by PI5P and, possibly, other mono-PIs. Unlike other phospholipid–protein complexes, the affinity and specificity of the Vav1–lipid interaction entail a new structural solution that involves the synergistic action of the Vav1 C1 domain and an adjacent polybasic tail. This new regulatory layer, which is not conserved in the Vav family paralogs, favors the engagement of optimal Vav1 signaling outputs in lymphocytes.

NKG2D-DAP10 signaling recruits EVL to the cytotoxic synapse to generate F-actin and promote NK cell cytotoxicity.

Natural killer (NK) cells eliminate abnormal cells through the release of cytolytic granule contents. In this process, NK cells must adhere to target cells through integrin-mediated adhesion, which is highly dependent on the generation of F-actin. Ena/VASP-like (EVL) is an actin regulatory protein previously shown to regulate integrin-mediated adhesion in other cell types, but its role in NK cell biology is not known. Herein, we show that EVL is recruited to the NK cell cytotoxic synapse and is required for NK cell cytotoxicity. Significantly, EVL is involved in the generation of F-actin at the cytotoxic synapse, antibody-stimulated spreading, and NK cell-target cell adhesion. EVL interacts with WASP (also known as WAS) and VASP and is required for localization of both proteins to the synapse. Recruitment of EVL to points of cellular activation occurs through the receptor NKG2D-DAP10 (also known as KLRK1 and HCST, respectively) via a binding site previously implicated in VAV1 and Grb2 recruitment. Taken together, this study implicates DAP10-mediated Grb2 and VAV1 signaling in the recruitment of an EVL-containing actin regulatory complex to the cytotoxic synapse where it can promote F-actin nucleation leading to NK cell-mediated killing.

SAT-197 Functional Cross-Talk Between MCP-1 and Integrin Linked Kinase Is Required for Endometriosis Disease Progression

Development of painful invasive endometriotic lesions is usually a combined function of the chronic inflammation and active sequential cellular events such as migration, cell adhesion, proliferation, colonization, and invasion in endometriosis. An elevated level of monocyte chemotactic protein-1 (MCP-1) in serum and peritoneal fluid has been reported in endometriosis. Further, Integrin-Linked Kinase (ILK) communicates with extracellular signals and regulates the sequential cellular events in uterine and ovarian cancer. The functional cross-talk of MCP-1 with ILK in the immune cells leads to the high MCP-1 production and increased ILK activity. However, the role of the elevated MCP-1 level and its functional interaction with ILK in the endometriosis development is not explored yet. In order to investigate this, we used the surgically induced heterologous mouse model of endometriosis and externally treated with MCP-1 intraperitoneally for two weeks. Our results demonstrated that MCP-1 boosted the growth of endometriotic lesions mediated through ILK, FAK, VAV and RAC1 signaling axis in endometriosis. In addition, in vivo pharmacological inhibition of ILK by CPD22 restricted the growth of endometriotic lesions in mice. Flow cytometric and inflammatory cytokines profiling in the peritoneal fluid demonstrated that ILK was involved in the MCP-1 mediated macrophageF4/80+ recruitment and inflammatory response in order to support the growth of endometriotic lesions. Inhibition of ILK induced the anti-inflammatory cytokine IL-10 and concomitantly suppressed the pro-inflammatory cytokines MCP-1, TNF-α and IL-10 levels in peritoneal fluid. In vitro studies on human ovarian cystic endometriosis cells (Hs832(C).T) and normal endometrial stromal cells (T-HESCs) revealed that MCP-1 accelerated the adhesion (on collagen and fibronectin substratum), colonization, migration and 3D-spheroids formation and invasion. As the basal level of CCR2, an MCP-1 receptor, expression was higher in ovarian endometriotic cells than the normal endometrial stromal cells giving the hint for the role of MCP-1 in endometriosis. Interestingly, the siRNA mediated knockdown of ILK renders the MCP-1 induced nuclear translocation of phosphorylated ILK and also reduced these accelerated cellular events. Taken together, our results provide compelling evidence that the functional cross-talk between MCP-1 and ILK drives endometriotic disease progression.

The costimulatory molecule CD226 signals through VAV1 to amplify TCR signals and promote IL-17 production by CD4+ T cells.

The activation of T cells requires the guanine nucleotide exchange factor VAV1. Using mice in which a tag for affinity purification was attached to endogenous VAV1 molecules, we analyzed by quantitative mass spectrometry the signaling complex that assembles around activated VAV1. Fifty VAV1-binding partners were identified, most of which had not been previously reported to participate in VAV1 signaling. Among these was CD226, a costimulatory molecule of immune cells. Engagement of CD226 induced the tyrosine phosphorylation of VAV1 and synergized with T cell receptor (TCR) signals to specifically enhance the production of interleukin-17 (IL-17) by primary human CD4+ T cells. Moreover, co-engagement of the TCR and a risk variant of CD226 that is associated with autoimmunity (rs763361) further enhanced VAV1 activation and IL-17 production. Thus, our study reveals that a VAV1-based, synergistic cross-talk exists between the TCR and CD226 during both physiological and pathological T cell responses and provides a rational basis for targeting CD226 for the management of autoimmune diseases.

New insights into the Vav1 activation cycle in lymphocytes

Vav1 is a hematopoietic-specific Rho GDP/GTP exchange factor and signaling adaptor. Although these activities are known to be stimulated by direct Vav1 phosphorylation, little information still exists regarding the regulatory layers that influence the overall Vav1 activation cycle. Using a collection of cell models and activation-mimetic Vav1 mutants, we show here that the dephosphorylated state of Vav1 in nonstimulated T cells requires the presence of a noncatalytic, phospholipase Cγ1–Slp76-mediated inhibitory pathway. Upon T cell stimulation, Vav1 becomes rapidly phosphorylated via the engagement of Lck and, to a much lesser extent, other Src family kinases and Zap70. In this process, Lck, Zap70 and the adaptor protein Lat contribute differently to the dynamics and amplitude of the Vav1 phosphorylated pool. Consistent with a multiphosphosite activation mechanism, the optimal stimulation of Vav1 can only be recapitulated by the combination of several activation-mimetic phosphosite mutants. The analysis of these mutants has also unveiled the presence of different Vav1 signaling competent states that are influenced by phosphosites present in the N- and C-terminal domains of the protein.

Activating mutations and translocations in the guanine exchange factor VAV1 in peripheral T-cell lymphomas

Peripheral T-cell lymphomas (PTCLs) are a heterogeneous group of non-Hodgkin lymphomas frequently associated with poor prognosis and for which genetic mechanisms of transformation remain incompletely understood. Using RNA sequencing and targeted sequencing, here we identify a recurrent in-frame deletion (VAV1 Δ778-786) generated by a focal deletion-driven alternative splicing mechanism as well as novel VAV1 gene fusions (VAV1-THAP4, VAV1-MYO1F, and VAV1-S100A7) in PTCL. Mechanistically these genetic lesions result in increased activation of VAV1 catalytic-dependent (MAPK, JNK) and non-catalytic-dependent (nuclear factor of activated T cells, NFAT) VAV1 effector pathways. These results support a driver oncogenic role for VAV1 signaling in the pathogenesis of PTCL.

VAV1 Activating Mutations and Translocations in Peripheral T-Cell Lymphomas

Peripheral T-cell lymphomas (PTCL) are malignant and highly aggressive hematologic tumors arising from mature post thymic T-cells. The diagnosis of PTCL includes diverse lymphoma subgroups, altogether accounting for about 15% of all non-Hodgkin lymphomas. Despite much effort in developing reliable diagnostic markers, the diagnosis of PTCLs is challenging and 20-30% of cases are diagnosed as PTCL-NOS (not otherwise specified). This heterogeneous and poorly defined group of lymphomas is frequently characterized by chemotherapy resistance and a very poor prognosis. Here we report the presence of recurrent driver activating genetic alterations in the VAV1 gene in PTCL, NOS. RNA-seq analysis of a comprehensive series of 154 PTCLs and targeted sequencing identified VAV1 gene fusions with different partners including VAV1-THAP4, VAV1-MYO1F and VAV1-S100A7. In all cases the resulting oncoproteins lack the C-terminal SH3 domain of VAV1, a motif implicated in the negative regulation of VAV1 signaling, leading to increased activation of VAV1 catalytic-dependent (MAPK, JNK) and non-catalytic-dependent (NFAT) VAV1 effector pathways. In addition, and most notably, we also identified focal microdeletions at the VAV1 intron 25-exon 26 boundary, which result in the activation of an alternative intraexonic splice acceptor site and the consequent expression of mis-splicing-driven mutant transcripts harboring a recurrent VAV1 Δ778-786 in-frame deletion. Mechanistically, the VAV1 Δ778-786 mutation removes 9 amino acids proximal to the C-terminal VAV1 SH3 domain and induces in increased VAV1 activation and signaling in biochemical assays. In all, these results support a driver role for oncogenic VAV1 signaling in T-cell transformation of major importance for the design of targeted therapies for the treatment of PTCL, NOS. DisclosuresNo relevant conflicts of interest to declare.

Ilex kaushue and Its Bioactive Component 3,5-Dicaffeoylquinic Acid Protected Mice from Lipopolysaccharide-Induced Acute Lung Injury.

Acute lung injury (ALI) is a severe respiratory disease with high mortality rates worldwide. Recent reports suggest that human neutrophil elastase (HNE) plays a key role in the inflammatory response that is characteristic of ALI, which indicates that the development of HNE inhibitors could be an efficient treatment strategy. In the current study, an enzyme-based screening assay was used to identify effective HNE inhibitors from a number of traditional Chinese medicines (TCMs). Among them, a water extract of Ilex kaushue (IKWE) effectively inhibited HNE activity (IC50, 11.37 ± 1.59 μg/mL). Using bioactivity-guided fractionation, one new compound and 23 known compounds were identified. Compound 6 (identified as 3,5-dicaffeoylquinic acid; 3,5-DCQA) exerted the most potent and selective inhibitory effect on HNE activity (IC50, 1.86 ± 0.06 μM). In a cell-based assay, 3,5-DCQA not only directly reduced superoxide generation and elastase activity but also attenuated the Src family kinase (SRKs)/Vav signaling pathway in N-formyl-L-Met-L-Leu-L-Phe (fMLF)-stimulated human neutrophils. In an animal disease model, both 3,5-DCQA and standardized IKWE protected against lipopolysaccharide-induced ALI in mice, which provides support for their potential as candidates in the development of new therapeutic agents for neutrophilic inflammatory diseases.

Targeting Pancreatic Cancer Metastasis by Inhibition of Vav1, a Driver of Tumor Cell Invasion.

Pancreatic cancer, one of the most lethal forms of human cancer, is largely resistant to many conventional chemotherapeutic agents. Although many therapeutic approaches focus on tumor growth, metastasis is a primary factor contributing to lethality. Therefore, novel therapies to target metastatic invasion could prevent tumor spread and recurrence resulting from local and distant metastasis. The protein Vav1 is aberrantly expressed in more than half of pancreatic cancers. Its expression promotes activation of Rac and Cdc42 and leads to enhanced invasion and migration, as well as increased tumor cell survival and proliferation, suggesting that Vav1 could be a potent therapeutic target for pancreatic cancer. The purine analogue azathioprine, well known for its function as an anti-inflammatory compound, was recently shown to function by inhibiting Vav1 signaling in immune cells. We therefore hypothesized that azathioprine could also inhibit Vav1 in pancreatic tumor cells to reduce its proinvasive functions. Indeed, we have found that treatment of cultured pancreatic tumor cells with azathioprine inhibited Vav1-dependent invasive cell migration and matrix degradation, through inhibition of Rac and Cdc42 signaling. Furthermore, azathioprine treatment decreased metastasis in both xenograft and genetic mouse models of pancreatic cancer. Strikingly, metastasis was dramatically reduced in Vav1-expressing tumors arising from p48(Cre/+), Kras(G12D/+), p53(F/+) mice. These inhibitory effects were mediated through Vav1, as Vav1-negative cell lines and tumors were largely resistant to azathioprine treatment. These findings demonstrate that azathioprine and related compounds could be potent antimetastatic agents for Vav1-positive pancreatic tumors.

CD28 Promotes Plasma Cell Survival, Sustained Antibody Responses, and BLIMP-1 Upregulation through Its Distal PYAP Proline Motif.

In health, long-lived plasma cells (LLPC) are essential for durable protective humoral immunity, and, conversely, in disease are a major source of pathogenic Abs in autoimmunity, graft rejection, and allergy. However, the molecular basis for their longevity is largely unknown. We have recently found that CD28 signaling in plasma cells (PC) is essential for sustaining Ab titers, by supporting the survival of LLPC, but not short-lived PC (SLPC). We now find that, unlike SLPC, CD28 activation in LLPC induces prosurvival downstream Vav signaling. Knockin mice with CD28 cytoplasmic tail mutations that abrogate Vav signaling (CD28-AYAA) had significantly fewer LLPC but unaffected SLPC numbers, whereas mice with mutations that abrogate PI3K signaling (CD28-Y170F) were indistinguishable from wild-type controls. This was consistent with the loss of CD28's prosurvival effect in LLPC from CD28-AYAA, but not CD28-Y170F, mice. Furthermore, the CD28 Vav motif in the B lineage was essential for the long-term maintenance of Ag-specific LLPC populations and Ab titers in vivo. Signaling downstream of the CD28 Vav motif induced previously undescribed transcriptional regulation of B lymphocyte-induced maturation protein-1, a key mediator of PC differentiation and maintenance. These findings suggest CD28 signaling in LLPC modulates the central B lymphocyte-induced maturation protein-1 transcriptional nexus involved in long-term survival and function.

Podoplanin-Rich Stromal Networks Induce Dendritic Cell Motility via Activation of the C-type Lectin Receptor CLEC-2

SummaryTo initiate adaptive immunity, dendritic cells (DCs) move from parenchymal tissues to lymphoid organs by migrating along stromal scaffolds that display the glycoprotein podoplanin (PDPN). PDPN is expressed by lymphatic endothelial and fibroblastic reticular cells and promotes blood-lymph separation during development by activating the C-type lectin receptor, CLEC-2, on platelets. Here, we describe a role for CLEC-2 in the morphodynamic behavior and motility of DCs. CLEC-2 deficiency in DCs impaired their entry into lymphatics and trafficking to and within lymph nodes, thereby reducing T cell priming. CLEC-2 engagement of PDPN was necessary for DCs to spread and migrate along stromal surfaces and sufficient to induce membrane protrusions. CLEC-2 activation triggered cell spreading via downregulation of RhoA activity and myosin light-chain phosphorylation and triggered F-actin-rich protrusions via Vav signaling and Rac1 activation. Thus, activation of CLEC-2 by PDPN rearranges the actin cytoskeleton in DCs to promote efficient motility along stromal surfaces.

Loss of Tankyrase-Mediated Destruction of 3BP2 Is the Underlying Pathogenic Mechanism of Cherubism

Cherubism is an autosomal-dominant syndrome characterized by inflammatory destructive bony lesions resulting in symmetrical deformities of the facial bones. Cherubism is caused by mutations in Sh3bp2, the gene that encodes the adaptor protein 3BP2. Most identified mutations in 3BP2 lie within the peptide sequence RSPPDG. A mouse model of cherubism develops hyperactive bone-remodeling osteoclasts and systemic inflammation characterized by expansion of the myelomonocytic lineage. The mechanism by which cherubism mutations alter 3BP2 function has remained obscure. Here we show that Tankyrase, a member of the poly(ADP-ribose)polymerase (PARP) family, regulates 3BP2 stability through ADP-ribosylation and subsequent ubiquitylation by the E3-ubiquitin ligase RNF146 in osteoclasts. Cherubism mutations uncouple 3BP2 from Tankyrase-mediated protein destruction, which results in its stabilization and subsequent hyperactivation of the SRC, SYK, and VAV signaling pathways.