Activation of the Rap1 GTPase by the B Cell Antigen Receptor

Self Cite

111

101

Stromal cell-derived factor-1 (SDF-1) is a potent chemoattractant for B cells and B cell progenitors. Although the binding of SDF-1 to its receptor, CXCR4, activates multiple signaling pathways, the mechanism by which SDF-1 regulates cell migration is not completely understood. In this report we show that activation of the Rap GTPases is important for B cells to migrate toward SDF-1. We found that treating B cells with SDF-1 resulted in the rapid activation of both Rap1 and Rap2. Moreover, blocking the activation of Rap1 and Rap2 via the expression of a Rap-specific GTPase-activating protein significantly reduced the ability of B cells to migrate toward SDF-1. Conversely, expressing a constitutively active form of Rap2 increased SDF-1-induced B cell migration. Thus, the Rap GTPases control cellular processes that are important for B cells to migrate toward SDF-1.

Section: Resultsmentioning

confidence: 99%

Section: Rap1 Rap2 and Rac1 Activation Assaysmentioning

confidence: 99%

The Rap GTPases Regulate B Cell Migration Toward the Chemokine Stromal Cell-Derived Factor-1 (CXCL12): Potential Role for Rap2 in Promoting B Cell Migration

McLeod

Lee

et al. 2002

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111

101

“…Engagement of the Fc⑀R leads to activation of the PLC␥ pathway, which, in turn, can promote and/or enhance activation of all three types of MAPKs, including ERKs, JNKs, and p38 MAPKs (29,30,35,44,45). Therefore, we evaluated the extent of ERK, JNK, and p38 MAPK activation in PLC␥2-deficient, relative to wild-type, mast cells in response to Fc⑀R cross-linking.…”

Section: Plc␥2-deficient Mast Cells Have Impaired Fc⑀r-induced Ca 2ϩ mentioning

confidence: 99%

Phospholipase Cγ2 Is Essential for Specific Functions of FcεR and FcγR

Wen

Jou

Chen

et al. 2002

Phospholipase Cγ2 (PLCγ2) plays a critical role in the functions of the B cell receptor in B cells and of the FcRγ chain-containing collagen receptor in platelets. Here we report that PLCγ2 is also expressed in mast cells and monocytes/macrophages and is activated by cross-linking of FcεR and FcγR. Although PLCγ2-deficient mice have normal development and numbers of mast cells and monocytes/macrophages, we demonstrate that PLCγ2 is essential for specific functions of FcεR and FcγR. While PLCγ2-deficient mast cells have normal mitogen-activated protein kinase activation and cytokine production at mRNA levels, the mutant cells have impaired FcεR-mediated Ca2+ flux and inositol 1,4,5-trisphosphate production, degranulation, and cytokine secretion. As a physiological consequence of the effect of PLCγ2 deficiency, the mutant mice are resistant to IgE-mediated cutaneous inflammatory skin reaction. Macrophages from PLCγ2-deficient mice have no detectable FcγR-mediated Ca2+ flux; however, the mutant cells have normal FcγR-mediated phagocytosis. Moreover, PLCγ2 plays a nonredundant role in FcγR-mediated inflammatory skin reaction.

“…It is not known how the TCR and Rap1 might connect to adhesionand degranulation-promoting adaptor protein signaling, but it is likely to involve Fyn and SLP-76 (54, 55) activating Rap1 via PLC , which contains a Ras-Rap-binding domain and can act as a guanine nucleotide exchange factor for Rap1 (57,58). Consistent with this, there is evidence that Rap1 activation after Ag-specific triggering of lymphocytes requires PLC activation and consequent calcium mobilization and 1,2-diacylglycerol generation (52,59,60).…”

Section: Discussionmentioning

confidence: 91%

Inverse Rap1 and Phospho-ERK Expression Discriminate the Maintenance Phase of Tolerance and Priming of Antigen-Specific CD4+ T Cells In Vitro and In Vivo

Morton

McManus

Garside

et al. 2007

T cell recognition of Ag can result in priming or tolerance depending on the context in which Ag is recognized. Previously, we have reported that these distinct functional outcomes are associated with marked differences in the amplitude, kinetics, and cellular localization of activated, pERK signals at the level of individual Ag-specific T cells in vitro. Here, we show that the GTPase Rap1, which can antagonize the generation of such pERK signals and has been reported to accumulate in tolerant cells, exhibits an inverse pattern of expression to pERK in individual Ag-specific primed and tolerized T cells. Although pERK is expressed by more primed than tolerized T cells when rechallenged with Ag in vitro, Rap1 is expressed by higher percentages of tolerant compared with primed Ag-specific T cells. Moreover, whereas pERK localizes to the TCR and lipid rafts in primed cells, but exhibits a diffuse cellular distribution in tolerized cells, Rap1 colocalizes with the TCR and lipid raft structures under conditions of tolerance, but not priming, in vitro. This inverse relationship between Rap1 and pERK expression is physiologically relevant, given that we observed the same patterns in Ag-specific T cells in situ, following induction of priming and tolerance in vivo. Together, these data suggest that the maintenance of tolerance of individual Ag-specific T cells may reflect the recruitment of up-regulated Rap1 to the immune synapse, potentially resulting in sequestration of Raf-1 and uncoupling of the TCR from the Ras-ERK-MAPK cascade.