SDF-1alpha (CXCL12) signaling via its receptor, CXCR4, stimulates T cell chemotaxis and gene expression. The ZAP-70 tyrosine kinase critically mediates SDF-1alpha-dependent migration and prolonged ERK mitogen-activated protein (MAP) kinase activation in T cells. However, the molecular mechanism by which CXCR4 or other G protein-coupled receptors activate ZAP-70 has not been characterized. Here we show that SDF-1alpha stimulates the physical association of CXCR4 and the T cell receptor (TCR) and utilizes the ZAP-70 binding ITAM domains of the TCR for signal transduction. This pathway is responsible for several of the effects of SDF-1alpha on T cells, including prolonged ERK MAP kinase activity, increased intracellular calcium ion concentrations, robust AP-1 transcriptional activity, and SDF-1alpha costimulation of cytokine secretion. These results suggest new paradigms for understanding the effects of SDF-1alpha and other chemokines on immunity.

Persistent T cell antigen receptor (TCR) signaling by CD8 T cells is a feature of cancer and chronic infections and results in the sustained expression of, and signaling by, inhibitory receptors, which ultimately impair cytotoxic activity via poorly characterized mechanisms. We have previously determined that the LPA 5 GPCR expressed by CD8 T cells, upon engaging the lysophosphatidic acid (LPA) bioactive serum lipid, functions as an inhibitory receptor able to negatively regulate TCR signaling. Notably, the levels of LPA and autotaxin (ATX), the phospholipase D enzyme that produces LPA, are often increased in chronic inflammatory disorders such as chronic infections, autoimmune diseases, obesity, and cancer. In this report, we demonstrate that LPA engagement selectively by LPA 5 on human and mouse CD8 T cells leads to the inhibition of several early TCR signaling events including intracellular calcium mobilization and ERK activation. We further show that, as a consequence of LPA 5 suppression of TCR signaling, the exocytosis of perforin-containing granules is significantly impaired and reflected by repressed in vitro and in vivo CD8 T cell cytolytic activity. Thus, these data not only document LPA 5 as a novel inhibitory receptor but also determine the molecular and biochemical mechanisms by which a naturally occurring serum lipid that is elevated under settings of chronic inflammation signals to suppress CD8 T cell killing activity in both human and murine cells. As diverse tumors have repeatedly been shown to aberrantly produce LPA that acts in an autocrine manner to promote tumorigenesis, our findings further implicate LPA in activating a novel inhibitory receptor whose signaling may be therapeutically silenced to promote CD8 T cell immunity.

Background:The chemokine receptor CXCR4 plays a role in AML. Results: SDF-1, the ligand of CXCR4, induces apoptosis in AML cell lines and patient samples via modulation of Bcl-2 family members. Conclusion: SDF-1 induces apoptosis of AML cells via up-regulation of Bak and Noxa and down-regulation of Bcl-X L . Significance: SDF-1/CXCR4 signaling could induce AML cell apoptosis if bone marrow survival cues can be disrupted.

Stimulation of T lymphocytes with the ligand for the CXCR4 chemokine receptor stromal cell-derived factor-1α (SDF-1α/CXCL12), results in prolonged activation of the extracellular signal-regulated kinases (ERK) ERK1 and ERK2. Because SDF-1α is unique among several chemokines in its ability to stimulate prolonged ERK activation, this pathway is thought to mediate special functions of SDF-1α that are not shared with other chemokines. However, the molecular mechanisms of this response are poorly understood. In this study we show that SDF-1α stimulation of prolonged ERK activation in Jurkat T cells requires both the ZAP-70 tyrosine kinase and the Src homology 2 domain-containing leukocyte protein of 76 kDa (SLP-76) scaffold protein. This pathway involves ZAP-70-dependent tyrosine phosphorylation of SLP-76 at one or more of its tyrosines, 113, 128, and 145. Because TCR activates ERK via SLP-76-mediated activation of the linker of activated T cells (LAT) scaffold protein, we examined the role of LAT in SDF-1α-mediated ERK activation. However, neither the SLP-76 proline-rich domain that links to GADS and LAT, nor LAT, itself are required for SDF-1α to stimulate SLP-76 tyrosine phosphorylation or to activate ERK. Together, our results describe the distinct mechanism by which SDF-1α stimulates prolonged ERK activation in T cells and indicate that this pathway is specific for cells expressing both ZAP-70 and SLP-76.

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