Role of Sphingosine-1 phosphate receptor 5 in Natural Killer and CD8 T cells migration – SPHINKS

We concentrate on four questions/tasks:
1) How is S1P5 regulated in lymphocytes (in particular what are the transcription factors inducing S1P5 expression)
2) How does S1P5 signal compared to S1P1?
3) How does S1P5 coordinate with chemokine receptors and integrins?
4) Is there a non-redundant role for S1P5 in CD8 T cell migration?

-molecular mechanism of NK cell exit from the bone marrow : our results show that two independent signals are required for this exit : engagement of S1P5 and desensitization of CXCR4
-molecular mechanisms of S1P5 induction in NK and CD8 T cells. Our results show that T-bet induce Zfhx1b expression and that a T-bet/Zfhx1B probably induces S1P5.

It will be important to understand whether or not T-bet and Zfhx1b form a complex that binds S1P5 promoter. Moreover, we envisage to test compounds that inhibit S1P5 activity in NK and CD8 T cells in mouse models of antiviral responses. If we see an effect, these compounds could be used as novel immunosuppressants.

1. Debien E, et al. S European Journal of Immunology. In press
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3. Mayol K, et al Blood 2011, 118(18):4863-71
4. T Walzer and E Vivier. Trends in Immunology. 2011 32(10):486-92.

Sphingosine-1 phosphate (S1P) is a lysophospholipid that regulates important biological functions in both intracellular and extracellular compartments. It binds to five distinct high-affinity GPCR subtypes, S1P1, S1P2, S1P3, S1P4 and S1P5. Coordinated activities of biosynthetic (sphingosine kinases) and biodegradative (sphingosine lyase and sphingosine phosphatases) enzymes maintain S1P gradients in vivo, with high S1P concentrations in blood / lymph (100–300 nM) and low S1P concentrations in lymphoid tissues (3–100 nM). S1P1, the best-studied S1P receptor which couples to Gai, has been shown to be a chemotactic receptor for T cells in vitro. S1P1 deletion leads to the retention of T cells in the thymus. Upon transfer into wild-type mice, S1P1 deficient T cells enter lymph nodes (LN) but are unable to exit them. These results led to the model of S1P1-induced T cell egress that proposes that an increasing S1P concentration gradient exists between the interior of the lymphoid tissue and the adjacent blood or lymph and the lymphocyte response to S1P via S1P1 overcomes the action of retention signals, such as lymphoid chemokines to promote egress. In a microarray-based screen for transcripts specifically expressed in human and mouse Natural Killer (NK) cells, we identified S1P5. We found that S1P5 was up regulated upon NK cell maturation, whereas S1P1 was barely expressed by either subset. In S1P5 deficient mice, there is a dramatic decrease in peripheral NK cells from the blood, spleen, lung and to a lesser extent liver that mostly affects mature NK cells. This defective homing correlates with an increased number of NK cells in the BM and LN. S1P5 operates in NK cells as a chemotactic receptor for S1P in vitro promoting NK cell homing in blood, spleen and lung. Altogether, these observations suggest that S1P5 provides an egress signal to NK cells allowing both their export from the BM and their exit from LN. A further look at public microarray experiments led us to revisit the specificity of S1P5 expression. Indeed, we noticed that besides NK cells, effector CD8 T cells at the peak of antiviral responses were S1P5 positive and S1P1 low. This results suggests that S1P5 might replace S1P1 in activated CD8 T cells to promote their exit from LN and their entry to inflamed zones where S1P concentration increases. However, S1P5 probably acts differently to S1P1, as suggested by their distinct signaling partners and the insensibility of S1P5 to FTY720, a S1P analog that induces downregulation of S1P1, thereby leading to T cell sequestration into LN. The aims of this project are four-fold : 1) to precisely measure the expression of S1P receptors in CD8 T cells upon activation by antigen in various conditions both in mouse and human. 2) to compare the chemotactic activity of S1P1 and S1P5. We postulate that S1P5 might be more adapted to respond to high S1P concentrations that occur at inflamed sites. Mice expressing S1P1 in place of S1P5 will be generated as one of the tools to respond to this question. 3) to understand how S1P5 coordinates with integrins and chemokine receptors that provide different migration cues to NK and activated CD8 T cells concomitantly to S1P5. 4) To use S1P5 KO mice to test the role of S1P5 in the migration of CD8 T cells during activation in vivo, in the course of a local (pulmonary Influenza) or systemic (Vaccinia) viral infection. Particular attention will be paid to the exit of these cells from LN and also to their entry to inflamed areas (lungs in the influenza model). These different studies should allow us to evaluate the interest of S1P5 as a therapeutic target in diseases where CD8 T cells are pathologic, such as allergies or autoimmune diseases. S1P1 is currently targeted by FTY720 in diseases like multiple sclerosis. But due to S1P1 widespread expression, FTY720 has many side-effects. The specificity of S1P5 expression offers a great advantage over S1P1 in this context.