Under the supervision of Clotilde Randriamampita, team Immune cell signaling and retroviral infection
Upon chemokine stimulation, T lymphocytes polarize (acquisition of a lamellipodium and an uropod) and start to migrate. This process is especially important for T cell entry into the lymph nodes and also increases their chance to interact with an antigen-presenting cell in order to get activated.
First, we are interested, in the early events after the chemokine response. By using biosensors, we followed the signaling vents following the stimulation by the chemokine CXCL12. We have shown that CXCL12 stimulation induces an increase in intracellular cyclic adenosine monophosphate (cAMP) followed by an activation of one of its targets, protein kinase A (PKA). The activation of this kinase seems to play a key role in the establishment of polarization along an axis predefined by the position of the centrosome but also in the regulation of centrosomal actin. Indeed, inhibition by a chemical compound, H89, or delocalization of PKA from the centrosome by the inhibitory peptide, Ht31, induces in the basal state, an accumulation of actin. Conversely, after stimulation by CXCL12, T lymphocytes whose PKA has been inhibited or delocalized are no longer able to polarize and the depletion of actin remains partial.
Next, we were interested in the events occurring during migration and direction changes of T lymphocytes in response to chemokines. Morphological changes driven by a dynamic remodeling of the actin cytoskeleton are observed during migration and direction changes. By using dynamic imaging, we investigated the involvement of the cAMP pathway in T lymphocytes directionality. We concomitantly monitored cAMP and acto-myosin variations. We show that spontaneous and transient increases in cAMP at the lamellipod of migrating LTs are sufficient to promote acto-myosin redistribution and direction changes. Although cAMP is considered to be an immunosuppressive factor, our results suggest that when cAMP variations are transient, it rather promotes exploratory behavior of T lymphocytes.
This project should lead to a better characterization of the signaling cascade triggered in T lymphocyte upon chemokine stimulation and to the understanding of interconnections between cAMP pathway and cytoskeleton.