Immune Regulatory Roles of Suppressor Of Cytokine Signaling (SOCS) Molecules

Division Of Basic Sciences - Nci

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Abstract

We previously reported that the expression of SOCS molecules, specifically of SOCS1 and SOCS3, is transcriptionally controlled by the zinc-finger protein ThPOK. Thus, ThPOK is a transcriptional activator of SOCS such that ThPOK also serves as a negative regulator of cytokine receptor signaling. Notably, ThPOK is not only necessary but also sufficient for the lineage specification and differentiation of CD4 T cells in the thymus as well, and we previously demonstrated that its requirement is associated with its role in upregulating SOSC molecule expression. Thus, a circuitry of ThPOK-driven SOCS expression is critical for the development and differentiation of CD4 T cells. Importantly, ThPOK expression is absent in immature preselection CD4, CD8 double-positive (DP) thymocytes, and is only induced upon strong and persistent TCR signaling during positive selection. In CD8 lineage T cells, on the other hand, ThPOK is absent, and ThPOK has been considered dispensable for their lineage specification and development. In contrast to this prevailing view, we have recently uncovered an unexpected requirement for ThPOK in the thymic generation of CD8 T cells, specifically mature CD8 T cells with innate-like effector function, also known as innate CD8 T cells. Mechanistically, we mapped the ThPOK requirement to a previously unappreciated role of ThPOK in generating a subset of invariant NKT cells specialized in IL-4 production, commonly referred to as NKT2 cells. NKT2 cells express high levels of ThPOK, and NKT2 cells were conspicuously absent in thymocytes of ThPOK-deficient mice. Using a series of TCR transgenic mice and other genetically engineered mice, we mapped the timing of their developmental arrest to an intermediate stage immediately after positive selection. Moreover, the failure to generate NKT2 cells resulted in dramatically decreased levels of intrathymic IL-4, a critical cytokine for innate CD8 T cell differentiation, such that their generation is severely impaired in ThPOK-deficient mice. These results unravel a cell-extrinsic requirement for ThPOK in innate CD8 T cell generation, expanding the role of CD4 lineage-specifying ThPOK into the development of CD8 effector T cells. We are currently testing whether the forced expression of SOCS1 can restore NKT2 cell generation, and in parallel also assessing the development of innate CD8 T cells in ThPOK-deficient mice. We expect that these results will further clarify the role SOCS molecules in T cell differentiation. In an expansion on our work on innate CD8 T cells, we further assessed their unique cytokine requirement, as conventional CD8 T cells require IL-7 but innate CD8 T cells depend on IL-4. Both conventional and innate CD8 T cells express large amounts of the receptor for IL-7 and IL-4. However, it has been unclear why IL-7 preferentially acts on conventional CD8 T cells while IL-4 is selectively required for innate CD8 T cells. We hypothesize that the distinct expression of molecules involved in the downstream signaling would be responsible for the difference. We have recently established CITE-seq analytic tools in profiling gene expression. We also introduced the technique of high-throughput cell surface analysis using LegendScreen, a commercially available kit to analyze 255 surface markers using flow cytometry. We are now in the process of analyzing the transcriptional and protein expression landscape of conventional versus innate CD8 T cells, with the final aim to examine differences in SOCS family molecule expression as the underlying mechanism of distinct cytokine responsiveness in lineage specification and differentiation of T cells.