Gfi1-Foxo1 axis controls the fidelity of effector gene expression and developmental maturation of thymocytes

Abstract

Double-positive (DP) thymocytes respond to intrathymic T-cell receptor (TCR) signals by undergoing positive selection and lineage differentiation into single-positive (SP) mature cells. Concomitant with these well-characterized events is the acquisition of a mature Tcell gene expression program characterized by the induction of the effector molecules IL-7Rα, S1P 1 , and CCR7, but the underlying mechanism remains elusive. We report here that transcription repressor Growth factor independent 1 (Gfi1) orchestrates the fidelity of the DP gene expression program and developmental maturation into SP cells. Loss of Gfi1 resulted in premature induction of effector genes and the transcription factors forkhead box protein O1 (Foxo1) and Klf2 in DP thymocytes and the accumulation of postselection intermediate populations and accelerated transition into SP cells. Strikingly, partial loss of Foxo1 function, but not restored survival fitness, rectified the dysregulated gene expression and thymocyte maturation in Gfi1-deficient mice. Our results establish the Gfi1-Foxo1 axis and the transcriptional circuitry that actively maintain DP identity and shape the proper generation of mature T cells. CD8+ double-positive (DP) stage to mature CD4 + or CD8 + single-positive (SP, namely CD4SP and CD8SP) thymocytes. Whereas the majority of thymocytes are eliminated due to either lack of T-cell receptor (TCR) signals (death by neglect) or high-affinity interaction with self-peptide MHC ligands (negative selection), DP cells with low affinity are rescued from death and undergo positive selection and develop into SP cells. Recent studies have identified a number of transcriptional regulators, such as RARrelated orphan receptor gamma (t) (RORγt), runt-related transcription factor 3 (Runx3), and Th-inducing POZ-kruppel factor (ThPOK), that control positive selection and lineage decision between CD4SP and CD8SP T cells (1-3).In contrast, we have a very limited understanding of the mechanisms underlying the progression of DP into SP cells, a related but rather distinct process from positive selection and CD4/CD8 lineage differentiation (1). Such developmental maturation is characterized by the acquisition of a mature T-cell gene expression program, notably the induction of effector molecules IL-7 receptor α chain (IL-7Rα), C-C motif chemokine receptor 7 (CCR7), and sphingosine 1-phosphate receptor 1 (S1P 1 ) in SP cells that are essential for their proper survival and trafficking (1). Among the few pathways identified to function in DP-to-SP transition, E-proteins play a pivotal role by serving as upstream "sensor" transcription factors in differentiating DP thymocytes (1). E-protein activity in DP thymocytes promotes TCRα gene rearrangement and expression of genes characteristic of immature thymocytes while repressing the expression of effector molecules unique to mature T cells (4). However, given the multifaceted functions of E-proteins in thymocyte selection and survival (5), how E-proteins propagate signals in DP cells is unclear (1). Ther...

Mevalonate metabolism–dependent protein geranylgeranylation regulates thymocyte egress

“…S2 B). Further, induction of CD69 and TCR on DP thymocytes, which are early events associated with positive selection (Shi et al, 2017), was comparable between WT and Pggt1b −/− mice ( Fig. S2 C).…”

Liver X receptor β is required for the survival of single-positive thymocytes by regulating IL-7Rα expression

“…4a and 5a, c), and there are several possible mechanisms by which this cell type-dependent regulation could be achieved. First, a transcriptional regulatory protein, possibly a transcription factor, the expression of which begins in SP thymocytes, such as Foxo1, 17 may cooperate with LXRβ to regulate Il7r transcription. In fact, the Il7r 5′-regulatory region, as described in Supplementary Fig.…”

“…S9a, also contains a Foxo-responsive element, 16 indicating that the interaction between LXRβ and Foxo1 may occur via binding to the same Il7r 5′-regulatory region and may thereby orchestrate Il7r transcription. Next, because of the "on-off-on" pattern of IL-7Rα expression at the DN, DP, and SP stages, 5,11 a transcriptional repressor that is highly expressed in DP thymocytes but expressed at low levels in SP thymocytes, such as Gfi1, 17 allows LXRβ to perform its transcriptional activity specifically in SP thymocytes. Finally, there are many transcription factors that regulate IL-7Rα expression in peripheral T cells.…”

“…16 In contrast, the transcriptional repressor Gfi1 controls developmental maturation during the DP-to-SP transition partially by suppressing the transcription of the Foxo1-Il7r axis. 17 Moreover, the transcription factor Foxp1 inhibits Il7r transcription by antagonizing Foxo1 at the same locus and then controls the quiescence of naive T cells. 18 In addition, GA binding protein α, a member of the Ets family, maintains Il7r transcription in DN thymocytes by occupying the promoter of the Il7r gene.…”

Blockade of CTLA-4 and PD-1 Enhances Adoptive T-cell Therapy Efficacy in an ICOS-Mediated Manner

“…In brief, ICOS and Eomes cDNAs were inserted into the polylinker site of the empty retroviral vector (a generous gift from Dr. Hongbo Chi lab at St. Jude Children's Research Hospital). For retroviral transduction, the aboveactivated CTLs were transduced with RV encoding either ICOS or Eomes by "spin inoculation" (650 g for 1 hour), as described previously (16). Cells were cultured for an additional 4 or 5 days to analyze IFNg production by intracellular cytokine staining (17) and Eomes expression after permeabilization and fixation of cells using the transcription factor fixation/permeabilization kit from eBioscience.…”