Michael A. Weinreich

Kruppel-like factor 2 regulates thymocyte and T-cell migration

Mammalian Kruppel-like transcription factors are implicated in regulating terminal differentiation of several tissue types. Deficiency in Kruppel-like factor (KLF) 2 (also known as LKLF) leads to a massive loss of the peripheral T-cell pool, suggesting KLF2 regulates T-cell quiescence and survival. Here we show, however, that KLF2 is essential for T-cell trafficking. KLF2-deficient (Klf2-/-) thymocytes show impaired expression of several receptors required for thymocyte emigration and peripheral trafficking, including the sphingosine-1-phosphate (S1P) receptor S1P1, CD62L and β7 integrin. Furthermore, KLF2 both binds and transactivates the promoter for S1P1—a receptor that is critical for thymocyte egress and recirculation through peripheral lymphoid organs. Our findings suggest that KLF2 serves to license mature T cells for trafficking from the thymus and recirculation through secondary lymphoid tissues.

T cells expressing the transcription factor PLZF regulate the development of memory-like CD8+ T cells.

Several gene-deficiency models promote the development of innate CD8+ T cells that have diverse T cell antigen receptors (TCRs) but have a memory phenotype and rapidly produce cytokines. We demonstrate here that similar cells developed in mice deficient in the transcription factor KLF2. However, this was not due to intrinsic deficiency in KLF2 but instead was due to interleukin 4 (IL-4) produced by an expanded population of T cells expressing the transcription factor PLZF. The development of innate CD8+ T cells in mice deficient in the tyrosine kinase Itk and coactivator CBP was also attributable to this IL-4-dependent mechanism. Finally, we show that the same mechanism drove the differentiation of innate CD8+ T cells in BALB/c mice. Our findings identify a previously unknown mechanism of regulation of CD8+ T cells via the production of IL-4 by PLZF+ T cells.Several gene deficiency models promote the development of “innate CD8+ T cells” that have diverse TCRs, but display a memory phenotype and rapidly produce cytokines. We here demonstrate that similar cells develop in Kruppel-Like Factor 2 (KLF2) deficient mice. However, this is not due to intrinsic deficiency in KLF2, but rather to interleukin 4 (IL-4) produced by an expanded population of T cells expressing the PLZF transcription factor. The development of innate CD8+ T cells in ITK and CBP transcription factor deficient mice is also attributable to this IL-4-dependent mechanism. Finally, we show that the same mechanism drives innate CD8+ T cell differentiation in BALB/c mice. These findings reveal a novel mechanism of regulation of CD8+ T cells via PLZF+ T cell production of IL-4.

KLF2 Transcription-Factor Deficiency in T Cells Results in Unrestrained Cytokine Production and Upregulation of Bystander Chemokine Receptors

The transcription factor KLF2 regulates T cell trafficking by promoting expression of the lipid-binding receptor S1P(1) and the selectin CD62L. Recently, it was proposed that KLF2 also represses the expression of chemokine receptors. We confirmed the upregulation of the chemokine receptor CXCR3 on KLF2-deficient T cells. However, we showed that this was a cell-nonautonomous effect, as revealed by CXCR3 upregulation on wild-type bystander cells in mixed bone-marrow chimeras with KLF2-deficient cells. Furthermore, KLF2-deficient T cells overproduced IL-4, leading to the upregulation of CXCR3 through an IL-4-receptor- and eomesodermin-dependent pathway. Consistent with the increased IL-4 production, we found high concentrations of serum IgE in mice with T cell-specific KLF2 deficiency. Our findings support a model where KLF2 regulates T cell trafficking by direct regulation of S1P(1) and CD62L and restrains spontaneous cytokine production in naive T cells.

Thymic Emigration: When and How T Cells Leave Home

The thymus supports the differentiation of multiple distinct T cell subsets that play unique roles in the immune system. CD4 and CD8 α/β T cells, γ/δ T cells, NKT cells, regulatory T cells, and intraepithelial lymphocytes all develop in the thymus and must leave it to provide their functions elsewhere in the body. This article will review recent research indicating differences in the time and migration patterns of T cell subsets found in the thymus. Additionally, we review current understanding of the molecules involved in thymocyte emigration, including the sphingolipid receptor S1P1 and its regulation by the Krüppel-like transcription factor KLF2.

Kruppel-Like Factor 2 Is Required for Trafficking but Not Quiescence in Postactivated T Cells

The transcription factor Kruppel-like factor 2 (KLF2) was proposed to regulate genes involved in cell cycle entry and T cell trafficking; however, the physiological role of its expression in postactivated T cells is not well defined. Previous studies suggested that the cytokines IL-2 and IL-15 differentially regulate KLF2 re-expression in postactivation T cells and that these cytokines also influence effector versus memory T cell differentiation. Using conditional and inducible KLF2-knockout model systems, we tested the specific role of KLF2 expression in activated CD8+ T cells cultured with these cytokines. KLF2 was required for effective transcription of sphingosine-1-phosphate receptor-1 (S1P1) and CD62L in postactivation T cells. However, although different cytokines dramatically altered the expression of cell-cycle–related genes, endogenous KLF2 had a minimal impact. Correspondingly, KLF2-deficient T cells showed dysregulated trafficking but not altered proliferative characteristics following in vivo responses to Ag. Thus, our data help to define KLF2-dependent and -independent aspects of activatedCD8+ T cell differentiation and argue against a physiological role in cell cycle regulation.

Krüppel-Like Factor 2 Regulates Trafficking and Homeostasis of γδ T Cells

γδ T cells are generated in the thymus and traffic to secondary lymphoid organs and epithelial surfaces, where they regulate immune responses. αβ T cells require sphingosine 1-phosphate receptor type 1 (S1P1) and CD62L for thymic emigration and circulation through secondary lymphoid organs. Both of these genes are regulated by the transcription factor Krüppel-like factor 2 (KLF2) in conventional αβ T cells. It is unclear if γδ T cells use similar mechanisms. In this study, we show that thymic γδ T cells express S1P1 and that it is regulated by KLF2. Furthermore, KLF2 and S1P1-deficient γδ T cells accumulate in the thymus and fail to populate the secondary lymphoid organs or gut, in contrast to the expectation from published work. Interestingly, KLF2 but not S1P1 deficiency led to the expansion of a usually rare population of CD4+ promyelocytic leukemia zinc finger+ “γδ NKT” cells. Thus, KLF2 is critically important for the homeostasis and trafficking of γδ T cells.

Postselection Thymocyte Maturation and Emigration Are Independent of IL-7 and ERK5

The transcription factor Krüppel-like factor 2 (KLF2) controls the emigration of conventional T cells from the thymus through its regulation of the cell surface receptor S1P1. Prior to KLF2 expression, developing T cells require a positive selection signal through the TCR. However, following positive selection there are time, spatial, and maturational events that occur before KLF2 is finally upregulated and emigration occurs. We are interested in determining the signals that upregulate KLF2 and allow thymocytes to emigrate into circulation and whether they are linked to functional maturation. In endothelial cells KLF2 expression has been shown to be dependent on the mitogen-activated protein kinase ERK5. Furthermore, it has been reported that IL-7 signaling leads to the phosphorylation of ERK5. Thus, we hypothesized that IL-7R signaling through ERK5 could drive the expression of KLF2. In this study, we provide evidence that this hypothesis is incorrect. We also found that CD8 lineage specification occurred normally in the absence of IL-7R signaling, in contrast to a recently proposed model. We showed that both CD4 and CD8 T cells complete maturation and express KLF2 independently of ERK5 and IL-7.

T-cell migration: Kruppeled T cells move again

Kruppel-like transcription factors are a large family of proteins that can both activate and repress genes and regulate a wide variety of biological processes in multiple organ systems. In T lymphocytes, Kruppel-like factor 2 (KLF2) is an essential gene, as very few T cells are found in the spleen and lymph nodes of mice with targeted deficiency of KLF2.1 This was initially thought to reflect a requirement for KLF2 in T-cell survival and homeostasis. However, subsequent studies showed that KLF2 was required for thymic emigration and lymph node homing by regulating cell surface receptors required for these processes, namely S1P1 and CD62L.2 Now Mark Kahns group3 adds a new twist to the story. They show that KLF2 also represses chemokine-receptor gene expression. Thus KLF2-deficient T cells aberrantly express multiple chemokine receptors that can cause T cells to home to various tissues in the body. Altogether, these studies establish KLF2 as a ‘master regulator’ that coordinates expression of multiple different types of cell surface receptors to control T-cell trafficking during an immune response.

Molecular biology: Dna replication reconstructed.

Chromosomes must be faithfully duplicated in each cell-division cycle to ensure genome integrity. The in vitro reconstitution of DNA-replication initiation in yeast allows mechanistic studies of this fundamental process. See Article p.431