LEF-1/TCF-1 in IL-4 expression and Th2 polarisation

A hallmark of allergic reactions is the presence of type 2 T helper cells (T H 2) in the immune system. Interleukin-4 (IL-4) is both one of the cytokines secreted by TH 2 cells, and the main factor which drives T cells towards TH 2 differentiation. Expression of IL-4 is modified through a large array of different regulatory elements that have been identified at or close to the IL4 locus. Most of these are located within the 5` proximal promoter region. The Wnt signaling pathway plays an important role in a number of developmental processes. Recent studies showed that Wnt signaling may also be involved in hematopoiesis. The high-mobility box transcription factors lymphoid enhancer binding factor-1 (LEF-1) and T cell factor-1 (TCF-1) are the main downstream effectors of the Wnt signaling pathway. Together with ß-catenin, LEF-1/TCF-1 can activate transcription of target genes by binding to the sequence motif 5`-CTTTG A / TA / T-3`. In the absence of ß-catenin, LEF-1 and TCF-1 were shown to have repressive function, too. Our preliminary data show that a functional LEF-1/TCF-1 binding motif is present on the proximal IL4 promoter. In addition, we found that LEF-1 and TCF-1 are downregulated upon T cell activation and IL-4 stimulation. Further, LEF-1 appears to be expressed selectively in murine TH 1 cells, while TCF-1 seems not to be expressed in fully differentiated T cells. These observations suggest involvement of the Wnt pathway in T cell activation and/or T helper cell polarization. The aim of the project will therefore be to unravel the roles of LEF-1 and TCF-1 in these subjects. The first issue to be addressed concerns the LEF-1/TCF-1 binding site in the IL4 promoter. We will study in detail the importance of this binding motif in the regulation of IL-4 expression. Experiments to characterize the involvement of LEF-1/TCF-1 in regulation of IL4 and ultimately T helper cell polarization will include realtime PCR, ectopic overexpression, small interfering RNA (siRNA), gelshifts, chromatin immunoprecipitation, and in vitro TH polarisation. Another goal of this project will be to unveil the mechanism of downregulation of LEF- 1/TCF-1 in T-cell activation.

A hallmark of allergic reactions is the presence of type 2 T helper cells (T H 2) in the immune system. Interleukin-4 (IL-4) is both one of the cytokines secreted by TH 2 cells, and the main factor which drives T cells towards TH 2 differentiation. Expression of IL-4 is modified through a large array of different regulatory elements that have been identified at or close to the IL4 locus. Most of these are located within the 5` proximal promoter region. The Wnt signaling pathway plays an important role in a number of developmental processes. Recent studies showed that Wnt signaling may also be involved in hematopoiesis. The high-mobility box transcription factors lymphoid enhancer binding factor-1 (LEF-1) and T cell factor-1 (TCF-1) are the main downstream effectors of the Wnt signaling pathway. Together with ß-catenin, LEF-1/TCF-1 can activate transcription of target genes by binding to the sequence motif 5`-CTTTG A / TA / T-3`. In the absence of ß-catenin, LEF-1 and TCF-1 were shown to have repressive function, too. Our preliminary data show that a functional LEF-1/TCF-1 binding motif is present on the proximal IL4 promoter. In addition, we found that LEF-1 and TCF-1 are downregulated upon T cell activation and IL-4 stimulation. Further, LEF-1 appears to be expressed selectively in murine TH 1 cells, while TCF-1 seems not to be expressed in fully differentiated T cells. These observations suggest involvement of the Wnt pathway in T cell activation and/or T helper cell polarization. The aim of the project will therefore be to unravel the roles of LEF-1 and TCF-1 in these subjects. The first issue to be addressed concerns the LEF-1/TCF-1 binding site in the IL4 promoter. We will study in detail the importance of this binding motif in the regulation of IL-4 expression. Experiments to characterize the involvement of LEF-1/TCF-1 in regulation of IL4 and ultimately T helper cell polarization will include realtime PCR, ectopic overexpression, small interfering RNA (siRNA), gelshifts, chromatin immunoprecipitation, and in vitro TH polarisation. Another goal of this project will be to unveil the mechanism of downregulation of LEF- 1/TCF-1 in T-cell activation.