Molecular mechanisms of interleukin-2 gene inducibility: developmental control and combinatorial action of transcription factors

Biology

Chen, Dan ; Rothenberg, Ellen V.

University:California Institute of Technology

Department:Biology

关键词: Biology;   

Others  :  https://thesis.library.caltech.edu/7636/1/Chen_d_1994.pdf

美国|英语

来源: Caltech THESIS

【 摘 要 】

Interleukin-2 is one of the lymphokines secreted by T helper type 1 cells uponactivation mediated by T-cell receptor (TCR) and accessory molecules. The ability toexpress IL-2 is correlated with T-lineage commitment and is regulated during T celldevelopment and differentiation. Understanding the molecular mechanism of how IL-2gene inducibility is controlled at each transition and each differentiation process of T-celldevelopment is to understand one aspect of T-cell development. In the present study, wefirst attempted to elucidate the molecular basis for the developmental changes of IL-2 geneinducibility. We showed that IL-2 gene inducibility is acquired early in immature CD4-CD8-TCR- thymocytes prior to TCR gene rearrangement. Similar to mature T cells, acomplete set of transcription factors can be induced at this early stage to activate IL-2 geneexpression. The progression of these cells to cortical CD4^+CD8^+TCR^(1o) cells isaccompanied by the loss of IL-2 gene inducibility. We demonstrated that DNA bindingactivities of two transcription factors AP-1 and NF-AT are reduced in cells at this stage.Further, the loss of factor binding, especially AP-1, is attributable to the reduced ability toactivate expression of three potential components of AP-1 and NF-AT, including c-Fos,FosB, and Fra-2. We next examined the interaction of transcription factors and the IL-2promoter in vivo by using the EL4 T cell line and two non-T cell lines. We showed an all-or-none phenomenon regarding the factor-DNA interaction, i.e., in activated T cells, theIL-2 promoter is occupied by sequence-specific transcription factors when all thetranscription factors are available; in resting T cells or non-T cells, no specific protein-DNAinteraction is observed when only a subset of factors are present in the nuclei.Purposefully reducing a particular set of factor binding activities in stimulated T cells usingpharmacological agents cyclosporin A or forskolin also abolished all interactions. Theresults suggest that a combinatorial and coordinated protein-DNA interaction is required forIL-2 gene activation.The thymocyte experiments clearly illustrated that multiple transcription factors areregulated during intrathymic T-cell development, and this regulation in tum controls theinducibility of the lineage-specific IL-2 gene. The in vivo study of protein-DNA interactionstressed the combinatorial action of transcription factors to stably occupy the IL-2 promoterand to initiate its transcription, and provided a molecular mechanism for changes in IL-2gene inducibility in T cells undergoing integration of multiple environmental signals.