| Interleukin 2 (IL-2) plays a central role in regulating the proliferation of T cell . the magnitude and duration of T cell immune response via its specific interaction with its cognate receptor (IL-2R). There are three forms of IL-2R with different affinity to IL-2: low affinity IL-2R( dissociation coefficient Kd 10-8 M), intermediate affinity IL-2R(Kd 10-9 M) and high affinity IL-2R (Kd 10-11 M). The high affinity IL-2R consists of three subunits: IL-2R α . IL-2R β, IL-2Rγ; the intermediate IL-2R consists of IL-2R β and IL-2Rγ: the low affinity IL-2R consists of only IL-2R α. IL-2R β and IL-2Rγ are constitutively expressed on the surfaces of resting periphery blood T lymphocyte and a human T cell leukemia cell line Jurkat cells. Expression of high affinity IL-2R and T cell proliferation are controlled by induced expression of IL-2Rα chain gene. Induction of IL-2Rα chain is necessary for T cell to respond to physiological concentrations of IL-2. In resting T cell IL-2Rα can be induced by antigen.nonspecific mitogen(e.g. PHA), tumor promoter PMA and some cytokines such as IL-1, TNF-α. Additional to expressed on activated T cells. IL-2Rα can also be found on activated B cell and NK cell , etc. Human type I T lymphotropic virus(HTLV-I ) infected T cells express high level of IL-2Rα on their cell surface.IL-2Rα chain gene transcription is initiated within 3 hrs of PHA treatment in resting T cells. Cis-elements responsible for the regulation of IL-2Rα chain gene expression in T cell locate within 470bp upstream of the major cap site(+l). The DNA sequence from -287 to -236bp contains a NF-κB-like site, a serum response elememt (SRE) and a SP1 site, this segment acts as a positive regulatory element and confers PHA inducibility on heterologous promoter such as tk promoter. Recently a second positive regulatory region was found between -137 and -64bp. This region contains one Elf-I binding site and four HMGI(Y) binding site. Deletion or mutation impair the binding of the above transcription factors will dramatically decrease IL-2Rα promoter activities in PMA activated normal human T cell and Jurkat cell. In addition to the two positive regulatory region , a negative regulatory element was found between -391 and -381bp(5'-TTCATCCCAGG-3') relative to the major cap site of IL-2Rα chain gene. This element is 82% homologous to HIV LTR NRE core sequence(5'-TTCATCACATG-3') Both of them bind the same tissue non-specific DNA binding protein . Previous work of our group using various deletion mutants of IL-2Rα 5' upstream sequence as templates in in vitro transcription experiments demonstrated that there is a negative regulation element in the sequence between -482 and -350bp. Our group found a previously unnoticed imperfect inverse repeated sequence(NIRS) of the NRE (-391 to -381) between -153 and -143bp(5'-CCCTGGTTTGAAA-3'). Deletion of NIRS or NRE both increase reporter gene expression in transient transfection experiment. We found a 83kDa protein binds to both NRE and NIRS by UV-crosslinking previously. In order to understand the role and mechanism of the protein(s) binding to NRE and NIRS in the regulation of IL-2Rα chain gene expression, it is necessary to purify this protein and obtain cDNA of this protein. To our knowledge, there is...
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