Abstract
The interleukin 13 alpha 2 receptor (IL-13Ra2) has been shown to be expressed in most malignant glioblastoma cells. Recent studies suggest that IL-13Ra2 serves as a dominant negative inhibitor or a decoy receptor for IL-13. To investigate the transcriptional regulation of this receptor, we cloned and characterized the promoter for the human IL-13Ra2 gene. Our results demonstrate that this promoter contains three TATA boxes and one CCAAT site. Several putative transcriptional factor binding sites for nuclear factor of activated T cells 1, AP1 (c-JUN and c-FOS), AP2, GABP, OCT1, GATA3, PRE, and C-ETS1 were predicted in the promoter region. Using the secreted alkaline phosphate reporter gene assay, we investigated the functional activity of the human IL-13Ra2 promoter by transient transfection in glioma cell lines U118, U87, and T98, which differ in their expression of the human IL-13Ra2 protein. The different secreted alkaline phosphate activities among these 3 cell lines suggest that the expression of human IL-13Ra2 is regulated at the transcriptional level. Methylation analysis showed that expression of IL-13Ra2 may not be the result of methylation of the CpG dinucleotides in the promoter region of the gene. Deletion analysis identified a 64 base pair (bp) region that is necessary for human IL-13Ra2 promoter activity. This 64-bp sequence contains cis-elements for AP1, nuclear factor of activated T cells, and AP2. The possible role of AP1 in the regulation of human IL-13Ra2 promoter activity was suggested by in vitro mutagenesis and c-JUN N-terminal kinase inhibition analysis.
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