Characterization of the rat intestinal Fc receptor (FcRn) promoter: transcriptional regulation ofFcRngene by the Sp family of transcription factors

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Abstract
The regulatory elements that control the transcriptional regulation of the intestinal Fc receptor ( FcRn) have not been elucidated. The objective of this study was to characterize the core promoter region of the rat FcRn gene. Chimeric clones that contained various regions of the promoter located upstream of the luciferase reporter were transiently transfected into either IEC-6 or Caco-2 cell lines and nuclear extracts were used to perform DNase I footprint and DNA binding assays (EMSA). Transfection of chimeric upstream nested deletions-luciferase reporter clones into either of these cell lines supported robust reporter activity and identified the location of the minimal promoter at −157/+135. DNase I footprint analysis revealed two complexes located within the gene's core promoter region, and site-directed mutagenesis identified two regions that were critical to maintain basal expression. EMSA identified the presence of five Sp elements within the immediate promoter region that are capable of binding members of the Sp family of proteins. Among the five Sp elements, one element appears to not bind Sp1, Sp2, or Sp3 while influencing the interaction of Sp proteins with an adjacent Sp site. Overexpression of either Sp1 or Sp3 augments activity of the minimal promoter in Sp-deficient Drosophila SL2 cells. In summary, we report on the characterization of the rat FcRn minimal promoter, including the characterization of five Sp elements within this region that interact with members of the Sp family of transcriptional factors and drive promoter activity in intestinal cell lines.