Regulation of 1,25D(3)-MARRS expression by TGFB1 in a rat intestinal epithelial cell line
Date
2006
Authors
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Publisher
University of Delaware
Abstract
Crohn's disease and ulcerative colitis are diseases of the intestine that are characterized by intestinal lesions, diarrhea and an inflammatory response. One key cytokine involved in the response is transforming growth factor β1 (TGFβ1), which is elevated during inflammation. Using the IEC6 cell line as a cell model for the intestine, I investigated the effect of the increased levels of (TGFβ1), on expression of 1,25D 3 -MARRS (M[barbelow]embrane A[barbelow]ssociated R[barbelow]apid R[barbelow]esponse to S[barbelow]teroid). The protein product of the 1,25D 3 -MARRS gene, also known as ERp57 or PDIA3, binds the hormonally active form of vitamin D, 1,25(OH) 2 D 3, and influences intestinal cell functions such as phosphate uptake and calcium homeostasis. I found that IEC6 cells respond to increased levels of TGFβ1 by increasing the steady state levels of 1,25D 3 -MARRS transcript and protein. It was also found that IEC6 cells secrete TGFβ1, supporting a likely autocrine response. Investigation of the 1,25D 3 -MARRS promoter revealed it contains a Smad3 response element which is normally involved in TGFβ1 induced transcription activation. Using a promoter-reporter assay to determine 1,25D 3 -MARRS promoter activity, I found that deletion or mutation of the Smad3 response element resulted in loss of response to TGFβ1 and decreased basal promoter activity. Finally, the ability of the Smad3 response element to bind to nuclear protein was determined by electromobility shift assay. These findings suggest that the IEC6 cells respond to the inflammatory signal mimicked by increased TGFβ1 levels by increasing 1,25D 3 -MARRS transcript and protein levels and that the TGFβ1 signaling pathway may be involved in maintaining the basal levels of the 1,25D 3 -MARRS promoter activity. A new model describing a potential interaction among TGFβ1, 1,25D 3 -MARRS and 1,25(OH) 2 D 3 during inflammatory events in the intestine is presented.