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Regulation and expression of multidrug resistance (MDR) transcripts in the intestinal epithelium
1Ontario Cancer Institute/Princess Margaret Hospital and Department of Medical Biophysics, University of Toronto, Canada.
Abstract:
A paucity of information exists on the regulation of gene expression in the undifferentiated intestine. The intestinal epithelium is one of the few normal tissues expressing the multidrug resistance (MDR) genes that confer the multidrug resistant phenotype to a variety of tumours. Expression of mdr1a has been observed in the primitive rat intestinal epithelial cell line, IEC-18. It is hypothesized that characterization of MDR gene expression in IEC-18 cells will provide insight into gene regulation in undifferentiated intestinal cells. A series of hamster mdr1a promoter deletion constructs was studied in IEC-18 and a region with 12-13-fold enhancer activity was identified. This region was shown to function in an orientation- and promoter context-independent manner, specifically in IEC-18 cells. Unexpectedly, Northern probing revealed a greater expression of mdr1b than mdr1a in IEC-18 cells. A quantitative reverse transcription polymerase chain reaction assay was used to compare the relative expression of MDR genes in IEC cells, fetal intestine, and in the undifferentiated and differentiated components of adult intestinal epithelium. MDR transcript levels in IEC cells were found to resemble those of fetal intestine and small intestinal crypts, where a conversion from mixed mdr1a/mdr1b to predominantly mdr1a expression occurs as cells mature. This work describes two contributions to the field of gene regulation in the undifferentiated intestine--first, the initial characterization of a putative mdr1a enhancer region with specificity for primitive intestinal cells and secondly, the first report of mdr1b detection in the intestine and its expression in primitive cell types.
Insights
Researchers identified a gene enhancer region specific to primitive intestinal cells, revealing novel insights into multidrug resistance (MDR) gene regulation in the undifferentiated intestine. This study also reports the presence of mdr1b in the intestine.
Area of Science:
- Molecular Biology
- Genetics
- Gastroenterology
Background:
- Limited information exists on gene expression regulation in the undifferentiated intestine.
- The intestinal epithelium expresses multidrug resistance (MDR) genes, contributing to drug resistance in tumors.
- The primitive rat intestinal epithelial cell line (IEC-18) expresses mdr1a.
Purpose of the Study:
- To characterize multidrug resistance (MDR) gene expression in primitive intestinal cells (IEC-18).
- To identify regulatory elements controlling MDR gene expression in the undifferentiated intestine.
- To compare MDR gene expression patterns in primitive, fetal, and adult intestinal cells.
Main Methods:
- Studied hamster mdr1a promoter deletion constructs in IEC-18 cells.
- Utilized Northern probing to assess mdr1a and mdr1b expression.
- Employed quantitative reverse transcription polymerase chain reaction (RT-PCR) to compare MDR gene transcript levels across different intestinal cell types.
Main Results:
- Identified a 12-13-fold enhancer region in the mdr1a promoter, active in IEC-18 cells.
- Observed higher expression of mdr1b than mdr1a in IEC-18 cells.
- MDR transcript levels in IEC cells mirrored those in fetal intestine and crypts, with a shift from mdr1a/mdr1b to mdr1a dominance during cell maturation.
Conclusions:
- Characterized a novel enhancer region for mdr1a with specificity for primitive intestinal cells.
- Reported the first detection and expression of mdr1b in the intestine, particularly in primitive cell types.
- Provided insights into the regulation of MDR gene expression during intestinal development and differentiation.