Abstract
MUC1, a membrane-tethered glycoprotein that is expressed on a number of epithelial cell types in vivo, is over-expressed in adenocarcinomas and thought to play a significant role in tumour progression and metastasis. Hence, elucidation of the mechanisms of regulation of MUC1 gene expression is of considerable biological importance. Our aim was to evaluate regulation of MUC1 expression in vivo. DNase I hypersensitive sites (DHS) were mapped in chromatin from human cell lines and human MUC1 transgenic mice. MUC1 expression was evaluated by RT-PCR and Northern blots. We identified two novel DHS in the MUC1 promoter at -750 bp and -250 bp from the transcriptional start site. These DHS were detected in human cell lines and in a human MUC1 transgene in mice. The -750 DHS was apparent in many cell types irrespective of the level of MUC1 expression but the -250 DHS was only evident in cells that express MUC1 and its intensity correlated with the abundance of MUC1 transcripts. The -250 DHS became undetectable in cell lines representing a transition from colon adenoma to carcinoma, commensurate with a significant reduction in MUC1 expression. The -750 and -250 regions are conserved between the human MUC1 and mouse Muc1 genes and may be associated with functionally important genetic elements. The DHS at -250 is in the vicinity of previously defined purine/pyrimidine mirror repeat elements that may form intramolecular H-DNA structures, which can alter the accessibility of chromatin to regulatory proteins.
Highlights
MUC1 is a cell surface-associated mucin glycoprotein that is highly overexpressed and differentially glycosylated by various adenocarcinomas [1]
DNase I hypersensitive sites in chromatin are often associated with regulatory elements and so can be informative in the identification of control elements that are active in vivo
We identified two novel DNase I hypersensitive sites (DHS) in the MUC1 gene promoter region at Ϫ250 and Ϫ750 bp with respect to the major transcriptional start site
Summary
MUC1 is a cell surface-associated mucin glycoprotein that is highly overexpressed and differentially glycosylated by various adenocarcinomas [1]. Sequential deletions, specific deletions and site specific mutations of sequences 5’ to the MUC1 gene revealed that at least 600 bp of upstream sequence was required for maximal promoter activity in transient transfections [2,3] This effect may be partly due to deletion of an Sp1 site located approximately Ϫ570 bp from the transcription start site, an AP-3 site adjacent to this, or several other potential cis elements just downstream. Results: We identified two novel DHS in the MUC1 promoter at Ϫ750 bp and Ϫ250 bp from the transcriptional start site These DHS were detected in human cell lines and in a human MUC1 transgene in mice. The DHS at Ϫ250 is in the vicinity of previously defined purine/pyrimidine mirror repeat elements that may form intramolecular H-DNA structures, which can alter the accessibility of chromatin to regulatory proteins
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