Differential regulation of the human nidogen gene promoter region by a novel cell-type-specific silencer element

Transfection analyses of the human nidogen promoter region in nidogen-produ cing fibroblasts from adult skin revealed multiple positive and negative ci s-acting elements controlling nidogen gene expression. Characterization of the positive regulatory domains by gel mobility-shift assays and co-transfe ction studies in Drosophila SL2 cells unequivocally demonstrated that Sp1-l ike transcription factors are essential for a high expression of the human nidogen gene. Analysis of the negative regulatory domains identified a nove l silencer element between nt - 1333 and - 1322, which is bound by a distin ct nuclear factor, by using extracts from adult but not from embryonal fibr oblasts. In embryonal fibroblasts, which express significantly higher amoun ts of nidogen mRNA as compared with adult fibroblasts, this inhibitory nido gen promoter region did not affect nidogen and SV40 promoter activities. Th e silencer element seems to be active only in nidogen-producing cells. Ther efore this regulatory element might function in vivo to limit nidogen gene expression in response to external stimuli. However, none of the identified regulatory elements, including the silencer, contribute significantly to c ell-specific expression of the human nidogen gene. Instead we provide evide nce that gene expression in epidermal keratinocytes that are not producing nidogen is repressed by methylation-specific and chromatin-dependent mechan isms.