Enhancer activation by a single type of transcription factor shows cell type dependence

Promoter and enhancer elements contain multiple binding sites for ubiquitous and cell type-specific transcription factors which stimulate transcription synergistically. Here we show that cell type-dependent enhancer activity can be achieved by mechanisms other than interactions between cell type-specific transcription factors and DNA. The ability of the SV40 enhancer and the E2 transactivator from bovine papillomavirus (BPV-1) to stimulate transcription from a reporter gene with different minimal promoters was tested in four cell lines. In lymphoid BJA-B cells all minimal promoters that synergized with the SV40 enhancer did so also with the E2-dependent enhancer. In sharp contrast to these results, the E2 enhancer stimulated transcription only from a subset of promoters in fibroblasts and in epithelial cells. The results suggest that lymphoid cells, unlike fibroblasts and epithelial cells, contain auxiliary factor(s) which are necessary for the activation of certain promoters by the E2 enhancer and infer that the specificity of enhancers also is regulated at a co-activator level.