Regulation of keratin 19 gene expression by estrogen in human breast cancer cells and identification of the estrogen responsive gene region

Estrogens regulate the proliferation, cytoarchitectural, and invasive prope rties of estrogen receptor (ER)-containing breast cancer cells. To identify genes under direct regulation by estrogen in breast cancer cells, we have used representational difference analysis (RDA) of cDNAs. In this way, we h ave identified (cyto)keratin 19 (K19), a major component of cell intermedia te filaments, as bring under rapid and direct regulation by estrogen in MCF -7 cells. Stimulation by estradiol (E-2) of K19 mRNA is rapid, with maximal increase at 3 h, and is not blocked by cycloheximide, suggesting that it i s a primary response to the hormone. Increased accumulation of K19 protein is observable by 8 h after E-2 and levels continue to increase at 24-48 h a fter E-2 treatment. Suppression of E-2-induced K19 gene expression by the a ntiestrogen ICI 182,780 suggests that ER mediates this regulation. Analysis of the human K19 chromosomal gene, by transient transfection assays employ ing reporter gene constructs with the 5' and 3' flanking regions and portio ns of the body of the K19 gene, has resulted in identification of a complex enhancer region in the first intron. This enhancer region consists of a ne ar-consensus estrogen response element (K19 ERE, which differs by only 1 bp from the consensus ERE) and two ERE half sites, as well as two AP1-like si tes. The results of transfections with either the K19 gene promoter or the heterologous thymidine kinase promoter and constructs containing mutated or deleted portions of the enhancer region shaw that the K19 ERE is responsib le for the E-2-dependent transactivation of the keratin 19 gene and for the synergism that is observed between E-2 and TPA with both ER alpha and ER b eta, These studies document ER regulation of the K19 gene, localize the est rogen responsive region, and suggest that up-regulation of keratin 19 gene expression by estrogen may contribute to the cytoskeletal and nuclear matri x reorganization, and increased metastatic potential of ER-containing breas t cancer cells upon exposure to estrogens. (C) 2000 Elsevier Science Irelan d Ltd. All rights reserved.