Identification of novel oestrogen receptor target genes in human ZR75-1 breast cancer cells by expression profiling.

Oligonucleotide microarrays were used to analyse gene expression profiles in human ZR75-1 breast cancer cells in the presence of 17beta-oestradiol and oestrogen antagonists. Differential gene expression of a number of genes was confirmed by quantitative RNA analysis. In addition to known oestrogen-responsive genes, an appreciable number of novel targets were identified, including growth factors and components of the cell cycle, adhesion molecules, enzymes, signalling molecules and transcription factors. The most pronounced oestrogen-sensitive gene was that for the cytochrome P450-IIB enzyme, involved in metabolising steroids and xenobiotics, which was increased 100-fold over a 24 h period. It is a direct target gene for oestrogens, because its expression was increased in the presence of cyclohexamide. In contrast, expression of cytochrome P450-IIB was not detected in human MCF7 breast cancer cells. Expressions of the cationic amino acid transporter E16, gap junction protein and insulin-like growth factor binding protein 4 were also markedly increased by oestrogens, but the kinetics of induction varied according to the target gene. With the exception of the cationic amino acid transporter E16 and the insulin-like growth factor binding protein 4, the expression of the majority of the genes was unaffected by antioestrogen treatment. Further analysis of this set of markers will provide alternative approaches to the investigation of the mitogenicity of oestrogens in breast cancer cells.