PDZK1 and GREB1 are estrogen-regulated genes expressed in hormone-responsive breast cancer

The function of estrogen in breast cancer proliferation and progression is likely to be due to the expression of a repertoire of genes regulated by estrogen receptor (ER). Using suppression subtractive hybridization, we have isolated a set of 14 estrogen-responsive genes that was differentially expressed in MCF7 cells stimulated by beta-estradiol as compared with unstimulated cells. Tamoxifen repressed the expression of all 14 estrogen-responsive genes. Thirteen of the genes were induced within 6 h of estrogen treatment, indicating that these were early response genes in the ER-regulated pathway. PDZK1 and a new gene, GREB1, demonstrated a significant correlation with ER phenotype in a panel of breast cancer cell lines. Treatment with cycloheximide indicated that ER directly controls GREB1 expression. Three cDNAs (GREB1a, GREB1b, and GREB1c) were isolated by screening a MCF7 cDNA library. These three cDNAs of GREB1 shared extensive sequences through the open reading frame but had divergent 5' untranslated regions, indicating the possibility of multiple promoters regulated by beta-estradiol. Studies in primary breast cancers showed that PDZK1 and GREB1 were overexpressed in ER-positive breast cancers as compared with ER-negative breast cancers by 19-fold and 3.5-fold, respectively. GREB1 was also induced by beta-estradiol in the ER-positive endometrial cell line ECC-1. The pattern of expression suggests a critical role for these two genes in the response of tissues and tumors to beta-estradiol.