Identification of estrogen-induced genes downregulated by AhR agonists in MCF-7 breast cancer cells using suppression subtractive hybridization

Aryl hydrocarbon receptor (AhR) agonists inhibit 17 beta -estradiol (E2) in duced growth of MCF-7 human breast cancer cells in vitro and rodent mammary tumor growth in vivo. Genes associated with inhibitory AhR-estrogen recept or (ER) crosstalk were investigated in MCF-7 human breast cancer cells usin g poly(A)(+)RNA from cells treated with either 1 nM E2 (target) or E2 plus 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (reference) or 25 muM diind olylmethane (DIM) as AhR agonists in MCF-7 cells. Suppression subtractive h ybridization (SSH) was subsequently used to identify 33 genes with sequence homology to known human genes that are induced by E2 and inhibited by AhR agonists in MCF-7 cells; two unknown genes: were also identified. Many of t hese genes are invoiced in cell proliferation and these include cell cycle regulators (cdc28/cdc2-associated protein), nucleotide synthases (thymidyla te synthase), early intermediate genes (early growth response alpha, EGR al pha) and other proteins involved in signaling pathways (calmodulin, ATP syn thase alpha subunit). Thus SSH has identified a diverse spectrum of new gen es that are affected by inhibitory AhR-ER crosstalk and among this group ar e a subset of genes that may be critical for the in vivo antitumorigenic ef fects of AhR agonists. (C) 2001 Elsevier Science B.V. All rights reserved.