CONTRIBUTION OF PROXIMAL PROMOTER ELEMENTS TO THE REGULATION OF BASALAND DIFFERENTIAL GLUTATHIONE-S-TRANSFERASE P1 GENE-EXPRESSION IN HUMAN BREAST-CANCER CELLS

Glutathione S-transferase P1 (GST P1-1) is normally expressed exclusiv ely in estrogen receptor negative (ER-) but not receptor positive (ER) cultured breast cancer cells. We examined the role of proximal promo ter elements in GST P1 gene expression in MCF7 (ER+, GST P1-) and HS57 8T (ER-, GST P1+) breast cancer cells. Transient transfection of GST P 1 promoter-CAT reporter genes confined that the GST P1 TRE (-69 to -60 ) and the adjacent distal GC box (-56 to -51) are required for basal p romoter activity in both cell lines, Other studies identified differen ces in the GST P1 promoter activity and DNA-protein interactions betwe en the two cell lines. Electrophoretic mobility shift assay revealed a protein-TRE interaction that is unique to nuclear proteins derived fr om GST P1 expressing HS578T cells. Furthermore, a putative silencer re gion contained within sequences -130 to -70 selectively reduced GST P1 promoter-CAT reporter gene expression in MCF7 but not HS578T cells. W hile this cell-line specific silencer contributed to the level of GST P1 promoter activity observed in the two cell lines, analysis of cells stably transfected with a novel genomic GST P1 minigene vector establ ished that the silencer is insufficient to completely repress GST P1 t ranscription in ER+, MCF7 cells that do not normally express endogenou s GST P1. (C) 1998 Elsevier Science B.V.