ESTROGEN-RECEPTOR DOES NOT DIRECTLY REGULATE THE MURINE MUC-1 PROMOTER

Muc-1 is a heavily O-glycosylated, type 1 membrane glycoprotein presen t on the surface of polarized secretory uterine epithelial cells. Prev ious studies have shown that treatment of ovariectomized mice with 17- beta-estradiol (E-2) strongly induces Muc-1 mRNA expression in an estr ogen receptor (ER)-mediated fashion in the uterus. In this study, the 5.4 kb Muc-1 gene promoter has been isolated from a mouse genomic libr ary and the proximal 1.85 kb region has been sequenced. Sequence analy sis revealed the presence of one potential full estrogen response elem ent (ERE) (GCTCGCGGTGACC) located at - 748 to - 735 bp in the Muc-1 pr omoter and several potential ERE half sites. Electrophoretic mobility shift assays (EMSA) showed that neither ER alpha nor ERP bind efficien tly to this sequence. Transient cotransfection assays using constructs containing various deletion mutations of the 5' Muc-1 flanking sequen ces showed that E-2 had no direct stimulation on promoter-driven repor ter in NMuMG cells or primary mouse uterine epithelial cells, but did stimulate a consensus ERE CAT-reporter gene activity. In addition, E-2 -treatment of Weg-ER cells, a mouse uterine epithelial cell line stabl y expressing human ER alpha, did not restore endogenous Muc-1 expressi on or activate Muc-1 promoter-driven CAT activity. These results indic ate that regions of the Muc-1 gene promoter within - 1838 to + 43 bp d o not respond to E-2 and ER stimulation and that ER alone is not suffi cient to restore Muc1 gene expression. Deletion analyses also revealed that the sequence between - 73 and + 43 bp of the Muc-1 promoter is t he minimal promoter region required for maximal Muc-1 promoter activit y. Collectively, these results demonstrate that ER does not directly r egulate the 1.85 kb murine Muc-1 gene promoter. Therefore, E-2 control of uterine Muc-1 gene expression is likely to be indirect, i.e. media ted by stromal cell-derived factors. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.