Modulation of the folate receptor alpha gene by the estrogen receptor: mechanism and implications in tumor targeting.
The folate receptor (FR) type alpha is a promising target for diagnostic imaging agents and therapeutic intervention in major subtypes of gynecological malignancies; however, the receptor levels in the tumors are variable and are generally relatively low in estrogen receptor (ER)-positive tumors. Here we report that the FR-alpha gene promoter is repressed in the presence of 17beta-estradiol and derepressed by the antiestrogens tamoxifen and ICI 182780 in a promoter-specific and ER-alpha-dependent manner in carcinoma cell lines including HeLa (cervical carcinoma), BG-1 (ovarian carcinoma), and IGROV-1 (ovarian carcinoma). The ligand and ER dose response of the FR-alpha promoter and its time course paralleled those of a classical estrogen response element-mediated effect. Antiestrogens produced an ER-dependent increase of up to 36-fold in the expression of the endogenous FR-alpha gene. Deletion analysis and FR-alpha/SV40 promoter chimeras showed that the ER effect is mediated exclusively within the G/C-rich region in the TATA-less P4 promoter of FR-alpha; electrophoretic mobility shift analysis demonstrated interaction of ER at only one of three G/C-rich elements. ER-beta only modestly affected FR-alpha promoter activity but did not diminish the ER-alpha-mediated effects. The ER corepressor, SMRT, enhanced the repression by 17beta-estradiol/ER, but ER coactivators, including SRC family members, did not appreciably impact the ER ligand response. The results suggest that in ER+ tumors, FR-alpha expression is directly and actively suppressed and predict that a brief treatment with antiestrogens will boost FR-alpha expression by passive derepression, enhancing the efficacy of FR-targeted diagnostic and therapeutic applications. They also reveal novel aspects of gene repression by ER.
Kelley
Karen M M
KM
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo, Ohio 43614-5804, USA.
Rowan
Brian G
BG
Ratnam
Manohar
M
D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D005260:Female; D058973:Folate Receptors, GPI-Anchored; D000077267:Fulvestrant; D020868:Gene Silencing / Q000187:drug effects / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011956:Receptors, Cell Surface; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D013629:Tamoxifen / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D011960:Receptors, Estrogen; D013629:Tamoxifen; D000077267:Fulvestrant; D004958:Estradiol