Activation of aromatase expression by retinoic acid receptor-related orphan receptor (ROR) alpha in breast cancer cells: identification of a novel ROR response element.
Estrogen is a key regulator of the proliferation and differentiation of breast cancer cells. In addition to the estrogen supply from the ovary, estrogen is produced locally from androgen by aromatase. However, the regulation of aromatase gene expression in breast cancer has not yet been fully clarified. Retinoic acid receptor-related orphan receptor (ROR) alpha plays an important role in the differentiation of many organs by regulating the transcription of target genes. Because aromatase and RORalpha are expressed in breast cancer, the effect of RORalpha on aromatase gene expression was studied. RORalpha significantly augmented the expression of aromatase mRNA, particularly those containing exon I.4, in MCF7 cells, and aromatase activities in T47D and MCF7 cells. RORalpha also stimulated the proliferation of these cells. Transient transfection-based reporter gene assays using the promoter at exon I.4 showed that RORalpha augmented the transcription. A series of truncated mutation studies revealed that RORalpha activated the transcription through -147 to +14 bp of the promoter I.4. Furthermore, RORalpha bound to the fragment containing -119 to -107 bp of the promoter in vitro, indicating that this region may contain a novel ROR response element. Chromatin immunoprecipitation assay showed that RORalpha bound to the region containing this site of the promoter I.4 in MCF7 cells. Moreover, we examined clinical samples and found a correlation between RORalpha and aromatase expression. These results suggest that RORalpha directly activates the aromatase expression to accelerate the local production of estrogen, which results in the proliferation of breast cancer cells.
Department of Thoracic and Visceral Organ Surgery, Gunma University Graduate School of Medicine, Gunma, Japan.
Hiroki
H
Odawara
Toshiharu
T
Iwasaki
Jun
J
Horiguchi
Nana
N
Rokutanda
Kazumi
K
Hirooka
Wataru
W
Miyazaki
Yukio
Y
Koibuchi
Noriaki
N
Shimokawa
Yuichi
Y
Iino
Izumi
I
Takeyoshi
Noriyuki
N
Koibuchi
D001141:Aromatase / Q000235:genetics* / Q000378:metabolism; D001665:Binding Sites; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism*; D049109:Cell Proliferation; D047369:Chromatin Immunoprecipitation; D024202:Electrophoretic Mobility Shift Assay; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology*; D006801:Humans; D008156:Luciferases; D009154:Mutation / Q000235:genetics; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D020218:Response Elements / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured
D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D012333:RNA, Messenger; C539738:RORA protein, human; D018160:Receptors, Cytoplasmic and Nuclear; D015534:Trans-Activators; D008156:Luciferases; D001141:Aromatase