The aim of this study is to investigate the relationship between CYP19 and 17-beta-HSD type 1A mRNA expression and clinico-pathological parameters of human breast cancer.
Because the expression of aromatase in breast cancer tissues is driven by unique promoters I.3 and II, a more complete understanding of the regulatory mechanism of aromatase expression through promoters I.3/II in breast tumors should be valuable in developing targeted therapies, which selectively suppress estrogen production in breast tumor tissue.
The analysis revealed that exons I.3 and PII are the two major exons I present in aromatase mRNA isolated from breast tumors, suggesting that promoters I.3 and II are the major promoters driving aromatase expression in breast cancer and surrounding adipose stromal cells (ASCs).
The object of the present study was to determine the distribution of these various exon-specific transcripts in breast adipose tissues from cancer-free women undergoing reduction mammoplasty and from patients with breast cancer, because this would provide important clues as to the nature of the factors regulating aromatase expression in these sites.
We investigated the effects of a nuclear receptor system constituted by retinoid X receptor (RXR) and its heterodimer partner on the aromatase activity in a cultured MCF-7 human breast cancer cell line and also in human ovarian granulosa cells, using each selective ligand for retinoic acid receptor, RAR (TTNPB), retinoid X receptor, RXR (LG100268), PPARgamma (troglitazone), and vitamin D3 receptor (cholecalciferol).
These studies have revealed a novel mechanism for regulating aromatase expression and plasma E2 concentrations in postmenopausal women with ER(+) breast cancer.
In the present study, we investigated the effects of a nuclear receptor system constituted by retinoid X receptor (RXR) and its heterodimer partner on the aromatase activity in a cultured MCF-7 human breast cancer cell line, using each selective ligand for retinoic acid receptor (RAR) (TTNPB), RXR (LG100268), PPARgamma (troglitazone), and vitamin D(3) receptor (vitamin D(3)).
First, clustering analysis of the gene expression profile among the breast cancer specimens before and after aromatase inhibitor treatment could separate patients into two groups showing different estrogen responses.
BT (n=108), NB (n=54), AA (n=41) and MA (n=34) from patients with breast cancer were subjected to real-time PCR assays for the mRNA levels of aromatase, TNF-alpha, IL-6 and COX-2.
Aromatase mRNA and enzyme activity and 17beta-hydroxysteroid dehydrogenase type 1 mRNA in breast carcinoma cell lines, including MCF-7 and SK-BR-3 cells, were up-regulated in the presence of patient-derived 32N or 74T intratumoral stromal cells.
The report, herein, uncovers a new regulator of CYP19A1 transcription and for the first time demonstrates that DVL, a critical mediator of WNT signaling, contributes to aberrant breast cancer-associated estrogen production.
These results, in conjunction with previous data, indicate that aromatase overexpression in breast cancer tissues is likely to result from a promoter switch of CYP19A1 and/or accumulation of CYP19A1-expressing cells, rather than from cryptic transactivation of CYP19A1 because of genomic rearrangements at 15q21.
In conclusion, the regulation of aromatase by CRTC2, in response to the altered hormonal milieu associated with menopause and obesity, provides a critical link between obesity and breast cancer.
The prostaglandin PGE(2) increases intracellular cAMP levels and stimulates estrogen biosynthesis, and our recent studies have shown a strong linear association between CYP19 expression and the sum of cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) expression in breast cancer specimens.
We suggest from these studies that overexpression of aromatase in breast tissue and its resultant increase in estradiol levels may contribute to the later development of breast cancer in women with ADH.
This is the first patient-matched gene expression study investigating long-term aromatase inhibitor-induced dormancy and acquired resistance in breast cancer.
By reviewing findings from our laboratory and other laboratories, a detailed mechanism for the transcriptional regulation of aromatase expression in breast cancer tissue is summarized and discussed.
In elucidating a novel mechanism by which androgens, through DAX-1, inhibit aromatase expression in breast cancer cell lines, these findings reinforce the theory of androgen- opposing estrogen-action, opening new avenues for therapeutic intervention in estrogen-dependent breast tumors.
Oral fluoropyrimidine may augment the efficacy of aromatase inhibitor via the down-regulation of estrogen receptor in estrogen-responsive breast cancer xenografts.