MicroRNA 'signature' during estrogen-mediated mammary carcinogenesis and its reversal by ellagic acid intervention.

Dysregulated miRNA expression has been associated with the development and progression of cancers, including breast cancer. The role of estrogen (E2) in regulation of cell proliferation and breast carcinogenesis is well-known. Recent reports have associated several miRNAs with estrogen receptors in breast cancers. Investigation of the regulatory role of miRNAs is critical for understanding the effect of E2 in human breast cancer, as well as developing strategies for cancer chemoprevention. In the present study we used the well-established ACI rat model that develops mammary tumors upon E2 exposure and identified a 'signature' of 33 significantly modulated miRNAs during the process of mammary tumorigenesis. Several of these miRNAs were altered as early as 3 weeks after initial E2 treatment and their modulation persisted throughout the mammary carcinogenesis process, suggesting that these molecular changes are early events. Furthermore, ellagic acid, which inhibited E2-induced mammary tumorigenesis in our previous study, reversed the dysregulation of miR-375, miR-206, miR-182, miR-122, miR-127 and miR-183 detected with E2 treatment and modulated their target proteins (ERα, cyclin D1, RASD1, FoxO3a, FoxO1, cyclin G1, Bcl-w and Bcl-2). This is the first systematic study examining the changes in miRNA expression associated with E2 treatment in ACI rats as early as 3 week until tumor time point. The effect of a chemopreventive agent, ellagic acid in reversing miRNAs modulated during E2-mediated mammary tumorigenesis is also established. These observations provide mechanistic insights into the new molecular events behind the chemopreventive action of ellagic acid and treatment of breast cancer.