Estrogen Repression of MicroRNAs Is Associated with High Guanine Content in the Terminal Loop Sequences of Their Precursors

17β-Estradiol Regulates miR-9-5p and miR-9-3p Stability and Function in the Aged Female Rat Brain

Clinical studies demonstrated that the ovarian hormone 17β-estradiol (E2) is neuroprotective within a narrow window of time following menopause, suggesting that there is a biological switch in E2 action that is temporally dependent. However, the molecular mechanisms mediating this temporal switch have not been determined. Our previous studies focused on microRNAs (miRNA) as one potential molecular mediator and showed that E2 differentially regulated a subset of mature miRNAs which was dependent on age and the length of time following E2 deprivation. Notably, E2 significantly increased both strands of the miR-9 duplex (miR-9-5p and miR-9-3p) in the hypothalamus, raising the possibility that E2 could regulate miRNA stability/degradation. We tested this hypothesis using a biochemical approach to measure miRNA decay in a hypothalamic neuronal cell line and in hypothalamic brain tissue from a rat model of surgical menopause. Notably, we found that E2 treatment stabilized both miRNAs in neuronal cells and in the rat hypothalamus. We also used polysome profiling as a proxy for miR-9-5p and miR-9-3p function and found that E2 was able to shift polysome loading of the miRNAs, which repressed the translation of a predicted miR-9-3p target. Moreover, miR-9-5p and miR-9-3p transcripts appeared to occupy different fractions of the polysome profile, indicating differential subcellular. localization. Together, these studies reveal a novel role for E2 in modulating mature miRNA behavior, independent of its effects at regulating the primary and/or precursor form of miRNAs.

Gene-Environment Interactions Relevant to Estrogen and Risk of Breast Cancer: Can Gene-Environment Interactions Be Detected Only among Candidate SNPs from Genome-Wide Association Studies?

In this study we aim to examine gene-environment interactions (GxEs) between genes involved with estrogen metabolism and environmental factors related to estrogen exposure. GxE analyses were conducted with 1970 Korean breast cancer cases and 2052 controls in the case-control study, the Seoul Breast Cancer Study (SEBCS). A total of 11,555 SNPs from the 137 candidate genes were included in the GxE analyses with eight established environmental factors. A replication test was conducted by using an independent population from the Breast Cancer Association Consortium (BCAC), with 62,485 Europeans and 9047 Asians. The GxE tests were performed by using two-step methods in GxEScan software. Two interactions were found in the SEBCS. The first interaction was shown between rs13035764 of NCOA1 and age at menarche in the GE|2df model (p-2df = 1.2 × 10-3). The age at menarche before 14 years old was associated with the high risk of breast cancer, and the risk was higher when subjects had homozygous minor allele G. The second GxE was shown between rs851998 near ESR1 and height in the GE|2df model (p-2df = 1.1 × 10-4). Height taller than 160 cm was associated with a high risk of breast cancer, and the risk increased when the minor allele was added. The findings were not replicated in the BCAC. These results would suggest specificity in Koreans for breast cancer risk.

Non-specific protein modifications may be novel mechanism underlying bioactive phytochemicals

In a variety of experimental models, dietary phytochemicals have been demonstrated to exhibit pronounced and versatile bioactivities. Importantly, the possibility of such phytochemicals for human application has been supported in part by epidemiological surveys, which have demonstrated that frequent ingestion of vegetables and fruits containing abundant phytochemicals lowers the risk of onset of various diseases. However, the action mechanisms underlying those dietary phytochemical activities remain to be fully elucidated. For example, even though the anti-oxidant effects of natural polyphenols have long received widespread attention from food scientists, their roles in and contribution to those bioactivities remain controversial because of their poor bioavailability, resulting in extremely low concentrations in the bloodstream. Meanwhile, another important question is why phytochemicals have beneficial effects for animals, including humans, since they are biosynthesized by plants as compounds necessary for adaptation to environmental stress. In regard to that fundamental question, we recently reported novel and unique mechanisms of action of zerumbone, a sesquiterpene with anti-inflammatory and chemopreventive properties. This agent was found to partially exhibit bioactivity through its non-specific interactions with cellular proteins. More strikingly, a non-specific protein binding action of zerumbone was revealed to partially contribute to its anti-inflammatory functions via activation of heat shock factor 1. The present review article highlights and introduces our recent findings regarding the proteo-stress-mediated mechanisms of this phytochemical, along with the concept of hormesis.