Oxysterol regulation of estrogen receptor alpha-mediated gene expression in a transcriptional activation assay system using HeLa cells

In order to test the estrogenic activity of sterol oxidation products from cholesterol and phytosterols, an estrogen-dependent gene expression assay was performed in estrogen receptor alpha-stably transformed HeLa cells. The ranking of the estrogenic potency of these compounds was different: 17beta-estradiol > genistein > beta-epoxycholesterol = daidzein = cholestanetriol = 22(R)-hydroxycholesterol = 20(S)-hydroxycholesterol = sitostanetriol > campestanetriol = beta-epoxysitosterol = 7beta-hydroxycholesterol. These compounds were not estrogenic in estrogen receptor-negative HeLa cells.     

Estrogen receptor alpha augments changes in hemostatic gene expression in HepG2 cells treated with estradiol and phytoestrogens

Phytoestrogens are popular alternatives to estrogen therapy however their effects on hemostasis in post-menopausal women are unknown. The aim of this study was to determine the effect of the phytoestrogens, genistein, daidzein and equol on the expression of key genes from the hemostatic system in human hepatocyte cell models and to determine the role of estrogen receptors in mediating any response seen. HepG2 cells and Hep89 cells (expressing estrogen receptor alpha (ERα)) were incubated for 24 h with 50 nM 17β-estradiol, genistein, daidzein or equol. Tissue plasminogen activator (tPA), plasminogen activator inhibitor-1 (PAI-1), Factor VII, fibrinogen γ, protein C and protein S mRNA expression were determined using TaqMan PCR. Genistein and equol increased tPA and PAI-1 expression in Hep89 cells with fold changes greater than those observed for estradiol. In HepG2 cells (which do not express ERα), PAI-1 and tPA expression were unchanged. Increased expression of Factor VII was observed in phytoestrogen treated Hep89 cells but not in similarly treated HepG2s. Prothrombin gene expression was increased in equol and daidzein treated HepG2 cells in the absence of the classical estrogen receptors. These data suggest that phytoestrogens can regulate the expression of coagulation and fibrinolytic genes in a human hepatocyte cell line; an effect which is augmented by ERα.     

转录后水平沉默与基因表达

基因沉默是1个非常复杂和普遍的现象。转录后水平的基因沉默是指转基因在细胞核里能稳定转录,细胞质里却无相应的稳定态mRNA存在的现象。它往往被称为共抑制、静息作用或RNA干预等。本文介绍了转录后水平的基因沉默现象的发现、分子机理和应用等方面的进展。提出了克服转录后水平基因沉默的一些对策。     

Reduction of caveolin 1 gene expression in lung carcinoma cell lines

Caveolae are plasma membrane microdomains that have been implicated in organizing and concentrating certain signaling molecules. Caveolins, constitute the main structural proteins of caveolae. Caveolae are abundant in terminally differentiated cell types. However, caveolin-1 is down-regulated in transformed cells and may have a potential tumor suppressor activity. In the lung, caveolae are present in the endothelium, smooth muscle cells, fibroblasts as well as in type I pneumocytes. The presence of caveolae and caveolin expression in the bronchial epithelium, although probable, has not been investigated in human. We were interested to see if the bronchial epithelia express caveolins and if this expression was modified in cancer cells. We thus tested for caveolin-1 and -2 expression several bronchial epithelial primary cell lines as well as eight lung cancer cell lines and one larynx tumor cell line. Both caveolin-1 and -2 are expressed in all normal bronchial cell lines. With the exception of Calu-1 cell line, all cancer cell lines showed very low or no expression of caveolin-1 while caveolin-2 expression was similar to the one observed in normal bronchial epithelial cells.     

Estrogen receptor and Wnt signaling interact to regulate early gene expression in response to mechanical strain in osteoblastic cells

Bone mass homeostasis is regulated by an interaction of various factors, including growth factors, systemic hormones and mechanical loading. Two signal transduction pathways, the estrogen receptor (ER) and the Wnt/β-catenin signal transduction pathway, have been shown to have an important role in regulating osteoblast and osteoclast function and to be involved in mechanotransduction. Therefore, dysfunction of these pathways can lead to osteoporotic bone loss. However, less is known about the modulation of gene expression by the interaction of these pathways in response to mechanical strain. We performed in vitro stretch experiments using osteoblastic MC3T3-E1 cells to study the effect of both pathways and mechanical strain on the expression of cyclooxygenase-2 (Cox-2), which is involved in the synthesis of prostaglandins, modulators of bone formation and resorption. Using specific agonists and antagonists, we demonstrated a regulation by an interaction of these pathways in mechantransduction. Estradiol (E2) had a sensitizing effect on mechanically induced Cox-2 expression, which seemed to be ligand-specific as it could be abolished using the antiestrogen ICI182,780. However, mechanical strain in the presence of Wnt signaling activators diminished both the E2 sensitizing effect and the stimulatory effect of Wnt signaling in the absence of strain. This interaction might be one regulatory mechanism by which mechanical loading exerts its role in bone mass homeostasis.