Dynamic pattern of estradiol binding to uterine receptors of the rat. Inhibition and stimulation by unsaturated fatty acids

Estrogenic activities of Fatty acids and a sterol isolated from royal jelly

We have previously reported that royal jelly (RJ) from honeybees (Apis mellifera) has weak estrogenic activity mediated by interaction with estrogen receptors that leads to changes in gene expression and cell proliferation. In this study, we isolated four compounds from RJ that exhibit estrogenic activity as evaluated by a ligand-binding assay for the estrogen receptor (ER) β. These compounds were identified as 10-hydroxy-trans-2-decenoic acid, 10-hydroxydecanoic acid, trans-2-decenoic acid and 24-methylenecholesterol. All these compounds inhibited binding of 17β-estradiol to ERβ, although more weakly than diethylstilbestrol or phytoestrogens. However, these compounds had little or no effect on the binding of 17β-estradiol to ERα. Expression assays suggested that these compounds activated ER, as evidenced by enhanced transcription of a reporter gene containing an estrogen-responsive element. Treatment of MCF-7 cells with these compounds enhanced their proliferation, but concomitant treatment with tamoxifen blocked this effect. Exposure of immature rats to these compounds by subcutaneous injection induced mild hypertrophy of the luminal epithelium of the uterus, but was not associated with an increase in uterine weight. These findings provide evidence that these compounds contribute to the estrogenic effect of RJ.

Molecular forms of the estrogen receptor in breast cancer

Estrogen receptors (ERs) of which two isoforms have been identified (alpha and beta) are subjected to phosphorylation, glycozylation, ubiquitination and other post-transcriptional conformational changes giving rise to a very high molecular heterogeneity. Partial proteolysis of these receptors, as well as their high tendency to associate within oligomeric structures, reinforces this property. Investigations demonstrated that this heterogeneity is not a biochemical artefact suggesting some biological relevance. Our purpose was to review this topic, especially with regard to ERalpha from breast cancers.

Effect of dietary GLA+/-tamoxifen on the growth, ER expression and fatty acid profile of ER positive human breast cancer xenografts

Gamma linolenic acid (GLA) possesses a number of selective anti-tumour properties including modulation of steroid receptor structure and function. We have investigated the effect of dietary GLA on the growth, oestrogen receptor (ER) expression and fatty acid profile of ER+ve human breast cancer xenografts. Experimental diets A, B, C, D were commenced after subcutaneous implantation of 40 female nude mice with the MCF-7 B1M cell line (Group A = control diet: B = control diet + GLA supplement: C = control diet + tamoxifen: D = control diet + GLA + tamoxifen; 10 mice/group). The mice were terminated when tumour cross-sectional area reached 250 mm(2). ER H-scores were assessed by immunohistochemical assay and fatty acid profiles by gas-liquid chromatography of termination tumour samples. Groups C and D displayed significantly slower tumour growth (p =.0002, p =.0006) with trend for slower growth in B (p =.065) compared to control Group A. ER was significantly reduced in all groups compared to A (p <.0001) with Group D (combined therapy) displaying markedly lower ER expression than with either therapy alone (p =.0002). There were significantly raised levels of tumour GLA and metabolites in the two groups (B and D) receiving GLA (p <.0001). This xenograft model of ER+ve breast cancer has demonstrated significantly lower tumour ER expression in those groups receiving GLA, an effect which appears to be additive to the reduced ER expression resulting from tamoxifen alone. The effects of GLA on ER function and the possibility of synergistic inhibitory action of GLA with tamoxifen via enhanced down-regulation of the ER pathway require further investigation.

Does high polyunsaturated free fatty acid level at the feto-maternal interface alter steroid hormone message during pregnancy?

Polyunsaturated fatty acids (PUFA) are important in pregnancy, fetal development and parturition. We measured free fatty acids (FFA), albumin and alpha-fetoprotein (AFP) in the maternal and fetal circulations of women undergoing elective Caesarean section at term. We also studied the impact of PUFAs on estrogen (ER) and progesterone receptors (PR) binding properties in vitro in the myometria of pregnant women and ex vivo in human myometrial cells in culture. FFA in intervillous blood (I) (feto-maternal interface) and maternal peripheral blood (M) were similar, while those in the umbilical vein (V) and arteries (A) were 2-4 fold lower (P<0.001). PUFA levels were low in M and 3 fold higher in I, A and V (P< 0.001); consequently C20:4 and C22:6 were most abundant in intervillous space. Albumin was uniformly distributed throughout the maternal-fetal unit, but there was a transplacental gradient in AFP. The AFP in the intervillous space had a special conformation (less immuno-reactive, more anionic), suggesting loading with PUFA. Physiological concentrations of C20:4 stimulated estradiol binding, but inhibited progestin binding. C20:4 inhibited progesterone binding by decreasing the number of binding sites, with no change in apparent affinity, in vitro in myometrial tissue and ex vivo in myometrial cells. Thus PUFA may modulate the steroid hormone message, so that the high C20:4 concentration at the maternal-fetal interface at term may help amplify the estrogen signal and inhibit the progesterone signal.

Unsaturated fatty acids inhibit glucocorticoid receptor binding of trout hepatic cytosol

1. The effect of free fatty acids [FFAs (saturated (S) and unsaturated (U))] on dexamethasone binding in vitro using liver cytosol from rainbow trout was examined. 2. All UFFAs but none of the SFFAs tested suppressed binding. This suppression is dose-dependent and correlated roughly with the degree of unsaturation of the FFAs. 3. Scatchard analysis indicated that the addition of linoleic C18:2 (150 microM) increased the dissociation constant (Kd = 5.1 +/- 0.4 x 10(-8) M vs control of 1.7 +/- 0.3 x 10(-8) M) but minimally affected the binding capacity (Bmax = 68 +/- 6.2 vs control of 88 +/- 15.2 fmol/mg protein) suggesting C18:2 caused a conformational change of the receptor. 4. Lineweaver-Burk plot revealed a mixed non-competitive type of inhibition by C18:2. 5. Free acid appeared to be required for inhibition as esterification or derivatization of the acid greatly diminished its potency. 6.C18:2 also promotes the dissociation of bound [3H]-dexamethasone from the steroid-receptor complex but slower in rate and lesser in magnitude compared to that caused by dexamethasone or the glucocorticoid antagonist RU 38486. 7. UFFAs and some of their derivatives can thus modulate glucocorticoid receptor function in vitro and might play essential roles in regulating glucocorticoid action in fish as well. 8. These fatty acids presumably acts at a site different from that of the glucocorticoid binding site.

Competitive inhibition of T3 binding to alpha 1 and beta 1 thyroid hormone receptors by fatty acids

This study was undertaken to investigate whether fatty acids inhibit the binding of T3 to the alpha 1 and beta 1 form of the thyroid hormone receptor. Fatty acids inhibited the binding of T3 to both receptor proteins isolated from a bacterial expression system. The effectiveness of inhibition depends on the chain length and degree of saturation of the fatty acids. The inhibition of T3 binding to the alpha 1 and beta 1 receptor by oleic acid is competitive in nature; the Ki value was 5.4 10(-6) M for the c-erbA alpha 1 protein and 3.3 10(-6) M for the c-erb beta 1 protein. The findings indicate a direct interaction of fatty acids with T3 receptor proteins.

Nuclear estradiol binding in rat adipocytes. Regional variations and regulatory influences of hormones

The nuclear estrogen receptor was characterised in isolated rat adipocytes. The binding reaction with [3H]estradiol was performed with intact isolated rat adipocytes and the radioactivity associated with the nucleus was subsequently determined after cell lysis. The nuclear uptake of [3H]estrogen in rat adipocytes was temperature dependent and steroid specific. The steady-state binding was achieved after 30 min at 37 degrees C and was constant for several hours. Estradiol was found to bind to a homogeneous class of nuclear receptors in epididymal adipocytes with an apparent Kd of 3.1 +/- 0.76 nM and a Bmax of 7.98 +/- 1.11 fmol/10(6) cells corresponding to about 4800 receptors per nucleus. The estradiol binding exhibited regional variations in isolated adipocytes. In lean rats the highest receptor number was found in epididymal adipocytes, whereas there was a significantly lower number of nuclear binding sites in perirenal and subcutaneous adipocytes (P less than 0.05), unlike in older and more obese rats where the nuclear estradiol binding was greatest in adipocytes from the perirenal fat depot. Incubations with isoproterenol (10 microM) and dibutyryl-cAMP (2.5 mM) both reduced estradiol binding by 56% (P less than 0.005), while insulin (1 nM) enhanced the estradiol binding by 37% (P less than 0.01). In conclusion, a specific and high affinity nuclear estradiol receptor was demonstrated in rat adipocytes and regional differences in nuclear estradiol binding were detected. Furthermore, it was demonstrated that nuclear estradiol binding could be modulated by other agents known to affect adipocyte metabolism.

Partial purification of androgen binding protein from bull epididymis

An androgen binding protein (ABP), with an equilibrium dissociation constant of 4.2 nM and a molecular weight of about 100 kDa, has been purified from bull epididymal extracts using a four-step procedure. These preliminary results underline the main difficulties encountered in the purification of this protein present at a very low concentration (i.e. 50-fold less than in rat or rabbit epididymides). Ammonium sulfate precipitation is not a suitable step due to the formation, in presence of salt, of insoluble material leading to a loss of ABP. Lipids, particularly phospholipids, might be implicated in this phenomenon. Several steps, including anion exchange in batch followed by concentration, affinity chromatography and HPLC gel filtration allowed us to obtain a 7667-fold purified protein with a 9% yield.

Inhibition of nuclear T3 binding by fatty acids: dependence on chain length, unsaturated bonds, cis-trans configuration and esterification

1. Fatty acids have the capacity for inhibition of nuclear T3 binding (INB). The present studies were undertaken to describe the INB-activity of fatty acids as a function of chain length, unsaturated bonds, cis-trans configuration, and esterification. 2. Isolated rat liver nuclei were incubated with [125I]T3 in the absence or presence of fatty acids in concentrations of 0.011, 0.033, 0.1 and 0.3 mM respectively. 3. INB-activity depended on the chain length, being greatest at 14 carbon atoms. 4. INB by unsaturated fatty acids was greater than that of saturated fatty acids, and increased with increasing number of double bonds. 5. Fatty acids in the cis configuration had greater INB-activity than those in trans configuration. 6. Esterification of fatty acids decreased INB-activity: monoglycerides still had some effect, but di- and triglycerides had no effect.