A G-quadruplex nanoswitch in the SGK1 promoter regulates isoform expression by K+/Na+ balance and resveratrol binding.

BACKGROUND: High sodium intake can up-regulate the level of renal serum- and glucocorticoid-inducible kinase-1 (SGK1), which plays a pivotal role in controlling blood pressure via activation of the epithelial sodium channel (ENaC), which can lead to salt-sensitive hypertension. Increased potassium intake, or a vegetarian diet, counteracts salt-sensitive hypertension, but the underlying mechanisms are not fully understood. METHODS: Bioinformatics and molecular modeling were used to identify G-quadruplex (G4) and their conformations in the SGK1 promoter. CD spectra and UV melting dynamics were measured to study the stability of G4 as influenced by potassium/sodium balance and resveratrol. RT-PCR and Western blot were employed to study the effects of potassium and resveratrol on the SGK1 isoform expression. RESULTS: The SGK1 gene encodes a G4 structure in the proximal upstream of promoter-2; the G4 structure is stabilized by potassium or resveratrol, but destabilized by sodium. Super-physiological levels of sodium stimulate the transcription of all SGK1 isoforms, whereas resveratrol or potassium supplementation inhibits the transcription of iso-2 and iso-3, but not iso-1. CONCLUSIONS: Stabilizing the G4 by potassium or resveratrol induces alternative promoter usage and/or pre-mRNA splicing in the transcription of SGK1. GENERAL SIGNIFICANCE: Potassium/sodium ion balance or resveratrol binding can act to regulate G4 molecular switches for controlling SGK1 gene expression, thereby presenting a new avenue for drug development.

Impact of heat treatment on size, structure, and bioactivity of elemental selenium nanoparticles.

BACKGROUND: Elemental selenium nanoparticles have emerged as a novel selenium source with the advantage of reduced risk of selenium toxicity. The present work investigated whether heat treatment affects the size, structure, and bioactivity of selenium nanoparticles. METHODS AND RESULTS: After a one-hour incubation of solution containing 80 nm selenium particles in a 90°C water bath, the nanoparticles aggregated into larger 110 nm particles and nanorods (290 nm × 70 nm), leading to significantly reduced bioavailability and phase II enzyme induction in selenium-deficient mice. When a solution containing 40 nm selenium nanoparticles was treated under the same conditions, the nanoparticles aggregated into larger 72 nm particles but did not transform into nanorods, demonstrating that the thermostability of selenium nanoparticles is size-dependent, smaller selenium nanoparticles being more resistant than larger selenium nanoparticles to transformation into nanorods during heat treatment. CONCLUSION: The present results suggest that temperature and duration of the heat process, as well as the original nanoparticle size, should be carefully selected when a solution containing selenium nanoparticles is added to functional foods.

Further insight into the impact of sodium selenite on selenoenzymes: high-dose selenite enhances hepatic thioredoxin reductase 1 activity as a consequence of liver injury.

Selenium (Se) at supranutritional levels can enhance the activity of glutathione S-transferase (GST), whose gene is a target of nuclear factor erythroid-2 related factor 2 (Nrf2). Recent studies indicated that the thioredoxin reductase 1 (TrxR1) gene could also be targeted by Nrf2. Thus, high-dose Se may stimulate TrxR1 provided it enhances GST activity. Indeed, one study found that Se at supranutritional levels transiently increased hepatic TrxR1 activity. However, another study reported that supranutritional Se had no such effect on hepatic TrxR1 activity. In view of this discrepancy, the present research investigated whether high-dose Se has any impact on hepatic TrxR1. Moreover, we investigated whether Se preferentially activates GST over TrxR1. We observed that when sodium selenite (SS) caused liver injury, both hepatic TrxR1 activity and hepatic GST activity increased. Further experiments indicated that SS increased hepatic GST activity at either toxic or high but non-toxic dose levels; however, increase in hepatic TrxR1 activity occurred only at toxic levels, suggesting that enhanced TrxR1 activity correlates with liver injury. To corroborate this, we showed that hepatotoxic agents, thioacetamide or carbon tetrachloride, caused marked increases in hepatic TrxR1 activity. In conclusion, high-dose SS indeed can enhance hepatic TrxR1 activity, but only on the condition that it causes liver injury. High-dose SS affects hepatic GST more readily than hepatic TrxR1. Thus, the cancer-preventive mechanism of Se at non-toxic supranutritional levels relies more on its modulation of GST rather than TrxR1, at least in liver tissue.

Inhibition of TNF-alpha induced ICAM-1, VCAM-1 and E-selectin expression by selenium.

The initiation of an atherosclerotic lesion involves an endothelial cell pro-inflammatory state that recruits leukocytes and promotes their movement across the endothelium. These processes require endothelial expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial-leukocyte adhesion molecule-1 (E-selectin). Tumor necrosis factor-alpha (TNF-alpha) is a powerful inducer of these adhesion molecules. Selenium status is known to affect the rate of atherosclerosis. These experiments tested whether selenium alters cytokine-induced expression of these adhesion molecules. Human umbilical vein endothelial cells (HUVECs) were pretreated for 24 h with sodium selenite (0-2 microM) and then treated with 0 or 50 U/ml TNF-alpha in the presence of 0-2 microM selenite. ICAM-1, VCAM-1 and E-selectin were detected by ELISA and their mRNAs were evaluated by Northern blots. Selenite significantly inhibited TNF-alpha-induced expression of each adhesion molecule in a dose-dependent manner and reduced the level of the respective mRNAs. Nuclear factor-kappa B (NF-kappa B) is required for transcription of these adhesion molecule genes. Western blot analysis revealed that selenite did not inhibit the translocation of the p65 subunit of NF-kappa B to the nucleus. In conclusion, these data indicate selenium can modulate cytokine-induced expression of ICAM-1, VCAM-1 and E-selectin in HUVECs without interfering with translocation of NF-kappa B.