Search

The sodium-coupled bicarbonate cotransporter 1 (NBCe1) plays an essential role in the maintenance of acid-base homeostasis in the human body. However, little research has been done regarding the modification of NBCe1. Nedd4-2 is one of the most important ubiquitin E3 ligases in the kidney where it is responsible for mediating the ubiquitylation level of many important ion channel proteins; therefore, influencing their expression and membrane localization. In this study, we performed experiments based on a prediction from bioinformatics analysis that NBCe1 might be a Nedd4-2 target protein. The results of co-immunoprecipitation and glutathione S-transferase pull-down assays showed that Nedd4-2 interacted with NBCe1. An in vitro ubiquitination assay further demonstrated that Nedd4-2 is indeed the NBCe1 ubiquitin E3 ligase. The overexpression of Nedd4-2 decreased NBCe1 expression, while MG132 rescued the changes. Nedd4-2 overexpression also altered the subcellular distribution of NBCe1. Furthermore, the kidney specific Nedd4-2-knockout mice certified the alteration of NBCe1. In addition, we speculate that neddylation activates Nedd4-2. A co-immunoprecipitation analysis indicated that Nedd4-2 interacted with Nedd8. In vitro neddylation experiments further demonstrated that Nedd4-2 underwent neddylation modification. The overexpression of Nedd8 led to decreased NBCe1 expression, while Nedd4-2 inhibition rescued the changes. These findings demonstrate that Nedd4-2 acts as the ubiquitin E3 ligase of NBCe1, mediating the degradation and altering the subcellular distribution of NBCe1, and that the neddylation modification downregulated NBCe1 expression by upregulating Nedd4-2 activity.

The effects of engineered nanoparticles (ENPs) on heavy metal fate and biotoxicity in farmland soil are mostly unknown. A flooding–drying simulation experiment was conducted to study the effects of three typical metal oxide nanoparticles (TiO2-NPs, ZnO-NPs and CuO-NPs) on the chemical speciation of heavy metals and micronutrient bioavailability in paddy soil. The results showed that the addition of ZnO-NPs and CuO-NPs caused significant increases in soil pH, Eh and EC after a 90-d flooding–drying process. ZnO-NPs and CuO-NPs addition caused clearly increase in the Zn and Cu concentrations in the acid-soluble fraction, Fe/Mn oxides-bound fraction and organic-bound fraction, leading to higher bioavailability in the soil. DTPA-extractable Zn and Cu increased to 184.6 mg kg−1 and 145.3 mg kg−1 in the maximum ZnO-NPs and CuO-NPs concentration treatments (500 mg kg−1). TiO2-NPs promoted the transformation of Mn from a Fe/Mn oxides-bound fraction to an acid-soluble fraction. Soil Cd bioavailability obviously decreased in the TiO2-NPs treatment but increased in the ZnO-NPs and CuO-NPs treatments.

With the widespread use of metal oxide nanoparticles (MNPs), agricultural soil is gradually becoming a primary sink for MNPs. The effect of these nanoparticles on the fate and the toxicity of co-existing heavy metals is largely unknown. In this paper, pot experiments were conducted to evaluate the impact of ZnO nanoparticles (ZnO-NPs) on Cd toxicity and bioaccumulation in a soil-rice system. Different amounts of ZnO-NPs were added to three different levels of Cd-contaminated paddy soil (L-Cd, 1.0 mg kg−1; M-Cd, 2.5 mg kg−1; H-Cd, 5.0 mg kg−1). The results showed that the addition of ZnO-NPs significantly increased the soil pH value, and the soil pH value increased with the increase in ZnO-NP concentration. Reductions in plant height and biomass under Cd stress were recovered and increased after the addition of ZnO-NPs; the addition of ZnO-NP promoted rice biomass increased by 13~22% and 25~43% in the M-Cd and H-Cd groups, respectively, compared with that of the respective control treatment. A high concentration of ZnO-NPs could increase the concentration of bioavailable Cd in rhizosphere soil. In the L-Cd group, the Cd concentration of the rice in the L-Z500 treatment increased to 0.51 mg kg−1, exceeding the limit for acceptable Cd concentrations in rice of China (0.2 mg kg−1). This work revealed that ZnO-NPs could improve plant growth, especially in the early-growth stage, and alleviate the toxic effects of Cd. However, the addition of high-concentration (500 mg kg−1) ZnO-NPs in the lower Cd pollution soil could significantly facilitate the accumulation of Cd by Oryza sativa L.

Mechanisms of angiotensin II and cAMP regulating the expression of angiotensin II type 1 (AT(1)) receptor mRNA were studied in neonatal rat cardiomyocytes. Angiotensin II induced a transient decrease of AT(1)-mRNA expression in time- and dose-dependent manner. Maximal decrease (49.2 +/- 9.5% of control) occurred at 6 h of angiotensin II (10 nmol/l) treatment. AT(1) receptor antagonists 4-ethyl-2-n-propyl-1-[2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole-5-carboxylic acid (DMP811) and losartan as well as 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7) reversed the down-regulation of AT(1)-mRNA expression. 6 h of phorbol 12-myristate 13-acetate (PMA) stimulation caused a decrease of AT(1)-mRNA level. Treatment by angiotensin II plus actinomycin D for 6 h produced the same effect as actinomycin D alone. These results suggest that angiotensin II down-regulates AT(1)-mRNA level of rat cardiomyocytes by inhibiting the transcription of AT(1) gene, which is mediated by AT(1) receptor and related to the activation of protein kinase C. Stimulation by forskolin plus 3-isobutyl-1-methyl-xanthine (IBMX) decreased the expression of AT(1)-mRNA to 68.1 +/- 21.5% of control at 6 h treatment; while increased to 207.9 +/- 27.1% of control at 48 h treatment. A series of 5'-upstream deletion mutants of AT(1A) promoter were produced and then were recombined with pGL(3) basic vector utilizing luciferase as reporter gene. Among all the constructors, p(-201/+ 74)Luc was of the highest luciferase activity (5.9 times higher than control) after stimulation by forskolin for 48 h. Further deletion from -201 to -61 resulted in a large decrease of activity. These results indicate that cAMP induces a time-dependent bi-directional regulation of AT(1)-mRNA expression. The cAMP responsible element (CRE) cis-element located in the region -201/-61 of rat AT(1A) promoter is forskolin inducible, which may mediate the up-regulation of AT(1)-mRNA expression induced by cAMP long-lasting stimulation.