Estrogen regulation of human with-no-lysine (K) kinase-4 gene expression involves AP-1 transcription factor

A regulatory mechanism of mouse kallikrein 1 gene expression by estrogen

Tissue kallikrein 1 (Klk1) is a serine protease that degrades several proteins including insulin-like growth factor binding protein-3 and extracellular matrix molecules. Klk1 mRNA expression in the mouse uterus was increased by estradiol-17β (E2). The present study aimed to clarify the regulatory mechanism for Klk1 expression by estrogen. The promoter analysis of the 5'-flanking region of Klk1 showed that the minimal promoter of Klk1 existed in the -136/+24 region, and the estrogen-responsive region in the -433/-136 region. Tamoxifen increased Klk1 mRNA expression and the promoter activity, suggesting the involvement of AP-1 sites. Site-directed mutagenesis for the putative AP-1 sites in the -433/-136 region showed that the two putative AP-1 sites were involved in the regulation of Klk1 expression. Binding of estrogen receptor α (ERα) to the -433/-136 region was revealed by Chip assay. These results indicated that ERα bound the two putative AP-1 sites and transactivated Klk1 in the mouse uterus.

Crosstalk between phosphorylation and ubiquitination is involved in high salt-induced WNK4 expression

With no lysine 4 (WNK4) is a serine/threonine kinase, which is expressed in the kidney and associated with salt-sensitive hypertension. However, how salt regulates WNK4 remains unclear. In the present study, the C57BL/6 mice and HEK293 cells were treated with high salt and the expression of WNK4 protein and its ubiquitination and phosphorylation levels were detected. Western blotting demonstrated that WNK4 expression was significantly increased in high salt-treated mice and cells. Meanwhile, co-immunoprecipitation analysis demonstrated that the ubiquitination of WNK4 was decreased under high-salt simulation. It was also identified that the Lys-1023 site was the most important ubiquitination site for WNK4, and it was found that phosphorylation at the Ser-1022 site was a prerequisite for ubiquitination. These results suggested that there was crosstalk between phosphorylation and ubiquitination in the WNK4 protein, and high salt may downregulate its phosphorylation and, in turn, decrease its ubiquitination, leading to a decrease in WNK4 degradation. This eventually resulted in an increase in the abundance of WNK4 protein.

Lack of influence of sex hormones on Brugada syndrome-associated mutant Nav1.5 sodium channel

Brugada syndrome (BS) is an autosomal dominant disease. The most common causes of BS are loss-of-function mutations occur in the SCN5A gene which encodes the sodium channel protein Nav1.5. BS has a higher incidence rate in males and the underlying mechanisms of the gender inequality are not yet fully understood. Considering sex hormones are among the most important factors behind gender differences and have previously been shown to regulate the activity of multiple cardiac ion channels, we hypothesized that sex hormones also affect Nav1.5 function which lead to BS predominantly affecting males. In this study, we investigate the protein expression level and current of Nav1.5 in the HEK293 cells cotransfected with SCN5A and sex hormone receptor plasmids using both wild-type SCN5A and BS-associated SCN5A channel mutants R878C and R104W. Our findings showed that sex hormones have no effects on the protein expression level and current of the wild-type Nav1.5, neither does it affect the protein expression level and current of BS-associated Nav1.5 mutants R878C and R104W, regardless of homozygous or heterozygous state. Our results suggest that the male preponderance of BS does not arise from the effects of the sex hormones on Nav1.5. Further studies are needed to explain the male preponderance of this disease.

20-HETE attenuates the response of glucose-stimulated insulin secretion through the AKT/GSK-3β/Glut2 pathway

We previously generated cytochrome P450 4F2 (CYP4F2) transgenic mice that have high levels of 20-hydroxyeicosatetraenoic acid (20-HETE) production; these mice exhibit both hypertension and hyperglycemia without insulin resistance. Currently, it is unclear whether and how 20-HETE affects insulin secretion, thus resulting in hyperglycemia. In this study, we found that 20-HETE attenuated glucose-stimulated insulin secretion (GSIS) in CYP4F2 transgenic mice as well as in rat insulinoma INS-1E cells treated with 0.5 μM 20-HETE. HET0016, a selective inhibitor of 20-HETE synthesis, reversed the reduction in GSIS leading to a decrease in blood glucose in the transgenic mice. Furthermore, the expression of glucose transporter 2 (Glut2), Ser⁴⁷³ phosphorylation of protein kinase B (AKT), and Ser⁹ phosphorylation of glycogen synthase kinase-3β (GSK-3β) were decreased in CYP4F2 transgenic mice compared with wild-type mice. In vitro experiments in INS-1E cells revealed that 20-HETE activated the AKT/GSK-3β pathway and thereby decreased Glut2 expression by inhibiting activator protein 1 (AP-1). TWS119, a GSK-3β selective inhibitor, blocked the 20-HETE-mediated reduction in Glut2 expression. Therefore, we concluded that 20-HETE inhibition of Glut2 contributes to the reduction in GSIS, at least in part, through the AKT/GSK-3β/AP-1/Glut2 pathway.

Upregulation of TLR2 expression is induced by estrogen via an estrogen-response element (ERE)

TLR2 and estrogen are both thought to be involved in the pathogenesis of RA; however, it is unknown if there is an association between estrogen and TLR2. In this report, we treated PMA-differentiated THP-1 cells with 17β-estradiol (E2) and observed increases in TLR2 mRNA and protein levels by real-time quantitative PCR and western blot. Transfection of THP-1 cells with a series of 5'-deleted TLR2 promoter-luciferase constructs revealed that E2 enhanced TLR2 transcriptional activity in an estrogen receptor alpha (ERα)-dependent pattern. An estrogen receptor response element (ERE) was identified 251 bases upstream of the TLR2 promoter, and electrophoretic mobility shift assay and chromatin immunoprecipitations showed ERα binding was increased by E2. In summary, this work demonstrated that TLR2 is a new estrogen-regulated gene whose expression is upregulated through the interaction of ERα with an ERE in the promoter region.