Upregulation of human with-no-lysine kinase-4 gene expression by GATA-1 acetylation

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.

Up-regulation of IRF-3 expression through GATA-1 acetylation by histone deacetylase inhibitor in lung adenocarcinoma A549 cells

Interferon regulatory factor 3 (IRF-3) is an important transcription factor for interferon genes. Although its functional activation by viral infection has been widely explicated, the regulatory mechanism of IRF-3 gene expression in cancer cells is poorly understood. In this study, we demonstrated treatment of lung adenocarcinoma A549 cells with trichostatin A (TSA) and valproic acid (VPA), two different classes of histone deacetylase inhibitors, strongly stimulated IRF-3 gene expression. Truncated and mutated IRF-3 promoter indicated that a specific GATA-1 element was responsible for TSA-induced activation of IRF-3 promoter. Chromatin immunoprecipitation and electrophoretic mobility shift assay showed that TSA treatment increased the binding affinity of GATA-1 to IRF-3 promoter. Using immunoprecipitation assay and immunoblotting, we demonstrated that TSA increased the level of acetylated GATA-1 in A549 cells. In summary, our study implied that TSA enhanced IRF-3 gene expression through increased GATA-1 recruitment to IRF-3 promoter and the acetylation level of GATA-1 in lung adenocarcinoma A549 cells.

Hypertensive epigenetics: from DNA methylation to microRNAs

The major epigenetic features of mammalian cells include DNA methylation, posttranslational histone modifications and RNA-based mechanisms including those controlled by small non-coding RNAs (microRNAs (miRNAs)). An important aspect of epigenetic mechanisms is that they are potentially reversible and may be influenced by nutritional-environmental factors and through gene-environment interactions. Studies on epigenetic modulations could help us understand the mechanisms involved in essential hypertension and further prevent it's progress. This review is focused on new knowledge on the role of epigenetics, from DNA methylation to miRNAs, in essential hypertension.

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.

Upregulation of Toll-like receptor 2 gene expression by acetylation of AP-2 alpha in THP-1 cells, a human monocytic cell line

Human Toll-like receptor 2 (TLR2) is a receptor for a variety of microbial products and mediates activation signals in cells of the innate immune system. Therefore, it is of great interest to investigate the molecular mechanisms that control the expression of TLR2. In this study, using real-time PCR and western blot assays, we show that trichostatin A (TSA), which is a histone deacetylase inhibitor, upregulates the expression of both TLR2 mRNA and protein in the human THP-1 cell line. A luciferase activity analysis of the truncated TLR2 promoter indicated that the region from -230 to -140 in the TLR2 promoter was sensitive to TSA. Moreover, using electrophoresis mobility shift and chromatin immunoprecipitation assays, we identified an AP-2 alpha (AP-2α) responsive element at position -184 and found that the binding of AP-2α to this element was enhanced by TSA under in vitro and in vivo conditions. Immunoprecipitation and western blot analyses showed that the levels of acetylated AP-2α were increased in THP-1 cells after TSA treatment, and this increase is consistent with the increased binding affinity to the AP-2α responsive elements. In summary, these data define a mechanism through which AP-2α acetylation and increased promoter access induce the expression of the TLR2 gene. This mechanism may provide insight into a regulatory mode of TLR2 expression and the molecular foundations of certain immunological diseases.

MicroRNA-296 is enriched in cancer cells and downregulates p21WAF1 mRNA expression via interaction with its 3' untranslated region

MicroRNAs (miRNAs) are a class of noncoding small RNAs that act as negative regulators of gene expression. To identify miRNAs that may regulate human cell immortalization and carcinogenesis, we performed comparative miRNA array profiling of human normal and SV40-T antigen immortalized cells. We found that miR-296 was upregulated in immortalized cells that also had activation of telomerase. By an independent experiment on genomic analysis of cancer cells we found that chromosome region (20q13.32), where miR-296 is located, was amplified in 28/36 cell lines, and most of these showed enriched miR-296 expression. Overexpression of miR-296 in human cancer cells, with and without telomerase activity, had no effect on their telomerase function. Instead, it suppressed p53 function that is frequently downregulated during human cell immortalization and carcinogenesis. By monitoring the activity of a luciferase reporter connected to p53 and p21(WAF1) (p21) untranslated regions (UTRs), we demonstrate that miR-296 interacts with the p21-3'UTR, and the Hu binding site of p21-3'UTR was identified as a potential miR-296 target site. We demonstrate for the first time that miR-296 is frequently upregulated during immortalization of human cells and contributes to carcinogenesis by downregulation of p53-p21(WAF1) pathway.

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

With-no-lysine (K) kinase-4 (WNK4) is a serine/threonine protein kinase and plays a crucial role in the regulation of blood pressure and electrolyte homeostasis. Whether or not estrogen, an important regulator of physiologic functions, modulates human WNK4 (hWNK4) gene expression is unknown. In the current study, real-time PCR assay showed that 17β-estradiol (E(2)) with estrogen receptor alpha (ERα) suppressed the level of hWNK4 mRNA in cultured human embryo kidney 293 cells (HEK293). Luciferase activity analysis of the truncated hWNK4 promoters indicated that a regulatory region from -216 to -202 is essential for the basal transcriptional activity and response to E(2)/ERα. Using an electrophoresis mobility shift assay and a chromatin immunoprecipitation assay, we identified an activator protein-1 (AP-1) element at position -215/-205, to which AP-1 binding was enhanced by E(2)/ERα. Accordingly, AP-1 protein was increased by E(2)/ERα using Western blot analysis. Moreover, re-chromatin-immunoprecipitation and co-immunoprecipitation assays showed a direct interaction between ERα and AP-1 in HEK293 cells. In summary, these data document that E(2)/ERα regulates hWNK4 expression partly through AP-1 binding to the hWNK4 promoter.

The WNKs: atypical protein kinases with pleiotropic actions

WNKs are serine/threonine kinases that comprise a unique branch of the kinome. They are so-named owing to the unusual placement of an essential catalytic lysine. WNKs have now been identified in diverse organisms. In humans and other mammals, four genes encode WNKs. WNKs are widely expressed at the message level, although data on protein expression is more limited. Soon after the WNKs were identified, mutations in genes encoding WNK1 and -4 were determined to cause the human disease familial hyperkalemic hypertension (also known as pseudohypoaldosteronism II, or Gordon's Syndrome). For this reason, a major focus of investigation has been to dissect the role of WNK kinases in renal regulation of ion transport. More recently, a different mutation in WNK1 was identified as the cause of hereditary sensory and autonomic neuropathy type II, an early-onset autosomal disease of peripheral sensory nerves. Thus the WNKs represent an important family of potential targets for the treatment of human disease, and further elucidation of their physiological actions outside of the kidney and brain is necessary. In this review, we describe the gene structure and mechanisms regulating expression and activity of the WNKs. Subsequently, we outline substrates and targets of WNKs as well as effects of WNKs on cellular physiology, both in the kidney and elsewhere. Next, consequences of these effects on integrated physiological function are outlined. Finally, we discuss the known and putative pathophysiological relevance of the WNKs.