The role of CpG methylation in cell type-specific expression of the aquaporin-5 gene

Aquaporin Expression and Regulation in Clinical and Experimental Sepsis

Sepsis is an inflammatory disorder caused by the host's dysfunctional response to infection. Septic patients present diverse clinical characteristics, and in the recent years, it has been the main cause of death in intensive care units (ICU). Aquaporins, membrane proteins with a role in water transportation, have been reported to participate in numerous biological processes. Their role in sepsis progression has been studied extensively. This review aims to examine recent literature on aquaporin expression and regulation in clinical sepsis, as well as established experimental models of sepsis. We will present how sepsis affects aquaporin expression at the molecular and protein level. Moreover, we will delve into the importance of aquaporin regulation at transcriptional, post-transcriptional, translational, and post-translational levels in sepsis by presenting data on aquaporin regulation by non-coding RNAs and selected chemical molecules. Finally, we will focus on the importance of aquaporin single-nucleotide polymorphisms in the setting of sepsis.

Aquaporin-5 Dynamic Regulation

Aquaporin-5 (AQP5), belonging to the aquaporins (AQPs) family of transmembrane water channels, facilitates osmotically driven water flux across biological membranes and the movement of hydrogen peroxide and CO₂. Various mechanisms have been shown to dynamically regulate AQP5 expression, trafficking, and function. Besides fulfilling its primary water permeability function, AQP5 has been shown to regulate downstream effectors playing roles in various cellular processes. This review provides a comprehensive overview of the current knowledge of the upstream and downstream effectors of AQP5 to gain an in-depth understanding of the physiological and pathophysiological processes involving AQP5.

AQP5-1364A/C Polymorphism Affects AQP5 Promoter Methylation

The quantity of aquaporin 5 protein in neutrophil granulocytes is associated with human sepsis-survival. The C-allele of the aquaporin (AQP5)-1364A/C polymorphism was shown to be associated with decreased AQP5 expression, which was shown to be relevant in this context leading towards improved outcomes in sepsis. To date, the underlying mechanism of the C-allele—leading to lower AQP5 expression—has been unknown. Knowing the detailed mechanism depicts a crucial step with a target to further interventions. Genotype-dependent regulation of AQP5 expression might be mediated by the epigenetic mechanism of promoter methylation and treatment with epigenetic-drugs could maybe provide benefit. Hence, we tested the hypothesis that AQP5 promoter methylation differs between genotypes in specific types of immune cells.: AQP5 promoter methylation was quantified in cells of septic patients and controls by methylation-specific polymerase chain reaction and quantified by a standard curve. In cell-line models, AQP5 expression was analyzed after demethylation to determine the impact of promoter methylation on AQP5 expression. C-allele of AQP5-1364 A/C promoter polymorphism is associated with a five-fold increased promoter methylation in neutrophils (p = 0.0055) and a four-fold increase in monocytes (p = 0.0005) and lymphocytes (p = 0.0184) in septic patients and healthy controls as well. In addition, a decreased AQP5 promoter methylation was accompanied by an increased AQP5 expression in HL-60 (p = 0.0102) and REH cells (p = 0.0102). The C-allele which is associated with lower gene expression in sepsis is accompanied by a higher methylation level of the AQP5 promoter. Hence, AQP5 promoter methylation could depict a key mechanism in genotype-dependent expression.

DNA methylation of a NF-κB binding site in the aquaporin 5 promoter impacts on mortality in sepsis

Altered aquaporin 5 (AQP5) expression in immune cells impacts on key mechanisms of inflammation and is associated with sepsis survival. Since epigenetic regulation via DNA methylation might contribute to a differential AQP5 expression in sepsis, we tested the hypotheses that DNA methylation of the AQP5 promotor (1) influences AQP5 expression, (2) is associated with the 30-day survival of septic patients, and (3) alters the nuclear transcription factor NF-κB binding. AQP5 mRNA expression was quantified by real-time PCR in whole blood samples of 135 septic patients. In silico computer analysis of the AQP5 promoter (nt-567 to nt-975) revealed seven putative inflammatory transcription factor binding sites and methylation of these sites was analyzed. Electrophoretic mobility shift assays were performed to assess the binding of nuclear NF-κB to the AQP5 promoter region nt-937. After adjustment for multiple testing, a greater methylation rate was found at cytosine site nt-937 in the AQP5 promoter linked to NF-κB binding in non-survivors compared to survivors (p = 0.002, p_adj = 0.014). This was associated with greater AQP5 mRNA expression in non-survivors (p = 0.037). Greater (≥16%) promoter methylation at nt-937 was also associated with an independently increased risk of death within 30 days (HR: 3.31; 95% CI: 1.54–6.23; p = 0.002). We detected a functionally important AQP5 promoter cytosine site (nt-937) linked to the binding of the inflammatorily acting nuclear transcription factor NF-κB, with increased methylation in sepsis non-survivors. Thus, nt-937 APQ5 promoter methylation, presumably related to NF-κB binding, is prognostically relevant in sepsis and demonstrates that epigenetic changes impact on sepsis outcome.

Functional analysis of the promoter of the molt-inhibiting hormone (mih) gene in mud crab Scylla paramamosain

In this study, the 5'-flanking region of molt-inhibiting hormone (MIH) gene was cloned by Tail-PCR. It is 2024 bp starting from the translation initiation site, and 1818 bp starting from the predicted transcription start site. Forecast analysis results by the bioinformatics software showed that the transcription start site is located at 207 bp upstream of the start codon ATG, and TATA box is located at 240 bp upstream of the start codon ATG. Potential transcription factor binding sites include Sp1, NF-1, Oct-1, Sox-2, RAP1, and so on. There are two CpG islands, located at -25- +183 bp and -1451- -1316 bp respectively. The transfection results of luciferase reporter constructs showed that the core promoter region was located in the fragment -308 bp to -26 bp. NF-kappaB and RAP1 were essential for mih basal transcriptional activity. There are three kinds of polymorphism CA in the 5'-flanking sequence, and they can influence mih promoter activity. These findings provide a genetic foundation of the further research of mih transcription regulation.

Procaine stimulates aquaporin‑5 expression in human salivary gland ductal cells via the suppression of DNA methyltransferase‑1

The present study aimed to investigate whether procaine may upregulate the expression of aquaporin‑5 (AQP5) in human salivary gland ductal cells and the underlying mechanisms of this upregulation. Immortalized normal human salivary gland ductal cells (NS‑SV‑DC), lacking AQP5 protein expression, were used to measure the glandular secretion rate following treatment with procaine, and the protein expression levels of AQP5 in NS‑SV‑DC cells were measured by western blotting. In order to investigate the mechanism of procaine action on AQP5 protein expression, the protein expression and activity of DNA methyltransferase (DNMT)1, and the CpG methylation of AQP5, were investigated further. In NS‑SV‑DC cells treated with procaine, the mRNA and protein levels of AQP5, and the secretion rate of cells, were significantly increased. Although no significant alterations were observed in the protein expression of DNMT1 following procaine treatment, its enzymatic activity was reduced, resulting in CpG island demethylation at Sp1‑2 and Sp1‑3 sites of the AQP5 gene, which may contribute to the significantly upregulated AQP5 gene expression. The results of the present study indicate that procaine may upregulate the protein expression of AQP5 in human submandibular glands by inhibiting the activity of DNMT1 and promoting liquid secretion. The procaine‑mediated expression of AQP5 may provide a novel regimen for the treatment of SS syndrome.

Cell-specific expression of aquaporin-5 (Aqp5) in alveolar epithelium is directed by GATA6/Sp1 via histone acetylation

Epigenetic regulation of differentiation-related genes is poorly understood. We previously reported that transcription factors GATA6 and Sp1 interact with and activate the rat proximal 358-bp promoter/enhancer (p358P/E) of lung alveolar epithelial type I (AT1) cell-specific gene aquaporin-5 (Aqp5). In this study, we found that histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) increased AQP5 expression and Sp1-mediated transcription of p358P/E. HDAC3 overexpression inhibited Sp1-mediated Aqp5 activation, while HDAC3 knockdown augmented AQP5 protein expression. Knockdown of GATA6 or transcriptional co-activator/histone acetyltransferase p300 decreased AQP5 expression, while p300 overexpression enhanced p358P/E activation by GATA6 and Sp1. GATA6 overexpression, SAHA treatment or HDAC3 knockdown increased histone H3 (H3) but not histone H4 (H4) acetylation within the homologous p358P/E region of mouse Aqp5. HDAC3 binds to Sp1 and HDAC3 knockdown increased interaction of GATA6/Sp1, GATA6/p300 and Sp1/p300. These results indicate that GATA6 and HDAC3 control Aqp5 transcription via modulation of H3 acetylation/deacetylation, respectively, through competition for binding to Sp1, and suggest that p300 modulates acetylation and/or interacts with GATA6/Sp1 to regulate Aqp5 transcription. Cooperative interactions among transcription factors and histone modifications regulate Aqp5 expression during alveolar epithelial cell transdifferentiation, suggesting that HDAC inhibitors may enhance repair by promoting acquisition of AT1 cell phenotype.

Temporal Expression Patterns of Clock Genes and Aquaporin 5/Anoctamin 1 in Rat Submandibular Gland Cells

Circadian rhythms are essential for health and regulate various physiological functions. These rhythms are regulated by a negative-feedback loop involving clock genes in the suprachiasmatic nucleus (SCN) and peripheral tissues. The rate of secretion of salivary substances, ions, and water follows a circadian rhythm, however, the relationship between the molecular mechanism of salivary secretion and peripheral circadian rhythm is not yet clear. Anoctamin 1 (ANO1, also known as TMEM16A) and Aquaporin 5 (AQP5) play an important role in the transport of ions and water in the submandibular glands (SGs). We examined the interaction between the rhythmic expression pattern of the clock genes, Ano1 and Aqp5, in rat whole SGs as well as isolated acinar and ductal cells. Circadian rhythmic expression for Bmal1, Per1, Per2, Clock, Cry1, Cry2, Rorα, and Rev-erbα mRNAs, also called the clock genes, was observed in rat SGs by semi-quantitative RT-PCR analysis. We also observed rhythmic patterns in Ano1 and Aqp5 mRNA expression. The expression of ANO1 protein also showed circadian rhythm, as confirmed by western blot analysis. We could not observe any time delay between the peak expression of ANO1 protein and its mRNA. Expression levels of the clock gene mRNAs in the ductal cells was higher than that in acinar cells, however, rhythmic oscillations were observed in both. Our results suggest that SGs have peripheral clocks, and rhythmic expressions of Ano1 and Aqp5 along with the clock genes, may play an important role in the circadian regulation of salivary secretion.

AQP1, AQP5, Bcl-2 and p16 in pharyngeal squamous cell carcinoma

Objective:

This study aimed to link expression patterns of AQP1, AQP5, Bcl-2 and p16 to clinicopathological characteristics of oro-hypopharyngeal squamous cell carcinomas.

Methods:

Immunohistochemical expression of AQP1, AQP5, Bcl-2 and p16 was investigated in 107 consecutive oro-hypopharyngeal squamous cell carcinoma cases. Molecular interrelationship and correlations with clinicopathological parameters and survival were computed.

Results:

AQP1 was expressed exclusively by a subgroup of basaloid-like squamous cell carcinomas. AQP5 was detected in 25.2 per cent of the samples, showing significant association with the absence of p16 and Bcl-2 (p = 0.018; p = 0.010). In multivariate analysis, overexpression of p16 was significantly correlated with favourable overall survival (p = 0.014).

Conclusion:

AQP5 defined a subset of patients with Bcl-2-negative and p16-negative tumours with a poor clinical outcome. AQP1 was found to be a marker of a subgroup of aggressive basaloid-like squamous cell carcinomas. These findings suggest that AQP1 and AQP5 are interesting candidates for further studies on risk group classification and personalised treatment of oro-hypopharyngeal squamous cell carcinomas.

Aquaporin 5 expression in mouse mammary gland cells is not driven by promoter methylation

Several studies have revealed that aquaporins play a role in tumor progression and invasion. In breast carcinomas, high levels of aquaporin 5 (AQP5), a membrane protein involved in water transport, have been linked to increased cell proliferation and migration, thus facilitating tumor progression. Despite the potential role of AQP5 in mammary oncogenesis, the mechanisms controlling mammary AQP5 expression are poorly understood. In other tissues, AQP5 expression has been correlated with its promoter methylation, yet, very little is known about AQP5 promoter methylation in the mammary gland. In this work, we used the mouse mammary gland cell line EpH4, in which we controlled AQP5 expression via the steroid hormone dexamethasone (Dex) to further investigate mechanisms regulating AQP5 expression. In this system, we observed a rapid drop of AQP5 mRNA levels with a delay of several hours in AQP5 protein, suggesting transcriptional control of AQP5 levels. Yet, AQP5 expression was independent of its promoter methylation, or to the presence of negative glucocorticoid receptor elements (nGREs) in its imminent promoter region, but was rather influenced by the cell proliferative state or cell density. We conclude that AQP5 promoter methylation is not a universal mechanism for AQP5 regulation and varies on cell and tissue type.

Aquaporin 5 expression is altered in ovarian tumors and ascites-derived ovarian tumor cells in the chicken model of ovarian tumor

BACKGROUND

Aquaporin 5 (AQP5), a member of the aquaporin family of transmembrane channel proteins, is involved in water transport and cellular proliferation in various tumors. The objective of this study was to determine cellular localization of aquaporin 5 (AQP5) in the ovarian tumors of chicken, a preclinical model for human ovarian tumor and to determine if AQP5 mRNA and protein expression levels in cancerous chicken ovaries and in ascites-derived chicken ovarian cancer (COVCAR) cell lines are different from normal ovaries and normal ovarian surface epithelial (NOSE) cells, respectively.

METHODS

Immunohistochemical staining was performed to determine the localization of AQP5-immunoreactive (ir) cells in normal and cancerous ovaries. To determine AQP5 mRNA and protein concentrations in cancerous ovaries and COVCAR cell lines, quantitative real time PCR and Western blotting analysis were performed, respectively. Student's t-test was performed to compare the levels of AQP5 mRNA or protein in cancerous ovaries and COVCAR cell lines with that of normal ovaries and NOSE cells, respectively.

RESULTS

AQP5-ir cells were localized in granulosa and theca layers of normal ovarian follicles whereas cancerous ovaries showed AQP5 immunostaining in the surface epithelium, fibroblast cells of the stroma, and in the cells lining tumor cysts and acini. AQP5 mRNA concentration were significantly lesser while AQP5 protein concentrations were significantly greater in cancerous ovaries compared to that in normal ovaries (P < 0.05). Whereas AQP5 mRNA concentrations were significantly greater while AQP5 protein concentrations were lesser (P < 0.05) in COVCAR cell lines compared with that in NOSE cells.

CONCLUSION

AQP5 is differentially expressed in ovarian tumor and in COVCAR cell lines suggesting a potential involvement of AQP5 in ovarian tumorigenesis, metastasis, and survival of ovarian tumor cells in ascites.

Aquaporin 5 increases keratinocyte-derived chemokine expression and NF-κB activity through ERK activation

Aquaporin-5 (AQP5) is a water-selective channel protein that is expressed in submucosal glands and alveolar epithelial cells in the lungs. Recent studies have revealed that AQPs regulate not only water metabolism, but also some cellular functions such as cell growth and migration. Here, we report the role of AQP5 in inflammatory responses. In MLE-12 cells, knockdown of AQP5 using siRNA (10-50 nM) attenuated TNF-α-induced expression of keratinocyte chemoattractant (KC) mRNA and protein. Conversely, in NIH-3T3 cells, overexpression of AQP5 increased KC expression, NF-κB activation, and ERK phosphorylation. The AQP5-induced increase of KC expression was diminished by treatment with ERK inhibitors. Taken together, we propose a new function of AQP5 as an inflammatory signal potentiator, which may be mediated by increased activation of ERK and NF-κB.

Expression of aquaporin 5 and the AQP5 polymorphism A(-1364)C in association with peritumoral brain edema in meningioma patients

Aquaporins (AQP) are a growing family of water-channel proteins, numbering 13 to date. Recent studies have reported AQP1 and AQP4 to be involved in the development and resorption of brain edemas of different origin. Other AQPs have also been detected in brain tissue, but their impact on brain edema remains to be shown. To evaluate a possible role of AQP5 in brain edema, we investigated the association of AQP5 expression and the functional AQP5 promoter polymorphism A(-1364)C with occurrence and intensity of peritumoral edema in meningioma patients. Peritumoral edema was classified in three degrees based on preoperative imaging in 89 meningioma patients treated at the University Hospital Essen between 2003 and 2006. AQP5 expression was assessed immunohistochemically in tumor tissue obtained during neurosurgical tumor resection. Genotypes of the A(-1364)C polymorphism were determined using the "slowdown" polymerase chain reaction. Higher levels of AQP5 expression were significantly correlated with the AQP5-1364 AA genotype (P = 0.02). AQP5 expression was positively correlated with edema (P = 0.04). AQP5 genotypes were not significantly associated with the occurrence, but with the intensity of peritumoral brain edema (P = 0.04). In our cohort, 40 % of patients with grade I, 66.7 % with grade II, and 76.5 % with grade III edema possessed at least one A allele. Development and intensity of peritumoral edema in meningiomas are associated with AQP5 expression. The intensity of edema correlates with the AQP5 A(-1364)C genotype. This suggests AQP5 as an interesting new candidate involved in peritumoral brain edema in meningioma patients.

Critical roles of Sp1 in gene expression of human and rat H+/organic cation antiporter MATE1

A H+/organic cation antiporter (multidrug and toxin extrusion 1: MATE1/SLC47A1) plays important roles in the tubular secretion of various clinically important cationic drugs such as cimetidine. We have recently found that the regulation of this transporter greatly affects the pharmacokinetic properties of cationic drugs in vivo. No information is available about the regulatory mechanisms for the MATE1 gene. In the present study, therefore, we examined the gene regulation of human (h) and rat (r) MATE1, focusing on basal expression. A deletion analysis suggested that the regions spanning -65/-25 and -146/-38 were essential for the basal transcriptional activity of the hMATE1 and rMATE1 promoter, respectively, and that both regions contained putative Sp1-binding sites. Functional involvement of Sp1 was confirmed by Sp1 overexpression, a mutational analysis of Sp1-binding sites, mithramycin A treatment, and an electrophoretic mobility shift assay. Furthermore, we found a single nucleotide polymorphism (SNP) in the promoter region of hMATE1 (G-32A), which belongs to a Sp1-binding site. The allelic frequency of this rSNP was 3.7%, and Sp1-binding and promoter activity were significantly decreased. This is the first study to clarify the transcriptional mechanisms of the MATE1 gene and to identify a SNP affecting the promoter activity of hMATE1.