Differential expression of aquaporin-4 in human gastric normal and cancer tissues

The role of Aquaporins in tumorigenesis: implications for therapeutic development

Aquaporins (AQPs) are ubiquitous channel proteins that play a critical role in the homeostasis of the cellular environment by allowing the transit of water, chemicals, and ions. They can be found in many different types of cells and organs, including the lungs, eyes, brain, glands, and blood vessels. By controlling the osmotic water flux in processes like cell growth, energy metabolism, migration, adhesion, and proliferation, AQPs are capable of exerting their regulatory influence over a wide range of cellular processes. Tumour cells of varying sources express AQPs significantly, especially in malignant tumours with a high propensity for metastasis. New insights into the roles of AQPs in cell migration and proliferation reinforce the notion that AQPs are crucial players in tumour biology. AQPs have recently been shown to be a powerful tool in the fight against pathogenic antibodies and metastatic cell migration, despite the fact that the molecular processes of aquaporins in pathology are not entirely established. In this review, we shall discuss the several ways in which AQPs are expressed in the body, the unique roles they play in tumorigenesis, and the novel therapeutic approaches that could be adopted to treat carcinoma.

AQP4-IgG-positive neuromyelitis optica spectrum disorder and temporally detected neoplasms: case report and systematic review

BACKGROUND

An increasing number of reports on associations between neoplasms and neuromyelitis optica spectrum disorder (NMOSD) have been published over the past decade. However, types of neoplasms and temporal relationships have not been widely studied.

OBJECTIVE

To report cases and determine the associations between neoplasms and NMOSD.

METHOD

A retrospective chart review of possible paraneoplastic NMOSD patients at a university hospital was performed. Articles related to "neoplasm" and "NMOSD" were systematically searched and reviewed. We included aquaporin-4 (AQP4)-IgG-seropositive NMOSD patients whose onset of NMOSD and cancer diagnosis or recurrence were within 24 months of one another. Temporal relationship, types of neoplasms involved, treatments, and outcomes of both NMOSD and neoplasms were determined. The subgroup analysis was based on the AQP4 expression of neoplasm histology.

RESULTS

We identified 3 cases (1.3%) from a cohort of 224 AQP4-IgG-seropositive NMOSD at our hospital and retrieved 68 cases from a systematic review, totaling 71 cases of possible paraneoplastic NMOSD. The median age at onset of NMOSD was 55 (IQR 41-64) years. Eighty percent were female. The most frequently identified types of neoplasms were lung and breast, accounting for 21.1% and 18.3%, respectively. The other tumor types were ovarian tumors and hematologic malignancy, both at 12.7%. The most commonly identified tissue histology was adenocarcinoma (52.1%). We also reported the first case of melanoma in an NMOSD patient. Twenty-eight patients (39.4%) were diagnosed with cancer before the onset of NMOSD with a median duration of 9.5 (range 1-24) months. Of those, eight patients had NMOSD after surgical removal of neoplasms, and one patient had NMOSD after radiotherapy of prostate adenocarcinoma. Twenty-three patients (32.4%) had NMOSD before cancer diagnosis by a median of 3 (range 1-24) months, and the rest were diagnosed concurrently during the same admission. Three cases were diagnosed with NMOSD around the time of tumor recurrence. Tumor tissue expressed AQP4 in 82.4%.

CONCLUSION

A small proportion of AQP4-IgG-positive NMOSD is associated with malignancy. In newly diagnosed NMOSD patients without symptoms of neoplasms, screening for age- and risk-appropriate cancer should be recommended, similar to the general population. The occurrence of NMOSD in cancer patients might suggest tumor recurrence.

Expression Profiles of AQP3 and AQP4 in Lung Adenocarcinoma Samples Generated via Bronchoscopic Biopsies

Aquaporins (AQPs) are highly conserved channel proteins which are mainly responsible for the exchange of water and small molecules and have shown to play a pivotal role in the development and progression of cancer. Lung adenocarcinoma is the most common primary lung cancer seen in patients in Europe and the United States. However, in patients it is often not diagnosed until the advanced tumor stage is present. Previous studies provided strong evidence that some members of the AQP family could serve as clinical biomarkers for different diseases. Therefore, we aimed to investigate how AQP3 and AQP4 protein expression in lung adenocarcinoma (ADC) biopsy samples correlate with clinical and pathological parameters. The protein expression of AQP3 and AQP4 was analyzed based on immunohistochemical staining. AQP3 protein was observed in the cytoplasmic membrane of cancer tissue in 82% of lung samples. Significant differences in relative protein expression of AQP3 were noted between advanced age patients compared to younger counterparts (p = 0.017). A high expression of AQP3 was significant in cancer tissue when compared to the control group (p < 0.001), whereas a low AQP4 membrane expression was noted as significantly common in cancer tissue compared to non-neoplastic lung tissue (p < 0.001). Moreover, a low AQP4 membrane expression was positively correlated with a more advanced disease status, e.g., lymph node metastases (p = 0.046). Based on our findings, AQP3 and AQP4 could be used as biomarkers in ADC patients.

Comprehensive Analysis of the Molecular Characteristics and Prognosis value of AT II-associated Genes in Non-small Cell Lung Cancer

Alveolar type II (AT II) is a key structure of the distal lung epithelium and essential to maintain normal lung homeostasis. Dedifferentiation of AT II cells is significantly correlated with lung tumor progression. However, the potential molecular mechanism and clinical significance of AT II-associated genes for lung cancer has not yet been fully elucidated. In this study, we comprehensively analyzed the gene expression, prognosis value, genetic alteration, and immune cell infiltration of eight AT II-associated genes (AQP4, SFTPB, SFTPC, SFTPD, CLDN18, FOXA2, NKX2-1, and PGC) in Nonsmall Cell Lung Cancer (NSCLC). The results have shown that the expression of eight genes were remarkably reduced in cancer tissues and observably relating to clinical cancer stages. Survival analysis of the eight genes revealed that low-expression of CLDN18, FOXA2, NKX2-1, PGC, SFTPB, SFTPC, and SFTPD were significantly related to a reduced progression-free survival (FP), and low CLDN18, FOXA2, and SFTPD mRNA expression led to a short postprogression survival (PPS). Meanwhile, the alteration of 8 AT II-associated genes covered 273 out of 1053 NSCLC samples (26%). Additionally, the expression level of eight genes were significantly correlated with the infiltration of diverse immune cells, including six types of CD4+T cells, macrophages, neutrophils, B cells, CD8+ T cells, and dendritic cells. In summary, this study provided clues of the values of eight AT II-associated genes as clinical biomarkers and therapeutic targets in NSCLC and might provide some new inspirations to assist the design of new immunotherapies.

Pathophysiological role of ion channels and transporters in gastrointestinal mucosal diseases

The incidence of gastrointestinal (GI) mucosal diseases, including various types of gastritis, ulcers, inflammatory bowel disease and GI cancer, is increasing. Therefore, it is necessary to identify new therapeutic targets. Ion channels/transporters are located on cell membranes, and tight junctions (TJs) affect acid–base balance, the mucus layer, permeability, the microbiota and mucosal blood flow, which are essential for maintaining GI mucosal integrity. As ion channel/transporter dysfunction results in various GI mucosal diseases, this review focuses on understanding the contribution of ion channels/transporters to protecting the GI mucosal barrier and the relationship between GI mucosal disease and ion channels/transporters, including Cl⁻/HCO₃⁻ exchangers, Cl⁻ channels, aquaporins, Na⁺/H⁺ exchangers, and K⁺ channels. Here, we provide novel prospects for the treatment of GI mucosal diseases.

RNA-Seq Analysis Reveals Dendrobium officinale Polysaccharides Inhibit Precancerous Lesions of Gastric Cancer through PER3 and AQP4

Purpose

There has been mounting evidence that Dendrobium officinale polysaccharides (DOP), a traditional Chinese medicine, are a potential candidate treatment for N-methyl-N'-nitro-N-nitrosoguanidine- (MNNG-) induced precancerous lesions of gastric cancer (PLGC). However, the underlying mechanisms have not been adequately addressed.

Method

We utilized RNA-Seq analysis to investigate possible molecular targets and then used Venn software to identify the differentially expressed genes (DEGs). Further, we analyzed these DEGs with core analysis, upstream analysis, and interaction network analysis by IPA software and validated the DEGs by real-time PCR and Western blot.

Result

78 DEGs were identified from the normal control group (CON), the PLGC model group (MOD), and the DOP-treated group (DOP) by the Venn software. Further analysis of these DEGs, including core analysis, upstream analysis, and interaction network analysis, was performed by Ingenuity Pathway Analysis (IPA). The main canonical pathways involved were SPINK1 Pancreatic Cancer Pathway (-log (P value) = 4.45, ratio = 0.0667) and Circadian Rhythm Signaling (-log (P value) = 2.33, ratio = 0.0606). Circadian Rhythm Signaling was strongly upregulated in the model group versus the DOP group. CLOCK was predicted to be strongly activated (z-score = 2.236) in upstream analysis and induced the downstream PER3. In addition, the relative mRNA expression levels of seven DEGs (CD2AP, ECM1, AQP4, PER3, CMTM4, ESRRG, and KCNJ15) from RT-PCR agreed with RNA-Seq data from MOD versus CON and MOD versus DOP groups. The gene and protein expression levels of PER3 and AQP4 were significantly downregulated in the PLGC model and significantly increased by DOP treatment (9.6 g/kg).

Conclusions

These findings not only showed DOP inhibits PLGC development by upregulating the PER3 and AQP4 gene and protein expression but also suggested that its mechanism of action involved modulating the Circadian Rhythm Signaling pathway.

Expression and clinical significance of aquaporin-1, vascular endothelial growth factor and microvessel density in gastric cancer

To investigate the expression and clinical significance of aquaporin-1 (AQP1), vascular endothelial growth factor (VEGF) and microvessel density (MVD) in gastric cancer.A total of 79 gastric cancer patients who were admitted into Beijing Chao-Yang Hospital from January, 2018 to December, 2019 were involved in this study. Tumor specimens and para-cancerous normal tissues (> 2 cm away from the tumor) of all the enrolled patients were collected. Immunohistochemistry were performed to identify the expression of AQP1, VEGF, and MVD and the correlation between AQP1, VEGF, MVD, and clinicopathological parameters was analyzed.The expression of AQP1, VEGF and MVD in gastric cancer tissue was increased significantly compared with those in para-cancerous tissue (P < .05). AQP1, VEGF, and MVD were closely correlated with gastric cancer differentiation, lymph node metastasis, vascular tumor thrombosis and clinical stage (P < .05). Spearman correlation analysis showed that AQP1 was positively associated with VEGF expression (r = 0.497, P < .05). MVD was enhanced in VEGF or AQP1 positive cancer tissues compared with that in VEGF or AQP1 negative tissue (P < .05).Synergistic effect among AQP1, VEGF, and MVD is involved in occurrence and development of gastric cancer.

Long noncoding RNA LINC00629 restrains the progression of gastric cancer by upregulating AQP4 through competitively binding to miR-196b-5p

Gastric cancer continues to be a common cancer in the world with high incidence and mortality. Accumulating evidence has implicated long noncoding RNAs (lncRNAs) in gastric cancer progression. Here, this study identified the potential role of a novel lncRNA, LINC00629 in gastric cancer and to elucidate the underlying mechanism. Initially, microarray-based gene expression profiling of gastric cancer was employed to identify differentially expressed genes. Next, the expression of LINC00629, microRNA-196b-5p (miR-196b-5p) and aquaporin 4 (AQP4) in clinical gastric cancer tissues was determined and the cell line presenting with the lowest LINC00629 expression was selected. The interaction among LINC00629, miR-196b-5p, and AQP4 was identified. Expression of LINC00629, miR-196b-5p, and AQP4 in gastric cancer cells were altered and then biological behaviors of gastric cancer cells were assessed by 5-ethynyl-2'-deoxyuridine and Transwell assays. Tumor formation in vivo was evaluated in nude mice. In gastric cancer, expression of LINC00629 and AQP4 was downregulated, and expression of miR-196b-5p was upregulated. Proliferation, invasion, and migration of gastric cancer cells were reduced after overexpression of LINC00629. LINC00629 competitively bound to miR-196b-5p, while AQP4 was a target of miR-196b-5p. Either downregulating miR-196b-5p or upregulating AQP4 could restrain the development of gastric cancer in vitro. LINC00629 overexpression repressed the growth of transplanted tumors in vivo. Taken together, LINC00629 competitively bound to miR-196b-5p to upregulate AQP4 expression, thereby inhibiting gastric cancer progression. Therefore, understanding of this mechanism may help to improve gastric cancer treatment.

Significance of aquaporins' expression in the prognosis of gastric cancer

Gastric carcinoma is one of the most lethal malignancy at present with leading cause of cancer-related deaths worldwide. Aquaporins (AQPs) are a family of small, integral membrane proteins, which have been evidenced to play a crucial role in cell migration and proliferation of different cancer cells including gastric cancers. However, the aberrant expression of specific AQPs and its correlation to detect predictive and prognostic significance in gastric cancer remains elusive. In the present study, we comprehensively explored immunohistochemistry based map of protein expression profiles in normal tissues, cancer and cell lines from publicly available Human Protein Atlas (HPA) database. Moreover, to improve our understanding of general gastric biology and guide to find novel predictive prognostic gastric cancer biomarker, we also retrieved 'The Kaplan-Meier plotter' (KM plotter) online database with specific AQPs mRNA to overall survival (OS) in different clinicopathological features. We revealed that ubiquitous expression of AQPs protein can be effective tools to generate gastric cancer biomarker. Furthermore, high level AQP3, AQP9, and AQP11 mRNA expression were correlated with better OS in all gastric patients, whereas AQP0, AQP1, AQP4, AQP5, AQP6, AQP8, and AQP10 mRNA expression were associated with poor OS. With regard to the clinicopathological features including Laurens classification, clinical stage, human epidermal growth factor receptor 2 (HER2) status, and different treatment strategy, we could illustrate significant role of individual AQP mRNA expression in the prognosis of gastric cancer patients. Thus, our results indicated that AQP's protein and mRNA expression in gastric cancer patients provide effective role to predict prognosis and act as an essential agent to therapeutic strategy.

Differential Expression of Aquaporins in Cervical Precursor Lesions and Invasive Cervical Cancer

OBJECTIVE

Aquaporins (AQPs) are highly expressed in tumor cells of different origins, particularly the aggressive tumors. The aim of this study was to investigate the expression of AQP isoforms during progression of squamous cervical cancer (SCC) and explore their associations with clinicopathologic variables of SCC.

METHODS

Expression of AQP isoforms (1, 3, 4, 5, and 8) was detected by immunohistochemistry in 47 SCCs, 37 cervical intraepithelial neoplasia (CIN), and 16 normal cervical tissues. Specific expression of AQP protein in SCC was detected by Western blot. Double immunohistochemistry was used to examine whether AQPs and vascular endothelial growth factor (VEGF) are coexpressed in SCC.

RESULTS

Aquaporin 1 showed higher positivity rate in CIN than in SCC and normal cervical tissues (P < .05). The expression intensity of AQP3, 4, 5, and 8 was higher in SCC than that in normal cervical tissues, respectively (P < .05). The expression of AQP3 and 8 was higher in SCC than that in CIN, respectively (P < .05). The AQP4 expression was higher in CIN than in normal cervical tissues (P < .05). The expression of AQP3 in CIN III was higher than that in CIN I and II (P < .05). There was a significant increase in the expression of AQP1 in stage I than that in stage II (P < .05). Aquaporin 3 showed lower positivity in moderately and well-differentiated tumors compared to that in poorly differentiated tumors (P < .05). Finally, double immunohistochemistry illustrated that AQP1/AQP3/AQP8 and VEGF were coexpressed in SCC.

CONCLUSIONS

Different AQP isoforms display specific expression patterns in normal cervical, CIN, and SCC tissues. This and the significant association with the clinicopathologic variables of SCC suggest that AQP isoforms might play different roles in the development of cervical cancer.

Aquaporins: Their role in gastrointestinal malignancies

Aquaporins (AQPs) are small (~30 kDa monomers) integral membrane water transport proteins that allow water to flow through cell membranes in reaction to osmotic gradients in cells. In mammals, the family of AQPs has thirteen (AQP0-12) unique members that mediate critical biological functions. Since AQPs can impact cell proliferation, migration and angiogenesis, their role in various human cancers is well established. Recently, AQPs have been explored as potential diagnostic and therapeutic targets in gastrointestinal (GI) cancers. GI cancers encompass multiple sites including the colon, esophagus, stomach and pancreas. Research in the last three decades has revealed biological aspects and signaling pathways critical for the development of GI cancers. Since the majority of these cancers are very aggressive and rapidly metastasizes, identifying effective targets is crucial for treatment. Preclinical studies have utilized inhibitors of specific AQPs and knock down of AQP expression using siRNA. Although several studies have explored the role of AQPs in colorectal, esophageal, gastric, hepatocellular and pancreatic cancers, there is no comprehensive review compiling the available information on GI cancers as has been published for other malignancies such as ovarian cancer. Due to the similarities and association of various sites of GI cancers, it is helpful to consider these results collectively in order to better understand the role of specific AQPs in critical GI cancers. This review summarizes the current knowledge of the role of AQPs in GI malignancies with particular focus on diagnosis and therapeutic applications.

Aquaporins: New Targets for Cancer Therapy

Aquaporins are a family of integral membrane proteins that are expressed in all living organisms and play vital roles in transcellular and transepithelial water movement. Cell viability and motility are critical for progression of cancer. Cell survival requires the suitable concentration of water and solutes. The balance is largely maintained by aquaporins whose major function is the transport of water and small solutes across the plasma membrane. The important role of aquaporins has received more and more attention in the recent years. A number of recent studies have revealed that aquaporins may be involved in cell migration and angiogenesis. This review will highlight the expression of aquaporins in different malignant neoplasms. Remarkably, we will summarize the influence of drugs on aquaporins, not only the traditional Chinese medicine but also the Western medicine. Therapeutic targeting of aquaporins may thus be advantageous for blocking the mechanism common for a number of key cancer phenotypes.

Mucosal expression of aquaporin-4 in the stomach of histamine type 2 receptor knockout mice and Helicobacter pylori-infected mice

BACKGROUND AND AIM

Basolateral water channel, aquaporin-4 (AQP4), is known to be expressed in gastric parietal cells, especially in the basal side of gastric mucosa. However, the role of AQP4 in the stomach is still unknown. Histamine type 2 receptor (H2R) knockout mice, which are characterized by suppressed gastric acid secretion, are known as formation of mucosal hyperplasia with cystic dilatation and spasmolytic polypeptide-expressing metaplasia (SPEM) in the stomach. The aim of the present study is to investigate whether the expression of AQP4 is changed by the condition of acid suppression and Helicobacter pylori infection.

METHODS

Male H2 R knockout mice and their controls (C57BL/6) were used. H. pylori was orally infected at the age of 5 weeks. The distributions of AQP4 and H+/K+-ATPase in the gastric mucosa were investigated by fluorescent immunohistochemistry. The mRNA expressions of AQP4, H+/K+-ATPase, sonic hedgehog (Shh), and trefoil factor-2 (TFF2) were investigated by quantitative reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

In the H2 R knockout mice, the distribution of AQP4-positive parietal cells was extended toward the surface of the fundic glands. Although the mRNA expression levels of AQP4 and H+/K+ATPase were elevated in H2 R knockout mice at the age of 20 weeks, the elevations were not maintained by aging or H. pylori infection. In H2 R knockout mice with H. pylori infection, the expression level of TFF2 mRNA was elevated while the ratio between AQP4 and H+/K+ ATPase mRNA expression was decreased compared with the H2 R knockout mice without H. pylori infection.

CONCLUSIONS

In the H2 R knockout mice, massive SPEM was induced by H. pylori colonization and the ratio between AQP4 and H+/K+ATPase mRNA expression was decreased.

Key roles of aquaporins in tumor biology

Aquaporins are protein channels that facilitate the flow of water across plasma cell membranes in response to osmotic gradients. This review summarizes the evidence that aquaporins play key roles in tumor biology including tumor-associated edema, tumor cell migration, tumor proliferation and tumor angiogenesis. Aquaporin inhibitors may thus be a novel class of anti-tumor agents. However, attempts to produce small molecule aquaporin inhibitors have been largely unsuccessful. Recently, monoclonal human IgG antibodies against extracellular aquaporin-4 domains have become available and could be engineered to kill aquaporin-4 over-expressing cells in the malignant brain tumor glioblastoma. We conclude this review by discussing future directions in aquaporin tumor research. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.

Involvement of Aquaporin 3 in Helicobacter pylori-related gastric diseases

Background

Gastric cancer is one of the most common and lethal malignant cancers worldwide, and numerous epidemiological studies have demonstrated that Helicobacter pylori (H. pylori) infection plays a key role in the development of gastric carcinomas. Our previous studies showed that aquaporin 3 (AQP3) is overexpressed in gastric carcinoma and promotes the migration and proliferation of human gastric carcinoma cells, suggesting that AQP3 may be a potentially important determinant of gastric carcinoma. However, the role of AQP3 in H. pylori carcinogenesis is unknown.

Methods

The AQP3 protein and H. pylori were detected in human gastric tissues by immunohistochemistry and modified Giemsa staining respectively. AQP3 knockdown was obtained by small interfering (si) RNA. Western blot assays and RT-PCR were used to evaluate the change of AQP3 in the human gastric cancer AGS and SGC7901 cell lines after co-culture with H. pylori. Sprague Dawley rats were orally inoculated with H. pylori to establish a rat model colonized by H. pylori.

Results

The present study found that AQP3 expression correlated with H. pylori infection status in gastric cancer tissues and corresponding normal mucosa, and H. pylori co-culture upregulated AQP3 expression in human gastric adenocarcinoma cells in vitro via the extracellular signal-regulated kinase signaling pathway. H. pylori infection also increased AQP3 expression in gastric mucosa colonized by H. pylori in a Sprague Dawley rat model.

Conclusions

These findings provide further information to understand the mechanism of H. pylori carcinogenesis and a potential strategy for the treatment of H. pylori-associated gastric carcinoma.

Water channel proteins in the gastrointestinal tract

Water transport through the human digestive system is physiologically crucial for maintaining body water homeostasis and ensure digestive and absorptive functions. Within the gastrointestinal tract, water recirculates, being secreted with the digestive juices and then almost entirely absorbed by the small and large intestine. The importance of aquaporins (AQPs), transmembrane water channel proteins, in the rapid passage of water across plasma membranes in the gastrointestinal tract appears immediately evident. Several AQP isoforms are found in gastrointestinal epithelia, with AQP1, 3, 7, 10 and 11 being the most abundantly expressed in the whole gut. On the other hand, AQP4 and 8 are located selectively in the stomach and colon, respectively. Here we review AQP expression and localization at the tissue, cellular and subcellular level in gastrointestinal epithelia, and their modification in various gut diseases.

Characterization of Aquaporin 4 Protein Expression and Localization in Tissues of the Dogfish (Squalus acanthias)

The role of aquaporin water channels such as aquaporin 4 (Aqp4) in elasmobranchs such as the dogfish Squalus acanthias is completely unknown. This investigation set out to determine the expression and cellular and sub-cellular localization of Aqp4 protein in dogfish tissues. Two polyclonal antibodies were generated (AQP4/1 and AQP4/2) and these showed somewhat different characteristics in Western blotting and immunohistochemistry. Western blots using the AQP4/1 antibody showed two bands (35.5 and 49.5 kDa) in most tissues in a similar fashion to mammals. Liver had an additional band of 57 kDa and rectal gland two further faint bands of 37.5 and 38.5 kDa. However, unlike in mammals, Aqp4 protein was ubiquitously expressed in all tissues including gill and liver. The AQP4/2 antibody appeared much less specific in Western blots. Both antibodies were used in immunohistochemistry and showed similar cellular localizations, although the AQP4/2 antibody had a more restricted sub-cellular distribution compared to AQP4/1 and therefore appeared to be more specific for Aqp4. In kidney a sub-set of tubules were stained which may represent intermediate tubule segments (In-III-In-VI). AQP4/1 and AQP4/2 antibodies localized to the same tubules segments in serial sections although the intensity and sub-cellular distribution were different. AQP4/2 showed a basal or basolateral membrane distribution whereas AQP4/1 was often distributed throughout the whole cell including the nuclear region. In rectal gland and cardiac stomach Aqp4 was localized to secretory tubules but again AQP/1 and AQP/2 exhibited different sub-cellular distributions. In gill, both antibodies stained large cells in the primary filament and secondary lamellae. Again AQP4/1 antibody stained most or all the cell including the nucleus, whereas AQP4/2 had a plasma membrane or plasma membrane and cytoplasmic distribution. Two types of large mitochondrial rich transport cells are known to exist in elasmobranchs, that express either Na, K-ATPase, or V-type ATPase ion transporters. Using Na, K-ATPase, and V-type ATPase antibodies, Aqp4 was colocalized with these proteins using the AQP4/1 antibody. Results show Aqp4 is expressed in both (and all) branchial Na, K-ATPase, and V-type ATPase expressing cells.

c-Met upregulates aquaporin 3 expression in human gastric carcinoma cells via the ERK signalling pathway

Aquaporin 3 (AQP3) and c-Met are both overexpressed in human gastric carcinoma and highly associated with its metastasis and invasion. However, it still remains unknown whether c-Met and AQP3 correlate with each other. Herein, we demonstrated that c-Met expression in gastric cancer tissues significantly correlated with differentiation, lymph node metastasis and lymphovascular invasion, and c-Met exhibited marked association with AQP3 expression. Immunoblotting assays showed that hHGF phosphorylated c-Met in SGC7901 and AGS cells and upregulated AQP3 expression in a dose- or time-dependent way. RNAi against c-Met reduced total c-Met levels by about two thirds in both AGS and SGC7901 cells and attenuated hHGF-induced AQP3 expression significantly. In vitro migration and proliferation assays showed that siRNA against AQP3 noticeably restrained HGF-promoted migration and proliferation of these cells. Furthermore, Immunoblotting studies revealed that HGF induced phosphorylation of ERK, and pre-treatment with U0126, a MAPK/ERK inhibitor, partially inhibited hHGF-induced increase in AQP3 expression. Together, these data provide initial evidence that c-Met regulates the expression of AQP3 via the ERK signalling pathway in gastric carcinoma. These findings assist in understanding the mechanism of growth and invasion of gastric carcinoma, and provide a possible strategy for the inhibition of gastric tumor metastasis.

Aquaporin 4 is a Ubiquitously Expressed Isoform in the Dogfish (Squalus acanthias) Shark

The dogfish ortholog of aquaporin 4 (AQP4) was amplified from cDNA using degenerate PCR followed by cloning and sequencing. The complete coding region was then obtained using 5' and 3' RACE techniques. Alignment of the sequence with AQP4 amino acid sequences from other species showed that dogfish AQP4 has high levels (up to 65.3%) of homology with higher vertebrate sequences but lower levels of homology to Agnathan (38.2%) or teleost (57.5%) fish sequences. Northern blotting indicated that the dogfish mRNA was approximately 3.2 kb and was highly expressed in the rectal gland (a shark fluid secretory organ). Semi-quantitative PCR further indicates that AQP4 is ubiquitous, being expressed in all tissues measured but at low levels in certain tissues, where the level in liver > gill >  intestine. Manipulation of the external environmental salinity of groups of dogfish showed that when fish were acclimated in stages to 120% seawater (SW) or 75% SW, there was no change in AQP4 mRNA expression in either rectal gland, kidney, or esophagus/cardiac stomach. Whereas quantitative PCR experiments using the RNA samples from the same experiment, showed a significant 63.1% lower abundance of gill AQP4 mRNA expression in 120% SW-acclimated dogfish. The function of dogfish AQP4 was also determined by measuring the effect of the AQP4 expression in Xenopus laevis oocytes. Dogfish AQP4 expressing-oocytes, exhibited significantly increased osmotic water permeability (P(f)) compared to controls, and this was invariant with pH. Permeability was not significantly reduced by treatment of oocytes with mercury chloride, as is also the case with AQP4 in other species. Similarly AQP4 expressing-oocytes did not exhibit enhanced urea or glycerol permeability, which is also consistent with the water-selective property of AQP4 in other species.

Aquaporin-3 positively regulates matrix metalloproteinases via PI3K/AKT signal pathway in human gastric carcinoma SGC7901 cells

BACKGROUND

matrix metalloproteinases (MMPs) are produced by tumor cells, so they may be associated with tumor progression including invasion, migration, angiogenesis and metastasis. Aquaporin-3 (AQP3) also plays a critical role in gastric cancer cell migration and proliferation.

METHODS

In this study, AQP3 was silenced or over-expressed in SGC7901 cells.

RESULTS

We found a significant decrease in MT1-MMP, MMP-2, and MMP-9 expression after AQP3 knockdown, and a significant increase in MT1-MMP, MMP-2, and MMP-9 expression after AQP3 over-expression in SGC7901 cells. We also found that AQP3 silence led to a significant decrease of phosphorylation of ser473 in AKT in SGC7901 cells.

CONCLUSION

Our findings showed that AQP3 might positively regulate MMPs proteins expression through PI3K/AKT signal pathway in human gastric carcinoma SGC7901 cells.

Loss of aquaporin-4 expression and putative function in non-small cell lung cancer

Background

Aquaporins (AQPs) have been recognized to promote tumor progression, invasion, and metastasis and are therefore recognized as promising targets for novel anti-cancer therapies. Potentially relevant AQPs in distinct cancer entities can be determined by a comprehensive expression analysis of the 13 human AQPs.

Methods

We analyzed the presence of all AQP transcripts in 576 different normal lung and non-small cell lung cancer (NSCLC) samples using microarray data and validated our findings by qRT-PCR and immunohistochemistry.

Results

Variable expression of several AQPs (AQP1, -3, -4, and -5) was found in NSCLC and normal lung tissues. Furthermore, we identified remarkable differences between NSCLC subtypes in regard to AQP1, -3 and -4 expression. Higher transcript and protein levels of AQP4 in well-differentiated lung adenocarcinomas suggested an association with a more favourable prognosis. Beyond water transport, data mining of co-expressed genes indicated an involvement of AQP4 in cell-cell signalling, cellular movement and lipid metabolism, and underlined the association of AQP4 to important physiological functions in benign lung tissue.

Conclusions

Our findings accentuate the need to identify functional differences and redundancies of active AQPs in normal and tumor cells in order to assess their value as promising drug targets.

Acid suppression by proton pump inhibitors enhances aquaporin-4 and KCNQ1 expression in gastric fundic parietal cells in mouse

BACKGROUND

The widespread use of proton pump inhibitors (PPIs) is known to cause sporadic gastric fundic gland polyps (FGPs). Altered expression and localization of the water or ion transport proteins might contribute to the excess fluid secretion into the cystic lumen for the development of FGPs.

AIMS

We investigated the alteration of the murine gastric fundic mucosa after PPI treatment, and examined the expression of water channel aquaporin-4 (AQP4) and potassium channel KCNQ1, which are expressed only in the parietal cells in the gastric mucosa.

METHODS

Male 5-week-old C57BL/6J mice were administered lansoprazole (LPZ) by subcutaneous injection for 8 weeks. The expression of AQP4 and KCNQ1 were investigated by Western blotting, quantitative RT-PCR, and immunohistochemistry. The expression of mucin-6 (Muc6), pepsinogen, and sonic hedgehog (Shh) were also investigated as mucosal cell lineage markers.

RESULTS

Gastric mucosal hyperplasia with multiple cystic dilatations, exhibiting similar histological findings to the FGPs, was observed in the LPZ-treated mice. An increase in the number of AQP4-positive parietal cells and KCNQ1-positive parietal cells was observed. The extension of the distribution of AQP4-positive cells toward the surface of the fundic glands was also observed. The expression levels of AQP4 mRNA and protein were significantly enhanced. The expression of KCNQ1 mRNA was correlated with that of AQP4 mRNA in the LPZ-treated mice. Mucous neck-to-zymogenic cell lineage differentiation was delayed in association with decreased expression of Shh in the LPZ-treated mice.

CONCLUSIONS

PPI administration increased the number of parietal cells with enhanced expression of AQP4 and KCNQ1.