No abstract

Aquaporin 9 (AQP9) is the main aquaglyceroporin in the liver. Few studies have been performed regarding the role of AQP9 in liver cancer. Here we report AQP9 expression and function in liver cancer. We found that AQP9 mRNA and protein levels were reduced in human hepatocellular cancer compared to the para-tumor normal liver tissues. Human hepatoma cell line SMMC7721 expressed low basal levels of AQP9. When AQP9 was overexpressed in SMMC7721 cell line, cell proliferation was inhibited due to cell cycle arrest at G1 phase and increased apoptosis. At the molecular level, AQP9 overexpression decreased the protein levels of phosphatidylinositol-3-kinase (PI3K), leading to reduced phosphorylation of Akt. Subsequently, the protein levels of forkhead box protein O1 (FOXO1) were increased, resulting in down-regulation of proliferating cell nuclear antigen (PCNA) expression and up-regulation of caspase-3 expression. AQP9 overexpression inhibited growth of subcutaneously xenografted liver tumors in nude mice. These findings suggest that AQP9 expression is down-regulated in liver cancer compared to the normal liver tissue and restoration of AQP9 expression can inhibit development of liver cancer.

Excess lipid deposition in hepatocytes is a hallmark feature of nonalcoholic fatty liver disease (NAFLD). The present study was designed to explore the expression and regulation of aquaporin (AQP) 3 and AQP9 in oleic acid-induced hepatic steatosis. HepG2 cells were incubated with oleic acid at different concentrations and time points. Oil-Red-O staining and triglyceride content measurement were done to assess the extent of hepatic steatosis. The expression of AQP3 and AQP9 was assessed using quantitative real-time PCR and Western blot analyses. The mitogen-activated protein kinase (MAPK) pathways involved in the regulation of AQP3 and AQP9 expression were checked. Compared to untreated control cells, oleic acid treatment significantly (p<0.05) induced hepatic steatosis in HepG2 cells in a dose- and time-dependent fashion. Oleic acid-treated cells showed a significant reduction in the AQP3 expression and a concomitant increase in the AQP9 expression. Oleic acid exposure led to enhanced phosphorylation of p38, but not ERK1/2 or JNK MAPK. Pharmacological inhibition of p38 rather than ERK1/2 signaling significantly blocked the regulation of AQP3 and AQP9 expression by oleic acid. Oleic acid-induced hepatic steatosis in HepG2 cells is associated with the coordinated regulation of AQP3 and AQP9 via activation of p38 signaling. These findings warrant functional studies of aquaglyceroporins in NAFLD.

Purpose: Hypoxia-induced changes are primarily activated in patients with hepatocellular carcinoma (HCC) and long-term sorafenib exposure, thereby reducing the sensitivity to the drug. Aquaporin-3 (AQP3), a member of the aquaporin family, is a hypoxia-induced substance that affects the chemosensitivity of non-hepatocellular tumors. However, its expression and role in the sensitivity of hypoxic HCC cells to sorafenib-induced apoptosis remain unclear. The purpose of this study was to detect changes in AQP3 expression in hypoxic HCC cells and to determine whether these changes alter the sensitivity of these cells to sorafenib. Materials and Methods: Huh7 and HepG2 hypoxic cell models were established and AQP3 expression was detected using quantitative real-time polymerase chain reaction (qPCR) and Western blotting. Furthermore, the role of AQP3 in cell sensitivity to sorafenib was evaluated via flow cytometry, Western blotting, and a CCK-8 assay. Results: The results of qPCR and Western blotting showed that AQP3 was overexpressed in the Huh7 and HepG2 hypoxic cell models. Furthermore, AQP3 protein levels were positively correlated with hypoxia-inducible factor-1α (HIF-1α) levels. Compared with cells transfected with lentivirus-GFP (Lv-GFP), hypoxic cells transfected with lentivirus-AQP3 (Lv-AQP3) were less sensitive to sorafenib-induced apoptosis. However, the sensitivity to the drug increased in cells transfected with lentivirus-AQP3RNAi (Lv-AQP3RNAi). Akt and Erk phosphorylation was enhanced in Lv-AQP3-transfected cells. Compared with UO126 (a Mek1/2 inhibitor), LY294002 (a PI3K inhibitor) attenuated the AQP3-induced insensitivity to sorafenib observed in hypoxic cells transfected with Lv-AQP3. Combined with LY294002-treated cells, hypoxic cells transfected with Lv-AQP3RNAi were more sensitive to sorafenib. Conclusion: The study results show that AQP3 is a potential therapeutic target for improving the sensitivity of hypoxic HCC cells to sorafenib.