FOXO1-mediated epigenetic modifications are involved in the insulin-mediated repression of hepatocyte 
aquaporin 9 expression

Qiu,Lie‑Wang; Gu,Lu‑Yun; Lü,Lin; Chen,Xiao‑Feng; Li,Chuan‑Fei; Mei,Zhe‑Chuan

doi:10.3892/mmr.2014.3085

FOXO1-mediated epigenetic modifications are involved in the insulin-mediated repression of hepatocyte aquaporin 9 expression

Authors:
- Lie‑Wang Qiu
- Lu‑Yun Gu
- Lin Lü
- Xiao‑Feng Chen
- Chuan‑Fei Li
- Zhe‑Chuan Mei
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Affiliations: Department of Gastroenterology, The Affiliated Yongchuan Hospital, Chongqing Medical University, Chongqing 402160, P.R. China, Department of Gastroenterology, The Second Affiliated Hospital, Chongqing Medical University, Chongqing 400010, P.R. China
Published online on: December 12, 2014 https://doi.org/10.3892/mmr.2014.3085
Pages: 3064-3068

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Abstract

Aquaporin (AQP) 9 transports glycerol and water, and belongs to the aquaglyceroporin subfamily. Insulin acts as a negative regulator of AQP9, and FOXO1 has the ability to mediate the regulatory effects of insulin on target gene expression. The aim of the present study was to determine whether insulin‑induced repression of AQP9 involved an epigenetic mechanism. HepG2 human hepatocyte cells were treated with 500 µM insulin for different durations. AQP9 mRNA expression levels were determined by quantitative polymerase chain reaction (qPCR), and histone H3 acetylation, phosphorylation and methylation at the insulin responsive element (IRE) of the AQP9 promoter was assessed using chromatin immunoprecipitation coupled with qPCR. The effects of lentiviral FOXO1 overexpression on AQP9 expression levels and H3 modifications at the AQP9 promoter were also determined. The insulin treatment resulted in a significant and time‑dependent reduction in AQP9 mRNA expression levels in HepG2 cells, as compared with untreated cells (P<0.05). In the insulin‑treated cells, the levels of H3 acetylation and phosphorylation were significantly reduced (P<0.05), but the level of H3 methylation was increased. Enforced expression of FOXO1 increased AQP9 mRNA and protein expression levels in HepG2 cells. Furthermore, FOXO1 overexpression promoted H3 acetylation and phosphorylation, and reduced H3 methylation at the IRE locus of the AQP9 promoter. These data provide, to the best of our knowledge, the first evidence that insulin‑induced transcriptional suppression of AQP9 expression in hepatocytes involves FOXO1‑mediated H3 modifications at the IRE locus in the promoter.

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