Michael J Haas1, Marilu Jurado-Flores2, Ramadan Hammoud2, Gabriela Plazarte2, Luisa Onstead-Haas2, Norman C W Wong3, Arshag D Mooradian2. 1. Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida Jacksonville College of Medicine, Jacksonville, FL, United States of America. Electronic address: Michael.haas@jax.ufl.edu. 2. Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida Jacksonville College of Medicine, Jacksonville, FL, United States of America. 3. Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta, CA, United States of America.
Abstract
AIMS: Earlier it had been found by us that apolipoprotein A-I (apo A-I) is suppressed by histamine in HepG2 cells. Histamine has been shown to regulate NF-κB activity, though not in hepatocytes. Therefore we examined the role of the histamine receptors and NF-κB in histamine-mediated apo A-I gene expression in HepG2 liver cells. MAIN METHODS: The effect of histamine on histamine H1 receptor expression, and NF-κB p65 and p50 subunits was examined by Western blot. Histamine H1 receptor involvement was examined by loss-of-function (via siRNA) and gain-of-function studies overexpressing the histamine H1 receptor. The requirement for the p65 subunit of NF-κB for histamines effect was elucidated by loss-of-function studies (siRNA). Finally, the effect of histamine on NF-κB binding to the apo A-I gene promoter was examined by chromatin immunoprecipitation. KEY FINDINGS: Treatment of HepG2 cells with histamine had no effect on histamine H1 receptor expression. However, treatment with histamine increased NF-κB p65 and p50 subunit expression significantly. At low levels, the exogenous histamine H1 receptor plasmid suppressed apo A-I gene promoter activity while addition of higher levels of plasmid DNA actually increased apo A-I gene promoter activity. Inhibition of NF-κB activity with SN50 prevented histamine from repressing apo A-I promoter activity as did silencing p65 expression via siRNA. Finally, treatment with histamine increased binding of the p65 subunit of NF-κB to the apo A-I gene promoter. SIGNIFICANCE: Histamine suppresses apo A-I gene expression in hepatocytes via the histamine H1 receptor by elevating NF-κB expression and binding to the apo A-I promoter.
AIMS: Earlier it had been found by us that apolipoprotein A-I (apo A-I) is suppressed by histamine in HepG2 cells. Histamine has been shown to regulate NF-κB activity, though not in hepatocytes. Therefore we examined the role of the histamine receptors and NF-κB in histamine-mediated apo A-I gene expression in HepG2 liver cells. MAIN METHODS: The effect of histamine on histamine H1 receptor expression, and NF-κB p65 and p50 subunits was examined by Western blot. Histamine H1 receptor involvement was examined by loss-of-function (via siRNA) and gain-of-function studies overexpressing the histamine H1 receptor. The requirement for the p65 subunit of NF-κB for histamines effect was elucidated by loss-of-function studies (siRNA). Finally, the effect of histamine on NF-κB binding to the apo A-I gene promoter was examined by chromatin immunoprecipitation. KEY FINDINGS: Treatment of HepG2 cells with histamine had no effect on histamine H1 receptor expression. However, treatment with histamine increased NF-κB p65 and p50 subunit expression significantly. At low levels, the exogenous histamine H1 receptor plasmid suppressed apo A-I gene promoter activity while addition of higher levels of plasmid DNA actually increased apo A-I gene promoter activity. Inhibition of NF-κB activity with SN50 prevented histamine from repressing apo A-I promoter activity as did silencing p65 expression via siRNA. Finally, treatment with histamine increased binding of the p65 subunit of NF-κB to the apo A-I gene promoter. SIGNIFICANCE: Histamine suppresses apo A-I gene expression in hepatocytes via the histamine H1 receptor by elevating NF-κB expression and binding to the apo A-I promoter.
Authors: Violeta G Trusca; Madalina Dumitrescu; Ioana M Fenyo; Irina F Tudorache; Maya Simionescu; Anca V Gafencu Journal: Int J Mol Sci Date: 2019-12-12 Impact factor: 5.923