Journal of Cellular Biochemistry

Inhibition of Apolipoprotein A-I Expression by TNF-Alpha in HepG2 Cells: Requirement for c-jun

Authors

  • Shant Parseghian,

    1. Division of Endocrinology, Diabetes, and Metabolism, Department of Internal Medicine, Saint Louis University, Saint Louis, Missouri
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  • Luisa M. Onstead-Haas,

    1. Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida College of Medicine, Jacksonville, Florida
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  • Norman C.W. Wong,

    1. Departments of Medicine and Biochemistry & Molecular Biology, University of Calgary, Calgary, Alberta, T2N 4N1, Canada
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  • Arshag D. Mooradian,

    1. Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida College of Medicine, Jacksonville, Florida
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  • Michael J. Haas

    Corresponding author
    1. Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida College of Medicine, Jacksonville, Florida
    • Correspondence to: Michael J. Haas, PhD, Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Florida College of Medicine, 653-1 West Eighth Street, L14, Jacksonville, FL 32209.

      E-mail: michael.haas@jax.ufl.edu

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  • The authors have no conflicts of interest to declare.

ABSTRACT

Tumor necrosis factor alpha (TNF α) signals in part through the mitogen activated protein (MAP) kinase c-jun-N-terminal kinase (JNK). Activation of JNK has been shown to promote insulin resistance and dyslipidemia, including reductions in plasma high-density lipoprotein (HDL) and apolipoprotein A-I (apo A-I). To examine how TNF α-mediated JNK activation inhibits hepatic apo A-I production, the effects of c-jun activation on apo A-I gene expression were examined in HepG2 cells. Apo A-I gene expression and promoter activity were measured by Northern and Western blotting and transient transfection. Transient transfection and siRNA were used to specifically over-express or knockout c-jun, c-jun-N-terminal kinase-1 and -2 (JNK1 and JNK2, respectively) and mitogen-activated protein kinase-4 (MKK4). TNF α-treatment of HepG2 cells induced rapid phosphorylation of c-jun on serine 63. In cells treated with phorbol-12-myristate-13-acetate (PMA), apo A-I gene promoter activity was inhibited and apo A-I mRNA content and apo A-I protein secretion decreased. Likewise, over-expression of JNK1 and JNK2 inhibited apo A-I promoter activity. Over-expression of constitutively active MKK4, an upstream protein kinase that directly activates JNK, also inhibited apo A-I promoter activity, while over-expression of a dominant-negative MKK4 de-repressed apo A-I promoter activity in TNF α-treated cells. Inhibition of c-jun synthesis using siRNA but not a control siRNA prevented TNF α-mediated inhibition of apo A-I. These results suggest that the MKK4/JNK/c-jun signaling pathway mediates TNF α-dependent inhibition of apo A-I synthesis. J. Cell. Biochem. 115: 253–260, 2014. © 2013 Wiley Periodicals, Inc.

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