Nuclear factor-κB mediates the inhibitory effects of tumor necrosis factor-α on growth hormone-inducible gene expression in liver

Mark D. Buzzelli, Murali Nagarajan, John F. Radtka, Margaret L. Shumate, Maithili Navaratnarajah, Charles H. Lang, Robert N. Cooney

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

TNF inhibits serine protease inhibitor 2.1 (Spi 2.1) and IGF-I gene expression by GH in CWSV-1 hepatocytes. The current study describes construction of a GH-inducible IGF-I promoter construct and investigates mechanisms by which TNF and nuclear factor-κB (NFκB) inhibit GH-inducible gene expression. CWSV-1 cells were transfected with GH-inducible Spi 2.1 or IGF-I promoter luciferase constructs, incubated with TNF signaling inhibitors (fumonisin B1 for sphingomyelinase and SP600125 for c-Jun N-terminal kinase), treated with or without TNF, and then stimulated with recombinant human GH. The 5- to 6-fold induction of Spi 2.1 and IGF-I promoter activity by GH was inhibited by TNF. Neither fumonisin B1 nor SP600125 prevented the inhibitory effects of TNF on GH-inducible promoter activity. Dominant-negative inhibitor-κBα (IκBα) expression vectors (IκBαS/A or IκBαTrunc), p65 and p50 expression vectors, and p65 deletion constructs were used to investigate the NFκB pathway. IκBαS/A and IκBαTrunc ameliorated the inhibitory effects of TNF on GH-inducible Spi 2.1 and IGF-I promoter activity. Cotransfection of CWSV-1 cells with expression vectors for p65 alone or p50 and p65 together inhibited GH-inducible Spi 2.1 and IGF-I promoter activity. Cotransfection with a C-terminal p65 deletion (1-450) enhanced GH-inducible promoter activity, whereas the N-terminal deletion (31-551) was inhibitory for IGF-I but not Spi 2.1. Cycloheximide did not antagonize the inhibitory effects of TNF on GH-inducible IGF-I expression. We conclude the inhibitory effects of TNF on GH-inducible promoter activity are mediated by NFκB, especially p65, by a mechanism that does not require protein synthesis.

Original languageEnglish (US)
Pages (from-to)6378-6388
Number of pages11
JournalEndocrinology
Volume149
Issue number12
DOIs
StatePublished - Dec 2008

All Science Journal Classification (ASJC) codes

  • Endocrinology

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