Tumor necrosis factor inhibits growth hormone-mediated gene expression in hepatocytes

Tamer Ahmed, Gladys Yumet, Margaret Shumate, Charles H. Lang, Peter Rotwein, Robert N. Cooney

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Growth hormone (GH) stimulates STAT5 phosphorylation by JAK2, which activates IGF-I and serine protease inhibitor 2.1 (Spi 2.1) transcription, whereas STAT5 dephosphorylation by protein tyrosine phosphatases (PTPs) terminates this signal. We hypothesized that the inhibitory effects of TNF on GH signaling and gene transcription were responsible for hepatic GH resistance. CWSV-1 hepatocytes were treated with TNF, pervanadate (a PTP inhibitor), or both, before GH stimulation. Total and tyrosine-phosphorylated JAK2, STAT5, ERK1/2, SHP-1 and SHP-2, IGF-I, and Spi 2.1 mRNA levels were measured. GH stimulated STAT5 and ERK1/2 phosphorylation, IGF-I, and Spi 2.1 mRNA expression. TNF attenuated JAK2/STAT5 and ERK1/2 phosphorylation and IGF-I and Spi 2.1 mRNA expression following GH stimulation. SHP-1 and SHP-2 protein levels were unaltered by TNF or GH, and the GH-induced increase in SHP-1 PTP activity was not further increased by TNF. In TNF-treated cells, pervanadate restored STAT5 and ERK1/2 phosphorylation to control levels following GH stimulation but did not restore IGF-I or Spi 2.1 mRNA induction. Cells transfected with a Spi 2.1 promoter-luciferase vector demonstrate a 50-fold induction in luciferase activity following GH stimulation or cotransfection with a constitutively active STAT5 vector. TNF prevented the induction of Spi 2.1 promoter activity by GH and the STAT5 construct. We conclude that TNF does not inhibit GH activity by inducing SHP-1 or -2 expression and that correction of GH signaling defects in TNF-treated cells by pervanadate does not restore GH-induced gene expression. The inhibitory effects of TNF on GH-mediated gene transcription appear independent of STAT5 activity and previously identified abnormalities in JAK2/STAT5 signaling.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Gastrointestinal and Liver Physiology
Volume291
Issue number1
DOIs
StatePublished - 2006

Fingerprint

Growth Hormone
Hepatocytes
Tumor Necrosis Factor-alpha
Gene Expression
Serine Proteinase Inhibitors
Insulin-Like Growth Factor I
Phosphorylation
Messenger RNA
Protein Tyrosine Phosphatases
Luciferases
Non-Receptor Type 6 Protein Tyrosine Phosphatase
STAT5 Transcription Factor
Genes
Tyrosine

Keywords

  • Growth hormone resistance
  • Insulin-like growth factor I
  • Serine protease inhibitor 2.1
  • STAT5

ASJC Scopus subject areas

  • Gastroenterology
  • Physiology

Cite this

Tumor necrosis factor inhibits growth hormone-mediated gene expression in hepatocytes. / Ahmed, Tamer; Yumet, Gladys; Shumate, Margaret; Lang, Charles H.; Rotwein, Peter; Cooney, Robert N.

In: American Journal of Physiology - Gastrointestinal and Liver Physiology, Vol. 291, No. 1, 2006.

Research output: Contribution to journalArticle

Ahmed, Tamer ; Yumet, Gladys ; Shumate, Margaret ; Lang, Charles H. ; Rotwein, Peter ; Cooney, Robert N. / Tumor necrosis factor inhibits growth hormone-mediated gene expression in hepatocytes. In: American Journal of Physiology - Gastrointestinal and Liver Physiology. 2006 ; Vol. 291, No. 1.
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AU - Cooney, Robert N.

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AB - Growth hormone (GH) stimulates STAT5 phosphorylation by JAK2, which activates IGF-I and serine protease inhibitor 2.1 (Spi 2.1) transcription, whereas STAT5 dephosphorylation by protein tyrosine phosphatases (PTPs) terminates this signal. We hypothesized that the inhibitory effects of TNF on GH signaling and gene transcription were responsible for hepatic GH resistance. CWSV-1 hepatocytes were treated with TNF, pervanadate (a PTP inhibitor), or both, before GH stimulation. Total and tyrosine-phosphorylated JAK2, STAT5, ERK1/2, SHP-1 and SHP-2, IGF-I, and Spi 2.1 mRNA levels were measured. GH stimulated STAT5 and ERK1/2 phosphorylation, IGF-I, and Spi 2.1 mRNA expression. TNF attenuated JAK2/STAT5 and ERK1/2 phosphorylation and IGF-I and Spi 2.1 mRNA expression following GH stimulation. SHP-1 and SHP-2 protein levels were unaltered by TNF or GH, and the GH-induced increase in SHP-1 PTP activity was not further increased by TNF. In TNF-treated cells, pervanadate restored STAT5 and ERK1/2 phosphorylation to control levels following GH stimulation but did not restore IGF-I or Spi 2.1 mRNA induction. Cells transfected with a Spi 2.1 promoter-luciferase vector demonstrate a 50-fold induction in luciferase activity following GH stimulation or cotransfection with a constitutively active STAT5 vector. TNF prevented the induction of Spi 2.1 promoter activity by GH and the STAT5 construct. We conclude that TNF does not inhibit GH activity by inducing SHP-1 or -2 expression and that correction of GH signaling defects in TNF-treated cells by pervanadate does not restore GH-induced gene expression. The inhibitory effects of TNF on GH-mediated gene transcription appear independent of STAT5 activity and previously identified abnormalities in JAK2/STAT5 signaling.

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