GSBS Student Publications

Title

Endotoxin-induced inhibition of growth hormone receptor signaling in rat liver in vivo

Student Author(s)

Timothy Fitzgibbons

GSBS Program

Interdisciplinary Graduate Program

UMMS Affiliation

Department of Cardiology; Department of Physiology

Date

12-1999

Document Type

Article

Medical Subject Headings

Animals; DNA-Binding Proteins; Endotoxins; Escherichia coli; Gene Expression; Human Growth Hormone; Janus Kinase 2; Liver; Male; *Milk Proteins; Phosphorylation; Phosphotyrosine; Protein-Tyrosine Kinases; Proteins; *Proto-Oncogene Proteins; RNA, Messenger; Rats; Rats, Sprague-Dawley; Receptors, Somatotropin; *Repressor Proteins; STAT5 Transcription Factor; *Signal Transduction; Suppressor of Cytokine Signaling Proteins; Trans-Activators; *Transcription Factors

Disciplines

Endocrinology | Physiology

Abstract

The bacterial lipopolysaccharide endotoxin induces a catabolic response characterized by resistance to multiple anabolic hormones. The objective of this study was to determine the effects of endotoxin on the GH signaling pathway in rat liver in vivo. After the iv injection of Escherichia coli endotoxin (1 mg/kg), there was a progressive decrease in liver STAT5 (signal transducer and activator of transcription-5) tyrosine phosphorylation in response to GH (40% decrease 6 h after endotoxin), which occurred in the absence of a change in abundance of the STAT5 protein. Endotoxin resulted in a rapid 40-fold increase in liver Janus family kinase-2 (JAK2) messenger RNA, followed by a 2-fold increase in JAK2 protein abundance. This was associated with a 50% decrease in phosphorylated/total JAK2 after GH stimulation. GH receptor abundance was unchanged, suggesting a postreceptor site of endotoxin-induced GH resistance. Rat complementary DNAs for three members of the suppressor of cytokine signaling gene family were cloned [cytokine-inducible sequence (CIS), suppressor of cytokine signaling-2 (SOCS-2), and SOCS-3] and, using these probes, messenger RNAs for SOCS-3 and CIS were shown to be increased 10- and 4-fold above control values, respectively, 2 h after endotoxin infusion. The finding of endotoxin inhibition of in vivo STAT5 tyrosine phosphorylation in response to a supramaximal dose of GH in the absence of a change in GH receptor abundance or total GH-stimulated JAK2 tyrosine phosphorylation provides the first demonstration of acquired postreceptor GH resistance. We hypothesize that this may occur through a specificity-spillover mechanism involving the induction of SOCS genes by cytokines released in response to endotoxin and subsequent SOCS inhibition of GH signaling.

Rights and Permissions

Citation: Endocrinology. 1999 Dec;140(12):5505-15.

Related Resources

Link to Article in PubMed

Journal Title

Endocrinology

PubMed ID

10579313