Interleukin-6 signal transduction in human intestinal epithelial cells.
The gut is an important source of inflammatory cytokines, but there is scant information on the mechanisms of cytokine action in gut epithelium. We hypothesized that in human Caco-2 cells, IL-6 acts directly through stimulation of Stat phosphorylation and that bacterial lipopolysaccharide (LPS) causes Stat activation indirectly because of its ability to cause the autocrine secretion and action of interleukin (IL)-6. Stat1, Stat5a, and Stat5b, but not Stat3, were detected in Caco-2 cells. DNA-binding activity corresponding to activated Stat5 was stimulated in a biphasic manner by IL-6, with a transient early phase, followed by sustained activation between 8 and 48 h. LPS also stimulated Stat5-like binding, but there was no early phase of activation. Functional tests of Stat5 activation showed that IL-6 stimulated Stat5-dependent reporter gene transcription but had no effect on Stat1-dependent transcription. LPS did not stimulate Stat-dependent transcription, nor did it alter the transcriptional response to IL-6. Tyrosine phosphorylation of both Stat5a and Stat5b was induced by IL-6. We infer from these data that IL-6 acts on intestinal epithelia through a Stat5-mediated transcriptional mechanism, whereas LPS does not induce gene expression through autocrine activation of enterocyte Stat signaling. These data provide a basis for testing the in vivo regulation of gut signaling and the interaction of gut reticuloendothelial cells with epithelial signal transduction.
Pratt
S L
SL
Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Ohio 45267-0576, USA.
Ogle
C K
CK
Mao
J X
JX
Zhao
W
W
Lovell
G
G
Horseman
N D
ND
D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis / Q000235:genetics; D003110:Colonic Neoplasms / Q000473:pathology; D004268:DNA-Binding Proteins / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects* / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D017930:Genes, Reporter; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008894:Milk Proteins; D009363:Neoplasm Proteins / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D050794:STAT1 Transcription Factor; D050799:STAT5 Transcription Factor; D015398:Signal Transduction / Q000187:drug effects*; D015534:Trans-Activators / Q000502:physiology; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D004268:DNA-Binding Proteins; D015850:Interleukin-6; D008070:Lipopolysaccharides; D008894:Milk Proteins; D009363:Neoplasm Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494095:STAT5B protein, human; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; D015500:Chloramphenicol O-Acetyltransferase