Transcriptional regulation of the junB promoter: analysis of STAT-mediated signal transduction.
The product of the junB gene is a member of the AP-1 family of transcription factors that activate transcription by binding to TPA-responsive elements (TREs) within the promoters of target genes. Components of AP-1 are immediate-early genes whose expression is upregulated by a plethora of extracellular stimuli and are important in mediating cellular proliferation and differentiation. Such stimuli include the pleiotropic cytokine interleukin-6 (IL-6) which plays a role in immune and inflammatory responses and ciliary neurotrophic factor (CNTF) which enhances survival and differentiation of neurons and glia. We have analysed expression from junB promoter-CAT reporter constructs in HepG2 cells and found that a region between -196 and -91 can mediate response to IL-6 and CNTF and was able to confer responsiveness to a heterologous promoter. We further show by gel retardation analysis that distinct nuclear factors induced by IL-6 specifically bind to this interleukin-6 response element (IRE). This region contains both a putative ETS- and a STAT-transcription factor binding site. We show by mutational analysis and supershift data that the IL-6 induced complex indeed contains the transcription factor APRF/Stat3 that is both necessary and sufficient for activation. Interestingly this site does not appear to bind Stat1 itself, as shown by supershift analysis and a lack of response to IFN-gamma both at the DNA-binding and transcriptional level. Furthermore, we demonstrate that the junB IRE-binding activity induced by IL-6 requires tyrosine kinase activity, whereas induced transactivation of IRE-constructs additionally occurs through an H7-sensitive pathway that is p21ras-independent, implicating serine/threonine kinases in the transactivation of IRE-binding factors.
Coffer
P
P
Hubrecht Laboratory for Developmental Biology, Utrecht, The Netherlands.
Lutticken
C
C
van Puijenbroek
A
A
Klop-de Jonge
M
M
Horn
F
F
Kruijer
W
W
D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D016758:Genes, jun; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D051379:Mice; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D015850:Interleukin-6; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D007371:Interferon-gamma; D004247:DNA; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)