CCAAT/enhancer-binding protein beta isoforms and the regulation of alpha-smooth muscle actin gene expression by IL-1 beta.
The role of IL-1beta in inflammation is amply documented, but its ability to inhibit myofibroblast differentiation and, in particular, the suppression of alpha-smooth muscle actin (alpha-SMA) gene expression is less well understood. Because IL-1beta can induce C/EBPbeta expression, the role of C/EBPbeta isoforms in IL-1beta regulation of alpha-SMA gene expression was investigated in rat lung myofibroblasts. The results showed that IL-1beta inhibited alpha-SMA expression in a dose-dependent manner, which was associated with stimulation of the expression of both C/EBPbeta isoforms, liver-enriched activating protein (LAP) and liver-enriched inhibitory protein (LIP). However, a greater increase in LIP relative to LAP expression resulted in a reduced LAP/LIP ratio after IL-1beta treatment. Transfection with an LAP-expressing plasmid stimulated, whereas an LIP-expressing plasmid inhibited, alpha-SMA expression. Cells from C/EBPbeta-deficient mice had reduced levels of alpha-SMA expression and promoter activity, which failed to respond to IL-1beta treatment. Sequence analysis identified the presence of a C/EBPbeta consensus binding sequence in the alpha-SMA promoter, which, when mutated, resulted in diminished promoter activity and abolished its responsiveness to IL-1beta treatment. EMSA revealed binding of C/EBPbeta to this C/EBPbeta consensus binding sequence from the alpha-SMA promoter. Finally, IL-1beta enhanced the expression of eukaryotic initiation factor 4E, a stimulator of LIP expression, which may account for a mechanism by which IL-1beta could alter the LAP/LIP ratio. These data taken together suggest that C/EBPbeta isoforms regulate alpha-SMA gene expression, and that its inhibition by IL-1beta was due to preferential stimulation of LIP expression.
Hu
Biao
B
Department of Pathology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Wu
Zhe
Z
Jin
Hong
H
Hashimoto
Naozumi
N
Liu
Tianju
T
Phan
Sem H
SH
D000199:Actins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000096:biosynthesis / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D002478:Cells, Cultured; D016384:Consensus Sequence; D039561:Eukaryotic Initiation Factor-4E / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D005260:Female; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism; D005786:Gene Expression Regulation / Q000276:immunology*; D007375:Interleukin-1 / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009130:Muscle, Smooth / Q000276:immunology / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D020033:Protein Isoforms / Q000096:biosynthesis / Q000172:deficiency / Q000378:metabolism / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D014162:Transfection
D000199:Actins; D022782:CCAAT-Enhancer-Binding Protein-beta; D039561:Eukaryotic Initiation Factor-4E; D007375:Interleukin-1; D020033:Protein Isoforms