Downregulation of hepatocyte nuclear factor-4alpha and its role in regulation of gene expression by TGF-beta in mammary epithelial cells.
We found that a specific isoform of hepatocyte nuclear factor 4alpha (HNF-4alpha), HNF-4alpha8, was expressed in mouse mammary epithelial NMuMG cells, and that its expression was repressed by TGF-beta. The repression was interfered by dominant negative forms of activin receptor-like kinase 5 (ALK5) and Smad3, and sensitive to cycloheximide, suggesting the involvement of additional protein(s) as well as ALK5 and Smad3 in the repression. Further study showed that high mobility group A2 (HMGA2), which is reported to be directly upregulated by Smads, repressed HNF-4alpha8 expression. Therefore, it is likely that HMGA2 mediates the downregulation of HNF-4alpha8 downstream of ALK5 and Smads To determine the significance of the downregulation of HNF-4alpha8 in TGF-beta signaling, we performed DNA microarray analysis and extracted a subgroup of TGF-beta1-regulated genes, including tenascin C and tissue inhibitor of metalloproteinase 3 (TIMP-3), whose regulation by TGF-beta1 was attenuated by forced expression of HNF-4alpha8. HMGA2 has recently emerged as a transcriptional organizer of TGF-beta signaling, regulating several key factors involved in epithelial-mesenchymal transition (EMT). In this study, we identified an isoform of HNF-4alpha as a new target downstream of HMGA2 and assigned a new role to HNF-4alpha in the TGF-beta signaling/transcriptional cascade driven by ALK5/Smad/HMGA2 and associated with the malignant transformation of cells.
Ishikawa
Fumihiro
F
Department of Microbiology, Showa University School of Pharmaceutical Sciences, Tokyo 142-8555, Japan.
Nose
Kiyoshi
K
Shibanuma
Motoko
M
D000818:Animals; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D015536:Down-Regulation; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology*; D005260:Female; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D025743:HMGA2 Protein / Q000235:genetics / Q000378:metabolism; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008321:Mammary Glands, Animal / Q000166:cytology*; D051379:Mice; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D012190:Retroviridae / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*
D025743:HMGA2 Protein; D051557:Hepatocyte Nuclear Factor 4; D020033:Protein Isoforms; D018125:Receptors, Transforming Growth Factor beta; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D053773:Transforming Growth Factor beta1; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; C000625841:TGFBR1 protein, human; C000625842:Tgfbr1 protein, mouse