Sumoylation of CCAAT/enhancer-binding protein alpha and its functional roles in hepatocyte differentiation.
The sumoylation of CCAAT/enhancer-binding proteins (C/EBPs) by small ubiquitin-related modifier-1 (SUMO-1) has been reported recently. In this study, we investigated the functional role of the sumoylation of C/EBPalpha in the differentiation of hepatocytes. The amount of sumoylated C/EBPalpha gradually decreased during the differentiation, which suggests that the sumoylation is important for the control of growth/differentiation especially in the fetal liver. To analyze the function of the sumoylation of C/EBPalpha in liver-specific gene expression, we studied its effects on the expression of the albumin gene. The C/EBPalpha-mediated transactivation of the albumin gene was reduced by sumoylation of C/EBPalpha in primary fetal hepatocytes. The enhancement of C/EBPalpha-mediated transactivation by BRG1, a core subunit of the SWI/SNF chromatin remodeling complex, was hampered by sumoylation in a luciferase reporter assay. In addition, we discovered that sumoylation of C/EBPalpha blocked its inhibitory effect on cell proliferation by leading to the disruption of a proliferation-inhibitory complex because of a failure of the sumoylated C/EBPalpha to interact with BRG1. BRG1 was recruited to the dihydrofolate reductase promoter in nonproliferating C33a cells but was not detected in proliferating cells where C/EBPalpha, BRG1, and SUMO-1 were overexpressed. This result suggests that BRG1 down-regulates the expression of the dihydrofolate reductase gene. These findings provide the insight that SUMO acts as a space regulator, which affects protein-protein interactions.
Sato
Yoshitaka
Y
Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
Miyake
Katsuhide
K
Ecotopia Science Institute, Nagoya University, Nagoya 464-8603, Japan. Electronic address: miyake@proc.nubio.nagoya-u.ac.jp.
Kaneoka
Hidenori
H
Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
Iijima
Shinji
S
Department of Biotechnology, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan.
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D005333:Fetus; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology*; D008099:Liver / Q000166:cytology; D008297:Male; D011485:Protein Binding; D051381:Rats; D017207:Rats, Sprague-Dawley; D025842:SUMO-1 Protein / Q000378:metabolism* / Q000502:physiology; D012709:Serum Albumin / Q000235:genetics; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics; D014157:Transcription Factors / Q000502:physiology
D022763:CCAAT-Enhancer-Binding Protein-alpha; D025842:SUMO-1 Protein; D012709:Serum Albumin; D014157:Transcription Factors; D013762:Tetrahydrofolate Dehydrogenase