Sterol regulatory element-binding proteins are negatively regulated through SUMO-1 modification independent of the ubiquitin/26 S proteasome pathway.
Sterol regulatory element-binding proteins (SREBPs) are major transcription factors that activate the genes involved in cholesterol and fatty acid biosynthesis. We here report that the nuclear forms of SREBPs are modified by the small ubiquitin-related modifier (SUMO)-1. Mutational analyses identified two major sumoylation sites (Lys(123) and Lys(418)) in SREBP-1a and a single site (Lys(464)) in SREBP-2. Mutant SREBPs lacking one or two sumoylation sites exhibited increased transactivation capacity on an SREBP-responsive promoter. Overexpression of SUMO-1 reduced whereas its dominant negative form increased mRNA levels of SREBP-responsive genes. Nuclear SREBPs interacted with the SUMO-1-conjugating enzyme Ubc9, and overexpression of a dominant negative form of Ubc9 increased the mRNA levels of SREBP-responsive genes. Pulse-chase experiments revealed that sumoylation did not affect the degradation of SREBPs through the ubiquitin-proteasome pathway. In vitro ubiquitylation assay showed no competition between ubiquitin and SUMO-1 for the same lysine. Considered together, our results indicate that SUMO-1 modification suppresses the transactivation capacity of nuclear SREBPs in a manner different from the negative regulatory mechanism mediated by proteolysis.
Hirano
Yuko
Y
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo 113-8657, Japan.
Murata
Shigeo
S
Tanaka
Keiji
K
Shimizu
Makoto
M
Sato
Ryuichiro
R
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D025801:Ubiquitin / Q000378:metabolism
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; D025842:SUMO-1 Protein; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D014157:Transcription Factors; D025801:Ubiquitin; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease