Inoue Jun, Miyata Shingo, Shimizu Makoto, Sato Ryuichiro
a Department of Agricultural Chemistry, Faculty of Applied Biosciences , Tokyo University of Agriculture , Tokyo , Japan.
b Food Biochemistry laboratory, Department of Applied Biological Chemistry , Graduate School of Agricultural and Life Sciences, The University of Tokyo , Tokyo , Japan.
Biosci Biotechnol Biochem. 2018 Sep;82(9):1591-1598. doi: 10.1080/09168451.2018.1478715. Epub 2018 May 26.
Sterol regulatory element-binding proteins (SREBPs) are transcription factors that regulate a wide variety of genes involved in fatty acid and cholesterol synthesis. In the present study, we identified that isoxanthohumol (IXN) suppressed SREBP activity. Low concentrations of IXN (10 and 30 μM) reduced the amount of mature forms of SREBPs, while high concentration of IXN (100 μM) reduced both precursor and mature forms of SREBPs in Huh-7 cells. The IXN-mediated decrease in the precursor forms of SREBPs in Huh-7 cells was completely abolished by culturing cells under sterol-supplemented conditions and was partly abolished by treatment with a proteasome inhibitor, MG132, but not a lysosome inhibitor, NHCl. Moreover, IXN accelerated the ubiquitination of the precursor forms of SREBP-1a. These results suggest that IXN suppresses SREBP activity, at least in part, via ubiquitin-proteasome-dependent degradation of the precursor forms of SREBPs.
ACC1: acetyl-CoA carboxylase 1; DMEM: Dulbecco's modified Eagle's medium; ER: endoplasmic reticulum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; 25-HC: 25-hydroxycholesterol; HMGCR: HMG-CoA reductase; HMGCS: HMG-CoA synthase; Insig: insulin-induced gene; IXN: isoxanthohumol; LPDS: lipoprotein-deficient serum; SCAP: SREBP cleavage-activating protein; SCD1: stearoyl-CoA desaturase; SREBPs: sterol regulatory element-binding proteins; XN: xanthohumol.
固醇调节元件结合蛋白（SREBPs）是一类转录因子，可调节多种参与脂肪酸和胆固醇合成的基因。在本研究中，我们发现异黄腐醇（IXN）可抑制SREBP活性。低浓度的IXN（10和30μM）可减少SREBPs成熟形式的量，而高浓度的IXN（100μM）可减少Huh-7细胞中SREBPs的前体和成熟形式。在补充固醇的条件下培养细胞可完全消除IXN介导的Huh-7细胞中SREBPs前体形式的减少，用蛋白酶体抑制剂MG132处理可部分消除这种减少，但用溶酶体抑制剂NHCl处理则不能。此外，IXN加速了SREBP-1a前体形式的泛素化。这些结果表明，IXN至少部分通过泛素-蛋白酶体依赖性降解SREBPs的前体形式来抑制SREBP活性。
ACC1：乙酰辅酶A羧化酶1；DMEM：杜氏改良 Eagle培养基；ER：内质网；GAPDH：甘油醛-3-磷酸脱氢酶；25-HC：25-羟基胆固醇；HMGCR：HMG-CoA还原酶；HMGCS：HMG-CoA合酶；Insig：胰岛素诱导基因；IXN：异黄腐醇；LPDS：脂蛋白缺乏血清；SCAP：SREBP裂解激活蛋白；SCD1：硬脂酰辅酶A去饱和酶；SREBPs：固醇调节元件结合蛋白；XN：黄腐醇。
