De Windt Aloys, Rai Myriam, Bernier Lise, Thelen Karin, Soini Juhani, Lefebvre Chantal, Chintawar Satyan, Lavigne Jacques, Saarinen Lilli, Kytömäki Leena, Munzer Jon Scott, Lütjohann Dieter, Pandolfo Massimo, Davignon Jean, Seidah Nabil G, Laaksonen Reijo
Department of Neurology, Free University of Brussels, Brussels, Belgium.
DNA Cell Biol. 2007 Nov;26(11):765-72. doi: 10.1089/dna.2007.0624.
Sterol regulatory element-binding proteins (SREBPs) are transcription factors governing transcription of genes related to cholesterol and fatty acid metabolism. To become active, SREBPs must undergo a proteolytic cleavage to allow an active NH(2)-terminal segment to translocate into the nucleus. SKI-1/S1P is the first protease in the proteolytic activation cascade of SREBPs. SREBP inhibition may be useful, for example, in the treatment of liver steatosis caused by homocysteine-induced lipid synthesis. Accordingly, we overexpressed inhibitory prodomains (proSKI) of SKI-1/S1P in HepG2 cells to block SREBP activation to evaluate the potential of SKI-1/S1P in controlling cellular cholesterol synthesis. SKI-1/S1P inhibition resulted in reduced cholesterol synthesis and mRNA levels of the rate-limiting enzymes, HMG-CoA reductase and squalene epoxidase, in the cholesterol synthetic pathway. The inhibitory effect was maintained in the presence of homocysteine-induced endoplasmic reticulum stress. A gene set enrichment analysis was performed to elucidate other metabolic effects caused by SKI-1/S1P inhibition. SKI-1/S1P inhibition was observed to affect a number of other metabolic pathways, including glycolysis and citric acid cycle. These results demonstrate that inhibition of SREBPs decreases cholesterol synthesis in HepG2 cells both in the absence and presence of homocysteine. SKI-1/S1P inhibition may cause widespread changes in other key metabolic pathways.
固醇调节元件结合蛋白（SREBPs）是调控与胆固醇和脂肪酸代谢相关基因转录的转录因子。为了激活，SREBPs必须经历蛋白水解切割，以使活性氨基末端片段易位进入细胞核。SKI-1/S1P是SREBPs蛋白水解激活级联反应中的首个蛋白酶。例如，SREBP抑制在治疗由同型半胱氨酸诱导的脂质合成所引起的肝脂肪变性中可能有用。因此，我们在HepG2细胞中过表达SKI-1/S1P的抑制性前结构域（proSKI）以阻断SREBP激活，从而评估SKI-1/S1P在控制细胞胆固醇合成中的潜力。SKI-1/S1P抑制导致胆固醇合成以及胆固醇合成途径中限速酶HMG-CoA还原酶和角鲨烯环氧化酶的mRNA水平降低。在同型半胱氨酸诱导的内质网应激存在的情况下，抑制作用得以维持。进行了基因集富集分析以阐明由SKI-1/S1P抑制引起的其他代谢效应。观察到SKI-1/S1P抑制会影响许多其他代谢途径，包括糖酵解和柠檬酸循环。这些结果表明，在不存在和存在同型半胱氨酸的情况下，SREBPs的抑制均会降低HepG2细胞中的胆固醇合成。SKI-1/S1P抑制可能会导致其他关键代谢途径发生广泛变化。
