Kawabe Y, Suzuki T, Hayashi M, Hamakubo T, Sato R, Kodama T
Fuji-Gotemba Research Laboratories, Chugai Pharmaceutical Co., Ltd., Shizuoka, Japan.
Biochim Biophys Acta. 1999 Jan 4;1436(3):307-18. doi: 10.1016/s0005-2760(98)00119-2.
To clarify the role of the sterol regulatory element-binding protein-2 (SREBP-2), we established cell lines in which human SREBP-2(1-481) could be induced by isopropyl-beta-D-thiogalactopyranoside (IPTG). The range of IPTG-induced changes in SREBP-2(1-481) levels in '23-11' cells, one of these cell lines, was almost the same as that of sterol-induced changes in the levels of mature SREBP-2, indicating that IPTG was able to regulate the expression of SREBP-2(1-481) within the normal physiological range in this cell line. Sterols regulate the expression of the LDL receptor, HMG-CoA reductase, squalene synthase and fatty acid synthase in 23-11 cells as they also do in the parental cell line HeLa S3. IPTG increased mRNA levels of the LDL receptor and HMG-CoA reductase but not squalene synthase both in the presence or absence of excess sterols. Fatty acid synthase mRNA was increased 2 h after the IPTG addition in the absence of excess sterol (10% FBS), but was slightly increased 6 h after the IPTG addition in the presence of excess sterols. In the absence of excess sterols, both SREBP-2(1-481) and endogenous mature SREBP-2 exist in the nucleus. This suggests that an increased amount of SREBP-2 over the normal physiological range is required for the regulation of fatty acid synthase. IPTG increased both the surface binding of 125I-LDL and cholesterol biosynthesis from [14C]acetate significantly in a similar time course. In contrast, fatty acid biosynthesis from [14C]acetate was almost unchanged by IPTG during the same incubation period. These results suggest that physiological amounts of SREBP-2 play a key role in the regulation of cholesterol but not fatty acid metabolism.
为阐明固醇调节元件结合蛋白2（SREBP - 2）的作用，我们构建了能通过异丙基 - β - D - 硫代半乳糖苷（IPTG）诱导人SREBP - 2(1 - 481)表达的细胞系。在其中一个细胞系“23 - 11”细胞中，IPTG诱导的SREBP - 2(1 - 481)水平变化范围与固醇诱导的成熟SREBP - 2水平变化范围几乎相同，这表明IPTG能够在该细胞系的正常生理范围内调节SREBP - 2(1 - 481)的表达。与在亲代细胞系HeLa S3中一样，固醇在23 - 11细胞中调节低密度脂蛋白受体、3 - 羟基 - 3 - 甲基戊二酰辅酶A还原酶、角鲨烯合酶和脂肪酸合酶的表达。无论是否存在过量固醇，IPTG均可增加低密度脂蛋白受体和3 - 羟基 - 3 - 甲基戊二酰辅酶A还原酶的mRNA水平，但对角鲨烯合酶无影响。在无过量固醇（10%胎牛血清）时，IPTG添加后2小时脂肪酸合酶mRNA增加，但在有过量固醇时，IPTG添加后6小时脂肪酸合酶mRNA略有增加。在无过量固醇时，SREBP - 2(1 - 481)和内源性成熟SREBP - 2均存在于细胞核中。这表明在正常生理范围之上增加SREBP - 2的量是调节脂肪酸合酶所必需的。IPTG在相似的时间进程中显著增加了125I - 低密度脂蛋白的表面结合以及[14C]乙酸盐的胆固醇生物合成。相反，在相同孵育期内，IPTG对[14C]乙酸盐的脂肪酸生物合成几乎没有影响。这些结果表明，生理量的SREBP - 2在胆固醇而非脂肪酸代谢的调节中起关键作用。
