Ross R S, Hoeg J M, Higuchi K, Schumacher U K, Fojo S, Gregg R E, Brewer H B
Molecular Disease Branch, National Heart, Lung and Blood Institute, Bethesda, MD 20892.
Biochim Biophys Acta. 1989 Jul 17;1004(1):29-35. doi: 10.1016/0005-2760(89)90208-7.
Apolipoprotein (apo) B is the principal apolipoprotein of chylomicrons, very-low-density lipoproteins (VLDL) and low-density lipoproteins (LDL). Patients with homozygous hypobetalipoproteinemia (HBL), characterized by apoB deficiency, have markedly decreased levels of hepatocyte mRNA as well as intracellular B apolipoprotein, and a virtual absence of plasma apoB. We have cloned, sequenced and analyzed the 5' regulatory region of the human apoB gene from -899 to +121 bp in normal and hypobetalipoproteinemic subjects. TATA and CAAT boxes were located at -30 and -61, respectively, and two GC-like boxes were identified at positions +56 and +108. The analysis of the HBL sequence revealed two substitutions at positions -838 and -517, when compared to the normal sequence. These substitutions were not present in any known apoB regulatory elements. The transcriptional activities of the homozygous hypobetalipoproteinemic and normal regulatory regions were compared by chloramphenicol acetyltransferase (CAT) assays in Hep G2 cells, and were found to be the same. Therefore, we conclude that the 5' regulatory region of the HBL apoB gene in this kindred is normal, and the two base substitutions do not affect promoter activity of the apoB gene. These studies suggest that a coding region abnormality in the apoB gene may lead to HBL.
载脂蛋白（apo）B是乳糜微粒、极低密度脂蛋白（VLDL）和低密度脂蛋白（LDL）的主要载脂蛋白。纯合子低β脂蛋白血症（HBL）患者以apoB缺乏为特征，其肝细胞mRNA水平以及细胞内B载脂蛋白水平显著降低，且血浆apoB几乎缺失。我们已对正常和低β脂蛋白血症患者的人apoB基因5'调控区从-899至+121 bp进行了克隆、测序和分析。TATA盒和CAAT盒分别位于-30和-61处，并且在+56和+108位置鉴定出两个类GC盒。与正常序列相比，对HBL序列的分析揭示了在-838和-517位置有两个替换。这些替换不存在于任何已知的apoB调控元件中。通过氯霉素乙酰转移酶（CAT）测定法在Hep G2细胞中比较了纯合子低β脂蛋白血症和正常调控区的转录活性，发现二者相同。因此，我们得出结论，该家系中HBL apoB基因的5'调控区是正常的，这两个碱基替换不影响apoB基因的启动子活性。这些研究表明，apoB基因的编码区异常可能导致HBL。
