Mathur S N, Born E, Murthy S, Field F J
Department of Internal Medicine, University of Iowa and Veterans Administration, Iowa City 52242, USA.
J Lipid Res. 1997 Jan;38(1):61-7.
As microsomal triglyceride transfer protein (MTP) is required for the assembly and secretion of apoB-containing lipoproteins by intestinal epithelial cells, the characterization and regulation of MTP in human intestinal cells, CaCo-2, was studied. CaCo-2 cells express MTP mRNA of 4.2 kb and a 97 kDa subunit of MTP protein. Similar to the expression of apoB mRNA, MTP mRNA expression was dependent upon cell differentiation and was directly related to the ability of the cells to assemble and secrete apoB-containing lipoproteins. MTP mRNA expression was highest in fully differentiated cells, with small but detectable amounts found in undifferentiated cells. Under conditions of increased apoB secretion by oleic acid, phosphatidylcholine, or lysophosphatidylcholine, MTP mass, MTP activity, and MTP gene expressions were not altered. In cells treated with calcium ionophore or phorbol 12-myristate 13-acetate, no relationship could be established between apoB secretion and MTP mRNA or activity. Similarly, in cells treated with sphingomyelinase, trifluoperazine, verapamil, okadaic acid, vanadate, or monensin, agents that decrease apoB secretion, no corresponding decrease in MTP activity or mass was observed. The results suggest that the various mediators of apoB secretion alter steps in lipoprotein assembly and secretion that are not dependent on MTP activity. CaCo-2 cells have an abundant supply of MTP for the assembly of lipoproteins when apoB secretion is stimulated by dietary lipids.
由于微粒体甘油三酯转移蛋白（MTP）是肠上皮细胞组装和分泌含载脂蛋白B（apoB）脂蛋白所必需的，因此对人肠细胞CaCo-2中MTP的特性和调节进行了研究。CaCo-2细胞表达4.2 kb的MTP mRNA和97 kDa的MTP蛋白亚基。与apoB mRNA的表达相似，MTP mRNA的表达依赖于细胞分化，并且与细胞组装和分泌含apoB脂蛋白的能力直接相关。MTP mRNA表达在完全分化的细胞中最高，在未分化的细胞中也有少量但可检测到的表达。在油酸、磷脂酰胆碱或溶血磷脂酰胆碱增加apoB分泌的条件下，MTP质量、MTP活性和MTP基因表达没有改变。在用钙离子载体或佛波醇12-肉豆蔻酸酯13-乙酸酯处理的细胞中，apoB分泌与MTP mRNA或活性之间无法建立关系。同样，在用鞘磷脂酶、三氟拉嗪、维拉帕米、冈田酸、钒酸盐或莫能菌素处理的细胞中，这些物质会减少apoB分泌，但未观察到MTP活性或质量相应降低。结果表明，apoB分泌的各种介质改变了脂蛋白组装和分泌过程中不依赖于MTP活性的步骤。当饮食脂质刺激apoB分泌时，CaCo-2细胞有丰富的MTP供应用于脂蛋白的组装。
