Dougan Stephanie K, Rava Paul, Hussain M Mahmood, Blumberg Richard S
Gastroenterology Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA.
J Exp Med. 2007 Mar 19;204(3):533-45. doi: 10.1084/jem.20062006. Epub 2007 Feb 20.
Microsomal triglyceride transfer protein (MTP), an endoplasmic reticulum lipid transfer protein critical for apolipoprotein B (apoB) secretion, regulates CD1d antigen presentation. We identified MTP variant 1 (MTPv1), a novel splice variant of mouse MTP, by polymerase chain reaction and Northern analysis in non-apoB-secreting tissues, including thymocytes and antigen-presenting cells (APCs). Edman degradation of MTPv1 isolated from transfected cells revealed three unique residues; however, recombinant MTP and MTPv1 had an equivalent protein disulfide isomerase association, subcellular localization, triglyceride transfer, phospholipid transfer, response to inhibitors, and ability to support apoB secretion. MTP and MTPv1 efficiently transferred phosphatidylethanolamine to CD1d in vitro. NKT cells fail to develop in fetal thymic organ culture (FTOC) treated with MTP antagonists. MTP-inhibited FTOCs produced negligible numbers of CD1d tetramer-positive cells and exhibited marked defects in IL-4 production upon stimulation with anti-CD3 or alpha-galactosylceramide-pulsed APCs. CD1d expression on CD4(+)CD8(+) FTOC cells was unaffected by MTP inhibition. Thus, our results demonstrate that MTPv1 in thymocytes is critical to NKT cell development. We hypothesize that, when MTP is inactive, CD1d traffics to the cell surface and presents no lipid or a lipid that is incapable of mediating NKT cell selection and/or is refractory to lysosomal editing.
微粒体甘油三酯转运蛋白（MTP）是一种对载脂蛋白B（apoB）分泌至关重要的内质网脂质转运蛋白，它调节CD1d抗原呈递。我们通过聚合酶链反应和Northern分析，在包括胸腺细胞和抗原呈递细胞（APC）在内的非apoB分泌组织中鉴定出MTP变体1（MTPv1），这是小鼠MTP的一种新型剪接变体。对从转染细胞中分离出的MTPv1进行埃德曼降解，发现了三个独特的残基；然而，重组MTP和MTPv1在蛋白质二硫键异构酶结合、亚细胞定位、甘油三酯转运、磷脂转运、对抑制剂的反应以及支持apoB分泌的能力方面相当。MTP和MTPv1在体外能有效地将磷脂酰乙醇胺转移到CD1d上。在用MTP拮抗剂处理的胎儿胸腺器官培养物（FTOC）中，自然杀伤T细胞（NKT细胞）无法发育。MTP抑制的FTOC产生的CD1d四聚体阳性细胞数量可忽略不计，并且在用抗CD3或α-半乳糖神经酰胺脉冲的APC刺激后，IL-4产生存在明显缺陷。MTP抑制对CD4(+)CD8(+) FTOC细胞上的CD1d表达没有影响。因此，我们的结果表明，胸腺细胞中的MTPv1对NKT细胞发育至关重要。我们推测，当MTP无活性时，CD1d转运至细胞表面，且不呈现脂质或呈现一种无法介导NKT细胞选择和/或对溶酶体编辑具有抗性的脂质。
