CHARACTERIZATION OF CELL SURFACE MOLECULES IMPORTANT FOR IMMUNE FUNCTION

虽然整合素受体已被证明在成熟胸腺细胞和T细胞上作为共刺激分子起作用，但尚不清楚这些受体是否能在未成熟胸腺细胞上作为共刺激分子起作用。先前的研究表明，α 4和α 5整合素在未成熟的、成年的CD4- CD8-胸腺细胞中的表达明显高于成熟的胸腺细胞或T细胞，这表明这些受体参与了早期胸腺细胞的发育。我们已经证明，第16天胎儿胸腺细胞表达的α 4和α 5水平与成人CD4- CD8胸腺细胞相当。研究发现，固定的纤维连接蛋白（α 4和α 5整合素的配体）可增强这些胎儿胸腺细胞的cd3依赖性增殖。在IL-7存在的情况下，增殖反应的幅度随着孵育时间的延长而增加，导致γ δ胸腺细胞的百分比急剧增加。针对α 4和α 5的可溶性抗体消除了纤维连接蛋白对增殖的增强作用，而针对α 4和α 5的固定单抗取代了纤维连接蛋白对CD3依赖性增殖的增强作用，这表明α 4和α 5整合素对纤维连接蛋白增强增殖负责。抗- α 4单抗可使胎儿胸腺细胞增殖增强100%，而抗- α 5单抗和抗cd28单抗可使增殖增强25%。其他共刺激分子，如CD2、FcR γ和Thy-1，对第16天胎儿胸腺细胞的CD3依赖性增殖没有影响。在另一项研究中，当检测肝癌细胞的核提取物与磷酸丙酮酸羧激酶-胞质（PEPCK-C）启动子中发现的cAMP反应元件的结合时，观察到几种蛋白质-核酸复合物。虽然cAMP反应元件结合蛋白和CCAAT/增强子结合蛋白α和β已被确定为结合该基序的肝脏因子，但也观察到一种未表征的、迁移速度较慢的复合物。我们确定了激活转录因子-2 （ATF-2）是该复合体的因子，并表明ATF-2刺激PEPCK-C启动子的表达。ATF-2是一种碱性亮氨酸拉链转录因子和应激激活蛋白激酶的靶标。我们证明p38 β -丝裂原活化蛋白（MAP）激酶增强了PEPCK-C启动子上的ATF-2反式活化活性，这与PEPCK-C启动子活性在胁迫下通过p38 MAP激酶依赖途径维持的解释一致。在这方面，我们发现用亚砷酸钠（一种已知的p38 MAP激酶激活剂）处理也可以刺激PEPCK启动子的表达。-整合素、共刺激分子、细胞粘附、转录因子、基因调控、胸腺分化、纤维连接蛋白

Although integrin receptors have been shown to function as costimulatory molecules on mature thymocytes and T cells, it was not known whether these receptors could function as costimulatory molecules on immature thymocytes. Previous studies have shown that the expression of alpha 4 and alpha 5 integrins were significantly higher on immature, adult CD4- CD8- thymocytes than on either mature thymocytes or T cells, suggesting that these receptors are involved in early thymocyte development. We have shown that day 16 fetal thymocytes express levels of alpha 4 and alpha 5 equivalent to those of adult CD4- CD8- thymocytes. Immobilized fibronectin, a ligand for alpha 4 and alpha 5 integrins, was found to enhance the CD3-dependent proliferation of these fetal thymocytes. In the presence of IL-7, the magnitude of the proliferative response increased with time of incubation, resulting in a dramatic increase in the percentage of gamma delta thymocytes. The enhancement of proliferation by fibronectin was abrogated by soluble antibodies against alpha 4 and alpha 5, whereas immobilized mAb to alpha 4 and alpha 5 substituted for fibronectin in enhancing CD3- dependent proliferation, demonstrating that alpha 4 and alpha 5 integrins were responsible for the enhanced proliferation by fibronectin. Anti-alpha 4 mAb enhanced proliferation of fetal thymocytes by 100%, whereas anti-alpha 5 mAb and anti-CD28 mAb enhanced proliferation by 25%. Other costimulatory molecules, such as CD2, FcR gamma, and Thy-1, had no effect on the CD3 dependent proliferation of day 16 fetal thymocytes.In another study, several protein-nucleic acid complexes were observed when nuclear extracts from hepatoma cells were assayed for binding to the cAMP response element found in the phosphenolpyruvate carboxykinase-cytosolic (PEPCK-C) promoter. Although cAMP response element-binding protein and CCAAT/enhancer binding proteins alpha and beta have been identified as liver factors that bind this motif, an uncharacterized, slower migrating complex was also observed. We identified activating transcription factor-2 (ATF-2) as the factor in this complex and showed that ATF-2 stimulates expression from the PEPCK-C promoter. ATF-2 is a basic-leucine zipper transcription factor and a target for stress-activated protein kinases. We demonstrated that p38 beta mitogen-activated protein (MAP) kinase augments ATF-2 transactivation activity on the PEPCK-C promoter, which is consistent with the interpretation that PEPCK-C promoter activity is maintained under stress through a p38 MAP kinase dependent pathway. In this regard, we showed that treatment with sodium arsenite, a known activator of p38 MAP kinases, also stimulates expression from the PEPCK promoter. - Integrins, costimulatory molecules, cell adhesion, transcription factors, gene regulation, thymic differentiation, fibronectin