Mechanism of externalization of phagocytosis markers in apoptotic cells

磷脂酰丝氨酸在细胞凋亡中的外化机制为了阐明膜磷脂磷脂酰丝氨酸(PS)从膜双层的内叶转移到外叶并作为吞噬标志物的机制，我们检测了负责PS在凋亡细胞中定位的候选酶的数量和活性的变化。我们已经克隆了一个编码推测的氨基磷脂转位酶的基因，并获得了其他候选酶，但它们都被证明与目的酶无关。因此，我们放弃了这个项目。候选新型吞噬标记的分析我们产生了一种名为PH2的单抗，它可以抑制巨噬细胞对凋亡细胞的吞噬。因此，PH2识别的抗原被认为是一种新的吞噬标记。然后我们对PH2抗原进行了鉴定，发现它由蛋白质组成，并定位于正常细胞的膜结构。此外，在反式高尔基体中可检测到该抗原的某些部分。这些结果表明，PH2抗原经历了膜泡运输，并在细胞凋亡诱导下暴露在细胞表面。核糖体蛋白在凋亡骨痂中的外部化我们确定了核糖体在凋亡过程中的结构变化。当分析79种人核糖体蛋白中的28种时，发现3种蛋白质在凋亡细胞中从核糖体中降解和释放。此外，6种核糖体蛋白在细胞凋亡时出现在细胞表面。这些结果表明，在细胞凋亡过程中，一些核糖体蛋白从核糖体移动到细胞表面，并作为吞噬标记。

Mechanism of phosphatidylserine externalization in apoptotic cellsIn order to elucidate the mechanism by which the membrane phospholipid phosphatidylserine (PS) translocates from the inner to the outer leaflet of the membrane bilayer and serves as a phagocytosis marker, we examined changes in the amount and activity of candidate enzymes responsible for the localization of PS in apoptotic cells. We have cloned a gene coding for presumed amino phospholipid translocase and obtained other candidate enzymes, but all of them turned out to be unrelated to the aimed enzymes. We thus gave up this project.Analysis of candidate novel phagocytosis markerWe generated a monoclonal antibody named PH2 that inhibits macrophage phagocytosis of apoptotic cells. The antigen recognized by PH2 was thus considered to be a novel phagocytosis marker. We then characterized the PH2 antigen and found that it consists of protein and is localized to the membranous structures in normal cells. Furthermore, some fractions of the antigen was detectable in trans-Golgi. These results suggest that the PH2 antigen undergoes membrane vesicle transport and is exposed to cell surface upon apoptosis induction.Externalization of ribosomal proteins in apoptotic callsWe determined structural change of ribosomes during apoptosis. When 28 out of 79 kinds of human ribosomal proteins were analyzed, 3 proteins were found to be degraded and released from ribosomes in apoptotic cells. In addition, 6 ribosomal proteins became detectable on cell surface upon apoptosis. These results suggest that some ribosomal proteins move from the ribosome to cell surface during apoptosis and serve as phagocytosis markers.