Miettinen A, Solin M L, Reivinen J, Juvonen E, Väisänen R, Holthöfer H
Division of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Finland.
Am J Pathol. 1999 Mar;154(3):813-22. doi: 10.1016/S0002-9440(10)65328-X.
Podocalyxin is a membrane protein of rat podocytes and endothelial cells. It has not been described in other cell types, and no amino acid or DNA sequence data are available about it. Here we show that podocalyxin antigens are present in rat platelets and megakaryocytes. In resting platelets, the antigens are mainly intracellular but become surface exposed after thrombin stimulation, as shown by immunofluorescence and flow cytometry. By Western blotting, platelet podocalyxin has an apparent Mr of 140,000. Cytocentrifuge slides of rat bone marrow show that anti-podocalyxin antibodies recognize large polyploid cells also expressing CD62P, indicating that the cells are megakaryocytes. From a rat glomerular cDNA library we isolated a clone covering the carboxyl-terminal nucleotides of rat podocalyxin. Its putative transmembrane or intracellular domains are 100% or >93% identical, respectively, with the human and rabbit podocalyxin-like proteins. The truncated extracellular domain extends to include two of the four conserved cysteines shared by podocalyxin-like proteins. By Northern blotting, a 5.5-kb renal cortical transcript is seen. By in situ hybridization, cRNA probes recognize podocytes, endothelial cells, and megakaryocytes, and by reverse transcription polymerase chain reaction, platelets are shown to contain podocalyxin mRNA. Our results show that rat podocalyxin is a homologue of the previously cloned podocalyxin-like proteins and suggest that also in mammals podocalyxin has a role in hematopoiesis, as previously shown in the chicken.
足突细胞蛋白是大鼠足细胞和内皮细胞的一种膜蛋白。尚未在其他细胞类型中发现该蛋白，也没有关于它的氨基酸或DNA序列数据。在此我们表明，足突细胞蛋白抗原存在于大鼠血小板和巨核细胞中。在静息血小板中，抗原主要位于细胞内，但在凝血酶刺激后会暴露于细胞表面，免疫荧光和流式细胞术结果显示了这一点。通过蛋白质印迹法，血小板足突细胞蛋白的表观分子量为140,000。大鼠骨髓细胞离心涂片显示，抗足突细胞蛋白抗体识别同时也表达CD62P的大的多倍体细胞，表明这些细胞是巨核细胞。我们从大鼠肾小球cDNA文库中分离出一个克隆，它覆盖了大鼠足突细胞蛋白的羧基末端核苷酸。其推测的跨膜或细胞内结构域与人及兔足突细胞蛋白样蛋白分别有100%或>93%的同源性。截短的细胞外结构域延伸至包括足突细胞蛋白样蛋白共有的四个保守半胱氨酸中的两个。通过Northern印迹法，可看到一个5.5 kb的肾皮质转录本。通过原位杂交，cRNA探针可识别足细胞、内皮细胞和巨核细胞，通过逆转录聚合酶链反应显示血小板含有足突细胞蛋白mRNA。我们的结果表明，大鼠足突细胞蛋白是先前克隆的足突细胞蛋白样蛋白的同源物，并提示在哺乳动物中，足突细胞蛋白也如先前在鸡中所显示的那样，在造血过程中发挥作用。
