Oshima R G
J Biol Chem. 1982 Apr 10;257(7):3414-21.
Murine extra-embryonic endodermal cell lines derived from either teratocarcinomas or mouse embryos contain a cytoskeletal protein (Endo A) of Mr = 55,000. Endo A was immunoprecipitated from [35S]methionine-labeled lysates of three parietal endodermal cell lines, A presumptive visceral endodermal cell line, and a fetal hepatoma cell line, but not from fibroblasts, myoblasts, erythroleukemic cells, neuroblastoma cells, keratinocytes, or embryonal carcinoma cells. Embryonal carcinoma cells induced to differentiate by exposure to retinoic acid synthesized increased amounts of Endo A approximately 48 h after exposure to the inducer. Two-dimensional gel analysis of immunoprecipitated samples confirmed that Endo A is distinct from vimentin and murine keratinocyte proteins recognized by two different keratin antisera. Comparison by two-dimensional gel electrophoresis of immunoprecipitated Endo A labeled with either [35S]methionine or [32P]orthophosphate indicated that the multiple forms of Endo A resolved by isoelectric focusing were due, at least in part, to phosphorylation. Serine was identified as the phosphorylated amino acid. Endo A was the only major antigenic protein found in a parietal endodermal cell line which was recognized by a monoclonal antibody prepared by other investigators against trophoblast cytoskeletons. The results indicate that Endo A, like the previously described Endo B protein, is distinct from other cytoskeletal proteins and will be useful as a marker of the differentiation of murine embryonal carcinoma cells to extra-embryonic endoderm.
源自畸胎瘤或小鼠胚胎的小鼠胚外内胚层细胞系含有一种分子量为55,000的细胞骨架蛋白（内胚层蛋白A）。从三个壁层内胚层细胞系、一个假定的脏层内胚层细胞系和一个胎儿肝癌细胞系的[35S]甲硫氨酸标记裂解物中免疫沉淀出了内胚层蛋白A，但在成纤维细胞、成肌细胞、红白血病细胞、神经母细胞瘤细胞、角质形成细胞或胚胎癌细胞中未检测到。通过暴露于视黄酸诱导分化的胚胎癌细胞在暴露于诱导剂后约48小时合成了增加量的内胚层蛋白A。免疫沉淀样品的二维凝胶分析证实，内胚层蛋白A与波形蛋白以及两种不同角蛋白抗血清识别的小鼠角质形成细胞蛋白不同。用[35S]甲硫氨酸或[32P]正磷酸盐标记的免疫沉淀内胚层蛋白A的二维凝胶电泳比较表明，通过等电聚焦分离的内胚层蛋白A的多种形式至少部分是由于磷酸化所致。丝氨酸被鉴定为磷酸化氨基酸。内胚层蛋白A是在壁层内胚层细胞系中发现的唯一主要抗原蛋白，该细胞系可被其他研究人员制备的针对滋养层细胞骨架的单克隆抗体识别。结果表明，内胚层蛋白A与先前描述的内胚层蛋白B一样，与其他细胞骨架蛋白不同，可作为小鼠胚胎癌细胞向胚外内胚层分化的标志物。
