Cappello Fanny, Gatti Evelina, Camossetto Voahirana, David Alexandre, Lelouard Hugues, Pierre Philippe
Centre d'Immunologie de Marseille-Luminy, CNRS-INSERM-Université de la Méditerranée, 13288 Marseille, Cedex 09, France.
Exp Cell Res. 2004 Jul 15;297(2):607-18. doi: 10.1016/j.yexcr.2004.03.048.
Cystatins constitute a superfamily of cysteine protease inhibitors. A member of the type II secreted cystatin family, cystatin F, has been identified through different gene array experiments to be specifically expressed in hematopoietic cells as well as to be associated with several malignant tumors, suggesting a role in immunity or cancer progression. Cystatin F specificity as a protease inhibitor is still elusive, and understanding the cellular traffic of this molecule is therefore a major step in its characterization. Although the mannosylation-6 phosphate of cystatin F has been suggested, no conclusive evidences of its endosomal targeting have been reported. Here we show using U937 cells that cystatin F is secreted as a disulfide bridge-linked dimer and is not associated with endosomes intracellularly. Interestingly, although cystatin F targeting to endosomes or lysosomes is not observed in U937, modification of its C-terminal end by the addition of several amino acids promotes its accumulation in the lysosomes of transfected HeLa cells. This observation suggests that cystatin F can be targeted to the endocytic pathway under specific conditions and its C-terminal domain might contribute to this event.
胱抑素构成了一个半胱氨酸蛋白酶抑制剂超家族。通过不同的基因阵列实验已鉴定出II型分泌型胱抑素家族的一个成员——胱抑素F，它在造血细胞中特异性表达，并且与几种恶性肿瘤相关，这表明它在免疫或癌症进展中发挥作用。胱抑素F作为蛋白酶抑制剂的特异性仍然难以捉摸，因此了解该分子的细胞转运是其特性描述的重要一步。尽管有人提出了胱抑素F的6-磷酸甘露糖基化，但尚未有其靶向内体的确凿证据报道。在这里，我们使用U937细胞表明，胱抑素F以二硫键连接的二聚体形式分泌，并且在细胞内不与内体相关。有趣的是，尽管在U937细胞中未观察到胱抑素F靶向内体或溶酶体，但通过添加几个氨基酸对其C末端进行修饰会促进其在转染的HeLa细胞的溶酶体中积累。这一观察结果表明，胱抑素F在特定条件下可以靶向内吞途径，并且其C末端结构域可能促成了这一事件。
