The N-terminal hydrophobic sequence of autotaxin (ENPP2) functions as a signal peptide
The N-terminal hydrophobic sequence of autotaxin (ENPP2) functions as a signal peptide
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DOI：
10.1111/j.1365-2443.2006.00924.x
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发表时间：
2006-02-01
期刊：
影响因子：
2.1
通讯作者：
Masu, M
中科院分区：
文献类型：
--
作者：
Koike, S;Keino-Masu, K;Masu, M
自分泌运动因子，也称为ENPP 2，最初作为细胞运动促进蛋白从黑素瘤细胞的培养基中分离。它通过产生溶血磷脂酸和1-磷酸鞘氨醇来调节细胞生长、运动和血管生成。由于自分泌运动因子显示出与充分表征的PC-1的总体结构相似性，因此其被认为是在细胞表面上表达并在蛋白水解裂解后释放到细胞外空间的II型跨膜蛋白。然而，我们发现，虽然autotaxin是有效地分泌到细胞外的空间在体外和体内，它既不表达autotaxin转染细胞的表面上，也不对那些autotaxin表达脉络丛上皮细胞。分泌的自分泌运动因子的N-末端测序显示，它在两个N-末端位点被切割，这两个位点与信号肽酶和弗林蛋白酶切割的共有序列相匹配。此外，当在体外翻译时，自分泌运动因子被协同易位到微粒体膜中，并且其N-末端对应于信号序列的3-kDa片段被切割。这些数据表明，自分泌运动因子的N-末端疏水序列作为信号肽，而不是作为跨膜区段，因此自分泌运动因子作为分泌蛋白合成。
Autotaxin, also known as ENPP2, was originally isolated from the culture medium of melanoma cells as a cell-motility promoting protein. It regulates cell growth, motility, and angiogenesis through the production of lysophosphatidic acid and sphingosine 1-phosphate. Because autotaxin shows overall structural similarity to the well-characterized PC-1, it has been assumed to be a type II transmembrane protein that is expressed on the cell surface and is released into the extracellular space after proteolytic cleavage. We found, however, that while autotaxin was efficiently secreted into the extracellular space both in vitro and in vivo, it was expressed neither on the surfaces of autotaxin-transfected cells nor on those of the autotaxin-expressing choroid plexus epithelium cells. N-terminal sequencing of the secreted autotaxin revealed that it was cleaved at two N-terminal sites that match the consensus sequences for cleavage by a signal peptidase and furin. In addition, when translated in vitro, autotaxin was co-translationally translocated into microsome membranes, and its N-terminal 3-kDa fragment corresponding to a signal sequence was cleaved. These data demonstrate that the N-terminal hydrophobic sequence of autotaxin functions as a signal peptide, not as a transmembrane segment, and thus autotaxin is synthesized as a secreted protein.