Post-translational processing of the insulin-like growth factor-2 precursor -: Analysis of O-glycosylation and endoproteolysis
Post-translational processing of the insulin-like growth factor-2 precursor -: Analysis of O-glycosylation and endoproteolysis
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DOI：
10.1074/jbc.273.29.18443
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发表时间：
1998-07-17
影响因子：
4.8
通讯作者：
Steiner, DF
中科院分区：
文献类型：
--
作者：
Duguay, SJ;Jin, Y;Steiner, DF
胰岛素样生长因子-2（IGF-2）在大多数胚胎组织中表达，并且是妊娠期间正常发育所必需的。出生后，IGF-2在大多数组织中的表达消失，但该基因通常在肿瘤发生期间重新激活。肿瘤分泌由pro-IGF-2的异常翻译后加工产生的高分子量形式的IGF-2。作为了解高分子量IGF-P肽如何促进肿瘤进展的第一步，我们表征了人胚胎细胞系中IGF-P的生物合成。我们已经发现，pro-IGF-α最初可以形成两个二硫键异构体，其在体内经历重排成单一构象。N-乙酰半乳糖胺与Ser（71）、Thr（72）、Thr（75）和Thr（139）的加成可能发生在顺式高尔基体中。唾液酸的添加开始于反式高尔基体，但IGF-2肽必须到达反式高尔基体网络才能完成寡糖成熟。内蛋白水解发生在寡糖成熟的同时或稍晚。仅在Arg（104）处观察到切割，导致IGF-2-（1-104）和游离Et-肽的分泌。蛋白水解需要在P1（Arg（104））和P4（Arg（101））位置的碱性残基，被弗林蛋白酶抑制剂完全阻断，并通过与弗林蛋白酶，PACE 4，PC 6A，PC6 B和LPC共表达增强。这些数据表明枯草杆菌蛋白酶相关前蛋白转化酶家族的成员介导了IGF-2前体在Arg的加工（104）。在该表达系统中，我们没有检测到在正常血清、成熟IGF-S和IGF-2-（1-87）中最丰富的IGF-S肽，这表明新的内切蛋白酶负责产生这些产物。
Insulin-like growth factor-2 (IGF-2) is expressed in most embryonic tissues and is required for normal development during gestation. After birth IGF-2 expression is extinguished in most tissues, but the gene is often reactivated during tumorigenesis. Tumors secrete high molecular weight forms of IGF-2 that result from aberrant post-translational processing of pro-IGF-2. As a first step toward understanding how high molecular weight IGF-P peptides might contribute to tumor progression, we have characterized the biosynthesis of IGF-P in a human embryonic cell line. We have found that pro-IGF-a can initially form two disulfide isomers that undergo rearrangement to a single conformation in vivo. The addition of N-acetylgalactosamine to Ser(71), Thr(72), Thr(75), and Thr(139) likely occurs in the cis-Golgi apparatus. Sialic acid addition begins in the trans Golgi apparatus, but IGF-2 peptides must reach the trans-Golgi network for oligosaccharide maturation to be completed. Endoproteolysis occurs concomitant to or slightly after oligosaccharide maturation. Cleavage was observed only at Arg(104), resulting in the secretion of IGF-2-(1-104) and free Et-peptide. Proteolysis required basic residues in the P1 (Arg(104)), and P4 (Arg(101)) positions, was completely blocked by a furin inhibitor, and was enhanced by coexpression with furin, PACE4, PC6A, PC6B, and LPC. These data suggest that members of the subtilisin-related proprotein convertase family mediate processing of pro-IGF-2 at Arg(104). We did not detect the IGF-S peptides that are most abundant in normal serum, mature IGF-S, and IGF-2-(1-87), in this expression system, which indicates that novel endoproteases are responsible for generating these products.