Subramanian S V, Fitzgerald M L, Bernfield M
Joint Program in Neonatology, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 1997 Jun 6;272(23):14713-20. doi: 10.1074/jbc.272.23.14713.
The syndecan family of transmembrane heparan sulfate proteoglycans is abundant on the surface of all adherent mammalian cells. Syndecans bind and modify the action of various growth factors/cytokines, proteases/antiproteases, cell adhesion molecules, and extracellular matrix components. Syndecan expression is highly regulated during wound repair, a process orchestrated by many of these effectors. Each syndecan ectodomain is shed constitutively by cultured cells, but the mechanism and significance of this shedding are not understood. Therefore, we examined (i) whether physiological agents active during wound repair influence syndecan shedding, and (ii) whether wound fluids contain shed syndecan ectodomains. Using SVEC4-10 endothelial cells we find that certain proteases and growth factors accelerate shedding of the syndecan-1 and -4 ectodomains. Protease-accelerated shedding is completely inhibited by serum-containing media. Thrombin activity is duplicated by the 14-amino acid thrombin receptor agonist peptide that directly activates the thrombin receptor and is not inhibited by serum. Epidermal growth factor family members accelerate shedding but FGF-2, platelet-derived growth factor-AB, transforming growth factor-beta, tumor necrosis factor-alpha, and vascular endothelial cell growth factor 165 do not. Shed ectodomains are soluble, stable in the conditioned medium, have the same size core proteins regardless whether shed at a basal rate, or accelerated by thrombin or epidermal growth factor-family members and are found in acute human dermal wound fluids. Thus, shedding is accelerated by activation of at least two distinct receptor classes, G protein-coupled (thrombin) and protein tyrosine kinase (epidermal growth factor). Proteases and growth factors active during wound repair can accelerate syndecan shedding from cell surfaces. Regulated shedding of syndecans suggests physiological roles for the soluble proteoglycan ectodomains.
跨膜硫酸乙酰肝素蛋白聚糖的Syndecan家族在所有贴壁哺乳动物细胞表面都很丰富。Syndecan能结合并改变各种生长因子/细胞因子、蛋白酶/抗蛋白酶、细胞粘附分子和细胞外基质成分的作用。在伤口修复过程中，Syndecan的表达受到高度调控，而伤口修复是由许多这些效应物精心安排的一个过程。每个Syndecan胞外域在培养细胞中会持续脱落，但其脱落的机制和意义尚不清楚。因此，我们研究了：（i）伤口修复过程中起作用的生理因子是否会影响Syndecan的脱落；（ii）伤口渗出液中是否含有脱落的Syndecan胞外域。利用SVEC4-10内皮细胞，我们发现某些蛋白酶和生长因子会加速Syndecan-1和-4胞外域的脱落。含血清的培养基能完全抑制蛋白酶加速的脱落。凝血酶活性可被14个氨基酸的凝血酶受体激动肽复制，该肽直接激活凝血酶受体且不受血清抑制。表皮生长因子家族成员会加速脱落，但FGF-2、血小板衍生生长因子-AB、转化生长因子-β、肿瘤坏死因子-α和血管内皮细胞生长因子165则不会。脱落的胞外域是可溶的，在条件培养基中稳定，无论以基础速率脱落，还是被凝血酶或表皮生长因子家族成员加速脱落，其核心蛋白大小相同，并且在急性人类皮肤伤口渗出液中也能找到。因此，至少通过激活两类不同的受体（G蛋白偶联受体（凝血酶）和蛋白酪氨酸激酶（表皮生长因子））可加速脱落。伤口修复过程中起作用的蛋白酶和生长因子可加速Syndecan从细胞表面的脱落。Syndecan的调控性脱落表明可溶性蛋白聚糖胞外域具有生理作用。
