We previously reported that binding to heparan sulfate (HS) is required for the ability of the placentally secreted pregnancy-specific glycoprotein 1 (PSG1) to induce endothelial tubulogenesis. PSG1 is composed of four immunoglobulin-like domains but which domains of the protein bind to HS remains unknown. To analyze the interaction of PSG1 with HS, we generated several recombinant proteins, including the individual domains, chimeric proteins between two PSG1 domains, and mutants. Using flow cytometric and surface plasmon resonance studies, we determined that the B2 domain of PSG1 binds to HS and that the positively charged amino acids encompassed between amino acids 43-59 are required for this interaction. Furthermore, we showed that the B2 domain of PSG1 is required for the increase in the formation of tubes by endothelial cells (EC) including a human endometrial EC line and two extravillous trophoblast (EVT) cell lines and for the pro-angiogenic activity of PSG1 observed in an aortic ring assay. PSG1 enhanced the migration of ECs while it increased the expression of matrix metalloproteinase-2 in EVTs, indicating that the pro-angiogenic effect of PSG1 on these two cell types may be mediated by different mechanisms. Despite differences in amino acid sequence, we observed that all human PSGs bound to HS proteoglycans and confirmed that at least two other members of the family, PSG6 and PSG9, induce tube formation. These findings contribute to a better understanding of the pro-angiogenic activity of human PSGs and strongly suggest conservation of this function among all PSG family members.

中文翻译：

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妊娠特异性糖蛋白在内皮和绒毛外滋养层细胞中的促血管生成作用

我们之前曾报道，胎盘分泌的妊娠特异性糖蛋白 1 (PSG1) 诱导内皮小管形成的能力需要与硫酸乙酰肝素 (HS) 结合。PSG1 由四个免疫球蛋白样结构域组成，但蛋白质的哪些结构域与 HS 结合尚不清楚。为了分析 PSG1 与 HS 的相互作用，我们生成了几种重组蛋白，包括单个域、两个 PSG1 域之间的嵌合蛋白和突变体。使用流式细胞术和表面等离子共振研究，我们确定 PSG1 的 B2 域与 HS 结合，并且这种相互作用需要包含在氨基酸 43-59 之间的带正电荷的氨基酸。此外，我们发现 PSG1 的 B2 结构域是内皮细胞 (EC) 形成管的增加所必需的，包括人子宫内膜 EC 系和两个绒毛外滋养层 (EVT) 细胞系，以及在主动脉环检测。PSG1 增强了内皮细胞的迁移，同时增加了 EVT 中基质金属蛋白酶-2 的表达，表明 PSG1 对这两种细胞类型的促血管生成作用可能由不同的机制介导。尽管氨基酸序列存在差异，但我们观察到所有人类 PSG 都与 HS 蛋白聚糖结合，并证实该家族的至少两个其他成员 PSG6 和 PSG9 诱导管形成。