Young B A, Wang P, Goldblum S E
Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, 21201, USA.
Biochem Biophys Res Commun. 1998 Oct 9;251(1):320-7. doi: 10.1006/bbrc.1998.9475.
SPARC (Secreted Protein Acidic and Rich in Cysteine) regulates the transendothelial flux of macromolecules through a paracellular pathway. We now have demonstrated that SPARC-induced increments in albumin flux across postconfluent endothelial cell (EC) monolayers are mediated, in part, through protein tyrosine phosphorylation. SPARC increased tyrosine phosphorylation of EC proteins up to 12-fold within 1 h. The phosphotyrosine-containing proteins were immunolocalized to the intercellular boundaries. Two substrates for SPARC-induced tyrosine phosphorylation were identified as beta-catenin and paxillin. Inhibition of tyrosine kinases with herbimycin A or genistein reversed the barrier dysfunction induced by SPARC by 71% and 49%, respectively. Herbimycin A also protected against SPARC-induced intercellular gap formation. In contrast, inhibition of tyrosine phosphatases with sodium orthovanadate or phenylarsine oxide enhanced the loss of barrier function associated with SPARC treatment by 120% and 88%, respectively. These data indicate that SPARC influences EC-EC interactions through a tyrosine phosphorylation-dependent signaling pathway.
富含半胱氨酸的酸性分泌蛋白（SPARC）通过旁细胞途径调节大分子的跨内皮通量。我们现已证明，SPARC诱导汇合后内皮细胞（EC）单层中白蛋白通量增加，部分是通过蛋白质酪氨酸磷酸化介导的。SPARC在1小时内使EC蛋白的酪氨酸磷酸化增加了12倍。含磷酸酪氨酸的蛋白免疫定位在细胞间边界。SPARC诱导的酪氨酸磷酸化的两个底物被鉴定为β-连环蛋白和桩蛋白。用赫曲霉素A或染料木黄酮抑制酪氨酸激酶，分别使SPARC诱导的屏障功能障碍逆转71%和49%。赫曲霉素A还可防止SPARC诱导的细胞间间隙形成。相反，用原钒酸钠或氧化苯胂抑制酪氨酸磷酸酶，分别使与SPARC处理相关的屏障功能丧失增加120%和88%。这些数据表明，SPARC通过酪氨酸磷酸化依赖性信号通路影响EC-EC相互作用。
