Effects of platelet-derived profilin on vascular smooth muscle cells and endothelial cells.

已知Profilin与肌动蛋白单体结合以调节肌动蛋白聚合，并与磷脂酰肌醇4，5-二磷酸结合以抑制非磷酸化磷脂酶C-γ1的水解。我们最近报道，profilin在抗Thy-1.1肾小球肾炎大鼠肾小球系膜细胞中过表达，并积聚在系膜细胞周围的细胞外间隙。在本研究中，我们研究了细胞外profilin的生物活性。Scatchard分析表明，纯化的脾profilin和重组profilin在体外培养的大鼠系膜细胞中存在单一的细胞表面结合位点，且Kds相似。Profilin以剂量依赖性方式增加[^3H]胸苷掺入，并对PDGF诱导的[^3H]胸苷掺入具有累加效应。用<50>凝胶迁移实验和竞争性逆转录PCR检测c-jun基因的瞬时表达，Profilin以浓度（艾德_ = 30 nM）和时间依赖的方式增加AP-1 DNA结合活性，用抗profilin抑制抗体预处理profilin可抑制profilin诱导的AP-1活化和[^3H]胸苷掺入。此外，profilin诱导的蛋白激酶C的快速和短暂的激活，和staurosporine和H-7减少profilin诱导的AP-1的激活，这表明AP-1的蛋白激酶C依赖性激活。这些结果表明，profilin在细胞外空间可以结合到系膜细胞的细胞表面受体，并作为一个诱导剂的信号转导。这些结果表明，细胞外profilin可能通过影响细胞生长参与肾小球疾病的进展。

Profilin is known to bind to actin monomers to regulate actin polymerization, and to phosphatidylinositol 4,5-bisphosphate to inhibit hydrolysis by unphosphorylated phospholipase C-γ1. We recently reported that profilin is overexpressed in glomerular mesangial cells of anti-Thy-1.1 glomerulonephritis rats and is accumulated in the extracellular space around mesangial cells. In the present study, we examined the biological activities of extracellular profilin. Scatchard analysis indicated the existence of a single class of cell surface binding site with similar K_ds for purified splenic and recombinant profilin in cultured rat mesangial cells. Profilin increased [^3H]thymidine incorporation in a dose-dependent manner and had additive effects on PDGF-induced [^3H]thymidine incorporation. Profilin increased AP-1 DNA binding activity in a concentration- (ED_<50> = 30 nM) and time-dependent manner followed the transient gene expression of c-jun measured by gel shift assay and competitive reverse transcribed-PCR.Pretreatment of profilin with anti-profilin inhibitory antibody suppressed profilin-induced AP-1 activation and [^3H]thymidine incorporation. Furthermore, profilin induced a rapid and transient activation of protein kinase C, and staurosporine and H-7 diminished profilin-induced activation of AP-1, suggesting protein kinase C-dependent activation of AP-1. These findings indicate that profilin in the extracellular space can bind to cell surface receptors of mesangial cells and act as an inducer of signal transduction. These results suggest that extracellular profilin may be involved in the progression of glomerular diseases by affecting cell growth.