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

Profilin与肌动蛋白单体结合调节肌动蛋白聚合，与磷脂酰肌醇4，5-二磷酸结合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高表达，并聚集在系膜细胞周围的细胞外间隙。在本研究中，我们检测了细胞外Profilin的生物学活性。Scatchard分析表明，在培养的大鼠肾小球系膜细胞中，纯化的脾和重组Profilin存在一类具有相似Kds的单一细胞表面结合位点。Profilin以剂量依赖的方式增加[~(3 H)]TdR掺入，并对PDGF诱导的[~(3 H)]TdR掺入有相加作用。凝胶漂移实验和竞争性逆转录-聚合酶链式反应检测到c-jun基因的瞬时表达后，Profilin以浓度和时间依赖的方式增加AP-1DNA结合活性，抑制Profilin诱导的AP-1激活和胸腺嘧啶核苷掺入。此外，Profilin诱导蛋白激酶C的快速和瞬时激活，星形孢子素和H-7减弱Profilin诱导的AP-1的激活，提示AP-1依赖蛋白激酶C的激活。这些发现表明，细胞外间隙中的Profilin可以与系膜细胞的表面受体结合，并作为信号转导的诱导剂。这些结果表明，细胞外Profilin可能通过影响细胞生长而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.