Plasmin-clipped β2-glycoprotein-I inhibits endothelial cell growth by down-regulating cyclin A, B and D1 and up-regulating p21 and p27

beta(2)-Glycoprotein-I (beta(2)gpl), an abundant plasma glycoprotein, functions as a regulator of thrombosis. Previously, we demonstrated that plasmin-clipped beta(2)gpl (c beta(2)gpl) exerts an anti-angiogenic effect on human umbilical vein endothelial cells (HUVEC). The present study was focused on the molecular background responsible for this phenomenon. c beta(2)gpl strongly reduced HUVEC growth and proliferation as evidenced by the MIT and BrdU assay and delayed cell cycle progression arresting HUVEC in the S-and G2/M-phase. Western blot analysis indicated that c beta(2)gpl inhibited cyclin A, B and D1, and enhanced p21 and p27 expression. Activity of p38 was down-regulated independently from the c beta(2)gpl incubation time. Phosphorylation of ERK1/2 was not changed early (30 and 60 min) but became enhanced later (90 min, 4 h). JNK activity was reduced rapidly after c beta(2)gpl treatment but compared to controls, increased thereafter. Annexin II blockade prevented growth inhibition and cell cycle delay evoked by c beta(2)gpl. We assume that c beta(2)gpl's effects on HUVEC growth is mediated via cyclin A, B and D1 suppression, up-regulation of p21 and p27 and coupled to modifications of the mitogen-activated protein (MAP) kinase signalling pathway. c beta(2)gpl may represent a potential endogenous angiogenesis-targeted compound, opening the possibility of a novel tool to treat cancer. (C) 2010 Elsevier Ireland Ltd. All rights reserved.