Angiostatin diminishes activation of the mitogen-activated protein kinasesERK-1 and ERK-2 in human dermal microvascular endothelial cells

Angiostatin is an endogenous inhibitor of angiogenesis that was isolated fr om tumor-bearing mice. It has been established that angiostatin inhibits en dothelial cell proliferation; however, the underlying mechanisms remain to be elucidated. Here we report that angiostatin reduces transiently the phos phorylation of the mitogen-activated protein kinases ERK-1 and ERK-2 in hum an dermal microvascular cells, but not in human vascular smooth muscle cell s or human dermal fibroblasts, We demonstrate that angiostatin diminishes E RK activation by basic fibroblast growth factor and vascular endothelial gr owth factor. Dephosphorylation of ERK and other tyrosine-phosphorylated pro teins was blocked by pretreatment of the cells with sodium meta-vanadate, a n inhibitor of protein tyrosine phosphatases, indicating that angiostatin s ignaling may require the activity of a tyrosine phosphatase. Concentrations of angiostatin that inhibited ERK activation also inhibited basic fibrobla st growth factor-stimulated collagen gel invasion by endothelial cells, but did not affect endothelial cell proliferation. We thus show that angiostat in inhibits primarily the invasion of endothelial cells and exerts minimal (if any) effects on their proliferation. Invasion is a process that involve s proteolysis, adhesion and migration, all of which have been linked to ERK signaling.