Mammalian aminoacyl tRNA synthetases form a macromolecular protein complex with three non-enzymatic cofactors. Among these factors, p43 is also secreted to work as a cytokine on endothelial as well as immune cells. Here we investigated the activity of p43 in angiogenesis and determined the related mediators. It promoted the migration of endothelial cells at low dose but induced their apoptosis at high dose. p43 at low concentration activated extracellular signal-regulating kinase, which resulted in the induction and activation of matrix metalloproteinase 9. In contrast, p43 at high concentration activated Jun N-terminal kinase, which mediated apoptosis of endothelial cells. These results suggest that p43 is a novel cytokine playing a dose-dependent biphasic role in angiogenesis.
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