Galectin-1 (Gal-1), a homodimeric prototype of the galectins with a single carbohydrate-recognition domain, was recently identified as being overexpressed in tumor-associated capillary endothelial cells. The role of Gal-1 in endothelial cellular functions and the mechanism of action of Gal-1 remain unknown. Neuropilin-1 (NRP1) is a neuronal receptor that mediates repulsive growth cone guidance, and NRP1 functions in endothelial cells as a coreceptor (with vascular endothelial growth factor receptors (VEGFRs)) for VEGF 165. In this study, we found that Gal-1 was overexpressed in the tumor-associated endothelial cells of oral squamous cell carcinomas (P<0.001). Gal-1 increased the proliferation and adhesion of endothelial cells, and enhanced cell migration in combination with VEGF165. Surprisingly, Gal-1 selectively bound NRP1 via the carbohydrate-recognition domain, but did not bind VEGFR-1, VEGFR-2 or VEGFR-3. The Gal-1-NRP1 interaction mediated the migration and adhesion of endothelial cells. The binding of Gal-1 to NRP1 enhanced VEGFR-2 phosphorylation and stimulated the activation of the mitogen activated protein (MAP) kinases SAPK1/JNK (stress activated protein kinase-1/c-Jun NH2-terminal kinase). These findings show, for the first time, that Gal-1 can directly bind to NRP1 on endothelial cells, and can promote the NRP1/VEGFR-2-mediated signaling pathway as well as NRP1-mediated biological activities.
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