Hypoxia induces tumor and endothelial cell migration in a semaphorin 3F- and VEGF-dependent manner via transcriptional repression of their common receptor neuropilin 2

Abstract

Neuropilin-2 (NRP2) is a receptor expressed by tumor cells and endothelial cells (EC) that binds both semaphorin 3F (SE MA3F), a potent inhibitor of tumor angiogenesis and metastasis, and vascular endothelial growth factor (VEGF), a potent stimulator of tumor angiogenesis. It was found that glioblastoma and melanoma cells repressed NRP2 expression when maintained under hypoxic conditions and after treatment with the hypoxia-mimetic agent desferrioxamine (DFO), at both the mRNA and protein levels. Silencing of HIF1-α, the hypoxia-induced subunit of the hypoxia inducible factor (HIF), abrogated DFO-induced NRP2 repression. Conversely, ectopic expression of HIF1-α directly repressed NRP2 promoter activity and expression. NRP2 is the sole receptor for SE MA3F. Loss of NRP2 expression in tumor cells inhibited SE MA3F-dependent activities, such as inactivation of RhoA, depolymerization of F-actin and inhibition of tumor cell migration. On the other hand, loss of NRP2 expression in tumor cells increased VEGF protein levels in conditioned media, with no effects on VEGF mRNA levels. This increase in VEGF protein levels promoted paracrine activation of EC, including VEGF receptor-2 phosphorylation and activation of downstream signaling proteins such as p44/42 MAPK and p38 MAPK. In addition, the elevated VEGF levels induced EC migration and sprouting, two key steps of tumor angiogenesis in vivo. It was concluded that hypoxia regulates VEGF and SE MA3F activities through transcriptional repression of their common receptor NRP2, providing a novel mechanism by which hypoxia induces tumor angiogenesis, growth and metastasis. © 2011 Landes Bioscience.