Endothelin-1 cooperates with hypoxia to induce vascular-like structures through vascular endothelial growth factor-C, -D and -A in lymphatic endothelial cells

Abstract

Aims: Lymphangiogenesis refers to the formation of new lymphatic vessels and is thought to constitute conduits for the tumor cells to metastasize. We previously demonstrated that endothelin (ET)-1 through its binding with ETB receptor (ET(B)R) expressed on lymphatic endothelial cells (LEC), induced cell growth and invasiveness. Since vascular endothelial growth factor (VEGF)-A/-C/-D, and hypoxia play key role in lymphatic differentiation, in this study we investigated the involvement of these growth factors and hypoxia in ET-1-induced lymphangiogenesis.

Main methods: Real time PCR and ELISA were used to quantify VEGF-A/-C/-D. LEC morphological differentiation was analyzed by tube formation assay on Matrigel.

Key findings: Hypoxia, as well as ET-1, induced an increase in VEGF-A/-C and -D expression that was reduced in the presence of a selective ET(B)R antagonist, BQ788, and enhanced when ET-1 was administered under hypoxic conditions. We analyzed the role of hypoxia on LEC morphological differentiation, and found that hypoxia increased the formation of vascular-like structures on Matrigel and that in combination with ET-1 this effect was markedly enhanced. The use of specific antibodies neutralizing VEGF-A, or recombinant VEGFR-3/(Flt-4)/Fc that block VEGF-C/-D, inhibited the effect of ET-1 as well that of hypoxia.

Significance: These results demonstrated that ET-1 and hypoxia act, at list in part, through VEGF to induce lymphangiogenic events and that these two stimuli may cooperate to induce VEGF-A/-C/-D expression and lymphatic differentiation. These data further support the role of ET-1 as potent lymphangiogenic factor that relies on the interplay with hypoxic microenvironment and with VEGF family members.