A repressor sequence in the juxtamembrane domain of Flt-1 (VEGFR-1) constitutively inhibits vascular endothelial growth factor-dependent phosphatidylinositol 3′-kinase activation and endothelial cell migration

Abstract

Vascular endothelial growth factor (VEGF) has two highly homologous tyrosine kinase receptors: Flt‐1 (VEGFR‐1) and KDR (VEGFR‐2). KDR is strongly phosphorylated on tyrosines and can transmit mitogenic and motogenic signals following VEGF binding, while Flt‐1 is markedly less effective in mediating such functions. To dissect the regions that account for the differences between the two receptors, we generated a series of chimeric Flt‐1–KDR molecules. We found that the juxtamembrane region of Flt‐1 prevents key signaling functions. When the juxtamembrane region of Flt‐1 is replaced by that of KDR, Flt‐1 becomes competent to mediate endothelial cell migration and phosphatidylinositol 3′‐kinase activation in response to VEGF. Further mutational analysis shows that a short divergent sequence is responsible for such repressor function. However, mutant Flt‐1 receptors lacking this sequence do not transmit effective proliferative signals, suggesting that this receptor function is regulated separately. These results define a novel functional domain that serves to repress Flt‐1 activity in endothelial cells.

Substitution of C-terminus of VEGFR-2 with VEGFR-1 promotes VEGFR-1 activation and endothelial cell proliferation

“…VEGFR-1 has no aberrant amino-acid replacement in these regions, suggesting that its kinasedefective phenotype is not associated with structural abnormality within the kinase domain. Replacement of the JM (Juxtamembrane) region of VEGFR-1 with that of VEGFR-2 also does not rescue its poor liganddependent kinase activation (Gille et al, 2000). Our current study shows that the kinase-defective phenotype of VEGFR-1 is linked to its carboxyl tail.…”

Etk/Bmx Transactivates Vascular Endothelial Growth Factor 2 and Recruits Phosphatidylinositol 3-Kinase to Mediate the Tumor Necrosis Factor-induced Angiogenic Pathway

“…Our study demonstrates that Etk mediates the TNF-induced PI3K-Akt angiogenic pathway, which has been well documented in growth factor-stimulated cell migration (41)(42)(43)(44). PI3K-Akt may induce angiogenesis by multiple downstream effectors including the Rho family of small GTPases, PAK1, and endothelial nitric-oxide synthase (14,(41)(42)(43)(44). Further investigation is required to determine which of these Etk effector(s) contributes to TNF-induced angiogenesis.…”

“…Similarly, Etk through its PH domain binds to and activates PAK1 (36), a 65-kDa serine/ threonine kinase implicated in integrin-induced EC migration and angiogenesis by modulating EC contraction (37). Our study demonstrates that Etk mediates the TNF-induced PI3K-Akt angiogenic pathway, which has been well documented in growth factor-stimulated cell migration (41)(42)(43)(44). PI3K-Akt may induce angiogenesis by multiple downstream effectors including the Rho family of small GTPases, PAK1, and endothelial nitric-oxide synthase (14,(41)(42)(43)(44).…”

VEGF Receptor Signaling and Endothelial Function

“…Two studies using chimeras of VEGFR-1 and VEGFR-2 have found that these chimeras suppress VEGFR-2-mediated proliferation, but not migration (63,64). Exchanging the juxtamembrane region of the VEGFR-2 with VEGFR-1 suppresses VEGFR-2-mediated signaling and migration (65).…”