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

Abstract

VEGFR-1 is devoid of ligand-dependent tyrosine autophosphorylation and its activation is not associated with proliferation of endothelial cells. The molecular mechanism responsible for this characteristic of VEGFR-1 is not known. In this study, we show that VEGFR-1 is devoid of ligand-dependent downregulation and failed to stimulate intracellular calcium release, cell migration and angiogenesis in vitro. To understand the molecular mechanisms responsible for the poor tyrosine autophosphorylation of VEGFR-1, we have either deleted the carboxyl terminus of VEGFR-1 or exchanged it with the carboxyl terminus of VEGFR-2. The deletion of carboxyl terminus of VEGFR-1 did not reverse its defective ligand-dependent autophosphorylation. The carboxyl terminus-swapped VEGFR-1, however, displayed ligand-dependent autophosphorylation, downregulation and also conveyed strong mitogenic responses. Thus, the carboxyl tail of VEGFR-1 restrains the ligand-dependent kinase activation and downregulation of VEGFR-1 and its ability to convey the angiogenic responses in endothelial cells.

Vascular endothelial growth factor receptors: Molecular mechanisms of activation and therapeutic potentials

“…Finally, deletion of the entire carboxyl terminus of VEGFR-2 is shown to impair its ligand-dependent autophosphorylation. It appears that this role of carboxyl terminus is independent of tyrosine 1212 and may involve residues other than tyrosines (Meyer et al, 2004a(Meyer et al, , 2004b. Altogether, the current literature provides a framework for understanding of regulation of VEGFR-2 activation and further demonstrates that the carboxyl terminus plays various important roles in VEGFR-2 functions ranging from its ability to regulate autophosphorylation and recruitment of signaling proteins to ligand-dependent downregulation.…”

“…2). VEGFR-1 also has a residual kinase activity and its selective activation that results only in homodimerization leads to activation of a limited number of signaling proteins such as p42/44 MAPK (Meyer et al, 2004a(Meyer et al, , 2004b. Thus, the unique signaling nature of VEGFR-1 and mechanisms by which it stimulates biological responses indicates that we have more to learn about RTK signaling than the current widely accepted and generalized RTK paradigm would suggest.…”

“…Mutation of serines 1188 and 1191 in the carboxyl terminus of VEGFR-2 is shown to impair the ligand-dependent down regulation of VEGFR-2 (Singh et al, 2005). This might explain why deletion of carboxyl terminus impairs the VEGFR's ability to undergo ligand-dependent downregulation (Meyer et al, 2004a(Meyer et al, , 2004b. Finally, deletion of the entire carboxyl terminus of VEGFR-2 is shown to impair its ligand-dependent autophosphorylation.…”

“…In these studies ligand stimulation of VEGFR-1 induced neither cell proliferation nor apoptosis. Selective activation of VEGFR-1 also did not promote cell migration or intracellular calcium release (Meyer et al, 2004a(Meyer et al, , 2004b. It could be argued that in a defined condition when VEGFR-1 is activated by a ligand that only allows receptor homodimerization and with no cross-talk with other RTKs such as VEGFR-2 and VEGFR-3, VEGFR-1 is not capable of promoting biological responses such as endothelial cell migration, cell proliferation and intercellular calcium release.…”

“…The carboxyl-terminus swapped VEGFR-1 promoted ligand-dependent autophosphorylation of VEGFR-1 and induction of endothelial cell proliferation (Meyer et al, 2004a(Meyer et al, , 2004b). It appears that this effect is selectively associated with its carboxyl terminus because replacement of the juxtamembrane (JM) region of VEGFR-1 with that of VEGFR-2 does not rescue its kinaseimpaired characteristic (Gille et al, 2000).…”