VEGFR2-PLCγ1 axis is essential for endothelial specification of VEGFR2+ vascular progenitor cells

Vascular endothelial growth factor receptor 2 (VEGFR2) plays crucial roles in vasculogenesis, a process involving cell proliferation, migration and differentiation. However, the molecular mechanism by which VEGFR2 signaling directs vascular endothelial differentiation of VEGFR2(+) mesodermal progenitors is not well understood. In this study, we examined the signal transduction pathway downstream of VEGFR2 for endothelial differentiation using an in vitro differentiation system of mouse embryonic stem-cell-derived VEGFR2(+) cells. Using chimeric receptors composed of VEGFR2 and VEGFR3, the third member of the VEGFR family, we found that signaling through tyrosine 1175 (Y1175, corresponding to mouse Y1173) of VEGFR2 is crucial for two processes of endothelial differentiation: endothelial specification of VEGFR2(+) progenitors, and subsequent survival of endothelial cells (ECs). Furthermore, we found that phospholipase Cgamma1 (PLCgamma1), which interacts with VEGFR2 through phosphorylated Y1175, is an inducer of endothelial specification. In contrast to VEGFR2, VEGFR3 does not transmit a signal for endothelial differentiation of VEGFR2(+) cells. We found that VEGFR3 does not activate PLCgamma1, although VEGFR3 has the ability to support endothelial cell survival. Taken together, these findings indicate that VEGFR2-PLCgamma1 signal relay gives rise to the unique function of VEGFR2, thus enabling endothelial differentiation from vascular progenitors.