Accumulation of unfolded proteins in the endoplasmic reticulum (ER) initiates IRE1α, ATF6, and PERK cascades, leading to a transcriptional/translational response known as unfolded protein response (UPR). Here we show that VEGF activates UPR mediators through a PLCγ-mediated crosstalk with the mTORC1 complex without accumulation of unfolded proteins in the ER. Activation of ATF6 and PERK contributes to the survival effect of VEGF on endothelial cells (ECs) by positively regulating mTORC2-mediated phosphorylation of AKT on Ser473, which is required for full activity of AKT. Low levels of CHOP allow ECs to evade the proapoptotic effect of this UPR product. Depletion of PLCγ, ATF6, or eIF2α dramatically inhibited VEGF-induced vascularization in mouse Matrigel plugs, suggesting that the ER and the UPR machinery constitute components of the VEGF signaling circuit that regulates EC survival and angiogenesis, extending their role beyond adaptation to ER stress.

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Fotsis T. VEGF autoregulates its proliferative and migratory ERK1/2 and p38 cascades by enhancing the expression of DUSP1 and DUSP5 phosphatases in endothelial cells. Am J Physiol Cell Physiol 297: C1477-C1489, 2009. First published September 9, 2009 doi:10.1152/ajpcell.00058.2009.-Vascular endothelial growth factor (VEGF) is a key angiogenic factor that regulates proliferation and migration of endothelial cells via phosphorylation of extracellular signal-regulated kinase-1/2 (ERK1/2) and p38, respectively. Here, we demonstrate that VEGF strongly induces the transcription of two dual-specificity phosphatase (DUSP) genes DUSP1 and DUSP5 in endothelial cells. Using fluorescence microscopy, fluorescence lifetime imaging (FLIM), and fluorescence cross-correlation spectroscopy (FCCS), we found that DUSP1/mitogen-activated protein kinases phosphatase-1 (MKP-1) was localized in both the nucleus and cytoplasm of endothelial cells, where it existed in complex with p38 (effective dissociation constant, K D eff , values of 294 and 197 nM, respectively), whereas DUSP5 was localized in the nucleus of endothelial cells in complex with ERK1/2 (K D eff 345 nM). VEGF administration affected differentially the K D eff values of the DUSP1/p38 and DUSP5/ERK1/2 complexes. Gain-of-function and lack-of-function approaches revealed that DUSP1/MKP-1 dephosphorylates primarily VEGF-phosphorylated p38, thereby inhibiting endothelial cell migration, whereas DUSP5 dephosphorylates VEGF-phosphorylated ERK1/2 inhibiting proliferation of endothelial cells. Moreover, DUSP5 exhibited considerable nuclear anchoring activity on ERK1/2 in the nucleus, thereby diminishing ERK1/2 export to the cytoplasm decreasing its further availability for activation. vascular endothelial growth factors; extracellular signal regulated kinase-1/2; p38; dual-specificity phosphatase 1/mitogen-activated protein kinase phosphatase-1; dual-specificity phosphatase-5 VASCULAR ENDOTHELIAL GROWTH FACTORS (VEGFs) are the most important regulators of vessel morphogenesis. Not only do they participate in the regulation of both vasculogenesis and angiogenesis, but they also are among the most important molecules involved in the pathogenesis of angiogenic diseases such as diabetic retinopathy and cancer (6). VEGFs are secreted dimeric glycoproteins of ϳ40 kDa, and in mammals the VEGF family consists of five members: VEFG-A, B, C, D and placental growth factor (PLGF) (6). Moreover, alternative splicing of several of the VEGF family members gives rise to isoforms with different biological activities. The VEGF ligands bind in an overlapping pattern to three receptor tyrosine kinases known as VEGF receptor-1, -2, and -3 (VEGFR1-3), as well as to coreceptors such as heparan sulfate proteoglycans and neuropilins (22). VEGFR2 promotes migration, proliferation, and differentiation of endothelial cells (ECs) being critical for the regulation of angiogenic sprouting (1). Indeed, during sprouting, tip cells need to acquire an invasive and motile phenotype, whereas ECs in the stalk exhibi...