title: Protein kinase C regulates FLT1 abundance and stimulates its cleavage in vascular endothelial cells with the release of a soluble PlGF/VEGF antagonist.
abstract: FLT1 and its soluble form (sFLT1) arise as alternate transcripts from the same gene and sFLT1 can antagonize the effect of vascular endothelial growth factor (VEGF) on its cognate receptors. We investigated the effect of VEGF and protein kinase C (PKC) activation on sFLT1 abundance. We demonstrated that VEGF stimulates sFLT1 and FLT1 mRNA and protein levels in vascular endothelial cells via VEGFR2 and PKC. Using an FLT1 expression vector with N and C-terminal epitope tags, we show that PKC activation increases the cleavage of FLT1 into an N-terminal extracellular fragment and a C-terminal intracellular fragment with the cleavage occurring adjacent to the transmembrane domain. The trafficking and glycosylation inhibitors brefeldin, monensin and tunicamycin substantially reduced cleavage and release of the N-terminal ectodomain of FLT1 and inhibited secretion of the isoforms of sFLT1. The shed FLT1 ectodomain can bind VEGF and PlGF and inhibit VEGF-induced vascular tube formation thus confirming that it is functionally equivalent to the alternately spliced and secreted sFLT1 isoforms.
authors.affiliation: Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, IA, USA.
authors.forename: Nandita S
authors.initials: NS
authors.lastname: Raikwar
authors.forename: Kang Z
authors.initials: KZ
authors.lastname: Liu
authors.forename: Christie P
authors.initials: CP
authors.lastname: Thomas
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D057809:HEK293 Cells; D061307:Human Umbilical Vein Endothelial Cells / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D014158:Transcription, Genetic; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; C098069:PIGF protein, human; D020033:Protein Isoforms; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; C501162:FLT1 protein, human; D040281:Vascular Endothelial Growth Factor Receptor-1; D040301:Vascular Endothelial Growth Factor Receptor-2; D011493:Protein Kinase C
keywords: Angiogenesis; Proteolytic cleavage; Soluble receptor
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