title: Post-transcriptional control of expression of sFlt-1, an endogenous inhibitor of vascular endothelial growth factor.
abstract: Vascular endothelial growth factor (VEGF) is a major modulator of angiogenesis. Biological effects of VEGF are mediated by endothelial cell-surface receptors, KDR and Flt-1. Alternative Flt-1 RNA processing, involving retention of intron 13 and the use of intronic cleavage-polyadenylation signals, produces a secreted form of Flt-1, "sFlt-1," that binds VEGF with high affinity and can inhibit VEGF signaling. To probe mechanisms controlling sFlt-1 expression, we have cloned and sequenced Flt-1 intron 13 from a mouse genomic library and located RNA processing signals potentially involved in sFlt-1 mRNA formation. A minigene construct containing Flt-1 intron 13 directed the expression of both secreted (i.e., cleaved/polyadenylated) and transmembrane (i.e., spliced) forms of Flt-1 mRNA and protein. Using rapid amplification of 3' cDNA ends (3'-RACE) and quantitative PCR (QPCR) analysis to test the activity of intronic cleavage-polyadenylation signals, we observed that multiple sites were utilized for sFlt-1 mRNA processing in both native tissues and Flt-1 minigene transfectants. In transfectants, the most distal signal was utilized preferentially. The potential for interaction between pathways leading to sFlt-1 or full-length Flt-1 was evaluated using QPCR to measure relevant mRNAs after transfection with signal mutants. Decreased expression of sFlt-1 mRNA in cleavage-polyadenylation mutants was accompanied by reciprocal increases in full-length Flt-1 mRNA. Multiple sFlt-1 mRNA species are formed that differ by up to 3.9 kb in their 3'-untranslated regions (UTRs), which contain sites of potential regulatory importance. The reciprocity between sFlt-1 and Flt-1 mRNA expression suggests a novel post-transcriptional mechanism by which sFlt-1 protein production and, thereby, responsiveness to VEGF, may be modulated.
authors.affiliation: Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia 24061, USA. wrhuckle@vt.edu
authors.forename: William R
authors.initials: WR
authors.lastname: Huckle
authors.forename: Rebecca I
authors.initials: RI
authors.lastname: Roche
mesh_terms: D020413:3' Untranslated Regions; D017398:Alternative Splicing / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D022202:Chromosomes, Artificial, Bacterial; D003001:Cloning, Molecular; D007438:Introns / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D017354:Point Mutation; D011061:Poly A / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D014162:Transfection; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors*; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D020413:3' Untranslated Regions; D012333:RNA, Messenger; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse; D011061:Poly A; D040281:Vascular Endothelial Growth Factor Receptor-1