A novel intracellular isoform of VEGFR-1 activates Src and promotes cell invasion in MDA-MB-231 breast cancer cells.
Two types of VEGFR-1 receptors have been characterized: a full-length transmembrane receptor and a truncated extracellular soluble isoform (sVEGFR-1). We report here the characterization, in normal and cancer cells, of a new family of intracellular isoforms of VEGFR-1 resulting from alternative initiation of transcription in intronic sequences of the gene. While the classical isoforms of VEGFR-1 were barely detectable in MDA-MB-231 breast cancer cells, one of the intracellular isoforms transcribed from intron 21 (i(21)VEGFR-1) was the main isoform expressed in these cells. The new transcript encodes for a protein that contains only the phosphotransferase domain and the carboxyterminal tail of VEGFR-1. Treatment of MDA-MB-231 cells with siRNA specific for the tyrosine domain of VEGFR-1 suppressed the expression of i(21)VEGFR-1, downregulated phosphorylation of Src at tyrosine 418, and reduced markedly the invasion capacity of these cells in vitro. Accordingly, overexpression of transfected i(21)VEGFR-1 in MDA-MB-231 cells upregulated the active form of Src and increased invasiveness of MDA-MB-231 cells. The expression of i(21)VEGFR-1 in MDA-MB-231 cells was inhibited by retinoic acid. Both, activation of Src and downregulation by retinoic acid, have been reported in other intracellular members of the Fms/Kit/PDGFR family of tyrosine kinases, particularly in the intracellular isoform of c-kit, analogous structurally to i(21)VEGFR-1 and frequently expressed in cancer cells.
Laboratori de Genètica Molecular, Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain.
Belén
B
Mezquita
Jovita
J
Mezquita
Montserrat
M
Pau
Cristóbal
C
Mezquita
D017398:Alternative Splicing; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D009361:Neoplasm Invasiveness / Q000235:genetics* / Q000473:pathology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D040281:Vascular Endothelial Growth Factor Receptor-1 / Q000235:genetics / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
D020033:Protein Isoforms; D034741:RNA, Small Interfering; D040281:Vascular Endothelial Growth Factor Receptor-1; D019061:src-Family Kinases