Antagonistic roles of four SR proteins in the biosynthesis of alternatively spliced tissue factor transcripts in monocytic cells.
Following recruitment to solid tissues, peripheral blood monocytes express a number of proinflammatory molecules including TF, a trigger of coagulation that also promotes cell-cell interactions and tissue remodeling. Monocytes express two forms of TF: flTF, a highly coagulant transmembrane form, and asTF, a highly proangiogenic, soluble TF form. Biosynthesis of the two TF forms occurs via alternative processing of exon 5 during pre-mRNA splicing. Its inclusion results in flTF mRNA and its exclusion, asTF mRNA. We developed a splicing reporter system recently and determined that two spliceosomal constituents, SR proteins ASF/SF2 and SRp55, play a pivotal role in exon 5 inclusion. In this report, we show for the first time that two other SR proteins expressed in human monocytes, SRp40 and SC35, antagonize ASF/SF2 and SRp55 by competing for binding to certain sites in exon 5, thereby promoting TF exon 5 exclusion, an event unique to asTF biosynthesis. We also show that the intron preceding TF exon 5 possesses characteristics rarely found in U2 introns. Our findings indicate that modulation of TF pre-mRNA splicing can be accomplished via modification of SR proteins' activity, facilitating development of novel therapeutic strategies to modulate the "TF profile" of monocytes/macrophages.
Chandradas
Sajiv
S
Department of Medicine, Mount Sinai School of Medicine, New York, NY, USA.
Deikus
Gintaras
G
Tardos
Jonathan G
JG
Bogdanov
Vladimir Y
VY
D017398:Alternative Splicing; D001051:Apoenzymes / Q000235:genetics* / Q000378:metabolism; D001667:Binding, Competitive; D002460:Cell Line / Q000378:metabolism; D005091:Exons / Q000235:genetics; D017930:Genes, Reporter; D006801:Humans; D009000:Monocytes / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D012322:RNA Precursors / Q000235:genetics; D016601:RNA-Binding Proteins / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012261:Ribonucleoproteins / Q000502:physiology*; D000068103:Serine-Arginine Splicing Factors; D013925:Thromboplastin / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
D001051:Apoenzymes; C052493:F3 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012322:RNA Precursors; D016601:RNA-Binding Proteins; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; C489470:SRSF6 protein, human; C073288:SRSF2 protein, human; D000068103:Serine-Arginine Splicing Factors; D013925:Thromboplastin