DNA topoisomerase I (Topo I) specifically phosphorylates arginine-serine-rich (SR proteins) splicing factors and is potentially involved in pre-mRNA-splicing regulation. Using a Topo I-deficient murine B lymphoma-derived subclone (P388-45/C) selected for its resistance to high dosage of the antitumor drug camptothecin, we show that Topo I depletion results in the hypophosphorylation of SR proteins and impairs exonic splicing enhancer (ESE)-dependent but not constitutive splicing. The Affymetrix GeneChip system analysis revealed that several alternatively spliced genes, characterized by small exons and large introns, are down-regulated in Topo I-deficient cells. Given that ectopic expression of green fluorescent protein-Topo I fusion in Topo I-deficient cells restores both wild-type phosphorylation of SR proteins and ESE-dependent splicing, we conclude that Topo I-mediated phosphorylation plays a specific role in ESE-regulated splicing.
Altered serine/arginine-rich protein phosphorylation and exonic enhancer-dependent splicing in Mammalian cells lacking topoisomerase I
Soret, J.; Gabut, M.; Dupon, C.; Kohlhagen, G.; Stevenin, J.; Pommier, Y.; Tazi, J.
2003-12-01 / vol 63 / pages 8203-11
Animals; Down-Regulation; Mice; Phosphorylation; Alternative Splicing; RNA Splicing/*physiology; Nuclear Proteins/*metabolism; Antineoplastic Agents/pharmacology; Camptothecin/pharmacology; DNA Topoisomerases, Type I/*deficiency/genetics; Drug Resistance, Neoplasm; Exons/physiology; Gene Expression Regulation, Leukemic; Green Fluorescent Proteins; Leukemia P388/enzymology/genetics; Luminescent Proteins/biosynthesis/genetics; Phosphoproteins/*metabolism; Recombinant Fusion Proteins/biosynthesis/genetics/metabolism; RNA-Binding Proteins; Trans-Activation (Genetics)