Nuclear eukaryotic initiation factor 4E (eIF4E) colocalizes with splicing factors in speckles.
The eukaryotic initiation factor 4E (eIF4E) plays a pivotal role in the control of protein synthesis. eIF4E binds to the mRNA 5' cap structure, m(7)GpppN (where N is any nucleotide) and promotes ribosome binding to the mRNA. It was previously shown that a fraction of eIF4E localizes to the nucleus (Lejbkowicz, F., C. Goyer, A. Darveau, S. Neron, R. Lemieux, and N. Sonenberg. 1992. Proc. Natl. Acad. Sci. USA. 89:9612-9616). Here, we show that the nuclear eIF4E is present throughout the nucleoplasm, but is concentrated in speckled regions. Double label immunofluorescence confocal microscopy shows that eIF4E colocalizes with Sm and U1snRNP. We also demonstrate that eIF4E is specifically released from the speckles by the cap analogue m(7)GpppG in a cell permeabilization assay. However, eIF4E is not released from the speckles by RNase A treatment, suggesting that retention of eIF4E in the speckles is not RNA-mediated. 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB) treatment of cells causes the condensation of eIF4E nuclear speckles. In addition, overexpression of the dual specificity kinase, Clk/Sty, but not of the catalytically inactive form, results in the dispersion of eIF4E nuclear speckles.
Dostie
J
J
Department of Biochemistry, McGill University, Montréal, Québec H3G 1Y6, Canada.
Lejbkowicz
F
F
Sonenberg
N
N
D001324:Autoantigens / Q000302:isolation & purification; D002467:Cell Nucleus / Q000648:ultrastructure*; D004004:Dichlororibofuranosylbenzimidazole / Q000494:pharmacology; D015226:Dinucleoside Phosphates / Q000494:pharmacology; D039561:Eukaryotic Initiation Factor-4E; D010448:Peptide Initiation Factors / Q000302:isolation & purification*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors; D012326:RNA Splicing; D016601:RNA-Binding Proteins / Q000302:isolation & purification; D017412:Ribonucleoprotein, U1 Small Nuclear / Q000302:isolation & purification; D017411:Ribonucleoproteins, Small Nuclear / Q000302:isolation & purification*; D055517:snRNP Core Proteins
D001324:Autoantigens; D015226:Dinucleoside Phosphates; D039561:Eukaryotic Initiation Factor-4E; D010448:Peptide Initiation Factors; D012315:RNA Caps; D016601:RNA-Binding Proteins; D017412:Ribonucleoprotein, U1 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins; D004004:Dichlororibofuranosylbenzimidazole; C062229:7-methyl-diguanosine triphosphate; C066780:Clk dual-specificity kinases; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D012319:RNA Polymerase II