Features in the N and C termini of the MAPK-interacting kinase Mnk1 mediate its nucleocytoplasmic shuttling.
Eukaryotic initiation factor eIF4E binds to the 5'-cap structure of the mRNA and also to the molecular scaffold protein eIF4G. eIF4E is a phosphoprotein, and the kinases that act on it have been identified as the MAPK-interacting kinases Mnk1 and Mnk2. Mnk1/2 also bind to the scaffold protein eIF4G. The N-terminal region of Mnk1 has previously been shown to bind to importin alpha, a component of the nuclear transport machinery, although Mnk1 itself is cytoplasmic. Here we identify a CRM1-type nuclear export motif in the C-terminal part of Mnk1. Substitution of hydrophobic residues in this motif results in Mnk1 becoming nuclear. This has allowed us to study the features of Mnk1 that are involved in its transport to the nucleus. This process requires part, but not all, of a polybasic region near the N terminus of Mnk1. Residues required for nuclear transport are also required for its interaction with importin alpha. This polybasic region also serves a second function in that it is required for the binding of Mnk1 to eIF4G, although the residues involved in this interaction are not identical to those involved in the binding of Mnk1 to importin alpha. Interaction of Mnk1 with eIF4G promotes the phosphorylation of eIF4E. Mutations that reduce the binding of Mnk1 to eIF4G in vivo and in vitro also decrease the ability of Mnk1 to enhance eIF4E phosphorylation in vivo, underlining the importance of the eIF4G-Mnk1 interaction in this process.
Parra-Palau
Josep-Lluis
JL
Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, United Kingdom.
Scheper
Gert C
GC
Wilson
Mary L
ML
Proud
Christopher G
CG
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology*; D003593:Cytoplasm / Q000201:enzymology*; D004622:Embryo, Mammalian; D039603:Eukaryotic Initiation Factor-4G / Q000235:genetics / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics; D049452:Green Fluorescent Proteins; D006801:Humans; D007163:Immunosorbent Techniques; D047908:Intracellular Signaling Peptides and Proteins; D007525:Isoelectric Focusing; D007668:Kidney; D008164:Luminescent Proteins / Q000235:genetics; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010446:Peptide Fragments / Q000502:physiology*; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D013329:Structure-Activity Relationship; D014162:Transfection; D028901:alpha Karyopherins / Q000378:metabolism
D039603:Eukaryotic Initiation Factor-4G; D047908:Intracellular Signaling Peptides and Proteins; D008164:Luminescent Proteins; D010446:Peptide Fragments; D011993:Recombinant Fusion Proteins; D028901:alpha Karyopherins; D049452:Green Fluorescent Proteins; D005982:Glutathione Transferase; C491395:MKNK1 protein, human; C106281:Mknk1 protein, mouse; D017346:Protein Serine-Threonine Kinases