The Drosophila protein kinase LK6 is regulated by ERK and phosphorylates the eukaryotic initiation factor eIF4E in vivo.
In Drosophila cells, phosphorylation of eIF4E (eukaryotic initiation factor 4E) is required for growth and development. In Drosophila melanogaster, LK6 is the closest homologue of mammalian Mnk1 and Mnk2 [MAPK (mitogen-activated protein kinase) signal-integrating kinases 1 and 2 respectively] that phosphorylate mammalian eIF4E. Mnk1 is activated by both mitogen- and stress-activated signalling pathways [ERK (extracellular-signal-regulated kinase) and p38 MAPK], whereas Mnk2 contains a MAPK-binding motif that is selective for ERKs. LK6 possesses a binding motif similar to that in Mnk2. In the present study, we show that LK6 can phosphorylate eIF4E at the physiological site. LK6 activity is increased by the ERK signalling pathway and not by the stress-activated p38 MAPK signalling pathway. Consistent with this, LK6 binds ERK in mammalian cells, and this requires an intact binding motif. LK6 can bind to eIF4G in mammalian cells, and expression of LK6 increases the phosphorylation of the endogenous eIF4E. In Drosophila S2 Schneider cells, LK6 binds the ERK homologue Rolled, but not the p38 MAPK homologue. LK6 phosphorylates Drosophila eIF4E in vitro. The phosphorylation of endogenous eIF4E in Drosophila cells is increased by activation of the ERK pathway but not by arsenite, an activator of p38 MAPK. RNA interference directed against LK6 significantly decreases eIF4E phosphorylation in Drosophila cells. These results show that LK6 binds to ERK and is activated by ERK signalling and it is responsible for phosphorylating eIF4E in Drosophila.
Parra-Palau
Josep L
JL
Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, UK.
Scheper
Gert C
GC
Harper
Daniel E
DE
Proud
Christopher G
CG
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000201:enzymology; D003593:Cytoplasm / Q000201:enzymology; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics / Q000378:metabolism*; D039603:Eukaryotic Initiation Factor-4G / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D020929:Mitogen-Activated Protein Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D011485:Protein Binding; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D029721:Drosophila Proteins; D039561:Eukaryotic Initiation Factor-4E; D039603:Eukaryotic Initiation Factor-4G; D010768:Phosphoserine; D048049:Extracellular Signal-Regulated MAP Kinases; C500415:Lk6 protein, Drosophila; D020929:Mitogen-Activated Protein Kinase Kinases; D013755:Tetradecanoylphorbol Acetate