Signaling from Akt to FRAP/TOR targets both 4E-BP and S6K in Drosophila melanogaster.
The eIF4E-binding proteins (4E-BPs) interact with translation initiation factor 4E to inhibit translation. Their binding to eIF4E is reversed by phosphorylation of several key Ser/Thr residues. In Drosophila, S6 kinase (dS6K) and a single 4E-BP (d4E-BP) are phosphorylated via the insulin and target of rapamycin (TOR) signaling pathways. Although S6K phosphorylation is independent of phosphoinositide 3-OH kinase (PI3K) and serine/threonine protein kinase Akt, that of 4E-BP is dependent on PI3K and Akt. This difference prompted us to examine the regulation of d4E-BP in greater detail. Analysis of d4E-BP phosphorylation using site-directed mutagenesis and isoelectric focusing-sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated that the regulatory interplay between Thr37 and Thr46 of d4E-BP is conserved in flies and that phosphorylation of Thr46 is the major phosphorylation event that regulates d4E-BP activity. We used RNA interference (RNAi) to target components of the PI3K, Akt, and TOR pathways. RNAi experiments directed at components of the insulin and TOR signaling cascades show that d4E-BP is phosphorylated in a PI3K- and Akt-dependent manner. Surprisingly, RNAi of dAkt also affected insulin-stimulated phosphorylation of dS6K, indicating that dAkt may also play a role in dS6K phosphorylation.
Miron
Mathieu
M
Department of Biochemistry and McGill Cancer Center, McGill University, 3655 Promenade Sir-William-Osler, Montréal, Québec H3G 1Y6, Canada.
Lasko
Paul
P
Sonenberg
Nahum
N
D064413:3-Phosphoinositide-Dependent Protein Kinases; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017124:Conserved Sequence; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism*; D007328:Insulin / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D051059:PTEN Phosphohydrolase; D010448:Peptide Initiation Factors; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D034622:RNA Interference; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
D064413:3-Phosphoinositide-Dependent Protein Kinases; D002352:Carrier Proteins; D029721:Drosophila Proteins; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D051059:PTEN Phosphohydrolase; D010448:Peptide Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D010744:Phosphoric Monoester Hydrolases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D020794:Receptor Protein-Tyrosine Kinases; D019893:Ribosomal Protein S6 Kinases; D025521:Tumor Suppressor Proteins; C410006:Thor protein, Drosophila; C080148:tor protein, Drosophila; C494917:Akt1 protein, Drosophila