Phosphorylation of eucaryotic translation initiation factor 4B Ser422 is modulated by S6 kinases.
The eucaryotic translation initiation factor 4B (eIF4B) stimulates the helicase activity of the DEAD box protein eIF4A to unwind inhibitory secondary structure in the 5' untranslated region of eucaryotic mRNAs. Here, using phosphopeptide mapping and a phosphospecific antiserum, we identify a serum-responsive eIF4B phosphorylation site, Ser422, located in an RNA-binding region required for eIF4A helicase-promoting activity. Ser422 phosphorylation appears to be regulated by the S6Ks: (a) Ser422 phosphorylation is sensitive to pharmacological inhibitors of phosphoinositide-3 kinase and the mammalian target of rapamycin; (b) S6K1/S6K2 specifically phosphorylate Ser422 in vitro; and (c) rapamycin-resistant S6Ks confer rapamycin resistance upon Ser422 phosphorylation in vivo. Substitution of Ser422 with Ala results in a loss of activity in an in vivo translation assay, indicating that phosphorylation of this site plays an important role in eIF4B function. We therefore propose that eIF4B may mediate some of the effects of the S6Ks on translation.
Raught
Brian
B
Department of Biochemistry and McGill Cancer Centre, McGill University, Montréal, Québec, Canada.
Peiretti
Franck
F
Gingras
Anne-Claude
AC
Livingstone
Mark
M
Shahbazian
David
D
Mayeur
Greg L
GL
Polakiewicz
Roberto D
RD
Sonenberg
Nahum
N
Hershey
John W B
JW
D002460:Cell Line; D004351:Drug Resistance; D039642:Eukaryotic Initiation Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation / Q000235:genetics; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
D039642:Eukaryotic Initiation Factors; D019869:Phosphatidylinositol 3-Kinases; D010768:Phosphoserine; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C031799:eIF-4B; C546842:MTOR protein, human