Ser-64 and Ser-111 in PHAS-I are dispensable for insulin-stimulated dissociation from eIF4E.
Insulin stimulates phosphorylation of multiple sites in the eIF4E-binding protein, PHAS-I, leading to dissociation of the PHAS-I.eIF4E complex and to an increase in cap-dependent translation. The Ser-64 and Ser-111 sites have been proposed to have key roles in controlling the association of PHAS-I and eIF4E. To determine whether the effects of insulin require these sites, we assessed the control of PHAS-I proteins having Ala-64 or Ala-111 mutations. The results indicate that phosphorylation of neither site is required for insulin to promote release of PHAS-I from eIF4E. Also, the mutation of Ser-111, which has been proposed to serve as a necessary priming site for the phosphorylation of other sites in PHAS-I, did not affect the phosphorylation of Thr-36/45, Ser-64, or Thr-69. Insulin promoted the release of eIF4E from PHAS-II, a PHAS isoform that lacks the Ser-111 site, but it was without effect on the amount of eIF4E bound to the third isoform, PHAS-III. The results demonstrate that contrary to widely accepted models, Ser-64 and Ser-111 are not required for the control of PHAS-I binding to eIF4E in cells, implicating phosphorylation of the Thr sites in dissociation of the PHAS-I.eIF4E complex. The findings also indicate that PHAS-II, but not PHAS-III, contributes to the control of protein synthesis by insulin.
D048868:Adaptor Proteins, Signal Transducing; D000409:Alanine / Q000737:chemistry; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000502:physiology; D018797:Cell Cycle Proteins; D002460:Cell Line; D018076:DNA, Complementary / Q000378:metabolism; D039561:Eukaryotic Initiation Factor-4E / Q000737:chemistry* / Q000378:metabolism; D039642:Eukaryotic Initiation Factors / Q000737:chemistry; D005822:Genetic Vectors; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D009154:Mutation; D010750:Phosphoproteins / Q000737:chemistry* / Q000502:physiology; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D014176:Protein Biosynthesis; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012694:Serine / Q000737:chemistry*; D020123:Sirolimus / Q000494:pharmacology; D013912:Threonine / Q000737:chemistry; D014162:Transfection
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D018076:DNA, Complementary; C087000:EIF4EBP1 protein, human; C104151:EIF4EBP2 protein, human; C112661:EIF4EBP3 protein, human; D039561:Eukaryotic Initiation Factor-4E; D039642:Eukaryotic Initiation Factors; D007328:Insulin; D010750:Phosphoproteins; D020033:Protein Isoforms; D013912:Threonine; D012694:Serine; D000409:Alanine; D020123:Sirolimus