Novel phosphorylation sites of eukaryotic initiation factor-4F and evidence that phosphorylation stabilizes interactions of the p25 and p220 subunits.

Bu X, Haas DW, Hagedorn CH
J Biol Chem. 1993 268 (7): 4975-8

PMID: 8444875

Only serine phosphorylation of eukaryotic initiation factor-4E (eIF-4E) has been previously reported in intact cells. We found that treatment of HepG2 cells with okadaic acid resulted in as much as 20% of eukaryotic initiation factor (eIF)-4E phosphorylation occurring on threonine residues and that tryptic phosphopeptide maps showed several previously unrecognized phosphopeptides. Analysis of p220 from control and okadaic acid-treated cells demonstrated serine and threonine phosphorylation under both conditions. However, a unique pattern of phosphopeptides in okadaic acid-treated cells was observed. The most notable finding was that hyperphosphorylation of eIF-4E and p220 increased binding of p220 but not eIF-4E to the m7GTP cap structure. We suggest that phosphorylation of eIF-4E is more complicated than previously recognized and that hyperphosphorylation of eIF-4E and p220 recruits more p220 into the protein complex that associates with mRNA caps. A better understanding of these protein-protein and protein-mRNA interactions may aid the design of anti-sense directed chemistries that disrupt such interactions for a specific target mRNA (Baker, B.F., Miraglia, L., and Hagedorn, C. H. (1992) J. Biol. Chem. 267, 11495-11499).

MeSH Terms (7)

Cells, Cultured Ethers, Cyclic Eukaryotic Initiation Factor-4F Okadaic Acid Peptide Initiation Factors Phosphorylation RNA, Messenger

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