Erythropoietin stimulates phosphorylation of eIF-4E and identification of a 37-kD phosphoprotein that binds mRNA caps in erythroblasts.
To explore the mechanism of erythropoietin action on differentiation of erythroblasts, we have examined its effect on regulating phosphorylation of the 25-kD mRNA cap binding protein (eIF-4E). Erythroblasts from the spleens of mice infected with the anemia strain of Friend virus (FVA cells) were studied. Erythropoietin stimulated phosphorylation of eIF-4E in FVA cells within 30 minutes, and this effect was maximal at 60 minutes. Phosphoamino acid analysis and tryptic phosphopeptide map analysis of eIF-4E isolated from both control and erythropoietin-treated cells identified a predominant phosphopeptide containing phosphoserine. However, when cells were incubated with 1 muM okadaic acid, eIF-4E was phosphorylated on both serine and threonine residues and three additional tryptic phosphopeptides were detected. We also identified a 37-kD phosphoprotein (pp37) that bound specifically to the m7GTP cap structure and coimmunoprecipitated with eIF-kD protein was phosphorylated on both serine and threonine residues. These results indicate that phosphorylation of eIF-4E is a target in erythropoietin-initiated signal transduction events and that this phosphorylation precedes observable effects of erythropoietin on macromolecular biosynthesis. Although of pp37 remains to be studied, it may represent a developmentally regulated mRNA cap binding protein.[1]References
- Erythropoietin stimulates phosphorylation of eIF-4E and identification of a 37-kD phosphoprotein that binds mRNA caps in erythroblasts. Bu, X., Bondurant, M.C., Hagedorn, C.H. Exp. Hematol. (1996) [Pubmed]
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