PLATELET-DERIVED GROWTH-FACTOR STIMULATES PHOSPHORYLATION OF THE 25 KDA MESSENGER-RNA CAP BINDING-PROTEIN (EIF-4E) IN HUMAN LUNG FIBROBLASTS

Platelet-derived growth factor exerts rapid effects on protein synthesis and polysome formation in cultured cells. We report that platelet-derived growth factor stimulates a rapid phosphorylation of eIF-4E in WI-38 human lung fibroblasts. The effect was dependent on both time and PDGF concentrations. Phosphoserine was the sole phosphoamino acid identified and tryptic phosphopeptide maps showed a single phosphopeptide under both control and PDGF conditions. Phosphorylation of eIF-4E may be one of the events required for initiating entry into G1 and commitment into S phase of the cell cycle.