Differential Stimulation of Phosphorylation of Initiation Factors eIF-4F, eIF-4B, eIF-3, and Ribosomal Protein S6 by Insulin and Phorbol Esters

摘要: Exposure of quiescent, serum-starved 3T3-L1 cells to insulin promotes phosphorylation initiation factors eIF-4F, eIF-4B, and eIF-3 p120, as well ribosomal protein S6. Phosphorylation both the p25 p220 subunits eIF-4F is stimulated typically by 2.5-5-fold, with a 2-4-fold increase in eIF-4B p120. Optimal stimulation observed 10(-9) M insulin. A similar pattern seen upon treatment 1 x 10(-6) phorbol 12-myristate 13-acetate (PMA). Two-dimensional phosphopeptide mapping p25, isolated from insulin- or PMA-stimulated cells, results single tryptic phosphopeptide, indicating site identical that obtained kinase C. more complex map subunit. Following PMA-stimulation vitro Ca2+/phospholipid-dependent (protein C). stimulation, appearance novel peptides. Upon prolonged exposure PMA, are no longer responsive this mitogen eIF-4b, S6 via C-dependent mechanism observed. Addition these down-regulated leads p220, S6, lesser extent, eIF-4B; little p120 Thus, phosphorylated PMA-dependent insulin-dependent pathways, whereas only activation Phosphopeptide maps suggest protease-activated II one kinases involved insulin-stimulated response C-depleted cells.