Serum growth factors cause rapid stimulation of protein synthesis and dephosphorylation of eIF-2 in serum deprived Ehrlich cells.
In Ehrlich ascites tumor cells maintained in serum-free medium for 16 h the rate of protein synthesis was about 50% of the rate in control (well-fed) cells. The addition of 10% calf serum led to a 1.5- to 2-fold stimulation of protein synthesis within 10 min. Stimulation was effected through a non-transcriptional mechanism which operated at the level of polypeptide chain initiation. The effect was due to non-dialyzable serum growth factors which were sensitive to treatment with dithiothreitol and iodoacetamide. Replacing the 16-h-conditioned serum-free medium with fresh serum-free medium stimulated protein synthesis about 30% in serum-deprived cells, and the effect of these low molecular weight nutrients was additive with the effect of serum factors. Phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF-2 alpha) inhibits protein synthesis by competitively inhibiting the guanine nucleotide exchange factor (GEF), and modulation of the extent of phosphorylation of eIF-2 alpha has been suggested as a probable regulatory mechanism in serum-deprived mammalian cells. We measured the ratio of phosphorylated to total eIF-2 alpha in serum-deprived cells. The ratio was elevated in serum-deprived cells compared to control (serum-fed) cells. eIF-2 was rapidly dephosphorylated in response to serum refeeding and returned to near control levels after 10 min. The rapidity of this response and the close temporal correlation between eIF-2 dephosphorylation and increased rate of protein synthesis provide evidence that eIF-2 plays an important role in the regulation of protein synthesis by serum growth factors.
Montine
K S
KS
University of Rochester Cancer Center, Department of Biochemistry, NY.
Henshaw
E C
EC
D000818:Animals; D001769:Blood; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism*; D003470:Culture Media; D004220:Disulfides / Q000378:metabolism; D004229:Dithiothreitol / Q000494:pharmacology; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D007460:Iodoacetamide / Q000494:pharmacology; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D011506:Proteins / Q000037:antagonists & inhibitors; D014407:Tumor Cells, Cultured
D003470:Culture Media; D004220:Disulfides; D015852:Eukaryotic Initiation Factor-2; D020662:Guanine Nucleotide Exchange Factors; D011506:Proteins; D007930:Leucine; D004229:Dithiothreitol; D007460:Iodoacetamide