Effects of serine on protein synthesis and insulin receptors.

Erythroblastic leukemic cells incubated in media containing essential amino acids, glutamine, and serine subsequently bound approximately 30% more [125I]insulin than those incubated without serine. The effect was due to an increase in receptor number, without change in affinity. Other nonessential amino acids had no effect. Increased insulin binding was observed with serine concentrations of 5.5 microM and maximum effects were seen at 22 microM. Serine-induced increases in insulin binding were detectable after 15 min of incubation and were abolished by the addition of cycloheximide (1 micrograms/ml) but not by actinomycin D (1 microgram/ml). Incorporation of [3H]leucine into protein was increased fourfold within 1 h by incubation with serine. The effect was detectable with 5.5 microM serine but, in contrast to insulin binding, reached a maximum at 88 microM serine. This differential dose responsiveness may represent selective posttranscriptional control of receptor synthesis, processing, insertion into the membrane, or recycling.