Effect of cellular growth on protein metabolism in chicken embryo fibroblasts

Abstract

Protein synthesis in cultures of chick embryo fibroblasts was measured as the incorporation of ~H-leucine into trichloroacetic acid-insoluble material. Intracellular protein degradation was measured as the release of trichloroacetic acid-soluble radioactivity after pre-labelling cell protein with 3H-leucine.The rate of degradation increased whereas the rates of protein synthesis and cell growth decreased as the cultures approached confluence in growth medium with 1% serum. The rate of protein degradation was reduced when the serum concentration in the culture medium was increased, and the effect of increasing serum concentration was higher in dense than in sparse cultures. There were linear correlations between the rate of protein turnover and culture density, but the slope was lower in medium with 4% chicken serum than in medium with 1% chicken serum.Cell growth was measured as the incorporation of 3H-thymidine into DNA. The correlation between culture density and thymidine incorporation was sigmoid. Density-dependent inhibition of growth was less complete in medium with 4% serum than in 1% serum. The correlations between protein degradation and growth rate were also sigmoid and seemed to differ in media with 1% and 4% serum.