Translational control of protein synthesis in stimulated WI-38 fibroblasts

A cell-free protein synthesis system employing ribosomes from WI-38 human diploid fibroblasts was developed and its optimum MgC12 and KC1 levels and pH value found. The rate at which ribosomes are able to incorporate radioactive leucine into proteins ([14C]leucine incorporation/10 min/100 mug rRNA) and the number of growing peptide chains [3H]puromycinpeptides formed/100 mug rRNA) was determined. When confluent monolayers of WI-38 cells were stimulated to proliferate by serum, a transient increase in the rate of peptide elongation by ribosomes was observed at 60 min after stimulation. This increase was not affected by the presence of actinomycin D (10 mug/ml) in the stimulating medium. A change in the relative amount of certain ribosome-associated proteins accompanied the increased elongation rate of peptide growth. The alteration in associated proteins could not be accounted for by an increased synthesis of protein. Finally, the early activation of ribosomes in stimulated WI-38 cells appears to result from the removal of an inhibitor(s) of ribosome function.