Protein synthesis in hyperoxic endothelial cells: evidence for translational defect.

To study the effects of hyperoxia on protein synthesis in primary cultures of porcine aortic endothelial cells, we exposed confluent cells to different O2 concentrations for various durations. Exposure to 95% O2 for 5 days resulted in a 71% inhibition of [3H]phenylalanine incorporation into total proteins. When compared with control cells, we observed no changes in 1) the pool size of free cytoplasmic phenylalanine and of phenylalanine attached to transfer RNA (tRNA), 2) the rate of protein degradation, and 3) the rate of charging of tRNA with phenylalanine. We found that under hyperoxic conditions 1) the incorporation of [3H]-uridine into total and polyadenylated RNA was increased, 2) the efficiency of extracted messenger RNA to direct protein synthesis in a reticulocyte lysate was maintained, 3) the proportion of polymeric to monomeric ribosomes was slightly increased, and 4) the rate of elongation, as measured by the ribosomal transit time, was decreased. Thus the reduction in protein synthesis in hyperoxic cells appears to result primarily from defects at the translational level in polypeptide chain elongation.