The prolongation of the limited lifespan of human embryonic lung fibroblasts by hydrocortisone was previously associated with increased uridine incorporation into ribosomal RNA (rRNA). Using polyacrylamide gel electrophoresis, we show here that the continuous treatment with 12 microM hydrocortisone results in increased uridine incorporation into rRNA precursors in cells stimulated to grow by serum, but not in resting cells, suggesting that the hormone does not directly activate rRNA transcription. Chase experiments indicate that the stability of 28S and 18S rRNA is enhanced by hydrocortisone in quiescent cells but not after serum refeeding. Similar results were also observed for transfer RNA (tRNA). Therefore, these effects of hydrocortisone seem to be indirect consequences of pleiotropic actions of glucocorticoid, such as stimulation of processes involved in cell proliferation and inhibition of lysosomal enzymes.
Blood Cell Division