Effect of 5-azacytidine on cytoplasmic ribosomal and messenger ribonucleic acids in BSC-1 cells.

5-Azacytidine (5-AzaCR) inhibited the accumulation of 28S and 18S ribonucleic acids (RNAs) in the cytoplasm of treated cells. The inhibition of 28S and 18S RNAs in the cytoplasm of BSC-1 cells was dependent upon the concentration of 5-AzaCR employed and the time of exposure. At a concentration of 200 mug/ml for 2 h, 5-AzaCR inhibited the cytoplasmic 28S and 18S RNAs by 80 and 70%, respectively. The 28S and 18S RNAs that appeared in the cytoplasm of treated cultures had no altered secondary structure, as analyzed by polyacrylamide gel electrophoresis. The inhibitory effect on cytoplasmic 28S and 18S RNAs was found to be reversible, and removal of 5-AzaCR from treated cultures allowed the accumulation of cytoplasmic 28S and 18S RNAs to almost normal levels by 20 h. 5-AzaCR appeared to have no effect upon the synthesis and processing of polyadenylic acid-containing messenger RNA in treated cultures. However, the formation of the 80S ribosomal subunit appeared to be inhibited in drug-treated cells. Moreover, 5-AzaCR treatment caused a disaggregation of polyribosomes and an accumulation of 80S ribosomes.