Nitric oxide-dependent ribosomal RNA cleavage is associated with inhibition of ribosomal peptidyl transferase activity in ANA-1 murine macrophages

NO can regulate specific cellular functions by altering transcriptional pro grams and protein reactivity. With respect to global cellular processes, NO has also been demonstrated to inhibit total protein synthesis and cell pro liferation. The underlying mechanisms are unknown. In a system of ANA-1 mur ine macrophages, iNOS expression and NO production were induced by exposure to endotoxin (LPS). In selected instances, cells were exposed to an exogen ous NO donor, S-nitroso-N-acetylpenicillamine or a substrate inhibitor of N O synthesis. Cellular exposure to NO, from both endogenous and exogenous so urces, was associated with a significant time-dependent decrease in total p rotein synthesis and cell proliferation. Gene transcription was unaltered. In parallel with decreased protein synthesis, cells exhibited a distinctive cleavage pattern of 28S and 18S rRNA that were the result of two distinct cuts in both 28S and 18S rRNA. Total levels of intact 28S rRNA, 18S rRNA, a nd the composite 60S ribosome were significantly decreased in the setting o f cell exposure to NO. Finally, 60S ribosome-associated peptidyl transferas e activity, a key enzyme for peptide chain elongation, was also significant ly decreased, Our data suggest that NO-mediated cleavage of 28S and 18S rRN A results in decreased 60S ribosome associated peptidyl transferase activit y and inhibition of total protein synthesis.