Entry into Cells and Selective Degradation of tRNAs by a Cytotoxic Member of the RNase A Family

• Published in: The Journal of biological chemistry Vol. 277; no. 17; pp. 15142 - 15146
• Main Authors: Saxena, Shailendra K., Sirdeshmukh, Ravi, Ardelt, Wojciech, Mikulski, Stanislaw M., Shogen, Kuslima, Youle, Richard J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 26.04.2002; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Biological Transport; Electrophoresis, Polyacrylamide Gel; Hydrolysis; Ribonucleases - metabolism; RNA, Transfer - metabolism; Transcriptional Activation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M108115200

Onconase (P-30 protein), an enzyme in the ribonuclease A superfamily, exerts cytostatic, cytotoxic, and antiviral activity when added to the medium of growing mammalian cells. We find that onconase enters living mammalian cells and selectively cleaves tRNA with no detectable degradation of rRNA. The RNA specificity of onconase in vitro using reticulocyte lysate and purified RNA substrates indicates that proteins associated with rRNA protect the rRNA from the onconase ribonucleolytic action contributing to the cellular tRNA selectivity of onconase. The onconase-mediated tRNA degradation in cells appears to be accompanied by increased levels of tRNA turnover and induction of tRNA synthesis perhaps in response to the selective toxin-induced loss of tRNA. Degradation products of tRNA3Lys, which acts as a primer for HIV-1 replication, were clearly detected in cells infected with HIV-1 and treated with sublethal concentrations of onconase. However, a new synthesis of tRNA3Lys also seemed to occur in these cells resulting in plateauing of the steady-state levels of this tRNA. We conclude that the degradation of tRNAs may be a primary factor in the cytotoxic activity of onconase.