Mechanism of Ribonuclease Cytotoxicity (∗)

Bovine seminal ribonuclease (BS-RNase), a dimeric homolog of bovine pancreatic ribonuclease A (RNase A), is toxic to mammalian cells. In contrast to dimeric BS-RNase, monomeric BS-RNase and RNase A are not cytotoxic and are bound tightly by cytosolic ribonuclease inhibitor. To elucidate the mechanis...

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Bibliographic Details
Published in:The Journal of biological chemistry 1995-12, Vol.270 (52), p.31097-31102
Main Authors: Kim, Jin-Soo, Soucek, Josef, Matousek, Josef, Raines, Ronald T.
Format: Article
Language:English
Subjects:
Amino Acid Sequence
Animals
Cattle
Cell Survival - drug effects
Cells, Cultured
Endoribonucleases - chemistry
Endoribonucleases - metabolism
Endoribonucleases - pharmacology
Humans
Macromolecular Substances
Molecular Sequence Data
Ribonuclease, Pancreatic - chemistry
Ribonuclease, Pancreatic - metabolism
Sequence Alignment
Tumor Cells, Cultured
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Summary:Bovine seminal ribonuclease (BS-RNase), a dimeric homolog of bovine pancreatic ribonuclease A (RNase A), is toxic to mammalian cells. In contrast to dimeric BS-RNase, monomeric BS-RNase and RNase A are not cytotoxic and are bound tightly by cytosolic ribonuclease inhibitor. To elucidate the mechanism of ribonuclease cytotoxicity, we constructed a series of hybrid and semisynthetic enzymes and examined their properties. In five hybrid enzymes, divergent residues in BS-RNase were replaced with the analogous residues of RNase A so as to diminish an interaction with a putative cellular receptor. In a semisynthetic enzyme, the disulfide bonds that cross-link the monomeric subunits of dimeric BS-RNase were replaced with thioether bonds, which can withstand the reducing environment of the cytosol. Each hybrid and semisynthetic enzyme had ribonucleolytic and cytotoxic activities comparable with those of wild-type BS-RNase. These results suggest that dimeric BS-RNase (pI = 10.3) enters cells by adsorptive rather than receptor-mediated endocytosis and then evades cytosolic ribonuclease inhibitor so as to degrade cellular RNA. This mechanism accounts for the need for a cytosolic ribonuclease inhibitor and for the cytotoxicity of other homologs of RNase A.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.270.52.31097