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Inhibition of protein synthesis in mouse myeloma cells by Ricinus communis toxin
Abstract:
The mechanism of inhibition of protein synthesis in mouse myeloma cells by Ricinus communis toxin was studied. No significant disaggregation of polysomes into monosomes was detected in the toxin-treated cells. The activity of the polysomes isolated from the cells treated with the toxin in protein synthesis was remarkably lower than that of the untreated cells, while the activity of the supernatant enzyme fraction was retained. The ribosomes derived from the polysomes of the toxin-treated cells were inactive in poly(U)-dependent polyphenylalanine synthesis. The activity of ribosomes reconstituted by hybridizing subunits derived from the ribosomes of normal and toxin-treated cells were measured in poly(U)-dependent polyphenylalanine synthesis, and the 60 S subunit was revealed to be inactive. These results indicate that the target of action of the toxin towards intact cells is the 60 S ribosomal subunit.
Insights
Ricinus communis toxin inhibits protein synthesis by inactivating the 60S ribosomal subunit in mouse myeloma cells. This toxin targets the 60S subunit, not polysome disaggregation, impacting protein synthesis efficiency.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Protein synthesis is crucial for cellular function.
- Ricinus communis toxin (RCA) is a known inhibitor of protein synthesis.
- The precise molecular target of RCA in intact cells requires elucidation.
Purpose of the Study:
- To investigate the mechanism by which Ricinus communis toxin inhibits protein synthesis in mouse myeloma cells.
- To identify the specific cellular component targeted by the toxin.
Main Methods:
- Analysis of polysome integrity and activity in toxin-treated cells.
- Assay of protein synthesis activity in isolated polysomes and supernatant fractions.
- Characterization of ribosome subunit activity using in vitro reconstitution assays with poly(U)-dependent polyphenylalanine synthesis.
Main Results:
- No significant polysome disaggregation was observed in toxin-treated cells.
- Isolated polysomes from treated cells showed markedly reduced protein synthesis activity.
- Ribosomes from treated cells were inactive in polyphenylalanine synthesis, with the 60S subunit identified as the inactive component upon reconstitution.
Conclusions:
- Ricinus communis toxin inhibits protein synthesis by targeting the 60S ribosomal subunit.
- The toxin's mechanism involves direct inactivation of the 60S subunit, not polysome disassembly.
- This study clarifies the molecular target of RCA in protein synthesis inhibition.