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Published on: April 25, 2018
Protection of mRNA against nucleases in cytoplasmic extracts of mouse sarcoma ascites cells
M Coutts1, A Krowczynska, G Brawerman
1Department of Biochemistry, Tufts University Health Sciences Schools, Boston, MA 02111.
Abstract:
The mRNA present in extracts of mouse sarcoma 180 (S-180) ascites cells is relatively resistant to degradation when compared to added tracer ribosomal RNA. Deproteinized mRNA added to the extract is about as resistant as the endogenous mRNA, an indication that the protection is not due to any protein present in the endogenous mRNP structure. A major determinant of protection lies at the 5' end of RNA chains, where the presence of a triphosphate or a cap enhances the stability of mRNA transcripts. Addition of poly(A) to a capped transcript had little effect on stability. Stabilization by the cap structure is apparently not due to association of transcripts with a cap-binding protein. The discrimination in RNA decay rates appears to be based on interaction of the different RNA species with an exonuclease, which represents the predominant ribonuclease activity in the extract. Other major cytoplasmic nucleases are suppressed by an RNase inhibitor that is present in excess.
Insights
Messenger RNA (mRNA) in sarcoma cells resists degradation, primarily due to its 5' cap structure. This stability is mediated by exonuclease interaction, not protective proteins.
Area of Science:
- Molecular Biology
- Biochemistry
- Cell Biology
Background:
- Messenger RNA (mRNA) stability is crucial for gene expression regulation.
- Ribonucleic acid (RNA) degradation is mediated by various nucleases within the cell.
- The specific mechanisms protecting mRNA from degradation in cancer cells are not fully understood.
Purpose of the Study:
- To investigate the factors contributing to the relative resistance of mRNA to degradation in mouse sarcoma 180 (S-180) ascites cells.
- To elucidate the role of the 5' end, protein association, and specific nucleases in mRNA decay rates.
Main Methods:
- Comparison of degradation rates between endogenous mRNA and added tracer ribosomal RNA in S-180 ascites cell extracts.
- Assessment of mRNA stability after deproteinization to isolate the role of RNA structure.
- Evaluation of the impact of 5' end modifications (triphosphate, cap, poly(A) tail) on mRNA stability.
- Identification of the predominant ribonuclease activity responsible for RNA decay.
Main Results:
- Endogenous mRNA from S-180 cells exhibits greater resistance to degradation than added ribosomal RNA.
- Deproteinized mRNA shows similar resistance to endogenous mRNA, indicating protein-independent protection.
- The 5' end of RNA, specifically the presence of a triphosphate or a cap structure, significantly enhances mRNA stability.
- Polyadenylation had minimal impact on the stability of capped transcripts.
- Stabilization by the cap structure is not mediated by cap-binding proteins.
- Exonuclease activity appears to be the primary determinant of RNA decay rate discrimination.
Conclusions:
- mRNA stability in S-180 ascites cells is significantly influenced by its 5' cap structure, not by associated proteins.
- The predominant ribonuclease, an exonuclease, dictates RNA decay rates, with other nucleases inhibited.
- These findings provide insights into mRNA turnover mechanisms in cancer cells.
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