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Rapamycin selectively inhibits translation of mRNAs encoding elongation factors and ribosomal proteins
Abstract:
The immunosuppressant rapamycin (RAP) has been demonstrated to specifically inhibit the activity of p70 S6 kinase (p70s6k) and subsequent phosphorylation of ribosomal S6 protein in mammalian cells. Addition of RAP to proliferating lymphoid cells resulted in inhibition of protein synthesis before any changes in the rate of cell proliferation. When the cellular composition of proteins was examined by gel electrophoresis, RAP dramatically inhibited synthesis of selective proteins, particularly elongation factor 2 (eEF-2). The inhibition of eEF-2 synthesis by RAP was at the translational level. Further, RAP inhibited the polysomal association of mRNAs encoding not only eEF-2 but also elongation factor 1-alpha and ribosomal proteins without affecting mRNA translation of any of a number of nonribosomal proteins. Since levels of activity of p70s6k are correlated with the rate of biosynthesis of eEF-2, p70s6k might be involved in coordinate translational regulation of ribosomal protein mRNAs in higher eukaryotes, which have a conserved sequence at their 5' end. Specific inhibition of ribosomal protein synthesis likely explains the differential antiproliferative effect of RAP on proliferating and mitogen-activated quiescent cells.
Insights
The immunosuppressant rapamycin (RAP) inhibits protein synthesis by targeting specific ribosomal proteins at the translational level. This selective inhibition, mediated by p70 S6 kinase (p70s6k), explains RAP's antiproliferative effects.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Rapamycin (RAP) is an immunosuppressant known to inhibit p70 S6 kinase (p70s6k).
- p70s6k activity is linked to ribosomal protein synthesis and cell proliferation.
Purpose of the Study:
- To investigate the precise mechanism by which rapamycin inhibits protein synthesis in mammalian cells.
- To determine the specific proteins and pathways affected by rapamycin treatment.
Main Methods:
- Treatment of proliferating lymphoid cells with rapamycin.
- Analysis of protein synthesis rates and cellular protein composition via gel electrophoresis.
- Examination of mRNA polysomal association.
Main Results:
- Rapamycin inhibited overall protein synthesis before affecting cell proliferation.
- Selective inhibition of specific protein synthesis, notably elongation factor 2 (eEF-2), occurred at the translational level.
- Rapamycin reduced the polysomal association of mRNAs for eEF-2 and ribosomal proteins, but not nonribosomal proteins.
Conclusions:
- p70 S6 kinase activity is implicated in the translational regulation of ribosomal protein mRNAs.
- Rapamycin's specific inhibition of ribosomal protein synthesis contributes to its differential antiproliferative effects on various cell types.