Cytosolic RNase inhibitor only affects RNases with intrinsic cytotoxicity
Daria Maria Monti1, Giuseppe D'Alessio
1Department of Biological Chemistry, University of Naples Federico II, Via Mezzocannone, 16, 80134 Napoli, Italy.
Abstract:
Cytosolic RNase inhibitor binds to and neutralizes most members of the pancreatic type RNase superfamily. However, there are a few exceptions, e.g. amphibian onconase and bovine seminal RNase, and these are endowed with cytotoxic activity. Also, RNase variants created by mutagenesis to partially evade the RNase inhibitor acquire cytotoxic activity. These findings have led to the proposal that the cytosolic inhibitor acts as a sentry to protect mammalian cells from foreign RNases. We silenced the expression of the gene encoding the cytosolic inhibitor in HeLa cells and found that the cells become more sensitive to foreign cytotoxic RNases. However foreign, non-cytotoxic RNases remain non-cytotoxic. These results indicate that the cytosolic inhibitor neutralizes those foreign RNases that are intrinsically cytotoxic and have access to the cytosol. However, its normal physiological role may not be to guard against foreign RNases in general.
Insights
The cytosolic RNase inhibitor protects cells from toxic foreign RNases. Silencing this inhibitor in HeLa cells increased sensitivity to cytotoxic RNases, suggesting a specific protective role.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Cytosolic RNase inhibitor (RI) neutralizes most pancreatic RNases.
- Certain RNases (e.g., onconase, bovine seminal RNase) and mutated variants evade RI and exhibit cytotoxicity.
- This led to the hypothesis that RI acts as a general cellular defense against foreign RNases.
Purpose of the Study:
- To investigate the role of cytosolic RNase inhibitor in cellular defense against foreign RNases.
- To determine if silencing RNase inhibitor affects sensitivity to both cytotoxic and non-cytotoxic foreign RNases.
Main Methods:
- Gene silencing of cytosolic RNase inhibitor in HeLa cells using RNA interference.
- Exposure of silenced and control HeLa cells to various foreign RNases (cytotoxic and non-cytotoxic).
- Assessment of cell viability and sensitivity to RNase-induced cytotoxicity.
Main Results:
- Silencing cytosolic RNase inhibitor significantly increased HeLa cell sensitivity to foreign cytotoxic RNases.
- Sensitivity to foreign non-cytotoxic RNases remained unchanged after RNase inhibitor gene silencing.
- These findings suggest a specific role for cytosolic RNase inhibitor.
Conclusions:
- Cytosolic RNase inhibitor specifically neutralizes intrinsically cytotoxic foreign RNases that can access the cytosol.
- The physiological role of cytosolic RNase inhibitor may not be general protection against all foreign RNases.
- RI's primary function appears to be defense against specific cytotoxic threats rather than a broad security mechanism.
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