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A nuclear localization sequence endows human pancreatic ribonuclease with cytotoxic activity
Montserrat Bosch1, Antoni Benito, Marc Ribó
1Laboratori d'Enginyeria de Proteïnes, Departament de Biologia, Facultat de Ciències, Universitat de Girona, Campus de Montilivi s/n, E-17071 Girona, Spain.
Biochemistry
|February 26, 2004
Summary
Introducing a novel cytotoxic human pancreatic ribonuclease variant, PE5, demonstrates that targeting ribonucleases to the nucleus induces cancer cell death. This finding offers new insights into ribonuclease-based cancer therapies.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Research
Background:
- Some ribonuclease superfamily members, like Onconase, exhibit cancer cell cytotoxicity.
- Human pancreatic ribonuclease (HPR) is not cytotoxic, likely due to inhibition by cytosolic ribonuclease inhibitor.
- Previously, cytotoxic HPR variants were inhibitor-resistant.
Purpose of the Study:
- To characterize a novel cytotoxic HPR variant, PE5, with an introduced Arg triplet.
- To investigate the mechanism of PE5-induced cytotoxicity, focusing on cellular localization and inhibitor interaction.
- To determine if nuclear targeting of ribonucleases can induce cytotoxicity.
Main Methods:
- Engineering of a human pancreatic ribonuclease variant (PE5) with an Arg triplet.
- Cellular uptake and localization studies using fluorescence microscopy.
- Nuclear import assays.
- Cytotoxicity assays comparing PE5 with control variants and Onconase.
Main Results:
- PE5 exhibits significant cytotoxicity, only 5-15 times less than Onconase, despite sensitivity to the ribonuclease inhibitor.
- PE5 localizes to late endocytic compartments and is efficiently transported to the nucleus, specifically the nucleolus.
- Nuclear targeting, not inhibitor resistance or charge modification alone, is crucial for cytotoxicity.
Conclusions:
- Targeting a ribonuclease to the nucleus effectively induces cytotoxicity in cancer cells.
- The Arg triplet in PE5 confers a nuclear localization signal, leading to nucleolar accumulation.
- Ribonuclease-induced cytotoxicity likely results from interference with rRNA processing and ribosome assembly in the nucleolus.