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The cytotoxic ribonuclease onconase targets RNA interference (siRNA)
Hong Zhao1, Barbara Ardelt, Wojciech Ardelt
1Department of Pathology, Brander Cancer Research Institute, New York Medical College, Valhalla, New York 10595, USA.
Abstract:
Onconase (Onc), a ribonuclease from oocytes of Northern Leopard frogs (Rana pipiens) is cytostatic and cytotoxic to a variety of tumor lines in vitro, inhibits growth of tumors in animal in vivo models and enhances sensitivity of tumor cells to a number of other cytotoxic agents with diverse mechanism of action. In Phase III clinical trials Onc demonstrated significant efficacy in patients with malignant mesothelioma that failed prior chemotherapy. We previously postulated that the antitumor activity of Onc and the observed synergisms with other antitumor modalities at least in part may be mediated by targeting RNA interference (RNAi). In the present study we observed that the silencing of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene in human lung adenocarcinoma A549 cells by siRNA was effectively prevented by Onc. While transfection of cells with GAPDH siRNA reduced expression of this protein by nearly 70%, the expression was restored in the cells exposed to 0.8 muM Onc for 48 or 72 h. The data thus provide evidence that one of the targets of Onc is siRNA, likely within the RNA-induced silencing complex (RISC). In light of the findings that microRNAs are involved in tumor pathogenesis as well as in enhancing cell resistance to anticancer therapy the present data may provide explanation for both, the antitumor Onc activity and its propensity to enhance effectiveness of cytotoxic drugs.
Insights
Onconase (Onc), a frog-derived ribonuclease, prevents cancer cells from silencing the GAPDH gene. This suggests Onc targets RNA interference (RNAi) pathways, potentially explaining its anti-tumor effects and synergy with other therapies.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- Onconase (Onc), a ribonuclease from Rana pipiens, exhibits anti-tumor activity in vitro and in vivo.
- Onc enhances tumor cell sensitivity to various cytotoxic agents.
- Previous studies suggested Onc's antitumor effects may involve RNA interference (RNAi).
Purpose of the Study:
- To investigate whether Onconase (Onc) interferes with RNA interference (RNAi) pathways.
- To determine if Onc impacts the silencing of specific genes, such as GAPDH.
- To provide mechanistic insights into Onc's antitumor activity and synergistic effects.
Main Methods:
- Human lung adenocarcinoma A549 cells were treated with Onconase (Onc) and GAPDH siRNA.
- Gene silencing efficacy was assessed by measuring glyceraldehyde 3-phosphate dehydrogenase (GAPDH) protein expression.
- Onc's effect on siRNA-mediated gene silencing was evaluated at 48 and 72 hours.
Main Results:
- Onconase (Onc) treatment prevented the silencing of the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) gene by siRNA in A549 cells.
- While GAPDH siRNA alone reduced protein expression by ~70%, Onc exposure restored expression levels.
- This indicates Onc interferes with the siRNA-mediated gene silencing process.
Conclusions:
- Onconase (Onc) likely targets small interfering RNA (siRNA) or components of the RNA-induced silencing complex (RISC).
- This interaction with RNAi machinery may explain Onc's direct antitumor effects.
- The findings suggest a mechanism for Onc's ability to enhance the efficacy of other anticancer therapies.
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