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Melittin-induced hyperactivation of phospholipase A2 activity and calcium influx in ras-transformed cells
1Department of Microbiology and Immunology, University of Tennessee, Memphis 38163.
Abstract:
The activated ras oncogene is a key mediator of cellular transformation and is present in a wide variety of primary human neoplasms. The biochemical role of the ras oncogene in cellular transformation is at present unclear, and hence approaches to control its activities in transformed cells have met with limited success. Previous studies have demonstrated the ability of melittin, a 26 amino acid amphipathic peptide from bee venom, to specifically counterselect for cells in culture that express high levels of the ras oncogene product. The biochemical basis for this counterselection is currently unknown. This study demonstrates the ability of melittin to hyperactivate phospholipase A2 (PLA2) in ras-transformed cells by the mediation of enhanced influx of calcium ions (Ca2+). This hyperactivation of PLA2 and Ca2+ mobilization in ras-transformed cells by melittin is mimicked by the calcium ionophore, A23187. Both melittin- and A23187-mediated PLA2 hyperactivation require Ca2+. However, the action of melittin is strongly dependent on extracellular Ca2+, whereas that of A23187 is not. Melittin-induced Ca2+ influx and PLA2 hyperactivation is inhibited by manganese ions (Mn2+). These studies reveal a close correlation between the extent of PLA2 hyperactivation and Ca2+ mobilization, suggesting a causal relationship.
Insights
Melittin hyperactivates phospholipase A2 (PLA2) in ras-transformed cells by increasing calcium ion (Ca2+) influx. This mechanism, dependent on extracellular Ca2+, offers a potential strategy for controlling ras oncogene activity in cancer.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- The ras oncogene is crucial in cellular transformation and prevalent in human neoplasms.
- The precise biochemical role of ras in transformation remains unclear, limiting therapeutic strategies.
- Melittin, a peptide from bee venom, selectively targets cells with high ras oncogene product levels.
Purpose of the Study:
- To elucidate the biochemical mechanism by which melittin counterselects ras-transformed cells.
- To investigate melittin's effect on phospholipase A2 (PLA2) and calcium ion (Ca2+) signaling pathways.
Main Methods:
- Investigated melittin's effect on PLA2 activity and Ca2+ levels in ras-transformed cells.
- Utilized calcium ionophore A23187 for comparative analysis.
- Assessed the role of extracellular Ca2+ and manganese ions (Mn2+) in melittin's action.
Main Results:
- Melittin hyperactivates PLA2 in ras-transformed cells via enhanced Ca2+ influx.
- Melittin-induced effects are mimicked by A23187 and require Ca2+.
- Melittin's action is dependent on extracellular Ca2+ and inhibited by Mn2+.
Conclusions:
- Melittin's ability to hyperactivate PLA2 and mobilize Ca2+ is a key mechanism in targeting ras-transformed cells.
- A strong correlation exists between PLA2 hyperactivation and Ca2+ mobilization, suggesting a causal link.
- This study provides insights into novel therapeutic approaches for cancers driven by the ras oncogene.