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Staphylococcus aureus alpha-toxin. 2. Reduction of epidermal growth factor receptor affinity in PC12 cells
Abstract:
Staphylococcus aureus alpha-toxin, at sub-cytotoxic concentrations, inhibits both the 125I-labeled epidermal growth factor (EGF) binding and autophosphorylation properties of EGF-receptors in PC12 cells. This inhibition occurred only in intact cells and is probably due to a decrease in the affinity of the receptor for EGF. Streptolysin S and parcelsin could mimic the alpha-toxin effect below cytotoxic concentrations, as measured by a 51Cr release assay. In contrast, other membrane perturbing toxins with different lipid specificity, such as tetanolysin and cobra direct lytic factor, inhibited [125I]EGF binding only at cytotoxic concentrations. Staphylococcal alpha-toxin also stimulated 3-fold the specific binding of a radioactive tumor-promoting phorbol ester (PDBu) to PC12 cells at concentrations similar to those required for the inhibition of [125I]EGF binding. Although the exact mechanism for the inhibition of EGF binding by alpha-toxin has not been established, our results suggest that protein kinase C may be involved in this time-dependent process.
Insights
Staphylococcus aureus alpha-toxin inhibits epidermal growth factor (EGF) receptor binding and function in intact cells. This effect, potentially mediated by protein kinase C, occurs at sub-cytotoxic concentrations.
Area of Science:
- Cell Biology
- Toxicology
- Biochemistry
Background:
- Staphylococcus aureus alpha-toxin is a pore-forming protein with known cytotoxic effects.
- Epidermal growth factor (EGF) receptors play crucial roles in cell growth and signaling.
- The interaction between bacterial toxins and cellular receptors is an area of active research.
Purpose of the Study:
- To investigate the effects of Staphylococcus aureus alpha-toxin on EGF receptor binding and function in PC12 cells.
- To explore the potential involvement of protein kinase C in the observed effects.
- To compare the effects of alpha-toxin with other membrane-perturbing toxins.
Main Methods:
- Utilized 125I-labeled epidermal growth factor (EGF) binding assays.
- Measured EGF receptor autophosphorylation.
- Employed 51Cr release assay to assess cytotoxicity.
- Investigated the binding of a radioactive tumor-promoting phorbol ester (PDBu).
Main Results:
- Staphylococcus aureus alpha-toxin, at sub-cytotoxic concentrations, inhibited both EGF binding and autophosphorylation of EGF receptors in intact PC12 cells.
- This inhibition appears to be due to a reduced affinity of the receptor for EGF.
- Other toxins like Streptolysin S and parcelsin mimicked this effect, while tetanolysin and cobra direct lytic factor required cytotoxic concentrations.
- Alpha-toxin also stimulated the binding of PDBu, suggesting a role for protein kinase C.
Conclusions:
- Staphylococcus aureus alpha-toxin modulates EGF receptor activity at non-lytic concentrations.
- The mechanism likely involves a decrease in receptor affinity for EGF and may be mediated by protein kinase C.
- Toxin specificity and concentration are critical factors in determining effects on EGF receptor signaling.