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The involvement of protein tyrosine kinase activity in a tumor necrosis factor resistance mechanism
1Department of Microbiology, University of Hawaii, Honolulu 96822, USA.
Abstract:
Certain cytokines activate pathways involving protein phosphorylation. Serine and threonine phosphorylation are most common, whereas tyrosine phosphorylation is a rare post-translational event, accounting for a very small percentage of phosphorylated amino acids. Nonetheless, protein tyrosine kinase activity is associated with several cell surface receptors and is involved in intracellular signaling. Here, we show that tumor necrosis factor (TNF) treatment of cells resistant to TNF-mediated lysis resulted in an increase in protein tyrosine kinase activity. Moreover certain TNF-resistant cell lines became sensitive to TNF-mediated cytolysis when treated with the inhibitors of protein tyrosine kinases, genistein, and herbimycin A. In contrast, genistein had no effect on the lysis a TNF-sensitive cell line. The increase in TNF-mediated lysis affected by genistein occurred only when it was present during TNF treatment, and the effect was maximal when the inhibitor was added 30 min after the TNF. These findings suggest that, in TNF-resistant cells, TNF activates a protein tyrosine kinase that contributes to the cell's resistance to lysis and this resistance mechanism does not function in the TNF-sensitive cell line.
Insights
Tumor necrosis factor (TNF) activates protein tyrosine kinases in resistant cells, increasing resistance to cell death. Inhibiting these kinases with genistein or herbimycin A restored TNF-induced cell lysis in resistant cells.
Area of Science:
- Molecular Biology
- Cellular Signaling
- Immunology
Background:
- Cytokines, like tumor necrosis factor (TNF), regulate cellular processes through signaling pathways.
- Protein phosphorylation, particularly serine/threonine, is common, while tyrosine phosphorylation is less frequent but crucial for signaling.
- Protein tyrosine kinases (PTKs) are involved in cell surface receptor signaling.
Purpose of the Study:
- To investigate the role of protein tyrosine kinase activity in tumor necrosis factor (TNF)-mediated cell lysis resistance.
- To determine if PTK inhibitors can overcome TNF resistance in specific cell lines.
Main Methods:
- Treatment of TNF-resistant and TNF-sensitive cell lines with TNF.
- Assay of protein tyrosine kinase activity following TNF treatment.
- Evaluation of TNF-mediated cytolysis in the presence of PTK inhibitors (genistein, herbimycin A).
Main Results:
- TNF treatment increased PTK activity in TNF-resistant cells.
- Genistein and herbimycin A sensitized TNF-resistant cells to TNF-mediated lysis.
- PTK inhibitors did not affect lysis in TNF-sensitive cells.
- Inhibitor effectiveness was dependent on timing relative to TNF exposure.
Conclusions:
- TNF activates a PTK in resistant cells, contributing to lysis resistance.
- This PTK-mediated resistance mechanism is specific to TNF-resistant cell lines.
- Targeting PTKs may offer a strategy to enhance TNF-based therapies.