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Interferon gamma-induced reduction in erbB-2 tyrosyl phosphorylation in human ovarian carcinoma cells
1University of Maryland Cancer Center, Baltimore 21201.
Abstract:
Interferon, which inhibits growth of ovarian cancer cells in vivo and in vitro, decreases expression of erbB-2 protein in ovarian carcinoma cell lines. We now show that interferon-gamma (IFN-gamma) also decreases constitutive tyrosine phosphorylation of erbB-2 and inhibits erbB-2 kinase activity in an ovarian cancer cell line. SK-OV3 ovarian cancer cells, which over-express erbB-2, were treated with IFN-gamma for 0-72 hr. Immunoblot analysis revealed that IFN decreased the levels of tyrosyl phosphorylated erbB-2 24 hr after IFN treatment. Protein levels of erbB-2 were not changed until 72 hr post-treatment. Tyrosine kinase (TK) activity of immunoprecipitated erbB-2 for an exogenous substrate was decreased in IFN-treated cells. Total cellular protein tyrosine phosphatase (PTPase) activity for the epidermal growth factor receptor was not changed by IFN treatment. Our results suggest that the decreased levels of tyrosyl phosphorylated proteins observed after IFN treatment in SK-OV3 cells may be due to inhibition of erbB-2 kinase activity.
Insights
Interferon-gamma (IFN-gamma) inhibits ovarian cancer cell growth by decreasing erbB-2 tyrosine phosphorylation and kinase activity. This suggests a novel therapeutic mechanism for ovarian carcinoma targeting erbB-2 signaling.
Area of Science:
- Oncology
- Molecular Biology
- Biochemistry
Background:
- Interferon inhibits ovarian cancer cell growth.
- Interferon reduces erbB-2 protein expression in ovarian carcinoma cell lines.
- erbB-2 is over-expressed in SK-OV3 ovarian cancer cells.
Purpose of the Study:
- To investigate the effect of interferon-gamma (IFN-gamma) on erbB-2 tyrosine phosphorylation and kinase activity in ovarian cancer cells.
- To determine if IFN-gamma inhibits erbB-2 kinase activity.
- To explore the mechanism by which IFN-gamma affects erbB-2 signaling.
Main Methods:
- SK-OV3 ovarian cancer cells over-expressing erbB-2 were treated with IFN-gamma for 0-72 hours.
- Immunoblot analysis was used to assess tyrosyl phosphorylated erbB-2 levels.
- Tyrosine kinase (TK) activity of immunoprecipitated erbB-2 was measured.
- Total cellular protein tyrosine phosphatase (PTPase) activity was assessed.
Main Results:
- IFN-gamma decreased tyrosyl phosphorylated erbB-2 levels within 24 hours.
- IFN-gamma inhibited the tyrosine kinase activity of erbB-2.
- Protein levels of erbB-2 remained unchanged until 72 hours post-treatment.
- No change was observed in total cellular PTPase activity.
Conclusions:
- IFN-gamma inhibits erbB-2 kinase activity in ovarian cancer cells.
- Decreased tyrosyl phosphorylation of erbB-2 is a key effect of IFN-gamma treatment.
- IFN-gamma's anti-cancer effects may be mediated through inhibition of erbB-2 signaling.