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Enhanced c-jun activity alters responsiveness to medroxyprogesterone acetate in Ishikawa human endometrial carcinoma
M Alkhalaf1, L J Murphy, L C Murphy
1Department of Biochemistry, University of Manitoba, Winnipeg, Canada.
Abstract:
The involvement of altered c-jun activity in medroxyprogesterone acetate (MPA)-induced growth responses in human endometrial carcinoma cells is examined in this paper. Under conditions of MPA-induced growth inhibition, c-jun mRNA and protein levels are decreased in Ishikawa cells. This decrease is accompanied by an overall decrease in endogenous AP-1 activity in these cells. Only a transient decrease in c-jun mRNA level without any effect on endogenous AP-1 activity is seen in HEC-50 human endometrial carcinoma cells after MPA treatment. Increased expression and activity of c-jun was achieved in Ishikawa cells by transient transfection of Rous sarcoma virus (RSV)-c-jun alone or RSV-c-jun plus AP-1 binding sites (5x-4-beta-phorobol 12-myristate 13-acetate response element-thymidine kinase-chloramphenicol acetyltransferase), respectively. These treatments were accompanied by an increase in cell numbers due to MPA treatment in Ishikawa cells. In contrast, MPA treatment of mock-transfected, RSV-jun-B-transfected, or 5x-4 beta-phorbol 12-myristate 13-acetate response element-thymidine kinase-chloramphenicol acetyltransferase alone transfected Ishikawa cells resulted in the expected decrease in cell numbers. The data presented in this paper are consistent with the hypothesis that altered c-jun activity in a target cell can alter proliferative responsiveness to MPA and suggest that such a mechanism may be associated with resistance to hormonal manipulative therapies used in the treatment of both human breast and endometrial cancer.
Insights
Altered c-jun activity influences medroxyprogesterone acetate (MPA) responses in endometrial cancer cells. Modulating c-jun impacts cell proliferation, suggesting a role in hormonal therapy resistance.
Area of Science:
- Oncology
- Molecular Biology
- Endocrinology
Background:
- Medroxyprogesterone acetate (MPA) is a progestin used in hormonal therapy.
- Endometrial carcinoma cell growth can be influenced by hormonal treatments.
- The role of c-jun in MPA-induced cellular responses requires further investigation.
Purpose of the Study:
- To investigate the involvement of c-jun activity in MPA-induced growth responses in human endometrial carcinoma cells.
- To determine if altered c-jun expression affects cell proliferation in response to MPA.
- To explore the potential link between c-jun activity and resistance to hormonal therapies.
Main Methods:
- Assessing c-jun mRNA and protein levels in Ishikawa and HEC-50 cells after MPA treatment.
- Measuring endogenous AP-1 activity in response to MPA.
- Transfecting Ishikawa cells with Rous sarcoma virus (RSV)-c-jun and AP-1 binding sites to modulate c-jun expression and activity.
- Evaluating cell proliferation following MPA treatment in transfected and mock-transfected cells.
Main Results:
- MPA treatment decreased c-jun mRNA, protein, and AP-1 activity in Ishikawa cells, correlating with growth inhibition.
- HEC-50 cells showed only a transient decrease in c-jun mRNA without affecting AP-1 activity after MPA treatment.
- Increased c-jun expression/activity in Ishikawa cells led to increased cell numbers upon MPA treatment.
- Conversely, MPA decreased cell numbers in mock-transfected or c-jun-downregulated Ishikawa cells.
Conclusions:
- Altered c-jun activity can modify endometrial carcinoma cell proliferation in response to MPA.
- This mechanism may contribute to resistance observed in hormonal manipulative therapies for breast and endometrial cancers.
- Targeting c-jun activity could be a strategy to overcome hormonal therapy resistance.