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Variable responsiveness of hormone-inducible hybrid genes in different cell lines
Abstract:
Altered steroid responsiveness leads to various pathological conditions and is a particular problem for the treatment of cancers arising in steroid-sensitive cells. To develop cellular model systems for the analysis of the molecular mechanisms mediating altered steroid responses, we have analyzed the inducibility of a steroid-responsive promoter in different cell lines. In vitro constructs containing the mouse mammary tumor virus promoter fused to the herpes simplex virus thymidine kinase gene or the bacterial neo gene were transfected into four different cell lines [Rat-2, CHO chinese hamster ovary cells, F9, and T47D). Thymidine kinase+ clones and neo-resistant clones were selected in the presence of dexamethasone (dex) and/or other steroid hormones. We find that the mouse mammary tumor virus promoter activity is completely dependent on the presence of dex in Rat-2 cells but is constitutively active in CHO cells and is inactive in F9 teratocarcinoma cells in the presence and absence of dex. In the human breast cancer cell line T47D, we observe no response to dex but do observe an inducibility by progesterone. Examination of glucocorticoid receptors in these cell lines showed that Rat-2, CHO, and F9 cells contain sufficient receptors to allow a hormonal response, whereas in T47D cells several glucocorticoid binding activities appear to be present. Our results indicate that the presence of receptor in cells is not always sufficient to allow hormonal activation and that, in some cell lines, like CHO, other factors are present that can substitute for an activated steroid hormone receptor complex.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Altered steroid response impacts cancer treatment. Researchers studied steroid-inducible promoters in cell models, finding cell-specific responses and identifying factors beyond receptor presence influencing hormone activation.
Area of Science:
- Molecular Biology
- Cell Biology
- Endocrinology
Background:
- Altered steroid responsiveness contributes to diseases, complicating cancer therapy.
- Developing cellular models is crucial for understanding molecular mechanisms of steroid response.
Purpose of the Study:
- To analyze steroid-inducible promoter activity across different cell lines.
- To investigate the molecular basis of variable steroid responsiveness.
Main Methods:
- Transfection of reporter constructs (MMTV promoter fused to TK or neo genes) into Rat-2, CHO, F9, and T47D cells.
- Selection of clones in the presence of steroid hormones like dexamethasone.
- Analysis of promoter activity and glucocorticoid receptor expression.
Main Results:
- Mouse mammary tumor virus promoter activity varied: dexamethasone-dependent in Rat-2, constitutive in CHO, inactive in F9.
- T47D cells showed progesterone inducibility but no dexamethasone response.
- Receptor presence did not always guarantee hormonal activation; CHO cells exhibited alternative activation pathways.
Conclusions:
- Cellular context and factors beyond receptor levels dictate steroid hormone response.
- This study provides insights into mechanisms of steroid resistance and potential therapeutic targets.
