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Nuclear translocation of the estrogen receptor in autonomous C3H mouse mammary tumors
Abstract:
The reason for estrogen independence of C3H mouse mammary tumors has been sought in the initial steps of estradiol action. The characteristics of the estrogen receptors were similar to those observed in estrogen-responsive tissues: high affinity and binding specificity, DNA binding and 8S sedimentation constant as shown by sucrose gradient centrifugation. Their concentration averaged 18.5 +/- 3.5 (S.E.) fmol/mg cytosol protein in the cytosol and 3.5 +/- 1.0 fmol/mg cytosol protein in the KCl nuclear extract. The nuclear translocation of the cytosol receptor was investigated with the use of biopsy and in vivo injections of radioactive estradiol. No nuclear translocation of estrogen receptor could be ascertained with the dextran-coated charcoal assay since the free and nonspecifically bound estrogen conjugate(s) were also assayed by this technique. However, when the estrogen-receptor complexes were estimated by more specific methods such as protamine sulfate or hydroxylapatite precipitations, the estrogen receptor translocation into the nucleus was clearly shown. We therefore conclude that the estrogen independence of C3H mammary tumors cannot be explained by a defect in the two initial steps of the mechanism of action of estradiol, namely, cytosol binding and nuclear translocation of receptors.
Insights
Estrogen receptors in C3H mouse mammary tumors bind estradiol and translocate to the nucleus. This indicates that defects in these initial steps do not cause estrogen independence in these tumors.
Area of Science:
- Endocrinology
- Molecular Biology
- Oncology
Background:
- C3H mouse mammary tumors exhibit estrogen independence, a phenomenon not fully understood.
- Investigating the initial steps of estradiol action is crucial for understanding this independence.
Purpose of the Study:
- To determine if defects in initial estradiol action steps, specifically estrogen receptor binding and nuclear translocation, contribute to estrogen independence in C3H mouse mammary tumors.
Main Methods:
- Characterization of estrogen receptors in cytosol and nuclear extracts.
- Assessment of estrogen receptor nuclear translocation using radioactive estradiol and specific precipitation assays (protamine sulfate, hydroxylapatite).
- Comparison of results with dextran-coated charcoal assay limitations.
Main Results:
- Estrogen receptors in C3H mammary tumors demonstrated high affinity, specificity, DNA binding, and appropriate sedimentation characteristics.
- Specific assays confirmed estrogen receptor translocation into the nucleus, contradicting findings from the dextran-coated charcoal assay.
- Estrogen receptor concentrations in cytosol and nuclear extracts were quantified.
Conclusions:
- The estrogen independence of C3H mouse mammary tumors is not attributable to defects in initial estradiol action, including cytosol binding or nuclear translocation of estrogen receptors.
- The study highlights the importance of using specific assays to accurately measure estrogen receptor nuclear translocation.