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A cell-specific and selective effect on transactivation by the androgen receptor
D A Gordon1, N L Chamberlain, F A Flomerfelt
1Department of Biochemistry, University of Arizona, Tucson 85721, USA.
Abstract:
The androgen (AR) and glucocorticoid receptors (GR) are related ligand-activated transcriptional regulators which bind the same cis-acting element and are coexpressed in a variety of cell types. Despite a shared DNA binding site, these receptors mediate diverse cellular responses. To explain this paradox, the existence of cell-specific factors that interact with, and modulate the function of, distinct receptors has been proposed. Prostate epithelial cell growth is sensitive to androgens, but is not affected by glucocorticoids, even though both AR and GR are expressed in these cells. We have recently isolated a unique panel of prostate epithelial cell lines from normal rats and have used these cell lines to examine cell-specific steroid responses. In this study, we compared the abilities of AR and GR to enhance transcription of several different reporter genes regulated by simple (i.e., noncompsite) hormone response elements (HREs) in prostate and nonprostate cell lines. The cell-specific effect occurred independently of the AR hormone binding domain and could be observed with a GAL4 fusion protein containing only the AR N-terminal regulatory domain. Gel shift analyses showed that the relative DNA binding affinity of AR for a probe containing a simple HRE was similar in prostate and nonprostate cell extracts. Presently, the only factors known to mediate steroid receptor-specific gene regulation are cJun and cFos, but there were no cell-specific differences in the functional levels of these proteins which could account for a preferential effect on AR-dependent transcription. Taken together, these results suggest that cell-specific activities exist which can preferentially modulate transcriptional transactivation by AR.
Insights
Cell-specific factors modulate androgen receptor (AR) and glucocorticoid receptor (GR) activity. These factors preferentially enhance AR-dependent transcription in prostate cells, explaining differential steroid responses.
Area of Science:
- Molecular Biology
- Endocrinology
- Cell Biology
Background:
- Androgen receptor (AR) and glucocorticoid receptor (GR) are related transcriptional regulators.
- Despite binding the same DNA elements, they mediate distinct cellular responses.
- Cell-specific factors are hypothesized to explain these differential effects.
Purpose of the Study:
- To investigate cell-specific modulation of AR and GR transcriptional activity.
- To compare AR and GR function in prostate versus non-prostate cell lines.
- To identify the domains and factors involved in cell-specific steroid responses.
Main Methods:
- Utilized rat prostate epithelial cell lines and non-prostate cell lines.
- Compared AR and GR transcriptional enhancement of reporter genes with simple hormone response elements (HREs).
- Performed gel shift analyses to assess DNA binding affinity and examined cJun/cFos levels.
Main Results:
- Cell-specific effects on AR and GR activity were observed.
- The cell-specific modulation was independent of the AR hormone binding domain, residing in the N-terminal domain.
- AR DNA binding affinity was similar in prostate and non-prostate cell extracts.
- No significant cell-specific differences in cJun or cFos levels were found.
Conclusions:
- Cell-specific activities preferentially modulate transcriptional transactivation by the androgen receptor.
- These findings suggest a mechanism for differential steroid hormone action in specific cell types, particularly in prostate biology.
- The N-terminal domain of AR plays a crucial role in mediating these cell-specific responses.