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Androgenic up-regulation of androgen receptor cDNA expression in androgen-independent prostate cancer cells
J L Dai1, C A Maiorino, P J Gkonos
1Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, FL 33101, USA.
Abstract:
The expression of the androgen receptor (AR) gene is regulated by androgens. Although androgens down-regulate AR mRNA in most cell lines and tissues, including the prostate, up-regulation occurs in some tissues. Androgen-mediated reduction in AR mRNA is reproduced in COS1 cells and in the androgen-sensitive human prostate cancer cell line LNCaP when each expresses the AR cDNA. We have previously established that the AR cDNA contains the requisite sequences for this down-regulation. Here we shown that androgen promoted up-regulation of AR mRNA in two androgen-independent human prostate cancer cell lines, PC3 and DU145, when each was transfected with a human AR cDNA. This effect was due to the AR cDNA and not to the heterologous promoter driving AR expression. In addition to up-regulation of AR mRNA, androgen induced comparable increases in AR protein levels in PC3 cells stably expressing an AR cDNA (PC3/AR). Up-regulation of AR in PC3/AR cells was accompanied by failure of these cells to undergo desensitization or inactivation of AR following prolonged (96 h) androgen administration, whereas the same conditions resulted in desensitization of AR transactivation in LNCaP cells and in CVl cells that stably express the AR cDNA. Androgen treatment of PC3/AR cells resulted in induction of an androgen-regulated reporter gene (MMTV-CAT) as well as the native prostate-specific antigen gene, which is silent in untransfected PC3 but is androgen up-regulated in LNCaP and in the prostate. These results suggest that ectopic expression of AR in androgen-independent prostate cancer cell lines establishes both typical and atypical androgenic responses in a target gene-specific manner. Androgenic up-regulation of AR cDNA expression may be due to distinct signaling mechanisms that influence androgen action in androgen-independent prostate cancer cells.
Insights
Androgens can up-regulate androgen receptor (AR) mRNA and protein in some prostate cancer cells, unlike typical down-regulation. This AR up-regulation leads to sustained signaling and gene activation in androgen-independent cells.
Area of Science:
- Molecular Endocrinology
- Cancer Biology
- Prostate Cancer Research
Background:
- Androgen receptor (AR) gene expression is typically down-regulated by androgens in most prostate tissues and cell lines.
- However, AR up-regulation by androgens has been observed in specific tissues.
- Previous studies confirmed AR cDNA contains sequences for androgen-mediated down-regulation.
Purpose of the Study:
- To investigate androgen's effect on AR mRNA expression in androgen-independent prostate cancer cell lines (PC3 and DU145).
- To determine if ectopic AR expression in these cells leads to altered androgenic responses and signaling.
- To explore potential distinct signaling mechanisms in androgen-independent cells.
Main Methods:
- Transfection of PC3 and DU145 cells with human AR cDNA.
- Analysis of AR mRNA and protein levels following androgen administration.
- Assessment of AR transactivation and target gene expression (MMTV-CAT, prostate-specific antigen) after prolonged androgen exposure.
- Comparison of cellular responses between androgen-dependent (LNCaP) and androgen-independent (PC3/AR) cells.
Main Results:
- Androgen promoted significant up-regulation of AR mRNA in PC3 and DU145 cells transfected with AR cDNA.
- Ectopic AR expression in PC3/AR cells led to increased AR protein levels and sustained AR signaling without desensitization.
- PC3/AR cells exhibited androgen-induced expression of reporter and prostate-specific antigen genes, unlike LNCaP cells which showed desensitization.
- These findings indicate target gene-specific androgenic responses.
Conclusions:
- Ectopic AR expression in androgen-independent prostate cancer cells establishes both typical and atypical androgenic responses.
- Androgenic up-regulation of AR cDNA expression suggests distinct signaling pathways in these cells.
- These findings may offer insights into novel therapeutic strategies targeting AR signaling in advanced prostate cancer.