[Show abstract][Hide abstract] ABSTRACT: The androgen receptor (AR) is a ligand-activated transcription factor that displays genomic actions characterized by binding to androgen-response elements in the promoter of target genes as well as nongenomic actions that do not require nuclear translocation and DNA binding. In this study, we report exclusive cytoplasmic actions of a splicing variant of the AR detected in a metastatic prostate cancer. This AR variant, named AR23, results from an aberrant splicing of intron 2, wherein the last 69 nucleotides of the intronic sequence are retained, leading to the insertion of 23 amino acids between the two zinc fingers in the DNA-binding domain. We show that the nuclear entry of AR23 upon dihydrotestosterone (DHT) stimulation is impaired. Alternatively, DHT-activated AR23 forms cytoplasmic and perinuclear aggregates that partially colocalize with the endoplasmic reticulum and are devoid of genomic actions. However, in LNCaP cells, this cytoplasmic DHT-activated AR23 remains partially active as evidenced by the activation of transcription from androgen-responsive promoters, the stimulation of NF-kappaB transcriptional activity and by the decrease of AP-1 transcriptional activity. Our data reveal novel cytoplasmic actions for this splicing AR variant, suggesting a contribution in prostate cancer progression.
[Show abstract][Hide abstract] ABSTRACT: The emergence of mutations in the androgen receptor (AR) gene is a recurrent event during progression of prostate cancer (PCa) on androgen ablation therapy. In this study, we show that nonsense mutations that lead to carboxyl-terminal end truncated ARs are found at high frequency in metastatic PCas. Transcriptional activities of the Q640X mutant AR in the androgen-sensitive LNCaP cell line differ to those of the wild-type AR. Indeed, this mutant AR exhibits strong and ligand-independent transcriptional activities from an artificial promoter construct containing two repeats of androgen-responsive elements, but is inactive on the human PSA gene promoter. Nevertheless, the expression of the Q640X mutant AR in LNCaP cells is accompanied by an increase in the level of PSA protein, and by an increase in the expression of the endogenous AR gene. This enhanced expression of the endogenous AR gene is not limited to the sole transfected cells, but is observed in non-transfected neighboring cells. Additionally, in co-cultures of transfected and non-transfected LNCaP cells, the Q640X mutant AR leads to an unpredicted nuclear localization of the endogenous AR protein in the two cellular populations and this, in the absence of androgen. These data indicate that cells expressing the Q640X mutant AR acquire the property to emit a signal that activates the AR in neighboring cells by a paracrine mechanism and in a ligand-independent manner. Our data strongly support the notion of cooperation among tumor cells in PCa and could be of relevance for the understanding of progression on androgen ablation therapy.
Preview · Article · Sep 2007 · International Journal of Cancer
[Show abstract][Hide abstract] ABSTRACT: Missense mutations in the androgen receptor (AR) contribute to the failure of hormonal therapy for prostate cancer (PCa), but the underlying molecular bases remain uncharacterized. Here, we describe a new AR variant found in a hormone-refractory metastatic PCa, in which threonine 575 in the DNA binding domain, and threonine 877 in the ligand-binding domain, were both replaced by an alanine. Using gene reporter assays, we demonstrate that the T575A mutation weakened transcriptional activity from promoters containing AR-specific responsive elements, while activity from promoters with AR-non-specific elements was enhanced. Data from gel shift experiments revealed a preferential binding of the T575A mutant to AR-non-specific motifs. We demonstrate that the two mutations T575A and T877A cooperate to confer new functional properties on the AR, and that the mutant AR functions simultaneously as a promiscuous AR due to the T877A mutation, and an unfaithful AR due to the T575A mutation.
No preview · Article · Mar 2006 · Cellular and Molecular Life Sciences CMLS