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Advanced prostate cancer (PCa) has emerged as a public health concern due to population aging. Although androgen deprivation has proven efficacy in this condition, most advanced PCa patients will have to face failure of androgen deprivation as a treatment. Mutations in the androgen receptor (AR) from tumor cells have been shown to induce androgen independency both in PCa cell lines and in the clinic. We have investigated the molecular events leading to androgen independency in the 22Rv1 cell line, a commonly used preclinical model of PCa. Besides AR mutants that have been described so far, including nonsense mutations, recent data have focused on AR pre-mRNA aberrant splicing as a new mechanism leading to constitutively active truncated AR variants. In this article, we describe two novel variants arising from aberrant splicing of AR pre-mRNA, characterized by long mRNA transcripts that encode truncated, constitutively active proteins. We also describe several new nonsense mutants that share ligand independency and transcriptional activity. Finally, we show that alongside these mutants, 22Rv1 cells also express a mutant AR lacking exon 3 tandem duplication, a major feature of this cell line. By describing unreported AR mutants in the 22Rv1 cell line, our data emphasize the complexity and heterogeneity of molecular events that occur in preclinical models, and supposedly in the clinic. Future work on the 22Rv1 cell line should take into account the concomitant expression of various AR mutants.

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., ((c) 2007 Wiley-Liss, Inc.)