Unexpected paracrine action of prostate cancer cells harboring a new class of androgen receptor mutation—A new paradigm for cooperation among prostate tumor cells

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. ' 2007 Wiley-Liss, Inc.Key words: androgen receptor mutation; hormone-refractory prostate cancer; paracrine action; transcriptional activities; clonal cooperation Androgens are involved in the normal development of the prostate gland as well as in the progression of prostate cancer (PCa). Their actions are mediated by the androgen receptor (AR) signaling pathway. The AR belongs to the nuclear receptor superfamily and is structured in 3 major domains necessary for liganddependent transcriptional activities. 1 The activation function AF-1 localized in the amino-terminal part of the AR is largely responsible for transactivation. 2 The central part of the AR contains the DNA binding domain (DBD), which is best conserved among the steroid hormone receptors subfamily, and allows specific recognition of androgen responsive element (ARE) in the promoter of AR target genes. The ligand binding domain (LBD) and the second activation function AF-2 are limited to the carboxyl-terminal end (CTE). This CTE plays an essential role in the regulation of AR transcriptional activities, being the site of ligand binding and allowing interactions with AR cofactors and with the amino terminus region of the AR. 3-5 Also, the CTE harbors 3 potential phosphorylation sites targeted by the EGFR (ser-650), c-erb2 (ser-791) and protein kinase A (ser-662) signaling pathways. 6-8 All these AR functional domains and phosphorylation sites can be affected by mut...

Effects of Sorafenib on C-Terminally Truncated Androgen Receptor Variants in Human Prostate Cancer Cells

“…Transactivational activity of AR Q640X was shown to be very strong on artificial androgen-responsive promoters (ARE(2x)) but was very weak on the PSA promoter [17,18]. In contrast to the wild type AR many ARΔLBD are unable to activate the full panel of androgen-dependent genes [17–19].…”

Androgen Receptor Controls EGFR and ERBB2 Gene Expression at Different Levels in Prostate Cancer Cell Lines

“…These authors identified low levels of expression of ARDCTD in AAR PCa xenografts. Interestingly, different point mutations introducing premature stop codons were identified in mRNA extracted from 16% of AAR PCa metastasis (29,(44)(45)(46).…”

Melatonin Inhibits Androgen Receptor Splice Variant-7 (AR-V7)-Induced Nuclear Factor-Kappa B (NF-κB) Activation and NF-κB Activator-Induced AR-V7 Expression in Prostate Cancer Cells: Potential Implications for the Use of Melatonin in Castration-Resistant Prostate Cancer (CRPC) Therapy

“…The expression plasmids which contain full-length AR (pEGFP-AR-FL) and AR-V7 (pEGFP-AR-V7) were kindly provided by Dr. J. Luo (Johns Hopkins University, Baltimore, MD, USA). The cDNAs encoding AR-V7 and full-length AR were inserted into the pEGFP-C3 vector to express the EGFP-AR-V7 and EGFP-AR-FL fusion protein respectively [8,37]. Melatonin (Cat.…”