Constitutive activation of the androgen receptor by a point mutation in the hinge region: A new mechanism for androgen‐independent growth in prostate cancer

Abstract

Androgen receptor (AR) mutations that modify both the ligand binding and the transactivation capacities of the AR represent one of the mechanisms involved in the transition of prostate cancer (PCa) from androgen-dependent to androgen-independent growth. We use a yeast-based functional assay to detect and analyze mutant ARs in PCa. We report the detection of 2 different mutant ARs within the same metastatic tumour sample harvested in a patient with advanced PCa who had escaped androgen deprivation. Concomitantly to the widely described T877A mutant AR, we identified an additional double mutant AR harboring the nonsense mutation Q640Stop just downstream the DNA binding domain together with the T877A point mutation. This type of mutation, which leads to a c-terminal truncated AR, has not been described yet in PCa. Using luciferase reporter assays we demonstrated that this truncated AR exhibited constitutive transactivation properties. In conclusion, our data suggest that mutation-induced constitutive activation of the AR could be a mechanism used by PCa cells to escape androgen deprivation. © 2003 Wiley-Liss, Inc. Key words: androgen receptor mutations; prostate cancer; androgen independence; constitutive transactivationProstate cancer (PCa) is the most frequently diagnosed malignancy in men and the second leading cause of cancer deaths in Western countries. As prostate cancer growth depends on androgens, the standard first line therapy for advanced PCa consists of decreasing the plasma concentration of testicular testosterone by medical or surgical castration. 1,2 This androgen ablation therapy is eventually combined to anti-androgens to further block the effects of androgens produced from adrenal precursors. The response to such androgen ablation is high and provides subjective relief to more than 80% of patients. Unfortunately, the benefit of this therapy is only transitory lasting some months or years, with a median duration of 12-18 months, and all patients will eventually relapse with tumour cells whose growth escapes the androgen deprivation. Although these relapsed tumours are clinically androgen-independent, many lines of evidence indicate that the androgen receptor (AR) signaling pathway remains active and may contribute to the escape to androgen ablation. 3 In this regard, the amplification and the overexpression of the AR gene or the stabilization of the AR may allow PCa cells to continue androgendependent growth even in very low levels of androgens left in serum after castration. 4 -6 Also, the cross-talk with the mitogenactivated protein kinase (MAPK) or the Akt/protein kinase B phosphorylation pathways 7 and the altered expression of AR coactivator proteins 8 may lead to the activation of AR in a ligandindependent manner. Finally, mutations in the ligand binding domain of the AR that expand the specificity or the affinity of the receptor to other hormones may allow it to respond to different steroids as well as anti-androgens. 9 We have described previously a yeast-based functional assay to simultane...

The Hinge Region Regulates DNA Binding, Nuclear Translocation, and Transactivation of the Androgen Receptor

“…The AR plays a key role in the development of prostate cancer and in resistance to hormone therapy (2, 3). Several point mutations in and around the hinge region have been identified in prostate cancer patients (6)(7)(8)(9)(10)(11). In our assays, both the R629Q and the K630T mutants (6, 7) have an increased potency (Fig.…”

“…Cancer Res 2007; 67: (9). May 1, 2007 We delineated the part of the hinge that inhibits the transcriptional activity of the full-length human AR to a highly basic motif between residue 629 and 636 (629-RKLKKLGN-636; Fig.…”

“…As a result, the cells are more sensitive to lower concentrations of hormone, respond to a broader range of ligands, or can be activated by other signaling pathways (4). Interestingly, several point mutations in and around the hinge region have been identified in prostate cancer patients (6)(7)(8)(9)(10)(11).…”

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

“…An important fraction of ARDCTD is nuclear and is able to bind DNA in the absence of ligand (28). Moreover, ARDCTD expression leads to constitutive activation of artificial androgen-responsive promoters in SDM (29)(30)(31)(32)…”

ERK Regulates Calpain 2-induced Androgen Receptor Proteolysis in CWR22 Relapsed Prostate Tumor Cell Lines

“…Structure function analysis of the AR showed that deletion of the LBD generates a constitutively active AR molecule (15). A subsequent study identified a nonsense mutation at Q640 that results in a truncated constitutively active AR in a tumor refractory to androgen ablation therapy (16). We and others previously reported that calpain cleaves the AR molecule to produce various LMW isoforms (17)(18)(19), including an ϳ80,000 C-terminally truncated AR.…”