Inactivation of androgen receptor coregulator ARA55 inhibits androgen receptor activity and agonist effect of antiandrogens in prostate cancer cells

Abstract

Antiandrogens given to antagonize androgen receptor (AR) activity gradually lose their efficacy as antagonists and eventually function as agonists to promote (instead of block) AR-mediated growth of prostate cancer cells. The mechanisms of how antiandrogens acquire this agonist activity during hormonal therapy are largely unknown. Here, we report that expression of a dominant-negative AR-associated protein 55 (dARA55) coregulator, inhibits AR transcriptional activity and reduces the agonist activity of antiandrogens. Inducibly expressed dARA55 inhibits prostate-specific antigen and cell growth in prostate cancer cells. Further dissection of the molecular mechanism shows dARA55 can selectively suppress endogenous AR-associated protein 55 (ARA55) enhanced AR transactivation by means of interruption of dimerization between ARA55 and ARA55. These results were confirmed by using RNA interference-mediated silencing of the ARA55 gene. These results therefore provide evidence that AR function could be suppressed without mutation or change in AR itself. Taken together, these findings not only demonstrate the important roles of the ARA55 coregulator in the AR-mediated growth of prostate cancer, they also may provide a critical target for developing therapeutic agents for the antiandrogen therapy that almost always fails in the treatment of hormone-refractory prostate cancer.

Paxillin: Adapting to Change

“…This mutation is within LIM4 where an androgen receptor-binding FXXLF motif, which is conserved among paxillin family members, also resides (92). RNA interference-mediated silencing of Hic-5 ␤ has provided further support for the importance of this molecule in normal androgen signaling (208).…”

“…In addition to these cytoplasmic LIM associations, Hic-5 LIM domains have been shown to be capable of binding to DNA (187), and the capacity of paxillin and Hic-5 to interact with the nuclear matrix (315) perhaps through LIM3 (121) has been described. Furthermore, both paxillin and Hic-5 can interact with the androgen and glucocorticoid receptors through LIM4 (208). The significance of these interactions and the function of paxillin and Hic-5 in gene expression is discussed below.…”

“…ion (208). This mutation is within LIM4 where an androgen receptor-binding FXXLF motif, which is conserved among paxillin family members, also resides (92).…”

Androgen receptor and prostate cancer

“…14 ARA55 is reported to enhance AR transcriptional activity in response not only to normally weak adrenal androgens, but also to the antiandrogens hydroxyflutamide and other nonandrogenic steroids. 15 Surgical or medical castration may reduce androgen concentration, but subsequent increases in AR coactivators may rescue cancerous cells, allowing them to progress to clinically androgen depletion independent form. Alternatively, acquired mutations in AR may promote hypersensitivity to coactivators.…”

Identification of steroid derivatives that function as potent antiandrogens

“…21 Cells that were seeded in 6-well tissue culture plates were incubated with medium supplemented with charcoal-stripped FBS containing either ETOH or ligands. After 6 days of treatment (changing media every 2 days), 200 ll of MTT (Sigma Chemical Co.) stock solution (5 mg/ml) was added into each well with 2 ml of medium for 3 hr at 37°C.…”