Faculty Bibliography

PURPOSE:: Development and differentiation of the human fetal prostate are androgen dependent and follow a specific pattern of solid bud-ductal morphogenesis, which involves stromal-epithelial interactions. Androgen receptor associated protein 55 (ARA55) an androgen receptor coactivator localized in stromal cells, binds to androgen receptor (AR) and regulates androgen receptor translocation and transcriptional activity. We investigated whether ARA55 has a role in human prostate development. MATERIALS AND METHODS:: ARA55 expression was examined in 25 human prostates from fetuses at gestational ages 10 to 40 weeks and compared to the expression of 34betaE12 (a basal cell marker), smooth muscle actin, desmin (a smooth muscle marker), vimentin (a mesenchymal marker) and Ki-67 (a proliferation marker) by immunohistochemistry. RESULTS:: Prostatic epithelium appeared as solid epithelial buds from the urogenital sinus. It underwent arborization and ductal differentiation from the center to the periphery. ARA55 was expressed in stromal cells with a zonal pattern, primarily in the peripheral zone surrounding the noncanalized acini. Most cells in solid buds were positive for 34betaE12, while only basal layer cells in the centrally located epithelial ducts stained with 34betaE12. Solid buds also had a higher proliferation index than ducts. In addition, ARA55 expressing stromal cells but not ARA55 negative stromal cells showed smooth muscle differentiation. CONCLUSIONS:: The intimate relationship between ARA55 expressing stromal cells and mitotically active, noncanalized acini suggests that ARA55 has a role in the stromal-epithelial interaction involved in fetal prostate development

The biological ramifications of phosphorylation of the androgen receptor (AR) are largely unknown. To examine the phosphorylation of AR at serine 213, a putative substrate for Akt, a phosphorylation site-specific antibody was generated. The use of this antibody indicated that AR Ser-213 is phosphorylated in vivo and that phosphorylation is tightly regulated in a cell type-specific manner. Furthermore, Ser-213 phosphorylation took place with rapid kinetics and was inhibited by the phosphatidylinositol 3-kinase inhibitor LY294002. Phosphorylation occurred in response to R1881 and dihydrotestosterone but weakly if at all in response to testosterone. It did not occur in response to AR antagonists or growth factor stimulation in the absence of an AR agonist. Transcription assays using an AR-responsive reporter gene construct showed that activated phosphatidylinositol 3-kinase inhibited transcription mediated by wild type AR but not that of a mutant AR variant (S213A), which could not be phosphorylated at Ser-213. By immunohistochemistry, the AR Ser(P)-213 antigen was detected in prostate epithelial but not stromal cells despite the fact that an antibody recognizing both phosphorylated and non-phosphorylated forms of AR demonstrates that AR is present in both cell types as expected. In fetal tissue the AR-Ser(P)-213 antigen was present in epithelial cells of the urogenital sinus when endogenous androgen levels were high and activated Akt was prevalent, but absent at a later stage of development when endogenous androgen levels were low and Akt activation was minimal. Immunoreactivity was evident in differentiated cells lining the lumen of the urogenital sinus but not in rapidly dividing, Ki67 positive cells within the developing prostate or stromal tissue, suggesting that site-specific phosphorylation of AR Ser-213 by cellular kinases occurs in a non-proliferating cellular milieu

Androgen receptor (AR)-associated coregulator 70 (ARA70) was the first identified AR coregulator. However, its molecular mechanism and biological relevance to prostate cancer remain unclear. Here we show that ARA70 interacts with and promotes AR activity via the consensus FXXLF motif within the ARA70-N2 domain (amino acids 176-401). However, it does not promote AR activity via the classic LXXLL motif located at amino acids 92-96, although this classic LXXLL motif is important for ARA70 to interact with other receptors, such as PPARgamma. The molecular mechanisms by which ARA70 enhances AR transactivation involve the increase of AR expression, protein stability, and nuclear translocation. Furthermore, ARA70 protein is more frequently detected in prostate cancer specimens (91.74%) than in benign tissues (64.64%, p < 0.0001). ARA70 expression is also increased in high-grade prostate cancer tissues as well as the hormone-refractory LNCaP xenografts and prostate cancer cell lines. Because ARA70 can promote the antiandrogen hydroxyflutamide (HF)-enhanced AR transactivation, the increased ARA70 expression in hormone-refractory prostate tumors may confer the development of HF withdrawal syndrome, commonly diagnosed in patients with the later stages of prostate cancer. Because ARA70-N2 containing the AR-interacting FXXLF motif without coactivation function can suppress HF-enhanced AR transactivation in the hormone-refractory LNCaP cells, using the ARA70-N2 inhibitory peptide at the hormone refractory stage to battle the HF withdrawal syndrome may become an alternative strategy to treat prostate cancer