The LKB1-TSSK1B axis controls YAP phosphorylation to regulate the Hippo-YAP pathway.

The Hippo pathway's main effector, Yes-associated protein (YAP), plays a crucial role in tumorigenesis as a transcriptional coactivator. YAP's phosphorylation by core upstream components of the Hippo pathway, such as mammalian Ste20 kinase 1/2 (MST1/2), mitogen-activated protein kinase kinase kinase kinases (MAP4Ks), and their substrate, large tumor suppressor 1/2 (LATS1/2), influences YAP's subcellular localization, stability, and transcriptional activity. However, recent research suggests the existence of alternative pathways that phosphorylate YAP, independent of these core upstream Hippo pathway components, raising questions about additional means to inactivate YAP. In this study, we present evidence demonstrating that TSSK1B, a calcium/calmodulin-dependent protein kinase (CAMK) superfamily member, is a negative regulator of YAP, suppressing cellular proliferation and oncogenic transformation. Mechanistically, TSSK1B inhibits YAP through two distinct pathways. Firstly, the LKB1-TSSK1B axis directly phosphorylates YAP at Ser94, inhibiting the YAP-TEAD complex's formation and suppressing its target genes' expression. Secondly, the TSSK1B-LATS1/2 axis inhibits YAP via phosphorylation at Ser127. Our findings reveal the involvement of TSSK1B-mediated molecular mechanisms in the Hippo-YAP pathway, emphasizing the importance of multilevel regulation in critical cellular decision-making processes.

JAG1 Intracellular Domain Enhances AR Expression and Signaling and Promotes Stem-like Properties in Prostate Cancer Cells.

JAG1 expression is upregulated in high-grade metastatic prostate carcinomas and associated with poor disease-free survival of patients with prostate cancer. Intriguingly, all JAG1-positive prostate carcinomas express JICD although JICD function in prostate cancer (PC) cells is poorly understood. In this study, we found that JICD overexpression increased the expression levels of AR, especially AR-Vs, in PC cell lines and significantly enhanced androgen-independent and androgen-dependent function of ARs. Interestingly, JICD overexpression upregulated the expression of the PCSC marker CD133 in PC cells as the expression of self-renewal markers; namely, NANOG and OCT3/4 increased. In addition, JICD overexpression highly increased the expression of anti-apoptotic BCL-XL protein, while it little affected the expression of apoptotic BIM protein. In 3D cell culture assays, the spheres formed by JICD-overexpressing PC subline cells (C4-2 and CWR22Rv1) were larger than those formed by control (EV) subline cells with undifferentiated morphology. Although JICD overexpression caused quiescence in cell proliferation, it activated the expression of components in PCSC-related signaling pathways, increased PC cell mobility, and promoted in vivo xenograft mouse tumorigenesis. Therefore, JICD may play a crucial role in enhancing androgen independence and promoting stem-like properties in PC cells and should be considered a novel target for CRPC and PCSC diagnostic therapy.

TR3 Enhances AR Variant Production and Transactivation, Promoting Androgen Independence of Prostate Cancer Cells.

The pro-oncogenic function of TR3, an orphan nuclear receptor, has been reported in prostate cancer. However, the roles of TR3 in androgen receptor (AR) expression and signaling in prostate cancer cells are poorly understood. Database analysis revealed that TR3 expression level is elevated in prostate tumors, and is positively, although weakly, correlated with that of AR. TR3 overexpression increased the production of AR splice variants in addition to general upregulation of AR expression. TR3 interacted with some spliceosomal complex components and AR precursor mRNA, altering the splice junction rates between exons. TR3 also enhanced androgen-independent AR function. Furthermore, TR3 overexpression increased cell proliferation and mobility of AR-positive prostate cancer cells and stimulated tumorigenesis of androgen-independent prostate cancer cells in mouse xenograft models. This is the first study to report that TR3 is a multifunctional regulator of AR signaling in prostate cancer cells. TR3 alters AR expression, splicing process, and activity in prostate cancer cells, increasing the androgen independence of AR signaling. Therefore, TR3 may play a crucial role in the progression of prostate cancer to an advanced castration-resistant form.

Leydig Cell-Specific DAX1-Deleted Mice Has Higher Testosterone Level in the Testis During Pubertal Development.

Testosterone, the male sex hormone, is necessary for the development and function of the male reproductive system. Biosynthesis of testosterone in mammals mainly occurs in testicular Leydig cells. Many proteins such as P450c17, 3ß-HSD, and StAR are involved in testicular steroidogenesis. DAX1 is essential for sex development and interacts with nuclear receptors such as steroidogenic factor 1 to inhibit steroidogenesis. In this study, we investigated the role of DAX1 in testicular steroidogenesis in vivo by generating Leydig cell-specific DAX1-knockout mice. Radioimmunoassay revealed that the levels of testosterone and progesterone were higher in Leydig cell-specific DAX1-knockout testes than in the testes from wild-type mice during the first 3-4 weeks of aging. In addition, the expression levels of steroidogenic genes, such as StAR, P450c17, P450scc, and 3ß-HSD, were considerably higher in the testes from DAX1-knockout mice. DAX1-deficient mouse testes seemed to attain early puberty with the acceleration of germ cell development. These data suggest that DAX1 regulates the expression of steroidogenic genes, and thereby controls and fine-tunes steroidogenesis during testis development.

FOXA3, a Negative Regulator of Nur77 Expression and Activity in Testicular Steroidogenesis.

Biosynthesis of testosterone occurs mainly in the testicular Leydig cells. Nur77, an orphan nuclear receptor that is expressed in response to the luteinizing hormone/cyclic adenosine monophosphate (LH/cAMP) signaling pathway, is one of the key factors that regulate steroidogenesis in Leydig cells. The function of Nur77 is modulated through interaction with other proteins. FOXA3, a transcription factor that is crucial for male fertility, is also expressed in Leydig cells. Here, we sought to elucidate the role of FOXA3 in testicular steroidogenesis by focusing on its interaction with Nur77. LH/cAMP signaling induces the onset of steroidogenesis in Leydig cells but has a repressive effect on the expression of FOXA3. Overexpression of FOXA3 in MA-10 Leydig cells repressed cAMP-induced expression of Nur77 and its target steroidogenic genes (StAR, P450c17, and Hsd3ß). Furthermore, FOXA3 suppressed Nur77 transactivation of the promoter of steroidogenic genes. In mouse primary Leydig cells, adenovirus-mediated overexpression of FOXA3 had similar effects and resulted in decreased production of testosterone. Taken together, these results suggest the role of FOXA3 in the regulation of steroidogenic genes in Leydig cells and fine-tuning steroidogenesis in the testis.

Jagged1 intracellular domain modulates steroidogenesis in testicular Leydig cells.

Leydig cells represent the steroidogenic lineage of mammalian testis, which produces testosterone. Genetic evidence indicates the requirement of Notch signaling in maintaining a balance between differentiated Leydig cells and their progenitors during fetal development. In primary Leydig cells, Notch1 expression decreases with testicular development, while the expression of its ligand, Jagged1, remains relatively unchanged, suggesting that the roles of Jagged1 extend beyond Notch signaling. In addition, Jagged1 is known to be processed into its intracellular domain, which then translocate to the nucleus. In this study, we investigated the effect of Jagged1 intracellular domain (JICD) on steroidogenesis in Leydig cells. The independent overexpression of JICD in MA-10 Leydig cells was found to inhibit the activity of cAMP-induced Nur77 promoter. In addition, JICD suppressed Nur77 transactivation of the promoter of steroidogenic genes such as P450scc, P450c17, StAR, and 3ß-HSD. Further, adenovirus-mediated overexpression of JICD in primary Leydig cells repressed the expression of steroidogenic genes, consequently lowering testosterone production. These results collectively suggest that steroidogenesis in testicular Leydig cells, which is regulated by LH/cAMP signaling, is fine-tuned by Jagged1 during testis development.

A new compound targets the AF-1 of androgen receptor and decreases its activity and protein levels in prostate cancer cells.

Increased expression levels of constitutively active androgen receptor splice variants (AR-Vs) cause alterations in AR signaling, resulting in drug resistance and failed hormone therapy among patients with advanced prostate cancers. Several available compounds targeting the androgen axis and AR signaling have not demonstrated efficacy in preventing prostate cancer recurrence. Here, we investigated whether a new agent, 6-[6-ethoxy-5-ispropoxy-3,4-dihydroisoquinolin-2[1H)-yl]-N-[6-methylpyridin-2-yl]nicotinamide (EIQPN), has the potential for treating advanced prostate cancer. EIQPN interacted with the AR-activation fragment-1 (AF-1) domain and blocked its androgen-independent activity, robustly decreased the protein levels of AR and variants in prostate cancer cells by inducing AR protein degradation, and inhibited the androgen-independent proliferation of various AR-positive prostate cancer cells. In xenograft mouse models, EIQPN blocked the tumor growth of androgen-independent prostate cancer cells. Overall, these findings indicate that EIQPN could serve as a novel therapeutic agent for advanced recurrent prostate cancers.

The expression of CKLFSF2B is regulated by GATA1 and CREB in the Leydig cells, which modulates testicular steroidogenesis.

CKLFSF is a protein family that serves as a functional bridge between chemokines and members of the transmembrane 4 superfamily (TM4SF). In the course of evolution, CKLFSF2 has evolved as two isoforms, namely CKLFSF2A and CKLFSF2B, in mice. CKLFSF2A, also known as CMTM2A and ARR19, is expressed in the testis and is important for testicular steroidogenesis. CKLFSF2B is also known to be highly expressed in the testis. In the prepubertal stage, CKLFSF2B is expressed only in Leydig cells, but it is highly expressed in haploid germ cells and Leydig cells in adult testis. CKLFSF2B is naturally processed inside the cell at its C-terminus to yield smaller proteins compared to its theoretical size of ≈25 kDa. The Cklfsf2b gene is regulated by GATA-1 and CREB protein, binding to their respective binding elements present in the 2-kb upstream promoter sequence. In addition, the overexpression of CKLFSF2B inhibited the activity of the Nur77 promoter, which consequently represses the promoter activity of Nur77-target steroidogenic genes such as P450c17, 3ß-HSD, and StAR in MA-10 Leydig cells. Adenovirus-mediated overexpression of CKLFSF2B in primary Leydig cells isolated from adult mice shows a repression of steroidogenic gene expression and consequently testosterone production. Moreover, intratesticular injection of CKLFSF2B-expressing adenovirus in adult mice clearly had a repressive effect compared to the control injected with only GFP-expressing adenovirus. Altogether, these findings suggest that CKLFSF2B might be involved in the development and function of Leydig cells and regulate testicular testosterone production by fine-tuning the expression of steroidogenic genes.

Estrogen receptor-related receptor γ regulates testicular steroidogenesis through direct and indirect regulation of steroidogenic gene expression.

Biosynthesis of testosterone, which mainly occurs in testicular Leydig cells, is controlled by steroidogenic proteins, such as StAR and P450c17. Although estrogen-related receptor gamma (ERRγ), an orphan nuclear receptor, is expressed in the testis, its role is not well understood. In this study, we investigated the expression of ERRγ in Leydig cells and its molecular action on testicular steroidogenesis. ERRγ is expressed in mouse Leydig cells from pre-pubertal stages. ERRγ overexpression in primary Leydig cells elevated the production of testosterone with a marked increase of P450c17 expression at both mRNA and protein levels, albeit decreased expression of StAR. Promoter-reporter analyses showed that ERRγ directly regulated the P450c17 promoter. Further deletion mutant analyses of the P450c17 promoter revealed that ERRγ activated expression of the P450c17 gene by binding to an ERRγ response element within the P450c17 promoter. Meanwhile, ERRγ suppressed cAMP-induced activation of the StAR promoter, which was likely due to ERRγ-mediated inhibition of the transcriptional activity of Nur77, which is induced by cAMP and regulates StAR gene expression in Leydig cells. Interestingly, ERRγ coexpression also decreased the protein level of Nur77, which occurred through proteasomal degradation, suggesting ERRγ-mediated regulation of steroidogenesis at another level. Taken together, these findings suggest that ERRγ regulates testicular steroidogenesis, both directly controlling and indirectly fine-tuning the expression of steroidogenic genes.

Hakai, an E3-ligase for E-cadherin, stabilizes δ-catenin through Src kinase.

Hakai ubiquitinates and induces endocytosis of the E-cadherin complex; thus, modulating cell adhesion and regulating development of the epithelial-mesenchymal transition of metastasis. Our previous published data show that δ-catenin promotes E-cadherin processing and thereby activates ß-catenin-mediated oncogenic signals. Although several published data show the interactions between δ-catenin and E-cadherin and between Hakai and E-cadherin separately, we found no published report on the relationship between δ-catenin and Hakai. In this report, we show Hakai stabilizes δ-catenin regardless of its E3 ligase activity. We show that Hakai and Src increase the stability of δ-catenin synergistically. Hakai stabilizes Src and Src, which in turn, inhibits binding between glycogen synthase kinase-3ß and δ-catenin, resulting in less proteosomal degradation of δ-catenin. These results suggest that stabilization of δ-catenin by Hakai is dependent on Src.

Autophagy negatively regulates tumor cell proliferation through phosphorylation dependent degradation of the Notch1 intracellular domain.

Autophagy is a highly conserved mechanism that degrades long-lived proteins and dysfunctional organelles, and contributes to cell fate. In this study, autophagy attenuates Notch1 signaling by degrading the Notch1 intracellular domain (Notch1-IC). Nutrient-deprivation promotes Notch1-IC phosphorylation by MEKK1 and phosphorylated Notch1-IC is recognized by Fbw7 E3 ligase. The ubiquitination of Notch1-IC by Fbw7 is essential for the interaction between Notch1-IC and p62 and for the formation of aggregates. Inhibition of Notch1 signaling prevents the transformation of breast cancer cells, tumor progression, and metastasis. The expression of Notch1 and p62 is inversely correlated with Beclin1 expression in human breast cancer patients. These results show that autophagy inhibits Notch1 signaling by promoting Notch1-IC degradation and therefore plays a role in tumor suppression.

Tumor Suppressor HIPK2 Regulates Malignant Growth via Phosphorylation of Notch1.

The receptor Notch1 plays an important role in malignant progression of many cancers, but its regulation is not fully understood. In this study, we report that the kinase HIPK2 is responsible for facilitating the Fbw7-dependent proteasomal degradation of Notch1 by phosphorylating its intracellular domain (Notch1-IC) within the Cdc4 phosphodegron motif. Notch1-IC expression was higher in cancer cells than normal cells. Under genotoxic stress, Notch1-IC was phosphorylated constitutively by HIPK2 and was maintained at a low level through proteasomal degradation. HIPK2 phosphorylated the residue T2512 in Notch1-IC. Somatic mutations near this residue rendered Notch1-IC resistant to degradation, as induced either by HIPK2 overexpression or adriamycin treatment. In revealing an important mechanism of Notch1 stability, the results of this study could offer a therapeutic strategy to block Notch1-dependent progression in many types of cancer. Cancer Res; 76(16); 4728-40. ©2016 AACR.

Efficacy of CD46-targeting chimeric Ad5/35 adenoviral gene therapy for colorectal cancers.

CD46 is a complement inhibitor membrane cofactor which also acts as a receptor for various microbes, including species B adenoviruses (Ads). While most Ad gene therapy vectors are derived from species C and infect cells through coxsackie-adenovirus receptor (CAR), CAR expression is downregulated in many cancer cells, resulting inefficient Ad-based therapeutics. Despite a limited knowledge on the expression status of many cancer cells, an increasing number of cancer gene therapy studies include fiber-modified Ad vectors redirected to the more ubiquitously expressed CD46. Since our finding from tumor microarray indicate that CD46 was overexpressed in cancers of the prostate and colon, fiber chimeric Ad5/35 vectors that have infection tropism for CD46 were employed to demonstrate its efficacy in colorectal cancers (CRC). CD46-overexpressed cells showed a significantly higher response to Ad5/35-GFP and to Ad5/35-tk/GCV. While CRC cells express variable levels of CD46, CD46 expression was positively correlated with Ad5/35-mediated GFP fluorescence and accordingly its cell killing. Injection of Ad5/35-tk/GCV caused much greater tumor-suppression in mice bearing CD46-overexpressed cancer xenograft compared to mock group. Analysis of CRC samples revealed that patients with positive CD46 expression had a higher survival rate (p=0.031), carried tumors that were well-differentiated, but less invasive and metastatic, and with a low T stage (all p<0.05). Taken together, our study demonstrated that species B-based adenoviral gene therapy is a suitable approach for generally CD46-overexpressed CRC but would require careful consideration preceding CD46 analysis and categorizing CRC patients.

SMILE upregulated by metformin inhibits the function of androgen receptor in prostate cancer cells.

Metformin, a diabetes drug, has been reported to inhibit the growth of prostate cancer cells. In this study, we investigated the effect and action mechanism of metformin on the function of androgen receptor (AR), a key molecule in the proliferation of prostate cancer cells. Metformin was found to reduce androgen-dependent cell growth and the expression of AR target genes by inhibiting AR function in prostate cancer cells such as LNCaP and C4-2 cells. Interestingly, metformin upregulated the protein level of small heterodimer partner-interacting leucine zipper (SMILE), a coregulator of nuclear receptors, and knockdown of SMILE expression with shRNA abolished the inhibitory effect of metformin on AR function. Further studies revealed that SMILE protein itself suppressed the transactivation of AR, and its ectopic expression resulted in the repressed expression of endogenous AR target genes, PSA and NKX3.1, in LNCaP cells. In addition, SMILE protein physically interacted with AR and competed with the AR coactivator SRC-1 to modulate AR transactivation. As expected, SMILE repressed androgen-dependent growth of LNCaP and C4-2 cells. Taken together, these results suggest that SMILE, which is induced by metformin, functions as a novel AR corepressor and may mediate the inhibitory effect of metformin on androgen-dependent growth of prostate cancer cells.

Transforming growth factor-ß1 signaling represses testicular steroidogenesis through cross-talk with orphan nuclear receptor Nur77.

Transforming growth factor- ß1 (TGF-ß1) has been reported to inhibit luteinizing hormone (LH) mediated-steroidogenesis in testicular Leydig cells. However, the mechanism by which TGF-ß1 controls the steroidogenesis in Leydig cells is not well understood. Here, we investigated the possibility that TGF-ß1 represses steroidogenesis through cross-talk with the orphan nuclear receptor Nur77. Nur77, which is induced by LH/cAMP signaling, is one of major transcription factors that regulate the expression of steroidogenic genes in Leydig cells. TGF-ß1 signaling inhibited cAMP-induced testosterone production and the expression of steroidogenic genes such as P450c17, StAR and 3ß-HSD in mouse Leydig cells. Further, TGF-ß1/ALK5 signaling repressed cAMP-induced and Nur77-activated promoter activity of steroidogenic genes. In addition, TGF-ß1/ALK5-activated Smad3 repressed Nur77 transactivation of steroidogenic gene promoters by interfering with Nur77 binding to DNA. In primary Leydig cells isolated from Tgfbr2flox/flox Cyp17iCre mice, TGF-ß1-mediated repression of cAMP-induced steroidogenic gene expression was significantly less than that in primary Leydig cells from Tgfbr2flox/flox mice. Taken together, these results suggest that TGF-ß1/ALK5/Smad3 signaling represses the expression of steroidogenic genes via the suppression of Nur77 transactivation in testicular Leydig cells. These findings may provide a molecular mechanism involved in the TGF-ß1-mediated repression of testicular steroidogenesis.

Puberty-related changes in cortisol, dehydroepiandrosterone, and estradiol-17ß secretions within the first hour after waking in premenarcheal girls.

OBJECTIVE: The onset of menstruation is the hallmark of female pubertal development. The present study determined whether pubertal girls experience adrenocortical and ovarian steroid secretions within their first waking hour before getting their period, similar to those observed in adult females with regular cycles. METHODS: Cortisol, dehydroepiandrosterone (DHEA), and estradiol-17ß concentrations were measured in saliva samples collected after awakening (0, 30, and 60 min after awakening) from 158 normal premenarcheal pubertal girls and 69 adult females with regular menstrual cycles. The girls were subgrouped according to self-reported Tanner breast (B) and pubic hair (PH) stages (B1PH1, B2PH1, B2PH2, B3PH1, and B3PH2). RESULTS: All the subgroups showed a similar pattern of cortisol secretion. However, cortisol levels were higher in girls at B3PH1 and at B3PH2 than other subgroups. DHEA secretion showed a similar pattern across the groups examined. The largest increase in DHEA levels occurred between B1PH1 and B2PH1 stages, and further increased with pubertal progression. DHEA levels in girls at B3PH2 were approximately one half of the adult value. Estradiol-17ß profiles in girls at B3PH1 and B3PH2 differed from those of other subgroups of girl. A sharp increase in estradiol-17ß levels after awakening which observed in adult females emerged in girls at B3PH1 and B3PH2. However, the estradiol-17ß levels did not reach adult values until B3PH2 stage. CONCLUSIONS: The progression of female puberty includes an increase in the levels of adrenocortical and ovarian steroid secretions and a gain of adult female-like patterns of estradiol-17ß secretion within their first waking hour.

Acetylshikonin induces apoptosis of hepatitis B virus X protein-expressing human hepatocellular carcinoma cells via endoplasmic reticulum stress.

Since it has been known that shikonin derived from a medicinal plant possesses anti-cancer activity, we wonder whether acetylshikonin (ASK), a derivate of shikonin, can be used to treat hepatocellular carcinoma cells expressing hepatitis B virus X protein (HBX), an oncoprotein from hepatitis B virus. When ASK was added to Hep3B cells stably expressing HBX, it induced apoptosis in a dose-dependent manner. ASK induced upregulation and export of Nur77 to the cytoplasm and activation of JNK. Likewise, suppression of Nur77 and JNK inactivation protected the cells from ASK-induced apoptosis, indicating that Nur77 upregulation and JNK activation were required for ASK-mediated apoptosis. Furthermore, ASK increased the expression of Bip and ubiquitination levels of cellular proteins, features of endoplasmic reticulum (ER) stress, via the production of reactive oxygen species in a dose-dependent manner. Suppression of reactive oxygen species with N-acetylcysteine reduced levels of Bip protein and ubiquitination levels of cellular proteins during ASK treatment, leading to protection of cells from apoptosis. Cycloheximide treatment reduced ASK-induced ER stress, suggesting that protein synthesis is involved in ASK-induced ER stress. Moreover, we showed using salubrinal, an ER stress inhibitor that reactive oxygen species production, JNK activation, and Nur77 upregulation and its translocation to cytoplasm are necessary for ER-induced stress. Interestingly, we found that JNK inactivation suppresses ASK-induced ER stress, whereas Nur77 siRNA treatment does not, indicating that JNK is required for ASK-induced ER stress. Accordingly, we report that ASK induces ER stress, which is prerequisite for apoptosis of HBX-expressing hepatocellular carcinoma cells.

Differential regulation of steroidogenic enzyme genes by TRα signaling in testicular Leydig cells.

Thyroid hormone signaling has long been implicated in mammalian testicular function, affecting steroidogenesis in testicular Leydig cells. However, its molecular mechanism is not well understood. Here, we investigated the molecular action of thyroid hormone receptor-α (TRα) on mouse testicular steroidogenesis. TRα/thyroid hormone (T3) signaling differentially affected the expression of steroidogenic enzyme genes, mainly regulating their promoter activity. TRα directly regulated the promoter activity of the cytochrome P450 17α-hydroxylase/C17-20 lyase gene, elevating its expression in the presence of T3. TRα also indirectly regulated the expression of steroidogenic enzyme genes, such as steroidogenic acute regulatory protein and 3ß-hydroxysteroid dehydrogenase, by modulating the transactivation of Nur77 on steroidogenic enzyme gene promoters through protein-protein interaction. TRα enhanced Nur77 transactivation by excluding histone deacetylases from Nur77 in the absence of T3, whereas liganded TRα inhibited Nur77 transactivation, likely due to interfering with the recruitment of coactivator such as the steroid receptor coactivator-1 to Nur77. Together, these findings suggest a role of TRα/T3 in testicular steroidogenesis and may provide molecular mechanisms for the differential regulation of steroidogenic enzyme genes by thyroid hormone.

SAR based design of nicotinamides as a novel class of androgen receptor antagonists for prostate cancer.

Molecular knowledge of pure antagonism and systematic SAR study offered a direction for structural optimization of DIMN to provide nicotinamides as a novel series of AR antagonists. Nicotinamides with extended linear scaffold bearing sterically bulky alkoxy groups on isoquinoline end were synthesized for H12 displacement. AR binding affinity and molecular basis of antiandrogenic effect establish the optimized derivatives, 7au and 7bb, as promising candidates of second generation AR antagonists for advanced prostate cancer.

The chicken ovalbumin upstream promoter-transcription factor II negatively regulates the transactivation of androgen receptor in prostate cancer cells.

Androgen receptor (AR) is involved in the development and progression of prostate cancers. However, the mechanisms by which this occurs remain incompletely understood. In previous reports, chicken ovalbumin upstream promoter-transcription factor II (COUP-TF II) has been suggested to play a role in the development of cancers. In the present study, we explored a putative role of COUP-TF II in prostate cancers by investigating its effect on cell proliferation and a cross-talk between COUP-TF II and AR. Overexpression of COUP-TF II results in the inhibition of androgen-dependent proliferation of prostate cancer cells. Further studies show that COUP-TF II functions as a corepressor of AR. It represses AR transactivation on target promoters containing the androgen response element (ARE) in a dose-dependent manner. In addition, COUP-TF II interacts physically with AR in vitro and in vivo. It binds to both the DNA binding domain (DBD) and the ligand-binding domain (LBD) of AR and disrupts the N/C terminal interaction of AR. Furthermore, COUP-TF II competes with coactivators such as ARA70, SRC-1, and GRIP1 to modulate AR transactivation as well as inhibiting the recruitment of AR to its ARE-containing target promoter. Taken together, our findings suggest that COUP-TF II is a novel corepressor of AR, and provide an insight into the role of COUP-TF II in prostate cancers.