Androgen depletion up‐regulates cadherin‐11 expression in prostate cancer

Men with castration‐resistant prostate cancer (PCa) frequently develop metastasis in bone. The reason for this association is unclear. We have previously shown that cadherin‐11 (also known as OB‐cadherin), a homophilic cell adhesion molecule that mediates osteoblast adhesion, plays a role in the metastasis of PCa to bone. Here, we report that androgen‐deprivation therapy up‐regulates cadherin‐11 expression in PCa. In human PCa specimens, immunohistochemical staining showed that 22/26 (85%) primary PCa tumours from men with castration‐resistant PCa expressed cadherin‐11. In contrast, only 7/50 (14%) androgen‐dependent PCa tumours expressed cadherin‐11. In the MDA–PCa‐2b xenograft animal model, cadherin‐11 was expressed in the recurrent tumours following castration. In the PCa cell lines, there is an inverse correlation between expression of cadherin‐11 and androgen receptor (AR), and cadherin‐11 is expressed in very low levels or not expressed in AR‐positive cell lines, including LNCaP, C4‐2B4 and VCaP cells. We showed that AR likely regulates cadherin‐11 expression in PCa through an indirect mechanism. Although re‐expression of AR in the AR‐negative PC3 cells led to the inhibition of cadherin‐11 expression, depletion of androgen from the culture medium or down‐regulation of AR by RNA interference in the C4‐2B4 cells or VCaP cells only produced a modest increase of cadherin‐11 expression. Promoter analysis indicated that cadherin‐11 promoter does not contain a typical AR‐binding element, and AR elicits a modest inhibition of cadherin‐11 promoter activity, suggesting that AR does not regulate cadherin‐11 expression directly. Together, these results suggest that androgen deprivation up‐regulates cadherin‐11 expression in prostate cancer, and this may contribute to the metastasis of PCa to bone. Our study suggests that therapeutic strategies that block cadherin‐11 expression or function may be considered when applying androgen‐ablation therapy. Copyright © 2010 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

血清饥饿条件下p21活化激酶6(PAK6)与雄激素受体表达的相关性及其意义

目的血清饥饿条件诱导前列腺癌细胞系中内源性p21活化激酶6(PAK6)与雄激素受体(AR)蛋白表达,探讨PAK6与AR蛋白表达的关系。方法在前列腺癌细胞系CWR22Rv1和LNcap细胞进行血清饥饿,诱导内源性PAK6与AR蛋白表达发生变化。结果血清饥饿处理的不同时间点,CWR22Rv1和LNCaP细胞中PAK6蛋白表达呈上升趋势,AR蛋白表达呈下降趋势。瞬时转染递增剂量的PAK6引起AR蛋白表达的抑制。结论血清饥饿条件诱导前列腺癌细胞中PAK6与AR蛋白表达呈负相关。1     

New Therapeutic Approach to Suppress Castration-Resistant Prostate Cancer Using ASC-J9 via Targeting Androgen Receptor in Selective Prostate Cells

Using androgen receptor (AR) knockout mice to determine AR functions in selective prostate cancer (PCa) cells, we determined that AR might play differential roles in various cell types, either to promote or suppress PCa development/progression. These observations partially explain the failure of current androgen deprivation therapy (ADT) to reduce/prevent androgen binding to AR in every cell. Herein, we identified the AR degradation enhancer ASC-J9, which selectively degrades AR protein via interruption of the AR-AR selective coregulator interaction. Such selective interruption could, therefore, suppress AR-mediated PCa growth in the androgen-sensitive stage before ADT and in the castration-resistant stage after ADT. Mechanistic dissection suggested that ASC-J9 could activate the proteasome-dependent pathway to promote AR degradation through the enhanced association of AR-Mdm2 complex. The consequences of ASC-J9-promoted AR degradation included reduced androgen binding to AR, AR N-C terminal interaction, and AR nuclear translocation. Such inhibitory regulation could then result in suppression of AR transactivation and AR-mediated cell growth in eight different mouse models, including intact or castrated nude mice xenografted with androgen-sensitive LNCaP cells or androgen-insensitive C81 cells and castrated nude mice xenografted with castration-resistant C4-2 and CWR22Rv1 cells, and TRAMP and Pten^+/− mice. These results demonstrate that ASC-J9 could serve as an AR degradation enhancer that effectively suppresses PCa development/progression in the androgen-sensitive and castration-resistant stages.Androgen/androgen receptor (AR) signaling plays essential roles in prostate cancer (PCa) progression and results in castration resistance.^1–4 Currently, most, if not all, androgen deprivation therapy (ADT) targets androgens via surgical and/or medical castration to reduce/prevent androgen binding to AR.⁵ However, few, if any, of these ADTs with various antiandrogens, including the recently developed enzalutamide,⁶ have the capacity to eliminate all PCa cells in the later castration-resistant stage. Therefore, degradation of AR during/after ADT can be considered to have clinical benefits for patients with advanced PCa with substantial AR.⁶ These conclusions suggest that identifying a novel compound(s) that could degrade/diminish AR protein in the castration-resistant stage, unlike currently used antiandrogens, may yield better therapeutic efficacies to battle PCa in the castration-resistant stage.Early studies via isolation of three PCa primary cells (PCa1, PCa2, and PCa3) from the same patient found that androgen/AR signaling could function differentially to either suppress or promote PCa growth.⁷ Using the cre-loxP strategy in mice to selectively knockout AR in various PCa cells, Niu and colleagues^3,4,8 observed that the loss of AR in cytokeratin 5/cytokeratin 8–positive basal intermediate epithelial cells led to increased PCa metastasis, yet loss of AR in cytokeratin 8–positive luminal epithelial cells resulted in suppressed PCa progression with increased cell apoptosis. In contrast, loss of AR in stromal fibroblasts and smooth muscle cells resulted in suppression of prostate/PCa growth.^9,10 These results conclude that AR can either promote or suppress PCa progression in different types of PCa cells.Because only one AR gene has been identified,¹¹ we hypothesized that these differential AR roles in various PCa cells in the same patient could be due to the existence of different AR-AR coregulator complexes. This hypothesis led us to screen the AR degradation enhancer 5-hydroxy-1,7-bis(3,4-dimethoxyphenyl)-1,4,6-heptatrien-3-one (ASC-J9) from natural products and their derivatives by selectively interrupting the interaction between AR and selective AR coregulators, such as AR–AR-associated protein (ARA) 70 and AR-ARA55, which are expressed mainly in luminal epithelial cells and stromal cells, respectively, in which AR may function with positive roles to either maintain cell survival or promote cell proliferation. Results from four different human PCa cell lines and eight different in vivo mouse models concluded that ASC-J9 could function as a promising AR degradation enhancer to suppress PCa progression before and after castration resistance with few adverse effects.     

Aberrant BRAF splicing as an alternative mechanism for oncogenic B‐Raf activation in thyroid carcinoma

Activating BRAF mutations have recently been reported in 28–83% of papillary thyroid carcinomas (PTCs). However, it is not known whether aberrant BRAF splicing occurs in thyroid carcinoma. To investigate aberrant BRAF splicing and its association with BRAF mutation in thyroid tumours, we studied aberrant BRAF splicing and BRAF mutation from 68 thyroid tumours. BRAF^V600E mutation was detected in 20 of 43 PTCs and all three anaplastic thyroid carcinomas (ATCs). There is a higher frequency of BRAF mutation in PTC patients with stage III and IV tumours compared with stage I and II. Novel BRAF splicing variants were detected in 12 PTCs, three follicular variants of PTC (FVPTCs), and one ATC, as well as in two thyroid carcinoma cell lines, ARO and NPA. These variants did not have the N‐terminal auto‐inhibitory domain of wild‐type B‐Raf, resulting in an in‐frame truncated protein that contained only the C‐terminal kinase domain and caused constitutive activation of B‐Raf. These variants were significantly associated with advanced disease stage and BRAF^V600E mutation (p < 0.001, Fisher exact test). Furthermore, expression of these variants in NIH3T3 and CHO cells could activate the MAP kinase signalling pathway, transform them in vitro, and induce tumours in nude mice. These data suggest that BRAF splicing variants may function as an alternative mechanism for oncogenic B‐Raf activation. Combination of the BRAF^V600E mutation and its splicing variants may contribute towards disease progression to poorly differentiated thyroid carcinoma. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

Alternative splicing and retinal degeneration

Alternative splicing is highly regulated in tissue‐specific and development‐specific patterns, and it has been estimated that 15% of disease‐causing point mutations affect pre‐mRNA splicing. In this review, we consider the cis‐acting splice site and trans‐acting splicing factor mutations that affect pre‐mRNA splicing and contribute to retinal degeneration. Numerous splice site mutations have been identified in retinitis pigmentosa (RP) and various cone‐rod dystrophies. Mutations in alternatively spliced retina‐specific exons of the widely expressed RPGR and COL2A1 genes lead primarily to X‐linked RP and ocular variants of Stickler syndrome, respectively. Furthermore, mutations in general pre‐mRNA splicing factors, such as PRPF31, PRPF8, and PRPF3, predominantly cause autosomal dominant RP. These findings suggest an important role for pre‐mRNA splicing in retinal homeostasis and the pathogenesis of retinal degenerative diseases. The development of novel therapeutic strategies to modulate aberrant splicing, including small molecule‐based therapies, has the potential to lead to new treatments for retinal degenerative diseases.     

Future directions for high‐throughput splicing assays in precision medicine

Classification of variants of unknown significance is a challenging technical problem in clinical genetics. As up to one‐third of disease‐causing mutations are thought to affect pre‐mRNA splicing, it is important to accurately classify splicing mutations in patient sequencing data. Several consortia and healthcare systems have conducted large‐scale patient sequencing studies, which discover novel variants faster than they can be classified. Here, we compare the advantages and limitations of several high‐throughput splicing assays aimed at mitigating this bottleneck, and describe a data set of ~5,000 variants that we analyzed using our Massively Parallel Splicing Assay (MaPSy). The Critical Assessment of Genome Interpretation group (CAGI) organized a challenge, in which participants submitted machine learning models to predict the splicing effects of variants in this data set. We discuss the winning submission of the challenge (MMSplice) which outperformed existing software. Finally, we highlight methods to overcome the limitations of MaPSy and similar assays, such as tissue‐specific splicing, the effect of surrounding sequence context, classifying intronic variants, synthesizing large exons, and amplifying complex libraries of minigene species. Further development of these assays will greatly benefit the field of clinical genetics, which lack high‐throughput methods for variant interpretation.     

Alteration of branch site consensus sequence and enhanced pre‐mRNA splicing of an NMDAR1 intron not associated with schizophrenia

Aberrant splicing of pre‐mRNA is recognized to account for a significant minority of disease‐causing mutations. The N‐methyl‐D ‐aspartate receptor (NMDA) subunit gene R1 (NMDAR1) is alternatively spliced to produce eight length variants. In an examination of the NMDAR1 as a candidate gene in schizophrenia, a presumed microdeletion/insertion (del/ins) was observed in intron 10 of an African‐American male near a weak putative branch‐site consensus sequence. Although exon 10 is not known to be alternatively spliced, the del/ins was posited to alter splicing efficiency. If splicing were abolished and intron retention occurred, an in‐frame translation product of more than 250 amino acids was predicted. To explore splicing efficiency, mini genes were examined through primer‐extension analyses in NIH293 embryonic kidney cell cultures. Rather than disruption of splicing, the del/ins allele exhibited a fivefold enhancement in splicing. In an association analysis with additional schizophrenic cases and unaffected controls, all of African‐American descent, the mutant allele was observed at equivalent frequencies. A family study also did not support cosegregation of the variant allele with psychiatric disease. © 2002 Wiley‐Liss, Inc.     

Role of SMG‐1‐mediated Upf1 phosphorylation in mammalian nonsense‐mediated mRNA decay

SMG‐1, a member of the PIKK (phosphoinositide 3‐kinase‐related kinase) family, plays a critical role in the mRNA quality control system known as nonsense‐mediated mRNA decay (NMD). NMD protects cells from the accumulation of aberrant mRNAs with premature termination codons (PTCs) which encode nonfunctional or potentially harmful truncated proteins. SMG‐1 directly phosphorylates Upf1 helicase, another key component of NMD, upon recognition of PTC on postspliced mRNA during the initial round of translation. Phosphorylated‐Upf1 recruits the SMG‐5/SMG‐7 complex to induce ribosome dissociation and decapping‐mediated decay. Phospho‐Upf1 also recruits the SMG‐6 endonuclease which might be involved in endo‐cleavage. Upf1 ATPase/helicase activities are likely required for the activation of other mRNA decay enzymes and the mRNA‐protein complex dissociation to complete NMD. At present, a variety of tools are available that can specifically suppress NMD, and it has become possible to examine the contribution of NMD in a variety of physiological and pathological conditions.     

A novel mutation in CDH11, encoding cadherin‐11, cause Branchioskeletogenital (Elsahy‐Waters) syndrome

Cadherins are cell‐adhesion molecules that control morphogenesis, cell migration, and cell shape changes during multiple developmental processes. Until now four distinct cadherins have been implicated in human Mendelian disorders, mainly featuring skin, retinal and hearing manifestations. Branchio‐skeleto‐genital (or Elsahy‐Waters) syndrome (BSGS) is an ultra‐rare condition featuring a characteristic face, premature loss of teeth, vertebral and genital anomalies, and intellectual disability. We have studied two sibs with BSGS originally described by Castori et al. in 2010. Exome sequencing led to the identification of a novel homozygous nonsense variant in the first exon of the cadherin‐11 gene (CDH11), which results in a prematurely truncated form of the protein. Recessive variants in CDH11 have been recently demonstrated in two other sporadic patients and a pair of sisters affected by BSGS. Although the function of this cadherin (also termed Osteoblast‐Cadherin) is not completely understood, its prevalent expression in osteoblastic cell lines and up‐regulation during differentiation suggest a specific function in bone formation and development. This study identifies a novel loss‐of‐function variant in CDH11 as a cause of BSGS and supports the role of cadherin‐11 as a key player in axial and craniofacial malformations.     

Retinitis Pigmentosa Mutations of SNRNP200 Enhance Cryptic Splice‐Site Recognition

Mutations in SNRP200 gene cause autosomal‐dominant retinal disorder retinitis pigmentosa (RP). The protein product of SNRNP200 is BRR2, a DExD/H box RNA helicase crucial for pre‐mRNA splicing. In this study, we prepared p.S1087L and p.R1090L mutations of human BRR2 using bacterial artificial chromosome recombineering and stably expressed them in human cell culture. Mutations in BRR2 did not compromise snRNP assembly and both mutants were incorporated into the spliceosome just as the wild‐type (wt) protein. Surprisingly, cells expressing RP mutants exhibited increased splicing efficiency of the LDHA gene. Next, we found that depletion of endogenous BRR2 enhanced usage of a β‐globin cryptic splice site while splicing at the correct splice site was inhibited. Proper splicing of optimal and cryptic splice sites was restored in cells expressing BRR2‐wt but not in cells expressing RP mutants. Taken together, our data suggest that BRR2 is an important factor in 5′‐splice‐site recognition and that the RP‐linked mutations c.3260C>T (p.S1087L) and c.3269G>T (p.R1090L) affect this BRR2 function.     

A premature termination codon within an alternative exon affecting only the metabolism of transcripts that retain this exon

Protein 4.1 pre‐mRNA splicing is regulated in tissue‐ and development‐specific manners. Exon 16, which encodes the N‐terminal region of the spectrin/actin‐binding domain, is one of the alternatively spliced sequence motifs. It is present in late differentiated erythroid cells but absent from early erythroblasts and from lymphoid cells. We describe a single nucleotide deletion of the erythroid protein 4.1 gene associated with hereditary elliptocytosis. The deletion located in exon 16 leads to a frameshift and a premature termination codon within the same exon. In an effort to examine the premature stop codon effect in relationship with exon 16 alternative splicing, we analyzed erythroid and lymphoid protein 4.1 mRNAs using the mutation and a linked downstream polymorphism as markers. We found that the premature stop codon does not affect the tissue‐specific alternative splicing among the two cell types analyzed and that the resulting alteration of mRNA metabolism correlates with the retention of exon 16 in reticulocytes. Conversely, skipping of exon 16 in lymphoid cells converts the mutant mRNA to a normal lymphoid‐specific mRNA isoform, hence bypassing the nonsense codon. Consistent with data obtained on constitutive nonsense exons, our observations argue in favor of a stop codon recognition mechanism that occurs after the regulated splicing status of the nonsense exon has been achieved. Hum Mutat 14:145–155, 1999. © 1999 Wiley‐Liss, Inc.     

Identification and Characterization of Aberrant GAA Pre‐mRNA Splicing in Pompe Disease Using a Generic Approach

Identification of pathogenic variants in monogenic diseases is an important aspect of diagnosis, genetic counseling, and prediction of disease severity. Pathogenic mechanisms involved include changes in gene expression, RNA processing, and protein translation. Variants affecting pre‐mRNA splicing are difficult to predict due to the complex mechanism of splicing regulation. A generic approach to systematically detect and characterize effects of sequence variants on splicing would improve current diagnostic practice. Here, it is shown that such approach is feasible by combining flanking exon RT‐PCR, sequence analysis of PCR products, and exon‐internal quantitative RT‐PCR for all coding exons. Application of this approach to one novel and six previously published variants in the acid‐alpha glucosidase (GAA) gene causing Pompe disease enabled detection of a total of 11 novel splicing events. Aberrant splicing included cryptic splice‐site usage, intron retention, and exon skipping. Importantly, the extent of leaky wild‐type splicing correlated with disease onset and severity. These results indicate that this approach enables sensitive detection and in‐depth characterization of variants affecting splicing, many of which are still unrecognized or poorly understood. The approach is generic and should be adaptable for application to other monogenic diseases to aid in improved diagnostics.     

Clostridium scindens metabolites trigger prostate cancer progression through androgen receptor signaling

Prostate cancer (PCa) is one of the most common malignancies in men; recently, PCa-related mortality has increased worldwide. Although androgen deprivation therapy (ADT) is the standard treatment for PCa, patients often develop aggressive castration-resistant PCa (CRPC), indicating the presence of an alternative source of androgen. Clostridium scindens is a member of the gut microbiota and can convert cortisol to 11β-hydroxyandrostenedione (11β-OHA), which is a potent androgen precursor. However, the effect of C. scindens on PCa progression has not been determined. In this study, androgen-dependent PCa cells (LNCaP) were employed to investigate whether C. scindens-derived metabolites activate androgen receptor (AR), which is a pivotal step in the development of PCa. Results showed that cortisol metabolites derived from C. scindens-conditioned medium promoted proliferation and enhanced migration of PCa cells. Furthermore, cells treated with these metabolites presented activated AR and stimulated AR-regulated genes. These findings reveal that C. scindens has the potential to promote PCa progression via the activation of AR signaling. Further studies on the gut–prostate axis may help unravel an alternative source of androgen that triggers CRPC exacerbation.     

Pleiotropic functional properties of androgen receptor mutants in prostate cancer

The androgen receptor (AR) signaling pathway plays an important role during the development of the normal prostate gland, but also during the progression of prostate cancer on androgen ablation therapy. Mutations in the AR gene emerge to keep active the AR signaling pathway and to support prostate cancer cells growth and survival despite the low levels of circulating androgens. Indeed, mutations affecting the ligand binding domain (LBD) of the AR have been shown to generate so-called "promiscuous" receptors that present widened ligand specificity and allow the stimulation of these receptors by a larger spectrum of endogenous hormones. Another class of mutations, arising in the amino-terminal domain (NTD) of the receptor, modulate AR interactions with coregulators involved in cell proliferation regulation. Besides characteristics of these well-known types of mutations, the properties of other classes of AR mutants recently described in prostate cancer are currently under investigation. Most interestingly, in addition to their potential role in the mechanisms which allow prostate cancer cells to escape androgen ablation therapy, data suggest that certain AR mutations are present early in the natural history of the disease and may play a role in many aspects of prostate cancer progression. Surprisingly, singular truncated AR devoid of their carboxy-terminal end (CTE) region seem to exert specific paracrine effects and to induce a clonal cooperation with neighboring prostate cancer cells, which may facilitate both the invasion and metastasis processes. In this article, we review the functional properties of different classes of AR mutants and their potential impact on the natural history of prostate cancer. Hum Mutat 0, 1-14, 2008. (c) 2008 Wiley-Liss, Inc.