BARD1 Expression During Spermatogenesis Is Associated with Apoptosis and Hormonally Regulated1

HuR Plays a Role in Double-Strand Break Repair in Pancreatic Cancer Cells and Regulates Functional BRCA1-Associated-Ring-Domain-1(BARD1) Isoforms

Human Antigen R (HuR/ELAVL1) is known to regulate stability of mRNAs involved in pancreatic ductal adenocarcinoma (PDAC) cell survival. Although several HuR targets are established, it is likely that many remain currently unknown. Here, we identified BARD1 mRNA as a novel target of HuR. Silencing HuR caused a >70% decrease in homologous recombination repair (HRR) efficiency as measured by the double-strand break repair (pDR-GFP reporter) assay. HuR-bound mRNAs extracted from RNP-immunoprecipitation and probed on a microarray, revealed a subset of HRR genes as putative HuR targets, including the BRCA1-Associated-Ring-Domain-1 (BARD1) (p < 0.005). BARD1 genetic alterations are infrequent in PDAC, and its context-dependent upregulation is poorly understood. Genetic silencing (siRNA and CRISPR knock-out) and pharmacological targeting of HuR inhibited both full length (FL) BARD1 and its functional isoforms (α, δ, Φ). Silencing BARD1 sensitized cells to olaparib and oxaliplatin; caused G2-M cell cycle arrest; and increased DNA-damage while decreasing HRR efficiency in cells. Exogenous overexpression of BARD1 in HuR-deficient cells partially rescued the HRR dysfunction, independent of an HuR pro-oncogenic function. Collectively, our findings demonstrate for the first time that BARD1 is a bona fide HuR target, which serves as an important regulatory point of the transient DNA-repair response in PDAC cells.

Expression of BARD1 β Isoform in Selected Pediatric Tumors

Currently, many new possible biomarkers and mechanisms are being searched and tested to analyse pathobiology of pediatric tumours for the development of new treatments. One such candidate molecular factor is BARD1 (BRCA1 Associated RING Domain 1)—a tumour-suppressing gene involved in cell cycle control and genome stability, engaged in several types of adult-type tumours. The data on BARD1 significance in childhood cancer is limited. This study determines the expression level of BARD1 and its isoform beta (β) in three different histogenetic groups of pediatric cancer—neuroblastic tumours, and for the first time in chosen germ cell tumours (GCT), and rhabdomyosarcoma (RMS), using the qPCR method. We found higher expression of beta isoform in tumour compared to healthy tissue with no such changes concerning BARD1 full-length. Additionally, differences in expression of BARD1 β between histological types of neuroblastic tumours were observed, with higher levels in ganglioneuroblastoma and ganglioneuroma. Furthermore, a higher expression of BARD1 β characterized yolk sac tumours (GCT type) and RMS when comparing with non-neoplastic tissue. These tumours also showed a high expression of the TERT (Telomerase Reverse Transcriptase) gene. In two RMS cases we found deep decrease of BARD1 β in post-chemotherapy samples. This work supports the oncogenicity of the beta isoform in pediatric tumours, as well as demonstrates the differences in its expression depending on the histological type of neoplasm, and the level of maturation in neuroblastic tumours.

Biophysical evaluation to categorize pathogenicity of cancer-predisposing mutations identified in the BARD1 BRCT domain

The BRCT domain of BARD1 (BARD1 BRCT) is involved in many cellular processes such as DNA damage repair (DDR) and cell-cycle checkpoint regulation. BARD1 BRCT performs tumor suppressor function by recruiting BRCA1 at DNA damage site via interactions with other DNA damage repair (DDR) proteins. Considering the importance of the BRCT domain in genomic integrity, we decided to evaluate reported mutations of BARD1 BRCT Cys645Arg, Val695Leu, and Ser761Asn for their pathogenicity. To explore the effect of the mutation on the structure and function, BARD1 BRCT wild-type proteins and the mutant proteins were studied using different biochemical, biophysical and in silico techniques. Comparative fluorescence, circular dichroism (CD) spectroscopy and limited proteolysis studies demonstrate the well-folded structural conformation of wild-type and mutant proteins. However, thermal and chemical denaturation studies revealed similarity in the folding pattern of BARD1 BRCT wild-type and Cys645Arg mutant proteins, whereas there was a significant loss in the thermodynamic stability of Val695Leu and Ser761Asn mutants. Molecular dynamics (MD) simulation studies on wild-type and mutant protein structures indicate the loss in structural integrity of mutants compared with the wild-type protein.

Dualistic Role of BARD1 in Cancer

BRCA1 Associated RING Domain 1 (BARD1) encodes a protein which interacts with the N-terminal region of BRCA1 in vivo and in vitro. The full length (FL) BARD1 mRNA includes 11 exons and encodes a protein comprising of six domains (N-terminal RING-finger domain, three Ankyrin repeats and two C-terminal BRCT domains) with different functions. Emerging data suggest that BARD1 can have both tumor-suppressor gene and oncogene functions in tumor initiation and progression. Indeed, whereas FL BARD1 protein acts as tumor-suppressor with and without BRCA1 interactions, aberrant splice variants of BARD1 have been detected in various cancers and have been shown to play an oncogenic role. Further evidence for a dualistic role came with the identification of BARD1 as a neuroblastoma predisposition gene in our genome wide association study which has demonstrated that single nucleotide polymorphisms in BARD1 can correlate with risk or can protect against cancer based on their association with the expression of FL and splice variants of BARD1. This review is an overview of how BARD1 functions in tumorigenesis with opposite effects in various types of cancer.

BARD1 mediates TGF-β signaling in pulmonary fibrosis

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a rapid progressive fibro-proliferative disorder with poor prognosis similar to lung cancer. The pathogenesis of IPF is uncertain, but loss of epithelial cells and fibroblast proliferation are thought to be central processes. Previous reports have shown that BARD1 expression is upregulated in response to hypoxia and associated with TGF-β signaling, both recognized factors driving lung fibrosis. Differentially spliced BARD1 isoforms, in particular BARD1β, are oncogenic drivers of proliferation in cancers of various origins. We therefore hypothesized that BARD1 and/or its isoforms might play a role in lung fibrosis.

METHODS

We investigated BARD1 expression as a function of TGF-β in cultured cells, in mice with experimentally induced lung fibrosis, and in lung biopsies from pulmonary fibrosis patients.

RESULTS

FL BARD1 and BARD1β were upregulated in response to TGF-β in epithelial cells and fibroblasts in vitro and in vivo. Protein and mRNA expression studies showed very low expression in healthy lung tissues, but upregulated expression of full length (FL) BARD1 and BARD1β in fibrotic tissues.

CONCLUSION

Our data suggest that FL BARD1 and BARD1β might be mediators of pleiotropic effects of TGF-β. In particular BARD1β might be a driver of proliferation and of pulmonary fibrosis pathogenesis and progression and represent a target for treatment.

Altered gene expression signature of early stages of the germ line supports the pre-meiotic origin of human spermatogenic failure

The molecular basis of spermatogenic failure (SpF) is still largely unknown. Accumulating evidence suggests that a series of specific events such as meiosis, are determined at the early stage of spermatogenesis. This study aims to assess the expression profile of pre-meiotic genes of infertile testicular biopsies that might help to define the molecular phenotype associated with human deficiency of sperm production. An accurate quantification of testicular mRNA levels of genes expressed in spermatogonia was carried out by RT-qPCR in individuals showing SpF owing to germ cell maturation defects, Sertoli cell-only syndrome or conserved spermatogenesis. In addition, the gene expression profile of SpF was compared with that of testicular tumour, which is considered to be a severe developmental disease of germ cell differentiation. Protein expression from selected genes was evaluated by immunohistochemistry. Our results indicate that SpF is accompanied by differences in expression of certain genes associated with spermatogonia in the absence of any apparent morphological and/or numerical change in this specific cell type. In SpF testicular samples, we observed down-regulation of genes involved in cell cycle (CCNE1 and POLD1), transcription and post-transcription regulation (DAZL, RBM15 and DICER1), protein degradation (FBXO32 and TM9SF2) and homologous recombination in meiosis (MRE11A and RAD50) which suggests that the expression of these genes is critical for a proper germ cell development. Interestingly, a decrease in the CCNE1, DAZL, RBM15 and STRA8 cellular transcript levels was also observed, suggesting that the gene expression capacity of spermatogonia is altered in SpF contributing to an unsuccessful sperm production. Altogether, these data point to the spermatogenic derangement being already determined at, or arising in, the initial stages of the germ line.

BARD1: an independent predictor of survival in non-small cell lung cancer

BRCA1 mRNA overexpression is correlated with poor survival in NSCLC. However, BRCA1 functions depend on the interaction with BARD1 for its stability, nuclear localization and ubiquitin ligase activity. Expression of alternatively spliced BARD1 isoforms that lack the BRCA1-interaction domain was found upregulated and correlated with poor prognosis in breast and ovarian cancer. These BARD1 isoforms are essential for proliferation of cancer cells in vitro. We investigated whether BARD1 isoforms are expressed in NSCLC. While in lung tissues from healthy controls BARD1 expression was undetectable on the mRNA level and protein level, we found two novel isoforms in addition to previously identified mRNAs expressed in all NSCLC samples tested. Furthermore, the pattern of BARD1 isoform expression was similar in tumor and morphologically normal peri-tumor tissues, and only one novel isoform π was specifically upregulated in tumors. Immunohistochemistry revealed that all 100 NSCLC cases tested expressed isoform-specific BARD1 epitopes, while BARD1 expression was undetectable in biopsies from healthy controls. Statistical analysis showed that the expression of epitopes PVC and WFS, present on isoform π, or epitope WFS alone, expressed on isoforms π, κ and β, were significantly correlated with decreased patient survival. These findings were corroborated in a mouse model of chemically induced lung cancer. Immunostaining of mouse tumors showed that BARD1 epitopes PVC and WFS were specifically upregulated in invasive, but not in confined lung tumors. Thus, BARD1 isoforms might be involved in tumor initiation and invasive progression and might represent a novel prognostic marker for NSCLC.

BARD1 expression predicts outcome in colon cancer

PURPOSE

BARD1 is a BRCA1-binding partner with tumor suppressive properties. Aberrant splice variants of BARD1 have been detected in various cancers, and it has been postulated that the presence of some splice variants is cancer specific. This is the first study assessing BARD1 expression patterns and correlation with clinical outcome in colon cancer.

EXPERIMENTAL DESIGN

We analyzed colon cancer samples for the occurrence of BARD1 splice variants, characterized novel BARD1 splice variants, and quantified the mRNA expression levels of these isoforms in primary colon cancers and their corresponding normal tissue. We tested the correlation of full-length BARD1 protein expression and clinical outcome in primary colon cancer samples.

RESULTS

In addition to the full-length BARD1 mRNA, we now find 19 distinct BARD1 splice variants in colon cancer. Contrary to previous assumptions, these splice variants also occur in the adjacent normal colon tissue. Although BARD1 splice variants account for a considerable amount of BARD1 mRNA in both cancer and normal colon samples, distinct variants show a cancer-specific regulation pattern. Consistent with its role as tumor suppressor, we further find that the expression of the full-length BARD1 protein predicts outcome in colon cancer and that loss of full-length BARD1 protein is associated with a poor prognosis (P = 0.0002).

CONCLUSION

Taken together, this is the first report to suggest that BARD1 regulation is an important pathway in colon cancer and that the BARD1 full-length protein may be a useful marker to improve risk stratification in colon cancer patients.

Thermodynamic study of the BRCT domain of BARD1 and its interaction with the -pSER-X-X-Phe- motif-containing BRIP1 peptide

The BRCA1-associated RING domain protein 1 (BARD1) is the heterodimeric partner of BRCA1. The BRCA1/BARD1 complex demonstrates ubiquitin ligase activity and has been implicated in genomic stability and tumor suppression. Both proteins possess a structurally conserved C-terminal domain (BRCT). While BRCA1-BRCT has been shown to mediate BRCA1 interactions with phosphoproteins such as BRIP1 by recognizing the pSer-X-X-Phe motif, attempts to demonstrate analogous interactions of its dimeric counterpart BARD1-BRCT, have so far been unsuccessful. In this study, chemical-denaturation experiments of BARD1-BRCT domain suggest that its low thermodynamic stability (DeltaG=2.5 kcal/mol) at room temperature, may affect some of its biochemical properties, such as its interaction with phosphopeptides. The stability of BARD1-BRCT domain at 10 degrees C, increases to 7.5 kcal/mol and isothermal titration calorimetry (ITC) experiments at this lower temperature showed binding to the BRIP1 phosphopeptide via an enthalpy-driven interaction, which appears to be specific to the pSer-X-X-Phe peptide-binding motif. Substitution of either pSer at position 0 with Ser (non-phosphorylated peptide) or Phe with Val at position +3, leads to no-binding ITC results. While these findings are indicative that BRIP1 is a potential BARD1 binding partner, it becomes evident that in vitro binding assays involving the entire BARD1 protein and in vivo experiments are also needed to establish its binding partners and its potential role in tumor suppression pathways.

Genomic landscape of developing male germ cells

Spermatogenesis is a highly orchestrated developmental process by which spermatogonia develop into mature spermatozoa. This process involves many testis- or male germ cell-specific gene products whose expressions are strictly regulated. In the past decade the advent of high-throughput gene expression analytical techniques has made functional genomic studies of this process, particularly in model animals such as mice and rats, feasible and practical. These studies have just begun to reveal the complexity of the genomic landscape of the developing male germ cells. Over 50% of the mouse and rat genome are expressed during testicular development. Among transcripts present in germ cells, 40% - 60% are uncharacterized. A number of genes, and consequently their associated biological pathways, are differentially expressed at different stages of spermatogenesis. Developing male germ cells present a rich repertoire of genetic processes. Tissue-specific as well as spermatogenesis stage-specific alternative splicing of genes exemplifies the complexity of genome expression. In addition to this layer of control, discoveries of abundant presence of antisense transcripts, expressed psuedogenes, non-coding RNAs (ncRNA) including long ncRNAs, microRNAs (miRNAs) and Piwi-interacting RNAs (piRNAs), and retrogenes all point to the presence of multiple layers of expression and functional regulation in male germ cells. It is anticipated that application of systems biology approaches will further our understanding of the regulatory mechanism of spermatogenesis.

Oncogenic BARD1 isoforms expressed in gynecological cancers

BARD1 is required for protein stability and tumor suppressor functions of BRCA1, which depend on the ubiquitin ligase activity of the BRCA1-BARD1 heterodimer. The NH(2)-terminal RING domains of both proteins act as interaction modules and form a ubiquitin ligase, which has functions in DNA repair, cell cycle checkpoint regulation, and mitosis. Interestingly, up-regulated expression of truncated BARD1 isoforms was found to be associated with poor prognosis in breast and ovarian cancers and, in a hormonally regulated fashion, in the human cytotrophoblast, a cell type with properties reminiscent of cancer cells. We therefore performed reverse transcription-PCR to determine the structure of BARD1 isoforms in cell lines derived from hormone-dependent and hormone-independent cancers. We found a specific combination of isoforms, generated by differential splicing and alternative transcription initiation, mostly lacking the BRCA1 interaction domain, in gynecologic but not hematologic cancer cell lines. To investigate the prevalence of BARD1 isoforms in tumors, we applied immunohistochemistry to ovarian cancers, using antibodies distinguishing full-length BARD1 and isoforms. Expression of NH(2) terminally truncated BARD1 was correlated with advanced stage of cancer, and expression of spliced isoforms was typical for clear cell carcinoma, the ovarian cancer with worst prognosis, suggesting a role of BARD1 isoforms in cancer progression. To challenge this hypothesis, we silenced BARD1 isoforms in ovarian cancer cells that lacked wild-type BARD1 by siRNA interference, which led to a complete proliferation arrest. Thus, BARD1 isoform expression is required for cancer cell proliferation, which is compatible with the notion that BARD1 isoforms act as cancer maintenance genes.

Estrogen-dependent cell signaling and apoptosis in BRCA1-blocked BG1 ovarian cancer cells in response to plumbagin and other chemotherapeutic agents

BACKGROUND

Cellular response to chemotherapeutic drugs in the absence of BRCA1 either completely or partially had drawn less attention. The present study evaluated whether there is a differential inhibition of cell growth by selected compounds with respect to BRCA1 status in estrogen receptor (ER)-positive ovarian cancer cells.

MATERIALS AND METHODS

The BG1 ovarian cancer cells used in the experiments were antisensely blocked with BRCA1 gene. Growth inhibition and apoptotic induction were analyzed to evaluate the cytotoxic effects. Small interfering RNA (SiRNA) transfection, western blot analysis, RT-PCR analysis and molecular modeling were carried out to analyze the estrogen-dependent action of plumbagin.

RESULTS

Although we found that all the compounds studied induce apoptosis, the induction was in the order of plumbagin > doxorubicin > tamoxifen > cisplatin. Plumbagin can bind to the active site of ER-alpha. Plumbagin, however, induced ER-alpha 46 kDa truncated isoform, which was found abundantly preempted in the cytoplasm compared with a 66-kDa full-length isoform. The truncated isoform is known to inhibit classical ER-alpha signaling pathways. SiRNA-transfected cells for ER-alpha exhibited lower cytotoxicity upon plumbagin treatment than the control-transfected cells.

CONCLUSION

Taken together, this study indicates that plumbagin has chemotherapeutic potential in BRCA1-mutated/defective ER-positive cancers.

Identification of novel alternatively splicedBRCA1-associated RING domain (BARD1) messenger RNAs in human peripheral blood lymphocytes and in sporadic breast cancer tissues

BARD1 (BRCA1-associated RING domain) is the dominant binding partner of BRCA1 in vivo. The BARD1 gene has been reported to be mutated in a subset of breast and ovarian cancer patients and BARD1 germ-line mutations have been identified in breast cancer patients negative for BRCA1 or BRCA2 gene alterations. In the present study, we show by RT-PCR and direct sequencing analysis the occurrence of seven novel and one previously identified BARD1 splicing variants in human lymphocytes and breast cancers. Two of the eight variants (BARD1delta and BARD1 DeltaRIN) preserve a correct open reading frame and could encode BARD1 internally deleted proteins, while the remaining six variants display premature stop codons. Characterization of the relative expression of BARD1 FL, BARD1delta, and BARD1 DeltaRIN using quantitative PCR analysis indicated that the mean expression levels of BARD1 FL, BARD1delta, and BARD1 DeltaRIN were significantly higher in tumors than in morphologically normal tissues and lymphocytes. However, we were unable to identify either qualitatively or quantitatively tumor-specific expression patterns of the identified BARD1 splicing variants.

Identification of BARD1 splice-isoforms involved in human trophoblast invasion

The tumor suppressor protein BARD1, originally discovered as BRCA1-binding protein, acts in conjunction with BRCA1 as ubiquitin ligase. BARD1 and BRCA1 form a stable heterodimer and dimerization, which is required for most tumor suppressor functions attributed to BRCA1. In addition, BARD1 has BRCA1-independent functions in apoptosis, and a role in control of tissue homeostasis was suggested. However, cancer-associated mutations of BARD1 are rare; on the contrary, overexpression of truncated BARD1 was found in breast and ovarian cancer and correlated with poor prognosis. Here we report that human cytotrophoblasts, which show a strong similarity with cancer cells in respect of their invasive behavior and capacity of matrix metalloprotease production, overexpress isoforms of BARD1 derived from differential splicing. We demonstrate that expression of BARD1 and its isoforms is temporally and spatially regulated by human chorionic gonadotropin and by hypoxia, both factors known to regulate the invasive phase and proliferation of cytotrophoblasts. Interestingly, we found a subset of BARD1 isoforms secreted by cytotrophoblasts. BARD1 repression by siRNAs, mitigates the interference of cytotrophoblasts with cell adhesion of collagen matrix-dependent epithelial cells, suggesting a role of BARD1 isoforms in extracellular matrix remodelling and in cytotrophoblasts invasion.

Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

Is there more to BARD1 than BRCA1?

It has been over a decade since mutations in BRCA1 and BRCA2 were found to be associated with a small number of familial breast cancer cases. BRCA1 is a large protein that interacts with many other proteins that have diverse functions, so it has been a challenge to determine how defects in its function could lead to cancer. One particular protein, BARD1, seems to be an important regulator of the tumour-suppressor function of BRCA1, as well as acting as a tumour suppressor itself. BARD1 is indispensable for cell viability, so loss-of-function mutations are rare, but mutations and truncations that alter its function might be involved in the pathogenesis of breast cancer.

Aberrant expression of BARD1 in breast and ovarian cancers with poor prognosis

Mutations in tumor-suppressor gene BARD1 have been found in inherited and spontaneous breast, ovarian and uterine cancers. BARD1 plays a critical role in DNA repair and ubiquitination as binding partner of BRCA1, with which it colocalizes to nuclear dots. Independently of BRCA1, BARD1 can induce p53-dependent apoptosis in response to genotoxic stress. Therefore, BARD1 or p53 might be defective in cancer cells spared from apoptosis. We investigated BARD1 and p53 expression in ovarian, breast and non-small-cell lung cancers. BARD1 expression was highly upregulated and cytoplasmic in most cancer cells, while weak nuclear staining was observed in the surrounding normal tissue. Maximal BARD1 expression was associated with the most malignant ovarian cancer, clear cell carcinoma. In breast cancer, BARD1 expression was correlated with poor differentiation and large tumor size, established factors of poor prognosis, as well as short disease-free survival. In contrast to breast and ovarian cancers, no correlation of BARD1 expression with either grade or stage could be determined for lung cancer. RT-PCR, performed on 10 ovarian cancers, revealed absence of the 5' portion of the BARD1 transcript in 7 tumors, and sequencing of the remaining 3 identified a missense mutation (A1291G) resulting in an amino acid change of glutamine 406 to arginine. These data suggest that genetic and epigenetic changes might lead to elevated cytoplasmic expression of BARD1 and that cytoplasmic BARD1 might be a poor prognostic factor for breast and ovarian cancers.

Maintenance of spermatogenesis requires TAF4b, a gonad-specific subunit of TFIID

The establishment and maintenance of spermatogenesis in mammals requires specialized networks of gene expression programs in the testis. The gonad-specific TAF4b component of TFIID (formerly TAF(II)105) is a transcriptional regulator enriched in the mouse testis. Herein we show that TAF4b is required for maintenance of spermatogenesis in the mouse. While young Taf4b-null males are initially fertile, Taf4b-null males become infertile by 3 mo of age and eventually exhibit seminiferous tubules devoid of germ cells. At birth, testes of Taf4b-null males appear histologically normal; however, at post-natal day 3 gonocyte proliferation is impaired and expression of spermatogonial stem cell markers c-Ret, Plzf, and Stra8 is reduced. Together, these data indicate that TAF4b is required for the precise expression of gene products essential for germ cell proliferation and suggest that TAF4b may be required for the regulation of spermatogonial stem cell specification and proliferation that is obligatory for normal spermatogenic maintenance in the adult.

BARD1 induces apoptosis by catalysing phosphorylation of p53 by DNA-damage response kinase

The BRCA1-associated RING domain protein BARD1 acts with BRCA1 in double-strand break repair and ubiquitination. BARD1 plays a role as mediator of apoptosis by binding to and stabilizing p53, and BARD1-repressed cells are resistant to apoptosis. We therefore investigated the mechanism by which BARD1 induces p53 stability and apoptosis. The apoptotic activity of p53 is regulated by phosphorylation. We demonstrate that BARD1 binds to unphosphorylated and serine-15 phosphorylated forms of p53 in several cell types and that the region required for binding comprises the region sufficient for apoptosis induction. In addition, BARD1 binds to Ku-70, the regulatory subunit of DNA-PK, suggesting that the mechanism of p53-induced apoptosis requires BARD1 for the phosphorylation of p53. Upregulation of BARD1 alone is sufficient for stabilization of p53 and phosphorylation on serine-15, as shown in nonmalignant epithelial cells and ovarian cancer cells, NuTu-19, which are defective in apoptosis induction and express aberrant splice variants of BARD1. Stabilization and phosphorylation of p53 in NuTu-19 cells, as well as apoptosis, can be induced by the exogenous expression of wild-type BARD1, suggesting that BARD1, by binding to the kinase and its substrate, catalyses p53 phosphorylation.

Post-transcriptional control in the male germ line

Post-transcriptional mechanisms play an important role in the biology of germ cells, where they control key developmental decisions in cell division, differentiation and death. Because these post-transcriptional controls are cell-type-specific, and often utilize germ-cell-specific RNA-binding proteins, they provide useful diagnostic markers for male infertility and testicular cancer. Investigation of the genetics of male infertility in men and model organisms suggests that disruption of post-transcriptional control mechanisms can cause specific germ cell pathologies, and these studies point to future possible therapeutic routes for restoring spermatogenesis.