Human, canine and murine BRCA1 genes: sequence comparison among species

Validation of AmpliSeq NGS Panel for BRCA1 and BRCA2 Variant Detection in Canine Formalin-Fixed Paraffin-Embedded Mammary Tumors

Mammary carcinomas are the most common neoplasms observed in women and in female dogs. Canine mammary tumors show epidemiological, clinical, genetic, and prognostic characteristics comparable to human breast cancers. The recent introduction of next generation sequencing (NGS) technologies has greatly improved research and diagnostics for humans, while these new tools still need to be implemented in animal models. In this study we developed and validated an AmpliSeq Panel assay for the identification of BRCA variants in twenty-two different dogs. The amplicon mean coverage was 5499× and uniformity was higher than 98% in all samples. The results of germline single nucleotide variants (SNVs) and insertions/deletions (INDELs) were fully concordant regardless of the types of samples considered (blood, fresh and FFPE tissues). Moreover, despite the high DNA degradation observed in older FFPE blocks (>5 years), the assay allowed full coverage of all amplicons for downstream analyses. We consider the NGS panel developed in this study as a useful tool for expanding information on BRCA genes in the veterinary field and for human health from a comparative oncology perspective.

DNA Damage Response (DDR) proteins in canine cancer as potential research targets in comparative oncology

The DNA damage response (DDR) is a complex signal transduction network that is activated when endogenous or exogenous genotoxins damage or interfere with the replication of genomic DNA. Under such conditions, the DDR promotes DNA repair and ensures accurate replication and division of the genome. High levels of genomic instability are frequently observed in cancers and can stem from germline loss‐of‐function mutations in certain DDR genes, such as BRCA1, BRCA2, and p53, that form the basis of human cancer predisposition syndromes. In addition, mutation and/or aberrant expression of multiple DDR genes are frequently observed in sporadic human cancers. As a result, the DDR is considered to represent a viable target for cancer therapy in humans and a variety of strategies are under investigation. Cancer is also a significant cause of mortality in dogs, a species that offers certain advantages for experimental oncology. Domestic dogs present numerous inbred lines, many of which display predisposition to specific forms of cancer and the study of which may provide insight into the biological basis of this susceptibility. In addition, clinical trials are possible in dogs and may lead to therapeutic insights that could ultimately be extended to humans. Here we review what is known specifically about the DDR in dogs and discuss how this knowledge could be extended and exploited to advance experimental oncology in this species.

A dog oviduct-on-a-chip model of serous tubal intraepithelial carcinoma

Ovarian cancer is the fifth cause of cancer-related mortality in women, with an expected 5-year survival rate of only 47%. High-grade serous carcinoma (HGSC), an epithelial cancer phenotype, is the most common malignant ovarian cancer. It is known that the precursors of HGSC originate from secretory epithelial cells within the Fallopian tube, which first develops as serous tubal intraepithelial carcinoma (STIC). Here, we used gene editing by CRISPR-Cas9 to knock out the oncogene p53 in dog oviductal epithelia cultured in a dynamic microfluidic chip to create an in vitro model that recapitulated human STIC. Similar to human STIC, the gene-edited oviduct-on-a-chip, exhibited loss of cell polarization and had reduced ciliation, increased cell atypia and proliferation, with multilayered epithelium, increased Ki67, PAX8 and Myc and decreased PTEN and RB1 mRNA expression. This study provides a biomimetic in vitro model to study STIC progression and to identify potential biomarkers for early detection of HGSC.

Cytological Grading of Breast Tumors-The Human and Canine Perspective

Human breast cancers (HBCs) are one of the leading causes of global cancer death among women. Domesticated canines are the most affected domestic species with a prevalence rate of breast cancer more than three times in women. While the human cancer patients receive substantial diagnostic and treatment facilities, inadequacy in canine cancer care, calls for greater attention. Fine Needle Aspiration Cytology (FNAC) is comparatively simple, quick, and easily reproducible technique, which aids in pre-surgical diagnosis. In humans, FNAC has a standard protocol, the Robinson's grading system, which has high correlation with the established histological grading system of Scarff Bloom- Richardson. However, Canine Mammary Tumors (CMTs), which are known to be similar to HBCs in biological behavior and gene expressions, still bank on the histopathological methods for diagnostic purposes. This review sheds light on various factors that could be considered for developing a standard FNAC technique for CMT grading and analyzes its future perspectives.

BRCA1/BARD1-dependent ubiquitination of NF2 regulates Hippo-YAP1 signaling

Coordination of growth and genomic stability is critical for normal cell physiology. Although the E3 ubiquitin ligase BRCA1 is a key player in maintenance of genomic stability, its role in growth signaling remains elusive. Here, we show that BRCA1 facilitates stabilization of YAP1 protein and turning "off" the Hippo pathway through ubiquitination of NF2. In BRCA1-deficient cells Hippo pathway is "turned On." Phosphorylation of YAP1 is crucial for this signaling process because a YAP1 mutant harboring alanine substitutions (Mt-YAP5SA) in LATS1 kinase recognition sites not only resists degradation but also rescues YAP1 transcriptional activity in BRCA1-deficient cells. Furthermore, an ectopic expression of the active Mt-YAP5SA, but not inactive Mt-YAP6SA, promotes EGF-independent proliferation and tumorigenesis in BRCA1^-/- mammary epithelial cells. These findings establish an important role of BRCA1 in regulating stability of YAP1 protein that correlates positively with cell proliferation.

Induced in vivo knockdown of the Brca1 gene in skeletal muscle results in skeletal muscle weakness

KEY POINTS

Breast cancer 1 early onset gene codes for the DNA repair enzyme, breast cancer type 1 susceptibility protein (BRCA1). The gene is prone to mutations that cause a loss of protein function. BRCA1/Brca1 has recently been found to regulate several cellular pathways beyond DNA repair and is expressed in skeletal muscle. Skeletal muscle specific knockout of Brca1 in mice caused a loss of muscle quality, identifiable by reductions in muscle force production and mitochondrial respiratory capacity. Loss of muscle quality was associated with a shift in muscle phenotype and an accumulation of mitochondrial DNA mutations. These results demonstrate that BRCA1 is necessary for skeletal muscle function and that increased mitochondrial DNA mutations may represent a potential underlying mechanism.

ABSTRACT

Recent evidence suggests that the breast cancer 1 early onset gene (BRCA1) influences numerous peripheral tissues, including skeletal muscle. The present study aimed to determine whether induced-loss of the breast cancer type 1 susceptibility protein (Brca1) alters skeletal muscle function. We induced genetic ablation of exon 11 in the Brca1 gene specifically in the skeletal muscle of adult mice to generate skeletal muscle-specific Brca1 homozygote knockout (Brca1KOsmi ) mice. Brca1KOsmi exhibited kyphosis and decreased maximal isometric force in limb muscles compared to age-matched wild-type mice. Brca1KOsmi skeletal muscle shifted toward an oxidative muscle fibre type and, in parallel, increased myofibre size and reduced capillary numbers. Unexpectedly, myofibre bundle mitochondrial respiration was reduced, whereas contraction-induced lactate production was elevated in Brca1KOsmi muscle. Brca1KOsmi mice accumulated mitochondrial DNA mutations and exhibited an altered mitochondrial morphology characterized by distorted and enlarged mitochondria, and these were more susceptible to swelling. In summary, skeletal muscle-specific loss of Brca1 leads to a myopathy and mitochondriopathy characterized by reductions in skeletal muscle quality and a consequent kyphosis. Given the substantial impact of BRCA1 mutations on cancer development risk in humans, a parallel loss of BRCA1 function in patient skeletal muscle cells would potentially result in implications for human health.

A monograph proposing the use of canine mammary tumours as a model for the study of hereditary breast cancer susceptibility genes in humans

Canines are excellent models for cancer studies due to their similar physiology and genomic sequence to humans, companion status and limited intra‐breed heterogeneity. Due to their affliction to mammary cancers, canines can serve as powerful genetic models of hereditary breast cancers. Variants within known human breast cancer susceptibility genes only explain a fraction of familial cases. Thus, further discovery is necessary but such efforts have been thwarted by genetic heterogeneity. Reducing heterogeneity is key, and studying isolated human populations have helped in the endeavour. An alternative is to study dog pedigrees, since artificial selection has resulted in extreme homogeneity. Identifying the genetic predisposition to canine mammary tumours can translate to human discoveries – a strategy currently underutilized. To explore this potential, we reviewed published canine mammary tumour genetic studies and proposed benefits of next generation sequencing canine cohorts to facilitate moving beyond incremental advances.

Roles of DNA mutation in the coding region and DNA methylation in the 5' flanking region of BRCA1 in canine mammary tumors

The Breast cancer 1, early onset gene (BRCA1) is known to be significantly associated with human familial breast cancer and is identified to play an important role in canine mammary tumors. Here, genetic variations in the coding region and DNA methylation in the 5' flanking region of BRCA1 in canine mammary tumor samples, 15 each of benign and malignant against 10 normal canine mammary tissue samples, were analyzed using the direct sequencing method. The results indicated two point mutations each in the coding region of canine BRCA1 in one benign mammary tumor sample (4702G >T and 4765G >T) and in one malignant canine mammary tumor sample (3619A >G and 4006G >A). No mutations were detected in the normal canine mammary tissue samples. The 4702G >T mutation was found to terminate further translation. The physical effect of the 4765G >T mutation was found to be the repalacement of the glutamate residue with glutamine. The physical effect of the 3619A >G mutation was found to be the replacement of the threonine residue with alanine, and that of mutation 4006G >A was the replacement of the valine residue with isoleucine in the BRCA1 protein. Bisulfite sequencing detected methylated CpG sites in one canine malignant mammary tumor sample. In conclusion, the present study elucidated the mutational status of the BRCA1 coding region and methylation status of the 5' flanking region of BRCA1 in canine mammary tumors.

Promoter mutation and reduced expression of BRCA1 in canine mammary tumors

Breast cancer 1, early onset (BRCA1) is one of the most important genes in human familial breast cancer, which also plays an important role in canine mammary tumors. The objectives of this study were to determine the promoter sequence of canine BRCA1, to investigate its promoter mutation status and to describe BRCA1 expression pattern in canine mammary tumors. The promoter sequence of canine BRCA1 was acquired by aligning human BRCA1 promoter sequence with canine genomic sequence and confirmed by standard promoter activity analysis. Same as human BRCA1 promoter, the CAAT box and G/C box were found in canine BRCA1 promoter. In order to explore the mutation status of the promoter region and to investigate the expression pattern of this gene, 10 normal canine mammary tissues, 15 benign mammary tumors and 15 malignant mammary tumors were used. By sequencing, 46.7% of the malignant mammary tumors were found with a deletion of one cytosine in the promoter region. The mRNA expression of BRCA1 was significantly reduced in benign and malignant mammary tumors (P<0.05), and the protein expression of BRCA1 was significantly reduced in malignant mammary tumors (P<0.05). This study is the first time to determine the canine BRCA1 promoter sequence and to describe the promoter mutation status in canine mammary tumors.

Growing recognition of the role for rare missense substitutions in breast cancer susceptibility

Most cancer susceptibility genes function as tumor suppressors; accordingly, the focus of mutation screening in breast cancer families has been to identify protein-truncating mutations. However, it is now clear that, for some breast cancer susceptibility genes, a significant proportion of the burden of disease comes from rare missense substitutions. Among genes that have been extensively evaluated, BRCA1, BRCA2, PALB2 and BRIP1 stand as examples where the majority of mutations lead to protein truncation;TP53 provides a counter example, where the majority of pathogenic variants are missense substitutions. In ATM and CHEK2, missense substitutions are probably equally or more important in terms of their frequency and attributable risk. Therefore, ongoing efforts to identify new susceptibility genes should not ignore missense variation.

Genetic variations of BRCA1 and BRCA2 genes in dogs with mammary tumours

Mammary tumours are the most common tumour type in female dogs. The formation of the mammary tumours is multifactorial but the high incidence of tumour disease in certain canine breeds suggests a strong genetic component. BRCA1 and BRCA2 are the most important genes significantly associated with mammary tumours. The aim of this study was to determine the association between the variations of these two genes and canine mammary tumours. 5'-untranslated region, intron 8 and exon 9 of BRCA1 and exons 12, 24, 27 of BRCA2 were sequenced in order to detect the genetic variations. In addition to six previously identified polymorphisms, six novel single nucleotide polymorphisms (SNPs) were detected. Five of the coding SNPs were synonymous and three of them were non-synonymous. The comparison of the sequences from 25 mammary tumour bearing and 10 tumour free dogs suggested that the two SNPs in intron 8 and exon 9 of BRCA1 and two SNPs in exon 24 and exon 27 of BRCA2, which are firstly identified in this study, might be associated with mammary tumour development in dogs. Especially one SNP in exon 9 of BRCA1 and one SNP in exon 24 of BRCA2 were found to be significantly associated with canine mammary tumours.

Increased Expression of BRCA2 and RAD51 in Lymph Node Metastases of Canine Mammary Adenocarcinomas

The BRCA/RAD51 complex of tumor suppressor genes plays a major role in the DNA damage response. In this explorative study, BRCA1, BRCA2, and RAD51 mRNA expression was quantified in highly defined laser microdissected tissue samples of simple adenomas, adenocarcinomas of the mammary gland, and their lymph node metastases by real-time quantitative reverse transcription polymerase chain reaction. Expression levels in the tumors were normalized to the geometric mean of 3 housekeeping genes and quantified relative to normal mammary epithelium of the same dog. In adenomas, mRNA expression was reduced for BRCA1 (6/10 dogs, 60%), BRCA2 (4/10 dogs, 40%), and RAD51 (4/10, 40%). In adenocarcinomas BRCA1 expression varied with increased expression in 3 of 10 (30%) dogs and no differences in 7 of 10 (70%) dogs when compared with normal mammary gland. BRCA2 and RAD51 were overexpressed in 5 of 10 (50%) and 6 of 10 (60%) of adenocarcinomas, respectively. An overexpression of RAD51 and BRCA2 was found in 8 of 10 (80%) and 5 of 10 (50%) of the lymph node metastases, respectively. Direct comparison of primary tumors and metastases revealed increased mRNA expression of BRCA1 (2/10 dogs, 20%), BRCA2 (2/10 dogs, 20%), and RAD51 (3/10 dogs, 30%) in lymph node metastases. Taken together, the results suggest that RAD51 is upregulated in the majority of lymph node metastases of canine mammary tumors. Further experimental studies are needed to clarify whether these changes in gene expression are a direct carcinogenetic stimulus or a protective response due to genetic instability during tumor progression.

Expression Patterns of the BRCA1 Splicing Variants in Canine Normal Tissues and Mammary Gland Tumors

Human BRCA1 is familial breast cancer susceptibility gene. Recently, decreased BRCA1 mRNA and protein expression has been identified in sporadic breast tumors. In the reported human BRCA1 splicing variants, delta11b lacks the majority of exon11 and is suspected to have a distinct function in normal tissues. The splicing variants display a variety of expression pattern in breast cancer samples. Although mammary gland tumor is important disease in dog, there are few reports for BRCA1 in the canine tumors. In this study, we examined the relative amounts of BRCA1 splicing variants mRNA in canine normal and mammary tumor samples by RT-PCR to investigate whether there is the altered expression of variant mRNAs in the canine tumor as reported in human. The exon11b-defecting RT-PCR products were observed in all the normal tissues examined and the nucleotide sequence was quite similar to that of human BRCA1 delta11b. In some tumor samples, we did not detect the products targeted for exon10-13 and exon14-15, while these products were observed in all the normal samples examined. Especially, the relative amounts of the exon11-defecting products were remarkably decreased in most of the tumors (11/16).

A homologue of the breast cancer-associated gene BARD1 is involved in DNA repair in plants

hBRCA1 and hBARD1 are tumor suppressor proteins that are involved as heterodimer via ubiquitinylation in many cellular processes, such as DNA repair. Loss of BRCA1 or BARD1 results in early embryonic lethality and chromosomal instability. The Arabidopsis genome carries a BRCA1 homologue, and we were able to identify a BARD1 homologue. AtBRCA1 and the putative AtBARD1 protein are able to interact with each other as indicated by in vitro and in planta experiments. We have identified T-DNA insertion mutants for both genes, which show no visible phenotype under standard growth conditions and are fully fertile. Thus, in contrast to animals, both genes have no indispensable role during development and meiosis in plants. The two single as well as the double mutant are to a similar extent sensitive to mitomycin C, indicating an epistatic interaction in DNA crosslink repair. We could further demonstrate that in Arabidopsis BARD1 plays a prominent role in the regulation of homologous DNA repair in somatic cells.

BRCA1 and BRCA2 germline mutational spectrum and evidence for genetic anticipation in Portuguese breast/ovarian cancer families

We present the first characterisation of the mutational spectrum of the entire coding sequences and exon-intron boundaries of the BRCA1 and BRCA2 genes as well as large BRCA1 rearrangements in Portuguese families with inherited predisposition to breast/ovarian cancer. Of the 100 probands studied, pathogenic mutations were identified in 22 (24.7%) of 89 breast and/or ovarian cancer families with more than one affected member (15 in BRCA1 and seven in BRCA2), but in none of the 11 patients without family history of cancer. One (6.7%) of the BRCA1 mutations is a large deletion involving exons 11-15. Seven pathogenic point mutations are novel: 2088C>T, 2156delinsCC, and 4255_4256delCT in BRCA1 and 4608_4609delTT, 5036delA, 5583_5584insT, and 8923C>T in BRCA2. The novel 2156delinsCC was identified in three probands from different families and probably represents a founder mutation in our population. We also found a previously reported 3450_3453del4 mutation in three unrelated patients. In addition to the 22 pathogenic mutations, we identified 19 missense mutations of uncertain pathogenic significance, three of them (5241G>C in BRCA1 and IVS6+13C>T and 3731T>C in BRCA2) previously undescribed. The percentage of cases with truncating mutations in BRCA1 and BRCA2 was higher in breast/ovarian cancer (37.0%, mostly BRCA1) and male breast cancer (40%, all BRCA2) families than in families with only female breast cancer (17.5%). Interestingly, we found evidence for genetic anticipation regarding age at diagnosis of both breast and ovarian cancer in those families presenting affected members in more than one generation. These findings should be taken into consideration while planning screening and prophylactic measures in families with inherited predisposition to breast and ovarian cancer.

Classification of BRCA1 missense variants of unknown clinical significance

BACKGROUND

BRCA1 is a tumour suppressor with pleiotropic actions. Germline mutations in BRCA1 are responsible for a large proportion of breast-ovarian cancer families. Several missense variants have been identified throughout the gene but because of lack of information about their impact on the function of BRCA1, predictive testing is not always informative. Classification of missense variants into deleterious/high risk or neutral/low clinical significance is essential to identify individuals at risk.

OBJECTIVE

To investigate a panel of missense variants.

METHODS AND RESULTS

The panel was investigated in a comprehensive framework that included (1) a functional assay based on transcription activation; (2) segregation analysis and a method of using incomplete pedigree data to calculate the odds of causality; (3) a method based on interspecific sequence variation. It was shown that the transcriptional activation assay could be used as a test to characterise mutations in the carboxy-terminus region of BRCA1 encompassing residues 1396-1863. Thirteen missense variants (H1402Y, L1407P, H1421Y, S1512I, M1628T, M1628V, T1685I, G1706A, T1720A, A1752P, G1788V, V1809F, and W1837R) were specifically investigated.

CONCLUSIONS

While individual classification schemes for BRCA1 alleles still present limitations, a combination of several methods provides a more powerful way of identifying variants that are causally linked to a high risk of breast and ovarian cancer. The framework presented here brings these variants nearer to clinical applicability.

Single nucleotide polymorphisms in clinical genetic testing: the characterization of the clinical significance of genetic variants and their application in clinical research for BRCA1

Clinical genetic testing is increasingly employed in the medical management of cancer patients. These tests support a variety of clinical decisions by providing results that indicate risk for future disease, confirmation of diagnoses, and more recently, therapeutic selection and prognosis. Most genetic variation detected during clinical testing involves single nucleotide polymorphisms (SNPs). Continued advances in the technologies of genetic analyses make these tests increasingly sensitive, cost-effective and timely, which contribute to their increased utilization. Conversely, it has proven difficult to characterize the clinical significance of genetic variants that do not obviously truncate the open reading frames of genes. These genetic variants of uncertain clinical significance diminish the value of genetic test results. This article highlights a variety of approaches that have emerged from research in diverse disciplines to solve the problem, including the application of information about common SNPs in multiple methods to better characterize clinically uncertain variants. Hereditary breast/ovarian cancer, and in particular BRCA1, provides a framework for this discussion. BRCA1 is particularly interesting in this respect since clinical genetic testing by direct DNA sequencing for over 50,000 patients in North America has revealed approximately 1500 genetic variants to date. This large data set combined with the clinical significance of BRCA1 have resulted in research groups selecting BRCA1 as a preferred gene to evaluate novel methods in this field. Finally, the lessons learned through work with BRCA1 are highly applicable to many other genes associated with cancer risk.

Analysis of missense variation in human BRCA1 in the context of interspecific sequence variation

INTRODUCTION

Interpretation of results from mutation screening of tumour suppressor genes known to harbour high risk susceptibility mutations, such as APC, BRCA1, BRCA2, MLH1, MSH2, TP53, and PTEN, is becoming an increasingly important part of clinical practice. Interpretation of truncating mutations, gene rearrangements, and obvious splice junction mutations, is generally straightforward. However, classification of missense variants often presents a difficult problem. From a series of 20,000 full sequence tests of BRCA1 carried out at Myriad Genetic Laboratories, a total of 314 different missense changes and eight in-frame deletions were observed. Before this study, only 21 of these missense changes were classified as deleterious or suspected deleterious and 14 as neutral or of little clinical significance.

METHODS

We have used a combination of a multiple sequence alignment of orthologous BRCA1 sequences and a measure of the chemical difference between the amino acids present at individual residues in the sequence alignment to classify missense variants and in-frame deletions detected during mutation screening of BRCA1.

RESULTS

In the present analysis we were able to classify an additional 50 missense variants and two in-frame deletions as probably deleterious and 92 missense variants as probably neutral. Thus we have tentatively classified about 50% of the unclassified missense variants observed during clinical testing of BRCA1.

DISCUSSION

An internal test of the analysis is consistent with our classification of the variants designated probably deleterious; however, we must stress that this classification is tentative and does not have sufficient independent confirmation to serve as a clinically applicable stand alone method.

Evolution of the tumor suppressor BRCA1 locus in primates: implications for cancer predisposition

Germ-line mutations in the BRCA1 gene predispose affected individuals to breast and ovarian cancer syndromes. In an attempt to systematically analyze a broader spectrum of genetic changes ranging from frequent exon deletions and duplications to amino acid replacements and protein truncations, we isolated and characterized full size BRCA1 homologues from a representative group of non-human primates. Our analysis represents the first comprehensive sequence comparison of primate BRCA1 loci and corresponding proteins. The comparison revealed an unusually high proportion of indels in non-coding DNA. The major force driving evolutionary changes in non-coding BRCA1 sequences was Alu-mediated rearrangements, including Alu transpositions and Alu-associated deletions, indicating that structural instability of this locus may be intrinsic in anthropoids. Analysis of the non-synonymous/synonymous ratio in coding portions of the gene revealed the presence of both conserved and rapidly evolving regions in the BRCA1 protein. Previously, a rapidly evolving region with evidence of positive evolutionary selection in human and chimpanzee had been identified only in exon 11. Here, we show that most of the internal BRCA1 sequence is variable between primates and evolved under positive selection. In contrast, the terminal regions of BRCA1, which encode the RING finger and BRCT domains, experienced negative selection, which left them almost identical between the compared primates. Distribution of the reported missense mutations, but not frameshift and nonsense mutations, is positively correlated with BRCA1 protein conservation. Finally, on the basis of protein sequence conservation, we identified missense changes that are likely to compromise BRCA1 function.

Structure-based assessment of missense mutations in human BRCA1: implications for breast and ovarian cancer predisposition

The BRCA1 gene from individuals at risk of breast and ovarian cancers can be screened for the presence of mutations. However, the cancer association of most alleles carrying missense mutations is unknown, thus creating significant problems for genetic counseling. To increase our ability to identify cancer-associated mutations in BRCA1, we set out to use the principles of protein three-dimensional structure as well as the correlation between the cancer-associated mutations and those that abolish transcriptional activation. Thirty-one of 37 missense mutations of known impact on the transcriptional activation function of BRCA1 are readily rationalized in structural terms. Loss-of-function mutations involve nonconservative changes in the core of the BRCA1 C-terminus (BRCT) fold or are localized in a groove that presumably forms a binding site involved in the transcriptional activation by BRCA1; mutations that do not abolish transcriptional activation are either conservative changes in the core or are on the surface outside of the putative binding site. Next, structure-based rules for predicting functional consequences of a given missense mutation were applied to 57 germ-line BRCA1 variants of unknown cancer association. Such a structure-based approach may be helpful in an integrated effort to identify mutations that predispose individuals to cancer.

BRCA1 and BRCA2 Mutations in Women from Shanghai China

Little is known about the frequency of germ-line mutations in the breast cancer susceptibility genes BRCA1 and BRCA2 among Asian populations. We investigated the distribution of BRCA1 and BRCA2 germ-line mutations and polymorphisms in a cohort of women from Shanghai, China. Study subjects totaled 1306, and included 645 women with breast cancer, 342 women with benign breast disease, and 319 unaffected controls, born between 1924 and 1958, selected from women enrolled in a randomized trial of Breast Self-Examination in Shanghai, China. Women were selected without regard to family history of breast or ovarian cancer. All of the coding regions and exon-intron boundaries were screened. Data were analyzed with respect to age at diagnosis, and family history of breast and ovarian cancer. The prevalence of known disease-associated mutations in women with breast cancer was 1.1% each, for BRCA1 and BRCA2. Among breast cancer cases with a family history of breast or ovarian cancer, 8.1% and 2.7% carried likely BRCA1 and BRCA2 disease-associated mutations, respectively. Overall, these results suggest that inherited susceptibility to breast cancer due to germ-line BRCA1/2 mutations among women with a family history of breast cancer is comparable between women from Shanghai and Caucasian women of Western European descent. Most alterations observed appear unique to the Chinese population, suggesting a resource that will be useful for assessing risk among both Chinese women and United States women of Chinese descent.

Analysis of BRCA1 and BRCA2 genes in Spanish breast/ovarian cancer patients: a high proportion of mutations unique to Spain and evidence of founder effects

We screened index cases from 410 Spanish breast/ovarian cancer families and 214 patients (19 of them males) with breast cancer for germ-line mutations in the BRCA1 and BRCA2 genes, using SSCP, PTT, CSGE, DGGE, and direct sequencing. We identified 60 mutations in BRCA1 and 53 in BRCA2. Of the 53 distinct mutations observed, 11 are novel and 12 have been reported only in Spanish families (41.5%). The prevalence of mutations in this set of families was 26.3%, but the percentage was higher in the families with breast and ovarian cancer (52.1%). The lowest proportion of mutations was found in the site-specific female breast cancer families (15.4%). Of the families with male breast cancer cases, 59.1% presented mutations in the BRCA2 gene. We found a higher frequency of ovarian cancer associated with mutations localized in the 5' end of the BRCA1 gene, but there was no association between the prevalence of this type of cancer and mutations situated in the ovarian cancer cluster region (OCCR) region of exon 11 of the BRCA2 gene. The mutations 187_188delAG, 330A>G, 5236G>A, 5242C>A, and 589_590del (numbered after GenBank U14680) account for 46.6% of BRCA1 detected mutations whereas 3036_3039del, 6857_6858del, 9254_9258del, and 9538_9539del (numbered after GenBank U43746) account for 56.6% of the BRCA2 mutations. The BRCA1 330A>G has a Galician origin (northwest Spain), and BRCA2 6857_6858del and 9254_9258del probably originated in Catalonia (northeast Spain). Knowledge of the spectrum of mutations and their geographical distribution in Spain will allow a more effective detection strategy in countries with large Spanish populations.

Bovine BRCA1 shows classic responses to genotoxic stress but low in vitro transcriptional activation activity

Human BRCA1 has a genetically demonstrated role in DNA repair, and has been proposed to act as a transcriptional activator in a limited number of specialized settings. To gain insight into biologically conserved functional motifs, we isolated an ortholog of BRCA1 from cattle (Bos taurus). The predicted protein product shows 72.5% sequence identity with the human protein and conservation of amino acids involved in BRCA1 structure and function. Although the bovine C-terminus is truncated by seven amino acids as compared to human, bovine BRCA1 protein exhibited a similar cell cycle-regulated nuclear expression pattern. Expression was characteristically low and diffuse in the nucleus of G1/G0 cells, followed by increasing BRCA1-positive nuclear speckles in late S phase and G2/M phase cells. Bovine BRCA1 was phosphorylated and nuclear speckling was enhanced in response to DNA-damaging agents. Consistent with evidence from studies of human BRCA1, bovine BRCA1 was shown to interact with RNA polymerase II in vivo, an activity that was mapped to the C-terminal domain (CTD) (bBRCA(1364-1849)). Interestingly, when tested in the GAL4 transcriptional activation assay, full-length bovine and human BRCA1 lacked any ability to act as transcriptional activators and the CTD of bovine BRCA1 had five-fold lower activity when compared to the more acidic human C-terminus. These results provide evidence that phosphorylation and nuclear relocalization are highly conserved features of the BRCA1 response to genotoxic stress. In addition, bovine BRCA1 binds the RNA polymerase II holoenzyme, but this interaction lacks significant ability to correctly orient or recruit RNA polymerase II for transcription in the classic GAL4 transcriptional activation system.

Similar contributions of BRCA1 and BRCA2 germline mutations to early-onset breast cancer in Germany

This study was undertaken to investigate the prevalence of BRCA1 and BRCA2 germline mutations in 91 German patients unselected for family history, who were diagnosed with breast cancer before the age of 41 years. Clinical information and blood samples were obtained from all patients. A comprehensive BRCA1 and BRCA2 mutational analysis was performed using the protein truncation assay and single-strand conformational polymorphism analysis followed by DNA sequencing of variant signals detected by these assays. Five different deleterious germline mutations including four frameshift mutations and one missense mutation were identified, three in BRCA1 (3.3%) and two mutations (2.2%) in BRCA2. Both BRCA2 mutations are novel and might be specific for the German population. An additional BRCA1 missense mutation previously described and classified as an unknown variant was found. This mutation was also detected in two breast cancer patients of family P 328 and not in 140 healthy controls suggesting that it is disease associated. In addition, one common polymorphism and five novel intronic sequence variants with unknown significance were found. Our findings show that mutations in BRCA1 and BRCA2 may contribute similarly to early-onset breast cancer in Germany. Given current constraints on health-care resources, these results support the notion that BRCA1 and BRCA2 mutation screening may have the strongest impact on health-care when targeted to high-risk populations.

BRCA1 expression in canine mammary dysplasias and tumours: relationship with prognostic variables

BRCA1 is a nuclear phosphoprotein that participates in the regulation of the cell cycle. The role of the BRCA1 gene in canine mammary tissue and mammary tumours has not been studied. The present study examined immunohistochemically the expression and intracellular distribution of BRCA1 protein in two normal, seven dysplastic and 44 neoplastic canine mammary glands and its relationship with clinical and pathological variables and other prognostic parameters. Strong nuclear immunolabelling of BRCA1 protein was observed in the epithelial cells of the normal mammary glands and mammary dysplasias. The majority of benign tumours, and more especially of malignant tumours, showed a significant reduction in the nuclear expression of BRCA1 protein and an increase in cytoplasmic expression. Loss of BRCA1 expression was associated with high proliferation marker Ki-67 and ER-alpha negative tumours. The reduction and aberrant distribution of BRCA1 in canine mammary tumours were significantly associated with malignant characteristics. The results may indicate that BRCA1 has a role in the malignant behaviour of these tumours.

Characterization of common BRCA1 and BRCA2 variants

Many missense variants identified in BRCA1 and BRCA2, two genes responsible for the majority of hereditary breast and ovarian cancer, are of unclear clinical significance. Characterizing the significance of such variants is important for medical management of patients in whom they are identified. The aim of this study was to characterize eight of the most common reported missense mutations in BRCA1 and BRCA2 occurring in patients tested for hereditary risk of breast and ovarian cancers. The prevalence of each variant in a control population, co-segregation of the variant with cancer within families, location of the variant within the gene, the nature of the amino acid substitution and conservation of the wild-type amino acid among species were considered. In a control population, the BRCA1 variants M1652I, R1347G, and S1512I, were each observed at a frequency of 4.08%, 2.04%, and 2.04%, respectively, and the BRCA2 variants A2951T, V2728I, and D1420Y, were seen at 1.02%, 0.68%, and 0.34%, respectively. Although the BRCA2 variants T598A and R2034C were not seen in this group of controls, other clinical and published observations indicate that these variants are not deleterious. Based on epidemiological and biological criteria, we therefore conclude that the BRCA1 missense mutations R1347G, S1512I and M1652I, and the BRCA2 missense mutations T598A, D1420Y, R2034C, V2728I, and A2951T, are not deleterious mutations.

Characterization of Arabidopsis thaliana ortholog of the human breast cancer susceptibility gene 1: AtBRCA1, strongly induced by gamma rays

hBRCA1 is involved in 20-45% of inherited breast cancer cases and is implicated in many mechanisms involved in response to DNA damage. To date, BRCA1 orthologs have been characterized in vertebrate genomes only. We have identified the ortholog of BRCA1 in Arabidopsis thaliana. AtBRCA1 is a 5.5 kb part of the locus At4g21070. The corresponding mRNA of 3.5 kb is composed of 14 exons and encodes a 941 amino acid protein (104 kDa). AtBRCA1, which has one N-terminal RING finger, two C-terminal BRCT and the p300/CBP interacting domain, shows a high similarity to hBRCA1 in these motifs and has the same characteristic molecular organization. We have also identified a putative ortholog in rice (OsBRCA1). With 941 and 968 amino acids, respectively, AtBRCA1 and OsBRCA1 are the shortest members of the BRCA1 family, and may represent a plant specificity. AtBRCA1 is expressed ubiquitously in plant tissues, at levels depending on organ type, with highest levels in flower buds and exponentially growing cell cultures. Increase of mRNA levels in all plant tissues 1 h after irradiation with the highest induction level of approximately 150 times for a 100 Gy dose is consistent with a putative role of AtBRCA1 in DNA repair and in cell-cycle control.

Understanding missense mutations in the BRCA1 gene: an evolutionary approach

The role of missense changes in BRCA1 in breast cancer susceptibility has been difficult to establish. We used comparative evolutionary methods to identify potential functionally important amino acid sites in exon 11 and missense changes likely to disrupt gene function, aligning sequences from 57 eutherian mammals and categorizing amino acid sites by degree of conservation. We used Bayesian phylogenetic analyses to determine relationships among orthologs and identify codons evolving under positive selection. Most conserved residues occur in a region with the highest concentration of protein-interacting domains. Rapidly evolving residues are concentrated in the RAD51-interacting domain, suggesting that selection is acting most strongly on the role of BRCA1 in DNA repair. Investigation of the functional role of missense changes in breast-cancer susceptibility should focus on 38 missense changes in conserved and 3 in rapidly evolving regions of exon 11.

BRCA1 Zinc RING Finger Domain Disruption Alters Caspase Response in Ovarian Surface Epithelial Cells

BACKGROUND: The frequently occurring 185delAG mutation occurs in the amino-terminal zinc RING domain of the breast and ovarian cancer susceptibility gene, BRCA1. We sought to determine differential cell viability and apoptotic response of human ovarian surface epithelial cells with and without the 185delAG mutation. RESULTS: BRCA1wt and BRCA1+ cells were treated with staurosporine. Cell proliferation assays showed BRCA1wt cells grew to a greater extent compared to BRCA1+ cells. Trypan blue exclusion assays confirmed this observation. Western immunoblot analysis revealed that caspase 3 levels were higher after staurosporine treatment in BRCA1+ cells than in wild type cells, while full length DNA Fragmentation Factor 45 levels were lower in BRCA1+ cells. While there was no significant difference in levels of excision repair cross complementing protein1 (ERCC1) with BRCA1 status, BRCA1+ cells demonstrated cleavage of polyribose ADP polymerase (PARP) before wild type cells. CONCLUSIONS: Disruption of the BRCA1 RING domain caused altered cell viability and caspase-dependent apoptotic response after chemotoxic stress.

Identification of proteins that interact with BRCA1 by Far-Western library screening

Protein-protein interactions control numerous biological processes. In the case of a protein with no known function, identification of interacting proteins may lend insight into its cellular function. Protein-protein interactions are often detected by yeast two-hybrid screening which is based on a transcriptional read-out. One limitation of this technique is that transcription factors, when used as bait, frequently impair the effectiveness of this screen because they give rise to high levels of false positives. The carboxyl terminus of the breast cancer tumor suppressor gene, BRCA1, contains two BRCT motifs, a motif found in several DNA repair and cell cycle checkpoint proteins. This region of BRCA1 also exhibits an intrinsic transcriptional transactivation activity when bound to DNA as a fusion protein, thereby limiting its use in yeast two-hybrid screen. In order to isolate proteins that interact with this domain of BRCA1, we utilized a Far-Western screen, a method based on direct protein binding. We used recombinant histidine-tagged BRCT as the primary protein probe. We isolated eight cDNAs that bind to the BRCT domain of BRCA1. Further analysis demonstrated that two of the clones encode for proteins that interact directly with the BRCT domain of BRCA1.

Nine novel conserved motifs in BRCA1 identified by the chicken orthologue

The breast cancer susceptibility gene BRCA1 encodes a multifunctional protein that is mutated in many hereditary breast and ovarian cancers. We have cloned a homologue of the human BRCA1 gene from chicken; the gene encodes a 1749 amino acid protein that is 33% identical to human BRCA1. Phylogenetic analyses of the chicken and mammalian proteins indicate that the chicken gene is a bona fide BRCA1 orthologue, the first to be described from a non-mammal. Most of the chicken protein has diverged considerably from its mammalian orthologues, although the RING and BRCT repeat regions are highly conserved. This marked overall sequence divergence has allowed us to identify nine additional highly-conserved motifs (ranging from 8--56 amino acids in length) which are likely important for BRCA1 function.

BRCA1 and BRCA2 mutation status and cancer family history of Danish women affected with multifocal or bilateral breast cancer at a young age

INTRODUCTION

A small fraction of breast cancer is the result of germline mutations in the BRCA1 and BRCA2 cancer susceptibility genes. Mutation carriers frequently have a positive family history of breast and ovarian cancer, are often diagnosed at a young age, and may have a higher incidence of double or multiple primary breast tumours than breast cancer patients in general.

OBJECTIVES

To estimate the prevalence and spectrum of BRCA1 and BRCA2 mutations in young Danish patients affected with bilateral or multifocal breast cancer and to determine the relationship of mutation status to family history of cancer.

SUBJECTS

From the files of the Danish Breast Cancer Cooperative Group (DBCG), we selected 119 breast cancer patients diagnosed before the age of 46 years with either bilateral (n=59) or multifocal (n=61) disease.

METHODS

DNA from the subjects was screened for BRCA1 and BRCA2 mutations using single strand conformation analysis (SSCA) and the protein truncation test (PTT). Observed and expected cancer incidence in first degree relatives of the patients was estimated using data from the Danish Cancer Registry.

RESULTS

Twenty four mutation carriers were identified (20%), of whom 13 had a BRCA1 mutation and 11 carried a BRCA2 mutation. Two mutations in BRCA1 were found repeatedly in the material and accounted for seven of the 24 (29%) mutation carriers. The mutation frequency was about equal in patients with bilateral (22%) and multifocal breast cancer (18%). The incidence of breast and ovarian cancer was greatly increased in first degree relatives of BRCA1 and BRCA2 mutation carriers, but to a much lesser degree in relatives of non-carriers. An increased risk of cancer was also noted in brothers of non-carriers.

CONCLUSIONS

A relatively broad spectrum of germline mutations was observed in BRCA1 and BRCA2 and most of the mutations are present in other populations. Our results indicate that a diagnosis of bilateral and multifocal breast cancer is predictive of BRCA1 and BRCA2 mutation status, particularly when combined with information on the patients' age at diagnosis and family history of breast/ovarian cancer.

Microsatellite polymorphism in intron 14 of the canine BRCA1 gene

Microsatellite polymorphism due to differences in CT dinucleotide repeats was demonstrated in intron 14 of the canine BRCA1 gene. Genotype analysis of 103 unrelated dogs from 30 different breeds detected the presence of five alleles, including 10 of the expected 15 genotypes. Gene frequencies were biased and all alleles with the exception of one were below 0.1. This polymorphism, which occurs at the intron of canine BRCA1 should prove to be a useful marker for detecting the loss of heterozygosity (LOH). One of the more notable findings of the present study was the detection of homozygotes of rare alleles. This finding identified an accumulation of rare alleles in specific canine breeds and demonstrated the usefulness of this characteristic for the biological study of dog evolution.

Functional analysis of BRCA1 C-terminal missense mutations identified in breast and ovarian cancer families

Germline mutations in the breast and ovarian cancer susceptibility gene BRCA1 are responsible for the majority of cases involving hereditary breast and ovarian cancer. Whereas all truncating mutations are considered as functionally deleterious, most of the missense variants identified to date cannot be readily distinguished as either disease-associated mutations or benign polymorphisms. The C-terminal domain of BRCA1 displays an intrinsic transactivation activity, and mutations linked to disease predisposition have been shown to confer loss of such activity in yeast and mammalian cells. In an attempt to clarify the functional importance of the BRCA1 C-terminus as a transcription activator in cancer predisposition, we have characterized the effect of C-terminal germline variants identified in Scandinavian breast and ovarian cancer families. Missense variants A1669S, C1697R, R1699W, R1699Q, A1708E, S1715R and G1738E and a truncating mutation, W1837X, were characterized using yeast- and mammalian-based transcription assays. In addition, four additional missense variants (V1665M, D1692N, S1715N and D1733G) and one in-frame deletion (V1688del) were included in the study. Our findings demonstrate that transactivation activity may reflect a tumor-suppressing function of BRCA1 and further support the role of BRCA1 missense mutations in disease predisposition. We also report a discrepancy between results from yeast- and mammalian-based assays, indicating that it may not be possible to unambiguously characterize variants with the yeast assay alone. We show that transcription-based assays can aid in the characterization of deleterious mutations in the C-terminal part of BRCA1 and may form the basis of a functional assay.

Hereditary breast cancer: a review

Breast cancer is the most common female malignancy and a major cause of death in middle-aged women. A positive family history of breast cancer is one of the strongest risk factors for the disease. In addition, many afflicted breast cancer families are characterized by early onset and bilateral tumors, and also, in some cases, associated malignancies, most commonly ovarian cancer. It is estimated that 5-10% of all breast cancer cases are due to autosomal dominant genes segregating with the disease. Mutations in the BRCA1 and BRCA2 genes are known to predispose to breast and ovarian cancer in many families. Other genes are only involved in very rare syndromes, and additional genes remain to be disclosed.

CBP/p300 interact with and function as transcriptional coactivators of BRCA1

BRCA1 is a breast and ovarian cancer-specific tumor suppressor, with properties of a transcription factor involved in DNA repair. We previously have shown the transactivation of heterologous promoters by the carboxyl terminus of BRCA1. We now describe that BRCA1-mediated transactivation is enhanced by p300/CBP (CREB binding protein) and that this effect was suppressed by the adenovirus E1A oncoprotein. We show a physical association of BRCA1 with the transcriptional coactivators/acetyltransferases p300 and CBP. Endogenous as well as overexpressed BRCA1 and p300 were found to associate in a phosphorylation-independent manner. BRCA1 interacts with the cAMP response element binding protein (CREB) domain of p300/CBP via both its amino and carboxyl termini. Finally, full-length BRCA1 is shown to transcriptionally activate the Rous sarcoma virus-long terminal repeat promoter, which was further stimulated by p300. Immunocolocalization analyses suggest that BRCA1 and p300 associate in a cell cycle-dependent manner. Our results support a role for BRCA1 in transcription.

The prevalence of BRCA1 mutations in Chinese patients with early onset breast cancer and affected relatives

The purpose of this study was to determine the prevalence of BRCA1 mutations in Chinese breast cancer patients in Singapore. BRCA1 analysis was conducted in consecutive patients with breast cancer before the age of 40 years (76 women), or whose relatives had breast or ovarian cancer (16 women). Ten patients had both early onset breast cancer and affected relatives. Genomic DNA from peripheral mononuclear blood cells was studied by using the protein transcription-translation assay (exon 11) and single-strand conformational polymorphism, with subsequent DNA sequencing. All six disease-causing mutations occurred in women under 40 years (8.6%) with three occurring in patients under 35 years (three out of 22 patients, 13.6%). Mis-sense mutations of unknown significance were found in three patients. Two of the ten women with affected relatives under 40 years had BRCA1 mutations. The prevalence of BRCA1 mutations in Chinese patients with early onset breast cancer is similar to that observed in Caucasian women. Most Chinese patients with affected relatives were not carriers of BRCA1 mutations.

Reproductive factors in hereditary breast cancer

BACKGROUND

An early age at menarche, a short menstrual cycle length, and a high age at first full term pregnancy or nulliparity are known risk factors for breast cancer. These risk factors have previously been reported to differ between breast cancer patients with and without a family history of breast cancer and also between breast cancer patients and controls.

METHODS

Self-administered questionnaires were filled out by 95 women belonging to 24 families with known BRCA1 mutations, 16 women belonging to nine families with known BRCA2 mutations, and 95 women belonging to 65 families with hereditary breast cancer where no BRCA1 or BRCA2 mutations could be detected. Thirty-nine women were BRCA1 mutation carriers and 56 women were BRCA1 negative, 11 women were BRCA2 carriers and five BRCA2 negative. All women were born between 1905 and 1979.

RESULTS

Age at menarche, physiological menstrual cycle length at age 30 or at current age in younger women (when not using oral contraceptives), age at first full term pregnancy, and nulliparity did not significantly differ between BRCA1 mutation carriers and BRCA1 negative women. Too few women were BRCA2 negative to serve as a control group. BRCA2 mutation carriers were therefore compared with BRCA1 negative and BRCA2 negative women. None of the above reproductive factors did significantly differ between BRCA2 mutation carriers and from BRCA1 and BRCA2 families. Women from non-BRCA1/BRCA2 hereditary breast cancer families had a higher age at menarche, but this was no longer significant after adjustment for other factors in a multivariate model.

CONCLUSION

Our results suggest that reproductive risk factors of breast cancer are not related to BRCA1 or BRCA2 carrier status. There was also no indication that these factors differ in carriers of unknown susceptibility genes compared with non-carriers from BRCA1 and BRCA2 families.

Two contiguously located germline BRCA1 mutations in a Spanish early-onset breast cancer family

We identified two BRCA1 mutations in a high risk breast cancer family: the missense 1240 C > T (Thr > Ile) and the 1241delAC at codon 374, which results in a stop at codon 376. Both were contiguously located in the same BRCA1 gene, in a motif of 11 amino acids, which is highly conserved across human, canine and murine species. The presence of missense mutations in this motif in breast-cancer families suggests an important functional role for this protein region and a potential deleterious effect of the 1240C > T mutation.

BRCA1 is phosphorylated at serine 1497 in vivo at a cyclin-dependent kinase 2 phosphorylation site

BRCA1 is a cell cycle-regulated nuclear protein that is phosphorylated mainly on serine and to a lesser extent on threonine residues. Changes in phosphorylation occur in response to cell cycle progression and DNA damage. Specifically, BRCA1 undergoes hyperphosphorylation during late G1 and S phases of the cell cycle. Here we report that BRCA1 is phosphorylated in vivo at serine 1497 (S1497), which is part of a cyclin-dependent kinase (CDK) consensus site. S1497 can be phosphorylated in vitro by CDK2-cyclin A or E. BRCA1 coimmunoprecipitates with an endogenous serine-threonine protein kinase activity that phosphorylates S1497 in vitro. This cellular kinase activity is sensitive to transfection of a dominant negative form of CDK2 as well as the application of the CDK inhibitors p21 and butyrolactone I but not p16. Furthermore, BRCA1 coimmunoprecipitates with CDK2 and cyclin A. These results suggest that the endogenous kinase activity is composed of CDK2-cyclin complexes, at least in part, concordant with the G1/S-specific increase in BRCA1 phosphorylation.

The second BRCT domain of BRCA1 proteins interacts with p53 and stimulates transcription from the p21WAF1/CIP1 promoter

Inherited mutations in the breast and ovarian cancer susceptibility gene BRCA1 are associated with high risk for developing breast and ovarian cancers. Several studies link BRCA1 to transcriptional regulation, DNA repair, apoptosis and growth/tumor suppression. BRCA1 associates with p53 and stimulates transcription in both p53 dependent and p53-independent manners. BRCA1 splice variants BRCA1a (p110) and BRCA1b (p100) associates with CBP/p300 co-activators. Here we show that BRCA1a and BRCA1b proteins stimulate p53-dependent transcription from the p21WAF1/CIP1 promoter. In addition, the C-terminal second BRCA1 (BRCT) domain is sufficient for p53 mediated transactivation of the p21 promoter. Previous studies emphasized the importance of the BRCT domain, which shows homology with p53 binding protein (53BP1), in transcriptional activation, growth inhibition and tumor suppression. Our findings demonstrate an additional function for this domain in protein-protein interaction and co-activation of p53. We also found that BRCA1a and BRCA1b proteins interact with p53 in vitro and in vivo. The p53 interaction domain of BRCA1a/1b maps, in vitro, to the second BRCT domain (aa 1760-1863). The BRCT domain binds to the central domain of p53 which is required for sequence specific DNA binding. These results demonstrate for the first time the presence of a second p53 interaction domain in BRCA1 proteins and suggests that BRCA1a and BRCA1b proteins, like BRCA1, function as p53 co-activators. This BRCT domain also binds in vitro to CBP. These results suggest that one of the mechanisms by which BRCA1 proteins function is through recruitment of CBP/p300 associated HAT/FAT activity for acetylation of p53 to specific promoters resulting in transcriptional activation.

Breast cancer susceptibility genes. BRCA1 and BRCA2

Mutations in the BRCA1 and BRCA2 genes lead to an increased susceptibility to breast, ovarian, and other cancers. It is estimated that 3%-8% of all women with breast cancer will be found to carry a mutation in 1 of these genes. Families with multiple affected first-degree relatives and patients with early-onset disease have been found to harbor mutations at a higher frequency. The BRCA1 and BRCA2 genes code for large proteins that bear no resemblance to other known genes. In the cell, they appear to act as tumor suppressor genes and play a role in the maintenance of genome integrity, although the precise function of these genes has yet to be discovered. A large number of distinct mutations have been found in cancer families around the world. The majority of the defined pathologic mutations result in premature truncation of the protein (frameshift and nonsense mutations). These mutations may substantially increase the risk for breast and ovarian cancer, but a precise risk estimate for each different mutation cannot be determined. Depending on the familial context, the risk of breast cancer associated with carrying a mutation has been estimated to range from 50% to 85%. The role of these genes in sporadic cancer remains unknown. Patients and physicians considering BRCA1 and BRCA2 genetic testing are faced with a difficult decision. The diversity of mutations and lack of general population data prevent accurate risk prediction. This is further complicated by the paucity of data on effective prevention strategies for those identified at higher risk. Thus, the nature of clinical testing for BRCA1 and BRCA2 continues to present challenges that reinforce the necessity of personal choice within the context of thorough genetic counseling.

Linkage analysis and comparative mapping of canine progressive rod-cone degeneration (prcd) establishes potential locus homology with retinitis pigmentosa (RP17) in humans

Progressive rod-cone degeneration (prcd) is the most widespread hereditary retinal disease leading to blindness in dogs and phenotypically is the canine counterpart of retinitis pigmentosa (RP) in humans. In previous efforts to identify the genetic locus for prcd, the canine homologs for many of the genes causally associated with RP in humans, such as RHO, PDE6B, and RDS/peripherin, have been excluded. In parallel with a recent undertaking to establish a framework map of the canine genome, multiple prcd-informative pedigrees have been typed with a panel of more than 100 anchor loci and microsatellite-based markers. Identification of a linkage group flanking prcd ([TK1, GALK1, prcd]-[MYL4, C09.173, C09.2263]-RARA-C09.250-C09.474-NF1) localizes prcd close to the centromeric end of canine chromosome 9 (CFA9), and excludes RARA as a candidate gene. The conserved synteny of this region of CFA9 and distal human chromosome 17q establishes the potential locus homology of prcd in the dog with RP17, a human retinitis pigmentosa locus for which no gene has yet been identified. Assignment of the prcd disease locus to an identified canine autosome represents a powerful application of the developing canine linkage map in medical genetics. The usefulness of this approach is further demonstrated by identification of the correspondence of the prcd interval to homologous human and mouse chromosomal regions. The rapid progress that is now occurring in the field of canine genetics will expedite the identification of the genes underlying many of the inherited traits and diseases that make the dog a unique asset for the study of mammalian traits.

BRCA1-positive patients are small for gestational age compared with their unaffected relatives

The BRCA1 gene is thought to exert its main function early in life. We, therefore, studied the effects of BRCA1 mutations on birth weight and birth length. This was carried out by comparing 33 women with and without mutations. Birth weight and length were obtained from a self-administered questionnaire. BRCA1 mutations carriers had a significantly lower birth weight (P = 0.0041) compared with non-carriers, after adjustment for gestational age. They were also significantly shorter at birth compared with their unaffected relatives (P = 0.0060), after adjustment for gestational age. The BRCA1 gene thus seems to influence the carriers in utero. The findings could imply that humans heterozygotic for the BRCA1 mutations may be influenced by the mutations during development in utero.