BARD1 and Breast Cancer: The Possibility of Creating Screening Tests and New Preventive and Therapeutic Pathways for Predisposed Women

Structural dynamics of clinically-reported VUS in the BARD1 ARD-BRCT region to predict the molecular basis of alterations

The functional domains of BARD1, comprise the Ankyrin Repeat Domain (ARD), C-Terminal domains (BRCTs), and a linker between ARD and the BRCTs, which are known to bind to Cleavage stimulation Factor complex-subunit of 50 kDa (CstF-50). The pathogenic mutation Q564H in the BARD1 ARD-linker-BRCT region has been reported to abrogate the binding between BARD1 and CstF-50. Intermediate penetrance variants of BARD1 are associated with the occurrence of breast cancer. Therefore, seven missense variants of unknown significance (VUS), L447V, P454L, N470S, V507M, I509T, C557S, and Q564H of BARD1, reported in the ARD domain and the linker region were evaluated via molecular dynamics (MD) simulations. The mutants revealed statistically significantly different distributions of RMSD (root mean square deviation), residuewise RMSF (root mean square fluctuation), Rg (radius of gyration), SASA (solvent accessible surface area), and COM (centre of mass)-to-COM distance between the ARD and the BRCT repeat, between the wild type and each mutant. The secondary structural composition of the mutants was slightly altered relative to that of the wild type. However, the reported in-silico based prediction require further validation using in-vitro, biophysical and structure-based approachCommunicated by Ramaswamy H. Sarma.

Zooming into the structure-function of RING finger proteins for anti-cancer therapeutic applications

Cancer is one of the most common and widely diagnosed diseases worldwide. With an increase in prevalence and incidence, many studies in cancer biology have been looking at the role pro-cancer proteins play. One of these proteins is the Really Interesting New Gene (RING), which has been studied extensively due to its structure and functions such as apoptosis, neddylation, and its role in ubiquitination. The RING domain is a cysteine-rich domain known to bind Cysteine and Histidine residues. It also binds two zinc ions that help stabilize the protein in various patterns, often with a 'cross-brace' topology. Different RING finger proteins have been studied and found to have suitable targets for developing anti-cancer therapeutics. These identified candidate proteins include Parkin, COP1, MDM2, BARD1, BRCA-1, PIRH2, c-CBL, SIAH1, RBX1 and RNF8. Inhibiting these candidate proteins provides opportunities for shutting down pathways associated with tumour development and metastasis.

Polygenic risk scores and breast cancer risk prediction

Polygenic Risk Scores (PRS) are a major component of accurate breast cancer risk prediction and have the potential to improve screening and prevention strategies. PRS combine the risk from Single nucleotide polymorphisms (SNPs) associated with breast cancer in Genome Wide Association Studies (GWAS) and explain over 30% of breast cancer heritability. When incorporated into risk models, the more personalised risk assessment derived from PRS, help identify women at higher risk of breast cancer development and enables the implementation of stratified screening and prevention approaches. This review describes the role of PRS in breast cancer risk prediction including the development of PRS and their clinical application. We have also examined the role of PRS within more well-established risk prediction models which incorporate known classic risk factors and discuss the interaction of PRS with these factors and their capacity to predict breast cancer subtypes. Before PRS can be implemented on a population-wide scale, there are several challenges that must be addressed. Perhaps the most pressing of these is the use of PRS in women of non-White European origin, where PRS have been shown to have attenuated risk prediction both in discrimination and calibration. We discuss progress in developing and applying PRS in non-white European populations. PRS represent a significant advance in breast cancer risk prediction and their further development will undoubtedly enhance personalisation.

BARD1 mystery: tumor suppressors are cancer susceptibility genes

The full-length BRCA1-associated RING domain 1 (BARD1) gene encodes a 777-aa protein. BARD1 displays a dual role in cancer development and progression as it acts as a tumor suppressor and an oncogene. Structurally, BARD1 has homologous domains to BRCA1 that aid their heterodimer interaction to inhibit the progression of different cancers such as breast and ovarian cancers following the BRCA1-dependant pathway. In addition, BARD1 was shown to be involved in other pathways that are involved in tumor suppression (BRCA1-independent pathway) such as the TP53-dependent apoptotic signaling pathway. However, there are abundant BARD1 isoforms exist that are different from the full-length BARD1 due to nonsense and frameshift mutations, or deletions were found to be associated with susceptibility to various cancers including neuroblastoma, lung, breast, and cervical cancers. This article reviews the spectrum of BARD1 full-length genes and its different isoforms and their anticipated associated risk. Additionally, the study also highlights the role of BARD1 as an oncogene in breast cancer patients and its potential uses as a prognostic/diagnostic biomarker and as a therapeutic target for cancer susceptibility testing and treatment.

Effective targeting of breast cancer stem cells by combined inhibition of Sam68 and Rad51

Breast cancer (BC) is the second cause of cancer-related deceases in the worldwide female population. Despite the successful treatment advances, 25% of BC develops resistance to current therapeutic regimens, thereby remaining a major hurdle for patient management. Current therapies, targeting the molecular events underpinning the adaptive resistance, still require effort to improve BC treatment. Using BC sphere cells (BCSphCs) as a model, here we showed that BC stem-like cells express high levels of Myc, which requires the presence of the multifunctional DNA/RNA binding protein Sam68 for the DNA-damage repair. Analysis of a cohort of BC patients displayed that Sam68 is an independent negative factor correlated with the progression of the disease. Genetic inhibition of Sam68 caused a defect in PARP-induced PAR chain synthesis upon DNA-damaging insults, resulting in cell death of TNBC cells. In contrast, BC stem-like cells were able to survive due to an upregulation of Rad51. Importantly, the inhibition of Rad51 showed synthetic lethal effect with the silencing of Sam68, hampering the cell viability of patient-derived BCSphCs and stabilizing the growth of tumor xenografts, including those TNBC carrying BRCA mutation. Moreover, the analysis of Myc, Sam68 and Rad51 expression demarcated a signature of a poor outcome in a large cohort of BC patients. Thus, our findings suggest the importance of targeting Sam68-PARP1 axis and Rad51 as potential therapeutic candidates to counteract the expansion of BC cells with an aggressive phenotype.

Mutations in exon region of BRCA1-related RING domain 1 gene and risk of breast cancer

Background

BRCA1‐associated RING Domain 1 (BARD1) is an important gene related to breast cancer development. However, the role of BARD1 mutations in breast cancer remains inconclusive. This study is to investigate the relationship between exon mutations of BARD1 gene and the risk of early‐onset breast cancer.

Methods

Totally, 60 cases of early‐onset breast cancer patients (age 30–40 years) and 240 healthy women (age 30–40 years) were enrolled. Exon mutations of BARD1 were detected and analyzed by direct sequencing and SNaPshot.

Results

The risk of breast cancer was increased by 3.475 times in carriers with deletion mutation at rs28997575 site of BARD1 (aOR₁ = 3.475, 95%CI = 1.302–9.276) (p = 0.013). The risk of breast cancer in carriers with GC genotype at rs2229571 site of BARD1 was reduced by 72.6% (aOR₁ = 0.274, 95%CI = 0.134–0.562) (p = 0.001), and that in carriers with CC genotype was reduced by 82.8% (aOR₁ = 0.172, 95%CI = 0.076–0.392) (p = 0.001). After stratification with family history, the difference of rs2229571 site mutation genotype was statistically significant (OR = −2.169, 95%CI = 0.016–0.828, p = 0.032). Additionally, the frequency distribution of breast cancer family history in the case group (15%) was significantly more than that in the control group (6.7%) (p = 0.037).

Conclusion

The deletion mutation at rs28997575 locus of the BARD1 gene can significantly increase the risk of breast cancer. The mutation genotype of rs2229571 locus can significantly reduce the risk of breast cancer. Family history is associated with BARD1 gene polymorphism. A family history of breast cancer may be a risk factor for breast cancer.

The fellowship of the RING: BRCA1, its partner BARD1 and their liaison in DNA repair and cancer

The breast cancer type 1 susceptibility protein (BRCA1) and its partner - the BRCA1-associated RING domain protein 1 (BARD1) - are key players in a plethora of fundamental biological functions including, among others, DNA repair, replication fork protection, cell cycle progression, telomere maintenance, chromatin remodeling, apoptosis and tumor suppression. However, mutations in their encoding genes transform them into dangerous threats, and substantially increase the risk of developing cancer and other malignancies during the lifetime of the affected individuals. Understanding how BRCA1 and BARD1 perform their biological activities therefore not only provides a powerful mean to prevent such fatal occurrences but can also pave the way to the development of new targeted therapeutics. Thus, through this review work we aim at presenting the major efforts focused on the functional characterization and structural insights of BRCA1 and BARD1, per se and in combination with all their principal mediators and regulators, and on the multifaceted roles these proteins play in the maintenance of human genome integrity.

Identification of a novel pathogenic variant in PALB2 and BARD1 genes by a multigene sequencing panel in triple negative breast cancer in Morocco

Pathogenic variants (PVs) in BRCA genes have been mainly associated with an increasing risk of triple negative breast cancer (TNBC). The contribution of PVs in non-BRCA genes to TNBC seems likely since the processing of homologous recombination repair of double-strand DNA breaks involves several genes. Here, we investigate the susceptibility of genetic variation of the BRCA and non-BRCA genes in 30 early-onset Moroccan women with TNBC. Methods: Targeted capture-based next generation sequencing (NGS) method was performed with a multigene panel testing (MGPT) for variant screening. Panel sequencing was performed with genes involved in hereditary predisposition to cancer and candidate genes whose involvement remains unclear using Illumina MiSeq platform. Interpretation was conducted by following the American College of Medical Genetics and Genomics-Association for Molecular Pathology (ACMG-AMP) criteria. Results: PVs were identified in 20% (6/30) of patients with TNBC. Of these, 16.7% (5/30) carried a BRCA PV [10% (3/30) in BRCA1, 6.7% (2/30) in BRCA2] and 6.6% (2/30) carried a non-BRCA PV. The identified PVs in BRCA genes (BRCA1 c.798_799delTT, BRCA1 c.3279delC, BRCA2 c.1310_1313del, and BRCA2 c.1658T>G) have been reported before and were classified as pathogenic. The identified founder PVs BRCA1 c.798_799del and BRCA2 c.1310_1313delAAGA represented 10% (3/30). Our MGPT allowed identification of several sequence variations in most investigated genes, among which we found novel truncating variations in PALB2 and BARD1 genes. The PALB2 c.3290dup and BARD1 c.1333G>T variants are classified as pathogenic. We also identified 42 variants of unknown/uncertain significance (VUS) in 70% (21/30) of patients with TNBC, including 50% (21/42) missense variants. The highest VUS rate was observed in ATM (13%, 4/30). Additionally, 35.7% (15/42) variants initially well-known as benign, likely benign or conflicting interpretations of pathogenicity have been reclassified as VUS according to ACMG-AMP. Conclusions: PALB2 and BARD1 along with BRCA genetic screening could be helpful for a larger proportion of early-onset TNBC in Morocco.

Understanding the Clinical Implications of Low Penetrant Genes and Breast Cancer Risk

OPINION STATEMENT

Since the 2013 Supreme Court declaration, panel testing for hereditary cancer syndromes has evolved into the gold standard for oncology germline genetic testing. With the advent of next-generation sequencing, competitive pricing, and developing therapeutic options, panel testing is now well integrated into breast cancer management and surveillance. Although many established syndromes have well-defined cancer risks and management strategies, several breast cancer genes are currently classified as limited-evidence genes by the National Comprehensive Cancer Network (NCCN). Follow-up for individuals with mutations in these genes is a point of contention due to conflicting information in the literature. The most recent NCCN guidelines have stratified management based on gene-specific cancer risks indicating that expanding data will allow for better recommendations as research progresses. The evolving management for these genes emphasizes the clinicians' need for evidence-based understanding of low penetrance breast cancer genes and their implications for patient care. This article reviews current literature for limited evidence genes, detailing cancer risks, association with triple-negative breast cancer, and recommendations for surveillance. A brief review of the challenges and future directions is outlined to discuss the evolving nature of cancer genetics and the exciting opportunities that can impact management.

Breast Cancer Predisposition Genes and Synthetic Lethality

BRCA1 and BRCA2 are tumor suppressor genes with pivotal roles in the development of breast and ovarian cancers. These genes are essential for DNA double-strand break repair via homologous recombination (HR), which is a virtually error-free DNA repair mechanism. Following BRCA1 or BRCA2 mutations, HR is compromised, forcing cells to adopt alternative error-prone repair pathways that often result in tumorigenesis. Synthetic lethality refers to cell death caused by simultaneous perturbations of two genes while change of any one of them alone is nonlethal. Therefore, synthetic lethality can be instrumental in identifying new therapeutic targets for BRCA1/2 mutations. PARP is an established synthetic lethal partner of the BRCA genes. Its role is imperative in the single-strand break DNA repair system. Recently, Olaparib (a PARP inhibitor) was approved for treatment of BRCA1/2 breast and ovarian cancer as the first successful synthetic lethality-based therapy, showing considerable success in the development of effective targeted cancer therapeutics. Nevertheless, the possibility of drug resistance to targeted cancer therapy based on synthetic lethality necessitates the development of additional therapeutic options. This literature review addresses cancer predisposition genes, including BRCA1, BRCA2, and PALB2, synthetic lethality in the context of DNA repair machinery, as well as available treatment options.