The role of BRCA1 in transcriptional regulation and cell cycle control

EGFR and Hippo signaling pathways are involved in organophosphate esters-induced proliferation and migration of triple-negative breast cancer cells

The widespread application of organophosphate flame retardants has led to pervasive exposure to organophosphate esters (OPEs), prompting considerable concerns regarding their potential health risk to humans. Despite hints from previous research about OPEs' association with breast cancer, their specific effects and underlying mechanisms of triple-negative breast cancer (TNBC) remain unclear. In this study, we investigated the effects of four representative OPEs on cell proliferation, cell cycle regulation, migration, and the expression of genes and proteins associated with the epidermal growth factor receptor (EGFR) and Hippo signaling pathways in TNBC (MDA-MB-231) cells. Our findings revealed that treatment with 1-25 μM triphenyl phosphate (TPHP) and tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) induced TNBC cell proliferation and accelerated cell cycle progression, with upregulation in MYC, CCND1, and BRCA1 mRNA. Moreover, exposure to 1-25 μM TPHP, 10-25 μM TDCIPP, and 1-10 μM tris (2-chloroethyl) phosphate (TCEP) induced MMP2/9 mRNA expression and enhanced migratory capacity, except for 2-ethylhexyl diphenyl phosphate (EHDPP). Mechanistically, four OPEs treatments activated the EGFR-ERK1/2 and EGFR-PI3K/AKT signaling pathways by increasing the transcript of EGFR, ERK1/2, PI3K, and AKT mRNA. OPEs treatment also suppressed the Hippo signaling pathway by inhibiting the expression of MST1 mRNA and phosphorylation of LATS1, leading to the overactivation of YAP1 protein, thereby promoting TNBC cell proliferation and migration. In summary, our study elucidated that activation of the EGFR signaling pathway and suppression of the Hippo signaling pathway contributed to the proliferation, cell cycle dysregulation, and migration of TNBC cells following exposure to OPEs.

Cellular mechanisms mediating the anti-cancer effects of carnosol on gingiva carcinoma

Carnosol, a rosemary polyphenol, displays anticancer properties and is suggested as a safer alternative to conventional surgery, radiotherapy, and chemotherapy. Given that its effects on gingiva carcinoma have not yet been investigated, the aim of this study was to explore its anti-tumor selectivity and to unravel its underlying mechanisms of action. Hence, oral tongue and gingiva carcinoma cell lines exposed to carnosol were analyzed to estimate cytotoxicity, cell viability, cell proliferation, and colony formation potential as compared with those of normal cells. Key cell cycle and apoptotic markers were also measured. Finally, cell migration, oxidative stress, and crucial cell signaling pathways were assessed. Selective anti-gingiva carcinoma activity was disclosed. Overall, carnosol mediated colony formation and proliferation suppression in addition to cytotoxicity induction. Cell cycle arrest was highlighted by the disruption of the c-myc oncogene/p53 tumor suppressor balance. Carnosol also increased apoptosis, oxidative stress, and antioxidant activity. On a larger scale, the alteration of cell cycle and apoptotic profiles was also demonstrated by QPCR array. This was most likely achieved by controlling the STAT5, ERK1/2, p38, and NF-ĸB signaling pathways. Lastly, carnosol reduced inflammation and invasion ability by modulating IL-6 and MMP9/TIMP-1 axes. This study establishes a robust foundation, urging extensive inquiry both in vivo and in clinical settings, to substantiate the efficacy of carnosol in managing gingiva carcinoma.

The deubiquitinating enzyme USP4 regulates BRCA1 stability and function

BRCA1 plays a suppressive role in breast tumorigenesis. Ubiquitin-dependent degradation is a common mechanism that regulates BRCA1 protein stability, and several ubiquitin ligases involved have been identified. However, the deubiquitinating enzyme for BRCA1 remains less defined. Here, we report that the deubiquitinase USP4 interacts with, deubiquitinates and stabilizes BRCA1, maintaining the protein level of BRCA1. USP4 knockdown results in a decreased BRCA1 protein level, impairment in homologous recombination mediated double-stranded break repair, and increased genome instability, and confers resistance to DNA damage-inducing agents and PARP inhibitors. Ectopic expression of USP4 stabilizes BRCA1 and reverse the effects caused by USP4 knockdown. Moreover, USP4 is low expressed in human breast cancer tissues and its low expression correlates with poorer survival of patients. Furthermore, we identified several loss-of-function mutations of USP4 in human gynecological cancers, the catalytic activity of which or their interaction with BRCA1 is disrupted. Together, we reveal that USP4 is a deubiquitinase for BRCA1. USP4 positively regulates the stability and function of BRCA1 through de-ubiquitination, and plays important role in the suppression of breast cancer.

Lau AT, Xu YM. The regulation of microRNAs on chemoresistance in triple-negative breast cancer: a recent update

Triple-negative breast cancer (TNBC) has negative expressions of ER, PR and HER2. Due to the insensitivity to both endocrine therapy and HER2-targeted therapy, the main treatment method for TNBC is cytotoxic chemotherapy. However, the curative effect of chemotherapy is limited because of the existence of acquired or intrinsic multidrug resistance. MicroRNAs (miRNAs) are frequently dysregulated in malignant tumors and involved in tumor occurrence and progression. Interestingly, growing studies show that miRNAs are involved in chemoresistance in TNBC. Thus, targeting dysregulated miRNAs could be a plausible way for better treatment of TNBC. Here, we present the updated knowledge of miRNAs associated with chemoresistance in TNBC, which may be helpful for the early diagnosis, prognosis and treatment of this life-threatening disease.

Structural implications of amyloidogenic rare variants Ser282Leu and Gln356Arg identified in h-BRCA1

Preliminary studies have shown BRCA1 (170-1600) residues to be intrinsically disordered with unknown structural details. However, thousands of clinically reported variants have been identified in this central region of BRCA1. Therefore, we aimed to characterize h-BRCA1(260-553) to assess the structural basis for pathogenicity of two rare missense variants Ser282Leu, Gln356Arg identified from the Indian and Russian populations respectively. Small-angle X-ray scattering analysis revealed WT scores Rg -32 Å, Dmax -93 Å, and Rflex-51% which are partially disordered, whereas Ser282Leu variant displayed a higher degree of disorderedness and Gln356Arg was observed to be aggregated. WT protein also possesses an inherent propensity to undergo a disorder-to-order transition in the presence of cruciform DNA and 2,2,2-Trifluoroethanol (TFE). An increased alpha-helical pattern was observed with increasing concentration of TFE for the Gln356Arg mutant whereas Ser282Leu mutant showed significant differences only at the highest TFE concentration. Furthermore, higher thermal shift was observed for WT-DNA complex compared to the Gln356Arg and Ser282Leu protein-DNA complex. Moreover, mature amyloid-like fibrils were observed with 30 μM thioflavin T (ThT) at 37°C for Ser282Leu and Gln356Arg proteins while the WT protein exists in a protofibril state as observed by TEM. Gln356Arg formed higher-order aggregates with amyloidogenesis over time as monitored by ThT fluorescence. In addition, computational analyses confirmed larger conformational fluctuations for Ser282Leu and Gln356Arg mutants than for the WT. The global structural alterations caused by these variants provide a mechanistic approach for further classification of the variants of uncertain clinical significance in BRCA1 into amyloidogenic variants which may have a significant role in disease pathogenesis.

BRCA1 deficiency enhances the aggressiveness of breast cancer cells expressing HPV16 oncoproteins

BACKGROUND INFORMATION

The precise etiology of breast cancer is not completely understood, although women with BRCA1 gene mutations have a significantly increased risk of developing the disease. In addition, sporadic breast cancer is frequently associated with decreased BRCA1 gene expression. Growing evidence of Human papillomaviruses (HPVs) infections in breast tumors has raised the possibility of the involvement of HPVs in the pathogenesis of breast cancer. We investigated whether the effects of HPV oncoproteins E6 and E7 were influenced by the expression levels of BRCA1. HPV16E6E7 (prototype or E6D25E/E7N29S Asian variant type) were stably expressed in MDA-MB231 breast cancer cells, wild type for BRCA1, or with BRCA1 knocked down.

RESULTS

Expression of HPV16E6E7 oncogenes did not affect BRCA1 levels and the abundance of HPV16E6E7 was not altered by BRCA1 knockdown. BRCA1 levels did not alter HPV16E6E7-dependent degradation of G1-S cell cycle proteins p53 and pRb. However, we found that the expression of G2-M cell cycle protein cyclin B1 enhanced by HPV16E6E7 was impacted by BRCA1 levels. Especially, we found the correlation between BRCA1 and cyclin B1 expression and this was also confirmed in breast cancer samples from a Thai cohort. We further demonstrated that the combination of HPV oncoproteins and low levels of BRCA1 protein appears to enhance proliferation and invasion. Transactivation activities of HPV16E6E7 on genes regulating cell proliferation and invasion (TGF-β and vimentin) were significantly increased in BRCA1-deficient cells.

CONCLUSIONS

Our results indicate that a deficiency of BRCA1 promotes the transactivation activity of HPV16E6E7 leading to increase of cell proliferation and invasion.

SIGNIFICANCE

HPV infection appears to have the potential to enhance the aggressiveness of breast cancers, especially those deficient in BRCA1.

Variant of uncertain significance Arg866Cys enhances disorderedness of h-BRCA1 (759-1064) region

High structural flexibility has been reported in the central region of BRCA1, which hinders the structural and functional evaluations of mutations identified in the domain. Additionally, the need to categorize variants of unknown significance (VUS) has increased due to the growth in the number of variants reported in clinical settings. Therefore, unraveling the disease-causing mechanism of VUS identified in different functional domains of BRCA1 is still challenging. The current study uses a multidisciplinary approach to assess the structural impact of BRCA1 Arg866Cys mutation discovered in the central domain of BRCA1. The structural alterations have been characterized using Circular-Dichroism spectroscopy, nano-DSF, and molecular-dynamics simulations. BRCA1 Arg866Cys mutant demonstrated more flexibility and lesser affinity to DNA than the wild-type protein. The BRCA1(759-1064) wild-type protein was shown to be a βII-rich protein with an induced D-O transition in the presence of DNA and 2,2,2-Trifluoroethanol (TFE). The protein's alpha-helical composition did not significantly change in the presence of TFE, besides an increase in β-turns and loops. Under Transmission Electron Microscopes (TEM), amyloid-like fibrils structure was detected for Arg866Cys mutant whereas the wild-type protein showed amorphous aggregates. An increased ThT fluorescence indicated β-rich composition and aggregation-prone behaviour for BRCA1 wild-type protein, while the fluorescence intensity was significantly quenched in the Arg866Cys mutant. Furthermore, increased conformational flexibility in the Arg866Cys variant was observed by principal component analysis. This work aims to comprehend the inherently disordered region of BRCA1 as well as the impact of missense mutations on folding patterns and binding to DNA for functional aspects.

BRCA1 and ELK-1 regulate neural progenitor cell fate in the optic tectum in response to visual experience in Xenopus laevis tadpoles

In developing Xenopus tadpoles, the optic tectum begins to receive patterned visual input while visuomotor circuits are still undergoing neurogenesis and circuit assembly. This visual input regulates neural progenitor cell fate decisions such that maintaining tadpoles in the dark increases proliferation, expanding the progenitor pool, while visual stimulation promotes neuronal differentiation. To identify regulators of activity-dependent neural progenitor cell fate, we profiled the transcriptomes of proliferating neural progenitor cells and newly differentiated neurons using RNA-Seq. We used advanced bioinformatic analysis of 1,130 differentially expressed transcripts to identify six differentially regulated transcriptional regulators, including Breast Cancer 1 (BRCA1) and the ETS-family transcription factor, ELK-1, which are predicted to regulate the majority of the other differentially expressed transcripts. BRCA1 is known for its role in cancers, but relatively little is known about its potential role in regulating neural progenitor cell fate. ELK-1 is a multifunctional transcription factor which regulates immediate early gene expression. We investigated the potential functions of BRCA1 and ELK-1 in activity-regulated neurogenesis in the tadpole visual system using in vivo time-lapse imaging to monitor the fate of GFP-expressing SOX2+ neural progenitor cells in the optic tectum. Our longitudinal in vivo imaging analysis showed that knockdown of either BRCA1 or ELK-1 altered the fates of neural progenitor cells and furthermore that the effects of visual experience on neurogenesis depend on BRCA1 and ELK-1 expression. These studies provide insight into the potential mechanisms by which neural activity affects neural progenitor cell fate.

Understanding the mechanistic pathways and clinical aspects associated with protein and gene based biomarkers in breast cancer

Cancer is one of the most widespread and severe diseases with a huge mortality rate. In recent years, the second-leading mortality rate of any cancer globally has been breast cancer, which is one of the most common and deadly cancers found in women. Detecting breast cancer in its initial stages simplifies treatment, decreases death risk, and recovers survival rates for patients. The death rate for breast cancer has risen to 0.024 % in some regions. Sensitive and accurate technologies are required for the preclinical detection of BC at an initial stage. Biomarkers play a very crucial role in the early identification as well as diagnosis of women with breast cancer. Currently, a wide variety of cancer biomarkers have been discovered for the diagnosis of cancer. For the identification of these biomarkers from serum or other body fluids at physiological amounts, many detection methods have been developed. In the case of breast cancer, biomarkers are especially helpful in discovering those who are more likely to develop the disease, determining prognosis at the time of initial diagnosis and choosing the best systemic therapy. In this study we have compiled various clinical aspects and signaling pathways associated with protein-based biomarkers and gene-based biomarkers.

Functional evaluation of BRCA1/2 variants of unknown significance with homologous recombination assay and integrative in silico prediction model

Numerous variants of unknown significance (VUSs) exist in hereditary breast and ovarian cancers. Although multiple methods have been developed to assess the significance of BRCA1/2 variants, functional discrepancies among these approaches remain. Therefore, a comprehensive functional evaluation system for these variants should be established. We performed conventional homologous recombination (HR) assays for 50 BRCA1 and 108 BRCA2 VUSs and complementarily predicted VUSs using a statistical logistic regression prediction model that integrated six in silico functional prediction tools. BRCA1/2 VUSs were classified according to the results of the integrative in vitro and in silico analyses. Using HR assays, we identified 10 BRCA1 and 4 BRCA2 VUSs as low-functional pathogenic variants. For in silico prediction, the statistical prediction model showed high accuracy for both BRCA1 and BRCA2 compared with each in silico prediction tool individually and predicted nine BRCA1 and seven BRCA2 variants to be pathogenic. Integrative functional evaluation in this study and the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) guidelines strongly suggested that seven BRCA1 variants (p.Glu272Gly, p.Lys1095Glu, p.Val1653Leu, p.Thr1681Pro, p.Phe1761Val, p.Thr1773Ile, and p.Gly1803Ser) and four BRCA2 variants (p.Trp31Gly, p.Ser2616Phe, p.Tyr2660Cys, and p.Leu2792Arg) were pathogenic. This study demonstrates that integrative evaluation using conventional HR assays and optimized in silico prediction comprehensively classified the significance of BRCA VUSs for future clinical applications.

BRCA1/BARD1 intrinsically disordered regions facilitate chromatin recruitment and ubiquitylation

BRCA1/BARD1 is a tumor suppressor E3 ubiquitin (Ub) ligase with roles in DNA damage repair and in transcriptional regulation. BRCA1/BARD1 RING domains interact with nucleosomes to facilitate mono-ubiquitylation of distinct residues on the C-terminal tail of histone H2A. These enzymatic domains constitute a small fraction of the heterodimer, raising the possibility of functional chromatin interactions involving other regions such as the BARD1 C-terminal domains that bind nucleosomes containing the DNA damage signal H2A K15-Ub and H4 K20me0, or portions of the expansive intrinsically disordered regions found in both subunits. Herein, we reveal novel interactions that support robust H2A ubiquitylation activity mediated through a high-affinity, intrinsically disordered DNA-binding region of BARD1. These interactions support BRCA1/BARD1 recruitment to chromatin and sites of DNA damage in cells and contribute to their survival. We also reveal distinct BRCA1/BARD1 complexes that depend on the presence of H2A K15-Ub, including a complex where a single BARD1 subunit spans adjacent nucleosome units. Our findings identify an extensive network of multivalent BARD1-nucleosome interactions that serve as a platform for BRCA1/BARD1-associated functions on chromatin.

Mutational Signatures in Gastric Cancer and Their Clinical Implications

Gastric cancer is characterised by high inter- and intratumour heterogeneity. The majority of patients are older than 65 years and the global burden of this disease is increasing due to the aging of the population. The disease is usually diagnosed at advanced stages, which is a consequence of nonspecific symptoms. Few improvements have been made at the level of noninvasive molecular diagnosis of sporadic gastric cancer, and therefore the mortality rate remains high. A new field of mutational signatures has emerged in the past decade with advances in the genome sequencing technology. These distinct mutational patterns in the genome, caused by exogenous and endogenous mutational processes, can be associated with tumour aetiology and disease progression, and could provide novel perception on the treatment possibilities. This review assesses the mutational signatures found in gastric cancer and summarises their potential for use in clinical setting as diagnostic or prognostic biomarkers. Associated treatment options and biomarkers already implemented in clinical use are discussed, together with those that are still being explored or are in clinical studies.

Adrenaline blocks key cell cycle genes and exhibits antifibrotic and vasoconstrictor effects in glaucoma surgery

Adrenaline is a sympathomimetic drug used to maintain pupil dilation and to decrease the risk of bleeding. The aim of this study was to demonstrate if adrenaline could exert antifibrotic effects in glaucoma surgery. Adrenaline was tested in fibroblast-populated collagen contraction assays and there was a dose-response decrease in fibroblast contractility: matrices decreased to 47.4% (P = 0.0002) and 86.6% (P = 0.0036) with adrenaline 0.0005% and 0.01%, respectively. There was no significant decrease in cell viability even at high concentrations. Human Tenon's fibroblasts were also treated with adrenaline (0%, 0.0005%, 0.01%) for 24 h and RNA-Sequencing was performed on the Illumina NextSeq 2000. We carried out detailed gene ontology, pathway, disease and drug enrichment analyses. Adrenaline 0.01% upregulated 26 G1/S and 11 S-phase genes, and downregulated 23 G2 and 17 M-phase genes (P < 0.05). Adrenaline demonstrated similar pathway enrichment to mitosis and spindle checkpoint regulation. Adrenaline 0.05% was also injected subconjunctivally during trabeculectomy, PreserFlo Microshunt and Baerveldt 350 tube surgeries, and patients did not experience any adverse effects. Adrenaline is a safe and cheap antifibrotic drug that significantly blocks key cell cycle genes when used at high concentrations. Unless contraindicated, we recommend subconjunctival injections of adrenaline (0.05%) in all glaucoma bleb-forming surgeries.

SMARCB1 regulates a TFCP2L1-MYC transcriptional switch promoting renal medullary carcinoma transformation and ferroptosis resistance

Renal medullary carcinoma (RMC) is an aggressive tumour driven by bi-allelic loss of SMARCB1 and tightly associated with sickle cell trait. However, the cell-of-origin and oncogenic mechanism remain poorly understood. Using single-cell sequencing of human RMC, we defined transformation of thick ascending limb (TAL) cells into an epithelial-mesenchymal gradient of RMC cells associated with loss of renal epithelial transcription factors TFCP2L1, HOXB9 and MITF and gain of MYC and NFE2L2-associated oncogenic and ferroptosis resistance programs. We describe the molecular basis for this transcriptional switch that is reversed by SMARCB1 re-expression repressing the oncogenic and ferroptosis resistance programs leading to ferroptotic cell death. Ferroptosis resistance links TAL cell survival with the high extracellular medullar iron concentrations associated with sickle cell trait, an environment propitious to the mutagenic events associated with RMC development. This unique environment may explain why RMC is the only SMARCB1-deficient tumour arising from epithelial cells, differentiating RMC from rhabdoid tumours arising from neural crest cells.

Regulation of DNA damage response by trimeric G-proteins

Upon sensing DNA double-strand breaks (DSBs), eukaryotic cells either die or repair DSBs via one of the two competing pathways, i.e., non-homologous end-joining (NHEJ) or homologous recombination (HR). We show that cell fate after DSBs hinges on GIV/Girdin, a guanine nucleotide-exchange modulator of heterotrimeric Giα•βγ protein. GIV suppresses HR by binding and sequestering BRCA1, a key coordinator of multiple steps within the HR pathway, away from DSBs; it does so using a C-terminal motif that binds BRCA1's BRCT-modules via both phospho-dependent and -independent mechanisms. Using another non-overlapping C-terminal motif GIV binds and activates Gi and enhances the "free" Gβγ→PI-3-kinase→Akt pathway, which promotes survival and is known to suppress HR, favor NHEJ. Absence of GIV, or loss of either of its C-terminal motifs enhanced cell death upon genotoxic stress. Because GIV selectively binds other BRCT-containing proteins suggests that G-proteins may fine-tune sensing, repair, and survival after diverse types of DNA damage.

Redox-dependent Igfbp2 signaling controls Brca1 DNA damage response to govern neural stem cell fate

Neural stem cell (NSC) maintenance and functions are regulated by reactive oxygen species (ROS). However, the mechanisms by which ROS control NSC behavior remain unclear. Here we report that ROS-dependent Igfbp2 signaling controls DNA repair pathways which balance NSC self-renewal and lineage commitment. Ncf1 or Igfbp2 deficiency constrains NSCs to a self-renewing state and prevents neurosphere formation. Ncf1-dependent oxidation of Igfbp2 promotes neurogenesis by NSCs in vitro and in vivo while repressing Brca1 DNA damage response genes and inducing DNA double-strand breaks (DDSBs). By contrast, Ncf1^-/- and Igfbp2^-/- NSCs favor the formation of oligodendrocytes in vitro and in vivo. Notably, transient repression of Brca1 DNA repair pathway genes induces DDSBs and is sufficient to rescue the ability of Ncf1^-/- and Igfbp2^-/- NSCs to lineage-commit to form neurospheres and neurons. NSC lineage commitment is dependent on the oxidizable cysteine-43 residue of Igfbp2. Our study highlights the role of DNA damage/repair in orchestrating NSC fate decisions downstream of redox-regulated Igfbp2.

Experimental analysis of bladder cancer-associated mutations in EP300 identifies EP300-R1627W as a driver mutation

BACKGROUND

Bladder cancer (BCa) is the most common malignant tumor of the urinary system, with transitional cell carcinoma (TCC) being the predominant type. EP300 encodes a lysine acetyltransferase that regulates a large subset of genes by acetylating histones and non-histone proteins. We previously identified several bladder cancer-associated mutations in EP300 using high-throughput sequencing; however, the functional consequences of these mutations remain unclear.

METHODS

Bladder cancer cells T24 and TCC-SUP were infected with shEP300 lentiviruses to generate stable EP300 knockdown cell lines. The expression levels of EP300, p16 and p21 were detected by real-time PCR and western blots. The transcriptional activity of p16 and p21 were detected by dual luciferase assay. Cell proliferation assay, flow cytometric analyses of cell cycle, invasion assay and xenograft tumor model were used to measure the effect of EP300-R1627W mutation in bladder cancer. Immunoprecipitation was used to explore the relationship between EP300-R1627W mutation and p53. Structural analysis was used to detect the structure of EP300-R1627W protein compared to EP300-wt protein.

RESULTS

we screened the mutations of EP300 and found that the EP300-R1627W mutation significantly impairs EP300 transactivation activity. Notably, we demonstrated that the R1627W mutation impairs EP300 acetyltransferase activity, potentially by interfering with substrate binding. Finally, we show that EP300-R1627W is more aggressive in growth and invasion in vitro and in vivo compared to cells expressing EP300-wt. We also found that the EP300-R1627W mutation occurs frequently in seven different types of cancers.

CONCLUSION

In summary, our work defines a driver role of EP300-R1627W in bladder cancer development and progression.

Differential requirement for BRCA1-BARD1 E3 ubiquitin ligase activity in DNA damage repair and meiosis in the Caenorhabditis elegans germ line

The tumor suppressor BRCA1-BARD1 complex regulates many cellular processes; of critical importance to its tumor suppressor function is its role in genome integrity. Although RING E3 ubiquitin ligase activity is the only known enzymatic activity of the complex, the in vivo requirement for BRCA1-BARD1 E3 ubiquitin ligase activity has been controversial. Here we probe the role of BRCA1-BARD1 E3 ubiquitin ligase activity in vivo using C. elegans. Genetic, cell biological, and biochemical analyses of mutants defective for E3 ligase activity suggest there is both E3 ligase-dependent and independent functions of the complex in the context of DNA damage repair and meiosis. We show that E3 ligase activity is important for nuclear accumulation of the complex and specifically to concentrate at meiotic recombination sites but not at DNA damage sites in proliferating germ cells. While BRCA1 alone is capable of monoubiquitylation, BARD1 is required with BRCA1 to promote polyubiquitylation. We find that the requirement for E3 ligase activity and BARD1 in DNA damage signaling and repair can be partially alleviated by driving the nuclear accumulation and self-association of BRCA1. Our data suggest that in addition to E3 ligase activity, BRCA1 may serve a structural role for DNA damage signaling and repair while BARD1 plays an accessory role to enhance BRCA1 function.

CtIP-dependent nascent RNA expression flanking DNA breaks guides the choice of DNA repair pathway

The RNA world is changing our views about sensing and resolution of DNA damage. Here, we develop single-molecule DNA/RNA analysis approaches to visualize how nascent RNA facilitates the repair of DNA double-strand breaks (DSBs). RNA polymerase II (RNAPII) is crucial for DSB resolution in human cells. DSB-flanking, RNAPII-generated nascent RNA forms RNA:DNA hybrids, guiding the upstream DNA repair steps towards favouring the error-free Homologous Recombination (HR) pathway over Non-Homologous End Joining. Specific RNAPII inhibitor, THZ1, impairs recruitment of essential HR proteins to DSBs, implicating nascent RNA in DNA end resection, initiation and execution of HR repair. We further propose that resection factor CtIP interacts with and helps re-activate RNAPII when paused by the RNA:DNA hybrids, collectively promoting faithful repair of chromosome breaks to maintain genomic integrity.

RNA has been implicated in DNA repair. This work shows that the interplay of RNAPII-generated nascent RNA, RNA:DNA hybrids and the resection factor CtIP guide DNA double strand break repair pathway choice towards error-free homologous recombination.

Insights into functional connectivity in mammalian signal transduction pathways by pairwise comparison of protein interaction partners of critical signaling hubs

Growth factors and cytokines activate signal transduction pathways and regulate gene expression in eukaryotes. Intracellular domains of activated receptors recruit several protein kinases as well as transcription factors that serve as platforms or hubs for the assembly of multi-protein complexes. The signaling hubs involved in a related biologic function often share common interaction proteins and target genes. This functional connectivity suggests that a pairwise comparison of protein interaction partners of signaling hubs and network analysis of common partners and their expression analysis might lead to the identification of critical nodes in cellular signaling. A pairwise comparison of signaling hubs across several related pathways might reveal novel signaling modules. Analysis of protein interaction connectome by Venn (PIC-Venn) of transcription factors STAT1, STAT3, NFKB1, RELA, FOS, and JUN, and their common interaction network suggested that BRCA1 and TSC22D3 function as critical nodes in immune responses by connecting the signaling hubs into signaling modules. Transcriptional regulation of critical hubs may play a major role in the lung epithelial cells in response to SARS-CoV-2 and in COVID-19 patients. Mutations and differential expression levels of these critical nodes and modules in pathological conditions might deregulate signaling pathways and their target genes involved in inflammation. Biological connectivity emerges from the structural connectivity of interaction networks across several signaling hubs in related pathways. The main objectives of this study are to identify critical hubs, critical nodes, and modules involved in the signal transduction pathways of innate and adaptive immunity. Application of PIC-Venn to several signaling hubs might reveal novel nodes and modules that can be targeted by small regulatory molecules to simultaneously activate or inhibit cell signaling in health and disease.

The Breast Cancer Protooncogenes HER2, BRCA1 and BRCA2 and Their Regulation by the iNOS/NOS2 Axis

The expression of inducible nitric oxide synthase (iNOS; NOS2) and derived NO in various cancers was reported to exert pro- and anti-tumorigenic effects depending on the levels of expression and the tumor types. In humans, the breast cancer level of iNOS was reported to be overexpressed, to exhibit pro-tumorigenic activities, and to be of prognostic significance. Likewise, the expression of the oncogenes HER2, BRCA1, and BRCA2 has been associated with malignancy. The interrelationship between the expression of these protooncogenes and oncogenes and the expression of iNOS is not clear. We have hypothesized that there exist cross-talk signaling pathways between the breast cancer protooncogenes, the iNOS axis, and iNOS-mediated NO mutations of these protooncogenes into oncogenes. We review the molecular regulation of the expression of the protooncogenes in breast cancer and their interrelationships with iNOS expression and activities. In addition, we discuss the roles of iNOS, HER2, BRCA1/2, and NO metabolism in the pathophysiology of cancer stem cells. Bioinformatic analyses have been performed and have found suggested molecular alterations responsible for breast cancer aggressiveness. These include the association of BRCA1/2 mutations and HER2 amplifications with the dysregulation of the NOS pathway. We propose that future studies should be undertaken to investigate the regulatory mechanisms underlying the expression of iNOS and various breast cancer oncogenes, with the aim of identifying new therapeutic targets for the treatment of breast cancers that are refractory to current treatments.

Combining Recombinase-Mediated Cassette Exchange Strategy with Quantitative Proteomic and Phosphoproteomic Analyses to Inspect Intracellular Functions of the Tumor Suppressor Galectin-4 in Colorectal Cancer Cells

Galectin-4 (Gal4) has been suggested to function as a tumor suppressor in colorectal cancer (CRC). In order to systematically explore its function in CRC, we established a CRC cell line where Gal4 expression can be regulated via the doxycycline (dox)-inducible expression of a single copy wildtype LGALS4 transgene generated by recombinase-mediated cassette exchange (RMCE). Using this model and applying in-depth proteomic and phosphoproteomic analyses, we systematically screened for intracellular changes induced by Gal4 expression. Overall, 3083 cellular proteins and 2071 phosphosites were identified and quantified, of which 1603 could be matched and normalized to their protein expression levels. A bioinformatic analysis revealed that most of the regulated proteins and phosphosites can be localized in the nucleus and are categorized as nucleic acid-binding proteins. The top candidates whose expression was modulated by Gal4 are PURB, MAPKAPK3, BTF3 and BCAR1, while the prime candidates with altered phosphorylation included ZBTB7A, FOXK1, PURB and CK2beta. In order to validate the (phospho)proteomic data, we confirmed these candidates by a radiometric metabolic-labelling and immunoprecipitation strategy. All candidates exert functions in the transcriptional or translational control, indicating that Gal4 might be involved in these processes by affecting the expression or activity of these proteins.

BRCA-Mutated Pancreatic Cancer: From Discovery to Novel Treatment Paradigms

Simple Summary

Approximately 10–20% of pancreatic cancer patients will have a mutation in their DNA, passed on in families, that contributes to the development of their pancreatic cancer. These mutations are important in that they effect the biology of the disease as well as contribute to sensitivity to specific treatments. We describe the critical role that these genes play in various cellular processes in the body that contribute to their role in cancer development and normal cellular function. In this review, we aim to describe the role of certain genes (BRCA1 and BRCA2) in the development of pancreatic cancer and the current and future research efforts underway to treat this subtype of disease.

Abstract

The discovery of BRCA1 and BRCA2 in the 1990s revolutionized the way we research and treat breast, ovarian, and pancreatic cancers. In the case of pancreatic cancers, germline mutations occur in about 10–20% of patients, with mutations in BRCA1 and BRCA2 being the most common. BRCA genes are critical in DNA repair pathways, particularly in homologous recombination, which has a serious impact on genomic stability and can contribute to cancerous cell proliferation. However, BRCA1 also plays a fundamental role in cell cycle checkpoint control, ubiquitination, control of gene expression, and chromatin remodeling, while BRCA2 also plays a role in transcription and immune system response. Therefore, mutations in these genes lead to multiple defects in cells that may be utilized when treating cancer. BRCA mutations seem to confer a prognostic benefit with an improved overall survival due to differing underlying biology. These mutations also appear to be a predictive marker, with patients showing increased sensitivity to certain treatments, such as platinum chemotherapy and PARP inhibitors. Olaparib is currently indicated for maintenance therapy in metastatic PDAC after induction with platinum-based chemotherapy. Resistance has been found to these therapies, and with a 10.8% five-year OS, novel therapies are desperately needed.

The Apoptotic Resistance of BRCA1-Deficient Ovarian Cancer Cells is Mediated by cAMP

Breast cancer type 1 susceptibility protein (BRCA1) is essential for homologous recombination repair of DNA double-strand breaks. Loss of BRCA1 is lethal to embryos due to extreme genomic instability and the activation of p53-dependent apoptosis. However, the apoptosis is resisted in BRCA1-deficient cancer cells even though their p53 is proficient. In this study, by analysis of transcriptome data of ovarian cancer patients bearing BRCA1 defects in TCGA database, we found that cAMP signaling pathway was significantly activated. Experimentally, we found that BRCA1 deficiency caused an increased expression of ADRB1, a transmembrane receptor that can promote the generation of cAMP. The elevated cAMP not only inhibited DNA damage-induced apoptosis through abrogating p53 accumulation, but also suppressed the proliferation of cytotoxic T lymphocytes by enhancing the expression of immunosuppressive factors DKK1. Inhibition of ADRB1 effectively killed cancer cells by abolishing the apoptotic resistance. These findings uncover a novel mechanism of apoptotic resistance in BRCA1-deficient ovarian cancer cells and point to a potentially new strategy for treating BRCA1-mutated tumors.

Mesenchymal and stem-like prostate cancer linked to therapy-induced lineage plasticity and metastasis

Bioinformatic analysis of 94 patient-derived xenografts (PDXs), cell lines, and organoids (PCOs) identifies three intrinsic transcriptional subtypes of metastatic castration-resistant prostate cancer: androgen receptor (AR) pathway + prostate cancer (PC) (ARPC), mesenchymal and stem-like PC (MSPC), and neuroendocrine PC (NEPC). A sizable proportion of castration-resistant and metastatic stage PC (M-CRPC) cases are admixtures of ARPC and MSPC. Analysis of clinical datasets and mechanistic studies indicates that MSPC arises from ARPC as a consequence of therapy-induced lineage plasticity. AR blockade with enzalutamide induces (1) transcriptional silencing of TP53 and hence dedifferentiation to a hybrid epithelial and mesenchymal and stem-like state and (2) inhibition of BMP signaling, which promotes resistance to AR inhibition. Enzalutamide-tolerant LNCaP cells re-enter the cell cycle in response to neuregulin and generate metastasis in mice. Combined inhibition of HER2/3 and AR or mTORC1 exhibits efficacy in models of ARPC and MSPC or MSPC, respectively. These results define MSPC, trace its origin to therapy-induced lineage plasticity, and reveal its sensitivity to HER2/3 inhibition.

Inhibition of Skp2 enhances doxorubicin-induced cell death in B cell precursor acute lymphoblastic leukemia

S-phase kinase-associated protein 2 (Skp2) is a well-defined component of the Skp2-Culin1-F-box (SCF) E3 ubiquitin ligase complex, which is involved in cell cycle progression and considered a prognostic marker in cancers. Overexpression of Skp2 is frequently observed in patients with Acute lymphoblastic leukemia (ALL). Inhibition of this protein may be a valuable strategy to induce apoptosis in malignant cells. Less well known is the effect of Skp2 inhibition on the potentiation of the chemotherapeutic-induced cell death in B cell precursor acute lymphoblastic leukemia (BCP-ALL). Our results demonstrated that inhibition of the Skp2 using SZL P1-41, not only resulted in caspase-mediated apoptosis but also potentiated doxorubicin-induced apoptosis in BCP-ALL cell lines (NALM-6 and SUP-B15). SZL P1-41 in combination with doxorubicin altered cell cycle distribution and the level of cyclins and CDKs in BCP-ALL cells. DNA damage response genes were also up-regulated in presence of the doxorubicin and SZL P1-41 in both cell lines. In conclusion, our results indicated that inhibition of Skp2 either alone or in a combination with doxorubicin may hold promise in the future treatment of BCP-ALL. This article is protected by copyright. All rights reserved.

Natural Compounds or Their Derivatives against Breast Cancer: A Computational Study

BACKGROUND

Breast cancer is one of the most common types of cancer diagnosed and the second leading cause of death among women. Breast cancer susceptibility proteins of type 1 and 2 are human tumor suppressor genes. Genetic variations/mutations in these two genes lead to overexpression of human breast tumor suppressor genes (e.g., BRCA1, BRCA2), which triggers uncontrolled duplication of cells in humans. In addition, multidrug resistance protein 1 (MDR1), an important cell membrane protein that pumps many foreign substances from cells, is also responsible for developing resistance to cancer chemotherapy. Aim of the Study. The aim of this study was to analyze some natural compounds or their derivatives as part of the development of strong inhibitors for breast cancer. Methodology. Molecular docking studies were performed using compounds known in the literature to be effective against BRCA1 and BRCA2 and MDR1, with positive control being 5-fluorouracil, an antineoplastic drug as a positive control.

RESULTS

The binding affinity of the compounds was analyzed, and it was observed that they had a better binding affinity for the target proteins than the standard drug 5-fluorouracil. Among the compounds analyzed, α-hederin, andrographolide, apigenin, asiatic acid, auricular acid, sinularin, curcumin, citrinin, hispolon, nerol, phytol, retinol palmitate, and sclareol showed the best binding affinity energy to the BRCA1, BRCA2, and MDR1 proteins, respectively.

CONCLUSIONS

α-Hederin, andrographolide, apigenin, asiatic acid, auricular acid, hispolon, sclareol, curcumin, citrinin, and sinularin or their derivatives can be a good source of anticancer agents in breast cancer.

BRCA1: An Endocrine and Metabolic Regulator

The breast and ovarian cancer susceptibility gene (BRCA1) is a tumor suppressor whose mutation has been associated with the development of breast, ovarian and, probably, other malignancies at young ages. The BRCA1 gene product participates in multiple biological pathways including the DNA damage response, transcriptional control, cell growth and apoptosis. Inactivating germline mutations of the BRCA1 gene can be detected in a substantial portion of families with inherited breast and/or ovarian cancer. While the genomic and cancer-related actions of BRCA1 have been extensively investigated, not much information exists regarding the cellular and circulating factors involved in regulation of BRCA1 expression and action. The present review article dissects the emerging role of BRCA1 as an important regulator of various endocrine and metabolic axes. Experimental and clinical evidence links BRCA1 with a number of peptide and steroid hormones. Furthermore, comprehensive analyses identified complex interactions between the insulin/insulin-like growth factor-1 (IGF1) signaling axis and BRCA1. The correlation between metabolic disorders, including diabetes and the metabolic syndrome, and BRCA1 mutations, are discussed in this article.

Molecular docking analysis of the BRCA1 protein with compounds from Justica adhatoda L

BRCA1 is a human tumour suppression gene. Therefore, it is of interest to document the Molecular docking analysis data of the BRCA1 protein with compounds from Justica adhatoda L (adhatoda). We report that Amrinone, Hexadecanoic acid, Pyrazinamide & Vasicinone have acceptable binding features with the BRCA1 protein for further consideration.

GC-MS Analysis, Molecular Docking and Pharmacokinetic Properties of Phytocompounds from Solanum torvum Unripe Fruits and Its Effect on Breast Cancer Target Protein

This study was designed to identify phytocompounds from the aqueous extract of Solanum torvum unripe fruits using GC–MS analysis against breast cancer. For this, the identified phytocompounds were subjected to perform molecular docking studies to find the effects on breast cancer target protein. Pharmacokinetic properties were also tested for the identified phytocompounds to evaluate the ADMET properties. Molecular docking studies were done using docking software PyRx, and pharmacokinetic properties of phytocompounds were evaluated using SwissADME. From the results, ten best compounds were identified from GC–MS analysis against breast cancer target protein. Of which, three compounds showed very good binding affinity with breast cancer target protein. They are ergost-25-ene-3,6-dione,5,12-dihydroxy-,(5.alpha.,12.beta.) (− 7.3 kcal/mol), aspidospermidin-17-ol,1-acetyl-16-methoxy (− 6.7 kcal/mol) and 2-(3,4-dichlorophenyl)-4-[[2-[1-methyl-2-pyrrolidinyl]ethyl amino]-6-[trichloromethyl]-s-triazine (− 6.7 kcal/mol). Further, docking study was performed for the synthetic drug doxorubicin to compare the efficiency of phytocompounds. The binding affinity of ergost-25-ene-3,6-dione,5,12-dihydroxy-,(5.alpha.,12.beta.) is higher than the synthetic drug doxorubicin (− 7.2 kcal/mol), and the binding affinity of other compounds is also very near to the drug. Hence, the present study concludes that the phytocompounds from the aqueous extract of Solanum torvum unripe fruits have the potential ability to treat 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.

A protein interaction landscape of breast cancer

[Figure: see text].

BRCA1-BARD1 regulates transcription through modulating topoisomerase IIβ

RNA polymerase II (Pol II)-dependent transcription in stimulus-inducible genes requires topoisomerase IIβ (TOP2B)-mediated DNA strand break and the activation of DNA damage response signalling in humans. Here, we report a novel function of the breast cancer 1 (BRCA1)-BRCA1-associated ring domain 1 (BARD1) complex in this process. We found that BRCA1 is phosphorylated at S1524 by the kinases ataxia-telangiectasia mutated and ATR during gene activation, and that this event is important for productive transcription. Our biochemical and genomic analyses showed that the BRCA1-BARD1 complex interacts with TOP2B in the EGR1 transcription start site and in a large number of protein-coding genes. Intriguingly, the BRCA1-BARD1 complex ubiquitinates TOP2B, which stabilizes TOP2B binding to DNA while BRCA1 phosphorylation at S1524 controls the TOP2B ubiquitination by the complex. Together, these findings suggest the novel function of the BRCA1-BARD1 complex in the regulation of TOP2B and Pol II-mediated gene expression.

The BRCA1/BARD1 ubiquitin ligase and its substrates

Mutations in breast cancer type 1 susceptibility protein (BRCA1) and its heterodimeric binding partner BARD1 confer a high risk for the development of breast and ovarian cancers. The sole enzymatic function of the BRCA1/BARD1 complex is as a RING-type E3 ubiquitin (Ub) ligase, leading to the deposition of Ub signals onto a variety of substrate proteins. Distinct types of Ub signals deposited by BRCA1/BARD1 (i.e. degradative vs. non-degradative; mono-Ub vs. poly-Ub chains) on substrate proteins mediate aspects of its function in DNA double-stranded break repair, cell-cycle regulation, and transcriptional regulation. While cancer-predisposing mutations in both subunits lead to the inactivation of BRCA1/BARD1 ligase activity, controversy remains as to whether its Ub ligase activity directly inhibits tumorigenesis. Investigation of BRCA1/BARD1 substrates using rigorous, well-validated mutants and experimental systems will ultimately clarify the role of its ligase activity in cancer and possibly establish prognostic and diagnostic metrics for patients with mutations. In this review, we discuss the Ub ligase function of BRCA1/BARD1, highlighting experimental approaches, mechanistic considerations, and reagents that are useful in the study of substrate ubiquitylation. We also discuss the current understanding of two well-established BRCA1/BARD1 substrates (nucleosomal H2A and estrogen receptor α) and several recently discovered substrates (p50, NF2, Oct1, and LARP7). Lessons from the current body of work should provide a road map to researchers examining novel substrates and biological functions attributed to BRCA1/BARD1 Ub ligase activity.

Mitochondrial Disruption by Amyloid Beta 42 Identified by Proteomics and Pathway Mapping

Alzheimer’s disease (AD) is marked by chronic neurodegeneration associated with the occurrence of plaques containing amyloid β (Aβ) proteins in various parts of the human brain. An increase in several Aβ fragments is well documented in patients with AD and anti-amyloid targeting is an emerging area of therapy. Soluble Aβ can bind to various cell surface and intracellular molecules with the pathogenic Aβ₄₂ fragment leading to neurotoxicity. Here we examined the effect of Aβ₄₂ on network adaptations in the proteome of nerve growth factor (NGF) differentiated PC12 cells using liquid-chromatography electrospray ionization mass spectrometry (LC-ESI MS/MS) proteomics. Whole-cell peptide mass fingerprinting was coupled to bioinformatic gene set enrichment analysis (GSEA) in order to identify differentially represented proteins and related gene ontology (GO) pathways within Aβ₄₂ treated cells. Our results underscore a role for Aβ₄₂ in disrupting proteome responses for signaling, bioenergetics, and morphology in mitochondria. These findings highlight the specific components of the mitochondrial response during Aβ₄₂ neurotoxicity and suggest several new biomarkers for detection and surveillance of amyloid disease.

Induction of Apoptosis and Autophagy by Ternary Copper Complex Towards Breast Cancer Cells

BACKGROUND

Copper complex has been gaining much attention in anticancer research as targeted agent since cancer cells uptake more copper than non-cancerous cells. Our group has synthesised a ternary copper complex which is composed of 1,10-phenanthroline and tyrosine [Cu(phen)(L-tyr)Cl].3H₂0. These two payloads are designed to cleave DNA and inhibit protein degradation system (proteasome) concurrently in cancer cells, making this copper complex a dual-target compound.

OBJECTIVE

Current study was carried out to investigate the mode of cell death and role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0 in MCF-7 and MDA-MB-231 breast cancer cells.

METHODS

Growth inhibition of [Cu(phen)(L-tyr)Cl].3H₂0 towards MDA-MB-231 and human non-cancerous MCF10A breast cells was determined by MTT assay. Annexin-V-FITC/PI and cell cycle analysis were evaluated by flow cytometry. The expression of p53, Bax, caspase-9, caspase-7, caspase-3 and LC3 were determined using western blot analysis. The cells were then co-treated with hydroxychloroquine to ascertain the role of autophagy induced by [Cu(phen)(L-tyr)Cl].3H₂0.

RESULTS

[Cu(phen)(L-tyr)Cl].3H20 inhibited the growth of cancer cells dose-dependently with less toxicity towards MCF10A cells. Additionally, [Cu(phen)(L-tyr)Cl].3H20 induced apoptosis and cell cycle arrest towards MCF-7 and MDA-MB-231 breast cancer cells possibly via regulation of p53, Bax, caspase-9, caspase-3 and capase-7. The expression of LC3II was upregulated in both cancer cell lines upon treatment with [Cu(phen)(L-tyr) Cl].3H₂0, indicating the induction of autophagy. Co-treatment with autophagy inhibitor hydroxychloroquine significantly enhanced growth inhibition of both cell lines, suggesting that the autophagy induced by [Cu(phen)(L-tyr) Cl].3H₂0 in both breast cancer cells was promoting cell survival.

CONCLUSION

[Cu(phen)(L-tyr)Cl].3H20 holds great potential to be developed for breast cancer treatment.

Regulation of DNA damage response by trimeric G-protein Signaling.. [DOI: 10.1101/2021.07.21.452842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Upon sensing DNA double-strand breaks (DSBs), eukaryotic cells either die or repair DSBs via one of two competing pathways, i.e., non-homologous end-joining (NHEJ) or homologous recombination (HR). We show that cell fate after DNA damage hinges on the guanine nucleotide-exchange modulator of heterotrimeric G-protein, Giα•βγ, GIV/Girdin. GIV suppresses HR by binding and sequestering BRCA1, a key coordinator of multiple steps within the HR pathway, away from DSBs; it does so using a C-terminal motif that binds BRCA1’s BRCT-modules via both phospho-dependent and -independent mechanisms. GIV promotes NHEJ, and binds and activates Gi and enhances the ‘free’ Gβγ→PI-3-kinase→Akt pathway, thus revealing the enigmatic origin of prosurvival Akt signals during dsDNA repair. Absence of GIV, or the loss of either of its two functions impaired DNA repair, and induced cell death when challenged with numerous cytotoxic agents. That GIV selectively binds few other BRCT-containing proteins suggests convergent signaling such that heterotrimeric G-proteins may finetune sensing, repair, and outcome after DNA damage.

GRAPHIC ABSTRACT

HIGHLIGHTS

Non-receptor G protein modulator, GIV/Girdin binds BRCA1

Binding occurs in both canonical and non-canonical modes

GIV sequesters BRCA1 away from dsDNA breaks, suppresses HR

Activation of Gi by GIV enhances Akt signals, favors NHEJ

IN BRIEF

In this work, the authors show that heterotrimeric G protein signaling that is triggered by non-receptor GEF, GIV/Girdin, in response to double-stranded DNA breaks is critical for decisive signaling events which favor non-homologous end-joining (NHEJ) and inhibit homologous recombination (HR).

Exploiting DNA Damage Repair in Precision Cancer Therapy: BRCA1 as a Prime Therapeutic Target

Simple Summary

Chemical inhibition of central DNA damage repair (DDR) proteins has become a promising approach in precision cancer therapy. In particular, BRCA1 and its DDR-associated proteins constitute important targets for developing DNA repair inhibiting drugs. This review provides relevant insights on DDR biology and pharmacology, aiming to boost the development of more effective DDR targeted therapies.

Abstract

Precision medicine aims to identify specific molecular alterations, such as driver mutations, allowing tailored and effective anticancer therapies. Poly(ADP)-ribose polymerase inhibitors (PARPi) are the prototypical example of targeted therapy, exploiting the inability of cancer cells to repair DNA damage. Following the concept of synthetic lethality, PARPi have gained great relevance, particularly in BRCA1 dysfunctional cancer cells. In fact, BRCA1 mutations culminate in DNA repair defects that can render cancer cells more vulnerable to therapy. However, the efficacy of these drugs has been greatly affected by the occurrence of resistance due to multi-connected DNA repair pathways that may compensate for each other. Hence, the search for additional effective agents targeting DNA damage repair (DDR) is of crucial importance. In this context, BRCA1 has assumed a central role in developing drugs aimed at inhibiting DNA repair activity. Collectively, this review provides an in-depth understanding of the biology and regulatory mechanisms of DDR pathways, highlighting the potential of DDR-associated molecules, particularly BRCA1 and its interconnected partners, in precision cancer medicine. It also affords an overview about what we have achieved and a reflection on how much remains to be done in this field, further addressing encouraging clues for the advance of DDR targeted therapy.

Untangling the crosstalk between BRCA1 and R-loops during DNA repair

R-loops are RNA:DNA hybrids assembled during biological processes but are also linked to genetic instability when formed out of their natural context. Emerging evidence suggests that the repair of DNA double-strand breaks requires the formation of a transient R-loop, which eventually must be removed to guarantee a correct repair process. The multifaceted BRCA1 protein has been shown to be recruited at this specific break-induced R-loop, and it facilitates mechanisms in order to regulate R-loop removal. In this review, we discuss the different potential roles of BRCA1 in R-loop homeostasis during DNA repair and how these processes ensure faithful DSB repair.

BRCA1-BARD1 regulates transcription through BRD4 in Xenopus nucleoplasmic extract

The tumor suppressor BRCA1 is considered a master regulator of genome integrity. Although widely recognized for its DNA repair functions, BRCA1 has also been implicated in various mechanisms of chromatin remodeling and transcription regulation. However, the precise role that BRCA1 plays in these processes has been difficult to establish due to the widespread consequences of its cellular dysfunction. Here, we use nucleoplasmic extract derived from the eggs of Xenopus laevis to investigate the role of BRCA1 in a cell-free transcription system. We report that BRCA1-BARD1 suppresses transcription initiation independent of DNA damage signaling and its established role in histone H2A ubiquitination. BRCA1-BARD1 acts through a histone intermediate, altering acetylation of histone H4K8 and recruitment of the chromatin reader and oncogene regulator BRD4. Together, these results establish a functional relationship between an established (BRCA1) and emerging (BRD4) regulator of genome integrity.

Surface Expression of Kynurenine 3-Monooxygenase Promotes Proliferation and Metastasis in Triple-Negative Breast Cancers

Kynurenine 3-monooxygenase (KMO) is the pivotal enzyme in the kynurenine pathway and is located on the mitochondrial outer membrane. The dysregulation of KMO leads to various neurodegenerative diseases; however, it is rarely mentioned in cancer progression. Our previous study showed that KMO overexpression in canine mammary gland tumors (cMGT) is associated with poor prognosis in cMGT patients. Surprisingly, it was also found that KMO can be located on the cell membranes of cMGT cells, unlike its location in normal cells, where KMO is expressed only within the cytosol. Since cMGT and human breast cancer share similar morphologies and pathogenesis, this study investigated the possibility of detecting surface KMO in human breast cancers and the role of surface KMO in tumorigenesis. Using immunohistochemistry (IHC), flow cytometry (FC), immunofluorescence assay (IFA), and transmission electron microscopy (TEM), we demonstrated that KMO can be aberrantly and highly expressed on the cell membranes of breast cancer tissues and in an array of cell lines. Masking surface KMO with anti-KMO antibody reduced the cell viability and inhibited the migration and invasion of the triple-negative breast cancer cell line, MDA-MB-231. These results indicated that aberrant surface expression of KMO may be a potential therapeutic target for human breast cancers.

BRCA1 degradation in response to mitochondrial damage in breast cancer cells

BRCA1 is a well-studied tumor suppressor involved in the homologous repair of DNA damage, whereas PINK1, a mitochondrial serine/threonine kinase, is known to be involved in mitochondrial quality control. Genetic mutations of PINK1 and Parkin cause autosomal recessive early-onset Parkinson's disease. We found that in breast cancer cells, the mitochondrial targeting reagents, which all induce mitochondrial depolarization along with PINK1 upregulation, induced proteasomal BRCA1 degradation. This BRCA1 degradation was dependent on PINK1, and BRCA1 downregulation upon mitochondrial damage caused DNA double-strand breaks. BRCA1 degradation was mediated through the direct interaction with the E3 ligase Parkin. Strikingly, BRCA1 and PINK1/Parkin expression were inversely correlated in cancerous mammary glands from breast cancer patients. BRCA1 knockdown repressed cancer cell growth, and high BRCA1 expression predicted poor relapse-free survival in breast cancer patients. These observations indicate a novel mechanism by which mitochondrial damage is transmitted to the nucleus, leading to BRCA1 degradation.

Plasma Metabolome Signature Indicative of BRCA1 Germline Status Independent of Cancer Incidence

Individuals carrying a pathogenic germline variant in the breast cancer predisposition gene BRCA1 (gBRCA1+) are prone to developing breast cancer. Apart from its well-known role in DNA repair, BRCA1 has been shown to powerfully impact cellular metabolism. While, in general, metabolic reprogramming was named a hallmark of cancer, disrupted metabolism has also been suggested to drive cancer cell evolution and malignant transformation by critically altering microenvironmental tissue integrity. Systemic metabolic effects induced by germline variants in cancer predisposition genes have been demonstrated before. Whether or not systemic metabolic alterations exist in gBRCA1+ individuals independent of cancer incidence has not been investigated yet. We therefore profiled the plasma metabolome of 72 gBRCA1+ women and 72 age-matched female controls, none of whom (carriers and non-carriers) had a prior cancer diagnosis and all of whom were cancer-free during the follow-up period. We detected one single metabolite, pyruvate, and two metabolite ratios involving pyruvate, lactate, and a metabolite of yet unknown structure, significantly altered between the two cohorts. A machine learning signature of metabolite ratios was able to correctly distinguish between gBRCA1+ and controls in ~82%. The results of this study point to innate systemic metabolic differences in gBRCA1+ women independent of cancer incidence and raise the question as to whether or not constitutional alterations in energy metabolism may be involved in the etiology of BRCA1-associated breast cancer.

Cyclin-dependent kinase inhibitors (CDKIs) and the DNA damage response: The link between signaling pathways and cancer

At the cellular level, DNA repair mechanisms are crucial in maintaining both genomic integrity and stability. DNA damage appears to be a central culprit in tumor onset and progression. Cyclin-dependent kinases (CDKs) and their regulatory partners coordinate the cell cycle progression. Aberrant CDK activity has been linked to a variety of cancers through deregulation of cell-cycle control. Besides DNA damaging agents and chromosome instability (CIN), disruptions in the levels of cell cycle regulators including cyclin-dependent kinase inhibitors (CDKIs) would result in unscheduled proliferation and cell division. The INK4 and Cip/Kip (CDK interacting protein/kinase inhibitor protein) family of CDKI proteins are involved in cell cycle regulation, transcription regulation, apoptosis, and cell migration. A thorough understanding of how these CDKIs regulate the DNA damage response through multiple signaling pathways may provide an opportunity to design efficient treatment strategies to inhibit carcinogenesis.

Spinal motor neuron loss occurs through a p53-and-p21-independent mechanism in the Smn2B/- mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a pediatric neuromuscular disease caused by genetic deficiency of the survival motor neuron (SMN) protein. Pathological hallmarks of SMA are spinal motor neuron loss and skeletal muscle atrophy. The molecular mechanisms that elicit and drive preferential motor neuron degeneration and death in SMA remain unclear. Transcriptomic studies consistently report p53 pathway activation in motor neurons and spinal cord tissue of SMA mice. Recent work has identified p53 as an inducer of spinal motor neuron loss in severe Δ7 SMA mice. Additionally, the cyclin-dependent kinase inhibitor P21 (Cdkn1a), an inducer of cell cycle arrest and mediator of skeletal muscle atrophy, is consistently increased in motor neurons, spinal cords, and other tissues of various SMA models. p21 is a p53 transcriptional target but can be independently induced by cellular stressors. To ascertain whether p53 and p21 signaling pathways mediate spinal motor neuron death in milder SMA mice, and how they affect the overall SMA phenotype, we introduced Trp53 and P21 null alleles onto the Smn^2B/- background. We found that p53 and p21 depletion did not modulate the timing or degree of Smn^2B/- motor neuron loss as evaluated using electrophysiological and immunohistochemical methods. Moreover, we determined that Trp53 and P21 knockout differentially affected Smn^2B/- mouse lifespan: p53 ablation impaired survival while p21 ablation extended survival through Smn-independent mechanisms. These results demonstrate that p53 and p21 are not primary drivers of spinal motor neuron death in Smn^2B/- mice, a milder SMA mouse model, as motor neuron loss is not alleviated by their ablation.

BRCA1/MAD2L1 Deficiency Disrupts the Spindle Assembly Checkpoint to Confer Vinorelbine Resistance in Mesothelioma

Mesothelioma is a universally lethal cancer lacking effective therapy. The spindle poison vinorelbine exhibits clinical activity in the relapsed setting, and in preclinical models requires BRCA1 to initiate apoptosis. However, the mechanisms underlying this regulation and the clinical implications have not been explored. Here, we show that BRCA1 silencing abrogated vinorelbine-induced cell-cycle arrest, recruitment of BUBR1 to kinetochores, and apoptosis. BRCA1 silencing led to codepletion of MAD2L1 at the mRNA and protein levels consistent with its status as a transcriptional target of BRCA1 Silencing of MAD2L1 phenocopied BRCA1 and was sufficient to confer resistance to vinorelbine. This was recapitulated in cell lines selected for resistance to vinorelbine, which acquired loss of both BRCA1 and MAD2L1 expression. Following ex vivo vinorelbine in 20 primary tumor explants, apoptotic response rate was 59% in BRCA1/MAD2L1-positive explants compared with 0% in BRCA1/MAD2L1-negative explants. In 48 patients, BRCA1 and/or MAD2L1 loss of expression was not prognostic; however, in a subset of patients treated with vinorelbine, survival was shorter for patients lacking BRCA1/MAD2L1 expression compared with double-positive patients (5.9 vs. 36.7 months, P = 0.03). Our data implicate BRCA1/MAD2L1 loss as a putative predictive marker of resistance to vinorelbine in mesothelioma and warrant prospective clinical evaluation.

Transcription factors in epithelial ovarian cancer: histotype-specific drivers and novel therapeutic targets

Transcription factors (TFs) are major contributors to cancer risk and somatic development. In preclinical and clinical studies, direct or indirect inhibition of TF-mediated oncogenic gene expression profiles have proven to be effective in many tumor types, highlighting this group of proteins as valuable therapeutic targets. In spite of this, our understanding of TFs in epithelial ovarian cancer (EOC) is relatively limited. EOC is a heterogeneous disease composed of five major histologic subtypes; high-grade serous, low-grade serous, endometrioid, clear cell and mucinous. Each histology is associated with unique clinical etiologies, sensitivity to therapies, and molecular signatures - including diverse transcriptional regulatory programs. While some TFs are shared across EOC subtypes, a set of TFs are expressed in a histotype-specific manner and likely explain part of the histologic diversity of EOC subtypes. Targeting TFs present with unique opportunities for development of novel precision medicine strategies for ovarian cancer. This article reviews the critical TFs in EOC subtypes and highlights the potential of exploiting TFs as biomarkers and therapeutic targets.