Cyclin D1 promotes BRCA2-Rad51 interaction by restricting cyclin A/B-dependent BRCA2 phosphorylation

Distinct roles of the two BRCA2 DNA binding domains in DNA damage repair and replication fork preservation

Homologous recombination (HR) is a highly conserved tool for the removal of DNA double-strand breaks (DSBs) and the preservation of stalled and damaged DNA replication forks. Successful completion of HR requires the tumor suppressor BRCA2. Germline mutations in BRCA2 lead to familial breast, ovarian, and other cancers, underscoring the importance of this protein for maintaining genome stability. BRCA2 harbors two distinct DNA binding domains, one that possesses three oligonucleotide/oligosaccharide binding (OB) folds (known as the OB-DBD), and with the other residing in the C-terminal recombinase binding domain (termed the CTRB-DBD) encoded by the last gene exon. Here, we employ a combination of genetic, biochemical, and cellular approaches to delineate contributions of these two DNA binding domains toward HR and the maintenance of stressed DNA replication forks. We show that OB-DBD and CTRB-DBD confer ssDNA and dsDNA binding capabilities to BRCA2, respectively, and that BRCA2 variants mutated in either DNA binding domain are impaired in the ability to load the recombinase RAD51 onto ssDNA pre-occupied by RPA. While the CTRB-DBD mutant is modestly affected for HR, it exhibits a strong defect in the protection of stressed replication forks. In contrast, the OB-DBD is indispensable for both BRCA2 functions. Our study thus defines the unique contributions of the two BRCA2 DNA binding domains in genome maintenance.

Combined strategies with PARP inhibitors for the treatment of BRCA wide type cancer

Genomic instability stands out as a pivotal hallmark of cancer, and PARP inhibitors (PARPi) emerging as a groundbreaking class of targeted therapy drugs meticulously crafted to inhibit the repair of DNA single-strand breaks(SSB) in tumor cells. Currently, PARPi have been approved for the treatment of ovarian cancer, pancreatic cancer, breast cancer, and prostate cancer characterized by homologous recombination(HR) repair deficiencies due to mutations in BRCA1/2 or other DNA repair associated genes and acquiring the designation of breakthrough therapy. Nonetheless, PARPi exhibit limited efficacy in the majority of HR-proficient BRCA1/2 wild-type cancers. At present, the synergistic approach of combining PARPi with agents that induce HR defects, or with chemotherapy and radiotherapy to induce substantial DNA damage, significantly enhances the efficacy of PARPi in BRCA wild-type or HR-proficient patients, supporting extension the use of PARPi in HR proficient patients. Therefore, we have summarized the effects and mechanisms of the combined use of drugs with PARPi, including the combination of PARPi with HR defect-inducing drugs such as ATRi, CHKi, HR indirectly inducing drugs like VEGFRi, CDKi, immune checkpoint inhibitors and drugs instigating DNA damage such as chemotherapy or radiotherapy. In addition, this review discusses several ongoing clinical trials aimed at analyzing the clinical application potential of these combined treatment strategies.

Cyclin D1 promotes radioresistance through regulation of RAD51 in melanoma

Melanoma is a notoriously radioresistant type of skin cancer. Elucidation of the specific mechanisms underlying radioresistance is necessary to improve the clinical efficacy of radiation therapy. To identify the key factors contributing to radioresistance, five melanoma cell lines were selected for study and genes that were upregulated in relatively radioresistant melanomas compared with radiosensitive melanoma cells determined via RNA sequencing technology. In particular, we focused on cyclin D1 (CCND1), a well known cell cycle regulatory molecule. In radiosensitive melanoma, overexpression of cyclin D1 reduced apoptosis. In radioresistant melanoma cell lines, suppression of cyclin D1 with a specific inhibitor or siRNA increased apoptosis and decreased cell proliferation in 2D and 3D spheroid cultures. In addition, we observed increased expression of γ-H2AX, a molecular marker of DNA damage, even at a later time after γ-irradiation, under conditions of inhibition of cyclin D1, with a response pattern similar to that of radiosensitive SK-Mel5. In the same context, expression and nuclear foci formation of RAD51, a key enzyme for homologous recombination (HR), were reduced upon inhibition of cyclin D1. Downregulation of RAD51 also reduced cell survival to irradiation. Overall, suppression of cyclin D1 expression or function led to reduced radiation-induced DNA damage response (DDR) and triggered cell death. Our collective findings indicate that the presence of increased cyclin D1 potentially contributes to the development of radioresistance through effects on RAD51 in melanoma and could therefore serve as a therapeutic target for improving the efficacy of radiation therapy.

D-Type Cyclins in Development and Disease

D-type cyclins encode G1/S cell cycle checkpoint proteins, which play a crucial role in defining cell cycle exit and progression. Precise control of cell cycle exit is vital during embryonic development, with defects in the pathways regulating intracellular D-type cyclins resulting in abnormal initiation of stem cell differentiation in a variety of different organ systems. Furthermore, stabilisation of D-type cyclins is observed in a wide range of disorders characterized by cellular over-proliferation, including cancers and overgrowth disorders. In this review, we will summarize and compare the roles played by each D-type cyclin during development and provide examples of how their intracellular dysregulation can be an underlying cause of disease.

DLGAP4 acts as an effective prognostic predictor for hepatocellular carcinoma and is closely related to tumour progression

Disc large associated protein 4 (DLGAP4) plays an important role in neurological diseases, but the role and mechanism of DLGAP4 in hepatocellular carcinoma (HCC) remain unclear. In this study, the prognostic effect of DLGAP4 on HCC patients was investigated by means of bioinformatics. The correlation of DLGAP4 expression with the prognosis of HCC patients was evaluated by TCGA data analysis, and the correlation between DLGAP4 expression and the clinical characteristics of HCC patients was evaluated by the Wilcoxon signed rank test and logistic regression analysis. Kaplan‒Meier and Cox regression methods were used to assess the effect of DLGAP4 expression level on overall survival, and nomograms were used to illustrate the correlation between DLGAP4 gene expression and HCC risk. The genes related to DLGAP4 in HCC were screened, and GO/KEGG enrichment analysis was performed. Furthermore, in vitro and in vivo experiments were conducted to detect the effect of DLGAP4 expression on the proliferation, migration and metastasis of HCC cells. We also examined the effect of DLGAP4 expression on enriched pathway proteins to explore the possible mechanism. The expression levels of DLGAP4 were significantly higher in HCC cell lines and tissue samples than in normal liver cell lines and tissues. The expression of DLGAP4 was significantly associated with clinical characteristics. Survival analysis showed that high expression of DLGAP4 was associated with a poor prognosis in HCC. Multivariate analysis showed that high expression of DLGAP4 was an independent risk factor affecting the overall survival rate in HCC patients. By means of ROC curve analysis and nomograms, we determined the value of DLGAP4 expression in the diagnosis and prognosis evaluation of HCC. GO/KEGG enrichment analysis showed that the PPAR signalling pathway was differentially enriched in patients with high expression of DLGAP4. According to in vitro and in vivo experiments, DLGAP4 knockdown inhibited the proliferation and metastasis of HCC cells and decreased the expression of PPARβ/δ protein. In contrast, overexpression of DLGAP4 promoted the proliferation and metastasis of HCC cell, and increased the expression of PPARβ/δ protein.In contrast, overexpression of DLGAP4 promoted the proliferation and metastasis of HCC cells and increased the expression of PPARβ/δ protein. The results show a close correlation between DLGAP4 expression and clinicopathological features of HCC, and DLGAP4 can be used as a prediction biomarker of HCC.

The Emerging Roles of Rad51 in Cancer and Its Potential as a Therapeutic Target

Defects in DNA repair pathways are emerging hallmarks of cancer. Accurate DNA repairs and replications are essential for genomic stability. Cancer cells require residual DNA repair capabilities to repair the damage from replication stress and genotoxic anti-tumor agents. Defective DNA repair also promotes the accumulation of genomic changes that eventually lead to tumorigenesis, tumor progression, and therapeutic resistance to DNA-damaging anti-tumor agents. Rad51 recombinase is a critical effector of homologous recombination, which is an essential DNA repair mechanism for double-strand breaks. Rad51 has been found to be upregulated in many malignant solid tumors, and is correlated with poor prognosis. In multiple tumor types, Rad51 is critical for tumor metabolism, metastasis and drug resistance. Herein, we initially introduced the structure, expression pattern of Rad51 and key Rad51 mediators involved in homologous recombination. Additionally, we primarily discussed the role of Rad51 in tumor metabolism, metastasis, resistance to chemotherapeutic agents and poly-ADP ribose polymerase inhibitors.

Guardians of the Genome: BRCA2 and Its Partners

The tumor suppressor BRCA2 functions as a central caretaker of genome stability, and individuals who carry BRCA2 mutations are predisposed to breast, ovarian, and other cancers. Recent research advanced our mechanistic understanding of BRCA2 and its various interaction partners in DNA repair, DNA replication support, and DNA double-strand break repair pathway choice. In this review, we discuss the biochemical and structural properties of BRCA2 and examine how these fundamental properties contribute to DNA repair and replication fork stabilization in living cells. We highlight selected BRCA2 binding partners and discuss their role in BRCA2-mediated homologous recombination and fork protection. Improved mechanistic understanding of how BRCA2 functions in genome stability maintenance can enable experimental evidence-based evaluation of pathogenic BRCA2 mutations and BRCA2 pseudo-revertants to support targeted therapy.

A synthetic mRNA cell reprogramming method using CYCLIN D1 promotes DNA repair, generating improved genetically stable human induced pluripotent stem cells

A key challenge for clinical application of induced pluripotent stem cells (iPSC) to accurately model and treat human pathologies depends on developing a method to generate genetically stable cells to reduce long-term risks of cell transplant therapy. Here, we hypothesized that CYCLIN D1 repairs DNA by highly efficient homologous recombination (HR) during reprogramming to iPSC that reduces genetic instability and threat of neoplastic growth. We adopted a synthetic mRNA transfection method using clinically compatible conditions with CYCLIN D1 plus base factors (OCT3/4, SOX2, KLF4, LIN28) and compared with methods that use C-MYC. We demonstrate that CYCLIN D1 made iPSC have (a) lower multitelomeric signal, (b) reduced double-strand DNA breaks, (c) correct nuclear localization of RAD51 protein expression, and (d) reduced single-nucleotide polymorphism (SNP) changes per chromosome, compared with the classical reprogramming method using C-MYC. CYCLIN D1 iPSC have reduced teratoma Ki67 cell growth kinetics and derived neural stem cells successfully engraft in a hostile spinal cord injury (SCI) microenvironment with efficient survival, differentiation. We demonstrate that CYCLIN D1 promotes double-stranded DNA damage repair predominantly through HR during cell reprogramming to efficiently produce iPSC. CYCLIN D1 reduces general cell stress associated with significantly lower SIRT1 gene expression and can rescue Sirt1 null mouse cell reprogramming. In conclusion, we show synthetic mRNA transfection of CYCLIN D1 repairs DNA during reprogramming resulting in significantly improved genetically stable footprint in human iPSC, enabling a new cell reprogramming method for more accurate and reliable generation of human iPSC for disease modeling and future clinical applications.

Molecular contribution of BRCA1 and BRCA2 to genome instability in breast cancer patients: review of radiosensitivity assays

BACKGROUND

DNA repair pathways, cell cycle arrest checkpoints, and cell death induction are present in cells to process DNA damage and prevent genomic instability caused by various extrinsic and intrinsic ionizing factors. Mutations in the genes involved in these pathways enhances the ionizing radiation sensitivity, reduces the individual's capacity to repair DNA damages, and subsequently increases susceptibility to tumorigenesis.

BODY

BRCA1 and BRCA2 are two highly penetrant genes involved in the inherited breast cancer and contribute to different DNA damage pathways and cell cycle and apoptosis cascades. Mutations in these genes have been associated with hypersensitivity and genetic instability as well as manifesting severe radiotherapy complications in breast cancer patients. The genomic instability and DNA repair capacity of breast cancer patients with BRCA1/2 mutations have been analyzed in different studies using a variety of assays, including micronucleus assay, comet assay, chromosomal assay, colony-forming assay, γ -H2AX and 53BP1 biomarkers, and fluorescence in situ hybridization. The majority of studies confirmed the enhanced spontaneous & radiation-induced radiosensitivity of breast cancer patients compared to healthy controls. Using G2 micronucleus assay and G2 chromosomal assay, most studies have reported the lymphocyte of healthy carriers with BRCA1 mutation are hypersensitive to invitro ionizing radiation compared to non-carriers without a history of breast cancer. However, it seems this approach is not likely to be useful to distinguish the BRCA carriers from non-carrier with familial history of breast cancer.

CONCLUSION

In overall, breast cancer patients are more radiosensitive compared to healthy control; however, inconsistent results exist about the ability of current radiosensitive techniques in screening BRCA1/2 carriers or those susceptible to radiotherapy complications. Therefore, developing further radiosensitivity assay is still warranted to evaluate the DNA repair capacity of individuals with BRCA1/2 mutations and serve as a predictive factor for increased risk of cancer mainly in the relatives of breast cancer patients. Moreover, it can provide more evidence about who is susceptible to manifest severe complication after radiotherapy.

The double dealing of cyclin D1

The cell cycle is tightly regulated by cyclins and their catalytic moieties, the cyclin-dependent kinases (CDKs). Cyclin D1, in association with CDK4/6, acts as a mitogenic sensor and integrates extracellular mitogenic signals and cell cycle progression. When deregulated (overexpressed, accumulated, inappropriately located), cyclin D1 becomes an oncogene and is recognized as a driver of solid tumors and hemopathies. Recent studies on the oncogenic roles of cyclin D1 reported non-canonical functions dependent on the partners of cyclin D1 and its location within tumor cells or tissues. Support for these new functions was provided by various mouse models of oncogenesis. Finally, proteomic and transcriptomic data identified complex cyclin D1 networks. This review focuses on these aspects of cyclin D1 pathophysiology, which may be crucial for targeted therapy.Abbreviations: aa, amino acid; AR, androgen receptor; ATM, ataxia telangectasia mutant; ATR, ATM and Rad3-related; CDK, cyclin-dependent kinase; ChREBP, carbohydrate response element binding protein; CIP, CDK-interacting protein; CHK1/2, checkpoint kinase 1/2; CKI, CDK inhibitor; DDR, DNA damage response; DMP1, cyclin D-binding myb-like protein; DSB, double-strand DNA break; DNA-PK, DNA-dependent protein kinase; ER, estrogen receptor; FASN, fatty acid synthase; GSK3β, glycogen synthase-3β; HAT, histone acetyltransferase; HDAC, histone deacetylase; HK2, hexokinase 2; HNF4α, and hepatocyte nuclear factor 4α; HR, homologous recombination; IR, ionizing radiation; KIP, kinase inhibitory protein; MCL, mantle cell lymphoma; NHEJ, non-homologous end-joining; PCAF, p300/CREB binding-associated protein; PGC1α, PPARγ co-activator 1α; PEST, proline-glutamic acid-serine-threonine, PK, pyruvate kinase; PPAR, peroxisome proliferator-activated receptor; RB1, retinoblastoma protein; ROS, reactive oxygen species; SRC, steroid receptor coactivator; STAT, signal transducer and activator of transcription; TGFβ, transforming growth factor β; UPS, ubiquitin-proteasome system; USP22, ubiquitin-specific peptidase 22; XPO1 (or CRM1) exportin 1.

DNA damage response manages cell cycle restriction of senile multipotent mesenchymal stromal cells

Multipotent mesenchymal stromal cells (MMSCs) are promising to treat a variety of traumatic and degenerative diseases. However, in vitro-passage aging induces cell cycle arrest and a series of genetic and biological changes, which greatly limits ex vivo cell number expansion and further clinical application of MMSCs. In most cases, DNA damage and DNA damage response (DDR) act as the main cause and executor of cellular senescence respectively. Mechanistically, DNA damage signals induce cell cycle arrest and DNA damage repair via DDR. If the DNA damage is indelible, MMSCs would entry into a permanent cell cycle arrest. It should be noted that apart from DDR signaling, certain proliferation or metabolism pathways are also occupied in DNA damage related cell cycle arrest. New findings of these aspects will also be summarized in this study. In summary, we aim to provide a comprehensive review of DDR associated cell cycle regulation and other major molecular signaling in the senescence of MMSCs. Above knowledge could contribute to improve the limited capacity of in vitro expansion of MMSCs, and then promote their clinical applications.

Roscovitine strongly enhances the effect of olaparib on radiosensitivity for HPV neg. but not for HPV pos. HNSCC cell lines

At present, advanced stage human Papillomavirus (HPV) negative and positive head and neck squamous cell carcinoma (HNSCC) are treated by intense multimodal therapy that includes radiochemotherapy, which are associated with relevant side effects. Patients with HPV positive tumors possess a far better prognosis than those with HPV negative cancers. Therefore, new therapeutic strategies are needed to improve the outcome especially of the latter one as well as quality of life for all HNSCC patients. Here we tested whether roscovitine, an inhibitor of cyclin-dependent kinases (CDKs), which hereby also blocks homologous recombination (HR), can be used to enhance the radiation sensitivity of HNSCC cell lines.

In all five HPV negative and HPV positive cell lines tested, roscovitine caused inhibition of CDK1 and 2. Surprisingly, all HPV positive cell lines were found to be defective in HR. In contrast, HPV negative strains demonstrated efficient HR, which was completely suppressed by roscovitine. In line with this, for HPV negative but not for HPV positive cell lines, treatment with roscovitine resulted in a pronounced enhancement of the radiation-induced G2 arrest as well as a significant increase in radiosensitivity. Due to a defect in HR, all HPV positive cell lines were efficiently radiosensitized by the PARP-1 inhibitor olaparib. In contrast, in HPV negative cell lines a significant radiosensitization by olaparib was only achieved when combined with roscovitine.

Synergy of WEE1 and mTOR Inhibition in Mutant KRAS-Driven Lung Cancers

Purpose:KRAS-activating mutations are the most common oncogenic driver in non-small cell lung cancer (NSCLC), but efforts to directly target mutant KRAS have proved a formidable challenge. Therefore, multitargeted therapy may offer a plausible strategy to effectively treat KRAS-driven NSCLCs. Here, we evaluate the efficacy and mechanistic rationale for combining mTOR and WEE1 inhibition as a potential therapy for lung cancers harboring KRAS mutations.Experimental Design: We investigated the synergistic effect of combining mTOR and WEE1 inhibitors on cell viability, apoptosis, and DNA damage repair response using a panel of human KRAS-mutant and wild type NSCLC cell lines and patient-derived xenograft cell lines. Murine autochthonous and human transplant models were used to test the therapeutic efficacy and pharmacodynamic effects of dual treatment.Results: We demonstrate that combined inhibition of mTOR and WEE1 induced potent synergistic cytotoxic effects selectively in KRAS-mutant NSCLC cell lines, delayed human tumor xenograft growth and caused tumor regression in a murine lung adenocarcinoma model. Mechanistically, we show that inhibition of mTOR potentiates WEE1 inhibition by abrogating compensatory activation of DNA repair, exacerbating DNA damage in KRAS-mutant NSCLC, and that this effect is due in part to reduction in cyclin D1.Conclusions: These findings demonstrate that compromised DNA repair underlies the observed potent synergy of WEE1 and mTOR inhibition and support clinical evaluation of this dual therapy for patients with KRAS-mutant lung cancers. Clin Cancer Res; 23(22); 6993-7005. ©2017 AACR.

Rare variants in BRCA2 and CHEK2 are associated with the risk of urinary tract cancers

Previous studies have shown that two rare variants, rs11571833 in BRCA2 and rs17879961 in CHEK2 were associated with lung cancer. However, the associations between these two variants and urinary tract cancers risk remain largely unexplored. We applied imputation of three genome-wide association studies published in the database of Genotypes and Phenotypes (dbGaP). Unconditional logistic regression analysis and meta-analysis were performed to assess the association between these two variants and the risk of urinary tract cancers. Our results showed that rs11571833[T] had an effect on urinary tract cancers predisposition (ORmeta = 1.45, Pmeta = 0.013), especially associated with increased the risk of bladder cancer (ORmeta = 1.60, Pmeta = 0.010). Moreover, rs17879961[C] had a protective effect on the urinary tract cancers (ORmeta = 0.67, Pmeta = 1.0 × 10(-3)) and was mostly associated with a lower incidence of renal cell carcinoma (ORmeta = 0.51, Pmeta = 2.0 × 10(-3)). Together, our study indicates that BRCA2 and CHEK2 play an important role in the genetic susceptibility to urinary tract cancers.

Jungermannenone A and B induce ROS- and cell cycle-dependent apoptosis in prostate cancer cells in vitro

AIM

Jungermannenone A and B (JA, JB) are new ent-kaurane diterpenoids isolated from Chinese liverwort Jungermannia fauriana, which show anti-proliferation activities in cancer cells. In this study we investigated the mechanisms underlying the anticancer action of JA and JB in PC3 human prostate cancer cells in vitro.

METHODS

A panel of 9 human cancer cell lines was tested. Cell proliferation was assessed with a real-time cell analyzer and MTT assay. Cell apoptosis, cell cycle distribution and ROS levels were measured using cytometry. Mitochondrial damage was examined by transmission electron microscopy. DNA damage was detected with comet assay. Apoptotic, DNA damage- and cell cycle-related proteins were analyzed using Western blotting. The expression of DNA repair genes was measured with qRT-PCR.

RESULTS

Both JA and JB exerted potent anti-proliferative action against the 9 cancer cell lines, and PC3 cells were more sensitive with IC50 values of 1.34±0.09 and 4.93±0.20 μmol/L, respectively. JA (1.5 μmol/L) and JB (5 μmol/L) induced PC3 cell apoptosis, which was attenuated by the caspase inhibitor Z-VAD. Furthermore, both JA and JB caused mitochondrial damage and ROS accumulation in PC3 cells, whereas vitamin C blocked the ROS accumulation and attenuated the cytotoxicity of JA and JB. Moreover, both JA and JB induced DNA damage, accompanied by downregulated DNA repair proteins Ku70/Ku80 and RDA51. JA induced marked cell cycle arrest at the G0/G1 phase, which was related to c-Myc suppression, whereas JB enforced the cell cycle blockade in the G2/M phase, which associated with activation of the JNK signaling.

CONCLUSION

Both JA and JB induce prostate cancer apoptosis via ROS accumulation and induction of cell cycle arrest.

Paradoxical roles of cyclin D1 in DNA stability

Maintenance of DNA integrity is vital for all of the living organisms. Consequence of DNA damaging ranges from, introducing harmless synonymous mutations, to causing disease-associated mutations, genome instability, and cell death. A cell cycle protein cyclin D1 is an established cancer-driving protein. However, contribution of cyclin D1 to cancer formation and cancer survival is not entirely known. In cancer tissues, overexpression of cyclin D1 is associated with both cancer genome instability, and resistance to DNA-damaging cancer drugs. Emerging evidence indicated that cyclin D1 may play novel direct roles in regulating DNA repair. Here we provide an insight how cyclin D1 expression may contribute to DNA repair and chromosome instability, and how these functions may facilitate cancer formation, and drug resistance.