Chromosome instability and carcinogenesis: insights from murine models of human pancreatic cancer associated with BRCA2 inactivation

Low-Pass Genomic Sequencing Reveals Novel Subtypes of Pancreatic Cystic Neoplasms

BACKGROUND

Over the years, the detection rate of pancreatic cystic neoplasms (PCNs) has significantly increased; however, the differential diagnosis and identification of high-risk PCNs remain challenging. We sought to investigate whether chromosomal instability (CIN) features in cell-free DNA in the cystic fluid of PCNs could help to identify high-risk PCNs.

METHODS

Pancreatic cystic fluid samples from 102 patients with PCNs were intraoperatively collected for detection of CIN using an ultrasensitive chromosomal aneuploidy detector. Clinical and imaging data were retrospectively collected, and statistical analysis was performed to assess the potential role of CIN in clinical practice.

RESULTS

CIN was investigated in a total of 100 patients. Sixteen of 26 serous cystic cystadenomas (SCAs) harbored deletions of chr3p and/or chr6p, whereas low rates of CIN were detected in mucinous cystic neoplasms. Most malignant PCNs presented with more than one type of CIN; amplification of chr1q and chr8q found in nine and seven of 11 malignant PCNs (81.8% and 63.6%), respectively, could aid in distinguishing high-risk IPMNs from low-risk ones, with a higher sensitivity than imaging. A combination of the mural nodule imaging feature and amplification of chr1q and chr8q achieved a sensitivity of 70.0% and a specificity of 82.4% in identifying high-risk IPMNs.

CONCLUSIONS

Our work revealed the distinct CIN signature of different types of PCNs. Deletions of chr3p and chr6p defined a subtype of SCAs. Gains of chr1q and chr8q were associated with insidious malignant PCNs and helped identify high-risk IPMNs.

Fisetin inhibits proliferation of pancreatic adenocarcinoma by inducing DNA damage via RFXAP/KDM4A-dependent histone H3K36 demethylation

Pancreatic adenocarcinoma (PDAC) is an extremely malignant tumor that is associated with low survival rates. Fisetin is a natural flavonoid that shows diverse antitumor effects, including DNA damage, in various cancers. Increasing studies have demonstrated that epigenetic modifications play critical roles in DNA-damage response. However, the epigenetic regulation mechanism of fisetin in cancers is hardly studied. RFXAP is a critical transcription factor for MHC II molecules, however, its transcriptional role in PDAC is poorly understood. The anti-PDAC effect of fisetin was measured by CCK-8, flow cytometry, xenograft tumor nude mice model. DNA-damage levels were examined by immunofluorescence. Bioinformatics analysis was used to examine the expression of RFXAP and other genes involved in DNA-damage response. ChIP sequencing was used to explore the transcriptional role of RFXAP. The expression of target gene KDM4A was measured by qRT-PCR and western blots. KDM4A promoter activity was analyzed using dual-luciferase reporter assay. RFXAP overexpressing or silencing of PDAC cells was used to explore the effect of RFXAP in DNA damage induced by fisetin. We found that fisetin inhibited cell proliferation and induced DNA damage and S-phase arrest in PDAC. Expression of RFXAP and other DNA-damage response genes were upregulated by fisetin. We revealed that RFXAP expression was relatively low in PDAC and correlated with tumor stage and poor prognosis. Then we explored the transcriptional role of RFXAP and found that RFXAP targeted KDM4A, a special demethylase specific for tri- and dimethylated histone H3K36. We found that overexpression of RFXAP upregulated KDM4A and attenuated methylation of H3K36, thereby impairing DNA repair and enhancing the DNA damage induced by fisetin, while RFXAP silencing showed the opposite effect. We also found the function of fisetin in enhancing the effect of chemotherapy on pancreatic cancer cells. Our findings revealed that fisetin induced DNA damage via RFXAP/KDM4A-dependent histone H3K36 demethylation, thus causing inhibition of proliferation in PDAC.

Hypovitaminosis D exacerbates the DNA damage load in human uterine fibroids, which is ameliorated by vitamin D3 treatment

Uterine fibroids (UFs) are the most common benign neoplastic threat to women's health and associated with DNA damage and genomic instability. Hypovitaminosis D is a known risk factor for UFs, especially among African Americans. Vitamin D3 has been shown to effectively inhibit UF phenotype, but its mechanisms remain unclear. We hypothesize that Vitamin D3 ameliorates UFs by recovering the damaged DNA repair system, thus inhibits tumor progression. We compared the DNA damage status and Vitamin D receptor (VDR) expression between normal myometrial and UF primary cells. Unrepaired DNA double-strand breaks (DSBs) accumulated but VDR expression decreased in UFs. The RNA and protein levels of key DNA repair members belonging to DNA DSB sensors (MRE11, NBS1, RAD50), mediators and effectors (CHECK2, BRCA1, RAD51) were downregulated in UFs compared with myometrial cells. VDR KD induced DSB accumulation and DNA damage response (DDR) defects in myometrial cells. Using the DNA damage PCR array, the expression of many additional DNA repair genes was downregulated in VDR KD cells. Treatment of UF cells with Vitamin D3 (100 nM) significantly decreased DNA damage and restored DDR concomitant with VDR induction. Notably, the PCR array demonstrated that among 75 downregulated genes after VDR KD, 67 (89.3%) were upregulated after vitamin D3 treatment. These studies demonstrate a novel link between DNA damage and the vitamin D3/VDR axis in UFs. Vitamin D3 suppresses the UF phenotype through orchestrated targeting at multiple molecules in DNA repair pathways, thus offering novel mechanistic insights into the clinical effectiveness of vitamin D3 on UFs.

BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were linked to genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Chronic low dose arsenic exposure preferentially perturbs mitotic phase of the cell cycle

Environmental pollution is a big challenge for human survival. Arsenic compounds are well-known biohazard, the exposure of which is closely linked to onsets of various human diseases, particularly cancers. Upon chronically exposing to arsenic compounds, genomic integrity is often disrupted, leading to tumor development. However, the underlying mechanisms by which chronic, low dose arsenic exposure targets genetic stability to initiate carcinogenesis still remain not fully understood. In this study, human lung epithelial BEAS-2B cells and keratinocytes were treated with 0.5 μM of sodium arsenite for one month (designated as BEAS-2B-SA cells or keratinocytes-SA), and its effect on cell cycle responses was analyzed. After being arrested in mitotic phase of the cell cycle by nocodazole treatment, BEAS-2B-SA cells or keratinocytes-SA were delayed to enter next cytokinesis. The lagging exit of the cells from mitosis was accompanied by a sustained Plk1 phosphorylation, which led to a persistent activation of the mitotic regulators BubR1 and Cdc27. As the result, cyclin B1 (clnB1) degradation was attenuated. BEAS-2B-SA cells or keratinocytes-SA also expressed a constitutively active Akt. The cytogenetic analysis showed an increased numbers of aneuploidy in these cells. The suppression of Akt reversed the aberrant expressions of the mitotic regulators, delay of mitotic exit as well as chromosomal aberrations. Our findings suggest that a long-term exposure to low dose sodium arsenite aberrantly retains the catenation of mitosis, which facilitates establishing genetic instability and predisposes the cells to tumorigenesis.

Germline Variants and Risk for Pancreatic Cancer: A Systematic Review and Emerging Concepts

Pancreatic cancer requires many genetic mutations. Combinations of underlying germline variants and environmental factors may increase the risk of cancer and accelerate the oncogenic process. We systematically reviewed, annotated, and classified previously reported pancreatic cancer-associated germline variants in established risk genes. Variants were scored using multiple criteria and binned by evidence for pathogenicity, then annotated with published functional studies and associated biological systems/pathways. Twenty-two previously identified pancreatic cancer risk genes and 337 germline variants were identified from 97 informative studies that met our inclusion criteria. Fifteen of these genes contained 66 variants predicted to be pathogenic (APC, ATM, BRCA1, BRCA2, CDKN2A, CFTR, CHEK2, MLH1, MSH2, NBN, PALB2, PALLD, PRSS1, SPINK1, TP53). Pancreatic cancer risk genes were organized into key biological mechanisms that promote pancreatic oncogenesis within an oncogenic model. Development of precision medicine approaches requires updated variant information within the framework of an oncogenic progression model. Complex risk modeling may improve interpretation of early biomarkers and guide pathway-specific treatment for pancreatic cancer in the future. Precision medicine is within reach.

Immunomodulatory Effectiveness of Fish Oil and omega-3 Fatty Acids in Human Non-melanoma Skin Carcinoma Cells

Fish oil is composed of various fatty acids among which omega-3 fatty acids are considered as most beneficial. The effects of fish oil on the activity of a topical anticancer drug, imiquimod, and the immunomodulatory activity of omega-3 fatty acids was investigated in human basal and squamous cell carcinoma cell lines. Imiquimod-fish oil mixture exhibited higher carcinoma cell growth inhibition and immunomodulatory activity than imiquimod alone, especially against squamous cell carcinoma cells. Omega-3 fatty acids exhibited growth inhibition of both basal cell and squamous cell carcinoma cell lines and modulated the immune response. Omega-3 fatty acids of fish oil serve as inducers of interleukin-10, an anti-inflammatory cytokine, and as suppressors of interleukin-6 and tumor necrosis factor-alpha, which not only depress tumor growth but also adequately control the inflammatory side effects of imiquimod. Thus, imiquimod administration with fish oil could be beneficial for inhibition of non-melanoma skin carcinoma cells but further in vivo studies are needed to understand their role in skin cancer.

Disruption of Mitotic Progression by Arsenic

Arsenic is an enigmatic xenobiotic that causes a multitude of chronic diseases including cancer and also is a therapeutic with promise in cancer treatment. Arsenic causes mitotic delay and induces aneuploidy in diploid human cells. In contrast, arsenic causes mitotic arrest followed by an apoptotic death in a multitude of virally transformed cells and cancer cells. We have explored the hypothesis that these differential effects of arsenic exposure are related by arsenic disruption of mitosis and are differentiated by the target cell's ability to regulate or modify cell cycle checkpoints. Functional p53/CDKN1A axis has been shown to mitigate the mitotic block and to be essential to induction of aneuploidy. More recent preliminary data suggest that microRNA modulation of chromatid cohesion also may play a role in escape from mitotic block and in generation of chromosomal instability. Other recent studies suggest that arsenic may be useful in treatment of solid tumors when used in combination with other cytotoxic agents such as cisplatin.

The emerging role of lysine demethylases in DNA damage response: dissecting the recruitment mode of KDM4D/JMJD2D to DNA damage sites

KDM4D is a lysine demethylase that removes tri- and di- methylated residues from H3K9 and is involved in transcriptional regulation and carcinogenesis. We recently showed that KDM4D is recruited to DNA damage sites in a PARP1-dependent manner and facilitates double-strand break repair in human cells. Moreover, we demonstrated that KDM4D is an RNA binding protein and mapped its RNA-binding motifs. Interestingly, KDM4D-RNA interaction is essential for its localization on chromatin and subsequently for efficient demethylation of its histone substrate H3K9me3. Here, we provide new data that shed mechanistic insights into KDM4D accumulation at DNA damage sites. We show for the first time that KDM4D binds poly(ADP-ribose) (PAR) in vitro via its C-terminal region. In addition, we demonstrate that KDM4D-RNA interaction is required for KDM4D accumulation at DNA breakage sites. Finally, we discuss the recruitment mode and the biological functions of additional lysine demethylases including KDM4B, KDM5B, JMJD1C, and LSD1 in DNA damage response.

A historical perspective of pancreatic cancer mouse models

Pancreatic cancer is an inherently aggressive disease with an extremely poor prognosis and lack of effective treatments. Over the past few decades, much has been uncovered regarding the pathogenesis of pancreatic cancer and the underlying genetic alterations necessary for tumour initiation and progression. Much of what we know about pancreatic cancer has come from mouse models of this disease. This review focusses on the development of genetically engineered mouse models that phenotypically and genetically recapitulate human pancreatic cancer, as well as the increasing use of patient-derived xenografts for preclinical studies and the development of personalised medicine strategies.

Chromosome instability and carcinogenesis: insights from murine models of human pancreatic cancer associated with BRCA2 inactivation

Chromosomal instability is a hallmark of human cancer cells, but its role in carcinogenesis remains poorly resolved. Insights into this role have emerged from studies on the tumour suppressor BRCA2, whose inactivation in human cancers causes chromosomal instability through the loss of essential functions of the BRCA2 protein in the normal mechanisms responsible for the replication, repair and segregation of DNA during cell division. Humans who carry heterozygous germline mutations in the BRCA2 gene are highly predisposed to cancers of the breast, ovary, pancreas, prostate and other tissues. Here, we review recent studies that describe genetically engineered mouse models (GEMMs) for pancreatic cancer associated with BRCA2 mutations. These studies not only surprisingly show that BRCA2 does not follow the classical Knudson "two hit" paradigm for tumour suppression, but also highlight features of the interplay between TP53 inactivation and carcinogenesis in the context of BRCA2 deficiency. Thus, the models reveal novel aspects of cancer evolution in carriers of germline BRCA2 mutations, provide new insights into the tumour suppressive role of BRCA2, and establish valuable new preclinical settings for testing approaches to pancreatic cancer therapy; together, these features emphasize the value of GEMMs in cancer research.