Genome and transcriptome sequencing of lung cancers reveal diverse mutational and splicing events

A review on trends in development and translation of omics signatures in cancer

The field of cancer genomics and transcriptomics has evolved from targeted profiling to swift sequencing of individual tumor genome and transcriptome. The steady growth in genome, epigenome, and transcriptome datasets on a genome-wide scale has significantly increased our capability in capturing signatures that represent both the intrinsic and extrinsic biological features of tumors. These biological differences can help in precise molecular subtyping of cancer, predicting tumor progression, metastatic potential, and resistance to therapeutic agents. In this review, we summarized the current development of genomic, methylomic, transcriptomic, proteomic and metabolic signatures in the field of cancer research and highlighted their potentials in clinical applications to improve diagnosis, prognosis, and treatment decision in cancer patients.

CCL22 mutations in large granular lymphocytic leukemia

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PrimPol Variant V102A with Altered Primase and Polymerase Activities

PrimPol is a human DNA primase-polymerase which restarts DNA synthesis beyond DNA lesions and non-B DNA structures blocking replication. Disfunction of PrimPol in cells leads to slowing of DNA replication rates in mitochondria and nucleus, accumulation of chromosome aberrations, cell cycle delay, and elevated sensitivity to DNA-damaging agents. A defective PrimPol has been suggested to be associated with the development of ophthalmic diseases, elevated mitochondrial toxicity of antiviral drugs and increased cell resistance to chemotherapy. Here, we describe a rare missense PrimPol variant V102A with altered biochemical properties identified in patients suffering from ovarian and cervical cancer. The Val102 to Ala substitution dramatically reduced both the primase and DNA polymerase activities of PrimPol as well as specifically decreased its ability to incorporate ribonucleotides. Structural analysis indicates that the V102A substitution can destabilize the hydrophobic pocket adjacent to the active site, affecting dNTP binding and catalysis.

Response of PRIMPOL-Knockout Human Lung Adenocarcinoma A549 Cells to Genotoxic Stress

Human DNA primase/polymerase PrimPol synthesizes DNA primers de novo after replication fork stalling at the sites of DNA damage, thus contributing to the DNA damage tolerance. The role of PrimPol in response to the different types of DNA damage is poorly understood. We knocked out the PRIMPOL gene in the lung carcinoma A549 cell line and characterized the response of the obtained cells to the DNA damage caused by hydrogen peroxide, methyl methanesulfonate (MMS), cisplatin, bleomycin, and ionizing radiation. The PRIMPOL knockout reduced the number of proliferating cells and cells in the G2 phase after treatment with MMS and caused a more pronounced delay of the S phase in the cisplatin-treated cells. Ionizing radiation at a dose of 10 Gy significantly increased the content of apoptotic cells among the PRIMPOL-deficient cells, while the proportion of cells undergoing necroptosis increased in both parental and knockout cells at any radiation dose. The viability of PRIMPOL-deficient cells upon the hydrogen peroxide-induced oxidative stress increased compared to the control cells, as determined by the methyl tetrazolium (MTT) assay. The obtained data indicate the involvement of PRIMPOL in the modulation of adaptive cell response to various types of genotoxic stress.

The ASH1L-AS1-ASH1L axis controls NME1-mediated activation of the RAS signaling in gastric cancer

Gastric cancer (GC) is one of the most leading cause of malignancies. However, the molecular mechanisms underlying stomach carcinogenesis remain incompletely understood. Dysregulated genetic and epigenetic alternations significantly contribute to GC development. Here, we report that ASH1L and its antisense lncRNA ASH1L-AS1, which are transcribed from the most significant GC-risk signal at 1q22, act as novel oncogenes. The high levels of ASH1L or lncRNA ASH1L-AS1 expression in GC specimens are associated with worse prognosis of patients. In line with this, ASH1L and ASH1L-AS1 are functionally important in promoting GC disease progression. LncRNA ASH1L-AS1 up-regulates ASH1L transcription, increases histone methyltransferase ASH1L expression and elevates genome-wide H3K4me3 modification levels in GC cells. Furthermore, ASH1L-AS1 directly interacts with transcription factor NME1 protein to form the ASH1L-AS1-NME1 ribonucleoprotein, which transcriptionally promotes expression of ASH1L, ASH1L-AS1, KRAS and RAF1, and activates the RAS signaling pathway in GC cells. Taken together, our data demonstrated that the ASH1L-AS1-ASH1L regulatory axis controls histone modification reprogram and activation of the RAS signaling in cancers. Thus, ASH1L-AS1 might be a novel targets of GC therapeutics and diagnosis in the clinic.

Case report: Heterogenous SMARCA4-deficient thoracic non-small cell lung carcinoma with various responses to nivolumab

SMARCA4-deficient non-small cell carcinoma is an aggressive neoplasm with poor outcome. Several studies have highlighted its immunochemistry, pathophysiology, and underlying mechanisms, but studies of its definite treatment are few. Here, we report on a 69-year-old male with heterogenous pathological presentations of SMARCA4-deficient non-small cell carcinoma. He initially presented with neck lymphadenopathies. Immunohistochemistry staining and genomic profiling confirmed the diagnosis of SMARCA4-deficient non-small cell carcinoma. The patient responded well to immune checkpoint inhibitors with nivolumab. However, new lesions with various pathological presentations and various responses to nivolumab appeared during the treatment course. The patient survived more than 3 years from the initial diagnosis. This case shows the efficacy of nivolumab to treat SMARCA4-deficient non-small cell lung carcinoma.

Uncovering novel mutational signatures by de novo extraction with SigProfilerExtractor

Mutational signature analysis is commonly performed in cancer genomic studies. Here, we present SigProfilerExtractor, an automated tool for de novo extraction of mutational signatures, and benchmark it against another 13 bioinformatics tools by using 34 scenarios encompassing 2,500 simulated signatures found in 60,000 synthetic genomes and 20,000 synthetic exomes. For simulations with 5% noise, reflecting high-quality datasets, SigProfilerExtractor outperforms other approaches by elucidating between 20% and 50% more true-positive signatures while yielding 5-fold less false-positive signatures. Applying SigProfilerExtractor to 4,643 whole-genome- and 19,184 whole-exome-sequenced cancers reveals four novel signatures. Two of the signatures are confirmed in independent cohorts, and one of these signatures is associated with tobacco smoking. In summary, this report provides a reference tool for analysis of mutational signatures, a comprehensive benchmarking of bioinformatics tools for extracting signatures, and several novel mutational signatures, including one putatively attributed to direct tobacco smoking mutagenesis in bladder tissues.

Analysis of genetic profiling, pathomics signature, and prognostic features of primary lymphoepithelioma‐like carcinoma of the renal pelvis

The genetic features of primary lymphoepithelioma‐like carcinoma (LELC) of the upper urinary tract have not been systematically explored. In this study, tumor mutation profiling was performed using whole‐genome sequencing in two patients with LELC of the renal pelvis. Novel candidate variants relevant to known disease genes were selected using rare‐variant burden analysis. Subsequently, a population‐based study was performed using the Surveillance, Epidemiology, and End Results (SEER), PubMed, MEDLINE, Embase, and Scopus databases to explore clinical features and prognostic risk factors. Immunohistochemical analysis revealed seven positive cytokeratin‐associated markers in tumor cells and five positive lymphocyte‐associated markers in and around the tumor area. Sub‐sequently, we identified KDM6A as the susceptibility gene and LEPR as the driver gene by Sanger sequencing in case 2 of LELC of the renal pelvis. Three mutation sites of the existing targeted drugs were screened: CA9, a therapeutic target for zonisamide; ARVCF, a therapeutic target for bupropion; and PLOD3, a therapeutic target for vitamin C. In a population‐based study, patients with primary LELC of the upper urinary tract had clinical outcomes similar to those of patients with primary upper urinary tract urothelial carcinoma (UUT‐UC) before and after propensity score matching at 1 : 5. Focal subtype was an independent prognostic factor for the overall survival of patients with LELC of the upper urinary tract. The carcinogenesis of primary LELC may be due to different genetic variations, including single‐nucleotide variants, insertion and deletions, structural variations, and repeat regions, which may provide the basis for clinical diagnosis and treatment. The prognosis of LELC in the upper urinary tract is similar to that of UUT‐UC. We suggest that the focal subtype can serve as a prognostic factor for LELC of the upper urinary tract; however, further studies are required to confirm this.

Modulation of DNA Damage Response by SAM and HD Domain Containing Deoxynucleoside Triphosphate Triphosphohydrolase (SAMHD1) Determines Prognosis and Treatment Efficacy in Different Solid Tumor Types

SAMHD1 is a deoxynucleotide triphosphate (dNTP) triphosphohydrolase with important roles in the control of cell proliferation and apoptosis, either through the regulation of intracellular dNTPs levels or the modulation of the DNA damage response. However, SAMHD1's role in cancer evolution is still unknown. We performed the first in-depth study of SAMHD1's role in advanced solid tumors, by analyzing samples of 128 patients treated with chemotherapy agents based on platinum derivatives and/or antimetabolites, developing novel in vitro knock-out models to explore the mechanisms driving SAMHD1 function in cancer. Low (or no) expression of SAMHD1 was associated with a positive prognosis in breast, ovarian, and non-small cell lung cancer (NSCLC) cancer patients. A predictive value was associated with low-SAMHD1 expression in NSCLC and ovarian patients treated with antimetabolites in combination with platinum derivatives. In vitro, SAMHD1 knock-out cells showed increased γ-H2AX and apoptosis, suggesting that SAMHD1 depletion induces DNA damage leading to cell death. In vitro treatment with platinum-derived drugs significantly enhanced γ-H2AX and apoptotic markers expression in knock-out cells, indicating a synergic effect of SAMHD1 depletion and platinum-based treatment. SAMHD1 expression represents a new strong prognostic and predictive biomarker in solid tumors and, thus, modulation of the SAMHD1 function may constitute a promising target for the improvement of cancer therapy.

HIF-1-Independent Mechanisms Regulating Metabolic Adaptation in Hypoxic Cancer Cells

In solid tumours, cancer cells exist within hypoxic microenvironments, and their metabolic adaptation to this hypoxia is driven by HIF-1 transcription factor, which is overexpressed in a broad range of human cancers. HIF inhibitors are under pre-clinical investigation and clinical trials, but there is evidence that hypoxic cancer cells can adapt metabolically to HIF-1 inhibition, which would provide a potential route for drug resistance. Here, we review accumulating evidence of such adaptions in carbohydrate and creatine metabolism and other HIF-1-independent mechanisms that might allow cancers to survive hypoxia despite anti-HIF-1 therapy. These include pathways in glucose, glutamine, and lipid metabolism; epigenetic mechanisms; post-translational protein modifications; spatial reorganization of enzymes; signalling pathways such as Myc, PI3K-Akt, 2-hyxdroxyglutarate and AMP-activated protein kinase (AMPK); and activation of the HIF-2 pathway. All of these should be investigated in future work on hypoxia bypass mechanisms in anti-HIF-1 cancer therapy. In principle, agents targeted toward HIF-1β rather than HIF-1α might be advantageous, as both HIF-1 and HIF-2 require HIF-1β for activation. However, HIF-1β is also the aryl hydrocarbon nuclear transporter (ARNT), which has functions in many tissues, so off-target effects should be expected. In general, cancer therapy by HIF inhibition will need careful attention to potential resistance mechanisms.

Repriming DNA synthesis: an intrinsic restart pathway that maintains efficient genome replication

To bypass a diverse range of fork stalling impediments encountered during genome replication, cells possess a variety of DNA damage tolerance (DDT) mechanisms including translesion synthesis, template switching, and fork reversal. These pathways function to bypass obstacles and allow efficient DNA synthesis to be maintained. In addition, lagging strand obstacles can also be circumvented by downstream priming during Okazaki fragment generation, leaving gaps to be filled post-replication. Whether repriming occurs on the leading strand has been intensely debated over the past half-century. Early studies indicated that both DNA strands were synthesised discontinuously. Although later studies suggested that leading strand synthesis was continuous, leading to the preferred semi-discontinuous replication model. However, more recently it has been established that replicative primases can perform leading strand repriming in prokaryotes. An analogous fork restart mechanism has also been identified in most eukaryotes, which possess a specialist primase called PrimPol that conducts repriming downstream of stalling lesions and structures. PrimPol also plays a more general role in maintaining efficient fork progression. Here, we review and discuss the historical evidence and recent discoveries that substantiate repriming as an intrinsic replication restart pathway for maintaining efficient genome duplication across all domains of life.

SUVA: splicing site usage variation analysis from RNA-seq data reveals highly conserved complex splicing biomarkers in liver cancer

Most of the current alternative splicing (AS) analysis tools are powerless to analyse complex splicing. To address this, we developed SUVA (Splice sites Usage Variation Analysis) that decomposes complex splicing events into five types of splice junction pairs. By analysing real and simulated data, SUVA showed higher sensitivity and accuracy in detecting AS events than the compared methods. Notably, SUVA detected extensive complex AS events and screened out 69 highly conserved and dominant AS events associated with cancer. The cancer-associated complex AS events in FN1 and the co-regulated RNA-binding proteins were significantly correlated with patient survival.

Next-generation sequencing-based identification of EGFR and NOTCH2 complementary mutations in non-small cell lung cancer

Although targeted therapy has emerged as an effective treatment strategy for non-small cell lung cancer (NSCLC), some patients cannot benefit from such therapy due to the limited number of therapeutic targets. The present study aimed to identify mutated genes associated with clinicopathological characteristics and prognosis and to screen for mutations that are not concurrent with applicable drug target sites in patients with NSCLC. Tumor tissue and blood samples were obtained from 97 patients with NSCLC. A lung cancer-specific panel of 55 genes was established and analyzed using next-generation sequencing (NGS). The results obtained from the clinical cohort were compared with the NSCLC dataset from The Cancer Genome Atlas (TCGA). Subsequently, 25 driver genes were identified by taking the intersection of the 55 lung-cancer-specific genes with three databases, namely, the Catalog of Somatic Mutations in Cancer database, the Network of Cancer Genes database and Vogelstein's list. Functional annotation and protein-protein interaction analysis were conducted on these 25 driver genes. The χ² test and logistic regression were used to evaluate the association between mutations in the 25 driver genes and the clinicopathological characteristics of 97 patients, and phosphatase and tensin homolog (PTEN) and kirsten rat sarcoma viral oncogene homolog (KRAS) were associated with stage at diagnosis and sex, respectively, while epidermal growth factor receptor (EGFR) was associated with sex, stage at diagnosis, metastasis, CEA and CYFRA21-1. Moreover, the association between the 25 driver gene mutations and overall survival were examined using Cox regression analysis. Age and Notch homolog 2 (NOTCH2) mutations were independent prognostic factors in TCGA dataset. The correlations between statistically significant mutations in EGFR, KRAS, PTEN and NOTCH2 were further examined, both in the clinical data and TCGA dataset. There was a negative correlation between EGFR and NOTCH2 mutations (correlation coefficient, −0.078; P=0.027). Thus, the present study highlights the importance of NOTCH2 mutations and might provide novel therapeutic options for patients with NSCLC who do not harbor EGFR mutations.

Significance of KDM6A mutation in bladder cancer immune escape

Background

Bladder cancer (BC) is the fourth most prevalent neoplasm in men and is associated with high tumour recurrence rates, leading to major treatment challenges. Lysine-specific demethylase 6A (KDM6A) is frequently mutated in several cancer types; however, its effects on tumour progression and clinical outcome in BC remain unclear. Here, we explored the potential role of KDM6A in regulating the antitumor immune response.

Methods

We mined The Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC) databases for somatic mutation and clinical data in patients with BC.

Results

We found frequent mutations in 12 genes in both cohorts, including TP53, KDM6A, CSMD3, MUC16, STAG2, PIK3CA, ARID1A, RB1, EP300, ERBB2, ERBB3, and FGFR3. The frequency o KDM6A mutations in the TCGA and ICGC datasets was 25.97 and 24.27%, respectively. In addition, KDM6A mutation was associated with a lower number of tumour-infiltrating immune cells (TIICs) and indicated a state of immune tolerance. KDM6A mutation was associated with lower KDM6A mRNA level compared with that in samples carrying the wild-type gene. Further, survival analysis showed that the prognosis of patients with low KDM6A expression was worse than that with high KDM6A expression. Using the CIBERSORT algorithm, Tumor Immune Estimation Resource site, and Gene Set Enrichment Analysis, we found that KDM6A mutation downregulated nine signalling pathways that participate in the immune system and attenuated the tumour immune response.

Conclusion

Overall, we conclude that KDM6A mutation is frequent in BC and promotes tumour immune escape, which may serve as a novel biomarker to predict the immune response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08372-9.

Biology of the mRNA Splicing Machinery and Its Dysregulation in Cancer Providing Therapeutic Opportunities

Dysregulation of messenger RNA (mRNA) processing—in particular mRNA splicing—is a hallmark of cancer. Compared to normal cells, cancer cells frequently present aberrant mRNA splicing, which promotes cancer progression and treatment resistance. This hallmark provides opportunities for developing new targeted cancer treatments. Splicing of precursor mRNA into mature mRNA is executed by a dynamic complex of proteins and small RNAs called the spliceosome. Spliceosomes are part of the supraspliceosome, a macromolecular structure where all co-transcriptional mRNA processing activities in the cell nucleus are coordinated. Here we review the biology of the mRNA splicing machinery in the context of other mRNA processing activities in the supraspliceosome and present current knowledge of its dysregulation in lung cancer. In addition, we review investigations to discover therapeutic targets in the spliceosome and give an overview of inhibitors and modulators of the mRNA splicing process identified so far. Together, this provides insight into the value of targeting the spliceosome as a possible new treatment for lung cancer.

Integrative reconstruction of cancer genome karyotypes using InfoGenomeR

Annotation of structural variations (SVs) and base-level karyotyping in cancer cells remains challenging. Here, we present Integrative Framework for Genome Reconstruction (InfoGenomeR)-a graph-based framework that can reconstruct individual SVs into karyotypes based on whole-genome sequencing data, by integrating SVs, total copy number alterations, allele-specific copy numbers, and haplotype information. Using whole-genome sequencing data sets of patients with breast cancer, glioblastoma multiforme, and ovarian cancer, we demonstrate the analytical potential of InfoGenomeR. We identify recurrent derivative chromosomes derived from chromosomes 11 and 17 in breast cancer samples, with homogeneously staining regions for CCND1 and ERBB2, and double minutes and breakage-fusion-bridge cycles in glioblastoma multiforme and ovarian cancer samples, respectively. Moreover, we show that InfoGenomeR can discriminate private and shared SVs between primary and metastatic cancer sites that could contribute to tumour evolution. These findings indicate that InfoGenomeR can guide targeted therapies by unravelling cancer-specific SVs on a genome-wide scale.

Cyclin-dependent kinase inhibitors in head and neck cancer and glioblastoma-backbone or add-on in immune-oncology?

Cyclin-dependent kinases (CDK) control the cell cycle and play a crucial role in oncogenesis. Pharmacologic inhibition of CDK has contributed to the recent clinical approval of dual CDK4/6 inhibitors for the treatment of breast and small cell lung cancer. While the anticancer cell effects of CDK inhibitors are well-established, preclinical and early clinical studies describe additional mechanisms of action such as chemo- and radiosensitization or immune stimulation. The latter offers great potential to incorporate CDK inhibitors in immune-based treatments. However, dosing schedules and accurate timing of each combination partner need to be respected to prevent immune escape and resistance. In this review, we provide a detailed summary of CDK inhibitors in the two solid cancer types head and neck cancer and glioblastoma multiforme; it describes the molecular mechanisms of response vs. resistance and covers strategies to avoid resistance by the combination of immunotherapy or targeted therapy.

RWSF-BLP: a novel lncRNA-disease association prediction model using random walk-based multi-similarity fusion and bidirectional label propagation

An increasing number of studies and experiments have demonstrated that long noncoding RNAs (lncRNAs) have a massive impact on various biological processes. Predicting potential associations between lncRNAs and diseases not only can improve our understanding of the molecular mechanisms of human diseases but also can facilitate the identification of biomarkers for disease diagnosis, treatment, and prevention. However, identifying such associations through experiments is costly and demanding, thereby prompting researchers to develop computational methods to complement these experiments. In this paper, we constructed a novel model called RWSF-BLP (a novel lncRNA-disease association prediction model using Random Walk-based multi-Similarity Fusion and Bidirectional Label Propagation), which applies an efficient random walk-based multi-similarity fusion (RWSF) method to fuse different similarity matrices and utilizes bidirectional label propagation to predict potential lncRNA-disease associations. Leave-one-out cross-validation (LOOCV) and 5-fold cross-validation (5-fold-CV) were implemented in the evaluation RWSF-BLP performance. Results showed that, RWSF-BLP has reliable AUCs of 0.9086 and 0.9115 ± 0.0044 under the framework of LOOCV and 5-fold-CV and outperformed other four canonical methods. Case studies on lung cancer and leukemia demonstrated that potential lncRNA-disease associations can be predicted through our method. Therefore, our method can accurately infer potential lncRNA-disease associations and may be a good choice in future biomedical research.

Translesion DNA Synthesis and Reinitiation of DNA Synthesis in Chemotherapy Resistance

Many chemotherapy drugs block tumor cell division by damaging DNA. DNA polymerases eta (Pol η), iota (Pol ι), kappa (Pol κ), REV1 of the Y-family and zeta (Pol ζ) of the B-family efficiently incorporate nucleotides opposite a number of DNA lesions during translesion DNA synthesis. Primase-polymerase PrimPol and the Pol α-primase complex reinitiate DNA synthesis downstream of the damaged sites using their DNA primase activity. These enzymes can decrease the efficacy of chemotherapy drugs, contribute to the survival of tumor cells and to the progression of malignant diseases. DNA polymerases are promising targets for increasing the effectiveness of chemotherapy, and mutations and polymorphisms in some DNA polymerases can serve as additional prognostic markers in a number of oncological disorders.

SMARCA4/BRG1-Deficient Non-Small Cell Lung Carcinomas: A Case Series and Review of the Literature

CONTEXT.—

Somatic mutations in SMARCA4 (SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 4) gene and/or BRG1 (Brahma-related gene 1) loss identifies a subset of non-small cell lung carcinomas (NSCLCs) lacking alterations in EGFR (epidermal growth factor receptor), ALK (anaplastic lymphoma kinase), and ROS1 (ROS proto-oncogene 1) genes. Preliminary observations suggest responsiveness to immunotherapy and targeted therapies.

OBJECTIVE.—

To study BRG1 loss in NSCLCs and elucidate the clinicopathologic profile of such SMARCA4-deficient NSCLCs.

DESIGN.—

Non-small cell lung carcinomas diagnosed during 6 years were subject to immunohistochemistry for BRG1 and BRM (Brahma). Tumors with BRG1 loss were stained with antibodies against thyroid transcription factor 1 (TTF-1), p40, cytokeratins, hepatocyte paraffin 1 (Hep Par 1), Sal-like protein 4 (SALL4), CD34, SRY-box 2 (SOX2), chromogranin, synaptophysin, p53, integrase interactor 1, ALK, and ROS1. EGFR mutation testing was performed by polymerase chain reaction-based method.

RESULTS.—

Among 100 NSCLCs tested, 4 cases (4%) showed BRG1 loss. The histology ranged from solid adenocarcinomas (n = 1) to large cell/poorly differentiated carcinomas (n = 3) with clear cell cytology in 2 cases. All showed loss/reduction of BRM with variable cytokeratin and SALL4 expression, and were negative for TTF-1, p40, Hep Par 1, ALK, ROS1, and EGFR mutations. CD34 and SOX2 were negative in all 4 cases. Isolated BRM loss was common (21%), distributed across all NSCLC subtypes including squamous cell carcinomas and a hepatoid adenocarcinoma.

CONCLUSIONS.—

BRG1 loss occurs in a subset of TTF-1/p40-negative poorly differentiated NSCLCs. Identification and follow-up will clarify the prognosis, diagnostic criteria, and potential for therapeutic personalization.

Combined blockade of polo-like kinase and pan-RAF is effective against NRAS-mutant non-small cell lung cancer cells

NRAS mutation is rarely observed in non-small cell lung cancer (NSCLC) patients, and there are no approved treatments for NRAS-mutant NSCLC. Here, we evaluated the effect of pan-RAF inhibitors on human NRAS-mutant NSCLC cell lines and performed high-throughput screening using human kinome small interfering (si)RNA or CRISPR/Cas9 libraries to identify new targets for combination NSCLC treatment. Our results indicate that human NRAS-mutant NSCLC cells are moderately sensitive to pan-RAF inhibitors. High-throughput kinome screenings further showed that G2/M arrest, particularly following knockdown of polo-like kinase 1 (PLK1), can inhibit the growth of human NRAS-mutant NSCLC cells and those treated with the type II pan-RAF inhibitor LXH254. In addition, treatment with volasertib plus LXH254, resulting in dual blockade of PLK1 and pan-RAF, was found to be more effective than LXH254 monotherapy for inhibiting long-term cell viability, suggesting that this combination therapeutic strategy may lead to promising results in the clinic.

Denoising Autoencoder, A Deep Learning Algorithm, Aids the Identification of A Novel Molecular Signature of Lung Adenocarcinoma

Precise biomarker development is a key step in disease management. However, most of the published biomarkers were derived from a relatively small number of samples with supervised approaches. Recent advances in unsupervised machine learning promise to leverage very large datasets for making better predictions of disease biomarkers. Denoising autoencoder (DA) is one of the unsupervised deep learning algorithms, which is a stochastic version of autoencoder techniques. The principle of DA is to force the hidden layer of autoencoder to capture more robust features by reconstructing a clean input from a corrupted one. Here, a DA model was applied to analyze integrated transcriptomic data from 13 published lung cancer studies, which consisted of 1916 human lung tissue samples. Using DA, we discovered a molecular signature composed of multiple genes for lung adenocarcinoma (ADC). In independent validation cohorts, the proposed molecular signature is proved to be an effective classifier for lung cancer histological subtypes. Also, this signature successfully predicts clinical outcome in lung ADC, which is independent of traditional prognostic factors. More importantly, this signature exhibits a superior prognostic power compared with the other published prognostic genes. Our study suggests that unsupervised learning is helpful for biomarker development in the era of precision medicine.

Evolution from adherent to suspension: systems biology of HEK293 cell line development

The need for new safe and efficacious therapies has led to an increased focus on biologics produced in mammalian cells. The human cell line HEK293 has bio-synthetic potential for human-like production attributes and is currently used for manufacturing of several therapeutic proteins and viral vectors. Despite the increased popularity of this strain we still have limited knowledge on the genetic composition of its derivatives. Here we present a genomic, transcriptomic and metabolic gene analysis of six of the most widely used HEK293 cell lines. Changes in gene copy and expression between industrial progeny cell lines and the original HEK293 were associated with cellular component organization, cell motility and cell adhesion. Changes in gene expression between adherent and suspension derivatives highlighted switching in cholesterol biosynthesis and expression of five key genes (RARG, ID1, ZIC1, LOX and DHRS3), a pattern validated in 63 human adherent or suspension cell lines of other origin.

Framework for quality assessment of whole genome cancer sequences

Bringing together cancer genomes from different projects increases power and allows the investigation of pan-cancer, molecular mechanisms. However, working with whole genomes sequenced over several years in different sequencing centres requires a framework to compare the quality of these sequences. We used the Pan-Cancer Analysis of Whole Genomes cohort as a test case to construct such a framework. This cohort contains whole cancer genomes of 2832 donors from 18 sequencing centres. We developed a non-redundant set of five quality control (QC) measurements to establish a star rating system. These QC measures reflect known differences in sequencing protocol and provide a guide to downstream analyses and allow for exclusion of samples of poor quality. We have found that this is an effective framework of quality measures. The implementation of the framework is available at: https://dockstore.org/containers/quay.io/jwerner_dkfz/pancanqc:1.2.2.

Working with cancer genomes from multiple projects can increase investigative power, but quality of sequences can vary. Here, the authors present a framework for comparing whole genome sequencing quality to help researchers guide downstream analyses and exclude poor quality samples.

A functional network of gastric-cancer-associated splicing events controlled by dysregulated splicing factors

Comprehensive understanding of aberrant splicing in gastric cancer is lacking. We RNA-sequenced 19 gastric tumor–normal pairs and identified 118 high-confidence tumor-associated (TA) alternative splicing events (ASEs) based on high-coverage sequencing and stringent filtering, and also identified 8 differentially expressed splicing factors (SFs). The TA ASEs occurred in genes primarily involved in cytoskeletal organization. We constructed a correlative network between TA ASE splicing ratios and SF expression, replicated it in independent gastric cancer data from The Cancer Genome Atlas and experimentally validated it by knockdown of the nodal SFs (PTBP1, ESRP2 and MBNL1). Each SF knockdown drove splicing alterations in several corresponding TA ASEs and led to alterations in cellular migration consistent with the role of TA ASEs in cytoskeletal organization. We have therefore established a robust network of dysregulated splicing associated with tumor invasion in gastric cancer. Our work is a resource for identifying oncogenic splice forms, SFs and splicing-generated tumor antigens as biomarkers and therapeutic targets.

Involvement of SAMHD1 in dNTP homeostasis and the maintenance of genomic integrity and oncotherapy (Review)

Sterile alpha motif and histidine/aspartic acid domain‑containing protein 1 (SAMHD1), the only deoxynucleotide triphosphate (dNTP) hydrolase in eukaryotes, plays a crucial role in regulating the dynamic balance and ratio of cellular dNTP pools. Furthermore, SAMHD1 has been reported to be involved in the pathological process of several diseases. Homozygous SAMHD1 mutations have been identified in immune system disorders, such as autoimmune disease Aicardi‑Goutières syndrome (AGS), whose primary pathogenesis is associated with the abnormal accumulation and disproportion of dNTPs. SAMHD1 is also considered to be an intrinsic virus‑restriction factor by suppressing the viral infection process, including reverse transcription, replication, packaging and transmission. In addition, SAMHD1 has been shown to promote genome integrity during homologous recombination following DNA damage, thus being considered a promising candidate for oncotherapy applications. The present review summarizes the molecular mechanisms of SAMHD1 regarding the regulation of dNTP homeostasis and DNA damage response. Additionally, its potential effects on tumorigenesis and oncotherapy are reported.

Bioinformatics Analysis of Gene Expression Profiles for Risk Prediction in Patients with Septic Shock

Background

Septic shock occurs when sepsis is associated with critically low blood pressure, and has a high mortality rate. This study aimed to undertake a bioinformatics analysis of gene expression profiles for risk prediction in septic shock.

Material/Methods

Two good quality datasets associated with septic shock were downloaded from the Gene Expression Omnibus (GEO) database, GSE64457 and GSE57065. Patients with septic shock had both sepsis and hypotension, and a normal control group was included. The differentially expressed genes (DEGs) were identified using OmicShare tools based on R. Functional enrichment of DEGs was analyzed using DAVID. The protein-protein interaction (PPI) network was established using STRING. Survival curves of key genes were constructed using GraphPad Prism version 7.0. Each putative central gene was analyzed by receiver operating characteristic (ROC) curves using MedCalc statistical software.

Results

GSE64457 and GSE57065 included 130 RNA samples derived from whole blood from 97 patients with septic shock and 33 healthy volunteers to obtain 975 DEGs, 455 of which were significantly down-regulated and 520 were significantly upregulated (P<0.05). Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis identified significantly enriched DEGs in four signaling pathways, MAPK, TNF, HIF-1, and insulin. Six genes, WDR82, ASH1L, NCOA1, TPR, SF1, and CREBBP in the center of the PPI network were associated with septic shock, according to survival curve and ROC analysis.

Conclusions

Bioinformatics analysis of gene expression profiles identified four signaling pathways and six genes, potentially representing molecular mechanisms for the occurrence, progression, and risk prediction in septic shock.

Purine-Metabolising Enzymes and Apoptosis in Cancer

The enzymes of both de novo and salvage pathways for purine nucleotide synthesis are regulated to meet the demand of nucleic acid precursors during proliferation. Among them, the salvage pathway enzymes seem to play the key role in replenishing the purine pool in dividing and tumour cells that require a greater amount of nucleotides. An imbalance in the purine pools is fundamental not only for preventing cell proliferation, but also, in many cases, to promote apoptosis. It is known that tumour cells harbour several mutations that might lead to defective apoptosis-inducing pathways, and this is probably at the basis of the initial expansion of the population of neoplastic cells. Therefore, knowledge of the molecular mechanisms that lead to apoptosis of tumoural cells is key to predicting the possible success of a drug treatment and planning more effective and focused therapies. In this review, we describe how the modulation of enzymes involved in purine metabolism in tumour cells may affect the apoptotic programme. The enzymes discussed are: ectosolic and cytosolic 5'-nucleotidases, purine nucleoside phosphorylase, adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase, and inosine-5'-monophosphate dehydrogenase, as well as recently described enzymes particularly expressed in tumour cells, such as deoxynucleoside triphosphate triphosphohydrolase and 7,8-dihydro-8-oxoguanine triphosphatase.

Epigenetic Metalloenzymes

Epigenetics controls the expression of genes and is responsible for cellular phenotypes. The fundamental basis of these mechanisms involves in part the post-translational modifications (PTMs) of DNA and proteins, in particular, the nuclear histones. DNA can be methylated or demethylated on cytosine. Histones are marked by several modifications including acetylation and/or methylation, and of particular importance are the covalent modifications of lysine. There exists a balance between addition and removal of these PTMs, leading to three groups of enzymes involved in these processes: the writers adding marks, the erasers removing them, and the readers able to detect these marks and participating in the recruitment of transcription factors. The stimulation or the repression in the expression of genes is thus the result of a subtle equilibrium between all the possibilities coming from the combinations of these PTMs. Indeed, these mechanisms can be deregulated and then participate in the appearance, development and maintenance of various human diseases, including cancers, neurological and metabolic disorders. Some of the key players in epigenetics are metalloenzymes, belonging mostly to the group of erasers: the zinc-dependent histone deacetylases (HDACs), the iron-dependent lysine demethylases of the Jumonji family (JMJ or KDM) and for DNA the iron-dependent ten-eleven-translocation enzymes (TET) responsible for the oxidation of methylcytosine prior to the demethylation of DNA. This review presents these metalloenzymes, their importance in human disease and their inhibitors.

Defective modulation of LINE-1 retrotransposition by cancer-associated SAMHD1 mutants

Long interspersed nuclear elements (LINE-1) is now considered as the only active autonomous mobile DNA in humans, LINE-1 retrotransposition activities are associated with and fluctuate during cancer initiation and progression; however, the mechanism underlying the increased LINE-1 activity in cancer is poorly understood. SAMHD1 has been reported to be a potent inhibitor of LINE-1 retrotransposition, and SAMHD1 mutations are frequently associated with cancer development. To gain insights on whether cancer-related SAMHD1 mutants affect LINE-1 activity, we explored the biochemical and cellular properties of some human mutants known correlate with the development of cancer. Most of the tested SAMHD1 cancer-related mutations were defective in LINE-1 inhibition. Interestingly we also found that SAMHD1 mutant K288T was defective for dNTPase activity but showed potent activity against LINE-1 retrotransposition. These findings suggest that LINE-1 inhibition does not depend solely on the dNTPase activity of SAMHD1. In contrast, SAMHD1's ability to inhibit ORF2p-mediated LINE-1 RNP reverse transcription was correlated with SAMHD1-mediated LINE-1 inhibition. Together, our data could also facilitate the deeper understanding for the inhibition of endogenous LINE-1 elements by SAMHD1.

PRC1 promotes cell proliferation and cell cycle progression by regulating p21/p27-pRB family molecules and FAK-paxillin pathway in non-small cell lung cancer

Background

This study aimed to demonstrate the function and molecular mechanism of protein regulator of cytokinesis 1 (PRC1) in the carcinogenesis of non-small cell lung cancer (NSCLC).

Methods

Bioinformatics analysis was performed. Cell culture and plasmid construction were conducted for cell transfection. mRNA and protein expression, cell proliferation, migration, and cell cycle were detected. Mice models were also constructed. The relationship between PRC1 and the prognosis of NSCLC patients was analyzed.

Results

PRC1 expression was higher in tumor tissues than adjacent non-tumor tissues (P<0.05). Cells transfected with the high-expression PRC1 plasmid (TOPO-PRC1 group) had the stronger ability of proliferation and migration (P<0.05) along with a lower incidence of stay at the G2/M phase (P<0.05) than the low-expression PRC1 plasmid. Mice models showed tumors obtained from mice in the TOPO-PRC1 group significantly grew faster, larger, and heavier (P<0.05) than the low-expression PRC1 group. Among the 150 NSCLC patients, patients with the higher PRC1 expression were more likely to have lymph node metastasis occur (P<0.05) and progress into an advanced stage (P<0.05), and showed shorter survival (P<0.05). Moreover, the TOPO-PRC1 group had a lower phosphorylation level, and a lower expression of Cip1/p21 (P<0.05) and Kip1/p27 (P<0.01).

Conclusions

PRC1 could promote cell proliferation and cell cycle progression through FAK-paxillin pathway molecules and the regulation of the phosphorylation level of p21/p27-pRB family molecules. PRC1 might be a new and promising therapeutic target for NSCLC.

A Pharmacogenomic Landscape in Human Liver Cancers

Liver cancers are highly heterogeneous with poor prognosis and drug response. A better understanding between genetic alterations and drug responses would facilitate precision treatment for liver cancers. To characterize the landscape of pharmacogenomic interactions in liver cancers, we developed a protocol to establish human liver cancer cell models at a success rate of around 50% and generated the Liver Cancer Model Repository (LIMORE) with 81 cell models. LIMORE represented genomic and transcriptomic heterogeneity of primary cancers. Interrogation of the pharmacogenomic landscape of LIMORE discovered unexplored gene-drug associations, including synthetic lethalities to prevalent alterations in liver cancers. Moreover, predictive biomarker candidates were suggested for the selection of sorafenib-responding patients. LIMORE provides a rich resource facilitating drug discovery in liver cancers.

Alternative mRNA splicing in cancer immunotherapy

Immunotherapies are yielding effective treatments for several previously untreatable cancers. Still, the identification of suitable antigens specific to the tumour that can be targets for cancer vaccines and T cell therapies is a challenge. Alternative processing of mRNA, a phenomenon that has been shown to alter the proteomic diversity of many cancers, may offer the potential of a broadened target space. Here, we discuss the promise of analysing mRNA processing events in cancer cells, with an emphasis on mRNA splicing, for the identification of potential new targets for cancer immunotherapy. Further, we highlight the challenges that must be overcome for this new avenue to have clinical applicability.

Using Naïve Bayes Algorithm to Estimate the Response to Drug in Lung Cancer Patients

AIM AND OBJECTIVE

Lung cancer is a highly heterogeneous cancer, due to the significant differences in molecular levels, resulting in different clinical manifestations of lung cancer patients there is a big difference. Including disease characterization, drug response, the risk of recurrence, survival, etc.

Method

Clinical patients with lung cancer do not have yet particularly effective treatment options, while patients with lung cancer resistance not only delayed the treatment cycle but also caused strong side effects. Therefore, if we can sum up the abnormalities of functional level from the molecular level, we can scientifically and effectively evaluate the patients' sensitivity to treatment and make the personalized treatment strategies to avoid the side effects caused by over-treatment and improve the prognosis.

RESULT & CONCLUSION

According to the different sensitivities of lung cancer patients to drug response, this study screened out genes that were significantly associated with drug resistance. The bayes model was used to assess patient resistance.

The cancer driver genes IDH1/2, JARID1C/ KDM5C, and UTX/ KDM6A: crosstalk between histone demethylation and hypoxic reprogramming in cancer metabolism

Recent studies on mutations in cancer genomes have distinguished driver mutations from passenger mutations, which occur as byproducts of cancer development. The cancer genome atlas (TCGA) project identified 299 genes and 24 pathways/biological processes that drive tumor progression (Cell 173: 371-385 e318, 2018). Of the 299 driver genes, 12 genes are involved in histones, histone methylation, and demethylation. Among these 12 genes, those encoding the histone demethylases JARID1C/KDM5C and UTX/KDM6A were identified as cancer driver genes. Furthermore, gain-of-function mutations in genes encoding metabolic enzymes, such as isocitrate dehydrogenases (IDH)1/2, drive tumor progression by producing an oncometabolite, D-2-hydroxyglutarate (D-2HG), which is a competitive inhibitor of α-ketoglutarate, O₂-dependent dioxygenases such as Jumonji domain-containing histone demethylases, and DNA demethylases. Studies on oncometabolites suggest that histone demethylases mediate metabolic changes in chromatin structure. We have reviewed the most recent findings regarding cancer-specific metabolic reprogramming and the tumor-suppressive roles of JARID1C/KDM5C and UTX/KDM6A. We have also discussed mutations in other isoforms such as the JARID1A, 1B, 1D of KDM5 subfamilies and the JMJD3/KDM6B of KDM6 subfamilies, which play opposing roles in tumor progression as oncogenes or tumor suppressors depending on the cancer cell type.

Genes involved in the removal of methyl groups from histones associated with DNA can promote or suppress tumor growth depending on the metabolic status of the cancer cell. Hyunsung Park and colleagues at the University of Seoul, South Korea, review current knowledge of two genes encoding histone demethylases which have been identified by The Cancer Genome Atlas (TCGA) project as cancer driver genes. Because these demethylase enzymes rely on cellular metabolites to function, their effect is influenced by metabolic conditions in the tumor microenvironment such as low oxygen. The mechanisms through which changes in histone methylation affect the expression of genes involved in tumor progression remain unknown. Further understanding of how cancer metabolism affects the modification of histones will help guide the development of more effective cancer treatments.

Small-Molecule Ferroptotic Agents with Potential to Selectively Target Cancer Stem Cells

Effective management of advanced cancer requires systemic treatment including small molecules that target unique features of aggressive tumor cells. At the same time, tumors are heterogeneous and current evidence suggests that a subpopulation of tumor cells, called tumor initiating or cancer stem cells, are responsible for metastatic dissemination, tumor relapse and possibly drug resistance. Classical apoptotic drugs are less effective against this critical subpopulation. In the course of generating a library of open-chain epothilones, we discovered a new class of small molecule anticancer agents that has no effect on tubulin but instead kills selected cancer cell lines by harnessing reactive oxygen species to induce ferroptosis. Interestingly, we find that drug sensitivity is highest in tumor cells with a mesenchymal phenotype. Furthermore, these compounds showed enhanced toxicity towards mesenchymal breast cancer populations with cancer stem cell properties in vitro. In summary, we have identified a new class of small molecule ferroptotic agents that warrant further investigation.

MicroRNAs and their target mRNAs as potential biomarkers among smokers and non-smokers with lung adenocarcinoma

Lung adenocarcinoma is one of the major causes of mortality. Current methods of diagnosis can be improved through identification of disease specific biomarkers. MicroRNAs are small non-coding regulators of gene expression, which can be potential biomarkers in various diseases. Thus, the main objective of this study was to gain mechanistic insights into genetic abnormalities occurring in lung adenocarcinoma by implementing an integrative analysis of miRNAs and mRNAs expression profiles in the case of both smokers and non-smokers. Differential expression was analysed by comparing publicly available lung adenocarcinoma samples with controls. Furthermore, weighted gene co-expression network analysis is performed which revealed mRNAs and miRNAs significantly correlated with lung adenocarcinoma. Moreover, an integrative analysis resulted in identification of several miRNA-mRNA pairs which were significantly dysregulated in non-smokers with lung adenocarcinoma. Also two pairs (miR-133b/Protein Kinase C Zeta (PRKCZ) and miR-557/STEAP3) were found specifically dysregulated in smokers. Pathway analysis further revealed their role in important signalling pathways including cell cycle. This analysis has not only increased the authors' understanding about lung adenocarcinoma but also proposed potential biomarkers. However, further wet laboratory studies are required for the validation of these potential biomarkers which can be used to diagnose lung adenocarcinoma.

A Novel Network-Based Computational Model for Prediction of Potential LncRNA⁻Disease Association

Accumulating studies have shown that long non-coding RNAs (lncRNAs) are involved in many biological processes and play important roles in a variety of complex human diseases. Developing effective computational models to identify potential relationships between lncRNAs and diseases can not only help us understand disease mechanisms at the lncRNA molecular level, but also promote the diagnosis, treatment, prognosis, and prevention of human diseases. For this paper, a network-based model called NBLDA was proposed to discover potential lncRNA⁻disease associations, in which two novel lncRNA⁻disease weighted networks were constructed. They were first based on known lncRNA⁻disease associations and topological similarity of the lncRNA⁻disease association network, and then an lncRNA⁻lncRNA weighted matrix and a disease⁻disease weighted matrix were obtained based on a resource allocation strategy of unequal allocation and unbiased consistence. Finally, a label propagation algorithm was applied to predict associated lncRNAs for the investigated diseases. Moreover, in order to estimate the prediction performance of NBLDA, the framework of leave-one-out cross validation (LOOCV) was implemented on NBLDA, and simulation results showed that NBLDA can achieve reliable areas under the ROC curve (AUCs) of 0.8846, 0.8273, and 0.8075 in three known lncRNA⁻disease association datasets downloaded from the lncRNADisease database, respectively. Furthermore, in case studies of lung cancer, leukemia, and colorectal cancer, simulation results demonstrated that NBLDA can be a powerful tool for identifying potential lncRNA⁻disease associations as well.

A cancer-associated point mutation disables the steric gate of human PrimPol

PrimPol is a human primase/polymerase specialized in re-starting stalled forks by repriming beyond lesions such as pyrimidine dimers, and replication-perturbing structures including G-quadruplexes and R-loops. Unlike most conventional primases, PrimPol proficiently discriminates against ribonucleotides (NTPs), being able to start synthesis using deoxynucleotides (dNTPs), yet the structural basis and physiological implications for this discrimination are not understood. In silico analyses based on the three-dimensional structure of human PrimPol and related enzymes enabled us to predict a single residue, Tyr¹⁰⁰, as the main effector of sugar discrimination in human PrimPol and a change of Tyr¹⁰⁰ to histidine to boost the efficiency of NTP incorporation. We show here that the Y100H mutation profoundly stimulates NTP incorporation by human PrimPol, with an efficiency similar to that for dNTP incorporation during both primase and polymerase reactions in vitro. As expected from the higher cellular concentration of NTPs relative to dNTPs, Y100H expression in mouse embryonic fibroblasts and U2OS osteosarcoma cells caused enhanced resistance to hydroxyurea, which decreases the dNTP pool levels in S-phase. Remarkably, the Y100H PrimPol mutation has been identified in cancer, suggesting that this mutation could be selected to promote survival at early stages of tumorigenesis, which is characterized by depleted dNTP pools.

Comparison of different functional prediction scores using a gene-based permutation model for identifying cancer driver genes

Background

Identifying cancer driver genes (CDG) is a crucial step in cancer genomic toward the advancement of precision medicine. However, driver gene discovery is a very challenging task because we are not only dealing with huge amount of data; but we are also faced with the complexity of the disease including the heterogeneity of background somatic mutation rate in each cancer patient. It is generally accepted that CDG harbor variants conferring growth advantage in the malignant cell and they are positively selected, which are critical to cancer development; whereas, non-driver genes harbor random mutations with no functional consequence on cancer. Based on this fact, function prediction based approaches for identifying CDG have been proposed to interrogate the distribution of functional predictions among mutations in cancer genomes (eLS 1–16, 2016). Assuming most of the observed mutations are passenger mutations and given the quantitative predictions for the functional impact of the mutations, genes enriched of functional or deleterious mutations are more likely to be drivers. The promises of these methods have been continually refined and can therefore be applied to increase accuracy in detecting new candidate CDGs. However, current function prediction based approaches only focus on coding mutations and lack a systematic way to pick the best mutation deleteriousness prediction algorithms for usage.

Results

In this study, we propose a new function prediction based approach to discover CDGs through a gene-based permutation approach. Our method not only covers both coding and non-coding regions of the genes; but it also accounts for the heterogeneous mutational context in cohort of cancer patients. The permutation model was implemented independently using seven popular deleteriousness prediction scores covering splicing regions (SPIDEX), coding regions (MetaLR, and VEST3) and pan-genome (CADD, DANN, Fathmm-MKL coding and Fathmm-MKL noncoding). We applied this new approach to somatic single nucleotide variants (SNVs) from whole-genome sequences of 119 breast and 24 lung cancer patients and compared the seven deleteriousness prediction scores for their performance in this study.

Conclusion

The new function prediction based approach not only predicted known cancer genes listed in the Cancer Gene Census (CGC), but also new candidate CDGs that are worth further investigation. The results showed the advantage of utilizing pan-genome deleteriousness prediction scores in function prediction based methods. Although VEST3 score, a deleteriousness prediction score for missense mutations, has the best performance in breast cancer, it was topped by CADD and Fathmm-MKL coding, two pan-genome deleteriousness prediction scores, in lung cancer.

Electronic supplementary material

The online version of this article (10.1186/s12920-018-0452-9) contains supplementary material, which is available to authorized users.

RAC1B: A Rho GTPase with Versatile Functions in Malignant Transformation and Tumor Progression

RAC1B is an alternatively spliced isoform of the monomeric GTPase RAC1. It differs from RAC1 by a 19 amino acid in frame insertion, termed exon 3b, resulting in an accelerated GDP/GTP-exchange and an impaired GTP-hydrolysis. Although RAC1B has been ascribed several protumorigenic functions such as cell cycle progression and apoptosis resistance, its role in malignant transformation, and other functions driving tumor progression like epithelial-mesenchymal transition, migration/invasion and metastasis are less clear. Insertion of exon 3b endows RAC1B with specific biochemical properties that, when compared to RAC1, encompass both loss-of-functions and gain-of-functions with respect to the type of upstream activators, downstream targets, and binding partners. In its extreme, this may result in RAC1B and RAC1 acting in an antagonistic fashion in regulating a specific cellular response with RAC1B behaving as an endogenous inhibitor of RAC1. In this review, we strive to provide the reader with a comprehensive overview, rather than critical discussions, on various aspects of RAC1B biology in eukaryotic cells.

Genomic and transcriptomic characterisation of undifferentiated pleomorphic sarcoma of bone

Undifferentiated pleomorphic sarcoma of bone (UPSb) is a rare primary bone sarcoma that lacks a specific line of differentiation. There is very little information about the genetic alterations leading to tumourigenesis or malignant transformation. Distinguishing between UPSb and other malignant bone sarcomas, including dedifferentiated chondrosarcoma and osteosarcoma, can be challenging due to overlapping features. To explore the genomic and transcriptomic landscape of UPSb tumours, whole-exome sequencing (WES) and RNA sequencing (RNA-Seq) were performed on UPSb tumours. All tumours lacked hotspot mutations in IDH1/2 132 or 172 codons, thereby excluding the diagnosis of dedifferentiated chondrosarcoma. Recurrent somatic mutations in TP53 were identified in four of 14 samples (29%). Moreover, recurrent mutations in histone chromatin remodelling genes, including H3F3A, ATRX and DOT1L, were identified in five of 14 samples (36%), highlighting the potential role of deregulated chromatin remodelling pathways in UPSb tumourigenesis. The majority of recurrent mutations in chromatin remodelling genes identified here are reported in COSMIC, including the H3F3A G34 and K36 hotspot residues. Copy number alteration analysis identified gains and losses in genes that have been previously altered in UPSb or UPS of soft tissue. Eight somatic gene fusions were identified by RNA-Seq, two of which, CLTC-VMP1 and FARP1-STK24, were reported previously in multiple cancers. Five gene fusions were genomically characterised. Hierarchical clustering analysis, using RNA-Seq data, distinctly clustered UPSb tumours from osteosarcoma and other sarcomas, thus molecularly distinguishing UPSb from other sarcomas. RNA-Seq expression profiling analysis and quantitative reverse transcription-polymerase chain reaction showed an elevated expression in FGF23, which can be a potential molecular biomarker for UPSb. To our knowledge, this study represents the first comprehensive WES and RNA-Seq analysis of UPSb tumours revealing novel protein-coding recurrent gene mutations, gene fusions and identifying a potential UPSb molecular biomarker, thereby broadening the understanding of the pathogenic mechanisms and highlighting the possibility of developing novel targeted therapeutics. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Nucleosome Positioning by an Evolutionarily Conserved Chromatin Remodeler Prevents Aberrant DNA Methylation in Neurospora

In the filamentous fungus Neurospora crassa, constitutive heterochromatin is marked by tri-methylation of histone H3 lysine 9 (H3K9me3) and DNA methylation. We identified mutations in the Neurospora defective in methylation-1 (dim-1) gene that cause defects in cytosine methylation and implicate a putative AAA-ATPase chromatin remodeler. Although it was well-established that chromatin remodelers can affect transcription by influencing DNA accessibility with nucleosomes, little was known about the role of remodelers on chromatin that is normally not transcribed, including regions of constitutive heterochromatin. We found that dim-1 mutants display both reduced DNA methylation in heterochromatic regions as well as increased DNA methylation and H3K9me3 in some intergenic regions associated with highly expressed genes. Deletion of dim-1 leads to atypically spaced nucleosomes throughout the genome and numerous changes in gene expression. DIM-1 localizes to both heterochromatin and intergenic regions that become hyper-methylated in dim-1 strains. Our findings indicate that DIM-1 normally positions nucleosomes in both heterochromatin and euchromatin and that the standard arrangement and density of nucleosomes is required for the proper function of heterochromatin machinery.

SAMHD1 inhibits epithelial cell transformation in vitro and affects leukemia development in xenograft mice

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a mammalian dNTP hydrolase (dNTPase) and functions as a negative regulator in the efficacy of cytarabine treatment of acute myeloid leukemia (AML). We have reported that SAMHD1 knockout (KO) increased the activity of phosphoinositide 3-kinase (PI3K) in AML-derived THP-1 cells and attenuated their ability to form subcutaneous tumors in xenografted immunodeficient mice. However, the functional significance of SAMHD1 in controlling AML leukemogenesis remains unclear. Previous studies show that in vitro transformation of Madin-Darby canine kidney (MDCK) epithelial cells by the Jaagsiekte sheep retrovirus (JSRV) envelope protein requires activation of the PI3K/Akt oncogenic signaling pathway. Using this cell transformation model, we demonstrated that ectopic expression of wild-type human SAMHD1 or a dNTPase-defective SAMHD1 mutant (HD/AA) significantly inhibited MDCK cell transformation, but did not affect cell proliferation. To visualize and quantify THP-1 cell growth and metastasis in xenografted immunodeficient mice, we generated luciferase-expressing stable SAMHD1 KO THP-1 cells and control THP-1 cells, which were injected intravenously into immunodeficient mice. Bioluminescence imaging and quantification analysis of xenografted mice revealed that SAMHD1 KO cell-derived tumors had similar growth and metastatic potential compared with control cells at 35 days post-injection. However, mice xenografted with SAMHD1 KO cells showed greater survival compared with mice injected with control cells. Our data suggest that exogenous SAMHD1 expression suppresses in vitro cell transformation independently of its dNTPase activity, and that endogenous SAMHD1 affects AML tumorigenicity and disease progression in vivo.

The Trithorax protein Ash1L promotes myoblast fusion by activating Cdon expression

Myoblast fusion (MF) is required for muscle growth and repair, and its alteration contributes to muscle diseases. The mechanisms governing this process are incompletely understood, and no epigenetic regulator has been previously described. Ash1L is an epigenetic activator belonging to the Trithorax group of proteins and is involved in FSHD muscular dystrophy, autism and cancer. Its physiological role in skeletal muscle is unknown. Here we report that Ash1L expression is positively correlated with MF and reduced in Duchenne muscular dystrophy. In vivo, ex vivo and in vitro experiments support a selective and evolutionary conserved requirement for Ash1L in MF. RNA- and ChIP-sequencing indicate that Ash1L is required to counteract Polycomb repressive activity to allow activation of selected myogenesis genes, in particular the key MF gene Cdon. Our results promote Ash1L as an important epigenetic regulator of MF and suggest that its activity could be targeted to improve cell therapy for muscle diseases.

Myoblast fusion in skeletal muscle is a complex process but how this is regulated is unclear. Here, the authors identify Ash1L, a histone methyltransferase, as modulating myoblast fusion via activation of the myogenesis gene Cdon, and observe decreased Ash1L expression in Duchenne muscular dystrophy.

ASH1-catalyzed H3K36 methylation drives gene repression and marks H3K27me2/3-competent chromatin

Methylation of histone H3 at lysine 36 (H3K36me), a widely-distributed chromatin mark, largely results from association of the lysine methyltransferase (KMT) SET-2 with RNA polymerase II (RNAPII), but most eukaryotes also have additional H3K36me KMTs that act independently of RNAPII. These include the orthologs of ASH1, which are conserved in animals, plants, and fungi but whose function and control are poorly understood. We found that Neurospora crassa has just two H3K36 KMTs, ASH1 and SET-2, and were able to explore the function and distribution of each enzyme independently. While H3K36me deposited by SET-2 marks active genes, inactive genes are modified by ASH1 and its activity is critical for their repression. ASH1-marked chromatin can be further modified by methylation of H3K27, and ASH1 catalytic activity modulates the accumulation of H3K27me2/3 both positively and negatively. These findings provide new insight into ASH1 function, H3K27me2/3 establishment, and repression in facultative heterochromatin.

Not all genes in a cell’s DNA are active all the time. There are several ways to control this activity. One is by altering how the DNA is packaged into cells. DNA strands are wrapped around proteins called histones to form nucleosomes. Nucleosomes can then be packed together tightly, to restrict access to the DNA at genes that are not active, or loosely to allow access to the DNA of active genes.

Chemical marks, such as methyl groups, can be attached to particular sites on histones to influence how they pack together. One important site for such marks is known as position 36 on histone H3, or H3K36 for short. Correctly adding methyl groups to this site is critical for normal development, and when this process goes wrong it can lead to diseases like cancer. An enzyme called SET-2 oversees the methylation of H3K36 in fungi, plants and animals. However, many species have several other enzymes that can also add methyl groups to H3K36, and their roles are less clear.

A type of fungus called Neurospora crassa contains just two enzymes that can add methyl groups to H3K36: SET-2, and another enzyme called ASH1. By performing experiments that inactivated SET-2 and ASH1 in this fungus, Bicocca et al. found that each enzyme works on a different set of genes. Genes in regions marked by SET-2 were accessible for the cell to use, while genes marked by ASH1 were inaccessible. ASH1 also affects whether a methyl group is added to another site on histone H3. This mark is important for controlling the activity of genes that are critical for development.

ASH1 is found in many other organisms, including humans. The results presented by Bicocca et al. could therefore be built upon to understand the more complicated systems for regulating H3K36 methylation in other species. From there, we can investigate how to intervene when things go wrong during developmental disorders and cancer.

Expressed HNSCC variants by HPV-status in a well-characterized Michigan cohort

While whole-exome DNA sequencing is the most common technology to study genetic variants in tumors in known exonic regions, RNA-seq is cheaper, covers most of the same exonic regions, and is often more readily available. In this study, we show the utility of mRNA-seq-based variant analysis combined with targeted gene sequencing performed on both tumor and matched blood as an alternative when exome data is unavailable. We use the approach to study expressed variant profiles in the well-characterized University of Michigan (UM) head and neck squamous carcinoma (HNSCC) cohort (n = 36). We found that 441 out of 455 (~97%) identified cancer genes with an expressed variant in the UM cohort also harbor a somatic mutation in TCGA. Fourteen (39%) patients had a germline variant in a cancer-related Fanconi Anemia (FA) pathway gene. HPV-positive patients had more nonsynonymous, rare, and damaging (NRD) variants in those genes than HPV-negative patients. Moreover, the known mutational signatures for DNA mismatch repair and APOBEC activation were attributive to the UM expressed NRD variants, and the APOBEC signature contribution differed by HPV status. Our results provide additional support to certain TCGA findings and suggest an association of expressed variants in FA/DNA repair pathways with HPV-associated HNSCC tumorigenesis. These results will benefit future studies on this and other cohorts by providing the genetic variants of key cancer-related genes.