Mutations In Human Cancers Research Articles

OncoBase: a platform for decoding regulatory somatic mutations in human cancers

Whole-exome and whole-genome sequencing have revealed millions of somatic mutations associated with different human cancers, and the vast majority of them are located outside of coding sequences, making it challenging to directly interpret their functional effects. With the rapid advances in high-throughput sequencing technologies, genome-scale long-range chromatin interactions were detected, and distal target genes of regulatory elements were determined using three-dimensional (3D) chromatin looping. Herein, we present OncoBase (http://www.oncobase.biols.ac.cn/), an integrated database for annotating 81 385 242 somatic mutations in 68 cancer types from more than 120 cancer projects by exploring their roles in distal interactions between target genes and regulatory elements. OncoBase integrates local chromatin signatures, 3D chromatin interactions in different cell types and reconstruction of enhancer-target networks using state-of-the-art algorithms. It employs informative visualization tools to display the integrated local and 3D chromatin signatures and effects of somatic mutations on regulatory elements. Enhancer-promoter interactions estimated from chromatin interactions are integrated into a network diffusion system that quantitatively prioritizes somatic mutations and target genes from a large pool. Thus, OncoBase is a useful resource for the functional annotation of regulatory noncoding regions and systematically benchmarking the regulatory effects of embedded noncoding somatic mutations in human carcinogenesis.

COSMIC: the Catalogue Of Somatic Mutations In Cancer.

COSMIC, the Catalogue Of Somatic Mutations In Cancer (https://cancer.sanger.ac.uk) is the most detailed and comprehensive resource for exploring the effect of somatic mutations in human cancer. The latest release, COSMIC v86 (August 2018), includes almost 6 million coding mutations across 1.4 million tumour samples, curated from over 26 000 publications. In addition to coding mutations, COSMIC covers all the genetic mechanisms by which somatic mutations promote cancer, including non-coding mutations, gene fusions, copy-number variants and drug-resistance mutations. COSMIC is primarily hand-curated, ensuring quality, accuracy and descriptive data capture. Building on our manual curation processes, we are introducing new initiatives that allow us to prioritize key genes and diseases, and to react more quickly and comprehensively to new findings in the literature. Alongside improvements to the public website and data-download systems, new functionality in COSMIC-3D allows exploration of mutations within three-dimensional protein structures, their protein structural and functional impacts, and implications for druggability. In parallel with COSMIC’s deep and broad variant coverage, the Cancer Gene Census (CGC) describes a curated catalogue of genes driving every form of human cancer. Currently describing 719 genes, the CGC has recently introduced functional descriptions of how each gene drives disease, summarized into the 10 cancer Hallmarks.

Zoledronic acid enhances the efficacy of the MEK inhibitor trametinib in KRAS mutant cancers

KRAS mutation is the most common type of mutation in human cancers. However, the direct pharmacological inhibition of KRAS has not been clinically successful. Trametinib (GSK1120212, Tram), a newer MEK inhibitor, inhibits RAS signaling through mitogen-activated protein kinase (MAPK) cascade suppression. The effectiveness of Tram in clinical practice is limited in KRAS mutant tumors compared to that in BRAF mutant tumors. Here, we found that Tram treatment provoked feedback activation of upstream RAS, thus causing an induction of phosphorylated MEK (pMEK) and phosphorylated ERK (pERK) rebound in KRAS mutant tumors. This failure of persistent ERK inhibition led to drug resistance. Zoledronic acid (ZA), a nitrogen-containing bisphosphonate, disrupts the biological activity of RAS by inhibiting its isoprenylation. Surprisingly, ZA overcame Tram resistance, and augmented antitumor activity was observed in KRAS mutant tumors both in vitro and in vivo. Furthermore, ZA enhanced the effect of Tram partially through the mevalonate pathway. In summary, the combination of the two FDA-approved drugs Tram and ZA may represent a novel therapeutic strategy for the treatment of KRAS mutant cancers.

Mutational processes shape the landscape of TP53 mutations in human cancer

Unlike most tumor suppressor genes, the most common genetic alterations in TP53 are missense mutations1,2. Mutant p53 protein is often abundantly expressed in cancers, and specific allelic variants exhibit dominant-negative or gain-of-function activities in experimental models3–8. To gain a systematic view of p53 function, we interrogated loss-of-function screens conducted in hundreds of human cancer cell lines and performed TP53 saturation mutagenesis screens in an isogenic pair of TP53-wild-type and -null cell lines. We found that loss or dominant-negative inhibition of p53 function reliably enhanced cellular fitness. By integrating these data with the COSMIC mutational signatures database9,10, we developed a statistical model that describes the TP53 mutational spectrum as a function of the baseline probability of acquiring each mutation and the fitness advantage conferred by attenuation of p53 activity. Collectively, these observations show that widely-acting and tissue-specific mutational processes combine with phenotypic selection to dictate the frequencies of recurrent TP53 mutations.

Disruption of gestational thyroid physiology: A vulnerable timeframe for fetal brain development

BRAF is a cytoplasmic protein kinase, which activates the MEK-ERK signalling pathway. Deregulation of the pathway is associated with the presence of BRAF mutations in human cancer, the most common being V600EBRAF, although structural rearrangements, which remove N-terminal regulatory sequences, have also been reported. RAF-MEK-ERK signalling is normally thought to occur in the cytoplasm of the cell. However, in an investigation of BRAF localisation using fluorescence microscopy combined with subcellular fractionation of Green Fluorescent Protein (GFP)-tagged proteins expressed in NIH3T3 cells, surprisingly, we detected N-terminally truncated BRAF (ΔBRAF) in both nuclear and cytoplasmic compartments. In contrast, ΔCRAF and full-length, wild-type BRAF (WTBRAF) were detected at lower levels in the nucleus while full-length V600EBRAF was virtually excluded from this compartment. Similar results were obtained using ΔBRAF tagged with the hormone-binding domain of the oestrogen receptor (hbER) and with the KIAA1549-ΔBRAF translocation mutant found in human pilocytic astrocytomas. Here we show that GFP-ΔBRAF nuclear translocation does not involve a canonical Nuclear Localisation Signal (NLS), but is suppressed by N-terminal sequences. Nuclear GFP-ΔBRAF retains MEK/ERK activating potential and is associated with the accumulation of phosphorylated MEK and ERK in the nucleus. In contrast, full-length GFP-WTBRAF and GFP-V600EBRAF are associated with the accumulation of phosphorylated ERK but not phosphorylated MEK in the nucleus. These data have implications for cancers bearing single nucleotide variants or N-terminal deleted structural variants of BRAF.

Mutant TP53 G245C and R273H promote cellular malignancy in esophageal squamous cell carcinoma

BackgroundTP53 gene mutations occur in more than 50% of human cancers and the vast majority of these mutations in human cancers are missense mutations, which broadly occur in DNA binding domain (DBD) (Amino acids 102–292) and mainly reside in six “hotspot” residues. TP53 G245C and R273H point mutations are two of the most frequent mutations in tumors and have been verified in several different cancers. In the previous study of the whole genome sequencing (WGS), we found some mutations of TP53 DBD in esophageal squamous cell carcinoma (ESCC) clinical samples. We focused on two high-frequent mutations TP53 p.G245C and TP53 p.R273H and investigated their oncogenic roles in ESCC cell lines, p53-defective cell lines H1299 and HCT116 p53−/−.ResultsMTS and colony formation assays showed that mutant TP53 G245C and R273H increased cell vitality and proliferation. Flow cytometry results revealed inhibition of ultraviolet radiation (UV)- and ionizing radiation (IR)- induced apoptosis and disruption of TP53-mediated cell cycle arrest after UV, IR and Nocodazole treatment. Transwell assays indicated that mutant TP53 G245C and R273H enhanced cell migration and invasion abilities. Moreover, western blot revealed that they were able to suppress the expression of TP53 downstream genes in the process of apoptosis and cell cycle arrest induced by UV, which suggests that these two mutations can influence apoptosis and growth arrest might be due, at least in part, to down-regulate the expression of P21, GADD45α and PARP.ConclusionsThese results indicate that mutant TP53 G245C and R273H can lead to more aggressive phenotypes and enhance cancer cell malignancy, which further uncover TP53 function in carcinogenesis and might be useful in clinical diagnosis and therapy of TP53 mutant cancers.

Oncogenic c-terminal cyclin D1 (CCND1) mutations are enriched in endometrioid endometrial adenocarcinomas.

Cyclin D1 (CCND1) is a core cell cycle regulator and is frequently overexpressed in human cancers, often via amplification, translocation or post-transcription regulation. Accumulating evidence suggests that mutations of the CCND1 gene that result in nuclear retention and constitutive activation of CDK4/6 kinases are oncogenic drivers in cancer. However, the spectrum of CCND1 mutations across human cancers has not been systematically investigated. Here, we retrospectively mined whole-exome sequencing data from 124 published studies representing up to 29,432 cases from diverse cancer types and sites of origin, including carcinoma, melanoma, sarcoma and lymphoma/leukemia, via online tools to determine the frequency and spectrum of CCND1 mutations in human cancers and their associated clinico-pathological characteristics. Overall, in contrast to gene amplification, which occurred at a frequency of 4.8% (1,419 of 28,769 cases), CCND1 mutations were of very low frequency (0.5%, 151 of 29,432 cases) across all cancers, but were predominantly enriched in uterine endometrioid-type adenocarcinoma (6.5%, 30 of 458 cases) in both primary tumors and in advanced, metastatic endometrial cancer samples. CCND1 mutations in endometrial endometrioid adenocarcinoma occurred most commonly in the c-terminus of cyclin D1, as putative driver mutations, in a region thought to result in oncogenic activation of cyclin D1 via inhibition of Thr-286 phosphorylation and nuclear export, thereby resulting in nuclear retention and protein overexpression. Our findings implicate oncogenic c-terminal mutations of CCND1 in the pathogenesis of a subset of human cancers and provide a key resource to guide future preclinical and clinical investigations.

Adaptation of an amplicon-based human cancer next-generation sequencing panel assay for murine tumors

Unlike humans, inbred genetically engineered mice have minimal inter-individual variation and, consequently, offer substantially increased statistical power for robust definition of recurrent cooperating cancer mutations. While technically feasible, whole exome sequencing is expensive and extremely data-intensive. Somatic mutation analysis using panels of 25–75 genes now provides detailed insight into the biology of human tumors. Here we report an adaptation for mouse tumors of a human PCR amplicon-based panel (Ion Torrent Cancer Hotspot Panel v2) allowing analysis of 18 cancer genes, including Kras, Nras, Hras, Pten, Pik3ca and Smad4, and encompassing regions homologous to more than 2000 known human cancer mutations.

Validating the concept of mutational signatures with isogenic cell models

The diversity of somatic mutations in human cancers can be decomposed into individual mutational signatures, patterns of mutagenesis that arise because of DNA damage and DNA repair processes that have occurred in cells as they evolved towards malignancy. Correlations between mutational signatures and environmental exposures, enzymatic activities and genetic defects have been described, but human cancers are not ideal experimental systems—the exposures to different mutational processes in a patient’s lifetime are uncontrolled and any relationships observed can only be described as an association. Here, we demonstrate the proof-of-principle that it is possible to recreate cancer mutational signatures in vitro using CRISPR-Cas9-based gene-editing experiments in an isogenic human-cell system. We provide experimental and algorithmic methods to discover mutational signatures generated under highly experimentally-controlled conditions. Our in vitro findings strikingly recapitulate in vivo observations of cancer data, fundamentally validating the concept of (particularly) endogenously-arising mutational signatures.

Subunits of human condensins are potential therapeutic targets for cancers

The main role of condensins is to regulate chromosome condensation and segregation during cell cycles. Recently, it has been suggested in the literatures that subunits of condensin I and condensin II are involved in some human cancers. This paper will first briefly discuss discoveries of human condensins, their components and structures, and their multiple cellular functions. This will be followed by reviews of most recent studies on subunits of human condensins and their dysregulations or mutations in human cancers. It can be concluded that many of these subunits have potentials to be novel targets for cancer therapies. However, hCAP-D2, a subunit of human condensin I, has not been directly documented to be associated with any human cancers to date. This review hypothesizes that hCAP-D2 can also be a potential therapeutic target for human cancers, and therefore that all subunits of human condensins are potential therapeutic targets for human cancers.

Gain of function in the mouse model of a recurrent mutation p53N236S promotes the formation of double minute chromosomes and the oncogenic potential of p19ARF.

The mutation p53N236S (p53S) has been identified as one of the recurrent mutations in human cancers by TCGA database. Our in vitro data revealed the oncogenic gain of function of p53S. To understand the function of p53S in vivo, we generated the p53S knock-in mouse. The p53S/S mice manifested highly invasive lymphomas and metastatic sarcomas with dramatically increased double minute chromosomes. The survival curve, the incidence of tumors and the tumor spectrum of p53S/S mice is very similar to the p53R172H mouse model. The p53S/+ mice showed delayed onset of tumorigenesis and a high metastasis rate (40%) and low loss of heterozygosity rate (2/16). The activation of CDKN2A pathway in p53S/S MEF and tumors, and the accumulation of p19ARF protein in tumor tissues suggested p19ARF might contribute to the accumulation of mutant p53S protein in the tumor and promote tumorigenesis. The high expression of p19ARF correlated with mutant p53 accumulation and tumor progression, suggesting a dual role of p19ARF in tumor promotion or suppression that might depend on the p53 mutation status in tumor cells. The oncogenic gain of function of this recurrent mutation p53S prompts the reconsideration of p53 mutations function that occurs at a low frequency.

Efforts to Develop KRAS Inhibitors.

The high prevalence of KRAS mutations in human cancers and the lack of effective treatments for patients ranks KRAS among the most highly sought-after targets for preclinical oncologists. Pharmaceutical companies and academic laboratories have tried for decades to identify small molecule inhibitors of oncogenic KRAS proteins, but little progress has been made and many have labeled KRAS undruggable. However, recent progress in in silico screening, fragment-based drug design, disulfide tethered screening, and some emerging themes in RAS biology have caused the field to reconsider previously held notions about targeting KRAS. This review will cover some of the historical efforts to identify RAS inhibitors, and some of the most promising efforts currently being pursued.

Somatic mutation driven codon transition bias in human cancer

Accumulation of DNA mutations alters amino acid sequence in the key domains of oncoproteins, leading to cellular malignant transformation. Due to redundancy of the genetic code, the same amino acid alteration can be achieved by multiple distinct genetic mutations, which are considered functionally identical and not actively distinguished in the current cancer genome research. For the first time, we analyzed the distribution of codon level transitions acquired by somatic mutations in human cancers. By analyzing the ~2.5 million nonsynonymous somatic single nucleotide variations (SNVs) found in the COSMIC database, we found 41 recurrent amino acid alterations whose DNA changes are significantly biased toward a specific codon transition. Additional analyses partially identified functional discrepancies between the favored and avoided codon transitions in terms of mutational process, codon usage, alternative splicing, and mRNA stability.

Mitochondrial mutations in human cancer: Curation of translation

ABSTRACTAs a genetic disease, cancer is caused by the activation of oncogenes and the inhibition of tumor suppressor genes via genetic and epigenetic mechanisms.Given the important role of energy metabolism in tumors, we analyzed the cancer-derived mutations occurring in the DNA of the mitochondrion. Mutations in the mitochondrial DNA (mtDNA) compared to nuclear DNA are 62% decreased relative to the coding length per chromosome. We find that the majority of these mutations affects highly conserved nucleotides – significantly exceeding the conservation of the mtDNA – and are devoid of single nucleotide polymorphisms (SNPs).Surprisingly, the leading resources for tumor genetics information universally use the standard genetic code for translation of nucleotide into amino acid sequences in their online resources. However, the nuclear and mitochondrial genetic codes differ for four codons and the usage of incomplete STOP codons. Hence, we analyze and curate the consequences for all mutations in the mtDNA and comprehensively reclassify missense, nonsense and synonymous mutations accordingly. In total, 10% of the mutations are incorrectly translated leading to significant changes in the distribution of mutation types with tripling of nonsense and 69% loss of nonstop extension mutations.Lastly, we provide a curated dataset of coding and non-coding mitochondrial mutations in cancer merged, standardized, duplicate-free and aggregated from two databases as a resource including orthogonal data on their high conservation and SNPs. This study generally highlights the need to universally regard the important differences between the standard and mitochondrial genetic code in life science research.

Mutational signatures efficiently identify different mutational processes underlying cancers with similar somatic mutation spectra

Compared to analyzing mutations with conventional spectra, deciphering mutational signatures provides much greater resolution of biological processes that generate somatic mutations during cancer development. Previous studies of bladder urothelial cancer (BLCA) and cervical squamous cell carcinoma (CESC) mutational signatures failed to uncover different mutational processes underlying the two cancers, which diminishes the capability of mutational signature to differentiate between the two cancers. In this study, we deciphered and compared the mutational signatures of BLCA and CESC. Four BLCA mutational signatures were deciphered from 37,098 somatic mutations of 130 exomes. Five CESC mutational signatures were deciphered from 44,206 somatic mutations of 194 exomes. Three BLCA mutational signatures were very similar to the three CESC signatures. These mutational signatures exhibited common endogenous mutational processes during BLCA and CESC development. The respective BLCA and CESC mutational signature 4 revealed the role of viral infection in both cancers. Noticeably, CESC mutational signature 4 is a novel one that has not been described in other studies. In summary, we have demonstrated the similarities and differences between BLCA and CESC by deciphering mutational signatures. This study will shed light on the use of mutational signatures to clarify the mechanisms of endogenous and exogenous carcinogens that cause somatic mutations in human cancers.

Extracellular inhibitors can attenuate tumorigenic Wnt pathway activity in adenomatous polyposis coli mutants: Predictions of a validated mathematical model.

BackgroundDespite considerable investigational efforts, no method to overcome the pathogenesis caused by loss of function (LoF) mutations in tumor suppressor genes has been successfully translated to the clinic. The most frequent LoF mutation in human cancers is Adenomatous polyposis coli (APC), causing aberrant activation of the Wnt pathway. In nearly all colon cancer tumors, the APC protein is truncated, but still retains partial binding abilities.Objective & methodsHere, we tested the hypothesis that extracellular inhibitors of the Wnt pathway, although acting upstream of the APC mutation, can restore normal levels of pathway activity in colon cancer cells. To this end, we developed and simulated a mathematical model for the Wnt pathway in different APC mutants, with or without the effects of the extracellular inhibitors, Secreted Frizzled-Related Protein1 (sFRP1) and Dickhopf1 (Dkk1). We compared our model predictions to experimental data in the literature.ResultsOur model accurately predicts T-cell factor (TCF) activity in mutant cells that vary in APC mutation. Model simulations suggest that both sFRP1 and DKK1 can reduce TCF activity in APC1638N/1572T and Apcmin/min mutants, but restoration of normal activity levels is possible only in the former. When applied in combination, synergism between the two inhibitors can reduce their effective doses to one-fourth of the doses required under single inhibitor application. Overall, re-establishment of normal Wnt pathway activity is predicted for every APC mutant in whom TCF activity is increased by up to 11 fold.ConclusionsOur work suggests that extracellular inhibitors can effectively restore normal Wnt pathway activity in APC-truncated cancer cells, even though these LoF mutations occur downstream of the inhibitory action. The insufficient activity of the truncated APC can be quantitatively balanced by the upstream intervention. This new concept of upstream intervention to control the effects of downstream mutations may be considered also for other partial LoF mutations in other signaling pathways.

Sirtuin 2 mutations in human cancers impair its function in genome maintenance

Sirtuin 2 (SIRT2) is a sirtuin family deacetylase, which maintains genome integrity and prevents tumorigenesis. Although Sirt2 deficiency in mice leads to tumorigenesis, the functional significance of somatic SIRT2 mutations in human tumors is unclear. Using structural insight combined with bioinformatics and functional analyses, we show that naturally occurring cancer-associated SIRT2 mutations at evolutionarily conserved sites disrupt its deacetylation of DNA-damage response proteins by impairing SIRT2 catalytic activity or protein levels but not its localization or binding with substrate. We observed that these SIRT2 mutant proteins fail to restore the replication stress sensitivity, impairment in recovery from replication stress, and impairment in ATR-interacting protein (ATRIP) focus accumulation of SIRT2 deficiency. Moreover, the SIRT2 mutant proteins failed to rescue the spontaneous induction of DNA damage and micronuclei of SIRT2 deficiency in cancer cells. Our findings support a model for SIRT2's tumor-suppressive function in which somatic mutations in SIRT2 contribute to genomic instability by impairing its deacetylase activity or diminishing its protein levels in the DNA-damage response. In conclusion, our work provides a mechanistic basis for understanding the biological and clinical significance of SIRT2 mutations in genome maintenance and tumor suppression.

Tissue-Specific Signaling Networks Rewired by Major Somatic Mutations in Human Cancer Revealed by Proteome-Wide Discovery.

Massive somatic mutations discovered by large cancer genome sequencing projects provide unprecedented opportunities in the development of precision oncology. However, deep understanding of functional consequences of somatic mutations and identifying actionable mutations and the related drug responses currently remain formidable challenges. Dysfunction of protein posttranslational modification plays critical roles in tumorigenesis and drug responses. In this study, we proposed a novel computational oncoproteomics approach, named kinome-wide network module for cancer pharmacogenomics (KNMPx), for identifying actionable mutations that rewired signaling networks and further characterized tumorigenesis and anticancer drug responses. Specifically, we integrated 746,631 missense mutations in 4,997 tumor samples across 16 major cancer types/subtypes from The Cancer Genome Atlas into over 170,000 carefully curated nonredundant phosphorylation sites covering 18,610 proteins. We found 47 mutated proteins (e.g., ERBB2, TP53, and CTNNB1) that had enriched missense mutations at their phosphorylation sites in pan-cancer analysis. In addition, tissue-specific kinase-substrate interaction modules altered by somatic mutations identified by KNMPx were significantly associated with patient survival. We further reported a kinome-wide landscape of pharmacogenomic interactions by incorporating somatic mutation-rewired signaling networks in 1,001 cancer cell lines via KNMPx. Interestingly, we found that cell lines could highly reproduce oncogenic phosphorylation site mutations identified in primary tumors, supporting the confidence in their associations with sensitivity/resistance of inhibitors targeting EGF, MAPK, PI3K, mTOR, and Wnt signaling pathways. In summary, our KNMPx approach is powerful for identifying oncogenic alterations via rewiring phosphorylation-related signaling networks and drug sensitivity/resistance in the era of precision oncology. Cancer Res; 77(11); 2810-21. ©2017 AACR.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Structural insights into POT1-TPP1 interaction and POT1 C-terminal mutations in human cancer

Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension. However, how POT1 interacts with TPP1 remains unknown. Here we present the crystal structure of the C-terminal portion of human POT1 (POT1C) complexed with the POT1-binding motif of TPP1. The structure shows that POT1C contains two domains, a third OB fold and a Holliday junction resolvase-like domain. Both domains are essential for binding to TPP1. Notably, unlike the heart-shaped structure of ciliated protozoan Oxytricha nova TEBPα–β complex, POT1–TPP1 adopts an elongated V-shaped conformation. In addition, we identify several missense mutations in human cancers that disrupt the POT1C–TPP1 interaction, resulting in POT1 instability. POT1C mutants that bind TPP1 localize to telomeres but fail to repress a DNA damage response and inappropriate repair by A-NHEJ. Our results reveal that POT1 C terminus is essential to prevent initiation of genome instability permissive for tumorigenesis.