Whole-genome sequencing of liver cancers identifies etiological influences on mutation patterns and recurrent mutations in chromatin regulators

Genomics-driven oncology: framework for an emerging paradigm

A majority of cancers are driven by genomic alterations that dysregulate key oncogenic pathways influencing cell growth and survival. However, the ability to harness tumor genetic information for its full clinical potential has only recently become manifest. Over the past several years, the convergence of discovery, technology, and therapeutic development has created an unparalleled opportunity to test the hypothesis that systematic knowledge of genomic information from individual tumors can improve clinical outcomes for many patients with cancer. Rigorous evaluation of this genomics-driven cancer medicine hypothesis will require many logistic innovations that are guided by overarching conceptual advances in tumor genomic profiling, data interpretation, clinical trial design, and the ethical return of genetic results to oncologists and their patients. The results of these efforts and the rigor with which they are implemented will determine whether and how comprehensive tumor genomic information may become incorporated into the routine care of patients with cancer.

Existing and emerging technologies for tumor genomic profiling

Ongoing global genome characterization efforts are revolutionizing our knowledge of cancer genomics and tumor biology. In parallel, information gleaned from these studies on driver cancer gene alterations--mutations, copy number alterations, translocations, and/or chromosomal rearrangements--an be leveraged, in principle, to develop a cohesive framework for individualized cancer treatment. These possibilities have been enabled, to a large degree, by revolutionary advances in genomic technologies that facilitate systematic profiling for hallmark cancer genetic alterations at increasingly fine resolutions. Ongoing innovations in existing genomics technologies, as well as the many emerging technologies, will likely continue to advance translational cancer genomics and precision cancer medicine.

Mutations in TP53, CTNNB1 and PIK3CA genes in hepatocellular carcinoma associated with hepatitis B and hepatitis C virus infections

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. Hepatocarcinogenesis is a multistep process mainly associated with persistent infection with hepatitis B (HBV) or C (HCV) viruses and always involving the accumulation of genetic alterations over decades of chronic liver disease. Mutations in TP53 and CTNNB1 genes are considered the cancer drivers for HCC development with variable frequencies depending on the etiology. Here we present a comprehensive review evaluating somatic mutations in TP53 and CTNNB1 genes in HBV- and HCV-related HCCs. Moreover, we report the mutational analysis of TP53 (exons 4-9) and CTNNB1 (exon 3) as well as PIK3CA (exon 9) genes in HCC from Southern Italy. The overall mutation frequency of TP53 and CTNNB1 was 33.3%, while hotspot variations in PIK3CA were completely absent. CTNNB1 mutations were significantly associated with young age (P=0.019) and moderately/poorly differentiated HCV-related HCC (P=0.015). The extended analysis of genetic alterations will help to identify molecular markers for liver cancer prevention, diagnosis and treatment of HBV and HCV-associated liver cancer.

Clinical relevance of cancer genome sequencing

The arrival of both high-throughput and bench-top next-generation sequencing technologies and sequence enrichment methods has revolutionized our approach to dissecting the genetic basis of cancer. These technologies have been almost invariably employed in whole-genome sequencing (WGS) and whole-exome sequencing (WES) studies. Both WGS and WES approaches have been widely applied to interrogate the somatic mutational landscape of sporadic cancers and identify novel germline mutations underlying familial cancer syndromes. The clinical implications of cancer genome sequencing have become increasingly clear, for example in diagnostics. In this editorial, we present these advances in the context of research discovery and discuss both the clinical relevance of cancer genome sequencing and the challenges associated with the adoption of these genomic technologies in a clinical setting.

Functional analysis of in-frame indel ARID1A mutations reveals new regulatory mechanisms of its tumor suppressor functions

AT-rich interactive domain 1A (ARID1A) has emerged as a new tumor suppressor in which frequent somatic mutations have been identified in several types of human cancers. Although most ARID1A somatic mutations are frame-shift or nonsense mutations that contribute to mRNA decay and loss of protein expression, 5% of ARID1A mutations are in-frame insertions or deletions (indels) that involve only a small stretch of peptides. Naturally occurring in-frame indel mutations provide unique and useful models to explore the biology and regulatory role of ARID1A. In this study, we analyzed indel mutations identified in gynecological cancers to determine how these mutations affect the tumor suppressor function of ARID1A. Our results demonstrate that all in-frame mutants analyzed lost their ability to inhibit cellular proliferation or activate transcription of CDKN1A, which encodes p21, a downstream effector of ARID1A. We also showed that ARID1A is a nucleocytoplasmic protein whose stability depends on its subcellular localization. Nuclear ARID1A is less stable than cytoplasmic ARID1A because ARID1A is rapidly degraded by the ubiquitin-proteasome system in the nucleus. In-frame deletions affecting the consensus nuclear export signal reduce steady-state protein levels of ARID1A. This defect in nuclear exportation leads to nuclear retention and subsequent degradation. Our findings delineate a mechanism underlying the regulation of ARID1A subcellular distribution and protein stability and suggest that targeting the nuclear ubiquitin-proteasome system can increase the amount of the ARID1A protein in the nucleus and restore its tumor suppressor functions.

Chromatin regulators with tumor suppressor properties and their alterations in human cancers

Key components of the cell epigenome include DNA CpG methylation profile and chromatin modification patterns. Chromatin regulators act as master controllers of gene transcription in normal cells through regulation of histone modifications and chromatin remodeling. During human cancer pathogenesis, the functions of chromatin regulators are frequently disrupted by genetic mutations and/or epigenetic alterations, causing perturbation of broad or even genome-wide scale gene-expression profiles. Thus, histone-modifying and chromatin-remodeling genes can be taken as critical 'cancer genes'. This review summarizes the current knowledge on chromatin regulators with tumor suppressor properties, as well as their aberrant alterations in human cancers.

Quantification of tumor DNA in serum and vascular invasion of human hepatocellular carcinoma

OBJECTIVES

Hepatocellular carcinoma (HCC) is one of the common cancers worldwide. Accurate diagnosis of tumor progression is critical for the appropriate management of HCC. Here, we established a sensitive assay to detect and quantify tumor-derived DNA in the serum of HCC patients.

METHODS

Aberrant methylation of the APC gene was quantified in 23 HCC patients and 8 healthy volunteers using 100 µl of serum. For sensitive detection and accurate quantification of tumor DNA, we combined seminested polymerase chain reaction (PCR) with TaqMan PCR, which could amplify the APC gene regardless of the methylation status and detect the methylated and unmethylated sequences separately. The ratio of methylated to unmethylated sequences was quantified.

RESULTS

The methylated APC gene was detected in all HCC patients examined, but no healthy volunteers showed amplification of methylated sequences in serum. HCC patients with portal vein thrombosis showed a significantly higher methylated to unmethylated APC gene ratio in serum than those without portal vein thrombosis (p = 0.0029).

CONCLUSIONS

Considering the strong association between the ratio of the methylated to unmethylated APC sequences in serum and the presence of portal vein thrombosis, methylation status of APC sequences could be a promising marker for improving HCC management.

Recent advancements in comprehensive genetic analyses for human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) typically develops in the liver with chronic hepatitis and cirrhosis, and activation of oncogenes and inactivation of tumor suppressor genes occurs during carcinogenesis via genetic and epigenetic mechanisms. Recent advancements in the development of analyses for examining the cancer genome have revealed information regarding genetic alterations in HCC tissues. According to previous studies, the incidence of recurrent genetic alterations in individual genes was thought to be relatively rare and limited to a subset of a few cancer-specific genes such as tumor suppressor p53, RB genes and oncogenes such as CTNNB1. However, recent whole-genome analyses and exome sequencing of tumor DNA have revealed numerous novel alterations of cancer-related genes and pathways critical for HCC development. In addition, various risk factors for HCC, such as the presence or absence of hepatitis B and C virus, may affect the mutation profile of the corresponding cancer genome. On the other hand, genome-wide association studies have also identified important single-nucleotide polymorphisms involved in HCC development, which may allow detection of a group at high risk of HCC emergence. Such analyses will clarify how this malignancy can be treated, diagnosed and prevented more effectively.

[Chromatin remodeling defects and cancer: the SWI/SNF example]

The SWI/SNF complex is a multiprotein complex essential for chromatin remodelling. As such, it plays a key role in the epigenetic regulation of genome expression. This complex is composed of a dozen of proteins, some of which are constant and ubiquitous, especially SMARCB1 and SMARCA4. Mutations in these genes are now described in an increasing number of tumors. Mutations in SMARCB1 characterize the majority of rhabdoid tumors, an aggressive malignancy that exquisitely depends on this single genetic event. Rare rhabdoid tumors have mutation in SMARCA4, a genetic abnormality also found in some medulloblastomas. Many other tumor types, of variable aggressiveness, show an abnormal loss of expression of SMARCB1, but the genetic underlying cause most often remains elusive. The recent sequencings of whole exomes have described frequent mutations in other genes of the SWI/SNF complex: mutations in ARID1A in liver, gastric or bladder carcinomas, and PBRM1 mutations in renal cancers. These data establish the wide role of SWI/SNF complex in cancers and justify that major efforts should now be devoted to this common mechanism of human oncogenesis.

Antitumor effect of SIRT1 inhibition in human HCC tumor models in vitro and in vivo

Sirtuins (SIRT1-7) are a highly conserved family of NAD(+)-dependent enzymes that control the activity of histone and nonhistone regulatory proteins. SIRT1 is purposed to promote longevity and to suppress the initiation of some cancers. Nevertheless, SIRT1 is reported to function as a tumor suppressor as well as an oncogenic protein. Our data show that compared with normal liver or surrounding tumor tissue, SIRT1 is strongly overexpressed in human hepatocellular carcinoma (HCC). In addition, human HCC cell lines (Hep3B, HepG2, HuH7, HLE, HLF, HepKK1, skHep1) were screened for the expression of the sirtuin family members and only SIRT1 was consistently overexpressed compared with normal hepatocytes. To determine its effect on HCC growth, SIRT1 activity was inhibited either with lentiviruses expressing short hairpin RNAs or with the small molecule inhibitor, cambinol. Knockdown or inhibition of SIRT1 activity had a cytostatic effect, characterized by an altered morphology, impaired proliferation, an increased expression of differentiation markers, and cellular senescence. In an orthotopic xenograft model, knockdown of SIRT1 resulted in 50% fewer animals developing tumors and cambinol treatment resulted in an overall lower tumor burden. Taken together, our data show that inhibition of SIRT1 in HCC cells impairs their proliferation in vitro and tumor formation in vivo. These data suggest that SIRT1 expression positively influences the growth of HCC and support further studies aimed to block its activity alone or in combination as a novel treatment strategy.

Minireview: Conversing with chromatin: the language of nuclear receptors

Nuclear receptors are transcription factors that are activated by physiological stimuli to bind DNA in the context of chromatin and regulate complex biological pathways. Major advances in nuclear receptor biology have been aided by genome scale examinations of receptor interactions with chromatin. In this review, we summarize the roles of the chromatin landscape in regulating nuclear receptor function. Chromatin acts as a central integrator in the nuclear receptor-signaling axis, operating in distinct temporal modalities. Chromatin effects nuclear receptor action by specifying its genomic localization and interactions with regulatory elements. On receptor binding, changes in chromatin operate as an effector of receptor signaling to modulate transcriptional events. Chromatin is therefore an integral component of the pathways that guide nuclear receptor action in cell-type-specific and cell state-dependent manners.

High-throughput sequencing for biology and medicine

Advances in genome sequencing have progressed at a rapid pace, with increased throughput accompanied by plunging costs. But these advances go far beyond faster and cheaper. High-throughput sequencing technologies are now routinely being applied to a wide range of important topics in biology and medicine, often allowing researchers to address important biological questions that were not possible before. In this review, we discuss these innovative new approaches-including ever finer analyses of transcriptome dynamics, genome structure and genomic variation-and provide an overview of the new insights into complex biological systems catalyzed by these technologies. We also assess the impact of genotyping, genome sequencing and personal omics profiling on medical applications, including diagnosis and disease monitoring. Finally, we review recent developments in single-cell sequencing, and conclude with a discussion of possible future advances and obstacles for sequencing in biology and health.

The mutational landscape of chromatin regulatory factors across 4,623 tumor samples

BACKGROUND

Chromatin regulatory factors are emerging as important genes in cancer development and are regarded as interesting candidates for novel targets for cancer treatment. However, we lack a comprehensive understanding of the role of this group of genes in different cancer types.

RESULTS

We have analyzed 4,623 tumor samples from thirteen anatomical sites to determine which chromatin regulatory factors are candidate drivers in these different sites. We identify 34 chromatin regulatory factors that are likely drivers in tumors from at least one site, all with relatively low mutational frequency. We also analyze the relative importance of mutations in this group of genes for the development of tumorigenesis in each site, and indifferent tumor types from the same site.

CONCLUSIONS

We find that, although tumors from all thirteen sites show mutations in likely driver chromatin regulatory factors, these are more prevalent in tumors arising from certain tissues. With the exception of hematopoietic, liver and kidney tumors, as a median, the mutated factors are less than one fifth of all mutated drivers across all sites analyzed. We also show that mutations in two of these genes, MLL and EP300, correlate with broad expression changes across cancer cell lines, thus presenting at least one mechanism through which these mutations could contribute to tumorigenesis in cells of the corresponding tissues.

Novel therapeutics in hepatocellular carcinoma: how can we make progress?

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death globally, and its prevalence and impact are even more profound because sorafenib is the only systemic therapy proven to prolong survival in patients with advanced disease. Randomized phase III trials of other novel targeted agents including sunitinib, linifanib, brivanib, and the combination of sorafenib plus erlotinib have failed to improve overall survival compared with sorafenib as a single agent in the first line setting, as well as compared with placebo in the second-line setting, in the case of brivanib. These negative studies are a sobering reminder of the challenges to clinical research in HCC, including the competing comorbidity of liver dysfunction, marked clinical and biologic heterogeneity, and the unreliability of surrogate endpoints to accurately predict survival. To address these challenges, HCC-specific phase I/Ib cohorts must be used to define the maximum tolerated dose and drug exposure in this organ dysfunction population with high background rates of adverse events and little tolerance for superimposed treatment-related toxicity. Pooled analyses of contemporary randomized trials and database studies should be undertaken to define the strongest prognostic factors for stratification in future phase III studies. Research blood and archival tumor specimens should be collected from patients on clinical trials to intensify the search for biomarkers of responsive or resistant subsets, in parallel with ongoing efforts to improve on radiographic response assessment. Collectively, these and other new strategies are needed to make progress in identifying active novel therapeutics for patients with HCC.

Understanding genomic alterations in cancer genomes using an integrative network approach

In recent years, cancer genome sequencing and other high-throughput studies of cancer genomes have generated many notable discoveries. In this review, novel genomic alteration mechanisms, such as chromothripsis (chromosomal crisis) and kataegis (mutation storms), and their implications for cancer are discussed. Genomic alterations spur cancer genome evolution. Thus, the relationship between cancer clonal evolution and cancer stems cells is commented. The key question in cancer biology concerns how these genomic alterations support cancer development and metastasis in the context of biological functioning. Thus far, efforts such as pathway analysis have improved the understanding of the functional contributions of genetic mutations and DNA copy number variations to cancer development, progression and metastasis. However, the known pathways correspond to a small fraction, plausibly 5-10%, of somatic mutations and genes with an altered copy number. To develop a comprehensive understanding of the function of these genomic alterations in cancer, an integrative network framework is proposed and discussed. Finally, the challenges and the directions of studying cancer omic data using an integrative network approach are commented.

Recurrent targeted genes of hepatitis B virus in the liver cancer genomes identified by a next-generation sequencing-based approach

Integration of the viral DNA into host chromosomes was found in most of the hepatitis B virus (HBV)–related hepatocellular carcinomas (HCCs). Here we devised a massive anchored parallel sequencing (MAPS) method using next-generation sequencing to isolate and sequence HBV integrants. Applying MAPS to 40 pairs of HBV–related HCC tissues (cancer and adjacent tissues), we identified 296 HBV integration events corresponding to 286 unique integration sites (UISs) with precise HBV–Human DNA junctions. HBV integration favored chromosome 17 and preferentially integrated into human transcript units. HBV targeted genes were enriched in GO terms: cAMP metabolic processes, T cell differentiation and activation, TGF beta receptor pathway, ncRNA catabolic process, and dsRNA fragmentation and cellular response to dsRNA. The HBV targeted genes include 7 genes (PTPRJ, CNTN6, IL12B, MYOM1, FNDC3B, LRFN2, FN1) containing IPR003961 (Fibronectin, type III domain), 7 genes (NRG3, MASP2, NELL1, LRP1B, ADAM21, NRXN1, FN1) containing IPR013032 (EGF-like region, conserved site), and three genes (PDE7A, PDE4B, PDE11A) containing IPR002073 (3′, 5′-cyclic-nucleotide phosphodiesterase). Enriched pathways include hsa04512 (ECM-receptor interaction), hsa04510 (Focal adhesion), and hsa04012 (ErbB signaling pathway). Fewer integration events were found in cancers compared to cancer-adjacent tissues, suggesting a clonal expansion model in HCC development. Finally, we identified 8 genes that were recurrent target genes by HBV integration including fibronectin 1 (FN1) and telomerase reverse transcriptase (TERT1), two known recurrent target genes, and additional novel target genes such as SMAD family member 5 (SMAD5), phosphatase and actin regulator 4 (PHACTR4), and RNA binding protein fox-1 homolog (C. elegans) 1 (RBFOX1). Integrating analysis with recently published whole-genome sequencing analysis, we identified 14 additional recurrent HBV target genes, greatly expanding the HBV recurrent target list. This global survey of HBV integration events, together with recently published whole-genome sequencing analyses, furthered our understanding of the HBV–related HCC.

Integration of the hepatitis B virus (HBV) into the human liver cells was found in most of the related hepatocellular carcinomas (HCCs). Here, taking the recent advances in high-throughput sequencing, we devised an efficient and cost-effective method that we named massive anchored parallel sequencing (MAPS) method, to conduct a global survey of HBV integration events in 40 pairs of HBV–related HCC tissues (cancer and adjacent tissues). We identified 286 unique integration sites (UISs) with precise HBV–Human DNA junctions. We identified a higher number of HBV integration events in cancer adjacent tissues than in HCC tissues, suggesting a clonal expansion process during HCC development. We also found that fibronectin and its related genes (fibronectin type III-like fold domain containing genes) were frequently targeted by HBV. Fibronectin is a protein produced abundantly by the liver cells and also serves as a linker in the extracellular matrix. Our findings might suggest a role for the disruption of fibronectin and associated cellular matrix in HBV related liver cancers. We also identified 14 additional recurrent HBV target genes, greatly expanding the HBV recurrent target list. This study would add significantly to our understanding of HCC development.

ARID1A mutations in cancer: another epigenetic tumor suppressor?

Although disordered chromatin organization has long been recognized as a feature of cancer, the molecular underpinnings of chromatin structure, epigenetic regulation, and their relationships to transcription are only beginning to be understood. Cancer genome sequencing studies have revealed a novel theme: frequent mutation of epigenetic regulators. Among these, the ARID1A/BAF250A subunit of the SWI/SNF (BRG1-associated factors) chromatin remodeling complex has emerged as recurrently mutated in a broad array of tumor types. We review the genomic and functional data supporting classification of ARID1A as a tumor suppressor.

SIGNIFICANCE

Mutations in chromatin remodeling complex genes are increasingly recognized in many cancer types. However, the mechanisms by which chromatin remodeling complexes contribute to gene expression and the cancer phenotype are poorly understood. Understanding how mutation of chromatin remodelers facilitates transformation may offer the potential for development and implementation of novel therapies for cancer.

Integrated genomic analyses identify ARID1A and ARID1B alterations in the childhood cancer neuroblastoma

Neuroblastomas are tumors of peripheral sympathetic neurons and are the most common solid tumor in children. To determine the genetic basis for neuroblastoma we performed whole-genome sequencing (6 cases), exome sequencing (16 cases), genome-wide rearrangement analyses (32 cases), and targeted analyses of specific genomic loci (40 cases) using massively parallel sequencing. On average each tumor had 19 somatic alterations in coding genes (range, 3–70). Among genes not previously known to be involved in neuroblastoma, chromosomal deletions and sequence alterations of chromatin remodeling genes, ARID1A and ARID1B, were identified in 8 of 71 tumors (11%) and were associated with early treatment failure and decreased survival. Using tumor-specific structural alterations, we developed an approach to identify rearranged DNA fragments in sera, providing personalized biomarkers for minimal residual disease detection and monitoring. These results highlight dysregulation of chromatin remodeling in pediatric tumorigenesis and provide new approaches for the management of neuroblastoma patients.

Genomic sequencing in cancer

Genomic sequencing has provided critical insights into the etiology of both simple and complex diseases. The enormous reductions in cost for whole genome sequencing have allowed this technology to gain increasing use. Whole genome analysis has impacted research of complex diseases including cancer by allowing the systematic analysis of entire genomes in a single experiment, thereby facilitating the discovery of somatic and germline mutations, and identification of the insertions, deletions, and structural rearrangements, including translocations and inversions, in novel disease genes. Whole-genome sequencing can be used to provide the most comprehensive characterization of the cancer genome, the complexity of which we are only beginning to understand. Hence in this review, we focus on whole-genome sequencing in cancer.

Next-generation sequencing in the clinic: promises and challenges

The advent of next generation sequencing (NGS) technologies has revolutionized the field of genomics, enabling fast and cost-effective generation of genome-scale sequence data with exquisite resolution and accuracy. Over the past years, rapid technological advances led by academic institutions and companies have continued to broaden NGS applications from research to the clinic. A recent crop of discoveries have highlighted the medical impact of NGS technologies on Mendelian and complex diseases, particularly cancer. However, the ever-increasing pace of NGS adoption presents enormous challenges in terms of data processing, storage, management and interpretation as well as sequencing quality control, which hinder the translation from sequence data into clinical practice. In this review, we first summarize the technical characteristics and performance of current NGS platforms. We further highlight advances in the applications of NGS technologies towards the development of clinical diagnostics and therapeutics. Common issues in NGS workflows are also discussed to guide the selection of NGS platforms and pipelines for specific research purposes.

Comprehensive genome sequencing of the liver cancer genome

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide. Recently, comprehensive whole genome and exome sequencing analyses for HCC revealed new cancer-associated genes and a variety of genomic alterations. In particular, frequent genetic alterations of the chromatin remodeling genes were observed, suggesting a new potential therapeutic target for HCC. Sequencing analysis has further identified the molecular complexities of multicentric lesions and intratumoral heterogeneity. Detailed analyses of the somatic substitution pattern of the cancer genome and the HBV virus genome integration sites by using whole-genome sequencing will elucidate the molecular basis and diverse etiological factors involved in liver cancer development.

Exome sequencing of serous endometrial tumors identifies recurrent somatic mutations in chromatin-remodeling and ubiquitin ligase complex genes

Endometrial cancer is the 6^th most commonly diagnosed cancer among women worldwide, causing ~74,000 deaths annually ¹. Serous endometrial cancers are a clinically aggressive subtype with a poorly defined genetic etiology ^2-4. We used whole exome sequencing (WES) to comprehensively search for somatic mutations within ~22,000 protein-encoding genes among 13 primary serous endometrial tumors. We subsequently resequenced 18 genes that were mutated in more than one tumor, and/or were genes that formed an enriched functional grouping, from 40 additional serous tumors. We identified high frequencies of somatic mutations in CHD4 (17%), EP300 (8%), ARID1A (6%), TSPYL2 (6%), FBXW7 (29%), SPOP (8%), MAP3K4 (6%) and ABCC9 (6%). Overall, 36.5% of serous tumors had mutated a chromatin-remodeling gene and 35% had mutated a ubiquitin ligase complex gene, implicating the frequent mutational disruption of these processes in the molecular pathogenesis of one of the deadliest forms of endometrial cancer.

Next generation sequencing reveals genetic landscape of hepatocellular carcinomas

Liver cancer is one of most deadly cancers worldwide. Hepatocellular carcinoma (HCC) represents a major histological subtype of liver cancers. As cancer is a genetic disease, genetic lesions play a major role in HCC tumorigenesis and progression. Although significant progress has been made to uncover genetic alterations in HCCs, our understanding of genetics involved in the initiation and progression of HCC is far from complete. Next generation sequencing (NGS) has provided a new paradigm in biomedical research to delineate the genetic basis of human diseases. While identification of cancer somatic mutations has been serendipitous, genome sequencing has provided an unbiased approach to systematically catalog somatic mutations and elucidate the mechanisms of tumourigenesis. A number of recently published NGS studies on HCCs have not only confirmed previously known mutations in CTNNB1 and TP53 in HCC, but also identified novel genetic alterations in HCC including mutations in genes involved in epigenetic regulation. WNT, cell cycle and chromatin remodeling pathways have emerged as key oncogenic drivers in HCCs. The frequently altered genes and pathways in HCC reflect classical cancer hallmarks. These findings have started to depict a genetic landscape in HCC and will facilitate development of novel therapeutics for the treatment of this deadly disease.

Emerging signaling pathways in hepatocellular carcinoma

Signaling pathways have become a major source of targets for novel therapies in hepatocellular carcinoma (HCC). Survival benefits achieved with sorafenib, a multikinase inhibitor, are unprecedented and underscore the importance of improving our understanding of how signaling networks interact in transformed cells. Numerous signaling modules are de-regulated in HCC, including some related to growth factor signaling (e.g., IGF, EGF, PDGF, FGF, HGF), cell differentiation (WNT, Hedgehog, Notch), and angiogenesis (VEGF). Intracellular mediators such as RAS and AKT/MTOR may also play a role in HCC development and progression. Different molecular mechanisms have been shown to induce aberrant pathway activation. These include point mutations, chromosomal aberrations, and epigenetically driven down-regulation. The use of novel molecular technologies such as next-generation sequencing in HCC research has enabled the identification of novel pathways previously underexplored in the HCC field, such as chromatin remodeling and autophagy. Considering recent failures of molecular therapies in advanced clinical trials (e.g., sunitinib, brivanib), survey of these and other new pathways may provide alternative therapeutic targets.

Histone methylase MLL1 has critical roles in tumor growth and angiogenesis and its knockdown suppresses tumor growth in vivo

Mixed lineage leukemias (MLL) are human histone H3 lysine-4 specific methyl transferases that play critical roles in gene expression, epigenetics, and cancer. Herein, we demonstrated that antisense-mediated knockdown of MLL1 induced cell cycle arrest and apoptosis in cultured cells. Intriguingly, application of MLL1-antisense specifically knocked down MLL1 in vivo and suppressed the growth of xenografted cervical tumor implanted in nude mouse. MLL1-knockdown downregulated various growth and angiogenic factors such as HIF1α, VEGF and CD31 in tumor tissue affecting tumor growth. MLL1 is overexpressed along the line of vascular network and localized adjacent to endothelial cell layer expressing CD31, indicating potential roles of MLL1 in vasculogenesis. MLL1 is also overexpressed in the hypoxic regions along with HIF1α. Overall, our studies demonstrated that MLL1 is a key player in hypoxia signaling, vasculogenesis, and tumor growth, and its depletion suppresses tumor growth in vivo, indicating its potential in novel cancer therapy.

Perspectives of integrative cancer genomics in next generation sequencing era

The explosive development of genomics technologies including microarrays and next generation sequencing (NGS) has provided comprehensive maps of cancer genomes, including the expression of mRNAs and microRNAs, DNA copy numbers, sequence variations, and epigenetic changes. These genome-wide profiles of the genetic aberrations could reveal the candidates for diagnostic and/or prognostic biomarkers as well as mechanistic insights into tumor development and progression. Recent efforts to establish the huge cancer genome compendium and integrative omics analyses, so-called "integromics", have extended our understanding on the cancer genome, showing its daunting complexity and heterogeneity. However, the challenges of the structured integration, sharing, and interpretation of the big omics data still remain to be resolved. Here, we review several issues raised in cancer omics data analysis, including NGS, focusing particularly on the study design and analysis strategies. This might be helpful to understand the current trends and strategies of the rapidly evolving cancer genomics research.