Pancreatic cancer

The past two decades have witnessed an explosion in our understanding of pancreatic cancer, and it is now clear that pancreatic cancer is a disease of inherited (germ-line) and somatic gene mutations. The genes mutated in pancreatic cancer include KRAS2, p16/CDKN2A, TP53, and SMAD4/DPC4, and these are accompanied by a substantial compendium of genomic and transcriptomic alterations that facilitate cell cycle deregulation, cell survival, invasion, and metastases. Pancreatic cancers do not arise de novo, and three distinct precursor lesions have been identified. Experimental models of pancreatic cancer have been developed in genetically engineered mice, which recapitulate the multistep progression of the cognate human disease. Although the putative cell of origin for pancreatic cancer remains elusive, minor populations of cells with stem-like properties have been identified that appear responsible for tumor initiation, metastases, and resistance of pancreatic cancer to conventional therapies.

High-throughput sequence analysis of the tyrosine kinome in acute myeloid leukemia

To determine whether aberrantly activated tyrosine kinases other than FLT3 and c-KIT contribute to acute myeloid leukemia (AML) pathogenesis, we used high-throughput (HT) DNA sequence ana-lysis to screen exons encoding the activation loop and juxtamembrane domains of 85 tyrosine kinase genes in 188 AML patients without FLT3 or c-KIT mutations. The screen identified 30 nonsynonymous sequence variations in 22 different kinases not previously reported in single-nucleotide polymorphism (SNP) databases. These included a novel FLT3 activating allele and a previously described activating mutation in MET (METT1010I). The majority of novel sequence variants were stably expressed in factor-dependent Ba/F3 cells. Apart from one FLT3 allele, none of the novel variants showed constitutive phosphorylation by immunoblot analysis and none transformed Ba/F3 cells to factor-independent growth. These findings indicate the majority of these alleles are not potent tyrosine kinase activators in this cellular context and that a significant proportion of nonsynonymous sequence variants identified in HT DNA sequencing screens may not have functional significance. Although some sequence variants may represent SNPs, these data are consistent with recent reports that a significant fraction of such sequence variants are "passenger" rather than "driver" alleles and underscore the importance of functional assessment of candidate disease alleles.

Snap-to-it probes: chelate-constrained nucleobase oligomers with enhanced binding specificity

We describe snap-to-it probes, a novel probe technology to enhance the hybridization specificity of natural and unnatural nucleic acid oligomers using a simple and readily introduced structural motif. Snap-to-it probes were prepared from peptide nucleic acid (PNA) oligomers by modifying each terminus with a coordinating ligand. The two coordinating ligands constrain the probe into a macrocyclic configuration through formation of an intramolecular chelate with a divalent transition metal ion. On hybridization with a DNA target, the intramolecular chelate in the snap-to-it probe dissociates, resulting in the probe 'snapping-to' and binding the target nucleic acid. Thermal transition analysis of snap-to-it probes with complementary and single-mismatch DNA targets revealed that the transition between free and target-bound probe conformations was a reversible equilibrium, and the intramolecular chelate provided a thermodynamic barrier to target binding that resulted in a significant increase in mismatch discrimination. A 4-6 degrees C increase in specificity (DeltaT(m)) was observed from snap-to-it probes bearing either terminal iminodiacetic acid ligands coordinated with Ni(2+), or terminal dihistidine and nitrilotriacetic acid ligands coordinated with Cu(2+). The difference in specificity of the PNA oligomer relative to DNA was more than doubled in snap-to-it probes. Snap-to-it probes labeled with a fluorophore-quencher pair exhibited target-dependent fluorescence enhancement upon binding with target DNA.

The effect of pedigree structure on detection of deletions and other null alleles

Deletions and other null alleles for genetic markers can be detected as a special case of non-Mendelian inheritance, ie when a parent and a child appear to be homozygous for different alleles. The probability to detect a deletion for a fixed overall number of investigated individuals was calculated for biallelic and multiallelic markers with varying allele frequencies. To determine the effect of increasing the number of parents and grandparents, the probability for this event was derived for a parent and one child, a trio, a trio with one grandparent and a trio with two grandparents. The results for biallelic markers show that for a fixed total number of individuals, a sample of trios with two grandparents is always more efficient than the other family types, despite a lower total number of founder chromosomes in the sample. For multiallelic markers the outcome varies. The effect of adding additional children to a nuclear family was also investigated. For nuclear families, the optimal number of children is two or three, depending on the allele frequencies. It is shown that adding children is more efficient than adding grandparents.

Replacing PCR with COLD-PCR enriches variant DNA sequences and redefines the sensitivity of genetic testing

PCR is widely employed as the initial DNA amplification step for genetic testing. However, a key limitation of PCR-based methods is the inability to selectively amplify low levels of mutations in a wild-type background. As a result, downstream assays are limited in their ability to identify subtle genetic changes that can have a profound impact in clinical decision-making and outcome. Here we describe co-amplification at lower denaturation temperature PCR (COLD-PCR), a novel form of PCR that amplifies minority alleles selectively from mixtures of wild-type and mutation-containing sequences irrespective of the mutation type or position on the sequence. We replaced regular PCR with COLD-PCR before sequencing or genotyping assays to improve mutation detection sensitivity by up to 100-fold and identified new mutations in the genes encoding p53, KRAS and epidermal growth factor in heterogeneous cancer samples that had been missed by the currently used methods. For clinically relevant microdeletions, COLD-PCR enabled exclusive amplification and isolation of the mutants. COLD-PCR will transform the capabilities of PCR-based genetic testing, including applications in cancer, infectious diseases and prenatal identification of fetal alleles in maternal blood.

From cytogenetics to next-generation sequencing technologies: advances in the detection of genome rearrangements in tumorsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Systems and Chemical Biology, and has undergone the Journal's usual peer review process

Genome rearrangements have long been recognized as hallmarks of human tumors and have been used to diagnose cancer. Techniques used to detect genome rearrangements have evolved from microscopic examinations of chromosomes to the more recent microarray-based approaches. The availability of next-generation sequencing technologies may provide a means for scrutinizing entire cancer genomes and transcriptomes at unparalleled resolution. Here we review the methods that have been used to detect genome rearrangements and discuss the scope and limitations of each approach. We end with a discussion of the potential that next-generation sequencing technologies may offer to the field.

SNP arrays in heterogeneous tissue: highly accurate collection of both germline and somatic genetic information from unpaired single tumor samples

SNP arrays provide reliable genotypes and can detect chromosomal aberrations at a high resolution. However, tissue heterogeneity is currently a major limitation for somatic tissue analysis. We have developed SOMATICs, an original program for accurate analysis of heterogeneous tissue samples. Fifty-four samples (42 tumors and 12 normal tissues) were processed through Illumina Beadarrays and then analyzed with SOMATICs. We demonstrate that tissue heterogeneity-related limitations not only can be overcome but can also be turned into an advantage. First, admixture of normal cells with tumor can be used as an internal reference, thereby enabling highly sensitive detection of somatic deletions without having corresponding normal tissue. Second, the presence of normal cells allows for discrimination of somatic from germline aberrations, and the proportion of cells in the tissue sample that are harboring the somatic events can be assessed. Third, relatively early versus late somatic events can also be distinguished, assuming that late events occur only in subsets of cancer cells. Finally, admixture by normal cells allows inference of germline genotypes from a cancer sample. All this information can be obtained from any cancer sample containing a proportion of 40-75% of cancer cells. SOMATICs is a ready-to-use open-source program that integrates all of these features into a simple format, comprehensively describing each chromosomal event.

Clinical effective analysis of chemo-radiotherapy for esophageal carcinoma patients with dietary and lifestyle factors of high and low risk

AIM: To study the clinical effects of chemo-radiotherapy for esophageal carcinoma patients with dietary and lifestyle factors of high risk.

METHODS: In a nested case-control study, data for esophageal carcinoma potential determinants from a survey that conducted on 496 patients in Wanzhou district of Chongqing municipality was analyzed. The classification tree model was constructed using exhaustice chi-square automatic interactiong detection method. The clinical effects of chemo-radiotherapy for esophageal carcinoma patients were observed.

RESULTS: In 7 out of the 15 risk factors selected, water pollution and fast eating were the most important factors. Furthermore, esophageal carcinoma was more frequent among smokers and fast eaters in alcohol drinkers. There were more survival benefits for esophageal carcinoma patients with high risk dietary and lifestyle factors (the median survival time, 21 month) relative to low risk patients (14 month) followed by chemo-radiotherapy. Significant difference was found between two groups (t = 15.87, P < 0.01).

CONCLUSION: It is possible that water pollution, and poor dietary and lifestyle factors such as hot-temperature food items and fast eating, smoking and alcohol drinking were the main risk factors for esophageal carcinoma of Wanzhou region. Chemo-radiotherapy has more clinical benefits for esophageal carcinoma patients with diet habits and lifestyle factors of high risk.

Meeting report: myelodysplastic syndromes at ASH 2007

Myelodysplastic syndromes (MDS) remain challenging to both clinicians and biologists. This year's edition of the Annual Meeting of the American Society of Hematology has provided several breakthroughs in the biology and therapeutics of MDS, such as uncovering of the molecular genetics of the 5q- syndrome and clear evidence of a survival advantage with a hypomethylating agent in high-risk MDS. We summarize those advances and delineate some perspectives for these diseases.

Molecular diagnostic testing in malignant gliomas: a practical update on predictive markers

Advances in understanding the molecular underpinnings of cancer and in molecular diagnostic technologies have changed the clinical practice of oncologic pathology. The development of targeted therapies against specific molecular alterations in cancer further portends changes in the role of the pathology laboratory to guide such custom therapies. To reconcile the flood of scientific discoveries in this area, the promises of highly touted novel therapeutics, and the practicality of applying this knowledge to the day-to-day practice of clinical neuropathology, the present review highlights the operative differences between diagnostic, predictive, and prognostic markers, and discusses issues surrounding the transition of prospective biomarkers to routine laboratory implementation. This review focuses on 3 predictive molecular markers that are either in clinical use or are contemplated for use in the evaluation of malignant gliomas: assessment of 1p/19q loss in oligodendroglial tumors, examination of O6-methylguanine DNA methyltransferase promoter methylation status in glioblastomas, and molecular dissection of the epidermal growth factor receptor-phosphatidylinositol 3-kinase pathway in glioblastomas. Implementation of such predictive markers is not straightforward and requires critical review of the available literature and attention to practical laboratory, compliance, financial, and clinical management issues.

Biomarkers, regerons, and pathways to lethal cancer

Cancer is a disease of "outlaw" cells that become mutated in regulatory mechanisms. They have lost normal self controls and relationships to the whole organism. Cancers can progress by several pathways from a normal cell to malignant cancer, from bad to worse. Questions about advisability of treatment for some cancers arise from the possibility that they are arrested during progression and so never become lethal. Techniques could be developed to determine the degree of progression and possibility for successful treatment. This article is intended to suggest a way of looking at cancer. It is not a review so references to research articles are infrequent.

Role of quercetin in modulating rat cardiomyocyte gene expression profile

Despite extensive studies, the fundamental mechanisms responsible for the development and progression of cardiovascular diseases have not yet been fully elucidated. Recent experimental and clinical studies have suggested that reactive oxygen species play a major pathological role. Oxidative stress reduction induced by flavonoids has been regarded by many as the most likely mechanism in the protective effects of these compounds; however, there is an emerging view that flavonoids may also exert modulatory actions on protein kinase and lipid kinase signaling pathways. Quercetin, a major flavonoid present in the human diet, has been widely studied, and its biological properties are consistent with its protective role in the cardiovascular system. However, it remains unknown whether the cardioprotective effects of quercetin may also occur through the modulation of genes involved in cell survival. The main goal of this study was to examine the gene expression profiling of cultured rat primary cardiomyocytes treated with quercetin using DNA microarrays and to relate these data to functional effects. Results showed distinct temporal changes in gene expression induced by quercetin and a strong upregulation of phase 2 enzymes, highlighting quercetin ability to act also with an indirect antioxidant mechanism.

Mechanisms of colorectal and lung cancer prevention by vegetables: a genomic approach

Colorectal cancer (CRC) and lung cancer (LC) occur at high incidence, and both can be effectively prevented by dietary vegetable consumption. This makes these two types of cancer highly suitable for elucidating the underlying molecular mechanisms of cancer chemoprevention. Numerous studies have shown that vegetables exert their beneficial effects through various different mechanisms, but effects on the genome level remain mostly unclear. This review evaluates current knowledge on the mechanisms of CRC and LC prevention by vegetables, thereby focusing on the modulation of gene and protein expressions. The majority of the effects found in the colon are changes in the expression of genes and proteins involved in apoptosis, cell cycle, cell proliferation and intracellular defense, in favor of reduced CRC risk. Furthermore, vegetables and vegetable components changed the expression of many more genes and proteins involved in other pathways for which biologic meaning is less clear. The number of studies investigating gene and protein expression changes in the lungs is limited to only a few in vitro and animal studies. Data from these studies show that mostly genes involved in biotransformation, apoptosis and cell cycle regulation are affected. In both colon and lungs, genomewide analyses of gene and protein expression changes by new genomics and proteomics technologies, as well as the investigation of whole vegetables, are few in number. Further studies applying these 'omics' approaches are needed to provide more insights on affected genetic/biologic pathways and, thus, in molecular mechanisms by which different chemopreventive compounds can protect against carcinogenesis. Particularly studies with combinations of phytochemicals and whole vegetables are needed to establish gene expression changes in the colon, but especially in the lungs.

Molecular biology of malignant mesothelioma

Human malignancies develop via a multi-step that involves the accumulation of several key gene alterations with associated genetic and epigenetic events. Although malignant mesothelioma (MM) has been demonstrated to be clearly correlated with asbestos exposure, it remains poorly understood how asbestos fibers confer key gene alterations and induce cellular transformation in normal mesothelial cells, which results in the acquisition of malignant phenotypes, including deregulated cell proliferation and invasion. Malignant mesothelioma presents with the frequent inactivation of tumor suppressor genes of p16(INK4a)/p14(ARF) on chromosome 9p21 and neurofibromatosis type 2 (NF2) on chromosome 22q12, with the latter being responsible for the NF2 familial cancer syndrome. In contrast, MM shows infrequent mutation of the p53 gene, which is one of the most frequently mutated tumor suppressor genes in human malignancies. Genetic abnormalities of oncogenes have also been studied in MM, but no frequent mutations have been identified, including the epidermal growth factor receptor (EGFR) and K-RAS genes. Recent studies have suggested the activation of other receptor tyrosine kinases, including Met, and the deregulations of mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K)-AKT signaling cascades, although the alterations responsible for their activation are still not clear. Thus, further genome-wide studies of genetic and epigenetic alterations as well as detailed analyses of deregulated signaling cascades in MM are necessary to determine the molecular mechanisms of MM, which would also provide some clues for establishing a new molecular target therapy for MM.

Immunologic and clinical effects of antibody blockade of cytotoxic T lymphocyte-associated antigen 4 in previously vaccinated cancer patients

Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) functions as a negative regulator of endogenous and vaccine-induced antitumor immunity. The administration of fully human anti-CTLA-4 blocking monoclonal antibodies to advanced-cancer patients increases immune-mediated tumor destruction in some subjects. Nonetheless, patients that respond also frequently manifest serious inflammatory pathologies, raising the possibility that the therapeutic and toxic effects of CTLA-4 blockade might be linked. Here we show that periodic infusions of anti-CTLA-4 antibodies after vaccination with irradiated, autologous tumor cells engineered to secrete GM-CSF (GVAX) generate clinically meaningful antitumor immunity without grade 3 or 4 toxicity in a majority of metastatic melanoma patients. The application of this sequential immunotherapy to advanced ovarian carcinoma patients also revealed that tumor destruction and severe inflammatory pathology could be dissociated, although further refinements are required to increase clinical responses and to minimize toxicity in this population. The extent of therapy-induced tumor necrosis was linearly related to the natural logarithm of the ratio of intratumoral CD8(+) effector T cells to FoxP3(+) regulatory T cells (Tregs) in posttreatment biopsies. Together, these findings help clarify the immunologic and clinical effects of CTLA-4 antibody blockade in previously vaccinated patients and raise the possibility that selective targeting of antitumor Tregs may constitute a complementary strategy for combination therapy.

Fingerprinting genomic instability in oral submucous fibrosis

BACKGROUND

Oral submucous fibrosis (OSF) is a high-risk pre-cancerous condition where 7-13% of these patients develop head and neck squamous cell carcinoma (HNSCC). To date there is no cancer predictive markers for OSF patients. Genomic instability hallmarks early genetic events during malignant transformation causing loss of heterozygosity (LOH) and chromosomal copy number abnormality. However, to date there is no study on genomic instability in OSF. Although this condition is known as a high-risk pre-cancerous condition, there is no data regarding the genomic status of this disease in terms of genetic susceptibility to malignant transformation.

METHODS

In this study, we investigated the existence of genetic signatures for carcinogenesis in OSF. We employed the high-resolution genome-wide Affymetrix Mapping single nucleotide polymorphism microarray technique to 'fingerprint' global genomic instability in the form of LOH in 15 patient-matched OSF-blood genomic DNA samples.

RESULTS

This rapid high-resolution mapping technique has revealed for the first time that a small number of discrete hot-spot LOH loci appeared in 47-53% of the OSF tissues studied. Many of these LOH loci were previously identified regions of genomic instability associated with carcinogenesis of the HNSCC.

CONCLUSION

To our knowledge, this is the first evidence that genomic instability in the form of LOH is present in OSF. We hypothesize that the genomic instability detected in OSF may play an important role in malignant transformation. Further functional association studies on these putative genes may reveal potential predictive oral cancer markers for OSF patients.

Global survey of phosphotyrosine signaling identifies oncogenic kinases in lung cancer. Cell. 2007;131:1190-1203. [PMID: 18083107 DOI: 10.1016/j.cell.2007.11.025]

Despite the success of tyrosine kinase-based cancer therapeutics, for most solid tumors the tyrosine kinases that drive disease remain unknown, limiting our ability to identify drug targets and predict response. Here we present the first large-scale survey of tyrosine kinase activity in lung cancer. Using a phosphoproteomic approach, we characterize tyrosine kinase signaling across 41 non-small cell lung cancer (NSCLC) cell lines and over 150 NSCLC tumors. Profiles of phosphotyrosine signaling are generated and analyzed to identify known oncogenic kinases such as EGFR and c-Met as well as novel ALK and ROS fusion proteins. Other activated tyrosine kinases such as PDGFRalpha and DDR1 not previously implicated in the genesis of NSCLC are also identified. By focusing on activated cell circuitry, the approach outlined here provides insight into cancer biology not available at the chromosomal and transcriptional levels and can be applied broadly across all human cancers.

Conjugative plasmids in multi-resistant bacterial isolates from Indian soil

AIMS

Determination of heavy metal and antibiotic resistance and presence of conjugative plasmids in bacteria isolated from soil irrigated with wastewater.

METHODS AND RESULTS

Composite soil samples were collected from Ghaziabad, Uttar Pradesh, India. Forty different bacteria were selected from nutrient agar and characterized by morphological, cultural and biochemical tests. All the isolates were tested for their resistance to different heavy metals and antibiotics. The DNA derived from multiple metal and antibiotic-resistant bacterial isolates was PCR amplified and plasmid-specific sequences (IncP, IncN, IncW, IncQ and pMV158-type) were analysed by dot blot hybridization. All isolates gave PCR products with trfA2 and oriT primers of the IncP group. These PCR products also hybridized with the RP4-derived probes. However, the samples were negative for all the other investigated plasmids as proved by PCR and dot blots.

CONCLUSIONS

The presence of conjugative/mobilizable IncP plasmids in the isolates indicates that these bacteria have gene-mobilizing capacity with implications for potential dissemination of introduced recombinant DNA.

SIGNIFICANCE AND IMPACT OF THE STUDY

The detection of IncP plasmids in all the bacterial isolates is another proof for the prevalence of these plasmids. We propose that IncP plasmids are mainly responsible for the spread of multi-resistant bacteria in these soils.

Antigen retrieval for proteomic characterization of formalin-fixed and paraffin-embedded tissues

Formalin-fixed and paraffin-embedded tissues represent the vast majority of archived tissue. Access to such tissue specimens via shotgun-based proteomic analyses may open new avenues for both prospective and retrospective translational research. In this study, we evaluate the effects of fixation time on antigen retrieval for the purposes of shotgun proteomics. For the first time, we demonstrate the capability of a capillary isotachophoresis (CITP)-based proteomic platform for the shotgun proteomic analysis of proteins recovered from FFPE tissues. In comparison to our previous studies utilizing capillary isoelectric focusing, the CITP-based analysis is more robust and increases proteome coverage. In this case, results from three FFPE liver tissues yield a total of 4098 distinct Swiss-Prot identifications at a 1% false-discovery rate. To judge the accuracy of these assignments, immunohistochemistry is performed on a panel of 17 commonly assayed proteins. These proteins span a wide range of protein abundances as inferred from relative quantitation via spectral counting. Among the panel were 4 proteins identified by a single peptide hit, including three clusters of differentiation (CD) markers: CD74, CD117, and CD45. Because single peptide hits are often regarded with skepticism, it is notable that all proteins tested by IHC stained positive.

The RTK/RAS/BRAF/PI3K pathways in melanoma: biology, small molecule inhibitors, and potential applications

The discovery of mutations in the BRAF signaling molecule in a large proportion of cutaneous melanomas immediately suggested the prospect of effective therapies for this disease. The most appealing initial target has been BRAF itself, as most mutations involve a single residue in the kinase domain of the protein. But the identification of the high mutation rate in this signaling intermediate also suggests that other molecules up- and downstream of BRAF might be productively targeted. Indeed, several receptor tyrosine kinases, as well as RAS, are mutated in a small number of melanoma cases. Moreover, genetic alterations in the phosphotidylinositol-3-kinase (PI3K) pathway, especially in PTEN, suggest that this route also poses opportunities for therapeutic exploitation. We will review here the genetic evidence suggesting the utility of targets on these pathways. We will also summarize the recent clinical data that have accumulated from initial trials designed to test BRAF inhibition and targeting of other molecules. Finally, we provide an overview of molecules entering the clinic and soon to be tested in clinical studies, as well as strategies for their employment as monotherapy and in combinations.

Modeling genomic diversity and tumor dependency in malignant melanoma

The classification of human tumors based on molecular criteria offers tremendous clinical potential; however, discerning critical and "druggable" effectors on a large scale will also require robust experimental models reflective of tumor genomic diversity. Here, we describe a comprehensive genomic analysis of 101 melanoma short-term cultures and cell lines. Using an analytic approach designed to enrich for putative "driver" events, we show that cultured melanoma cells encompass the spectrum of significant genomic alterations present in primary tumors. When annotated according to these lesions, melanomas cluster into subgroups suggestive of distinct oncogenic mechanisms. Integrating gene expression data suggests novel candidate effector genes linked to recurrent copy gains and losses, including both phosphatase and tensin homologue (PTEN)-dependent and PTEN-independent tumor suppressor mechanisms associated with chromosome 10 deletions. Finally, sample-matched pharmacologic data show that FGFR1 mutations and extracellular signal-regulated kinase (ERK) activation may modulate sensitivity to mitogen-activated protein kinase/ERK kinase inhibitors. Genetically defined cell culture collections therefore offer a rich framework for systematic functional studies in melanoma and other tumors.

Innovative genomic-based model for personalized treatment of gastric cancer: integrating current standards and new technologies

In the era of network biology, understanding the complexity of the signaling pathways network in cancer origin, progression and metastasis will dramatically alter and improve treatment strategies. Prognosis of gastric cancer remains poor. Clinical decisions on treatment are based on tumor-node-metastasis (TNM) staging, but are suboptimal. This perspective review, integrating several concepts, including cancer stem cells, provides a novel treatment model for tailoring the best treatment in individual patients with gastric cancer. Biologic metastatic steps (invasion, angiogenesis, intra/extravasation, colonization and microenvironment at distant organs) are orchestrated by mutated genes. Identifying and profiling these key genes and their interactions with environmental factors such as Helicobacter pylori, driver mutations and interacting signaling pathways using high-throughput technologies (including omics, resequencing, genome-wide associations studies and RNAi) in unbiased studies can lead to the development of both novel biomarkers and targeted agents. A comprehensive bench-to-bedside treatment-guided algorithm is provided for optimum preoperative or postoperative combination of cytotoxic and targeted agents. The protocol can be applied with adequate modification for most solid tumors.

Genetic constraints on protein evolution

Evolution requires the generation and optimization of new traits ("adaptation") and involves the selection of mutations that improve cellular function. These mutations were assumed to arise by selection of neutral mutations present at all times in the population. Here we review recent evidence that indicates that deleterious mutations are more frequent in the population than previously recognized and that these mutations play a significant role in protein evolution through continuous positive selection. Positively selected mutations include adaptive mutations, i.e. mutations that directly affect enzymatic function, and compensatory mutations, which suppress the pleiotropic effects of adaptive mutations. Compensatory mutations are by far the most frequent of the two and would allow potentially adaptive but deleterious mutations to persist long enough in the population to be positively selected during episodes of adaptation. Compensatory mutations are, by definition, context-dependent and thus constrain the paths available for evolution. This provides a mechanistic basis for the examples of highly constrained evolutionary landscapes and parallel evolution reported in natural and experimental populations. The present review article describes these recent advances in the field of protein evolution and discusses their implications for understanding the genetic basis of disease and for protein engineering in vitro.

Biochemical and biological characterization of tumor-associated mutations of p110alpha

Signaling by class I phosphatidylinositol 3-kinase (PI3K) controls cell growth, replication, motility, and metabolism. The PI3K pathway commonly shows gain of function in cancer. Two small GTPases, Rheb (Ras homolog enriched in brain) and Ras (rat sarcoma viral oncogene), play important roles in PI3K signaling. Rheb activates the TOR (target of rapamycin) kinase in a GTP-dependent manner; it links TOR to upstream signaling components, including the tuberous sclerosis complex (TSC) and Akt (homolog of the Akt8 murine lymphoma viral oncoprotein). Constitutively active, GTP-bound Rheb is oncogenic in cell culture, and activity that requires farnesylation. Ras activates PI3K by recruitment to the plasma membrane and possibly by inducing a conformational change in the catalytic subunit p110 of PI3K. In return, Ras signaling through the MAP kinase (MAPK) pathway is activated by PIP(3), the product of PI3K. Loss of Ras function can interfere with PI3K signaling. Various lines of evidence suggest complementary roles for PI3K and MAPK signaling in oncogenesis.

Acute Myeloid Leukemia: The Challenge of Capturing Disease Variety

The difference between success and failure of treatment of acute myeloid leukemia (AML) is largely determined by genotypic leukemia-specific differences among patients. The diversity of AML genotypes result from somatic genetic alterations settling down in succession in an individual’s leukemia clone during the development of the disease. Gene mutations, gene expression abnormalities and other molecular alterations (e.g., microRNA variations) affect critical functions in AML cells, and may exert profound effects on the therapeutic response and outcome of the disease. Prototypes of common clinically significant gene aberrations involve transcription factors, signaling molecules and growth factor receptors. The expanding knowledge in this area allowing for risk stratified therapy decisions and the development of targeted drug therapy, is becoming an increasingly important part of the modern individualized clinical management of AML. This chapter highlights recent insights into the diagnostic, prognostic and therapeutic impact of chromosomal (e.g., the so-called monosomal karyotype) as well as particular genomic abnormalities, and presents examples of decision algorithms for individualized therapy.

Next-generation sequencing transforms today's biology

A new generation of non-Sanger-based sequencing technologies has delivered on its promise of sequencing DNA at unprecedented speed, thereby enabling impressive scientific achievements and novel biological applications. However, before stepping into the limelight, next-generation sequencing had to overcome the inertia of a field that relied on Sanger-sequencing for 30 years.

A map of human cancer signaling

We conducted a comprehensive analysis of a manually curated human signaling network containing 1634 nodes and 5089 signaling regulatory relations by integrating cancer-associated genetically and epigenetically altered genes. We find that cancer mutated genes are enriched in positive signaling regulatory loops, whereas the cancer-associated methylated genes are enriched in negative signaling regulatory loops. We further characterized an overall picture of the cancer-signaling architectural and functional organization. From the network, we extracted an oncogene-signaling map, which contains 326 nodes, 892 links and the interconnections of mutated and methylated genes. The map can be decomposed into 12 topological regions or oncogene-signaling blocks, including a few ‘oncogene-signaling-dependent blocks' in which frequently used oncogene-signaling events are enriched. One such block, in which the genes are highly mutated and methylated, appears in most tumors and thus plays a central role in cancer signaling. Functional collaborations between two oncogene-signaling-dependent blocks occur in most tumors, although breast and lung tumors exhibit more complex collaborative patterns between multiple blocks than other cancer types. Benchmarking two data sets derived from systematic screening of mutations in tumors further reinforced our findings that, although the mutations are tremendously diverse and complex at the gene level, clear patterns of oncogene-signaling collaborations emerge recurrently at the network level. Finally, the mutated genes in the network could be used to discover novel cancer-associated genes and biomarkers.

Targeted agents: the rules of combination

The success of molecularly targeted agents (MTA) in the treatment of cancer has led to the investigation of their use in combination with other MTAs and with conventional chemotherapies. An overview of the MTAs that have emerged as Food and Drug Administration-approved drugs is presented, along with a framework for the consideration of how MTAs can best be combined to maximize therapeutic effect.

Mutation analysis of BRAF, MEK1 and MEK2 in 15 ovarian cancer cell lines: implications for therapy

Background

Among gynecologic cancers, ovarian cancer is the second most common and has the highest death rate. Cancer is a genetic disorder and arises due to the accumulation of somatic mutations in critical genes. An understanding of the genetic basis of ovarian cancer has implications both for early detection and for therapeutic intervention in this population of patients.

Methodology/Principal Findings

Fifteen ovarian cancer cell lines, commonly used for in vitro experiments, were screened for mutations using bidirectional direct sequencing in all coding regions of BRAF, MEK1 and MEK2. BRAF mutations were identified in four of the fifteen ovarian cancer cell lines studied. Together, these four cell lines contained four different BRAF mutations, two of which were novel. ES-2 had the common B-Raf p.V600E mutation in exon 15 and Hey contained an exon 11 missense mutation, p.G464E. The two novel B-Raf mutants identified were a 5 amino acid heterozygous deletion p.N486-P490del in OV90, and an exon 4 missense substitution p.Q201H in OVCAR 10. One of the cell lines, ES-2, contained a mutation in MEK1, specifically, a novel heterozygous missense substitution, p.D67N which resulted from a nt 199 G→A transition. None of the cell lines contained coding region mutations in MEK2. Functional characterization of the MEK1 mutant p.D67N by transient transfection with subsequent Western blot analysis demonstrated increased ERK phosphorylation as compared to controls.

Conclusions/Significance

In this study, we report novel BRAF mutations in exon 4 and exon 12 and also report the first mutation in MEK1 associated with human cancer. Functional data indicate the MEK1 mutation may confer alteration of activation through the MAPK pathway. The significance of these findings is that BRAF and MEK1/2 mutations may be more common than anticipated in ovarian cancer which could have important implications for treatment of patients with this disease and suggests potential new therapeutic avenues.

Identification of driver and passenger mutations of FLT3 by high-throughput DNA sequence analysis and functional assessment of candidate alleles

Mutations in the juxtamembrane and kinase domains of FLT3 are common in AML, but it is not known whether alterations outside these regions contribute to leukemogenesis. We used a high-throughput platform to interrogate the entire FLT3 coding sequence in AML patients without known FLT3 mutations and experimentally tested the consequences of each candidate leukemogenic allele. This approach identified gain-of-function mutations that activated downstream signaling and conferred sensitivity to FLT3 inhibition and alleles that were not associated with kinase activation, including mutations in the catalytic domain. These findings support the concept that acquired mutations in cancer may not contribute to malignant transformation and underscore the importance of functional studies to distinguish "driver" mutations underlying tumorigenesis from biologically neutral "passenger" alterations.

Network modeling links breast cancer susceptibility and centrosome dysfunction

Many cancer-associated genes remain to be identified to clarify the underlying molecular mechanisms of cancer susceptibility and progression. Better understanding is also required of how mutations in cancer genes affect their products in the context of complex cellular networks. Here we have used a network modeling strategy to identify genes potentially associated with higher risk of breast cancer. Starting with four known genes encoding tumor suppressors of breast cancer, we combined gene expression profiling with functional genomic and proteomic (or 'omic') data from various species to generate a network containing 118 genes linked by 866 potential functional associations. This network shows higher connectivity than expected by chance, suggesting that its components function in biologically related pathways. One of the components of the network is HMMR, encoding a centrosome subunit, for which we demonstrate previously unknown functional associations with the breast cancer-associated gene BRCA1. Two case-control studies of incident breast cancer indicate that the HMMR locus is associated with higher risk of breast cancer in humans. Our network modeling strategy should be useful for the discovery of additional cancer-associated genes.

PIK3CA mutation is predictive of poor survival in patients with colorectal cancer

The PI3K-AKT pathway is activated in a variety of human cancers, resulting in disturbance of cell growth, proliferation and survival. Among the factors affecting the pathway, the K-Ras mutation and PIK3CA mutation are the most common oncogenic alterations in colorectal cancer. We hypothesized that these two mutations are important in activation of the PI3K pathway and colorectal carcinogenesis. In this study, we aimed to examine the influence of PIK3CA mutation and K-Ras mutation on AKT activation, and to clarify whether PIK3CA mutation, K-Ras mutation and p-AKT expression may be used as parameters for predicting prognosis in colorectal cancer. Tissue samples from 158 colorectal cancer patients who underwent surgical resection were examined. The sequences of exon 1 of K-Ras and exons 9 and 20 of PIK3CA were determined by direct sequencing using genomic DNA extracted from paraffin-embedded blocks. Activation status of AKT was evaluated by immunohistochemical staining using phospho-specific AKT antibody (Ser473). Correlation between these factors and clinicopathologic findings/patient survival were examined. As a result, PIK3CA mutation was significantly associated with shorter relapse-free survival (RFS) in stage II/III patients (p = 0.0216) and shorter disease-specific survival in all patients (p = 0.0357). In the multivariate analysis, PIK3CA mutation was the only independent and significant prognostic factor for RFS in stage II/III patients (p = 0.0433, HR 2.478). This study revealed the prognostic value of PIK3CA mutation in colorectal cancer patients. Patients with PIK3CA mutation should be followed up carefully. Moreover, our result suggests that inhibition of PIK3CA mutant may be a new molecular target therapy.

Functional and evolutionary implications of enhanced genomic analysis of rhomboid intramembrane proteases

Rhomboids are a recently discovered family of widely distributed intramembrane serine proteases. They have diverse biological functions, including the regulation of growth factor signaling, mitochondrial fusion, and parasite invasion. Despite their existence in all branches of life, the sequence identity between rhomboids is low. We have combined BLAST-based database mining with functional and structural data to generate a comprehensive genomic analysis of eukaryotic rhomboid-like proteins. We show that robust membrane topology models are necessary to classify active rhomboid proteases unambiguously, and we define rules for distinguishing predicted active proteases from the larger evolutionary group of rhomboid-like proteins. This leads to a revision of estimates of numbers of proteolytically active rhomboids. We identify three groups of eukaryotic rhomboid-like proteins: true active rhomboids, a tightly clustered group of novel inactive rhomboids that we name the iRhoms, and a small number of other inactive rhomboid-like proteins. The active proteases are themselves subdivided into secretase and PARL-type (mitochondrial) subfamilies; these have distinct transmembrane topologies. This enhanced genomic analysis leads to conclusions about rhomboid enzyme function. It suggests that a given rhomboid can only cleave a single orientation of substrate, and that both products of rhomboid catalyzed intramembrane cleavage can be released from the membrane. Our phylogeny predictions also have evolutionary implications: Despite the complex classification of rhomboids, our data suggest that a rhomboid-type intramembrane protease may have been present in the last eukaryotic common ancestor.

The genomic landscapes of human breast and colorectal cancers

Human cancer is caused by the accumulation of mutations in oncogenes and tumor suppressor genes. To catalog the genetic changes that occur during tumorigenesis, we isolated DNA from 11 breast and 11 colorectal tumors and determined the sequences of the genes in the Reference Sequence database in these samples. Based on analysis of exons representing 20,857 transcripts from 18,191 genes, we conclude that the genomic landscapes of breast and colorectal cancers are composed of a handful of commonly mutated gene "mountains" and a much larger number of gene "hills" that are mutated at low frequency. We describe statistical and bioinformatic tools that may help identify mutations with a role in tumorigenesis. These results have implications for understanding the nature and heterogeneity of human cancers and for using personal genomics for tumor diagnosis and therapy.

Diagnostic significance of allelic imbalance in cancer

Allelic imbalance (AI), a deviation from the normal 1:1 ratio of maternal and paternal alleles, occurs in virtually all solid and blood-borne malignancies. The frequency and spectrum of AI in a tumor cell reflects the karyotypic complexity of the cancer genome. Hence, many investigations have assessed the extent of AI to analyze differences between normal and tumor tissues in a variety of different organs. In this review, the authors describe established and emerging technologies used to assess the extent of AI in human tissues, and their application in the diagnosis of cancer. The four major methods to be reviewed represent powerful and widely used tools for the identification of allelic imbalances accompanying cancer initiation and progression. These are fluorescent in situ hybridization, comparative genomic hybridization, single nucleotide polymorphism arrays and the use of microsatellite markers. For each method, the authors provide a brief description of the approach and elaborate on specific studies that highlight its utility in the diagnosis of human cancers.

Copy number variants and genetic traits: closer to the resolution of phenotypic to genotypic variability

A considerable and unanticipated plasticity of the human genome, manifested as inter-individual copy number variation, has been discovered. These structural changes constitute a major source of inter-individual genetic variation that could explain variable penetrance of inherited (Mendelian and polygenic) diseases and variation in the phenotypic expression of aneuploidies and sporadic traits, and might represent a major factor in the aetiology of complex, multifactorial traits. For these reasons, an effort should be made to discover all common and rare copy number variants (CNVs) in the human population. This will also enable systematic exploration of both SNPs and CNVs in association studies to identify the genomic contributors to the common disorders and complex traits.

Epidermal growth factor signaling induces behavioral quiescence in Caenorhabditis elegans

The epidermal growth factor receptor (EGFR)/ErbB receptor tyrosine kinases regulate several aspects of development, including the development of the mammalian nervous system. ErbB signaling also has physiological effects on neuronal function, with influences on synaptic plasticity and daily cycles of activity. However, little is known about the effectors of EGFR activation in neurons. Here we show that EGF signaling has a nondevelopmental effect on behavior in Caenorhabditis elegans. Ectopic expression of the EGF-like ligand LIN-3 at any stage induces a reversible cessation of feeding and locomotion. These effects are mediated by neuronal EGFR (also called LET-23) and phospholipase C-gamma (PLC-gamma), diacylglycerol-binding proteins, and regulators of synaptic vesicle release. Activation of EGFR within a single neuron, ALA, is sufficient to induce a quiescent state. This pathway modulates the cessation of pharyngeal pumping and locomotion that normally occurs during the lethargus period that precedes larval molting. Our results reveal an evolutionarily conserved role for EGF signaling in the regulation of behavioral quiescence.

Pharmacogenomics of lung cancer: with a view to address EGFR-targeted therapies

Epidermal growth factor receptor (EGFR)-targeted therapies have demonstrated variable success in treating individuals with non-small-cell lung cancer. Understanding the molecular mechanisms of response and resistance to this class of treatment has led to patient selection strategies that may improve outcomes. The second generation of EGFR-targeted therapies is now under clinical evaluation and may prove to be successful at circumventing a portion of primary or acquired resistance to first-generation tyrosine kinase inhibitors. These principles are generally applicable to the field of targeted therapy and predictive pharmacogenomics.

Enzymatic manipulations of DNA oligonucleotides on microgel: towards development of DNA-microgel bioassays

We demonstrate that DNA oligonucleotides covalently coupled to colloidal microgel can be manipulated by T4 DNA ligase for DNA ligation and by Phi29 DNA polymerase for rolling circle amplification (RCA). We also show that the long single-stranded RCA product can generate intensive fluorescence upon hybridization with complementary fluorescent DNA probe. We believe DNA-microgel conjugates can be explored for the development of DNA based bioassays and biosensors.

Comprehensive Analysis of Copy Number and Allele Status Identifies Multiple Chromosome Defects Underlying Follicular Lymphoma Pathogenesis

PURPOSE

Follicular lymphoma (FL) constitutes the second most common non-Hodgkin's lymphoma in the Western world. The clinical course is variable and only in part explained by known tumor-intrinsic or -extrinsic factors. FL carries the hallmark chromosomal translocation t(14;18), deregulating the expression of Bcl-2, but this is not sufficient to explain either FL biology or clinical behavior.

EXPERIMENTAL DESIGN

We have employed high-density genomic profiling technology using the Affymetrix 50K-XbaI oligonucleotide single nucleotide polymorphism-chip platform to interrogate the genomes of 58 fluorescence-activated cell-sorted (FACS) FL specimens for chromosomal copy number changes and 46 specimens for loss of heterozygosity (LOH).

RESULTS

We report (a) previously unknown high-frequency copy-neutral LOH (uniparental disomy) in FL on chromosomes 1p (approximately 50%) and 6p (approximately 30%); (b) that del6q is complex, as reported, with at least two regions of minimal common loss at 6q13-15 and 6q23-24, and that in addition, approximately 8% of FL specimens contain a homozygous deletion at 6q23.3-24.1 that spans the negative NFkappaB regulator A20 and the p53 apoptosis effector PERP; (c) that combined analysis of chromosome 17p for LOH, copy number, and p53 mutations shows that most p53 mutations in FL do not involve del17p. Finally, we map high-frequency LOH with and without copy loss on chromosomes 9p, 10q, and 16p and genomic gains on 2p15-16 and 8q24.22-24.3.

CONCLUSIONS

This comprehensive description of the pathologic anatomy of the FL genome uncovers novel genetic lesions and should aid with identification of genes relevant to FL biology and clinical behavior.

Fusion transcripts and transcribed retrotransposed loci discovered through comprehensive transcriptome analysis using Paired-End diTags (PETs)

Identification of unconventional functional features such as fusion transcripts is a challenging task in the effort to annotate all functional DNA elements in the human genome. Paired-End diTag (PET) analysis possesses a unique capability to accurately and efficiently characterize the two ends of DNA fragments, which may have either normal or unusual compositions. This unique nature of PET analysis makes it an ideal tool for uncovering unconventional features residing in the human genome. Using the PET approach for comprehensive transcriptome analysis, we were able to identify fusion transcripts derived from genome rearrangements and actively expressed retrotransposed pseudogenes, which would be difficult to capture by other means. Here, we demonstrate this unique capability through the analysis of 865,000 individual transcripts in two types of cancer cells. In addition to the characterization of a large number of differentially expressed alternative 5' and 3' transcript variants and novel transcriptional units, we identified 70 fusion transcript candidates in this study. One was validated as the product of a fusion gene between BCAS4 and BCAS3 resulting from an amplification followed by a translocation event between the two loci, chr20q13 and chr17q23. Through an examination of PETs that mapped to multiple genomic locations, we identified 4055 retrotransposed loci in the human genome, of which at least three were found to be transcriptionally active. The PET mapping strategy presented here promises to be a useful tool in annotating the human genome, especially aberrations in human cancer genomes.