Induction Of Genetic Instability Research Articles

Up-down regulation of HIF-1α in cancer progression.

Hypoxia induicible factor-1 alpha (HIF-1α) is a key transcription factor in cancer progression and target therapy in cancer. HIF-1α acts differently depending on presence or absence of Oxygen. In an oxygen-immersed environment, HIF-1α completely deactivated and destroyed by the ubiquitin proteasome pathway (UPP). In contrast, in the oxygen-free environment, it escapes destruction and enters to the nucleus of cells then upregulates many genes involved in cancer progression. Overexpressed HIF-1α and downstream genes support cancer progression through various mechanisms including angiogenesis, proliferation and survival of cells, metabolism reprogramming, invasion and metastasis, cancer stem cell maintenance, induction of genetic instability, and treatment resistance. HIF-1α can be provoked by signaling pathways unrelated to hypoxia during cancer progression. Therefore, cancer development and progression can be modulated by targeting HIF-1α and its downstream signaling molecules. In this regard, HIF-1α inhibitors which are categorized into the agents that regulate HIF-1α in gene, mRNA and protein levels used as an efficient way in cancer treatment. Also, HIF-1α expression can be negatively affected by the agents suppressing the activation of mTOR, PI3k/Akt and MAPK pathways.

Reactive Oxygen Species: A Promising Therapeutic Target for SDHx-Mutated Pheochromocytoma and Paraganglioma.

Simple SummaryPheochromocytoma and paraganglioma are rare neuroendocrine tumors that arise from chromaffin cells of the adrenal medulla or their neural crest progenitors located outside the adrenal gland, respectively. About 10–15% of patients develop metastatic disease for whom treatment options and availability are extremely limited. The risk of developing metastatic disease is increased for patients with mutations in succinate dehydrogenase subunit B, which leads to metabolic reprogramming and redox imbalance. From this perspective, we focus on redox imbalance caused by this mutation and explore potential opportunities to therapeutically target reactive oxygen species production in these rare tumors.Pheochromocytoma (PHEO) and paraganglioma (PGL) are rare neuroendocrine tumors derived from neural crest cells. Germline variants in approximately 20 PHEO/PGL susceptibility genes are found in about 40% of patients, half of which are found in the genes that encode succinate dehydrogenase (SDH). Patients with SDH subunit B (SDHB)-mutated PHEO/PGL exhibit a higher likelihood of developing metastatic disease, which can be partially explained by the metabolic cell reprogramming and redox imbalance caused by the mutation. Reactive oxygen species (ROS) are highly reactive molecules involved in a multitude of important signaling pathways. A moderate level of ROS production can help regulate cellular physiology; however, an excessive level of oxidative stress can lead to tumorigenic processes including stimulation of growth factor-dependent pathways and the induction of genetic instability. Tumor cells effectively exploit antioxidant enzymes in order to protect themselves against harmful intracellular ROS accumulation, which highlights the essential balance between ROS production and scavenging. Exploiting ROS accumulation can be used as a possible therapeutic strategy in ROS-scavenging tumor cells. Here, we focus on the role of ROS production in PHEO and PGL, predominantly in SDHB-mutated cases. We discuss potential strategies and approaches to anticancer therapies by enhancing ROS production in these difficult-to-treat tumors.

Human Papillomaviruses Preferentially Recruit DNA Repair Factors to Viral Genomes for Rapid Repair and Amplification.

ABSTRACTHigh-risk human papillomaviruses (HPVs) activate the ataxia telangiectasia mutated-dependent (ATM) DNA damage response as well as the ataxia telangiectasia mutated-dependent DNA-related (ATR) pathway in the absence of external DNA damaging agents for differentiation-dependent genome amplification. Through the use of comet assays and pulsed-field gel electrophoresis, our studies showed that these pathways are activated in response to DNA breaks induced by the viral proteins E6 and E7 alone and independently of viral replication. The majority of these virally induced DNA breaks are present in cellular DNAs and only minimally in HPV episomes. Treatment of HPV-positive cells with inhibitors of both ATM and ATR leads to the generation of DNA breaks and the fragmentation of viral episomes, indicating that DNA breaks are introduced into HPV genomes. These breaks, however, are rapidly repaired through the preferential recruitment of homologous recombination repair enzymes, such as RAD51 and BRCA1, to viral genomes at the expense of cellular DNAs. When HPV-positive cells are treated with hydroxyurea, this recruitment of RAD51 and BRCA1 to viral genomes is greatly enhanced with little recruitment to damaged cellular DNAs and with retention of the ability of viral genomes to amplify. Overall, our studies demonstrated that human papillomaviruses induce breaks into cellular and viral DNAs and that the preferential repair of these lesions in viral episomes leads to genome amplification.

Is auxin involved in the induction of genetic instability in barley homeotic double mutants?

The triggers of genetic instability in barley homeotic double mutants are tweaky spike -type mutations associated with an auxin imbalance in separate spike phytomeres. Barley homeotic tweaky spike;Hooded (tw;Hd) double mutants are characterized by an inherited instability of spike and flower development, which is absent in the single parental constituents. The aim of the present study was to show that the trigger of genetic instability in the double mutants is the tw mutations, which are associated with an auxin imbalance in the developing spikes. Their pleiotropic effects on genes related to spike/flower development may cause the genetic instability of double mutants. The study of four double-mutant groups composed of different mutant alleles showed that the instability arose only if the mutant allele tw was a constituent of the double mutants. Application of auxin inhibitors and 2,4-dichlorophenoxyacetic acid (2,4-D) demonstrated the relationship of the instability of the double mutants and the phenotype of the tw mutants to auxin imbalance. 2,4-D induced phenocopies of the tw mutation in wild-type plants and rescued the phenotypes of three allelic tw mutants. The differential display (dd-PCR) method allowed the identification of several putative candidate genes in tw that may be responsible for the initiation of instability in the double mutants by pleiotropic variations of their expression in the tw mutant associated with auxin imbalance in the developing spikes. The results of the present study linked the genetic instability of homeotic double mutants with an auxin imbalance caused by one of the constituents (tw). The genetic instability of the double mutants in relation to auxin imbalance was studied for the first time. A matrocliny on instability expression was also observed.

Production dynamics in relation to ontogenetic development and induction of genetic instability through in vitro approaches in Pelargonium graveolens: A potential essential oil crop of commercial significance

AbstractRose‐scented geranium (Pelargonium graveolens L’ Hért.) is a fragrant and bushy essential oil bearing crop of significant industrial and commercial importance. In an attempt to overcome the constraints imposed by sexual sterility for genetic improvement and restricted environmental adaptability of Pelargonium, the present study was aimed at exploring new niches for its cultivation in northern most sub‐tropical part of India (Jammu). The flowering stage was found to be the optimum stage for harvesting in relation to essential oil quantity (0.16–0.18%, Fresh Weight Basis; FWB) and quality (geraniol 18% and citronellol 37%) during different phenophases of plant growth. Dynamics of essential oil turnover correlated well with the glandular trichome ontogeny using scanning electron microscopy (SEM). The present study also entailed induction of somaclonal variations via in vitro organogenesis. Organogenetic callus induction was achieved on B5 (Gamborg's) basal medium supplemented with kinetin/2,4‐dichlorophenoxyacetic acid (Kn/2,4‐D) and kinetin/indole‐3‐butyric acid (Kn/IBA). Frequency of callus induction ranged from 54–85%. Field established in vitro regenerated plants/somaclones displayed appreciable variability in fresh leaf biomass (365–2020 g, FWB), essential oil content (0.06%–0.26%) and quality (geraniol and citronellol as major constituents). To evaluate the genetic instability of calliclones, RAPD (Random Amplification of Polymorphic DNA) markers were used to assess the genetic basis of variability. Further, the identity of Pelargonium was confirmed by DNA bar‐code analyses using three plant based barcoding loci (ITS, rbcL and psbA/trnH). They may be used as a standard reference system for varietal identification and protection of Intellectual Property Rights (IPR). Overall, the present investigation demonstrates the feasibility of Pelargonium cultivation in sub‐tropical niches as a short duration winter crop, with desirable essential oil content and composition for commercial purposes. It also establishes a viable method for induction of variability for genetic amelioration of sexually sterile crop.

Therapy-related myeloid neoplasms: does knowing the origin help to guide treatment?

Therapy-related myeloid neoplasms (t-MN) combine t-MDS and therapy related acute myeloid leukemia (t-AML) patients in one entity because of their similar pathogenesis, rapid progression from t-MDS to t-AML, and their equally poor prognosis. Treatment with epipodophyllotoxins like etoposide has been associated with a short interval between treatment and development of t-AML, with fusion oncogenes like KMT2A/MLL-MLLT3 and a better prognosis. In contrast, treatment with alkylating agents has been associated with a longer latency, an initial MDS phase, adverse cytogenetics, and a poor prognosis. The pathogenesis of t-MN can be explained by direct induction of an oncogene through chromosomal translocations, induction of genetic instability, or selection of a preexisting treatment-resistant hematopoietic stem cell clone. Recent evidence has highlighted the importance of the last mechanism and explains the high frequency of TP53 mutations in patients with t-MN. After previous cytotoxic therapy, patients present with specific vulnerabilities, especially evident from the high nonrelapse mortality in patients with t-MN after allogeneic hematopoietic cell transplantation. Here, the prognostic impact of currently known risk factors and the therapeutic options in different patient subgroups will be discussed.

Therapy-related myeloid neoplasms: does knowing the origin help to guide treatment?

Therapy-related myeloid neoplasms (t-MN) combine t-MDS and therapy related acute myeloid leukemia (t-AML) patients in one entity because of their similar pathogenesis, rapid progression from t-MDS to t-AML, and their equally poor prognosis. Treatment with epipodophyllotoxins like etoposide has been associated with a short interval between treatment and development of t-AML, with fusion oncogenes like KMT2A/MLL-MLLT3 and a better prognosis. In contrast, treatment with alkylating agents has been associated with a longer latency, an initial MDS phase, adverse cytogenetics, and a poor prognosis. The pathogenesis of t-MN can be explained by direct induction of an oncogene through chromosomal translocations, induction of genetic instability, or selection of a preexisting treatment-resistant hematopoietic stem cell clone. Recent evidence has highlighted the importance of the last mechanism and explains the high frequency of TP53 mutations in patients with t-MN. After previous cytotoxic therapy, patients present with specific vulnerabilities, especially evident from the high nonrelapse mortality in patients with t-MN after allogeneic hematopoietic cell transplantation. Here, the prognostic impact of currently known risk factors and the therapeutic options in different patient subgroups will be discussed.

Radiation Induced Bystander Effect: From <i>in Vitro</i> Studies to Clinical Application

In the past 20 years, the classic paradigm in radiobiology recognizing DNA as the main target for the action of radiation has changed. The new paradigm assumes that both targeted and non-targeted effects of radiation determine the final outcome of irradiation. Radiotherapy is one of the main modality treatments of neoplastic diseases with intent to cure, or sometimes to palliate only, thus radiation-induced non-targeted effect, commonly referred to as the radiation-induced bystander effect (RIBE) may have a share in cancer treatment. RIBE is mediated by molecular signaling from radiation targeted cells to their non-irradiated neighbors, and comprises such phenomena as bystander effect, genomic instability, adaptive response and abscopal effect. Whereas first three phenomena may appear both in vitro and in vivo, an abscopal effect is closely related to partial body irradiation and is a systemic effect mediated by immunologic system which synergizes with radiotherapy. From the clinical point of view abscopal effect is particularly interesting due to both its possible valuable contribution to the treatment of metastases, and the potential harmful effects as induction of genetic instability and carcinogenesis. This review summarized the main results of investigations of non-targeted effects coming from in vitro monolayer cultures, 3-dimentional models of tissues, preclinical studies on rodents and clinically observed beneficial abscopal effects with particular emphasis on participation of immunotherapy in the creation of abscopal effects.

MicroRNAs in cervical cancer: evidences for a miRNA profile deregulated by HPV and its impact on radio-resistance.

Cervical carcinoma (CC) is one of the most common cancers and a leading cause of mortality in women worldwide. Epidemiologic and experimental data have clearly demonstrated a causal role of high-risk Human Papillomavirus (HR-HPV) types in CC initiation and progression, affecting the cellular processes by targeting and inactivating p53 and pRB host proteins. HR-HPV E5, E6 and E7 oncoproteins have the ability to deregulate several cellular processes, mostly apoptosis, cell cycle control, migration, immune evasion, and induction of genetic instability, which promote the accumulation of mutations and aneuploidy. In this scenario, genomic profiles have shown that aberrant expression of cellular oncogenic and tumor suppressive miRNAs have an important role in CC carcinogenesis. It has been stated that HPV infection and E6/E7 expression are essential but not sufficient to lead to CC development; hence other genetic and epigenetic factors have to be involved in this complex disease. Recent evidence suggests an important level of interaction among E6/E7 viral proteins and cellular miRNA, and other noncoding RNAs. The aim of the current review is to analyze recent data that mainly describe the interaction between HR-HPV established infections and specific cellular miRNAs; moreover, to understand how those interactions could affect radio-therapeutic response in tumor cells.

Evidence that the insertion events of IS2 transposition are biased towards abrupt compositional shifts in target DNA and modulated by a diverse set of culture parameters.

Insertion specificity of mobile genetic elements is a rather complex aspect of DNA transposition, which, despite much progress towards its elucidation, still remains incompletely understood. We report here the results of a meta-analysis of IS2 target sites from genomic, phage, and plasmid DNA and find that newly acquired IS2 elements are consistently inserted around abrupt DNA compositional shifts, particularly in the form of switch sites of GC skew. The results presented in this study not only corroborate our previous observations that both the insertion sequence (IS) minicircle junction and target region adopt intrinsically bent conformations in IS2, but most interestingly, extend this requirement to other families of IS elements. Using this information, we were able to pinpoint regions with high propensity for transposition and to predict and detect, de novo, a novel IS2 insertion event in the 3' region of the gfp gene of a reporter plasmid. We also found that during amplification of this plasmid, process parameters such as scale, culture growth phase, and medium composition exacerbate IS2 transposition, leading to contamination levels with potentially detrimental clinical effects. Overall, our findings provide new insights into the role of target DNA structure in the mechanism of transposition of IS elements and extend our understanding of how culture conditions are a relevant factor in the induction of genetic instability.

Induction of genetic instability by transfer of a UV-A-irradiated chromosome

Exposure of cells to ultraviolet (UV)-A radiation induces oxidative damage in DNA, such as 8-oxo-7,8-dihydroguanine (8-oxoG), single-strand breaks, a-basic sites, and DNA–protein cross-links, via reactions with reactive oxygen species (ROS). In this study we examine whether the damage other than double-strand breaks (non-DSB damage), which is UV-A-induced oxidative damage, plays a role in the induction of chromosomal instability. We exposed human chromosome 21 to UV-A and transferred the chromosome into non-irradiated mouse recipient cells by microcell-mediated chromosome transfer. The chromosomal instability of both the transferred human chromosome and the recipient mouse chromosomes was examined by whole-chromosome painting and fluorescence in situ hybridization (WCP-FISH). The ploidy of the mouse recipient cells increased, and chromosomal aberrations occurred not only in the UV-A-irradiated human chromosome but also in the non-irradiated mouse chromosomes. The frequencies of these abnormalities increased with the radiation dose received by the transferred human chromosome. In contrast, in the control experiment, in which an non-irradiated human chromosome was transferred, the micro-cell hybrids remained diploid, and the frequency of chromosomal aberrations in both the transferred human chromosome and recipient mouse chromosomes remained low. Thus, the present study indicates that a chromosome harboring non-DSB damage induced by UV-A irradiation is unstable and transmits instability to chromosomes of non-irradiated recipient mouse cells.

Liver Cell Transformation in Chronic HBV Infection

Epidemiological studies have provided overwhelming evidence for a causal role of chronic HBV infection in the development of hepatocellular carcinoma (HCC), but the molecular mechanisms underlying virally-induced tumorigenesis remain largely debated. In the absence of a dominant oncogene encoded by the HBV genome, indirect roles have been proposed, including insertional activation of cellular oncogenes by HBV DNA integration, induction of genetic instability by viral integration or by the regulatory protein HBx, and long term effects of viral proteins in enhancing immune-mediated liver disease. In this chapter, we discuss different models of HBV-mediated liver cell transformation based on animal systems of hepadnavirus infection as well as functional studies in hepatocyte and hepatoma cell lines. These studies might help identifying the cellular effectors connecting HBV infection and liver cell transformation.

An Essential Role of the HIF‐1α–c‐Myc Axis in Malignant Progression

Cancer is a disease of genomic aberration. The hypoxic microenvironment is believed to promote tumor progression via the induction of genetic instability. To understand how hypoxia drives tumor progression, we have shown recently that the hypoxia-inducible transcription factor, HIF-1alpha, is critical for transcriptional repression of DNA repair genes by a noncanonical mode of action referred to as the "HIF-1alpha-c-Myc axis." HIF-1alpha action via the HIF-1alpha-c-Myc axis is independent of its DNA-binding and transactivation domains; instead it requires the PAS-B domain to displace the transcription activator c-Myc from the target gene promoter for gene repression. Owing to the functional compromise on DNA repair, tumor cells with activated HIF-1alpha-c-Myc axis display persistent DNA damage, genetic alterations, and malignant progression. However, apoptosis-proficient cells are resistant to such changes. These findings argue that the hypoxic microenvironment plays a critical role in driving genetic alterations especially in apoptosis-deficient cells for malignant progression.

Cancer-related inflammation, the seventh hallmark of cancer: links to genetic instability

Inflammatory conditions in selected organs increase the risk of cancer. An inflammatory component is present also in the microenvironment of tumors that are not epidemiologically related to inflammation. Recent studies have begun to unravel molecular pathways linking inflammation and cancer. In the tumor microenvironment, smoldering inflammation contributes to proliferation and survival of malignant cells, angiogenesis, metastasis, subversion of adaptive immunity, reduced response to hormones and chemotherapeutic agents. Recent data suggest that an additional mechanism involved in cancer-related inflammation (CRI) is induction of genetic instability by inflammatory mediators, leading to accumulation of random genetic alterations in cancer cells. In a seminal contribution, Hanahan and Weinberg [(2000) Cell, 100, 57-70] identified the six hallmarks of cancer. We surmise that CRI represents the seventh hallmark.

Pathways to Tumorigenesis—Modeling Mutation Acquisition in Stem Cells and Their Progeny

Most adult tissues consist of stem cells, progenitors, and mature cells, and this hierarchical architecture may play an important role in the multistep process of carcinogenesis. Here, we develop and discuss the important predictions of a simple mathematical model of cancer initiation and early progression within a hierarchically structured tissue. This work presents a model that incorporates both the sequential acquisition of phenotype altering mutations and tissue hierarchy. The model simulates the progressive effect of accumulating mutations that lead to an increase in fitness or the induction of genetic instability. A novel aspect of the model is that symmetric self-renewal, asymmetric division, and differentiation are all incorporated, and this enables the quantitative study of the effect of mutations that deregulate the normal, homeostatic stem cell division pattern. The model is also capable of predicting changes in both tissue composition and in the progression of cells along their lineage at any given time and for various sequences of mutations. Simulations predict that the specific order in which mutations are acquired is crucial for determining the pace of cancer development. Interestingly, we find that the importance of genetic stability differs significantly depending on the physiological expression of mutations related to symmetric self-renewal and differentiation of stem and progenitor cells. In particular, mutations that lead to the alteration of the stem cell division pattern or the acquisition of some degree of immortality in committed progenitors lead to an early onset of cancer and diminish the impact of genetic instability.

Pituitary tumor-transforming gene in endocrine and other neoplasms: a review and update

Pituitary tumor-transforming gene (PTTG) was only recently discovered. Its overexpression occurs in a wide variety of endocrine and non-endocrine tumors, including ones of pituitary, thyroid, ovary, breast, prostate, lung, esophagus, colon, and the central nervous system. It affects tumor invasiveness and recurrence in several systems, functions as a securin during cell cycle progression, and inhibits premature sister chromatid separation. PTTG is involved in multiple cellular pathways, including proliferation, DNA repair, transformation, angiogenesis induction, invasion, and the induction of genetic instability. In thyroid carcinomas, PTTG expression is a marker of invasiveness. PTTG is overexpressed in most pituitary adenomas, where it appears to correlate with recurrence and angiogenesis. Increasing evidence also points to the role of PTTG in endocrine organ development. For example, PTTG knockout mice show defective pancreatic beta-cell proliferation. Herein, we review the current knowledge regarding PTTG-mediated pathways based on evidence from in vivo and in vitro studies as well as knockout mice models. We also summarize the issue of PTTG expression and its correlation with clinicopathologic parameters in patients with neoplasms, particularly of endocrine organs. In addition, we discuss in vitro and in vivo therapeutic models targeting PTTG overexpression.

Induction of genetic instability by gain-of-function p53 cancer mutants

p53 plays critical roles in tumor suppression and the loss of its function is required for cancer progression. In this context, the p53 gene is the most commonly mutated tumor suppressor gene in human cancers. The majority of the p53 gene mutations in human cancers are missense mutations, leading to the expression of the full-length mutant p53 protein in cancer cells. In addition to the loss of tumor suppression activity, p53 cancer mutants gain new oncogenic activities to promote tumorigenesis and drug resistance. Recent studies have identified a novel gain-of-function of p53 cancer mutants in inducing genetic instability by inactivating critical tumor suppressors such as ATM. Genetic instability is a common mechanism by which cancer cells efficiently accumulate genetic mutations to promote their growth, survival and metastatic potential. Therefore, this gain-of-function of p53 cancer mutants could play important roles in tumorigenesis and drug resistance of various types of human cancers. In addition, because many cancer therapies such as radiation therapy suppress or kill cancer cells by activating ATM-dependent responses to DNA double-stranded break damage, elucidation of this gain-of-function of p53 cancer mutants will have important implications on cancer therapy.

Hypoxia-induced genetic instability—a calculated mechanism underlying tumor progression

The cause of human cancers is imputed to the genetic alterations at nucleotide and chromosomal levels of ill-fated cells. It has long been recognized that genetic instability-the hallmark of human cancers-is responsible for the cellular changes that confer progressive transformation on cancerous cells. How cancer cells acquire genetic instability, however, is unclear. We propose that tumor development is a result of expansion and progression-two complementary aspects that collaborate with the tumor microenvironment-hypoxia in particular, on genetic alterations through the induction of genetic instability. In this article, we review the recent literature regarding how hypoxia functionally impairs various DNA repair pathways resulting in genetic instability and discuss the biomedical implications in cancer biology and treatment.

Telomere length dynamics in normal hematopoiesis and in disease states characterized by increased stem cell turnover

Telomeres both reflect and limit the replicative lifespan of normal somatic cells. Immature sub-populations of human CD34+38- hematopoietic stem cell (HSC) can be identified in vitro based on their growth kinetics and telomere length. Fluorescence in situ hybridization and flow cytometry (flow-FISH) has been used to characterize telomere length dynamics as a surrogate marker for HSC turnover in vivo. Investigations in normal steady-state hematopoiesis provided the basis for follow-up studies in model scenarios characterized by increased HSC turnover. Disorders with underlying malignant transformation of HSC (e.g., chronic myeloid leukemia (CML)) can be discriminated from disease states with increased HSC turnover rates secondary to depletion of the stem cell compartment, for example, as in defined bone marrow failure syndromes. In some of these model scenarios, the degree of telomere shortening can be correlated with disease duration, disease stage and severity as well as with response to disease-modifying treatment strategies. Whether increased telomere shortening represents a causal link between HSC turnover, replicative senescence and/or the induction of genetic instability in acquired HSC disorders remains to be shown. However, data from congenital disorders, like dyskeratosis congenita (DKC), suggest that disturbed telomere maintenance may play a role for replicative exhaustion of the HSC pool in vivo.

YB-1 Provokes Breast Cancer through the Induction of Chromosomal Instability That Emerges from Mitotic Failure and Centrosome Amplification

YB-1 protein levels are elevated in most human breast cancers, and high YB-1 levels have been correlated with drug resistance and poor clinical outcome. YB-1 is a stress-responsive, cell cycle-regulated transcription factor with additional functions in RNA metabolism and translation. In this study, we show in a novel transgenic mouse model that human hemagglutinin-tagged YB-1 provokes remarkably diverse breast carcinomas through the induction of genetic instability that emerges from mitotic failure and centrosome amplification. The increase of centrosome numbers proceeds during breast cancer development and explanted tumor cell cultures show the phenotype of ongoing numerical chromosomal instability. These data illustrate a mechanism that might contribute to human breast cancer development.