Cancer. Aneuploidy advantages?

Clinical Applications of Aneuploidies in Evolution of NSCLC Patients: Current Status and Application Prospect

As one of the first characteristics of cancer cells, chromosomal aberrations during cell division have been well documented. Aneuploidy is a feature of most cancer cells accompanied by an elevated rate of mis-segregation of chromosomes, called chromosome instability (CIN). Aneuploidy causes ongoing karyotypic changes that contribute to tumor heterogeneity, drug resistance, and treatment failure, which are considered predictors of poor prognosis. Lung cancer (LC) is the leading cause of cancer-related deaths worldwide, and its genome map shows extensive aneuploid changes. Elucidating the role of aneuploidy in the pathogenesis of LC will reveal information about the key factors of tumor occurrence and development, help to predict the prognosis of cancer, clarify tumor evolution, metastasis, and drug response, and may promote the development of precision oncology. In this review, we describe many possible causes of aneuploidy and provide evidence of the role of aneuploidy in the evolution of LC, providing a basis for future biological and clinical research.

Ras-Mediated Activation of NF-κB and DNA Damage Response in Carcinogenesis

Cancer is a multi-step process during which cells acquire mutations that eventually lead to uncontrolled cell growth and division and evasion of programmed cell death. The oncogenes such as Ras and c-Myc may be responsible in all three major stages of cancer i.e., early, intermediate, and late. The NF-κB has been shown to control the expression of genes linked with tumor pathways such as chronic inflammation, tumor cell survival, anti-apoptosis, proliferation, invasion, and angiogenesis. In the last few decades, various biomarker pathways have been identified that play a critical role in carcinogenesis such as Ras, NF-κB and DNA damage.

Cancer from the perspective of stem cells and misappropriated tissue regeneration mechanisms

Tumorigenesis can be considered as pathologically misappropriated tissue regeneration. In this review we will address some unresolved issues that support this concept. First, we will address the issue of the identity of cancer-initiating cells and the presence of cancer stem cells in growing tumors. We will also ask are there rare and distinct populations of cancer stem cells in established tumor cell lines, or are all of the cells cancer stem cells? Second, the most important clinical problem with cancer is its metastasis, and here a challenging question arises: by employing radio-chemotherapy for tumor treatment, do we unintentionally create a prometastatic microenvironment in collateral organs? Specifically, many factors upregulated in response to radio-chemotherapy-induced injury may attract highly migratory cancer cells that survived initial treatment. Third, what is the contribution of normal circulating stem cells to the growing malignancy? Do circulating normal stem cells recognize a tumor as a hypoxia-damaged tissue that needs vascular and stromal support and thereby contribute to tumor expansion? Fourth, is it reasonable to inhibit only one prometastatic ligand-receptor axis when cancer stem cells express several receptors for several chemotactic factors that may compensate for inhibition of the targeted receptor? Fifth, since most aggressive cancer cells mimic early-development stem cells, which properties of embryonic stem cells are retained in cancer cells? Would it be reasonable to inhibit cancer cell signaling pathways involved in the migration and proliferation of embryonic stem cells? We will also briefly address some new players in cancerogenesis, including extracellular microvesicles, bioactive phospholipids, and extracellular nucleotides.

Genomic instability and proliferation/survival pathways in RB1-deficient malignancies

Genomic instability (GIN) is a hallmark of most cancer cells. However, compared to most human cancer cell types, the retinoblastoma tumor cells show a relatively stable genome. The fundamental basis of this genomic stability has yet to be elucidated, and the role of certain proteins involved in cell cycle regulation may be the key to the development of these specific genotypes. We examined whether thyroid hormone receptor beta 1 and 2 (TRβ1 and TRβ2), known to regulate tumorigenesis, and PTTG1, a mitotic checkpoint protein, play a role in maintaining genomic stability in retinoblastoma. In order to elucidate the role of these proteins in development of aneuploidy/polyploidy, an indicator of GIN, we first studied comparative GIN in retinoblastomas and multiple RB mutant cancer cell lines using single nucleotide polymorphism (SNP) analysis. We then utilized pLKO lentiviral vectors to selectively modify expression of the targeted cell cycle proteins and interpret their effect on downstream cell cycle proteins and their relative effects on the development of polyploidy in multiple tumor cell lines. The SNP analysis showed that retinoblastomas displayed relatively fewer genomic copy number changes as compared to other RB1-deficient cancer cell lines. Both TRβ1 and TRβ2 knockdown led to accumulation of E2F1 and PTTG1 and increased GIN as demonstrated by an increase in polyploidy. Downregulation of PTTG1 led to a relative decrease in GIN while upregulation of PTTG1 led to a relative increase in GIN. Knockdown of E2F1 led to a downstream decrease in PTTG1 expression. Rb-knockdown also upregulated E2F1 and PTTG1 leading to increased GIN. We showed that Rb is necessary for PTTG1 inhibition and genomic stability. A relatively stable genome in retinoblastoma tumor cells is maintained by TRβ1 and TRβ2-mediated PTTG1 inhibition, counteracting Rb-deficiency-related GIN. TRβ1, TRβ2 and Rb-KD all led to the downstream PTTG1 accumulation, apparently through an activation of E2F1 resulting in extensive genomic instability as seen in other Rb-deficient tumors.

A sequential methodology that allows apoptotic cell sorting and FISH analysis in human testicular cells

The objective of this study was to develop a methodology that permits the detection and separation of apoptotic cells in human testicular tissue and their subsequent cytogenetic analysis by fluorescence in situ hybridization (FISH). The sequential methodology consisted of five steps: 1) enzymatic disaggregation of testicular tissue, 2) specific staining of apoptotic cells, 3) cell sorting by flow cytometry, 4) cell fixation, and 5) FISH. Enzymatic disaggregation yielded cell counts that ranged from 1.7x10(5) to 5x10(6) cells, and viability values greater than 72%. The apoptotic (mean ± SD: 22% ± 5.3%) and viable (45.5% ± 7.3%) populations were identified and selected by flow cytometry and demonstrated purity values ranging between 62% and 100%. The paraformaldehyde fixation of the selected fractions resulted in cell loss values of less than 10%. The application of three treatments before FISH (membrane permeabilization, elimination of cytoplasmic components, and re-fixation of the sample) resulted in hybridization frequencies of greater than 98%. In both selected fractions, cells of all spermatogenic stages and Sertoli cells were identified. The methodology developed has enabled the preparation of a cellular suspension with optimal viability and counting, the efficient selection of the apoptotic population, and its analysis by cytogenetic techniques. The application of this methodology in testicular cells should help establish whether there is a direct relationship between chromosome anomalies and apoptosis.

Epiblast/germ line hypothesis of cancer development revisited: lesson from the presence of Oct-4+ cells in adult tissues

The morphology of several tumors mimics developmentally early tissues; tumors often express early developmental markers characteristic for the germ line lineage. Recently, our group identified a population of very small stem cells (SCs) in murine bone marrow (BM) and other adult organs that express several markers characteristic for epiblast/germ line-derived SCs. We named these rare cells "Very Small Embryonic/Epiblast-like Stem Cells (VSELs)." We hypothesized that these cells that express both epiblast and germ line markers are deposited during early gastrulation in developing tissues and organs and play an important role in the turnover of tissue-committed (TC) SCs. To support this, we envision that the germ line is not only the origin of SCs, but also remains as a scaffold or back-up for the SC compartment in adult life. Furthermore, we noticed that VSELs are protected from uncontrolled proliferation and teratoma formation by a unique DNA methylation pattern in some developmentally crucial imprinted genes, which show hypomethylation or erasure of imprints in paternally methylated genes and hypermethylation of imprints in the maternally methylated. In pathological situations, however, we hypothesize that VSELs could be involved in the development of several malignancies. Therefore, potential involvement of VSELs in cancerogenesis could support century-old concepts of embryonic rest- or germ line-origin hypotheses of cancer development. However, we are aware that this working hypothesis requires further direct experimental confirmation.

BUB3 that dissociates from BUB1 activates caspase-independent mitotic death (CIMD)

The cell death mechanism that prevents aneuploidy caused by a failure of the spindle checkpoint has recently emerged as an important regulatory paradigm. We previously identified a new type of mitotic cell death, termed caspase-independent mitotic death (CIMD), which is induced during early mitosis by partial BUB1 (a spindle checkpoint protein) depletion and defects in kinetochore-microtubule attachment. In this study, we have shown that survived cells that escape CIMD have abnormal nuclei, and we have determined the molecular mechanism by which BUB1 depletion activates CIMD. The BUB3 protein (a BUB1 interactor and a spindle checkpoint protein) interacts with p73 (a homolog of p53), specifically in cells wherein CIMD occurs. The BUB3 protein that is freed from BUB1 associates with p73 on which Y99 is phosphorylated by c-Abl tyrosine kinase, resulting in the activation of CIMD. These results strongly support the hypothesis that CIMD is the cell death mechanism protecting cells from aneuploidy by inducing the death of cells prone to substantial chromosome missegregation.

Models for prevention and treatment of cancer: problems vs promises

Current estimates from the American Cancer Society and from the International Union Against Cancer indicate that 12 million cases of cancer were diagnosed last year, with 7 million deaths worldwide; these numbers are expected to double by 2030 (27 million cases with 17 million deaths). Despite tremendous technological developments in all areas, and President Richard Nixon's initiative in the 1974 "War against Cancer", the US cancer incidence is the highest in the world and the cancer death rate has not significantly changed in the last 50 years (193.9 per 100,000 in 1950 vs 193.4 per 100,000 in 2002). Extensive research during the same time, however, has revealed that cancer is a preventable disease that requires major changes in life style; with one third of all cancers assigned to Tobacco, one third to diet, and remaining one third to the environment. Approximately 20 billion dollars are spent annually to find a cure for cancer. We propose that our inability to find a cure to cancer lies in the models used. Whether cell culture or animal studies, no model has yet been found that can reproduce the pathogenesis of the disease in the laboratory. Mono-targeted therapies, till know in most cases, have done a little to make a difference in cancer treatment. Similarly, molecular signatures/predictors of the diagnosis of the disease and response are also lacking. This review discusses the pros and cons of current cancer models based on cancer genetics, cell culture, animal models, cancer biomarkers/signature, cancer stem cells, cancer cell signaling, targeted therapies, therapeutic targets, clinical trials, cancer prevention, personalized medicine, and off-label uses to find a cure for cancer and demonstrates an urgent need for "out of the box" approaches.

Aneuploidy and improved growth are coincident but not causal in a yeast cancer model

Aneuploidy is a hallmark of cancer cells and is assumed to play a causative role. This relationship is dissected in a yeast, with results that show that anueploidy can be removed, but cells maintain their proliferative advantage.

Cancer cells have acquired mutations that alter their growth. Aneuploidy that typify cancer cells are often assumed to contribute to the abnormal growth characteristics. Here we test the idea of a link between aneuploidy and mutations allowing improved growth, using Saccharomyces cerevisiae containing a mcm4 helicase allele that was shown to cause cancer in mice. Yeast bearing this mcm4 allele are prone to undergoing a “hypermutable phase” characterized by a changing karyotype, ultimately yielding progeny with improved growth properties. When such progeny are returned to a normal karyotype by mating, their improved growth remains. Genetic analysis shows their improved growth is due to mutations in just a few loci. In sum, the effects of the mcm4 allele in mice are recapitulated in yeast, and the aneuploidy is not required to maintain improved growth.

Aneuploidy, an abnormality in chromosome number and structure, occurs commonly in cancers and has been suggested to be required to maintain accelerated cell proliferation. However, this hypothesis remains untested as it is not possible to selectively remove the acquired aneuploidy in cells that already have altered growth. Using a yeast model bearing mcm4^Chaos3, an allele that causes mammary tumors in mice, these technical hurdles in animal cells can be overcome. We show that aneuploidy is not responsible for accelerated proliferation in yeast but mutations in just a few loci are. This study provides an excellent example of how a complex disease can be dissected in a simple model organism, and that the information extracted from yeast may be used to guide mammalian studies.

Very small embryonic/epiblast-like stem cells: a missing link to support the germ line hypothesis of cancer development?

The morphology of several tumors mimics developmentally early tissues, and tumors often express early developmental markers characteristic of the germ line lineage. The presence of these markers in neoplastic cells could reflect the dedifferentiation of somatic cells in which cancer develops or cancer origination in primitive stem cells closely related to the epiblast/germ line. The identification of primitive germ line-derived very small embryonic/epiblast-like stem cells, which are deposited early in embryogenesis in developing organs and persist in several organs into adulthood, raised the possibility that cancer may originate in these cells. In this review, we hypothesize that very small embryonic/epiblast-like stem cells could be a missing link that support the more than 100-year-old concepts of the embryonic rest or germ line origin hypotheses of cancer development; however, further experimental evidence is needed to support this hypothesis.