Aneuploidy correlated 100% with chemical transformation of Chinese hamster cells

Clinically significant cancer evolves from transient mutated and/or aneuploid neoplasia by cell fusion to form unstable syncytia that give rise to ecologically viable parasite species

Following the idea of Duesberg and Rasnick (Cell Motil Cytoskeleton 2000; 47:81-107) that cancer is a separate species of organism, the ecology of cancer as a parasite is examined. The most important ecological feature of cancer is its ability to evolve. The mutation hypothesis and the "unstable genome" hypothesis of cancer evolution are considered but neither of these current hypotheses is believed to adequately explain how cancer successfully evolves. In particular, either of these processes alone should lead to extinction of the cell line before a clinically significant neoplasm is achieved. Moreover, the term "unstable genome" probably should be replaced by "labile genome" because cancer genomes must be stable enough to reproduce themselves through many generations if the clone is to expand. The key step in productive evolution of undetectable neoplasia into clinically significant cancer is hypothesized to be sex-like resorting of chromosomes from different cells (e.g., normal and abnormal cells). The sex-like process begins with cell fusion to form a syncytium, which may be stable (producing multinucleated giant cells seen in many tumors) or which may undergo "mitotic catastrophe" to produce polyploidy cells. The nuclei of polyploid cells may undergo a process called "neosis" in which they form buds and undergo karyokinesis followed by cytokinesis to yield karyoplasts (small cells with little cytoplasm) that found new cancer clone lines. Although both mutations and unstable (aneuploid) genomes are seen as dead ends in cancer evolution (i.e., using only these modes of genome modification, cancers would not likely advance to clinical significance before becoming extinct), they each produce transient genetic material, which can be incorporated into stable genomes with aggressive (i.e., ecologically fit) phenotypes by cell fusion. It is proposed that inhibition of cell fusion (or other steps in this sex-like process) concurrent with classical chemotherapy might prevent evolution of the clones and recurrence of the cancer. Similarly, active suppression of viruses or other conditions that catalyze cell fusion should also slow down evolution of cancer clones.

Random aneuploidy in neoplastic and pre-neoplastic diseases, multiple myeloma, and monoclonal gammopathy

In this study we evaluated the aneuploidy rate of cells from patients considered to have a premalignant condition (monoclonal gammopathy or MGUS) and patients with multiple myeloma, as well as healthy controls. By applying a fluorescence situ hybridization technique, we estimated the random aneuploidy rate of alpha-satellite (centromeres) probes from chromosomes 9 and 18. The monosomy and total aneuploidy rates were higher in the two study groups compared to the control group. The monosomy rate was significantly higher in the MGUS group compared to the group with chromosome 18 alpha-satellite probes, a finding that was reported before in preneoplastic conditions. Our results support the cancer aneuploidy theory that carcinogenesis is initiated by a random aneuploidy, which is induced either spontaneously or by a carcinogen. The resulting karyotype instability sets a chain reaction of aneuploidization, which generates even more abnormal and eventually cancer-specific combinations and rearrangements of chromosomes.

Centromere protein H is up-regulated in primary human colorectal cancer and its overexpression induces aneuploidy

Chromosomal instability (CIN) has been recognized as a hallmark of human cancer and is caused by continuous chromosome missegregation during mitosis. Proper chromosome segregation requires a physical connection between spindle microtubules and centromeric DNA and this attachment occurs at proteinaceous structures called kinetochore. Several centromere proteins such as CENP-A and CENP-H are the fundamental components of the human active kinetochore, and inappropriate expression of the centromere proteins could be a major cause of CIN. We have previously shown that CENP-A was overexpressed in primary human colorectal cancer. In this study, we show that CENP-H was also up-regulated in all of 15 primary human colorectal cancer tissues as well as in CIN tumor cell lines. Surprisingly, transient transfection of CENP-H expression plasmid into the diploid cell line HCT116 remarkably induced aneupoidy. Moreover, CENP-H stable transfectant of mouse embryonic fibroblast/3T3 cell lines showed aberrant interphase micronuclei, characteristic of chromosome missegregation. In these CENP-H overexpressed cells, CENP-H completely disappeared from the centromere of mitotic chromosomes, which might be the cause of the chromosome segregation defect. These results suggest that the aberrant expression and localization of a kinetochore protein CENP-H plays an important role in the aneuploidy frequently observed in colorectal cancers.

Induction of cell proliferation, micronuclei and hyperdiploidy/polyploidy in the mammary cells of DDT- and DMBA-treated pubertal rats

The environmental estrogen, dichlorodiphenyltrichloroethane (DDT), and its metabolites have been implicated in the development of breast cancer through mechanisms that remain to be elucidated. It has been hypothesized that exposure to DDT and its metabolites, during critical periods of development, can contribute to an elevated risk for breast cancer in adults. In the present study, we have investigated the effect of o,p'-DDT on mammary gland cell proliferation and chromosomal alterations, in a rat mammary cancer model (commonly used to study human cancer), to gain insights into its potential role in the development of breast cancer. Twenty-one-day-old female Sprague-Dawley (SD) rats were administered o,p'-DDT, 7,12-dimethylbenz[a]anthracene (DMBA), genistein, DDT+DMBA, or DDT+DMBA+genistein, over a 14-day period. To determine changes in chromosome number and structure, we used the micronucleus assay as well as multicolor fluorescence in situ hybridization (FISH) region-specific DNA probes for rat chromosomes 4 and 19. Cell proliferation was evaluated using 5-bromo-2'-deoxyuridine (BrdU). Significant increases in BrdU-incorporated cells were seen in the rats treated with DDT+DMBA. Although micronucleus frequencies were somewhat elevated in several of the treatment groups, significant increases were not seen in any of them. Significant increases in numerical chromosomal aberrations were detected in all of the DDT- and DMBA-treated groups. Genistein significantly reduced BrdU incorporation and polyploidy in the DDT+DMBA-treated rats. These initial studies indicate that DDT and DMBA can induce cellular and chromosomal alterations in the rat mammary gland, which is consistent with the hypothesis that these agents can induce early events in mammary carcinogenesis.

Chronic myeloid leukemia: a model for oncology

Leukemias have traditionally served as model systems for research on neoplasia because of the easy availability of cell material from blood and marrow for diagnosis, monitoring and studies on pathophysiology. Beyond these more technical aspects, chronic myeloid leukemia (CML) became the first neoplasia in which the elucidation of the genotype led to a rationally designed therapy of the phenotype. Targeting of the pathogenetically relevant BCR-ABL tyrosine kinase with the selective kinase inhibitor imatinib has induced remissions with almost complete disappearance of any signs and symptoms of CML. This therapeutic success has triggered an intensive search for target structures in other cancers and has led to the development of numerous inhibitors of potential targets, which are being studied in preclinical and clinical trials worldwide. This review deals with some of the recent developments that have evolved since our last review in this journal in 2000 (Hehlmann R, Hochhaus A, Berger U, Reiter A (2000) Current trends in the management of chronic myelogenous leukemia.

High-grade neuroendocrine carcinomas display unique cytogenetic aberrations

Neuroendocrine tumors represent a spectrum of tumor types with different biologic and clinical features. The morphologic types include the low-grade typical and atypical carcinoids and the high-grade small cell and large cell neuroendocrine carcinomas (NECs). Cytogenetic descriptions of high-grade NECs are rare. Complete karyotypic descriptions of 34 high-grade NECs are reviewed: 7 extrapulmonary small cell NECs, 3 metastatic NECs of unknown primary, and 24 small cell lung carcinomas (SCLCs). Chromosomal deletions are more frequent than gains and often involve the entire chromosome arm. Typical aberrations are deletions of chromosome 3p, 5q, 10q, and 17p and gains of 1q, 3q, and 5p occurring as isochromosomes. Non-small cell lung cancers (NSCLCs) have different cytogenetic aberrations, but those with a metastatic phenotype display the identical aberrations as SCLC, a tumor known for its metastatic phenotype at onset. A genetic classification of lung cancer that incorporates the pattern of recurrent chromosome aberrations may be a better predictor of clinical outcome than a morphologic classification.

Truncating APC mutations have dominant effects on proliferation, spindle checkpoint control, survival and chromosome stability

The majority of human tumour cells are aneuploid owing to an underlying chromosome instability phenotype. While the genetic lesions that cause chromosome instability remain undefined, mouse ES cells harbouring homozygous adenomatous polyposis coli (APC) mutations are frequently tetraploid. In addition, colon cancer cells with APC mutations have weakened kinetochore-microtubule interactions. Furthermore, mitotic spindles assembled in APC-depleted Xenopus egg extracts are aberrant. Therefore, to determine whether APC mutations can initiate chromosome instability in human cells, we expressed N-terminal APC fragments in HCT-116 cells, a near diploid colon cancer cell line with two wild-type APC alleles. We show that cells expressing N-APC mutants exit mitosis prematurely in the presence of spindle toxins, consistent with a spindle checkpoint defect. In addition, N-APC cells show enhanced survival following prolonged spindle damage. In contrast to controls, the N-APC survivors frequently contain dicentric chromosomes and then go on to become highly aneuploid. These observations suggest that truncating APC mutations can exert dominant effects which in turn can initiate chromosome instability. As such, APC mutation not only compromises tumour suppressor function but may also have oncogenic properties. We suggest therefore that the initial APC mutation acts as a 'double whammy', destabilising the genome and setting the stage for deregulated proliferation upon loss of the second APC allele.

Primary biliary cirrhosis: does X mark the spot?

Primary biliary cirrhosis (PBC) is an autoimmune disease of unknown etiology leading to progressive destruction of intrahepatic bile duct, with cholestasis, cirrhosis, and eventually liver failure. Epidemiological data indicate that environmental factors trigger autoimmunity in genetically susceptible individuals, although no definitive association of PBC with specific genes has been found. Further, no convincing explanation has been provided for the strong female predominance observed in the prevalence of PBC. However, we recently suggested that the enhanced monosomy X in peripheral white blood cells, and particularly in lymphocytes, of affected women might play a role in the induction of PBC. Such observations appear independent from the degree of cholestasis and specific for PBC. In this review we discuss the implications of these findings and their immunological implications.

A trivalent dimethylarsenic compound, dimethylarsine iodide, induces cellular transformation, aneuploidy, centrosome abnormality and multipolar spindle formation in Syrian hamster embryo cells

The abilities of dimethylarsine iodide (DMI), a model compound of trivalent dimethylarsenicals, to induce cellular transformation, aneuploidy, centrosome abnormality, and multipolar spindle formations were investigated using the Syrian hamster embryo (SHE) cell model. Cellular growth was decreased in a concentration-dependent manner by treatment with DMI at concentrations over 0.1 microM. Treatment with DMI at concentrations from 0.1 to 1.0 microM induced morphological transformation in SHE cells. The transforming activity of DMI, determined by the frequency of morphologically transformed colonies, was approximately 30 times higher than that induced by treatment with the same concentration of sodium arsenite. Flow cytometry suggested an increase in the aneuploid population caused by DMI, as shown by the appearance of hypo-2N, hypo-4N and hypo-8N. DMI also caused abnormal staining of gamma-tubulin, indicating loss of centrosome integrity and a resultant induction of multipolar spindles in mitotic cells. Mitotic cells with centrosomes that coalesced partly at the cell periphery, not the cell center, were detected as early changes that resulted in multipolar spindles. These findings indicate that DMI has transforming activity in SHE cells. Moreover, the results suggest the importance of centrosome abnormalities as a causal change of DMI-induced aneuploidy.

Spontaneous transformation of an immortalized hepatocyte cell line: potential role of a nuclear protease

In this study, we utilized an in vitro model of spontaneous transformation/progression, an SV40 large T antigen-immortalized rat hepatocyte cell line (designated CWSV14) that is very weakly tumorigenic at low-passage, but acquires a transformed phenotype upon extended passage in cell culture. Here we show that this mid-passage transformation is accompanied by development of aneuploidy and disorganization of the actin cytoskeleton, concomitant with a large increase in a chymotrypsin-like nuclear protease activity which we have previously implicated in chemical transformation of fibroblasts and ras-transformation of hepatocytes. Passage of the CWSV14 cells with AAPF(cmk), a relatively selective inhibitor of the nuclear protease activity, abrogates the acquisition of the transformed phenotype and prevents the changes in the actin cytoskeleton. We hypothesize that the nuclear protease may play a role in initiating development of genomic instability, paralleling the archetypical role of proteases in paradigms such as the SOS-type responses in bacteria and yeast.

Expression of a Dominant Negative Heat Shock Factor-1 Construct Inhibits Aneuploidy in Prostate Carcinoma Cells*

Recent studies have implicated heat shock proteins (HSP) and heat shock transcription factor 1 (HSF1) in tumor progression. We have examined the role of HSF1 in the malignant phenotype of PC-3 prostate carcinoma cells. We have developed a dominant negative construct of HSF1 that antagonizes transcription from HSP promoters and results in the depletion of intracellular HSP 70. Our studies indicate that expression of DN-HSF1 dramatically alters the DNA content of PC-3 cells (derived from p53 null prostatic carcinoma) and inhibits aneuploidy in these cells. This effect is due to prolonged expression of DN-HSF1, and transient expression of the dominant negative factor from an inducible promoter failed to cause the effect. Inhibition of aneuploidy in p53 null PC-3 cells by DN-HSF1 expression was recapitulated by expression within the cells of wild type p53. Furthermore, cells expressing DN-HSF1 showed a profound inhibition in the development of aneuploidy when exposed to chemical agents that disrupt the mitotic spindle and prevent progression through metaphase. Inhibition of aneuploidy in PC-3 cells expressing DN-HSF1 was associated with delayed breakdown of cyclin B1 compared with controls, consistent with a role for wild type HSF1 in the regulation of cyclin B1 degradation, a key step in the control of mitosis. Our experiments therefore demonstrate that HSF1 plays a functional role in cancer cells under nonstress conditions and influences cell cycle behavior and progression through mitosis and promotes the development of the aneuploid state.

Acquired Robertsonian translocations are not rare events in acute leukemia and lymphoma

Robertsonian translocations are the most common constitutional structural abnormalities but are rarely reported as acquired aberrations in hematologic malignancies. The nonhomologous acrocentric rearrangements are designated as Robertsonian translocations, whereas the homologous acrocentric rearrangements are referred to as isochromosomes. Robertsonian rearrangements have the highest mutation rates of structural chromosome rearrangements based on surveys of newborns and spontaneous abortions. It would be expected that Robertsonian recombinations would be more common than suggested by the literature. A survey of the cytogenetics database from a single institution found 17 patients with acquired Robertsonian rearrangement and hematologic malignancies. This is combined with data from the literature for a total of 237 patients. All of the possible types of Robertsonian rearrangements have been reported in hematologic malignancies, with the i(13q), i(14q), and i(21q) accounting for nearly 60%. Complex karyotypic changes are seen in the majority of cases, corresponding with disease evolution. These karyotypes consistently show loss of chromosomes 5 and/or 7 in the myelocytic disorders, nonacrocentric isochromosomes, and centromeric breakage and reunion. However, nearly 25% of the acquired rearrangements were found as the sole abnormality or in addition to an established cytogenetic aberration. Most of these were the i(14q) with the myelodysplasia subtypes refractory anemia and chronic myelomonocytic leukemia.

Prevalence of liver tumours in HIV-1 tat-transgenic mice treated with urethane

The human immunodeficiency virus type 1 (HIV-1) Tat protein stimulates cell proliferation, inhibits apoptosis, displays angiogenic functions and is believed to be involved in the pathogenesis of Kaposi's sarcoma (KS) and other tumours arising in AIDS patients. Tat-transgenic (TT) mice, which constitutively express Tat in all tissues and organs, may therefore be predisposed to tumorigenesis. To test this hypothesis, we treated TT mice with urethane, a general carcinogen inducing tumours of various organs. The results indicate that, after injection of urethane, the incidence of lung tumours and lymphomas is not significantly different in the TT and control (CC) mice, whereas liver preneoplastic lesions and tumours show a significantly greater incidence in TT than in CC mice. This remarkable carcinogenic effect of urethane for the liver may be due to a tat-induced predisposition, manifested as a liver cell dysplasia (LCD), spontaneously affecting most of the TT mice. LCD may exert a promoting effect by stimulating proliferation of cell clones initiated by the mutagenic effect of urethane. In addition, LCD, which is associated with aneuploidy and chromosome instability, may enhance the progression to malignancy of the preneoplastic lesions induced by urethane. Interestingly, a significantly greater incidence of vascular ectasias and haemangiomas was detected in the liver of urethane-treated TT mice, most likely due to the marked angiogenic properties of Tat. This study suggests a role for Tat in the promotion and progression of tumours initiated by exogenous and endogenous carcinogens in HIV-1-infected patients, thereby contributing to the tumorigenesis in the course of AIDS.

Frequency of monosomy X in women with primary biliary cirrhosis

The mechanisms that cause the female predominance of primary biliary cirrhosis (PBC) are uncertain, but the X chromosome includes genes involved in immunological tolerance. We assessed the rate of X monosomy in peripheral white blood cells from 100 women with PBC, 50 with chronic hepatitis C, and 50 healthy controls, by fluorescence in-situ hybridisation. Frequency of X monosomy increased with age in all groups, but was significantly higher in women with PBC than in controls (p<0.0001); age-adjusted back-transformed mean frequencies were 0.050 (95% CI 0.046-0.055) in women with PBC, 0.032 (0.028-0.036) in those with chronic hepatitis C, and 0.028 (0.025-0.032) in controls. We suggest that haploinsufficiency for specific X-linked genes leads to female susceptibility to PBC.

Induction of structural and numerical changes of chromosome, centrosome abnormality, multipolar spindles and multipolar division in cultured Chinese hamster V79 cells by exposure to a trivalent dimethylarsenic compound

Dimethylarsine iodide (DMI) was used as a model compound of trivalent dimethylarsenicals [DMA(III)], and the biological effects were extensively investigated in cultured Chinese hamster V79 cells. When the cytotoxic effects of DMA(III) were compared with those of inorganic arsenite and dimethylarsinic acid [DMA(V)], DMA(III) was about 10,000 times more potent than DMA(V), and it was even 10 times more toxic than arsenite. Depletion of cell glutathione (GSH) did not influence the cytotoxic effects of DMA(III), whereas it enhanced the cytotoxicity of arsenite. Chromosome structural aberrations, such as gaps, breaks and pulverizations, and numerical changes, such as aneuploidy, hyper- and hypo-tetraploidy, were induced by DMA(III) in a concentration-dependent manner. Mitotic index increased 9-12h after the addition of DMA(III), and then declined. By contrast, the incidence of multinucleated cells increased conversely with the decrease in mitotic index at and after 24h of exposure. The mitotic cell-specific abnormality of centrosome integrity and multipolar spindles were induced by DMA(III) in a time- and concentration-dependent manner. Moreover, DMA(III) caused abnormal cytokinesis (multipolar division) at concentrations that were effective in causing centrosome abnormality, multipolar spindles and aneuploidy. These results showed that DMA(III) was genotoxic on cultured mammalian cells. Results also suggest that DMA(III)-induced multipolar spindles and multipolar division may be associated with the induction of aneuploidy. In addition, the centrosome may be a primary target for cell death via multinucleated cells.

Chromosome malsegregation induced by the rodent carcinogens acetamide, pyridine and diethanolamine in Drosophila melanogaster females

The effect of the rodent carcinogens acetamide (AC), pyridine (PY) and diethanolamine (DEA) on meiotic chromosome segregation was assessed in 4-day-old Drosophila melanogaster females. After oral treatment with 0.05, 0.1, 0.2 and 0.3% PY; 0.5, 1, 1.5, 2 and 4% AC; or 5, 10, 20, 40 and 80% DEA, the females were mated to 7-day-old males and three 24h broods were obtained to sample cells exposed mainly as mature oocytes (brood I), and nearly mature oocytes (brood II) with an increasing proportion of early oocytes (brood III). Viability was not affected at the two (PY) or three (AC, DEA) lowest concentrations, decreasing thereafter. PY increased the frequency of nondisjunction exclusively in brood II suggesting its interaction with specific targets. AC and DEA (the most active of the three) induced similar frequencies of nondisjunction in all broods suggesting unspecific cell division perturbations probably due to toxicity. No clear dose effect relationships were observed.

Instability of chromosome structure in cancer cells increases exponentially with degrees of aneuploidy

Structurally altered or marker chromosomes are the cytogenetic hallmarks of cancer cells, but their origins are still debated. Here we propose that aneuploidy, which is ubiquitous in cancer and inevitably unbalances thousands of synergistic genes, destabilizes the structure of chromosomes by catalyzing DNA breaks. Aneuploidy catalyzes such breaks by unbalancing teams of enzymes, which synthesize and maintain DNA and nucleotide pools, and even unbalancing histones via the corresponding genes. DNA breaks then initiate deletions, amplifications, and intra- and interchromosomal rearrangements. Our hypothesis predicts that the rate at which chromosomes are altered is proportional to the degree of aneuploidy: the more abnormal the number and balance of chromosomes, the higher the rate of structural alterations. To test this prediction, we have determined the rates at which clonal cultures of diploid and aneuploid Chinese hamster cells generate new, and thus nonclonal, structurally altered chromosomes per mitosis. Based on about 20 metaphases, the number of new, structurally altered chromosomes was 0 per diploid, 0-0.23 per near-diploid, 0.2-1.4 per hypotriploid, 3.25-4.8 per hypertriploid, and 0.4 per near-tetraploid cell. Thus, instability of chromosome structure increases exponentially with the deviation of ploidy from the normal diploid and tetraploid balances. The particular chromosomes engaged in aneuploidy also affected the rates of chromosome alteration, particularly at low aneuploidy indices. We conclude that aneuploidy is sufficient to cause structural instability of chromosomes. Further, we suggest that certain structurally altered chromosomes encode cancer-specific phenotypes that cannot be generated by unbalancing intact chromosomes. We also extend the evidence for aneuploidy causing numerical instability of chromosomes autocatalytically, and adduce evidence that aneuploidy can cause the many gene mutations of cancer cells that have been attributed to various mutator genes.

The ch-TOG/XMAP215 protein is essential for spindle pole organization in human somatic cells

The ch-TOG/XMAP215 family of proteins bind directly to microtubules and appear to play an essential role in stabilizing spindle microtubules. These proteins stabilize microtubules mainly by influencing microtubule plus-end dynamics, yet, in vivo, they are all strongly concentrated at spindle poles, where the minus ends of the microtubules are concentrated. In Drosophila embryos, the centrosomal protein D-TACC is required to efficiently recruit ch-TOG/Msps to centrosomes. In humans, ch-TOG and the three known TACC proteins have been implicated in cancer, but their functions are unknown. Here we extensively depleted TACC3 and ch-TOG from HeLa cells using RNA interference. In TACC3-depleted cells, spindles are well organized, but microtubules are partially destabilized and ch-TOG is no longer concentrated on spindle microtubules. In ch-TOG-depleted cells, relatively robust spindles form, but the spindles are highly disorganized. Thus, in human somatic cells, ch-TOG appears to play a major role in organizing spindle poles, and a more minor role in stabilizing spindle microtubules that is, at least in part, mediated via an interaction with TACC3.

Microarray analysis reveals a major direct role of DNA copy number alteration in the transcriptional program of human breast tumors

Genomic DNA copy number alterations are key genetic events in the development and progression of human cancers. Here we report a genome-wide microarray comparative genomic hybridization (array CGH) analysis of DNA copy number variation in a series of primary human breast tumors. We have profiled DNA copy number alteration across 6,691 mapped human genes, in 44 predominantly advanced, primary breast tumors and 10 breast cancer cell lines. While the overall patterns of DNA amplification and deletion corroborate previous cytogenetic studies, the high-resolution (gene-by-gene) mapping of amplicon boundaries and the quantitative analysis of amplicon shape provide significant improvement in the localization of candidate oncogenes. Parallel microarray measurements of mRNA levels reveal the remarkable degree to which variation in gene copy number contributes to variation in gene expression in tumor cells. Specifically, we find that 62% of highly amplified genes show moderately or highly elevated expression, that DNA copy number influences gene expression across a wide range of DNA copy number alterations (deletion, low-, mid- and high-level amplification), that on average, a 2-fold change in DNA copy number is associated with a corresponding 1.5-fold change in mRNA levels, and that overall, at least 12% of all the variation in gene expression among the breast tumors is directly attributable to underlying variation in gene copy number. These findings provide evidence that widespread DNA copy number alteration can lead directly to global deregulation of gene expression, which may contribute to the development or progression of cancer.

Understanding cancer as a formless phenomenon

Complex living organisms possess qualities that cannot be reduced to the simple addition of quantities. Among such qualities are a specific form and a specific organization. Thinking about morphological aspects is a prime example of the qualitative approach to biological matters. Such a morphogenetic perspective has been continuously developed, both theoretically and experimentally, along the past century, even though it is now rather marginal within a mainstream dominated by molecular biology. However, the morphogenetic outlook can be applied to the understanding of complex biological phenomena, such as cancer. This phenomenon is currently explained as a cellular problem caused by specific gene mutations and/or specific loss of gene regulation. Nevertheless, cancer is a problem that affects the whole organism. Contemporary research based on the genetic paradigm of cancer causation has led to paradoxes and anomalies that cannot be explained within such a reductionist paradigm. Here it is proposed that real, non-experimental, sporadic cancer may be understood as a conflict between an organized morphology (the organism) and a part of such a morphology that drifts towards an amorphous state (the tumour). Thus, rare, sporadic cancer in children can be the result of early disruption of the developmental constraints before the organism has achieved its morphological maturity. While common sporadic cancer in aged individuals may ensue as a result of the weakening or exhaustion of the developmental constraints that determine the morphological stability of the organism, once the organism is past its reproductive prime.

Epithelial and fibroblast cell lines derived from a spontaneous mammary carcinoma in a MMTV/neu transgenic mouse

Female murine mammary tumor virus (MMTV)/neu transgenic mice, expressing a wild-type rat neu oncogene driven by an MMTV promoter, develop focal mammary adenocarcinomas that are pathologically very similar to human breast tumors. Two new cell lines were established from a mammary tumor that arose in a female MMTV/neu transgenic mouse. One of these lines, mammary carcinoma from Neu transgenic mouse A (MCNeuA), has an epithelial morphology, is cytokeratin positive, and expresses high levels of the neu transgene. Karyotyping and comparative genomic hybridization analyses demonstrated genomic alterations in the MCNeuA cell line. The other line, N202Fb3, has a fibroblast morphology, is cytokeratin negative, and expresses the neu transgene at a very low level. This cell line also expresses smooth muscle alpha-actin, suggesting that it is a myofibroblast line. The MCNeuA cell line is tumorigenic when injected into syngeneic MMTV/neu transgenic mice, with an in vivo doubling time of about 14 d. The rationale for establishing this tumor cell line was to provide a tumor transplantation system for rapidly assessing immunotherapeutic interventions before testing in the more cumbersome model of spontaneous tumor development in the MMTV/neu transgenic mice. Mice immunized with a Neu extracellular domain protein vaccine were protected against a subsequent inoculation of MCNeuA cells, indicating that this cell line will be useful for evaluating cancer vaccine strategies. This tumor cell line may also prove useful in studying the biological properties of the neu oncogene and its role in the malignant process. In addition, the tumor-derived fibroblast line may be useful for studying tumor-stromal cell interactions.

Specific aneusomies in Chinese hamster cells at different stages of neoplastic transformation, initiated by nitrosomethylurea

Aneuploidy is ubiquitous in cancer, and its phenotypes are inevitably dominant and abnormal. In view of these facts we recently proposed that aneuploidy is sufficient for carcinogenesis generating cancer-specific aneusomies via a chain reaction of autocatalytic aneuploidizations. According to this hypothesis a carcinogen initiates carcinogenesis via a random aneuploidy. Aneuploidy then generates transformation stage-specific aneusomies and further random aneusomies autocatalytically, because it renders chromosome segregation and repair mechanisms error-prone. The hypothesis predicts that several specific aneusomies can cause the same cancers, because several chromosomes also cooperate in normal differentiation. Here we describe experiments on the Chinese hamster (CH) that confirm this hypothesis. (i) Random aneuploidy was detected before transformation in up to 90% of CH embryo cells treated with the carcinogen nitrosomethylurea (NMU). (ii) Several specific aneusomies were found in 70-100% of the aneuploid cells from colonies transformed with NMU in vitro and from tumors generated by NMU-transformed cells in syngeneic animals. Among the aneuploid in vitro transformed cells, 79% were trisomic for chromosome 3, and 59% were monosomic for chromosome 10, compared with 8% expected for random distribution of any aneusomy among the 12 CH chromosomes. Moreover, 52% shared both trisomy 3 and monosomy 10 compared with 0.6% expected for random distribution of any two aneusomies. Among the tumor cells, 65% were trisomic for chromosome 3, 51% were trisomic for chromosome 5, and 30% shared both trisomies. Aneuploid cells without these specific aneusomies may contain minor transformation-specific aneusomies or may be untransformed. (iii) Random aneusomies and structurally altered chromosomes increased with the generations of transformed cells to the point where their origins became unidentifiable in tumors. We conclude that specific aneusomies are necessary for carcinogenesis.

Modelling the molecular circuitry of cancer

Cancer arises from a stepwise accumulation of genetic changes that liberates neoplastic cells from the homeostatic mechanisms that govern normal cell proliferation. In humans, at least four to six mutations are required to reach this state, but fewer seem to be required in mice. By rationalizing the shared and unique elements of human and mouse models of cancer, we should be able to identify the molecular circuits that function differently in humans and mice, and use this knowledge to improve existing models of cancer.

Centrosome replication, genomic instability and cancer

Karyotypic alterations, including whole chromosome loss or gain, ploidy changes, and a variety of chromosome aberrations are common in cancer cells. If proliferating cells fail to coordinate centrosome duplication with DNA replication, this will inevitably lead to a change in ploidy, and the formation of monopolar or multipolar spindles will generally provoke abnormal segregation of chromosomes. Indeed, it has long been recognized that errors in the centrosome duplication cycle may be an important cause of aneuploidy and thus contribute to cancer formation. This view has recently received fresh impetus with the description of supernumerary centrosomes in almost all solid human tumors. As the primary microtubule organizing center of most eukaryotic cells, the centrosome assures symmetry and bipolarity of the cell division process, a function that is essential for accurate chromosome segregation. In addition, a growing body of evidence indicates that centrosomes might be important for initiating S phase and completing cytokinesis. Centrosomes undergo duplication precisely once before cell division. Recent reports have revealed that this process is linked to the cell division cycle via cyclin-dependent kinase (cdk) 2 activity that couples centriole duplication to the onset of DNA replication at the G(1)/S phase transition. Alterations in G(1)/S phase regulating proteins like the retinoblastoma protein, cyclins D and E, cdk4 and 6, cdk inhibitors p16(INK4A) and p15(INK4B), and p53 are among the most frequent aberrations observed in human malignancies. These alterations might not only lead to unrestrained proliferation, but also cause karyotypic instability by uncontrolled centrosome replication. Since several excellent reports on cell cycle regulation and cancer have been published, this review will focus on the role of centrosomes in cell cycle progression, as well as causes and consequences of aberrant centrosome replication in human neoplasias.

Frequent impairment of the spindle assembly checkpoint in hepatocellular carcinoma

BACKGROUND

Chromosomal instability (CI) leading to aneuploidy is one form of genetic instability, a characteristic feature of various types of cancers. Recent work has suggested that CI can be induced by a spindle assembly checkpoint defect. The aim of the current study was to determine the frequency of a defect of the checkpoint in hepatocellular carcinoma (HCC) and to establish whether alterations of genes encoding the checkpoint were associated with CI in HCC.

METHODS

Aneuploidy and the function of the spindle assembly checkpoint were examined using DNA flow cytometry and morphologic analysis with microtubule disrupting drugs. To explore the molecular basis, the authors examined the expression and alterations of the mitotic checkpoint gene, BUB1, using Northern hybridization and direct sequencing in 8 HCC cell lines and 50 HCC specimens. Furthermore, the authors examined the alterations of other mitotic checkpoint genes, BUBR1, BUB3, MAD2B, and CDC20, using direct sequencing in HCC cell lines with aneuploidy.

RESULTS

An impaired spindle assembly checkpoint was found in five (62.5%) of the eight aneuploid cell lines. Transcriptional expressions of the BUB1 gene appeared in all cell lines. While some polymorphic base changes were noted in BUB1, BUBR1, and CDC20, no mutations responsible for impairment of the mitotic checkpoint were found in either the HCC cell lines or HCC specimens, which suggests that these genes did not seem to be involved in tumor development in HCC.

CONCLUSIONS

The loss of spindle assembly checkpoint occurred with a high frequency in HCC with CI. However, other mechanisms might also contribute to CI in HCC.

Comparative cytotoxicity of low-osmolar nonionic and high-osmolar ionic contrast media to dog gallbladder epithelial cells

BACKGROUND

Most studies of the adverse effects of x-ray contrast media used in ERCP have focused on post-ERCP pancreatitis. However, the biliary epithelial cells are also exposed to contrast media during ERCP and acute cholangitis is also a serious complication of ERCP. The present study compared the cytotoxicity with gallbladder epithelial cells of ionic and nonionic contrast agents.

METHODS

A high-osmolar ionic contrast agent (meglumine ioxithalamate) and a low-osmolar nonionic contrast agent (iopromide) were tested. Monolayer cell cultures of dog gallbladder epithelial cells were used. The cells were exposed to the 2 contrast agents with increasing iodine concentration and osmolality for 2 days. Cell number, S-phase fraction, aneuploidy, and supernatant LDH activities were measured each day.

RESULTS

Cell growth was more severely inhibited by ioxithalamate than iopromide (p < 0.05) and strongly dependent on the osmolality of contrast agent. The cytostatic effect estimated by S-phase fraction was more pronounced for ioxithalamate. Chromosomal damage determined by aneuploidy was more frequently detected with ioxithalamate.

CONCLUSIONS

High-osmolar ionic contrast media are more cytotoxic than low-osmolar nonionic contrast media to gallbladder epithelial cells. Animal and clinical studies are needed to estimate the clinical implications of these findings.

The origin of transformed cells. studies of spontaneous and induced cell transformation in cell cultures from marsupials, a snail, and human amniocytes

Transformation of cells in culture is a model system for carcinogenesis, and two major theories (i.e., mutagenesis and aneuploidy) have emerged from in vitro and in vivo studies. A third view is presented here on the initial steps in the change of primary cells to extended life cells, and their change to immortalized cells. Both changes involve identical, microscopically visible cell abnormalities hitherto dismissed as cell degenerative characteristics. The major cell changes (i.e., giant cells, nuclear fragmentation to form multinucleated cells [MNC]) translated into genetic terms begin with the creation of polyploidy by DNA endoreduplication, followed by amitotic division of these giant cells to produce MNC. Individual nuclei, surrounded by a cell membrane, bud from the surface of the MNC, and represent the origin of the transformed cells. Induced budding by a protease treatment of MNC suggests that the extracellular matrix is an inhibitor of the budding process from human MNC. The production of the MNC is a genetic process determined by two abnormal events (i.e., overproduction of DNA and amitotic chromosomal segregation) during which there are possibilities for different genetic mechanisms to produce inherited variability within and between MNC. These concepts are discussed in regard to carcinogenesis, and by extension its possible prevention by use of the special cytopathic cell changes in carcinogen testing and in clinical screening programs.

Merotelic kinetochore orientation versus chromosome mono-orientation in the origin of lagging chromosomes in human primary cells

Defects in chromosome segregation play a critical role in producing genomic instability and aneuploidy, which are associated with congenital diseases and carcinogenesis. We recently provided evidence from immunofluorescence and electron microscopy studies that merotelic kinetochore orientation is a major mechanism for lagging chromosomes during mitosis in PtK1 cells. Here we investigate whether human primary fibroblasts exhibit similar errors in chromosome segregation and if at least part of lagging chromosomes may arise in cells entering anaphase in the presence of mono-oriented chromosomes. By using in situ hybridization with alphoid probes to chromosome 7 and 11 we showed that loss of a single sister is much more frequent than loss of both sisters from the same chromosome in anatelophases from human primary fibroblasts released from a nocodazole-induced mitotic arrest, as predicted from merotelic orientation of single kinetochores. Furthermore, the lagging of pairs of separated sisters was higher than expected from random chance indicating that merotelic orientation of one sister may promote merotelic orientation of the other. Kinetochores of lagging chromosomes in anaphase human cells were found to be devoid of the mitotic checkpoint phosphoepitopes recognized by the 3F3/2 antibody, suggesting that they attached kinetochore microtubules prior to anaphase onset. Live cell imaging of H2B histone-GFP-transfected cells showed that cells with mono-oriented chromosomes never enter anaphase and that lagging chromosomes appear during anaphase after chromosome alignment occurs during metaphase. Thus, our results demonstrate that the mitotic checkpoint efficiently prevents the possible aneuploid burden due to mono-oriented chromosomes and that merotelic kinetochore orientation is a major limitation for accurate chromosome segregation and a potentially important mechanism of aneuploidy in human cells.

Differentiation genes: are they primary targets for human carcinogenesis?

In spite of extensive research in molecular carcinogenesis, genes that can be considered primary targets in human carcinogenesis remain to be identified. Mutated oncogenes or cellular growth regulatory genes, when incorporated into normal human epithelial cells, failed to immortalize or transform these cells. Therefore, they may be secondary events in human carcinogenesis. Based on some experimental studies we have proposed that downregulation of a differentiation gene may be the primary event in human carcinogenesis. Such a gene could be referred to as a tumor-initiating gene. Downregulation of a differentiation gene can be accomplished by a mutation in the differentiation gene, by activation of differentiation suppressor genes, and by inactivation of tumor suppressor genes. Downregulation of a differentiation gene can lead to immortalization of normal cells. Mutations in cellular proto-oncogenes, growth regulatory genes, and tumor suppressor genes in immortalized cells can lead to transformation. Such genes could be called tumor-promoting genes. This hypothesis can be documented by experiments published on differentiation of neuroblastoma (NB) cells in culture. The fact that terminal differentiation can be induced in NB cells by adenosine 3',5'-cyclic monophosphate (cAMP) suggests that the differentiation gene in these cells is not mutated, and thus can be activated by an appropriate agent. The fact that cAMP-resistant cells exist in NB cell populations suggests that a differentiation gene is mutated in these cancer cells, or that differentiation regulatory genes have become unresponsive to cAMP. In addition to cAMP, several other differentiating agents have been identified. Our proposed hypothesis of carcinogenesis can also be applied to other human tumors such as melanoma, pheochromocytoma, medulloblastoma, glioma, sarcoma, and colon cancer.

Origin of multidrug resistance in cells with and without multidrug resistance genes: chromosome reassortments catalyzed by aneuploidy

Cancer cells and aneuploid cell lines can acquire resistance against multiple unrelated chemotherapeutic drugs that are over 3,000-fold those of normal levels and display spontaneous resistances up to 20-fold of normal levels. Two different mechanisms were proposed for this phenotype: (i) classical mutation of drug metabolizing genes or (ii) chromosome reassortments, catalyzed by cancer- and cell line-specific aneuploidy, which generate, via new gene dosage combinations, a plethora of cancer phenotypes, including drug resistance. To distinguish between these mechanisms, we have asked whether three mouse cell lines can become drug resistant, from which two or three genes have been deleted, and on which multidrug resistance is thought to depend: Mdr1a, Mdr1b, and Mrp1. Because all three lines could acquire multidrug resistance and were aneuploid, whereas diploid mouse cells could not, we conclude that aneuploid cells become drug resistant via specific chromosome assortments, independent of putative resistance genes. We have asked further whether aneuploid drug-resistant Chinese hamster cells revert spontaneously to drug sensitivity in the absence of cytotoxic drugs at the high rates that are typical of chromosome reassortments catalyzed by aneuploidy or at the very low or zero rates (i.e., deletion) of gene mutation. We found that four drug-resistant hamster cell lines reverted to drug sensitivity at rates of about 2-3% per generation, whereas two closely related lines remained resistant under our conditions. Thus, the karyotypic instability generated by aneuploidy emerges as the common source of the various levels of drug resistance of cancer cells: minor spontaneous resistances reflect accidental chromosome assortments, the high selected resistances reflect complex specific assortments, and multidrug resistance reflects new combinations of unselected genes located on the same chromosomes as selected genes.

Tetraploid state induces p53-dependent arrest of nontransformed mammalian cells in G1

A "spindle assembly" checkpoint has been described that arrests cells in G1 following inappropriate exit from mitosis in the presence of microtubule inhibitors. We have here addressed the question of whether the resulting tetraploid state itself, rather than failure of spindle function or induction of spindle damage, acts as a checkpoint to arrest cells in G1. Dihydrocytochalasin B induces cleavage failure in cells where spindle function and chromatid segregation are both normal. Notably, we show here that nontransformed REF-52 cells arrest indefinitely in tetraploid G1 following cleavage failure. The spindle assembly checkpoint and the tetraploidization checkpoint that we describe here are likely to be equivalent. Both involve arrest in G1 with inactive cdk2 kinase, hypophosphorylated retinoblastoma protein, and elevated levels of p21(WAF1) and cyclin E. Furthermore, both require p53. We show that failure to arrest in G1 following tetraploidization rapidly results in aneuploidy. Similar tetraploid G1 arrest results have been obtained with mouse NIH3T3 and human IMR-90 cells. Thus, we propose that a general checkpoint control acts in G1 to recognize tetraploid cells and induce their arrest and thereby prevents the propagation of errors of late mitosis and the generation of aneuploidy. As such, the tetraploidy checkpoint may be a critical activity of p53 in its role of ensuring genomic integrity.

Induction of aneuploidy by nickel sulfate in V79 Chinese hamster cells

The ability of nickel sulfate (NiSO(4)) to induce chromosome aneuploidy was investigated in vitro using the V79 Chinese hamster cell line. V79 cells were treated with 100-400 microM NiSO(4) for 24h, and monitored up to 72 h following treatment with a chromosome aberration assay, a micronuclei assay using antikinetochore antibodies (CREST assay) and an anaphase/telophase assay. Aneuploid cells were induced in a significant fraction of the cell population 24-48 h following treatment with nickel sulfate. The majority of these cells were hyperdiploid. In addition, nickel sulfate caused increased frequency of cells with kinetochore-positive micronuclei as well as kinetochore-negative micronuclei. Abnormal chromosome segregation such as lagging chromosomes, chromosome bridges and asymmetric segregation were also observed in more than 50% of anaphase or telophase cells following treatment with NiSO(4). The incidences of these abnormalities were dose-dependent in general, although the effects were prominent in a sublethal dose. These results indicate that NiSO(4) has the ability to induce aneuploidy in V79 cells. In addition, the results in anaphase/telophase assay suggest that the compound may have an effect on spindle apparatus, which could result in aneuploidy following abnormal chromosome segregation.

Merotelic kinetochore orientation is a major mechanism of aneuploidy in mitotic mammalian tissue cells

In mitotic cells, an error in chromosome segregation occurs when a chromosome is left near the spindle equator after anaphase onset (lagging chromosome). In PtK1 cells, we found 1.16% of untreated anaphase cells exhibiting lagging chromosomes at the spindle equator, and this percentage was enhanced to 17.55% after a mitotic block with 2 microM nocodazole. A lagging chromosome seen during anaphase in control or nocodazole-treated cells was found by confocal immunofluorescence microscopy to be a single chromatid with its kinetochore attached to kinetochore microtubule bundles extending toward opposite poles. This merotelic orientation was verified by electron microscopy. The single kinetochores of lagging chromosomes in anaphase were stretched laterally (1.2--5.6-fold) in the directions of their kinetochore microtubules, indicating that they were not able to achieve anaphase poleward movement because of pulling forces toward opposite poles. They also had inactivated mitotic spindle checkpoint activities since they did not label with either Mad2 or 3F3/2 antibodies. Thus, for mammalian cultured cells, kinetochore merotelic orientation is a major mechanism of aneuploidy not detected by the mitotic spindle checkpoint. The expanded and curved crescent morphology exhibited by kinetochores during nocodazole treatment may promote the high incidence of kinetochore merotelic orientation that occurs after nocodazole washout.

Dermal benzene and trichloroethylene induce aneuploidy in immature hematopoietic subpopulations in vivo

Accumulation of genetic damage in long-lived cell populations with proliferative capacity is implicated in tumorigenesis. Hematopoietic stem cells (hsc) maintain lifetime hematopoiesis, and recent studies demonstrate that hsc in leukemic patients are cytogenetically aberrant. We postulated that exposure to agents associated with increased leukemia risk would induce genomic changes in cells in the hsc compartment. Aneusomy involving chromosomes 2 and 11 in sorted hsc (Lin(-)c-kit(+)Sca-1(+)) and maturing lymphoid and myeloid cells from mice that received topical doses of benzene (bz) or trichloroethylene (TCE) was quantified using fluorescence in situ hybridization. Six days after bz or TCE exposure, aneuploid cells in the hsc compartment increase four- to eightfold in a dose- and schedule-independent manner. Aneuploid lymphoid and myeloid cells from bz- and TCE-treated mice approximate controls, except after repeated benzene exposures. Aneuploid cells are more frequent in the hsc compartment than in mature hematopoietic subpopulations. Hematotoxicity was also quantified in bz- and TCE-exposed hematopoietic subpopulations using two colony-forming assays: CFU-GM (colony-forming units/granulocyte-macrophage progenitors) and CAFC (cobblestone area-forming cells). Data indicate that bz is transiently cytotoxic (< or =1 week) to hsc subpopulations, and induces more persistent toxicity (>2 weeks) in maturing, committed progenitor subpopulations. TCE is not hematotoxic at the doses applied. In conclusion, we provide direct evidence for induction of aneuploidy in cells in the hsc compartment by topical exposure to bz and TCE. Disruption of genomic integrity and/or toxicity in hsc subpopulations may be one step in leukemic progression.

Explaining the high mutation rates of cancer cells to drug and multidrug resistance by chromosome reassortments that are catalyzed by aneuploidy

The mutation rates of cancer cells to drug and multidrug resistance are paradoxically high, i.e., 10(-3) to 10(-6), compared with those altering phenotypes of recessive genes in normal diploid cells of about 10(-12). Here the hypothesis was investigated that these mutations are due to chromosome reassortments that are catalyzed by aneuploidy. Aneuploidy, an abnormal number of chromosomes, is the most common genetic abnormality of cancer cells and is known to change phenotypes (e.g., Down's syndrome). Moreover, we have shown recently that aneuploidy autocatalyzes reassortments of up to 2% per chromosome per mitosis because it unbalances spindle proteins, even centrosome numbers, via gene dosage. The hypothesis predicts that a selected phenotype is associated with multiple unselected ones, because chromosome reassortments unbalance simultaneously thousands of regulatory and structural genes. It also predicts variants of a selected phenotype based on variant reassortments. To test our hypothesis we have investigated in parallel the mutation rates of highly aneuploid and of normal diploid Chinese hamster cells to resistance against puromycin, cytosine arabinoside, colcemid, and methotrexate. The mutation rates of aneuploid cells ranged from 10(-4) to 10(-6), but no drug-resistant mutants were obtained from diploid cells in our conditions. Further selection increased drug resistance at similar mutation rates. Mutants selected from cloned cells for resistance against one drug displayed different unselected phenotypes, e.g., polygonal or fusiform cellular morphology, flat or three-dimensional colonies, and resistances against other unrelated drugs. Thus our hypothesis offers a unifying explanation for the high mutation rates of aneuploid cancer cells and for the association of selected with unselected phenotypes, e.g., multidrug resistance. It also predicts drug-specific chromosome combinations that could become a basis for selecting alternative chemotherapy against drug-resistant cancer.

The TACC domain identifies a family of centrosomal proteins that can interact with microtubules

We recently showed that the Drosophila transforming acidic coiled-coil (D-TACC) protein is located in the centrosome, interacts with microtubules, and is required for mitosis in the Drosophila embryo. There are three known human TACC proteins that share a conserved, C-terminal, coiled-coil region with D-TACC. These proteins have all been implicated in cancer, but their normal functions are unknown. We show that all three human TACC proteins are concentrated at centrosomes, but with very different characteristics: TACC1 is weakly concentrated at centrosomes during mitosis; TACC2 is strongly concentrated at centrosomes throughout the cell cycle; and TACC3 is strongly concentrated in a more diffuse region around centrosomes during mitosis. When the C-terminal TACC domain is overexpressed in HeLa cells, it forms large polymers in the cytoplasm that can interact with both microtubules and tubulin. The full-length TACC proteins form similar polymers when overexpressed, but their interaction with microtubules and tubulin is regulated during the cell cycle. At least one of the human TACC proteins appears to increase the number and/or stability of centrosomal microtubules when overexpressed during mitosis. Thus, the TACC domain identifies a family of centrosomal proteins that can interact with microtubules. This may explain the link between the TACC genes and cancer.

Yeast Eap1p, an eIF4E-associated protein, has a separate function involving genetic stability

A rate-limiting step during translation initiation in eukaryotic cells involves binding of the initiation factor eIF4E to the 7-methylguanosine-containing cap of mRNAs. Overexpression of eIF4E leads to malignant transformation [1-3], and eIF4E is elevated in many human cancers [4-7]. In mammalian cells, three eIF4E-binding proteins each interact with eIF4E and inhibit its function [8-10]. In yeast, EAP1 encodes a protein that binds eIF4E and inhibits cap-dependent translation in vitro [11]. A point mutation in the canonical eIF4E-binding motif of Eap1p blocks its interaction with eIF4E [11]. Here, we characterized the genetic interactions between EAP1 and NDC1, a gene whose function is required for duplication of the spindle pole body (SPB) [12], the centrosome-equivalent organelle in yeast that functions as the centrosome. We found that the deletion of EAP1 is lethal when combined with the ndc1-1 mutation. Mutations in NDC1 or altered NDC1 gene dosage lead to genetic instability [13,14]. Yeast strains lacking EAP1 also exhibit genetic instability. We tested whether these phenotypes are due to loss of EAP1 function in regulating translation. We found that both the synthetic lethal phenotype and the genetic instability phenotypes are rescued by a mutant allele of EAP1 that is unable to bind eIF4E. Our findings suggest that Eap1p carries out an eIF4E-independent function to maintain genetic stability, most likely involving SPBs.

Enhancement of chemical hepatocarcinogenesis by the HIV-1 tat gene

The human immunodeficiency virus-1 Tat protein is suspected to be involved in the neoplastic pathology arising in AIDS patients. tat-transgenic (TT) mice, which constitutively express Tat in the liver, develop liver cell dysplasia (LCD) that may represent a preneoplastic lesion. To test if TT mice are predisposed to liver carcinogenesis, we treated them with diethylnitrosamine, a hepatotropic carcinogen. Diethylnitrosamine-treated TT mice developed both preneoplastic and neoplastic lesions in the liver. They showed an enhancement of LCD and developed basophilic liver cell nodules (BLCN), hepatocellular adenomas (HA), and hepatocellular carcinomas (HC). Both preneoplastic (LCD and BLCN) and neoplastic (HA and HC) lesions were significantly more frequent in TT than in control mice: 29.7% versus 12.7% for LCD, 57.9% versus 23.3% for BLCN, 40.6% versus 10.0% for HA, and 50.0% versus 12.7% for HC. These results indicate that Tat expression in the liver predisposes to both initiation of hepatocarcinogenesis and to malignant progression of liver tumors. This study supports a role for Tat in enhancing the effect of endogenous and exogenous carcinogens in human immunodeficiency virus-1-infected patients, thereby contributing to tumorigenesis in the course of AIDS.

Auto-catalysed progression of aneuploidy explains the Hayflick limit of cultured cells, carcinogen-induced tumours in mice, and the age distribution of human cancer

Evidence continues to accumulate that aneuploidy, an imbalance in the number of chromosomes, is responsible for the characteristic phenotypes of cancer, including the abnormal cellular size and morphology of cancer cells, the appearance of tumour-associated antigens, as well as the high levels of membrane-bound and secreted proteins responsible for invasiveness and loss of contact inhibition. Aneuploidy has also been demonstrated to be the self-perpetuating source of the karyotypic instability of cancer cells. Here it is shown that the auto-catalysed progression of aneuploidy explains the kinetics of the finite lifetime of diploid cells in culture, the time course of the appearance of papillomas and carcinomas in benzo[a]pyrene-treated mice, and the age-dependence of human cancers. Modelling studies indicate that the ease of spontaneous transformation of mouse cells in culture may be due to a chaotic progression of aneuploidy. Conversely, the strong preference towards senescence and resistance to transformation of human cells in culture may be the result of a non-chaotic progression of aneuploidy. Finally, a method is proposed for quantifying the aneuploidogenic potencies of carcinogens.

Aneuploidy precedes and segregates with chemical carcinogenesis

A century ago, Boveri proposed that cancer is caused by aneuploidy, an abnormal balance of chromosomes, because aneuploidy correlates with cancer and because experimental aneuploidy generates "pathological" phenotypes. Half a century later, when cancers were found to be nonclonal for aneuploidy, but clonal for somatic gene mutations, this hypothesis was abandoned. As a result, aneuploidy is now generally viewed as a consequence, and mutated genes as a cause of cancer. However, we have recently proposed a two-stage mechanism of carcinogenesis that resolves the discrepancy between clonal mutation and nonclonal karyotypes. The proposal is as follows: in stage 1, a carcinogen "initiates" carcinogenesis by generating a preneoplastic aneuploidy; in stage 2, aneuploidy causes asymmetric mitosis because it biases balance-sensitive spindle and chromosomal proteins and alters centrosomes both numerically and structurally (in proportion to the degree of aneuploidy). Therefore, the karyotype of an initiated cell evolves autocatalytically, generating ever-new chromosome combinations, including neoplastic ones. Accordingly, the heterogeneous karyotypes of "clonal" cancers are an inevitable consequence of the karyotypic instability of aneuploid cells. The notorious long latent periods, of months to decades, from carcinogen to carcinogenesis, would reflect the low probability of evolving by chance karyotypes that compete favorably with normal cells, in principle analagous to natural evolution. Here, we have confirmed experimentally five predictions of the aneuploidy hypothesis: (1) the carcinogens dimethylbenzanthracene and cytosine arabinoside induced aneuploidy in a fraction of treated Chinese hamster embryo cells; (2) aneuploidy preceded malignant transformation; (3) transformation of carcinogen-treated cells occurred only months after carcinogen treatment, i.e., autocatalytically; (4) preneoplastic aneuploidy segregated with malignant transformation in vitro and with 14 of 14 tumors in animals; and (5) karyotypes of tumors were heterogeneous. We conclude that, with the carcinogens studied, aneuploidy precedes cancer and is necessary for carcinogenesis.

Sensitivity of cytokinesis to hydrophobic interactions. Chemical induction of bi-and multinucleated cells

We have tested whether cytokinesis is as sensitive to hydrophobic interactions as karyokinesis, and evaluated the usefulness of the frequency of binucleated cells as end-point. Treating cultured cells for 2 or 24 h, with different lipophilic alcohols and chlorinated hydrocarbons made this possible. Colcemid and cytochalasin B were applied as positive controls for inhibition of karyokinesis and cytokinesis, respectively. Several-fold increases of binucleated cells could be seen with cytochalasin B after 2 h of treatment, while there was no increase with colcemid, which instead blocked cells in prometaphase/metaphase. The solvent acted primarily through hydrophobic interactions. For each solvent, the blocking of cells in prometaphase/metaphase and a minor increase in binucleated cells, were seen at approximately the same concentration; the binucleated cells probably emanated from cells in anaphase/telophase at the start of treatment. We conclude that the spindle function and cleavage show similar sensitivity to hydrophobic interactions. After prolonged treatment, allowing escape from the metaphase block, the solvents induced binucleated and multinucleated cells. By forming the quotient between multinucleated (MULTI) and binucleated (BIN) cells one could distinguish between effects primarily on the spindle or cytokinesis, respectively. All solvents, and a combination of colcemid and cytochalasin B, showed quotients intermediate between those observed with colcemid (high MULTI/BIN) and cytochalasin B (low MULTI/BIN), respectively. Both protocols revealed the same relationship between lowest active concentration and lipophilicity for the solvents, implying that concentration, not dose were of prime importance. The specific inhibitors acted at low concentrations in relation to lipophilicity, clearly demonstrating their chemical mechanisms. This approach can be used for rapid screening of potential aneugens, distinguishing between routes, and when lipophilicity is known, also reveal the principal mechanism of action, i.e. physico-chemical or chemical.

Mammalian cell transformation and aneuploidy induced by five bisphenols

Bisphenol-A (BP-A), a monomer of plastics used in numerous consumer products and a xenoestrogen, induces cellular transformation and aneuploidy in Syrian hamster embryo (SHE) cells. In this study, the abilities of 4 other bisphenols to induce cellular transformation and genetic effects in SHE cells were examined and compared to BP-A. Cellular growth was inhibited by all bisphenols in a concentration-related manner. The growth inhibitory effect of the bisphenols ranked: BP-5 > BP-4 > BP-3 > BP-2 or BP-A. Morphological transformation of SHE cells was induced by BP-A, BP-3, BP-4 and BP-5, and the induced-transformation frequencies were highest with BP-4. None of the bisphenols induced gene mutations at the Na(+)/K(+) ATPase locus or the hprt locus, or chromosomal aberrations in SHE cells. By contrast, aneuploidy induction in the near-diploid range was exhibited by BP-A, BP-3, BP-4 or BP-5, corresponding to the transforming activity of each compound. The results indicate that BP-A, BP-3, BP-4 and BP-5 exhibit transforming activity in SHE cells, while BP-2 does not, and that aneuploidy induction may be a causal mechanism of the transforming activity.

Induction of mammalian cell transformation and genotoxicity by 2-methoxyestradiol, an endogenous metabolite of estrogen

2-methoxyestradiol (2-MeOE(2)) is an endogenous metabolite of 17beta-estradiol and a proposed inhibitor of tumor growth and angiogenesis. However, 2-MeOE(2) is also an inhibitor of microtubule assembly and other microtubule inhibitors, e.g. colcemid and diethylstilbestrol, induce aneuploidy and cell transformation in cultured mammalian cells. To assess the in vitro carcinogenicity and related activity of 2-MeOE(2), the abilities of this metabolite to induce cell transformation and genetic effects were studied simultaneously using Syrian hamster embryo (SHE) fibroblasts. Growth of these cells was reduced by treatment with 2-MeOE(2) at 0.1-1.0 microg/ml in a concentration-dependent manner. Treatment of SHE cells with 2-MeOE(2) at 0.3 or 1.0 microg/ml for 2-48 h also resulted in a concentration- and treatment time-related increase in the mitotic index and the percentage of multinucleated cells. Treatment with 2-MeOE(2) at 0.1-1.0 microg/ml for 48 h induced a statistically significant increase in the frequencies of morphological transformation of SHE cells in a concentration-dependent manner. A statistically significant increase in the frequencies of somatic mutations at the Na(+)/K(+) ATPase or hprt locus was also observed in cells treated with 2-MeOE(2) for 48 h at 0.1 or 0.3 microg/ml, respectively. Treatment of SHE cells with 2-MeOE(2) at 0.3 or 1.0 microg/ml for 24 h induced chromosome aberrations, mainly breaks, exchanges and chromosome pulverization. The incidence of chromosome aberrations was not affected by co-treatment with alpha-naphthoflavone, an inhibitor of 2-hydroxylase that inhibits oxidative conversion of 2-MeOE(2) to 2-hydroxyestradiol, but the incidence was slightly increased by co-treatment with L-ascorbic acid. Numerical chromosomal changes in the near diploid range and in the tetraploid and near tetraploid ranges were also detected in 2-MeOE(2)-treated cells. These findings indicate that 2-MeOE(2) has cell transforming and genotoxic activities in cultured mammalian cells and potential carcinogenic activity.

Aneuploidy vs. gene mutation hypothesis of cancer: recent study claims mutation but is found to support aneuploidy

For nearly a century, cancer has been blamed on somatic mutation. But it is still unclear whether this mutation is aneuploidy, an abnormal balance of chromosomes, or gene mutation. Despite enormous efforts, the currently popular gene mutation hypothesis has failed to identify cancer-specific mutations with transforming function and cannot explain why cancer occurs only many months to decades after mutation by carcinogens and why solid cancers are aneuploid, although conventional mutation does not depend on karyotype alteration. A recent high-profile publication now claims to have solved these discrepancies with a set of three synthetic mutant genes that "suffices to convert normal human cells into tumorigenic cells." However, we show here that even this study failed to explain why it took more than "60 population doublings" from the introduction of the first of these genes, a derivative of the tumor antigen of simian virus 40 tumor virus, to generate tumor cells, why the tumor cells were clonal although gene transfer was polyclonal, and above all, why the tumor cells were aneuploid. If aneuploidy is assumed to be the somatic mutation that causes cancer, all these results can be explained. The aneuploidy hypothesis predicts the long latent periods and the clonality on the basis of the following two-stage mechanism: stage one, a carcinogen (or mutant gene) generates aneuploidy; stage two, aneuploidy destabilizes the karyotype and thus initiates an autocatalytic karyotype evolution generating preneoplastic and eventually neoplastic karyotypes. Because the odds are very low that an abnormal karyotype will surpass the viability of a normal diploid cell, the evolution of a neoplastic cell species is slow and thus clonal, which is comparable to conventional evolution of new species.

Aneuploidy vs. gene mutation hypothesis of cancer: Recent study claims mutation but is found to support aneuploidy

For nearly a century, cancer has been blamed on somatic mutation. But it is still unclear whether this mutation is aneuploidy, an abnormal balance of chromosomes, or gene mutation. Despite enormous efforts, the currently popular gene mutation hypothesis has failed to identify cancer-specific mutations with transforming function and cannot explain why cancer occurs only many months to decades after mutation by carcinogens and why solid cancers are aneuploid, although conventional mutation does not depend on karyotype alteration. A recent high-profile publication now claims to have solved these discrepancies with a set of three synthetic mutant genes that "suffices to convert normal human cells into tumorigenic cells." However, we show here that even this study failed to explain why it took more than "60 population doublings" from the introduction of the first of these genes, a derivative of the tumor antigen of simian virus 40 tumor virus, to generate tumor cells, why the tumor cells were clonal although gene transfer was polyclonal, and above all, why the tumor cells were aneuploid. If aneuploidy is assumed to be the somatic mutation that causes cancer, all these results can be explained. The aneuploidy hypothesis predicts the long latent periods and the clonality on the basis of the following two-stage mechanism: stage one, a carcinogen (or mutant gene) generates aneuploidy; stage two, aneuploidy destabilizes the karyotype and thus initiates an autocatalytic karyotype evolution generating preneoplastic and eventually neoplastic karyotypes. Because the odds are very low that an abnormal karyotype will surpass the viability of a normal diploid cell, the evolution of a neoplastic cell species is slow and thus clonal, which is comparable to conventional evolution of new species.

D-TACC: a novel centrosomal protein required for normal spindle function in the early Drosophila embryo

We identify Drosophila TACC (D-TACC) as a novel protein that is concentrated at centrosomes and interacts with microtubules. We show that D-TACC is essential for normal spindle function in the early embryo; if D-TACC function is perturbed by mutation or antibody injection, the microtubules emanating from centrosomes in embryos are short and chromosomes often fail to segregate properly. The C-terminal region of D-TACC interacts, possibly indirectly, with microtubules, and can target a heterologous fusion protein to centrosomes and microtubules in embryos. This C-terminal region is related to the mammalian transforming, acidic, coiled-coil-containing (TACC) family of proteins. The function of the TACC proteins is unknown, but the genes encoding the known TACC proteins are all associated with genomic regions that are rearranged in certain cancers. We show that at least one of the mammalian TACC proteins appears to be associated with centrosomes and microtubules in human cells. We propose that this conserved C-terminal 'TACC domain' defines a new family of microtubule-interacting proteins.