The Price of Human Evolution: Cancer-Testis Antigens, the Decline in Male Fertility and the Increase in Cancer

The increasing frequency of general and particularly male cancer coupled with the reduction in male fertility seen worldwide motivated us to seek a potential evolutionary link between these two phenomena, concerning the reproductive transcriptional modules observed in cancer and the expression of cancer-testis antigens (CTA). The phylostratigraphy analysis of the human genome allowed us to link the early evolutionary origin of cancer via the reproductive life cycles of the unicellulars and early multicellulars, potentially driving soma-germ transition, female meiosis, and the parthenogenesis of polyploid giant cancer cells (PGCCs), with the expansion of the CTA multi-families, very late during their evolution. CTA adaptation was aided by retrovirus domestication in the unstable genomes of mammals, for protecting male fertility in stress conditions, particularly that of humans, as compensation for the energy consumption of a large complex brain which also exploited retrotransposition. We found that the early and late evolutionary branches of human cancer are united by the immunity-proto-placental network, which evolved in the Cambrian and shares stress regulators with the finely-tuned sex determination system. We further propose that social stress and endocrine disruption caused by environmental pollution with organic materials, which alter sex determination in male foetuses and further spermatogenesis in adults, bias the development of PGCC-parthenogenetic cancer by default.

The Role of Mitotic Slippage in Creating a "Female Pregnancy-like System" in a Single Polyploid Giant Cancer Cell

In our recent work, we observed that triple-negative breast cancer MDA-MB-231 cells respond to doxorubicin (DOX) via "mitotic slippage" (MS), discarding cytosolic damaged DNA during the process that provides their resistance to this genotoxic treatment. We also noted two populations of polyploid giant cells: those budding surviving offspring, versus those reaching huge ploidy by repeated MS and persisting for several weeks. Their separate roles in the recovery from treatment remained unclear. The current study was devoted to characterising the origin and relationship of these two sub-populations in the context of MS. MS was hallmarked by the emergence of nuclear YAP1/OCT4A/MOS/EMI2-positivity featuring a soma-germ transition to the meiotic-metaphase-arrested "maternal germ cell". In silico, the link between modules identified in the inflammatory innate immune response to cytosolic DNA and the reproductive module of female pregnancy (upregulating placenta developmental genes) was observed in polyploid giant cells. Asymmetry of the two subnuclei types, one repairing DNA and releasing buds enriched by CDC42/ACTIN/TUBULIN and the other persisting and degrading DNA in a polyploid giant cell, was revealed. We propose that when arrested in MS, a "maternal cancer germ cell" may be parthenogenetically stimulated by the placental proto-oncogene parathyroid-hormone-like-hormone, increasing calcium, thus creating a "female pregnancy-like" system within a single polyploid giant cancer cell.

Spatial-Temporal Genome Regulation in Stress-Response and Cell-Fate Change

Complex functioning of the genome in the cell nucleus is controlled at different levels: (a) the DNA base sequence containing all relevant inherited information; (b) epigenetic pathways consisting of protein interactions and feedback loops; (c) the genome architecture and organization activating or suppressing genetic interactions between different parts of the genome. Most research so far has shed light on the puzzle pieces at these levels. This article, however, attempts an integrative approach to genome expression regulation incorporating these different layers. Under environmental stress or during cell development, differentiation towards specialized cell types, or to dysfunctional tumor, the cell nucleus seems to react as a whole through coordinated changes at all levels of control. This implies the need for a framework in which biological, chemical, and physical manifestations can serve as a basis for a coherent theory of gene self-organization. An international symposium held at the Biomedical Research and Study Center in Riga, Latvia, on 25 July 2022 addressed novel aspects of the abovementioned topic. The present article reviews the most recent results and conclusions of the state-of-the-art research in this multidisciplinary field of science, which were delivered and discussed by scholars at the Riga symposium.

The Transcriptome and Proteome Networks of Malignant Tumours Reveal Atavistic Attractors of Polyploidy-Related Asexual Reproduction

The expression of gametogenesis-related (GG) genes and proteins, as well as whole genome duplications (WGD), are the hallmarks of cancer related to poor prognosis. Currently, it is not clear if these hallmarks are random processes associated only with genome instability or are programmatically linked. Our goal was to elucidate this via a thorough bioinformatics analysis of 1474 GG genes in the context of WGD. We examined their association in protein-protein interaction and coexpression networks, and their phylostratigraphic profiles from publicly available patient tumour data. The results show that GG genes are upregulated in most WGD-enriched somatic cancers at the transcriptome level and reveal robust GG gene expression at the protein level, as well as the ability to associate into correlation networks and enrich the reproductive modules. GG gene phylostratigraphy displayed in WGD+ cancers an attractor of early eukaryotic origin for DNA recombination and meiosis, and one relative to oocyte maturation and embryogenesis from early multicellular organisms. The upregulation of cancer-testis genes emerging with mammalian placentation was also associated with WGD. In general, the results suggest the role of polyploidy for soma-germ transition accessing latent cancer attractors in the human genome network, which appear as pre-formed along the whole Evolution of Life.

Bacteriophage-Derived Double-Stranded RNA Exerts Anti-SARS-CoV-2 Activity In Vitro and in Golden Syrian Hamsters In Vivo

Bacteriophage-derived dsRNA, known as Larifan, is a nationally well-known broad-spectrum antiviral medication. This study aimed to ascertain the antiviral activity of Larifan against the novel SARS-CoV-2 virus. Larifan’s effect against SARS-CoV-2 in vitro was measured in human lung adenocarcinoma (Calu3) and primary human small airway epithelial cells (HSAEC), and in vivo in the SARS-CoV-2 infection model in golden Syrian hamsters. Larifan inhibited SARS-CoV-2 replication both in vitro and in vivo. Viral RNA copy numbers and titer of infectious virus in the supernatant of Calu3 cells dropped significantly: p = 0.0296 and p = 0.0286, respectively. A reduction in viral RNA copy number was also observed in HSAEC, especially when Larifan was added before infection (p = 0.0218). Larifan markedly reduced virus numbers in infected hamsters’ lungs post-infection, with a more pronounced effect after intranasal administration (p = 0.0032). The administration of Larifan also reduced the amount of infections virus titer in the lungs (p = 0.0039). Improvements in the infection-induced pathological lesion severity in the lungs of animals treated with Larifan were also demonstrated. The inhibition of SARS-CoV-2 replication in vitro and the reduction in the viral load in the lungs of infected hamsters treated with Larifan alongside the improved lung histopathology suggests a potential use of Larifan in also controlling the COVID-19 disease in humans.

Heterochromatin Networks: Topology, Dynamics, and Function (a Working Hypothesis)

Open systems can only exist by self-organization as pulsing structures exchanging matter and energy with the outer world. This review is an attempt to reveal the organizational principles of the heterochromatin supra-intra-chromosomal network in terms of nonlinear thermodynamics. The accessibility of the linear information of the genetic code is regulated by constitutive heterochromatin (CHR) creating the positional information in a system of coordinates. These features include scale-free splitting-fusing of CHR with the boundary constraints of the nucleolus and nuclear envelope. The analysis of both the literature and our own data suggests a radial-concentric network as the main structural organization principle of CHR regulating transcriptional pulsing. The dynamic CHR network is likely created together with nucleolus-associated chromatin domains, while the alveoli of this network, including springy splicing speckles, are the pulsing transcription hubs. CHR contributes to this regulation due to the silencing position variegation effect, stickiness, and flexible rigidity determined by the positioning of nucleosomes. The whole system acts in concert with the elastic nuclear actomyosin network which also emerges by self-organization during the transcriptional pulsing process. We hypothesize that the the transcriptional pulsing, in turn, adjusts its frequency/amplitudes specified by topologically associating domains to the replication timing code that determines epigenetic differentiation memory.

Differentiating cancer cells reveal early large-scale genome regulation by pericentric domains

Finding out how cells prepare for fate change during differentiation commitment was our task. To address whether the constitutive pericentromere-associated domains (PADs) may be involved, we used a model system with known transcriptome data, MCF-7 breast cancer cells treated with the ErbB3 ligand heregulin (HRG), which induces differentiation and is used in the therapy of cancer. PAD-repressive heterochromatin (H3K9me3), centromere-associated-protein-specific, and active euchromatin (H3K4me3) antibodies, real-time PCR, acridine orange DNA structural test (AOT), and microscopic image analysis were applied. We found a two-step DNA unfolding after 15–20 and 60 min of HRG treatment, respectively. This behavior was consistent with biphasic activation of the early response genes (c-fos - fosL1/myc) and the timing of two transcriptome avalanches reported in the literature. In control, the average number of PADs negatively correlated with their size by scale-free distribution, and centromere clustering in turn correlated with PAD size, both indicating that PADs may create and modulate a suprachromosomal network by fusing and splitting a constant proportion of the constitutive heterochromatin. By 15 min of HRG treatment, the bursting unraveling of PADs from the nucleolus boundary occurred, coinciding with the first step of H3K4me3 chromatin unfolding, confirmed by AOT. The second step after 60 min of HRG treatment was associated with transcription of long noncoding RNA from PADs and peaking of fosL1/c-myc response. We hypothesize that the bursting of PAD clusters under a critical silencing threshold pushes the first transcription avalanche, whereas the destruction of the PAD network enables genome rewiring needed for differentiation repatterning, mediated by early response bivalent genes.

Paradoxes of cancer: Survival at the brink

The fundamental understanding of how Cancer initiates, persists and then progresses is evolving. High-resolution technologies, including single-cell mutation and gene expression measurements, are now attainable, providing an ever-increasing insight into the molecular details. However, this higher resolution has shown that somatic mutation theory itself cannot explain the extraordinary resistance of cancer to extinction. There is a need for a more Systems-based framework of understanding cancer complexity, which in particular explains the regulation of gene expression during cell-fate decisions. Cancer displays a series of paradoxes. Here we attempt to approach them from the view-point of adaptive exploration of gene regulatory networks at the edge of order and chaos, where cell-fate is changed by oscillations between alternative regulators of cellular senescence and reprogramming operating through self-organisation. On this background, the role of polyploidy in accessing the phylogenetically pre-programmed "oncofetal attractor" state, related to unicellularity, and the de-selection of unsuitable variants at the brink of cell survival is highlighted. The concepts of the embryological and atavistic theory of cancer, cancer cell "life-cycle", and cancer aneuploidy paradox are dissected under this lense. Finally, we challenge researchers to consider that cancer "defects" are mostly the adaptation tools of survival programs that have arisen during evolution and are intrinsic of cancer. Recognition of these features should help in the development of more successful anti-cancer treatments.

INDUCED POLYPLOIDY AND SORTING OF DAMAGED DNA BY MICRONUCLEATION IN RADIORESISTANT RAT LIVER EPITHELIAL STEM-LIKE CELLS EXPOSED TO X-RAYS

OBJECTIVE

Rat liver stem-like epithelial cells (WB-F344) that under certain conditions may differentiate into hepa- tocyte and biliary lineages were subjected to acute X-irradiation with the aim to examine cell cycle peculiarities dur- ing the course of survival.

MATERIALS AND METHODS

Suspensions of WB-F344 cells that grew as a monolayer and reached sub-confluence were irradiated with 1, 5, and 10 Gy of X-rays (2 Gy/min). As an intact control, sham-irradiated cells were used. After irra- diation, cells were plated into 25-cm2 tissue culture flasks to culture them for over several days without reaching contact inhibition. On days 1, 2, 3, and 5 post-irradiation, cells were harvested and examined for nuclear morpholo- gy and DNA ploidy by stoichiometric toluidine blue reaction and image cytometry. On days 7 and 9 post-irradiation, only heavily irradiated (10 Gy) cells were examined. Also, 10 Gy-irradiated cells were chosen for immunofluorescence staining to monitor persistence of DNA lesions (γ-H2AX), cell proliferation (Ki-67), and self-renewal factors charac- teristic for stem cells (OCT4 and NANOG).

RESULTS

Radioresistance of WB-F344 cells was evidenced by the findings that they do not undergo rapid and mas- sive cell death that in fact was weakly manifested as apoptotic even in heavily irradiated cells. Instead, there was cell cycle progression delay accompanied by polyploidization (via Ki-67-positive mitotic slippage or via impaired cytokinesis) and micronucleation in a dose-dependent manner, although micronucleation to some extent went ahead of polyploidization. Polyploid cells amenable for recovering from DNA damage can mitotically depolyploidize. Many micronuclei contained γ-H2AX clusters, suggesting isolation of severely damaged DNA fragments. Both factors, OCT4 and NANOG, were expressed in the intact control, but became enhanced after irradiation.

CONCLUSIONS

Although the fact of micronucleation is indicative of genotoxic effect, WB-F344 cells can probably escape cell death via sorting of damaged DNA by micronuclei. Induction of polyploidy in these cells can be adaptive to promote cell survival and tissue regeneration with possible involvement of self-renewal mechanism.

Differential staining of peripheral nuclear chromatin with Acridine orange implies an A-form epichromatin conformation of the DNA

The chromatin observed by conventional electron microscopy under the nuclear envelope constitutes a single layer of dense 30–35 nm granules, while ∼30 nm fibrils laterally attached to them, form large patches of lamin-associated domains (LADs). This particular surface “epichromatin” can be discerned by specific (H2A+H2B+DNA) conformational antibody at the inner nuclear envelope and around mitotic chromosomes. In order to differentiate the DNA conformation of the peripheral chromatin we applied an Acridine orange (AO) DNA structural test involving RNAse treatment and the addition of AO after acid pre-treatment. MCF-7 cells treated in this way revealed yellow/red patches of LADs attached to a thin green nuclear rim and with mitotic chromosomes outlined in green, topologically corresponding to epichromatin epitope staining by immunofluorescence. Differentially from LADs, the epichromatin was unable to provide metachromatic staining by AO, unless thermally denatured at 94^oC. DNA enrichment in GC stretches has been recently reported for immunoprecipitated ∼ 1Kb epichromatin domains. Together these data suggest that certain epichromatin segments assume the relatively hydrophobic DNA A-conformation at the nuclear envelope and surface of mitotic chromosomes, preventing AO side dimerisation.  We hypothesize that epichromatin domains form nucleosome superbeads. Hydrophobic interactions stack these superbeads and align them at the nuclear envelope, while repulsing the hydrophilic LADs. The hydrophobicity of epichromatin explains its location at the surface of mitotic chromosomes and its function in mediating chromosome attachment to the restituting nuclear envelope during telophase.

When Three Isn't a Crowd: A Digyny Concept for Treatment-Resistant, Near-Triploid Human Cancers

Near-triploid human tumors are frequently resistant to radio/chemotherapy through mechanisms that are unclear. We recently reported a tight association of male tumor triploidy with XXY karyotypes based on a meta-analysis of 15 tumor cohorts extracted from the Mitelman database. Here we provide a conceptual framework of the digyny-like origin of this karyotype based on the germline features of malignant tumors and adaptive capacity of digyny, which supports survival in adverse conditions. Studying how the recombinatorial reproduction via diploidy can be executed in primary cancer samples and HeLa cells after DNA damage, we report the first evidence that diploid and triploid cell sub-populations constitutively coexist and inter-change genomes via endoreduplicated polyploid cells generated through genotoxic challenge. We show that irradiated triploid HeLa cells can enter tripolar mitosis producing three diploid sub-subnuclei by segregation and pairwise fusions of whole genomes. Considering the upregulation of meiotic genes in tumors, we propose that the reconstructed diploid sub-cells can initiate pseudo-meiosis producing two "gametes" (diploid "maternal" and haploid "paternal") followed by digynic-like reconstitution of a triploid stemline that returns to mitotic cycling. This process ensures tumor survival and growth by (1) DNA repair and genetic variation, (2) protection against recessive lethal mutations using the third genome.

PROBING BREAST CANCER THERAPEUTIC RESPONSES BY DNA CONTENT PROFILING

Background. Discrepancies in the interpretation of breast cancer therapeutic responses still exist mainly because of lack of standardized assessment criteria and methods. Objective. DNA content profiling of cells in the affected (cancerous) tissue before and after neoadjuvant chemotherapy (NAC) was applied to facilitate interpretation of therapeutic responses. Methods. Both diagnostic biopsy and operation materials representing the tissue of primary tumors surgically removed after NAC were subjected to DNA image cytometry. Polyploidy and aneuploidy in DNA histograms were evaluated with a prognostic Auer typing. Stemline DNA index (DI) values and percentages of cells that polyploidize (>4.5C) were also determined. Immunofluorescence staining was applied to evaluate proliferation (Ki-67), invasiveness (CD44), and self-renewal factors characteristic for stem cells (SOX2 and NANOG). Results. DNA content profiles of 12 breast cancer cases, of which 7 were triple-negative, revealed the features of tumor non-responsiveness to NAC in 7 cases, of which 5 were triple-negative. Among non-responsive cases there were 3 cases that showed enhanced polyploidization, suggesting the negative NAC effect. Near-triploid (DI=1.26-1.74) triple-negative cases were determined as most resistant to NAC. Cycling near-triploid cells may contribute to the excessive numbers of >4.5C cells. Polyploid cells were positive for Ki-67, CD44, SOX2, and NANOG. Conclusions. DNA content profiling data provide additional helpful information for interpreting therapeutic responses in NAC-treated breast cancers. Polyploid tumor cells possessing stem cell features can be induced by NAC. Because NAC effects in some cases may be unfavorable, the use of the further treatment strategy should be carefully considered.

The Cancer Aneuploidy Paradox: In the Light of Evolution

Aneuploidy should compromise cellular proliferation but paradoxically favours tumour progression and poor prognosis. Here, we consider this paradox in terms of our most recent observations of chemo/radio-resistant cells undergoing reversible polyploidy. The latter perform the segregation of two parental groups of end-to-end linked dyads by pseudo-mitosis creating tetraploid cells through a dysfunctional spindle. This is followed by autokaryogamy and a homologous pairing preceding a bi-looped endo-prophase. The associated RAD51 and DMC1/γ-H2AX double-strand break repair foci are tandemly situated on the AURKB/REC8/kinetochore doublets along replicated chromosome loops, indicative of recombination events. MOS-associated REC8-positive peri-nucleolar centromere cluster organises a monopolar spindle. The process is completed by reduction divisions (bi-polar or by radial cytotomy including pedogamic exchanges) and by the release of secondary cells and/or the formation of an embryoid. Together this process preserves genomic integrity and chromosome pairing, while tolerating aneuploidy by by-passing the mitotic spindle checkpoint. Concurrently, it reduces the chromosome number and facilitates recombination that decreases the mutation load of aneuploidy and lethality in the chemo-resistant tumour cells. This cancer life-cycle has parallels both within the cycling polyploidy of the asexual life cycles of ancient unicellular protists and cleavage embryos of early multicellulars, supporting the atavistic theory of cancer.

DNA methylation of the Oct4A enhancers in embryonal carcinoma cells after etoposide treatment is associated with alternative splicing and altered pluripotency in reversibly senescent cells

The epigenetic mechanisms underlying chemoresistance in cancer cells resulting from drug-induced reversible senescence are poorly understood. Chemoresistant ESC-like embryonal carcinoma PA1 cells treated with etoposide (ETO) were previously found to undergo prolonged G2 arrest with transient p53-dependent upregulation of opposing fate regulators, p21CIP1 (senescence) and OCT4A (self-renewal). Here we report on the analysis of the DNA methylation state of the distal enhancer (DE) and proximal enhancer (PE) of the Oct4A gene during this dual response. When compared to non-treated controls the methylation level increased from 1.3% to 12.5% and from 3% to 19.4%, in the DE and PE respectively. It included CpG and non-CpG methylation, which was not chaotic but presented two patterns in each enhancer. Discorrelating with methylation of enhancers, the transcription of Oct4A increased, however, a strong expression of the splicing form Oct4B was also induced, along with down-regulation of the Oct4A partners of in the pluripotency/self-renewal network Sox2 and Lin28. WB demonstrated disjoining of the OCT4A protein from the chromatin-bound fraction. In survival clones, methylation of the DE was considerably erased, while some remnant of methylation of the PE was still observed. The alternative splicing for Oct4B was reduced, Oct4A level insignificantly decreased, while the expression of Sox2 and Lin28 recovered, all three became proportionally above the control. These findings indicate the involvement of the transient patterned methylation of the Oct4A enhancers and alternative splicing in the adaptive regulation of cell fate choice during the p53-dependant dual state of reversible senescence in ESC-like cancer stem cells.

Somatic polyploidy is associated with the upregulation of c-MYC interacting genes and EMT-like signature

The dependence of cancer on overexpressed c-MYC and its predisposition for polyploidy represents a double puzzle. We address this conundrum by cross-species transcription analysis of c-MYC interacting genes in polyploid vs. diploid tissues and cells, including human vs. mouse heart, mouse vs. human liver and purified 4n vs. 2n mouse decidua cells. Gene-by-gene transcriptome comparison and principal component analysis indicated that c-MYC interactants are significantly overrepresented among ploidy-associated genes. Protein interaction networks and gene module analysis revealed that the most upregulated genes relate to growth, stress response, proliferation, stemness and unicellularity, as well as to the pathways of cancer supported by MAPK and RAS coordinated pathways. A surprising feature was the up-regulation of epithelial-mesenchymal transition (EMT) modules embodied by the N-cadherin pathway and EMT regulators from SNAIL and TWIST families. Metabolic pathway analysis also revealed the EMT-linked features, such as global proteome remodeling, oxidative stress, DNA repair and Warburg-like energy metabolism. Genes associated with apoptosis, immunity, energy demand and tumour suppression were mostly down-regulated. Noteworthy, despite the association between polyploidy and ample features of cancer, polyploidy does not trigger it. Possibly it occurs because normal polyploidy does not go that far in embryonalisation and linked genome destabilisation. In general, the analysis of polyploid transcriptome explained the evolutionary relation of c-MYC and polyploidy to cancer.

Abstract P3-03-17: Can polyploid tumor cells possessing stem cell features be induced in resistant breast carcinomas?

Cancer stem cells are believed to be responsible for radio- and chemoresistance of malignant tumors. In vitro studies demonstrate that ionizing radiation is capable of reprogramming cancer cells from non-stem state into stem state [1, 2]. Moreover, the embryonic stemness cassette was found to be expressed in tumor cells (including breast cancer cells) after they were polyploidized as a result of genotoxic stress [2, 3], thus prompting us to suppose that the polyploid cells and their descendants released by depolyploidization can possess stem cell characteristics. The aim of the current work is to test whether polyploid cells having stem cell features can be also induced in vivo, namely in locally advanced breast carcinomas as a result of neoadjuvant chemotherapy (NAC), assuming that this process is not autonomous, but rather stipulated by the tumor microenvironment.

The study population consisted of 30 breast cancer patients of age ranged from 31 to 75 y. o. diagnosed in the Latvian Oncology Center of the Riga East University Hospital between 2013 and 2015. The tissue specimens were collected after the patients' informed consent was obtained in accordance with the Ethics regulations. The clinico-pathologic information about these patients, including Ki-67 index and the status of ER, PR and HER2 receptors, was obtained from the aforementioned clinics. The majority of patients (n = 28) had locally advanced breast cancer, predominantly Stage III disease. Both diagnostic biopsy and operation material, such as primary tumors surgically removed after NAC using standard doses of paclitaxel and doxorubicin, were subjected to DNA content analysis with image cytometry. Ploidy-related parameters, such as DNA index and the percentage of cells exceeding 4.5c (presumably proliferating and polyploid cells), were determined. Immunofluorescence staining was applied to evaluate expression of such markers/factors as proliferation (Ki-67), stemness (SOX2 and NANOG) and invasiveness (CD44).

At the time of diagnosis, 14 patients had primary tumors possessing near-triploid clones, and these cases in comparison with 16 other cases comprised of near-euploid clones had 4.5-fold increase of percentages of cells exceeding the ploidy of 4.5c (p < 0.05) and 1.3-fold increase of percentages of cells positive for Ki-67 (p > 0.05). Of 10 cases diagnosed as “triple-negative”, 6 were near-triploid. Among those cases that showed the resistance to NAC (grades 1 and 2 by Miller-Payne histopathologic scoring), 67% were near-triploid. Polyploidization, which in some resistant cases is gained by NAC, was likely to be attributed to near-triploid clones. Notably, polyploid cells were positive for Ki-67, SOX2, NANOG, and CD44. Thus, these non-quiescent polyploid cells can possess the invasiveness and self-renewal features that were also seen in descendants after depolyploidization. Perhaps, reversible polyploidy plays a definite role in gaining the resistance of tumor cells to chemo- and radiotherapy in vivo.

1. Ghisolfi L. et al. PLoS ONE 2012; 7: e43628.

2. Lagadec C. et al. Stem Cells 2012; 30: 833-44.

3. Salmina K. et al. Exp Cell Res 2010; 316: 2099-112.

Citation Format: Gerashchenko BI, Salmina K, Eglitis J, Erenpreisa J. Can polyploid tumor cells possessing stem cell features be induced in resistant breast carcinomas? [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-17.

Nucleolar aggresomes mediate release of pericentric heterochromatin and nuclear destruction of genotoxically treated cancer cells

The role of the nucleolus and autophagy in maintenance of nuclear integrity is poorly understood. In addition, the mechanisms of nuclear destruction in cancer cells senesced after conventional chemotherapy are unclear. In an attempt to elucidate these issues, we studied teratocarcinoma PA1 cells treated with Etoposide (ETO), focusing on the nucleolus. Following treatment, most cells enter G2 arrest, display persistent DNA damage and activate p53, senescence, and macroautophagy markers. 2-5 µm sized nucleolar aggresomes (NoA) containing fibrillarin (FIB) and damaged rDNA, colocalized with ubiquitin, pAMPK, and LC3-II emerge, accompanied by heterochromatin fragments, when translocated perinuclearly. Microscopic counts following application of specific inhibitors revealed that formation of FIB-NoA is dependent on deficiency of the ubiquitin proteasome system coupled to functional autophagy. In contrast, the accompanying NoAs release of pericentric heterochromatin, which exceeds their frequency, is favored by debilitation of autophagic flux. Potential survivors release NoA in the cytoplasm during rare mitoses, while exit of pericentric fragments often depleted of H3K9Me3, with or without encompassing by NoA, occurs through the nucleolar protrusions and defects of the nuclear envelope. Foci of LC3-II are accumulated in the nucleoli undergoing cessation of rDNA transcription. As an origin of heterochromatin fragmentation, the unscheduled DNA synthesis and circular DNAs were found in the perinucleolar heterochromatin shell, along with activation and retrotransposition of ALU elements, colocalized with 45S rDNA in NoAs. The data indicate coordination of the basic nucleolar function with autophagy regulation in maintenance of the integrity of the nucleolus associated domains secured by inactivity of retrotransposons.

Disentangling the aneuploidy and senescence paradoxes: a study of triploid breast cancers non-responsive to neoadjuvant therapy

Aneuploid cells should have a reduced proliferation rate due to difficulty in proceeding through mitosis. However, contrary to this, high aneuploidy is associated with aggressive tumour growth and poor survival prognosis, in particular in triploid breast cancer. A further paradox revolves around the observation that, while cell senescence should inhibit proliferation, the senescence marker p16INK4a correlates with poor treatment outcome in patients with a very aggressive triple-negative breast carcinoma (TNBC). In this study, we aim to pour light on the possible relationship of these conundrums with polyploidy of tumour cells. We performed detailed analysis of DNA histogram profiles in diagnostic core biopsies of 30 cases of operable breast cancer and found that near triploidy in TNBC and other forms correlated with weak or no response to neoadjuvant chemotherapy (NAC) as scored by Miller-Payne index. Polyploid cells in operation samples from tumours that were non-responsive to NAC treatment were Ki67 and CD44 positive. In addition, polyploid cells were positive for markers of embryonic stemness (OCT4, SOX2, NANOG) and senescence (p16INK4a). The relationship patterns between p16INK4a and NANOG were heterogeneous, with predominantly mutually exclusive expression but also synergistic and intermediate variants in the same samples. We conclude that the aneuploidy and senescence paradoxes can be explained by the mutual platform of polyploidy, conferring genomic and epigenetic instability as a survival advantage. Such cells are able to bypass aneuploidy restrictions of conventional mitosis and overcome the barrier of senescence by a shift to self-renewal, resulting in progression of cancer.

Role of stress-activated OCT4A in the cell fate decisions of embryonal carcinoma cells treated with etoposide

Tumor cellular senescence induced by genotoxic treatments has recently been found to be paradoxically linked to the induction of “stemness.” This observation is critical as it directly impinges upon the response of tumors to current chemo-radio-therapy treatment regimens. Previously, we showed that following etoposide (ETO) treatment embryonal carcinoma PA-1 cells undergo a p53-dependent upregulation of OCT4A and p21Cip1 (governing self-renewal and regulating cell cycle inhibition and senescence, respectively). Here we report further detail on the relationship between these and other critical cell-fate regulators. PA-1 cells treated with ETO display highly heterogeneous increases in OCT4A and p21Cip1 indicative of dis-adaptation catastrophe. Silencing OCT4A suppresses p21Cip1, changes cell cycle regulation and subsequently suppresses terminal senescence; p21Cip1-silencing did not affect OCT4A expression or cellular phenotype. SOX2 and NANOG expression did not change following ETO treatment suggesting a dissociation of OCT4A from its pluripotency function. Instead, ETO-induced OCT4A was concomitant with activation of AMPK, a key component of metabolic stress and autophagy regulation. p16ink4a, the inducer of terminal senescence, underwent autophagic sequestration in the cytoplasm of ETO-treated cells, allowing alternative cell fates. Accordingly, failure of autophagy was accompanied by an accumulation of p16ink4a, nuclear disintegration, and loss of cell recovery. Together, these findings imply that OCT4A induction following DNA damage in PA-1 cells, performs a cell stress, rather than self-renewal, function by moderating the expression of p21Cip1, which alongside AMPK helps to then regulate autophagy. Moreover, this data indicates that exhaustion of autophagy, through persistent DNA damage, is the cause of terminal cellular senescence.

The "virgin birth", polyploidy, and the origin of cancer

Recently, it has become clear that the complexity of cancer biology cannot fully be explained by somatic mutation and clonal selection. Meanwhile, data have accumulated on how cancer stem cells or stemloids bestow immortality on tumour cells and how reversible polyploidy is involved. Most recently, single polyploid tumour cells were shown capable of forming spheroids, releasing EMT-like descendents and inducing tumours in vivo. These data refocus attention on the centuries-old embryological theory of cancer. This review attempts to reconcile seemingly conflicting data by viewing cancer as a pre-programmed phylogenetic life-cycle-like process. This cycle is apparently initiated by a meiosis-like process and driven as an alternative to accelerated senescence at the DNA damage checkpoint, followed by an asexual syngamy event and endopolyploid-type embryonal cleavage to provide germ-cell-like (EMT) cells. This cycle is augmented by genotoxic treatments, explaining why chemotherapy is rarely curative and drives resistance. The logical outcome of this viewpoint is that alternative treatments may be more efficacious - either those that suppress the endopolyploidy-associated ‘life cycle’ or, those that cause reversion of embryonal malignant cells into benign counterparts. Targets for these opposing strategies are components of the same molecular pathways and interact with regulators of accelerated senescence.

Macroautophagy-aided elimination of chromatin: sorting of waste, sorting of fate?

How tumor cells process damaged or unwanted DNA is a matter of much interest. Recently, Rello-Varona et al. (Cell Cycle 2012; 11:170–76) reported the involvement of macroautophagy (hereon autophagy) in the elimination of micronuclei (MN) from osteosarcoma cells. Prior to that, diminution of whole nuclei from multinucleated TP53-mutant tumor cells was described. Here, we discuss these two kinds of chromatin autophagy evoked after genotoxic stress in the context of the various biological processes involved: (1) endopolyploidy and the ploidy cycle; (2) the timing of DNA synthesis; (3) DNA repair; (4) chromatin:nuclear envelope interactions; and (5) cytoplasmic autophagy. We suggest that whereas some MN can be reunited with the main nucleus (through interactions with envelope-limited chromatin sheets) and participate in DNA repair, failure of repair serves as a signal for the chromatin autophagy of MN. In turn, autophagy of whole sub-nuclei in multi-nucleated cells appears to favor de-polyploidization, mitigation of aneuploidy with its adverse effects, thereby promoting the survival fitness of descendents and treatment resistance. Thus, both kinds of chromatin autophagy provide tumor cells with the opportunity to repair DNA, sort and resort chromatin, reduce DNA content, and enhance survival.

DNA damage causes TP53-dependent coupling of self-renewal and senescence pathways in embryonal carcinoma cells

Recent studies have highlighted an apparently paradoxical link between self-renewal and senescence triggered by DNA damage in certain cell types. In addition, the finding that TP53 can suppress senescence has caused a re-evaluation of its functional role in regulating these outcomes. To investigate these phenomena and their relationship to pluripotency and senescence, we examined the response of the TP53-competent embryonal carcinoma (EC) cell line PA-1 to etoposide-induced DNA damage. Nuclear POU5F1/OCT4A and P21CIP1 were upregulated in the same cells following etoposide-induced G 2M arrest. However, while accumulating in the karyosol, the amount of OCT4A was reduced in the chromatin fraction. Phosphorylated CHK2 and RAD51/γH2AX-positive nuclear foci, overexpression of AURORA B kinase and moderate macroautophagy were evident. Upon release from G 2M arrest, cells with repaired DNA entered mitoses, while the cells with persisting DNA damage remained at this checkpoint or underwent mitotic slippage and gradually senesced. Reduction of TP53 using sh- or si-RNA prevented the upregulation of OCT4A and P21CIP1 and increased DNA damage. Subsequently, mitoses, micronucleation and senescence were all enhanced after TP53 reduction with senescence confirmed by upregulation of CDKN2A/P16INK4A and increased sa-β-galactosidase positivity. Those mitoses enhanced by TP53 silencing were shown to be multicentrosomal and multi-polar, containing fragmented and highly deranged chromosomes, indicating a loss of genome integrity. Together, these data suggest that TP53-dependent coupling of self-renewal and senescence pathways through the DNA damage checkpoint provides a mechanism for how embryonal stem cell-like EC cells safeguard DNA integrity, genome stability and ultimately the fidelity of self-renewal.

Self-Renewal Signalling in Presenescent Tetraploid IMR90 Cells

Endopolyploidy and genomic instability are shared features of both stress-induced cellular senescence and malignant growth. Here, we examined these facets in the widely used normal human fibroblast model of senescence, IMR90. At the presenescence stage, a small (2–7%) proportion of cells overcome the 4n-G1 checkpoint, simultaneously inducing self-renewal (NANOG-positivity), the DNA damage response (DDR; γ-H2AX-positive foci), and senescence (p16inka4a- and p21CIP1-positivity) signalling, some cells reach octoploid DNA content and divide. All of these markers initially appear and partially colocalise in the perinucleolar compartment. Further, with development of senescence and accumulation of p16inka4a and p21CIP1, NANOG is downregulated in most cells. The cells increasingly arrest in the 4n-G1 fraction, completely halt divisions and ultimately degenerate. A positive link between DDR, self-renewal, and senescence signalling is initiated in the cells overcoming the tetraploidy barrier, indicating that cellular and molecular context of induced tetraploidy during this period of presenescence is favourable for carcinogenesis.

Up-regulation of the embryonic self-renewal network through reversible polyploidy in irradiated p53-mutant tumour cells

We have previously documented that transient polyploidy is a potential cell survival strategy underlying the clonogenic re-growth of tumour cells after genotoxic treatment. In an attempt to better define this mechanism, we recently documented the key role of meiotic genes in regulating the DNA repair and return of the endopolyploid tumour cells (ETC) to diploidy through reduction divisions after irradiation. Here, we studied the role of the pluripotency and self-renewal stem cell genes NANOG, OCT4 and SOX2 in this polyploidy-dependent survival mechanism. In irradiation-resistant p53-mutated lymphoma cell-lines (Namalwa and WI-L2-NS) but not sensitive p53 wild-type counterparts (TK6), low background expression of OCT4 and NANOG was up-regulated by ionising radiation with protein accumulation evident in ETC as detected by OCT4/DNA flow cytometry and immunofluorescence (IF). IF analysis also showed that the ETC generate PML bodies that appear to concentrate OCT4, NANOG and SOX2 proteins, which extend into complex nuclear networks. These polyploid tumour cells resist apoptosis, overcome cellular senescence and undergo bi- and multi-polar divisions transmitting the up-regulated OCT4, NANOG and SOX2 self-renewal cassette to their descendents. Altogether, our observations indicate that irradiation-induced ETC up-regulate key components of germ-line cells, which potentially facilitate survival and propagation of the tumour cell population.

The role of meiotic cohesin REC8 in chromosome segregation in gamma irradiation-induced endopolyploid tumour cells

Escape from mitotic catastrophe and generation of endopolyploid tumour cells (ETCs) represents a potential survival strategy of tumour cells in response to genotoxic treatments. ETCs that resume the mitotic cell cycle have reduced ploidy and are often resistant to these treatments. In search for a mechanism for genome reduction, we previously observed that ETCs express meiotic proteins among which REC8 (a meiotic cohesin component) is of particular interest, since it favours reductional cell division in meiosis. In the present investigation, we induced endopolyploidy in p53-dysfunctional human tumour cell lines (Namalwa, WI-L2-NS, HeLa) by gamma irradiation, and analysed the sub-cellular localisation of REC8 in the resulting ETCs. We observed by RT-PCR and Western blot that REC8 is constitutively expressed in these tumour cells, along with SGOL1 and SGOL2, and that REC8 becomes modified after irradiation. REC8 localised to paired sister centromeres in ETCs, the former co-segregating to opposite poles. Furthermore, REC8 localised to the centrosome of interphase ETCs and to the astral poles in anaphase cells where it colocalised with the microtubule-associated protein NuMA. Altogether, our observations indicate that radiation-induced ETCs express features of meiotic cell divisions and that these may facilitate chromosome segregation and genome reduction.

Vectors of tick-borne diseases and epidemiological situation in Latvia in 1993-2002

During the period of 1993-2002 an increase and the remarkable changes in the incidence of tick-borne encephalitis (TBE) and Lyme borreliosis (LB) as well as annual activities of vector species were noticed. The highest increase of TBE morbidity in Latvia has been observed in 1994 and 1995, and less expressed also in 1998 which was followed by a significant decrease during subsequent years. Whereas the highest peak of LB morbidity has been noticed in 1998 with only a minor decrease during subsequent years. Two epidemiologically significant Ixodes tick species are common in Latvia. Ixodes ricinus L. spread in the western and central part of Latvia; but rarely and in small numbers also in the eastern part. Ixodes persulcatus P. Sch. seems to dominate only in the eastern part of the country. The changes of seasonal and annual activities of I. ricinus were observed in two types of monitoring sites--sylvatic and peridomestic, located in the central part of Latvia. Observations of I. persulcatus were made in the eastern districts. Comparing geographically the Tick-borne diseases (TBD) incidence data for three tick distribution regions (I. ricinus dominated, I. persulcatus dominated and mixed regions), it was observed that the trend of annual changes in LB incidence during the last decade is almost of the same kind for all regions. Whereas TBE incidence extremes in 1994 and 1995 were observed almost only in I. ricinus dominated region. The annual field-collected adult tick infection rate with TBE virus (TBEV) from 1993 to 2002 for I. ricinus adults varied between 1.7% and 26.6% and for I. persulcatus--between 0% and 37.3%. The infection level in ticks removed from humans was much higher and from 1998 to 2002 surpassed 30%. TBEV investigations of removed adults and nymphs in 2002 discovered a high TBEV prevalence also in I. ricinus nymphs (43%). Typing of TBE virus isolated from ticks and patient serum samples in collaboration with German and Swedish virologists revealed that all three TBEV subtypes were co-circulating in Latvia. The mean annual tick infection rate with Borrelia burgdorferi s.l. analysed by means of a nested polymerase chain reaction of OspA gene fragment during the period of 1999-2001 was 18%-38% for I. ricinus adults and 25%-51% for I. persulcatus adults. Typing of Borrelia-positive DNA samples indicated that B. afzelii was dominant in Borrelia-positive I. ricinus (64.9%) and I. persulcatus (81.2%) followed by B. garinii (I. ricinus: 24.3%; in I. persulcatus: 14.5%). Investigations of Ehrlichia phagocytophila genogroup (by nested PCR targeted the 16S rRNA gene) revealed the presence of Ehrlichia sp. in I. ricinus from the central part of Latvia. Obtained data on TBD vectors and the epidemiological situation during the last decade indicates the complex impact of different factors influencing TBE and LB morbidity in Latvia.

Identification of three clinically relevant Borrelia burgdorferi sensu lato genospecies by PCR-restriction fragment length polymorphism analysis of 16S-23S ribosomal DNA spacer amplicons

We report the results of a study of the prevalences of three clinically relevant Borrelia burgdorferi sensu lato genospecies (Borrelia burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii) in 1,040 questing Ixodes ticks from all regions of Latvia, where Lyme borreliosis is endemic. The prevalences of Borrelia in Ixodes ricinus and Ixodes persulcatus were 22.6 and 27.9%, respectively. Molecular typing of B. burgdorferi from infected ticks was performed by restriction fragment length polymorphism (RFLP) analysis of PCR-amplified fragments of the 16S-23S (rrs-rrlA) rRNA intergenic spacer by using species-specific primers and subsequent sequencing. The dominant Borrelia species in both Ixodes species was B. afzelii. In addition, different restriction patterns of B. garinii and B. afzelii were also identified. This study demonstrates that the 16S-23S rRNA PCR-RFLP typing method is simple, sensitive, and fast and that it allows one to differentiate among B. burgdorferi species and subspecies with various degrees of pathogenic potential directly in ticks. These features are important in monitoring Lyme disease.