A cellular machine generating apoptosis-prone aneuploid cells

Telomere Shortening in Hematological Malignancies with Tetraploidization-A Mechanism for Chromosomal Instability?

Aneuploidy, the presence of an abnormal number of chromosomes in a cell, is one of the most obvious differences between normal and cancer cells. There is, however, debate on how aneuploid cells arise and whether or not they are a cause or a consequence of tumorigenesis. Further, it is important to distinguish aneuploidy (the “state” of the karyotype) from chromosomal instability (CIN; the “rate” of karyotypic change). Although CIN leads to aneuploidy, not all aneuploid cells exhibit CIN. One proposed route to aneuploid cells is through an unstable tetraploid intermediate because tetraploidy promotes chromosomal aberrations and tumorigenesis. Tetraploidy or near-tetraploidy (T/NT) (81–103 chromosomes) karyotypes with or without additional structural abnormalities have been reported in acute leukemia, T-cell and B-cell lymphomas, and solid tumors. In solid tumors it has been shown that tetraploidization can occur in response to loss of telomere protection in the early stages of tumorigenesis in colon cancer, Barrett’s esophagus, and breast and cervical cancers. In hematological malignancies T/NT karyotypes are rare and the role of telomere dysfunction for the induction of tetraploidization is less well characterized. To further our understanding of possible telomere dysfunction as a mechanism for tetrapolydization in hematological cancers we here characterized the chromosomal complement and measured the telomere content by interphase nuclei quantitative fluorescence in situ hybridization (iQFISH) in seven hematological cancer patients with T/NT karyotypes, and after cytogenetic remission. The patients were identified after a search in our local cytogenetic registry in the 5-year period between June 2012 and May 2017 among more than 12,000 analyzed adult patients in this period. One advantage of measuring telomere content by iQFISH is that it is a single-cell analysis so that the telomere content can be distinguished between normal karyotype cells and cells with T/NT karyotypes. We find that the telomeres are particularly short in cells with T/NT karyotypes as compared with normal cells, and in T/NT karyotypes harboring additional chromosomal aberrations as well. These findings suggest that telomere dysfunction in hematological malignancies may be a mechanism for tetraploidization and CIN.

Aglycone rich extracts of phytoestrogens cause ROS-mediated DNA damage in breast carcinoma cells

Phytoestrogens are known for their physiological role in lowering risk of osteoporosis, heart disease, breast cancer and menopausal symptoms. They are plant derived potent anti-oxidants, but tend to show pro-oxidant effect at higher concentrations. This study has been undertaken to exploit their pro-oxidant effect in the management of cancer. Cancer cells inherently possess high intracellular ROS levels, however, these levels do not cause harm to the cancer cells because of the anti-oxidant enzyme system. So, there is a need for a treatment strategy which could modulate the ROS levels. Breast cancer cell lines MCF-7 and MDA-MB-231 are treated with various concentrations of soyabean aglycone rich extracts (SARE) and flaxseed aglycone rich extracts (FSARE). The treatment brings about a significant decrease in super oxide dismutase (SOD) and glutathione peroxidase (GPx) activity, thereby leading to accumulation of superoxide ion and peroxide in the cells. The catalase (CAT) activity however, did not show a dose dependent change. The intra-cellular reactive oxygen species (ROS) levels increased and a marked change in mitochondrial membrane potential was detected. Cell cycle arrest was seen at S and G2/M phase in MCF-7 cells and high accumulation of cells in Sub G1 phase was seen in MDA-MB-231 cells. Microscopic evaluation indicated apoptotic morphology and DNA damage. This study suggests an important role of soyabean and flaxseed aglycones in modulating intracellular ROS in breast carcinoma.

A novel source of tetraploid cancer cell precursors: telomere insufficiency links aging to oncogenesis

Epithelial cancers of the elderly are caused by a combination of telomere dysfunction and the mutational invalidation of major tumor suppressors including p53. A recent article published in Cell by Davoli et al. shows that the simultaneous elimination of p53 and telomerase causes a state of chronic DNA damage that results in tetraploidization through endoreplication, that is, two consecutive S phases that are not separated by mitosis. As tetraploid cells represent a metastable intermediate between normal diploidy and cancer-associated aneuploidy, this novel route to tetraploidization may constitute (one of) the functional link(s) between aging and carcinogenesis.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

Susceptibility of rheumatoid arthritis synovial fibroblasts to FasL- and TRAIL-induced apoptosis is cell cycle-dependent

Introduction

The rheumatoid arthritis (RA) synovium is characterised by the presence of an aggressive population of activated synovial fibroblasts (RASFs) that are prominently involved in the destruction of articular cartilage and bone. Accumulating evidence suggests that RASFs are relatively resistant to Fas-ligand (FasL)-induced apoptosis, but the data concerning tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) have been conflicting. Here, we hypothesise that the susceptibility of RASFs to receptor-mediated apoptosis depends on the proliferation status of these cells and therefore analysed the cell cycle dependency of FasL- and TRAIL-induced programmed cell death of RASFs in vitro.

Methods

Synovial fibroblasts were isolated from patients with RA by enzymatic digestion and cultured under standard conditions. Cell cycle analysis was performed using flow cytometry and staining with propidium iodide. RASFs were synchronised or arrested in various phases of the cell cycle with 0.5 mM hydroxyurea or 2.5 μg/ml nocodazol and with foetal calf serum-free insulin-transferrin-sodium selenite supplemented medium. Apoptosis was induced by stimulation with 100 ng/ml FasL or 100 ng/ml TRAIL over 18 hours. The apoptotic response was measured using the Apo-ONE^® Homogenous Caspase-3/7 Assay (Promega GmbH, Mannheim, Germany) and the Cell Death Detection (ELISA^Plus) (enzyme-linked immunosorbent assay) (Roche Diagnostics GmbH, Mannheim, Germany). Staurosporin-treated cells (1 μg/ml) served as a positive control. Expression of Fas and TRAIL receptors (TRAILR1-4) was determined by fluorescence-activated cell sorting analysis.

Results

Freshly isolated RASFs showed only low proliferation in vitro, and the rate decreased further over time, particularly when RASFs became confluent. RASFs expressed Fas, TRAIL receptor-1, and TRAIL receptor-2, and the expression levels were independent of the cell cycle. However, the proliferation rate significantly influenced the susceptibility to FasL- and TRAIL-induced apoptosis. Specifically, proliferating RASFs were less sensitive to FasL- and TRAIL-induced apoptosis than RASFs with a decreased proliferation rate. Furthermore, RASFs that were synchronised in S phase or G₂/M phase were less sensitive to TRAIL-induced apoptosis than synchronised RASFs in G₀/G₁ phase.

Conclusions

Our data indicate that the susceptibility of RASFs to FasL- and TRAIL-induced apoptosis depends on the cell cycle. These results may explain some conflicting data on the ability of RASFs to undergo FasL- and TRAIL-mediated cell death and suggest that strategies to sensitise RASFs to apoptosis may include the targeting of cell cycle-regulating genes.

Association of stem cells and cancer stem cells with tumorigenesis

The research on cancer stem cells is a new hot spot in at present. The hypothesis indicates cancer stem cells, which were possibly the origin of the cancer, come from normal stem cells. For their special characters, normal stem cells can differentiate into tumor cells more easily than adult cells. Stem cells transform into malignant cancer stem cells possibly because of gene mutation, abnormal asymmetry and cell fusion. It is a main method to obtain cancer stem cells by flow cytometer using different protein markers and fluorescent probes. It is demonstrated that cancer stem cells are very powerful in self-renewal, proliferation, and differentiation. Targeting on cancer stem cells, early diagnosis for cancers might be achieved.

Selective Resistance of Tetraploid Cancer Cells against DNA Damage-Induced Apoptosis

Aneuploidy and chromosomal instability, which are frequent in cancer, can result from the asymmetric division of tetraploid precursors. Genomic instability may favor the generation of more aggressive tumor cells with a reduced propensity for undergoing apoptosis. To assess the impact of tetraploidization on apoptosis regulation, we generated a series of stable tetraploid HCT116 and RKO colon carcinoma cell lines. When comparing diploid parental cells with tetraploid clones, we found that such cells were equally sensitive to a series of cytotoxic agents (staurosporine [STS], hydroxyurea, etoposide), as well as to the lysis by natural killer cells. In strict contrast, tetraploid cells were found to be relatively resistant against a series of DNA-damaging agents, namely cisplatin, oxaliplatin, camptothecin, and gamma- and UVC-irradiation. This increased resistance correlated with a reduced manifestation of apoptotic parameters (such as the dissipation of the mitochondrial transmembrane potential and the degradation of nuclear DNA) in tetraploid as compared to diploid cells subjected to DNA damage. Moreover, tetraploid cells manifested an enhanced baseline level of p53 activation. Inhibition of p53 abolished the difference in the susceptibility of diploid and tetraploid cancer cells to DNA damage-induced apoptosis. These data point to an intrinsic resistance of tetraploid cells against radiotherapy and DNA-targeted chemotherapy that may be linked to the status of the p53 system.

Cytopathic effects of the cytomegalovirus-encoded apoptosis inhibitory protein vMIA

Replication of human cytomegalovirus (CMV) requires the expression of the viral mitochondria–localized inhibitor of apoptosis (vMIA). vMIA inhibits apoptosis by recruiting Bax to mitochondria, resulting in its neutralization. We show that vMIA decreases cell size, reduces actin polymerization, and induces cell rounding. As compared with vMIA-expressing CMV, vMIA-deficient CMV, which replicates in fibroblasts expressing the adenoviral apoptosis suppressor E1B19K, induces less cytopathic effects. These vMIA effects can be separated from its cell death–inhibitory function because vMIA modulates cellular morphology in Bax-deficient cells. Expression of vMIA coincided with a reduction in the cellular adenosine triphosphate (ATP) level. vMIA selectively inhibited one component of the ATP synthasome, namely, the mitochondrial phosphate carrier. Exposure of cells to inhibitors of oxidative phosphorylation produced similar effects, such as an ATP level reduced by 30%, smaller cell size, and deficient actin polymerization. Similarly, knockdown of the phosphate carrier reduced cell size. Our data suggest that the cytopathic effect of CMV can be explained by vMIA effects on mitochondrial bioenergetics.