Dcaf11 facilitates telomere elongation in early embryos and embryonic stem cells (ESCs) through activating the Zscan4-mediated alternative lengthening telomere (ALT) mechanism
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ABSTRACT:
ORGANISM(S): Mus musculus
PROVIDER: GSE132746 | GEO | 2021/01/01
REPOSITORIES: GEO
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Project description:Dcaf11 facilitates telomere elongation in early embryos and embryonic stem cells (ESCs) through activating the Zscan4-mediated alternative lengthening telomere (ALT) mechanism
| PRJNA548906 | ENA
Project description:Proper telomere length is essential for indefinite self-renewal of embryonic stem (ES) cells and cancer cells. Telomerase-deficient late generation mouse ES cells and human ALT cancer cells are able to propagate for numerous passages, suggesting telomerase-independent mechanisms responding for telomere maintenance. However, the underlying mechanisms ensuring the telomere length maintenance are unclear. Here, using late generation telomerase KO (G4 Terc-/-) ESCs as a model, we show that Zscan4, highly upregulated in G4 Terc-/- ESCs, is responsible for the prolonged culture of these cells with stably short telomeres. Mechanistically, G4 Terc-/- ESCs showed reduced levels of DNA methylation and H3K9me3 at Zscan4 promoter and subtelomeres, which relieved the expression of Zscan4. Similarly, human ZSCAN4 was also derepressed by reduced H3K9me3 at its promoter in ALT U2 OS cells, and depletion of ZSCAN4 significantly shortened telomeres. Our results define a similar conserved pathway contributing to the telomere maintenance in telomerase-deficient late generation mESCs and human ALT U2OS cancer cells.
| S-EPMC8834411 | biostudies-literature
Project description:Tumors, including osteosarcoma (OS), are capable of evading senescence and cell death, which is caused by telomere loss with cell division. Alternative lengthening of telomeres (ALT) is considered as the main telomere maintenance mechanism in OS. In this study, we investigated the expression of ALT-associated proteins and mRNAs in human OS cell lines. Western blotting was used to detect the protein expression in OS cell lines, while the expression of mRNA was determined by reverse-transcriptase PCR and quantitative real-time PCR analysis. Whole-genome expression arrays were used to analyze the expression of all the mRNAs involved in telomere maintenance mechanisms (TMMs) including human telomerase reverse transcriptase, promyelocytic leukemia proteins and other related proteins. OS and normal cell lines do not express telomerase reverse transcriptase (hTERT) as a key subunit of telomerase, although they show varying levels of ALT-associated proteins and mRNAs such as PML, Rad52, MRE11 and FEN1 by Western blotting and quantitative real-time PCR analysis. A number of mRNAs that play essential roles in ALT are expressed more in OS cell lines than in the osteoblast cell line, as shown by whole-genome expression arrays. In conclusion, OS cell lines maintain their telomere length primarily through the ALT mechanism. There are numerous other proteins that regulate this process in OS; therefore, anti-ALT therapy may be a more effective method to treat OS than anti-telomerase therapy.
| S-EPMC3406509 | biostudies-literature
Project description:Eukaryotic cells undergo continuous telomere shortening as a consequence of multiple rounds of replications. During tumorigenesis, cells have to acquire telomere DNA maintenance mechanisms (TMMs) in order to counteract telomere shortening, to preserve telomeres from DNA damage repair systems and to avoid telomere-mediated senescence and/or apoptosis. For this reason, telomere maintenance is an essential step in cancer progression. Most human tumors maintain their telomeres expressing telomerase, whereas a lower but significant proportion activates the alternative lengthening of telomeres (ALT) pathway. However, evidence about the coexistence of ALT and telomerase has been found both in vivo in the same cancer populations and in vitro in engineered cellular models, making the distinction between telomerase- and ALT-positive tumors elusive. Indeed, after the development of drugs able to target telomerase, the capability for some cancer cells to escape death, switching from telomerase to ALT, was highlighted. Unfortunately, to date, the mechanism underlying the possible switching or the coexistence of telomerase and ALT within the same cell or populations is not completely understood and different factors could be involved. In recent years, different studies have tried to shed light on the complex regulation network that controls the transition between the two TMMs, suggesting a role for embryonic cancer origin, epigenetic modifications, and specific genes activation-both in vivo and in vitro. In this review, we examine recent findings about the cancer-associated differential activation of the two known TMMs and the possible factors implicated in this process. Furthermore, some studies on cancers are also described that did not display any TMM.
| S-EPMC5855828 | biostudies-literature
Project description:Telomere maintenance is an important genetic mechanism controlling cellular proliferation. Normally, telomeres are maintained by telomerase which is downregulated upon cellular differentiation in most somatic cell lineages. Telomerase activity is upregulated in immortalized cells and cancers to support an infinite lifespan and uncontrolled cell growth; however, some immortalized and transformed cells lack telomerase activity. Telomerase-negative tumors and immortalized cells utilize an alternative mechanism for maintaining telomeres termed alternative lengthening of telomeres (ALT). This research explored evidence for the ALT pathway in chicken cell lines by studying nontransformed immortalized cell lines (DF-1 and OU2) and comparing them to a normal (mortal) cell line and a transformed cell line (DT40). The research consisted of molecular and cellular analyses including profiling of telomeric DNA (array sizing and total content), telomerase activity, and expression of genes involved in the telomerase, recombination, and ALT pathways. In addition, an immunofluorescence analysis for an ALT marker, i.e. ALT-associated promyelocytic leukemia bodies (APBs), was conducted. Evidence for ALT was observed in the telomerase-negative immortalized cell lines. Additionally, the APB marker was also found in the other cell systems. The attributes of the chicken provide an additional vertebrate model for investigation of the ALT pathway.
| S-EPMC3214677 | biostudies-literature
Project description:Only few drugs have shown activity in patients with advanced soft-tissue and the median overall survival is only 18 months. Alterations of genes involved in the DNA damage repair pathway have been associated with sarcoma risk and prognosis. ATR plays a crucial role in maintaining genomic integrity by responding to a large spectrum of DNA damage, including double strand breaks (DSBs) that interfere with replication. The objective of this study is to evaluate the pre-clinical activity of ATR inhibition in soft tissue sarcomas (STS). We explored the ability of the ATR inhibitor, VE-822, to prevent chemotherapy-induced intra-S-phase checkpoint activation and evaluated the antitumor potential of this combination in vitro and in vivo in STS cell lines and in a patient-derived xenograft model. The combination of VE-822 and gemcitabine in vitro was synergistic, inhibited cell proliferation, induced apoptosis, and accumulated in the S phase of the cell cycle with higher efficacy than either single agent alone. The combination also resulted in enhanced ?H2AX intranuclear accumulation as a result of DNA damage induction. These effects were unrelated to the alternative lengthening of telomeres pathway. In vivo, the combination of VE-822 and gemcitabine significantly enhanced tumor growth inhibition and progression-free survival in an aggressive model of undifferentiated pleomorphic sarcoma. The combination of ATR inhibitor and chemotherapy is beneficial in pre-clinical models of soft-tissue sarcoma and deserves further exploration in the clinical setting.
| S-EPMC7198496 | biostudies-literature
Project description:Exceptional genomic stability is one of the hallmarks of mouse embryonic stem (ES) cells. However, the genes contributing to this stability remain obscure. We previously identified Zscan4 as a specific marker for two-cell embryo and ES cells. Here we show that Zscan4 is involved in telomere maintenance and long-term genomic stability in ES cells. Only 5% of ES cells express Zscan4 at a given time, but nearly all ES cells activate Zscan4 at least once during nine passages. The transient Zscan4-positive state is associated with rapid telomere extension by telomere recombination and upregulation of meiosis-specific homologous recombination genes, which encode proteins that are colocalized with ZSCAN4 on telomeres. Furthermore, Zscan4 knockdown shortens telomeres, increases karyotype abnormalities and spontaneous sister chromatid exchange, and slows down cell proliferation until reaching crisis by passage eight. Together, our data show a unique mode of genome maintenance in ES cells.
| S-EPMC2851843 | biostudies-literature
Project description:A substantial number of human cancers are telomerase-negative and elongate physiologically damaged telomeres through a break-induced replication (BIR)-based mechanism known as alternative lengthening of telomeres (ALT). We recently demonstrated that inhibiting the transcription of the telomeric long noncoding RNA TERRA suppresses telomere damage and ALT features, indicating that telomere transcription is a main trigger of ALT activity. Here we show that experimentally increased TERRA transcription not only increases ALT features, as expected, but also causes rapid loss of telomeric DNA through a pathway that requires the endonuclease Mus81. Our data indicate that the ALT mechanism can endanger telomere integrity if not properly controlled and point to TERRA transcription as a uniquely versatile target for therapy.
| S-EPMC9522348 | biostudies-literature
Project description:Glioblastoma multiforme is the most aggressive primary tumor of the central nervous system. Glioma stem cells (GSCs), a small population of tumor cells with stem-like properties, are supposedly responsible for glioblastoma multiforme relapse after current therapies. In approximately thirty percent of glioblastoma multiforme tumors, telomeres are not maintained by telomerase but through an alternative mechanism, termed alternative lengthening of telomere (ALT), suggesting potential interest in developing specific therapeutic strategies. However, no preclinical model of ALT glioma was available until the isolation of TG20 cells from a human ALT glioma. Herein, we show that TG20 cells exhibit a high level of telomeric recombination but a stable karyotype, indicating that their telomeres retain their protective function against chromosomal instability. TG20 cells possess all of the characteristic features of GSCs: the expression of neural stem cell markers, the generation of intracerebral tumors in NOD-SCID-IL2Rγ (NSG) mice as well as in nude mice, and the ability to sustain serial intracerebral transplantations without expressing telomerase, demonstrating the stability of the ALT phenotype in vivo. Furthermore, we also demonstrate that 360B, a G-quadruplex ligand of the pyridine derivative series that impairs telomere replication and mitotic progression in cancer cells, prevents the development of TG20 tumors. Together, our results show that intracerebral grafts of TG20 cells in immunodeficient mice constitute an efficient preclinical model of ALT glioblastoma multiforme and that G-quadruplex ligands are a potential therapy for this specific type of tumor.
| S-EPMC4303977 | biostudies-literature
Project description:Approximately 10% to 15% of human cancers lack detectable telomerase activity, and a subset of these maintain telomere lengths by the telomerase-independent telomere maintenance mechanism termed alternative lengthening of telomeres (ALT). The ALT phenotype, relatively common in subtypes of sarcomas and astrocytomas, has rarely been reported in epithelial malignancies. However, the prevalence of ALT has not been thoroughly assessed across all cancer types. We therefore comprehensively surveyed the ALT phenotype in a broad range of human cancers. In total, two independent sets comprising 6110 primary tumors from 94 different cancer subtypes, 541 benign neoplasms, and 264 normal tissue samples were assessed by combined telomere-specific fluorescence in situ hybridization and immunofluorescence labeling for PML protein. Overall, ALT was observed in 3.73% (228/6110) of all tumor specimens, but was not observed in benign neoplasms or normal tissues. This is the first report of ALT in carcinomas arising from the bladder, cervix, endometrium, esophagus, gallbladder, kidney, liver, and lung. Additionally, this is the first report of ALT in medulloblastomas, oligodendrogliomas, meningiomas, schwannomas, and pediatric glioblastoma multiformes. Previous studies have shown associations between ALT status and prognosis in some tumor types; thus, further studies are warranted to assess the potential prognostic significance and unique biology of ALT-positive tumors. These findings may have therapeutic consequences, because ALT-positive cancers are predicted to be resistant to anti-telomerase therapies.
| S-EPMC3181356 | biostudies-literature