Induction of the alternative lengthening of telomeres pathway by trapping of proteins on DNA

Orphan nuclear receptors-induced ALT-associated PML bodies are targets for ALT inhibition

Orphan nuclear receptors (NRs), such as COUP-TF1, COUP-TF2, EAR2, TR2 and TR4, are implicated in telomerase-negative cancers that maintain their telomeres through the alternative lengthening of telomeres (ALT) mechanism. However, how telomere association of orphan NRs is involved in ALT activation remains unclear. Here, we demonstrate that telomeric tethering of orphan NRs in human fibroblasts initiates formation of ALT-associated PML bodies (APBs) and features of ALT activity, including ALT telomere DNA synthesis, telomere sister chromatid exchange, and telomeric C-circle generation, suggesting de novo ALT induction. Overexpression of orphan NRs exacerbates ALT phenotypes in ALT cells, while their depletion limits ALT. Orphan NRs initiate ALT via the zinc finger protein 827, suggesting the involvement of chromatin structure alterations for ALT activation. Furthermore, we found that orphan NRs and deficiency of the ALT suppressor ATRX-DAXX complex operate in concert to promote ALT activation. Moreover, PML depletion by gene knockout or arsenic trioxide treatment inhibited ALT induction in fibroblasts and ALT cancer cells, suggesting that APB formation underlies the orphan NR-induced ALT activation. Importantly, arsenic trioxide administration abolished APB formation and features of ALT activity in ALT cancer cell line-derived mouse xenografts, suggesting its potential for further therapeutic development to treat ALT cancers.

Outdoor fine particulate matter exposure and telomere length in humans: A systematic review and meta-analysis

Although the association between changes in human telomere length (TL) and ambient fine particulate matter (PM2.5) has been documented, there remains disagreement among the related literature. Our study conducted a systematic review and meta-analysis of epidemiological studies to investigate the health effects of outdoor PM2.5 exposure on human TL after a thorough database search. To quantify the overall effect estimates of TL changes associated with every 10 μg/m3 increase in PM2.5 exposure, we focused on two main topics, which were outdoor long-term exposure and prenatal exposure of PM2.5. Additionally, we included a summary of short-term PM2.5 exposure and its impact on TL due to limited data availability. Our qualitative analysis included 20 studies with 483,600 participants. The meta-analysis showed a statistically significant association between outdoor PM2.5 exposure and shorter human TL, with pooled impact estimates (β) of -0.12 (95% CI: -0.20, -0.03, I2= 95.4%) for general long-term exposure and -0.07 (95% CI: -0.15, 0.00, I2= 74.3%) for prenatal exposure. In conclusion, our findings suggest that outdoor PM2.5 exposure may contribute to TL shortening, and noteworthy associations were observed in specific subgroups, suggesting the impact of various research variables. Larger, high-quality studies using standardized methodologies are necessary to strengthen these conclusions further.

TERRA and the alternative lengthening of telomeres: a dangerous affair

Eukaryotic telomeres are transcribed into the long noncoding RNA TERRA. A fraction of TERRA remains associated with telomeres by forming RNA:DNA hybrids dubbed telR-loops. TERRA and telR-loops are essential to promote telomere elongation in human cancer cells that maintain telomeres through a homology-directed repair pathway known as alternative lengthening of telomeres or ALT. However, TERRA and telR-loops compromise telomere integrity and cell viability if their levels are not finely tuned. The study of telomere transcription in ALT cells will enormously expand our understanding of the ALT mechanism and of how genome integrity is maintained. Moreover, telomere transcription, TERRA and telR-loops are likely to become exceptionally suited targets for the development of novel anti-cancer therapies.

Oxidative guanine base damage plays a dual role in regulating productive ALT-associated homology-directed repair

Cancer cells maintain telomeres by upregulating telomerase or alternative lengthening of telomeres (ALT) via homology-directed repair at telomeric DNA breaks. 8-Oxoguanine (8oxoG) is a highly prevalent endogenous DNA lesion in telomeric sequences, altering telomere structure and telomerase activity, but its impact on ALT is unclear. Here, we demonstrate that targeted 8oxoG formation at telomeres stimulates ALT activity and homologous recombination specifically in ALT cancer cells. Mechanistically, an acute 8oxoG induction increases replication stress, as evidenced by increased telomere fragility and ATR kinase activation at ALT telomeres. Furthermore, ALT cells are more sensitive to chronic telomeric 8oxoG damage than telomerase-positive cancer cells, consistent with increased 8oxoG-induced replication stress. However, telomeric 8oxoG production in G2 phase, when ALT telomere elongation occurs, impairs telomeric DNA synthesis. Our study demonstrates that a common oxidative base lesion has a dual role in regulating ALT depending on when the damage arises in the cell cycle.

Identification of telomere-associated gene signatures to predict prognosis and drug sensitivity in glioma

OBJECTIVE

Gliomas are a heterogeneous group of brain tumors with distinct biological and clinical properties, leading to significant mortality and morbidity. Emerging evidence shows telomere maintenance has implicated in glioma susceptibility and prognosis. In this study, we comprehensively analyzed gene signatures related to telomere maintenance in glioma and their predictive values for predicting the prognosis and drug sensitivity in glioma.

METHODS

We initially identified telomere-related genes differentially expressed between low-grade glioma (LGG) and glioblastoma (GBM) and accordingly developed a risk model by univariate and multivariate Cox analysis to assess the expressions of telomere-related genes across the risk groups. Finally, to assess these genes in immune function the anti-tumor medications often used in the clinical treatment of glioma, we computed immune cell infiltration analysis and drug sensitivity analysis.

RESULTS

The consensus clustering analysis identified 20 telomere-related genes which split LGG patients into two distinct subtypes. The patient survival, the expressions of key telomere-related DEGs, and immune cell infiltration significantly differed between Cluster 1 and Cluster 2. The LASSO risk model [riskScore=(0.086)*HOXA7+(0.242)*WEE1+(0.247)*IGF2BP3+(0.052)*DUSP10] showed significant differences regarding the 1-, 3-, 5-year overall survival, immune cell infiltration, and drug sensitivity between high- and low-risk groups. The predictive nomogram constructed to quantify the survival probability of each sample at 1, 3, and 5 years was consistent with the actual patient survival.

CONCLUSION

Our comprehensive characterization of telomere-associated gene signatures in glioma reveals their possible roles in the development, tumor microenvironment, and prognosis. The study provides some suggestive relationships between four telomere-related genes (HOXA7, WEE1, IGF2BP3, and DUSP10) and glioma prognosis.

Telomere sequence variability in genotypes from natural plant populations: unusual block-organized double-monomer terminal telomeric arrays

BACKGROUND

Telomeres are the nucleoprotein complexes that physically cap the ends of eukaryotic chromosomes. Most plants possess Arabidopsis-type telomere sequences (TSs). In addition to terminal TSs, more diverse interstitial TSs exists in plants. Although telomeres have been sufficiently studied, the actual diversity of TSs in land plants is underestimated.

RESULTS

We investigate genotypes from seven natural populations with contrasting environments of four Chenopodium species to reveal the variability in TSs by analyzing Oxford Nanopore reads. Fluorescent in situ hybridization was used to localize telomeric repeats on chromosomes. We identified a number of derivative monomers that arise in part of both terminal and interstitial telomeric arrays of a single genotype. The former presents a case of block-organized double-monomer telomers, where blocks of Arabidopsis-type TTTAGGG motifs were interspersed with blocks of derivative TTTAAAA motifs. The latter is an integral part of the satellitome with transformations specific to the inactive genome fraction.

CONCLUSIONS

We suggested two alternative models for the possible formation of derivative monomers from telomeric heptamer motifs of Arabidopsis-type. It was assumed that derivatization of TSs is a ubiquitous process in the plant genome but occurrence and frequencies of derivatives may be genotype-specific. We also propose that the formation of non-canonical arrays of TSs, especially at chromosomal termini, may be a source for genomic variability in nature.