POT1-TPP1 binding stabilizes POT1, promoting efficient telomere maintenance

Structural Motifs at the Telomeres and Their Role in Regulatory Pathways

Telomeres are specialized structures, found at the ends of linear chromosomes in eukaryotic cells, that play a crucial role in maintaining the stability and integrity of genomes. They are composed of repetitive DNA sequences, ssDNA overhangs, and several associated proteins. The length of telomeres is linked to cellular aging in humans, and deficiencies in their maintenance are associated with various diseases. Key structural motifs at the telomeres serve to protect vulnerable chromosomal ends. Telomeric DNA also has the ability to form diverse complex DNA higher-order structures, including T-loops, D-loops, R-loops, G-loops, G-quadruplexes, and i-motifs, in the complementary C-rich strand. While many essential proteins at telomeres have been identified, the intricacies of their interactions and structural details are still not fully understood. This Perspective highlights recent advancements in comprehending the structures associated with human telomeres. It emphasizes the significance of telomeres, explores various telomeric structural motifs, and delves into the structural biology surrounding telomeres and telomerase. Furthermore, telomeric loops, their topologies, and the associated proteins that contribute to the safeguarding of telomeres are discussed.

Silencing PinX1 enhances radiosensitivity and antitumor-immunity of radiotherapy in non-small cell lung cancer

BACKGROUND

We aimed to investigate the effects of PinX1 on non-small cell lung cancer(NSCLC) radiosensitivity and radiotherapy-associated tumor immune microenvironment and its mechanisms.

METHODS

The effect of PinX1 silencing on radiosensitivity in NSCLC was assessed by colony formation and CCK8 assay, immunofluorescence detection of γ- H2AX and micronucleus assay. Western blot was used to assess the effect of PinX1 silencing on DNA damage repair pathway and cGAS-STING pathway. The nude mouse and Lewis lung cancer mouse model were used to assess the combined efficacy of PinX1 silencing and radiotherapy in vivo. Changes in the tumor immune microenvironment were assessed by flow cytometry for different treatment modalities in the Lewis luuse model. The interaction protein RBM10 was screened by immunoprecipitation-mass spectrometry.

RESULTS

Silencing PinX1 enhanced radiosensitivity and activation of the cGAS-STING pathway while attenuating the DNA damage repair pathway. Silencing PinX1 further increases radiotherapy-stimulated CD8+ T cell infiltration and activation, enhances tumor control and improves survival in vivo; Moreover, PinX1 downregulation improves the anti-tumor efficacy of radioimmunotherapy, increases radioimmune-stimulated CD8+ T cell infiltration, and reprograms M2-type macrophages into M1-type macrophages in tumor tissues. The interaction of PinX1 and RBM10 may promote telomere maintenance by assisting telomerase localization to telomeres, thereby inhibiting the immunostimulatory effects of IR.

CONCLUSIONS

In NSCLC, silencing PinX1 significantly contributed to the radiosensitivity and promoted the efficacy of radioimmunotherapy. Mechanistically, PinX1 may regulate the transport of telomerase to telomeres through interacting with RBM10, which promotes telomere maintenance and DNA stabilization. Our findings reveal that PinX1 is a potential target to enhance the efficacy of radioimmunotherapy in NSCLC patients.

Germline POT1 Variants: A Critical Perspective on POT1 Tumor Predisposition Syndrome

The Protection of Telomere 1 (POT1) gene was identified as a melanoma predisposition candidate nearly 10 years ago. Thereafter, various cancers have been proposed as associated with germline POT1 variants in the context of the so-called POT1 Predisposition Tumor Syndrome (POT1-TPD). While the key role, and related risks, of the alterations in POT1 in melanoma are established, the correlation between germline POT1 variants and the susceptibility to other cancers partially lacks evidence, due also to the rarity of POT1-TPD. Issues range from the absence of functional or segregation studies to biased datasets or the need for a revised classification of variants. Furthermore, a proposal of a surveillance protocol related to the cancers associated with POT1 pathogenic variants requires reliable data to avoid an excessive, possibly unjustified, burden for POT1 variant carriers. We propose a critical perspective regarding data published over the last 10 years that correlate POT1 variants to various types of cancer, other than cutaneous melanoma, to offer food for thought for the specialists who manage cancer predisposition syndromes and to stimulate a debate on the grey areas that have been exposed.

Epigenetic mechanism of Gtl2-miRNAs causes the primitive sheep characteristics found in purebred Merino sheep

BACKGROUND

It is not uncommon for some individuals to retain certain primitive characteristics even after domestication or long-term intensive selection. Wild ancestors or original varieties of animals typically possess strong adaptability to environmental preservation, a trait that is often lacking in highly artificially selected populations. In the case of the Merino population, a world-renowned fine wool sheep breed, a phenotype with primitive coarse wool characteristic has re-emerged. It is currently unclear whether this characteristic is detrimental to the production of fine wool or whether it is linked to the adaptability of sheep. The underlying genetic/epigenetic mechanisms behind this trait are also poorly understood.

RESULTS

This study identified lambs with an ancestral-like coarse (ALC) wool type that emerged during the purebred breeding of Merino fine wool sheep. The presence of this primitive sheep characteristic resulted in better environmental adaptability in lambs, as well as improved fine wool yield in adulthood. Reciprocal cross experiments revealed that the ALC phenotype exhibited maternal genetic characteristics. Transcriptomic SNP analysis indicated that the ALC phenotype was localized to the imprinted Gtl2-miRNAs locus, and a significant correlation was found between the ALC wool type and a newly identified short Interstitial Telomeric Sequences (s-ITSs) at this locus. We further confirmed that a novel 38-nt small RNA transcribed from these s-ITSs, in combination with the previously reported 22-nt small RNAs cluster from the Gtl2-miRNAs locus, synergistically inhibited PI3K/AKT/Metabolic/Oxidative stress and subsequent apoptotic pathways in wool follicle stem cells, resulting in the ALC wool type. The necessity of Gtl2-miRNAs in controlling primary hair follicle morphogenesis, as well as the wool follicle type for ALC wool lambs, was verified using intergenic differentially methylated region-knockout mice.

CONCLUSION

The ALC wool type of Merino sheep, which does not reduce wool quality but increases yield and adaptability, is regulated by epigenetic mechanisms in the imprinted Gtl2-miRNAs region on sheep chromosome 18, with the maternally expressed imprinted gene responsible for the ALC phenotype. This study highlights the significance of epigenetic regulation during embryonic and juvenile stages and emphasizes the advantages of early adaptation breeding for maternal parents in enhancing the overall performance of their offspring.

POT1 involved in telomeric DNA damage repair and genomic stability of cervical cancer cells in response to radiation

Though telomeres play a crucial role in maintaining genomic stability in cancer cells and have emerged as attractive therapeutic targets in anticancer therapy, the relationship between telomere dysfunction and genomic instability induced by irradiation is still unclear. In this study, we identified that protection of telomeres 1 (POT1), a single-stranded DNA (ssDNA)-binding protein, was upregulated in γ-irradiated HeLa cells and in cancer patients who exhibit radiation tolerance. Knockdown of POT1 delayed the repair of radiation-induced telomeric DNA damage which was associated with enhanced H3K9 trimethylation and enhanced the radiosensitivity of HeLa cells. The depletion of POT1 also resulted in significant genomic instability, by showing a significant increase in end-to-end chromosomal fusions, and the formation of anaphase bridges and micronuclei. Furthermore, knockdown of POT1 disturbed telomerase recruitment to telomere, and POT1 could interact with phosphorylated ATM (p-ATM) and POT1 depletion decreased the levels of p-ATM induced by irradiation, suggesting that POT1 could regulate the telomerase recruitment to telomeres to repair irradiation-induced telomeric DNA damage of HeLa cells through interactions with p-ATM. The enhancement of radiosensitivity in cancer cells can be achieved through the combination of POT1 and telomerase inhibitors, presenting a potential approach for radiotherapy in cancer treatment.

Alternative telomere maintenance mechanism in Alligator sinensis provides insights into aging evolution

Lifespan is a life-history trait that undergoes natural selection. Telomeres are hallmarks of aging, and shortening rate predicts species lifespan, making telomere maintenance mechanisms throughout different lifespans a worthy topic for study. Alligators are suitable for the exploration of anti-aging molecular mechanisms, because they exhibit low or even negligible mortality in adults and no significant telomere shortening. Telomerase reverse transcriptase (TERT) expression is absent in the adult Alligator sinensis, as in humans. Selection analyses on telomere maintenance genes indicated that ATM, FANCE, SAMHD1, HMBOX1, NAT10, and MAP3K4 experienced positive selection on A. sinensis. Repressed pleiotropic ATM kinase in A. sinensis suggests their fitness optimum shift. In ATM downstream, Alternative Lengthening of Telomeres (ALT)-related genes were clustered in a higher expression pattern in A. sinensis, which covers 10-15% of human cancers showing no telomerase activities. In summary, we demonstrated how telomere shortening, telomerase activities, and ALT contributed to anti-aging strategies.