G quadruples reveal molecular links between telomeres and telomerase: key findings in tumor transformation, aging and regeneration therapy
Normal cells age and die when they reach their maximum lifespan. In these telomeres, the ends of chromosomes cannot be synthesized due to the inhibition of human telomerase reverse transcriptase (HTERT) enzyme, resulting in telomeres shortening.
Although the link is still unclear, many studies have shown that reactivation of HTERT can lead to telomere maintenance, which may lead to cancer. At the same time, the results showed that several telomeres binding proteins interacted with the g quadrimer.
Since the HTERT promoter contains multiple G quadrimer formation sequences, in a recent study, scientists investigated whether telomeres repeat binding factor 2 (TRF2) is associated with the promoter and whether this has an effect on HTERT regulation. Professor Shantanu Chowdhury, Shalu Sharma, Ananda Kishore Mukherjee, Shuvra Shekhar Roy, Sulochana Bagri, Dr. Meenakshi Verma, Antara Sengupta, Manish Kumar at the CSIR-Institute of Genomics and Integrative Biology in collaboration with Dr. Deo Prakash Pandey Silje Lier, and Gaute Nesse at the Oslo University Hospital discovered a telomeric factor-mediated mechanism of hTERT regulation, establishing molecular links between telomeres and telomerase that could be critical for neoplastic transformation, ageing, and regenerative therapy which was published in Cell Reports.
Scientists identified the G-quadrilateral body of the TERT promoter sequence across vertebrates. They also performed a ChIP (chromatin immunoprecipitation) assay and performed analysis. Meanwhile, since TRF2 is a true telomerular binding protein, telomerular PCR is used as a positive control for the TRF2 chip. Later, they performed continuous experiments, including immunoprecipitation of proteins, with immunofluorescence microscopy imaging to calculate TRF2 and HTERT signal intensity, immune flow cell calculation, real-time PCR, blot analysis, ELISA, ELISA, ELISA and several other molecular tests.
Chowdhury and colleagues show that TRF2 directly interacts with the HTERT promoter and controls HTERT expression and telomerase activity in cancer and normal cells. They also found that the main domains of MyB and TRF2 are required for HTERT transcriptional regulation. TRF2 regulates the epigenetic status of chromatin at the HTERT promoter; TRF2-induced polycomb inhibitor complex (PRC2) is recruited to the HTERT promoter.
The team found that the association of TRF2 with the HTERT promoter was not telomere-dependent, but was dependent on G Quadruplex. Furthermore, in cancers with HTERT promoter mutations, TRF2 occupancy is lost, and by stabilizing G Quadruplex with ligands, TRF2 binding is restored and activated telomerase is inhibited.
Their findings will help understand the aging, cancer, cellular senescence and DNA damage response processes associated with telomeres maintaining and regulating telomerase. “The case of telomeres in cancer is particularly important. Although further work will be needed to test this, based on our findings here, the establishment of telomeres through TRF2 (as well as non-aggregated binding of the HTERT promoter) – lectinase crosstalk may be key to telomeres in cancer cells.”
He also added: “Relatively enhanced telomerase and long telomeres levels are crucial for the maintenance/survival of pluripotent stem cells.” Therefore, TRF2-mediated HTERT regulation associated with telomeres may be important in pluripotency.
This study shows for the first time that TRF2-induced HTERT reinhibition in glioblastoma and other cancers using small molecule ligands provides potential therapeutic opportunities. Small molecules are tailored to bind and stabilize the G quadrilateral. “These results provide an interesting opportunity for the development of G-tetrasome binding molecules for therapeutic interventions in glioblastoma polymorphism-destructive brain cancer,” said Professor Chowdhury. In addition, the mechanisms that enable HTER to remain inhibitory in normal cells and the mechanisms that lead to HTERT reactivation in cancer cells have been shown.
“In summary, these results suggest that the molecular link between telomeres and telomerase is crucial to advance the understanding of cell neutral function, including tumor transformation, aging, and pluripotency/differentiation,” said Professor Chowdhury.
Journal Reference:
Sharma S, Mukherjee AK, Roy SS, Bagri S, Lier S, Verma M, Sengupta A, Kumar M, Nesse G, Nesse G, Pandey DP, ChowdhuryS. Human telomerase is directly regulated by non-TELF2-G TRF2-G TRF2-G-Quadruplex interactions. CellRep. 20215-18; 35 (7): 109154. doi:10.1016/j.celrep.2021.109154. PMID: 34010660.
About the Author
Dr. Shalu Sharma
After completing my Master of Microbiology, Dr. Shalu Sharma joined Dr. Shantanu Chowdhury at CSIR-IGIB for a Ph.D. SC Laboratory studies cancer with a focus on telomerular biology. She first explores the regulatory effects of telomeres on cell aging and genome-wide transcriptomics. Gradually, she became interested in understanding the regulation of human telomerase, overactivated in >90% of cancers. The team’s latest findings reveal how telomeres signal telomerase regulation. How clinical mutations in the telomerase promoter cause excessive activation of telomerase. Based on this, the team discovered the potential of DNA-binding small molecules to be used in therapeutic interventions.
Dr. Ananda K Mukherjee,,,,, PhD
Dr. Ananda K Mukherjee was joined in 2014 at the graduate student at Shantanu Chowdhury’s Laboratory at IGIB, where he was introduced to telomer biology and telomer binding protein-TRF2. The group’s telomere length dependence on the atypical transcriptional effect of TRF2. They then pointed out that TRF2 directly inhibits telomerase by maintaining inhibitory histones using G-season strands on gene promoters. They further found that the specific G-quadrilateral that disrupts glioblastoma mutations resulted in the loss of this regulation. He is currently trying to understand how telomere length heterogeneity in tumor cells affects the immune response to cancer.
Professor Shantanu Chowdhury
Shantanu Chowdhury is currently a professor of genome and integrated biology at CSIR Delhi. His research interests include understanding the functions of non-single-stranded DNA structures called G quadrilaterals. Especially in telomerase control and telomer function in cancer. In 2002, he moved to his current position, where he started his own lab. In 2012, Shantanu won the Shanti Swarup Bhatnagar Biological Science Award (the most prestigious science award in India). He is a senior fellow at the DBT/Wellcome Trust India Alliance and is a member of the editorial board of the Journal of Biochemistry.
Main image source: Chowdhury et al.
