Bhatt, A. K. | Search bioRxiv

bioRxiv2025

TRF2 Non-Telomeric Function is Indispensable for Neural stemness

Depletion of TRF2 from chromosome ends results in telomeric fusions and genome instability in mammals. Here we show that although TRF2 is indispensable for the proliferation and survival of mouse neural stem cells (mNSCs), surprisingly, this is due to non-telomeric transcriptional function of TRF2, and not telomere protection. Complementing recent work showing TRF2 is dispensable for telomere protection in pluripotent stem cells. Deletion of TRF2 in adult mNSCs (TRF2fl/fl, Nestin-Cre) resulted in markedly reduced proliferation and impaired differentiation into neurons. However, telomere dysregulation-induced DNA damage was not observed, as indicated by the unaltered DNA damage response. Similarly, in SH-SY5Y cells, TRF2 depletion induced differentiation without causing telomere dysfunction. Mechanistically, non-telomeric TRF2 directly binds to the promoters of key genes that regulate differentiation. TRF2-dependent recruitment of the polycomb repressor complex (PRC2) and subsequent H3K27 trimethylation repress differentiation-associated genes, thereby maintaining NSC identity. Interestingly, G-quadruplex (G4) motifs are necessary for TRF2 binding. Disrupting the TRF2-G4 interaction-- either through G4-binding ligands or the G4-specific helicase DHX36--induces differentiation genes, thereby promoting neurogenesis. These findings reveal a pivotal non-telomeric role of TRF2 in NSC survival, providing key mechanistic insights into neurogenesis with implications for aging-related neurodegeneration.

molecular biology↗

bioRxiv2023

Telomeres control regulation of the human Telomerase (hTERT) gene through non-telomeric TRF2 and independent of Telomere looping

The function of the human telomerase reverse transcriptase (hTERT) in the synthesis and maintenance of chromosome ends, or telomeres, is widely understood. Whether and how telomeres, on the other hand, influence hTERT regulation is relatively less studied. We found hTERT was transcriptionally altered depending on telomere length (TL). This resulted from TL-dependent binding of TRF2 between telomeres and the hTERT promoter. hTERT promoter-bound TRF2 was non-telomeric and did not involve the looping of telomeres to the hTERT promoter. Cell lines from different tissue types (fibrosarcoma (HT1080), colon cancer (HCT116), and breast cancer (MDA-MB-231), engineered for either telomere elongation/shortening gave increase/decrease in hTERT, respectively. Mechanistically, we show hTERT promoter-bound non-telomeric TRF2 recruits the canonical PRC2-complex inducing repressor histone H3K27-trimethylation in a TL-dependent fashion. This was further supported by TL-dependent promoter activity from an exogenously inserted hTERT reporter. Increase in TL over days followed by gradual decline, resulted in activation followed by repression of hTERT in a concerted manner, further implicating TL as a key factor for hTERT regulation. Notably on reprogramming primary fibroblasts to induced pluripotent stem cells (iPSCs), TRF2 loss from the hTERT promoter was evident along with telomere elongation and hTERT upregulation. Conversely, on telomere shortening in iPSCs, hTERT promoter-bound TRF2 was restored with marked reduction in hTERT further supporting the causal role of TL in hTERT transcription. Mechanisms of tight control of hTERT by TL shown here are likely to have major implications in telomere-related physiologies, particularly, cancer, ageing and pluripotency. TeaserTelomere length controls hTERT expression by modulating TRF2 distribution and PRC2-mediated repression, highlighting a self-regulatory mechanism in cancer.

cancer biology↗