hTERT Increases TRF2 to Induce Telomere Compaction and Extend Cell Replicative Lifespan.

Area of Science:

• Cellular senescence
• Telomere biology
• DNA damage response

Background:

• Replicative senescence, a process limiting cell proliferation, is triggered by short telomeres and DNA damage signaling via ATM and TP53.
• Human telomerase reverse transcriptase (hTERT) is known to lengthen telomeres, potentially preventing senescence.

Purpose of the Study:

• To investigate the role of hTERT mutants in telomere maintenance and senescence.
• To elucidate the mechanism by which hTERT variants influence DNA damage signaling and cell replication.

Main Methods:

• Utilized normal diploid fibroblasts expressing various hTERT mutants.
• Assessed telomere length, DNA damage signaling (ATM, TP53), and cell replication.
• Measured levels of E3 ubiquitin ligases (Siah1, CDC20, FBXO5) and shelterin complex components (TRF1, TRF2).
• Employed super-resolution microscopy to analyze telomere conformation.

Main Results:

• hTERT mutants, even those not maintaining telomere length, prevented DNA damage signaling and senescence.
• Mutant hTERT expression altered E3 ligase levels, stabilizing TRF2 and restoring the TRF2:TRF1 ratio.
• Telomeres adopted a more compact, denser conformation, independent of length, which correlated with reduced DNA damage signaling.
• This telomere compaction mediated by TRF2 was identified as a key factor in blocking senescence.

Conclusions:

• hTERT variants can inhibit senescence through telomere compaction, a mechanism distinct from telomere lengthening.
• Telomere compaction, regulated by the shelterin complex and E3 ligases, plays a dominant role in preventing replicative senescence.
• Short telomeres in cancer cells might evade senescence due to stabilized shelterin components and increased telomere density, rather than solely due to lack of hTERT activity.