Catalytic subunit of telomerase that maintains chromosome ends by adding TTAGGG repeats to telomeres. Normally silenced in somatic cells but reactivated in ~85-90% of cancers, enabling unlimited replicative potential. Essential for stem cell maintenance, iPSC generation, and therapeutic cell line development. Beyond telomere maintenance, hTERT exhibits extra-telomeric activities including transcriptional regulation and cell immortalization.
Length: 3399 bp (1133 aa)
Type: Enzyme
Function: Telomere maintenance and cell immortalization
Origin: Homo sapiens
Characteristics
Reverse transcriptase enzyme that forms active telomerase holoenzyme with TERC (telomerase RNA component). Adds hexameric TTAGGG repeats to chromosome 3-prime ends, counteracting progressive telomere shortening from incomplete DNA replication. Expression tightly regulated and silenced in most differentiated somatic cells, leading to replicative senescence after 50-70 divisions. Constitutively expressed in stem cells, germ cells, and activated lymphocytes. Reactivated in approximately 85-90% of human cancers, providing unlimited replicative capacity. Beyond canonical telomere extension, exhibits extra-telomeric functions including transcriptional regulation of genes involved in cell proliferation, apoptosis resistance, and chromatin remodeling. Catalytically inactive mutants retain some immortalization activities, suggesting telomere-independent mechanisms.
Applications: Cell immortalization for establishing research and therapeutic cell lines. Essential component for iPSC generation and maintenance of pluripotency. Enables expansion of CAR-T cells and therapeutic T cells for adoptive immunotherapy. Used in cancer research to study mechanisms of cellular immortalization and oncogenesis. Cellular senescence and aging studies examining replicative lifespan control. Regenerative medicine applications requiring long-term cell culture and propagation. Gene therapy vector production in stable packaging cell lines. Functional genomics requiring extended culture of primary cells.
Limitations: Constitutive expression may promote oncogenic transformation and genomic instability in certain contexts. Reactivation strongly associated with cancer progression in most tumor types, complicating therapeutic applications. Extra-telomeric activities can alter cellular gene expression patterns beyond intended telomere maintenance. Requires careful monitoring when used in therapeutic cell production to ensure cells retain normal karyotype and function. Expression alone insufficient to fully immortalize some primary cell types without additional genetic modifications.
Modifications: Works as ribonucleoprotein complex with TERC RNA component; requires proper nuclear localization
Miller et al. (2013).
HPV16 E7 protein and hTERT proteins defective for telomere maintenance cooperate to immortalize human keratinocytes.
PLoS Pathog - Miller 2013 hTERT Immortalization
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