Written by: Frank

Category: Mechanisms underlying the activation of TERT transcription and telomerase activity in human cancer: old actors and new players.

Published: May 10, 2020

Long-lived species Homo sapiens have advanced strong safety mechanisms towards most cancers by repressing telomerase and sustaining brief telomeres, thereby delaying the onset of the majority of most cancers varieties till post-reproductive age.

Indeed, telomerase is silent in most differentiated human cells, predominantly on account of the transcriptional repression of its catalytic element telomerase reverse transcriptase (TERT) gene.

The lack of telomerase/TERT expression results in progressive telomere erosion in dividing human cells, whereas critically shortened telomere size induces a everlasting development arrest stage named replicative senescence.

TERT/telomerase activation has been experimentally proven to be important to mobile immortalization and malignant transformation by stabilizing telomere size and erasing the senescence barrier. Consistently, TERT expression/telomerase activity is detectable in as much as 90% of human major cancers.

Compelling proof has additionally gathered that TERT contributes to most cancers growth and development by way of a number of actions past its canonical telomere-lengthening perform. Given these key roles of telomerase and TERT in oncogenesis, nice efforts have been made to decipher mechanisms underlying telomerase activation and TERT induction.

In the final 20 years since the TERT gene and promoter had been cloned, the derepression of the TERT gene has been proven to be achieved usually at a transcriptional stage via dysregulation of oncogenic components or signaling, post-transcriptional/translational regulation and genomic amplification.

However, advances in high-throughput next-generation sequencing applied sciences have prompted a revolution in most cancers genomics, which results in the latest discovery that genomic alterations take heart stage in activating the TERT gene.

In this evaluation article, we summarize essential mechanisms activating TERT transcription, with particular emphases on the contribution of TERT promoter mutations and structural alterations at the TERT locus, and briefly focus on the underlying implications of these genomic events-driven TERT hyperactivity in most cancers initiation/development and potential scientific functions as nicely.

Inhibition of nucleotide synthesis promotes replicative senescence of human mammary epithelial cells.

Cellular senescence is a mechanism by which cells completely withdraw from the cell cycle in response to stresses together with telomere shortening, DNA injury, or oncogenic signaling. Senescent cells contribute to each age-related degeneration and hyperplastic pathologies, together with most cancers.

In tradition, regular human epithelial cells enter senescence after a restricted quantity of cell divisions, generally known as replicative senescence.

Here, to analyze how metabolic pathways regulate replicative senescence, we used LC-MS-based metabolomics to investigate senescent major human mammary epithelial cells (HMECs).

We didn’t observe vital adjustments in glucose uptake or lactate secretion in senescent HMECs. However, evaluation of intramobile metabolite pool sizes indicated that senescent cells exhibit depletion of metabolites from nucleotide synthesis pathways.

Furthermore, secure isotope tracing with ¹³C-labeled glucose or glutamine revealed a dramatic blockage of flux of these two metabolites into nucleotide synthesis pathways in senescent HMECs. To take a look at whether or not mobile immortalization would reverse these observations, we expressed telomerase in HMECs.

In addition to stopping senescence, telomerase expression maintained metabolic flux from glucose into nucleotide synthesis pathways. Finally, we investigated whether or not inhibition of nucleotide synthesis in proliferating HMECs is ample to induce senescence.

In proliferating HMECs, each pharmacological and genetic inhibition of ribonucleotide reductase regulatory subunit M2 (RRM2), a rate-limiting enzyme in dNTP synthesis, induced untimely senescence with concomitantly decreased metabolic flux from glucose into nucleotide synthesis. Taken collectively, our outcomes counsel that nucleotide synthesis inhibition performs a causative position in the institution of replicative senescence in HMECs.