1. Telomeres cap DNA strands to protect chromosomes
Telomeres- repeating DNA end of chromosomes
cap DNA strands to protect chromosomes  genomic stability
Fusion, degradation, recombination
Telomere Diagnostics

2. Telomerase elongates telomeres by adding TTAGGG sequences to ends of existing chromosomes
TERT
TERC
Telomeres- repeating DNA end of chromosomes
cap DNA strands to protect chromosomes  genomic stability
Fusion, degradation, recombination
Telomerase = ribonucleoprotein with 2 components
TERT: Reverse transcriptase catalytic subunit
TERC: RNA component
Recharge Biomedical

3. Most normal human cells lack telomerase activity
bone marrow blood cells, basal layer skin cells, and epithelial cells of mucosae also during S phase mainly
Telomers
Shorten with aging
W each cell division telomeres shorten by ~ bp bc the lagging strand of DNA synthesis can’t replicate extreme 3’ end (end replication problem)
conventional DNA polymerases are unidirectional and cannot copy all bases at the 3’ end of a linear duplex (33), resulting in the slow loss of genetic material from the ends of chromosomes with
each replication round
@ critical shortened length: DDR (DNA damage response) induced  triggers p53-dependent G1/S cycle arrest  senescence
Can also gauge aging using telomeres
Research shown ppl > 60 who have longer telomeres than others their age have better heart & immune system health
TWA Medical Center

4. Telomere stability and telomerase expression reactivation allow cells to escape senescence
Cells without cell cycle checkpoints escape senescence and grow and divide
Eventually they enter crisis – 2nd arrest state
Shortened chromosome ends fuse  apoptosis
Cells that escape crisis: telomere stability & reactivation of telomerase expression
BIG step in carcinogenesis maybe
In presence of intact p 53 pathway: mice w/o telomerase don’t get cancer but forced TERT overexpression = increased spontaneous tumors
**Telomerase stability is required for long-term proliferation of tumors
Escape senescence by activating telomerase OR alternative mech to maintain telomeres

5. TERT overexpression observed in many types of human cancer
In presence of intact p 53 pathway: mice w/o telomerase don’t get cancer but forced TERT overexpression = increased spontaneous tumors
Overexpression of the hTERT gene causes (1) immortalization of primary human cells; (2) proliferation of tumor cells, (3) tumor metastasis and invasive potential and (4) maintenance of stem cell pluripotency. Repression of hTERT results in telomere loss and the following: (5) non-prevention of stress-induced aging of normal cells and (6) apoptosis of the tumor cell.
Ex vivo studies show telomerase expressed in 90% malignant tumors
Biomarker?
Telomerase levels correlate w severity of prognosis for different tumor types
Polymorphisms in 5p1533 locus – encodes TERT – amplified in many types of human cancer
TERT variability  cancer predisposition
Molecular mechanisms unknown
Labiotech

6. Mice without telomerase exhibit chromosomal abnormalities
Telomerase KO mice (Lansdorp)
Telomeres 5-10x longer in murine cells also faster senescence in culture
No telomerase detected in homozygous KO animals- single telomerase RNA gene in murine genome
Surprise- KO mice alive and normal  telomerase not essential for maintaining telomeres in somatic cells of renewing tissues ALSO fertile- multiple subseqent generations of KO animals -> not necessary to maintain telomeres in germ line
Difference in telomere length seen by quantitative fluorescence in situ hybridization (Q-FISH)
Telomerase essential to maintain telomere LENGTH in germ line- w/o it repeats lost 2-7kb/generation
Chromosomes w/o detectable TTAGGG least one end from gen 2 and higher
Increasing frequency and unstable
Figure- chromosomal abnormalities in embryonic fibroblasts from 6th gene telomerase null mice
Yellow & orange- CCCTAA peptide nucleic acid (PNA) sequence probes for telomeress
Blue- DAPI stained chromosomal DNA
* = Robertsonian fusion products
# = no detectable TTAGGG
(Adobe Photoshop)
Other studies
Used recombinant adeno-associated viruses (rAAV) vectors to integrate into host genome at very low rates (Boccardi)
mTERT DOES NOT promote cancer bc episodmal vector would be lost in rapidly dividng cells
Using AAV serotype of high tropism & capable of crossing blood brain barrier : AAV9-mTERT virus via tail vein in normal adult mice 1 & 2 yrs old= detect overexpression in liver, kidney, lung, heart, brain, muscle
Didn’t display higher cancer incidence than normal mice => In short lived mice this approach is safe
Less osteoporosis & insulin R
Better metabolic functions, cognitive skills, & physical performances
Median lifespan increased by up to 24% in 1-yr olds & 13% in 2 yr olds
Mice have longer telomeres than humans  still shorten w age (and contribute to aging probably)
In presence of intact p 53 pathway: mice w/o telomerase don’t get cancer but forced TERT overexpression = increased spontaneous (Mocellin)
Journal of Cell Biology

7. Telomerase-targeting anticancer strategies
Targeted inhibition of telomerase  critically short telomeres?

8. Clinical trials of telomerase-targeting anticancer therapies
As of 2013
b: stopped in Sep 2012 (worse survival outcome)
TRENDS in Molecular Medicine

9. References
Alonso, Laura, and Elaine Fuchs. "Stem cells in the skin: waste not, Wnt not." Genes & development (2003): Bancroft, Dani. "Novel Infant Cancer Biomarker Discovered in Cologne." Labiotech.eu. Labiotech, 14 Oct Web. Boccardi, Virginia, and Utz Herbig. “Telomerase gene therapy: a novel approach to combat aging.” EMBO molecular medicine 4.8 (2012): Chiba, Kunitoshi, et al. “Cancer-associated TERT promoter mutations abrogate telomerase silencing.” Elife 4 (2015): e07918 Lansdorp, Peter M. "Lessons from mice without telomerase." The Journal of cell biology (1997): Mocellin, Simone, Karen A. Pooley, and Donato Nitti. "Telomerase and the search for the end of cancer." Trends in molecular medicine 19.2 (2013): Recharge Biomedical. Telomeres. N.p., n.d. Web Science. Telomere Diagnostics. N.p., n.d. Web Shay/Wright Lab. "Facts About Telomeres and Telomerase." UT Southwestern Medical Center. N.p., n.d. Web. TWA Medical Center. "Telomerase Activation with TA-65." Telomerase Activation with TA-65. N.p., n.d. Web. Zakian, Virginia A. “Life and cancer without telomerase.” Cell 91.1 (1997): 1-3.