CEITEC scientists revealed vital evidence to understand the mechanism of telomere protection


In the nucleus of our cells, DNA molecules are packed into structures called chromosomes.


Telomeres are segments of the DNA molecule, which act like protective plugs at the ends of chromosomes.


Telomeres are analogous to the protective aglets of shoelaces.



When the aglet wears off, the lace will unsettle. Similarly, shortening of telomere will lead to DNA damage – the onset of aging, cancer, and eventually cell death.




Telomeres shorten after every round of cell division. Telomerase reverts shortening of telomeres in cancer cells. (source: Dr. Ctirad Hofr)



How would you protect the telomeres?


Telomerase is an enzyme that makes sure that the vital length of the telomeres is maintained as the cell continues to divide.


Is that sufficient? No! A multi-protein complex called shelterin plays an essential role in telomere protection. It also positively regulates the activity of telomerase.


Shelterin regulates the access of telomerase to very ends of telomeric DNA (source: Dr. Ctirad Hofr)




The hero of this story is the shelterin complex.



The research group of Dr. Ctirad Hofr adds critical know-how (1) to properly understand the formation of this protective complex.


Dr. Hofr mentioned, “I started my research career at the DNA level, characterizing the effects of anti-cancer drugs on DNA structure, and also on DNA thermodynamic parameters. But later on, I accepted the challenge to work on something more sensitive and challenging to work on – proteins. I got fascinated by telomerase and cell aging and continued on that path.”


The Hofr team – LifeB (Left to right): Dr. Ctirad Hofr, Pavel Veverka, Tomaš Janovič (the lead author of the study), and Martin Stojaspal



New information, the study brings


Dr. Hofr passionately states, “We studied the assembly of human shelterin, which protects the very ends of telomeric DNA and also regulates the access of telomerase. In simpler terms, it regulates the elongation of the telomeric DNA. We looked into the assembly of this complex at the single-molecule level. It is the major highlight of the story.”


“We have utilized the technique named Fluorescence cross-correlation spectroscopy to study shelterin assembly. It was known that the complex of three key proteins –TRF1, TRF2, and TIN2 forms the core hub of the shelterin complex.”


“The wow moment came about when we discovered something that nobody had observed before. These two proteins – TRF1 and TRF2, which are more or less similar – compete for one site on the TIN2 protein. TRF1 and TRF2, both are life-essential; if you miss one, another cannot compensate.”



TPP1 – the fourth keystone to achieving a stable shelterin


“The activity of telomerase is controlled by one of the shelterin proteins, TPP1. This is, in reality, the fourth protein, which is vital for the complete assembly of the shelterin."


"We revealed at the single-molecule level that TPP1 upon binding to TIN2 encourages changes that expand the binding capacity of TIN2. Thus, TPP1 assists TIN2 to accommodate both TRF1 and TRF2 simultaneously.”




A model representing TPP1 requirement for simultaneous binding of TRF1 and TRF2 to TIN2 (source: Dr. Ctirad Hofr)




The bigger picture and future directions


“We have recently shown (2) the benefits of our research, in the light of anticancer therapy."


"We tried to find the weakest points of shelterin assembly that could be utilized in anti-cancer drug design. If you want to decrease the activity of cancer cells, the practical idea would be to reduce the action of telomerase. Most cells in the human body are somatic cells that do not divide. The somatic cell have inactive telomerase. On the contrary, cancerous cells divide widely and need active telomerase to trick molecular mechanisms strictly regulating the number of healthy cell divisions.”


“TPP1 guides the telomerase to reach the telomere. To stop telomerase contacting the telomere, you need to eliminate TPP1 interaction with telomerase; thus, TPP1 could be an excellent anticancer drug-target,” adds Dr. Hofr.


The Hofr team avidly expressed their future plans, “We would like to use our methodology also for proteins that are important for glioblastoma development – the most aggressive brain cancer in adults. The next target of our research is the REST transcription factor that is essential for glioblastoma growth.”



Acknowledgements

The Czech Science Foundation (16-20255S and 19-18226S to C.H.) has primarily supported this research. The research has been carried out with institutional support of the Ministry of Education, Youth and Sports of the Czech Republic (MEYS CR) under the project CEITEC 2020 (LQ1601). CIISB research infrastructure project LM2015043, funded by MEYS CR, is acknowledged for the financial support of the measurements at the CF Proteomics and CF Biomolecular Interactions and Crystallization, and the CF CELLIM of CEITEC supported by the Czech-BioImaging RI project - LM2015062 funded by MEYS CR.


References

  1. Janovič, T.; Stojaspal, M.; Veverka, P.; Horáková, D.; Hofr, C. Human telomere repeat binding factor TRF1 replaces TRF2 bound to shelterin core hub TIN2 when TPP1 is absent. J. Mol. Biol. 2019. https://doi.org/10.1016/j.jmb.2019.05.038
  2. Veverka, P.; Janovič, T.; Hofr, C. Quantitative Biology of Human Shelterin and Telomerase: Searching for the Weakest Point. Int. J. Mol. Sci. 2019, 20, 3186. https://doi.org/10.3390/ijms20133186



Authors: Somsuvro Basu and Ctirad Hofr