Telomeri recombination in immortalized human cells

Each round of cell division is associated with the loss of DNA from the very chromosomal end, called telomeres. Telomere homeostasis is essential for limitless proliferation of immortalized cells. Without such a mechanism cells would exhaust their telomere reserve, like normal somatic cells, with cell death being the inevitable consequence. To date we know about two mechanisms of telomere homeostasis. The first is achieved by telomerase, an enzyme that adds telomeric repeats onto chromosomal ends thereby compensating for the replication associated loss of telomeric DNA. However, there is a second mechanism present in vitro as well as in vivo that is also capable of telomere length control, commonly known as the ALT pathway (alternative lengthening of telomeres). This second mechanism is characterized by the complete lack of telomerase expression despite the fact that these cells are immortal. It is also characterized by the typical heterogeneity of telomere length with chromosomal ends having very long and other chromosomal ends having extremely short telomeric ends. Little is known about the ALT pathway except the fact that the mechanism of telomere length control is based on homologous recombination. My research proposal deals with the molecular mechanism of homologous recombination at telomeric ends in human cells. Specifically I would like to explore whether or not there are different types of homologous recombination mechanisms (namely intra-telomeric and inter-telomeric recombination) present in human ALT cells. Furthermore I would like to address if thesedifferent types of recombination mechanisms serve different functions in ALT pathway cells. By doing so, I intend to establish an experimental cell system that will allow to dissect intertelomericfrom intra-telomeric recombination. The results from the experiments proposed will help to identify proteins involved in the engagement and the maintenance of homologous recombination at telomeric ends. This will further lead the way to device new diagnostic tools as well as new molecular targeted therapies for ALT tumors. The circumstance that little is known about the ALT pathway and the consequent lack of a specific ALT marker hampers diagnosis of ALT positive tumors dramatically. Disruption of telomere homeostasis is an intriguing new therapeutic concept. While anti-telomerase therapy is at the verge of entering clinical trials there is still no concept for targeting telomeric recombination in ALT tumors. More basic research is therefore needed to explore the mechanisms of telomeric recombination and to provide the basis for molecular targeted therapies.

Each round of cell division is associated with the loss of DNA from the very chromosomal end, called telomeres. Telomere homeostasis is essential for limitless proliferation of immortalized cells. Without such a mechanism cells would exhaust their telomere reserve, like normal somatic cells, with cell death being the inevitable consequence. To date we know about two mechanisms of telomere homeostasis. The first is achieved by telomerase, an enzyme that adds telomeric repeats onto chromosomal ends thereby compensating for the replication associated loss of telomeric DNA. However, there is a second mechanism present in vitro as well as in vivo that is also capable of telomere length control, commonly known as the ALT pathway (alternative lengthening of telomeres). This second mechanism is characterized by the complete lack of telomerase expression despite the fact that these cells are immortal. It is also characterized by the typical heterogeneity of telomere length with chromosomal ends having very long and other chromosomal ends having extremely short telomeric ends. Little is known about the ALT pathway except the fact that the mechanism of telomere length control is based on homologous recombination. My research proposal deals with the molecular mechanism of homologous recombination at telomeric ends in human cells. Specifically I would like to explore whether or not there are different types of homologous recombination mechanisms (namely intra-telomeric and inter-telomeric recombination) present in human ALT cells. Furthermore I would like to address if thesedifferent types of recombination mechanisms serve different functions in ALT pathway cells. By doing so, I intend to establish an experimental cell system that will allow to dissect intertelomericfrom intra-telomeric recombination. The results from the experiments proposed will help to identify proteins involved in the engagement and the maintenance of homologous recombination at telomeric ends. This will further lead the way to device new diagnostic tools as well as new molecular targeted therapies for ALT tumors. The circumstance that little is known about the ALT pathway and the consequent lack of a specific ALT marker hampers diagnosis of ALT positive tumors dramatically. Disruption of telomere homeostasis is an intriguing new therapeutic concept. While anti-telomerase therapy is at the verge of entering clinical trials there is still no concept for targeting telomeric recombination in ALT tumors. More basic research is therefore needed to explore the mechanisms of telomeric recombination and to provide the basis for molecular targeted therapies.