Telomere End-Protection and the Anti-Checkpoint

Cleveland Clinic Foundation, Cleveland OH

Investigators

Abstract

The DNA of organisms from yeast to humans is packaged in linear chromosomes, the ends of which are called telomeres. When chromosomes are broken, the broken ends can be degraded or fused with other chromosomes to cause mutations and diseases such as cancer. Broken chromosomes and telomeres both present DNA ends, but telomeres have special DNA sequences and proteins bound to them that block degradation and fusion. The laboratory recently discovered a new way that cells can distinguish a broken DNA end from a telomere: the Ccq1 protein protects telomere DNA from being degraded. This project will investigate how Ccq1 accomplishes this protection and what other proteins act with Ccq1 in the process. Telomeres play important roles in aging and cancer, and results from this research will provide fundamental new information that can be applied to medicine, agriculture and biotechnology. This project includes community outreach activities that provide laboratory research and training opportunities for undergraduate and high school students during the summer and school year, summer lectures on a broad range of biological topics for these students, and mentoring opportunities for experienced laboratory members. Telomeres are DNA repeat tracts bound by a set of proteins called “shelterin”. This project builds on prior research on the role of individual shelterin proteins in distinguishing a short telomere from a double strand break (DSB), and uses a “proto-telomere” system in the fission yeast Schizosaccharomyces pombe where an inducible nuclease cuts DNA bearing telomere repeats to generate a short telomere or creates a control DSB without telomere repeats. The results yielded a novel function for the shelterin protein Ccq1 in protecting new telomeres from nucleases. A second, surprising discovery involved telomere “anti-checkpoint” activity, which prevents telomeres from activating the damage response to DSBs. Initial findings indicate that Ccq1 anti-checkpoint function is separable from end-protection, and identify other genes that are required for the anti-checkpoint. Using a combination of genetics, chromatin immunoprecipitation and microscopy, Aim 1 will explore and test candidate end-binding proteins for protection of the short telomere. Aim 2 will test the role of Ccq1 and the discovered genes in regulating assembly of the DNA damage signaling complex. The outcomes are expected to provide novel insights into the long-standing question of how cells can distinguish broken DNA ends from telomeres and process them appropriately to maintain genome stability and cellular health. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.