Molecular interactions and regulatory events in telomere maintenance

PROJECT SUMMARY/ABSTRACT All genetic information is stored in DNA that is intricately wrapped by proteins to form chromosomes. Telomeres are the nucleoprotein complexes that cap and protect the ends of chromosomes to prevent them from fraying, fusing together, and degrading. In addition to capping and protecting the ends of chromosomes,

telomeres regulate the recruitment of telomerase, a specialized enzyme that synthesizes telomere DNA to collaborate with replicative polymerases and ensure complete chromosome replication. Over the past several years, multiple single nucleotide polymorphisms have been identified in the genes of telomere end-binding

proteins in patients diagnosed with a range of disorders, including many different types of cancer. These observations indicate that subtle changes in the structure and/or function of telomere proteins contributes to genome instability. POT1 (Protection of Telomeres 1) is the most mutated telomere protein associated with

human disorders. POT1 forms a heterodimeric complex with another telomere end-binding protein, TPP1, to perform diverse but equally critical functions. Specifically, POT1-TPP1 binds to the extreme 3’ end of telomeres and helps to resolve DNA secondary structure, to recruit telomerase to the telomere, and regulate telomerase-

mediated telomere synthesis. In addition, the POT1-TPP1 proteins shield telomere DNA from being recognized and repaired by DNA damage machinery. Finally, the POT1-TPP1 heterodimer exhibits extraordinary sequence specificity that provides discrimination against binding to RNA or to DNA with non-telomere sequence. The

objective of the present proposal is to investigate the multiple and diverse roles of POT1-TPP1 in telomere maintenance. We will further interrogate the intricate details of telomerase-mediated extension of telomere DNA and identify how changes in nucleotide pools affect telomerase function and fidelity. Additionally, we will examine

the role of FDA-approved and developing nucleotide and nucleoside analogs in telomerase rates and fidelity. To accomplish these objectives, we combine structure-function studies to determine the molecular interactions that dictate POT1-TPP1 function and we corroborate the mechanistic studies with cellular outcome. The results from

this investigation will reveal both structural and functional alterations introduced by pathogenic mutations and drug administration and will be used to better understand the diverse functions of specialized telomere proteins and telomerase in maintaining telomere integrity and genomic stability. The project includes a translational

component as we will define the understudied contributions that chemotherapeutic and antiviral agents have on telomere integrity. On a fundamental level, the work performed in this study will shed light on the assembly, organization, and functional motions that regulate chromosome end protection.