POT1-TPP1 differentially regulates telomerase via POT1 His266 and as a function of single-stranded telomere DNA length

Abstract

SignificanceTelomere length homeostasis is an important mechanism for maintaining genomic stability. Telomere length is regulated by numerous events that include protein–DNA interactions, the length and structure of telomere DNA, and recruitment of telomerase. Here we used hydroxyl radical footprinting to identify environmental changes in the telomere end-binding heterodimer, POT1-TPP1, as a function of telomere length. Our data identified a specific residue (histidine 266) of the POT1 protein that reports differences in solvent accessibility as a function of telomere DNA length. We further show that the chronic lymphocytic leukemia-related H266L POT1 mutation disrupts the ability of POT1-TPP1 to negatively regulate telomerase activity in vitro and in cancer cells.

POT1-TPP1 telomere length regulation and disease

“…3 B and C), exhibited a reduction in POT1C-TPP1 binding, consistent with the structural data showing that these residues made direct contacts with TPP1. Biochemical studies show that these mutant proteins bind telomeric DNA with lower affinity than the wild type POT1 [79] . A decrease in DNA binding is expected to translate into defective telomere capping and an increase in DDR.…”

“…It is worth noting that short telomeres are preferentially extended by telomerase [78] . Long telomeres are coated with a large number of POT1-TPP1 complexes which render the telomeric overhang inaccessible to telomerase thus inhibiting telomerase-dependent telomere extension [79] . These results may suggest a model whereby POT1-TPP1 recruits and stimulates telomerase recruitment during late S-phase triggering telomere extension.…”

Role of POT1 in Human Cancer

“…Both cell lines and patient samples harboring POT1 mutations tend to have evidence of genomic instability, manifesting as increased telomere fragility, DDR, chromosomal aberrations, and alternative non-homologous end joining-mediated chromosomal fusions. These findings suggest a connection between the presence of POT1 mutations and the occurrence of telomere dysfunction and genomic instability [ 50 , 69 , 70 , 72 , 89 , 93 , 99 , 109 , 110 ].…”

Structural Features of Nucleoprotein CST/Shelterin Complex Involved in the Telomere Maintenance and Its Association with Disease Mutations

“…Altogether, these data strongly support a role for TPP1 p.G223V mutant in promoting leukemia cell maintenance. Interestingly, recurrent somatic mutations in the OB-fold domains of POT1 reported causing telomere dysfunction in CLL signifying that alteration of TPP1-telomere binding could lead to genomic instability and cancer [114].…”