Structural insights into POT1-TPP1 interaction and POT1 C-terminal mutations in human cancer

Cong Chen,Peili Gu,Min Huang,Chandan Kumar‐Sinha ,Lajos Pusztai,Sandy Chang,Shaohua Shi,Catherine C L Wong,Na Li,Hong Sun,Cuiying Fan,Qingguo Gong,Rekha Rai,Jian Wu,Lijie Wu,Shubin Niu ,Junhui Peng,Xianyun Chen,Rongguang Zhang,Ming Lei

doi:10.1038/ncomms14929

Abstract

Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension. However, how POT1 interacts with TPP1 remains unknown. Here we present the crystal structure of the C-terminal portion of human POT1 (POT1C) complexed with the POT1-binding motif of TPP1. The structure shows that POT1C contains two domains, a third OB fold and a Holliday junction resolvase-like domain. Both domains are essential for binding to TPP1. Notably, unlike the heart-shaped structure of ciliated protozoan Oxytricha nova TEBPα–β complex, POT1–TPP1 adopts an elongated V-shaped conformation. In addition, we identify several missense mutations in human cancers that disrupt the POT1C–TPP1 interaction, resulting in POT1 instability. POT1C mutants that bind TPP1 localize to telomeres but fail to repress a DNA damage response and inappropriate repair by A-NHEJ. Our results reveal that POT1 C terminus is essential to prevent initiation of genome instability permissive for tumorigenesis.

Highlights

Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension
The crystal structures of the two N-terminal OB folds of POT1 bound with telomeric ssDNA and the OB fold of TPP1 suggested that POT1 and TPP1 are the homologues of TEBPa and b subunits, respectively[4,15,24,25,26,27]
In addition to familial melanoma (FM), we investigated the possibility that mutations in POT1C might be present in other human cancers

Summary

Introduction

Mammalian shelterin proteins POT1 and TPP1 form a stable heterodimer that protects chromosome ends and regulates telomerase-mediated telomere extension. We present the crystal structure of the C-terminal portion of human POT1 (POT1C) complexed with the POT1-binding motif of TPP1. POT1 and TPP1 function together by forming a stable heterodimer that protects chromosome ends and regulates telomerase activity[15,16,17,18]. POT1 was initially identified through its limited sequence similarity to the a-subunit of the ciliated protozoan Oxytricha nova TEBPa–b complex, the first characterized telomeric ssDNA-binding protein complex[4]. TPP1 interacts with both TIN2 and POT1, forming an intimate connection within the shelterin complex between the duplex and ss telomeric DNAs17,29,30. A Q623H mutation in the POT1 C terminus identified in FM raises the intriguing possibility that the POT1 C terminus might play a role in maintaining telomere stability distinct from that of the N-terminal two OB folds[36]

Methods

Results

Conclusion