title: A critical role for TPP1 and TIN2 interaction in high-order telomeric complex assembly.
abstract: Mammalian telomeric proteins function through dynamic interactions with each other and telomere DNA. We previously reported the formation of a high-molecular-mass telomeric complex (the mammalian telosome) that contains the six core proteins TRF1, TRF2, RAP1, TIN2, POT1, and TPP1 (formerly named PTOP/PIP1/TINT1) and mediates telomere end-capping and length control. In this report, we sought to elucidate the mechanism of six-protein complex (or shelterin) formation and the function of this complex. Through reconstitution experiments, we demonstrate here that TIN2 and TPP1 are key components in mediating the six-protein complex assembly. We demonstrate that not only TIN2 but also TPP1 are required to bridge the TRF1 and TRF2 subcomplexes. Specifically, TPP1 helps to stabilize the TRF1-TIN2-TRF2 interaction and promote six-protein complex formation. Consistent with this model, overexpression of TPP1 enhanced TIN2-TRF2 association. Conversely, knocking down TPP1 reduced the ability of endogenous TRF1 to associate with the TRF2 complex. Our results suggest that coordinated interactions among TPP1, TIN2, TRF1, and TRF2 may ensure robust assembly of the telosome, telomere targeting of its subunits, and, ultimately, regulated telomere maintenance.
authors.affiliation: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: O'Connor
authors.forename: Amin
authors.initials: A
authors.lastname: Safari
authors.forename: Huawei
authors.initials: H
authors.lastname: Xin
authors.forename: Dan
authors.initials: D
authors.lastname: Liu
authors.forename: Zhou
authors.initials: Z
authors.lastname: Songyang
mesh_terms: D000818:Animals; D006367:HeLa Cells; D006801:Humans; D007313:Insecta; D008954:Models, Biological; D009687:Nuclear Proteins / Q000502:physiology; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D000089804:Shelterin Complex; D035182:TATA Box Binding Protein-Like Proteins / Q000502:physiology; D016615:Telomere / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D034501:Telomere-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D035321:Telomeric Repeat Binding Protein 1 / Q000502:physiology; D035341:Telomeric Repeat Binding Protein 2
chemical_list: C495876:ACD protein, human; D009687:Nuclear Proteins; D000089804:Shelterin Complex; D035182:TATA Box Binding Protein-Like Proteins; C504753:TERF2 protein, human; C440868:TINF2 protein, human; D034501:Telomere-Binding Proteins; D035321:Telomeric Repeat Binding Protein 1; D035341:Telomeric Repeat Binding Protein 2