Plk1 Phosphorylation of TRF1 Is Essential for Its Binding to Telomeres

Zhao-Qiu Wu,Xiaoming Yang,Gregory Weber,Xiaoqi Liu

doi:10.1074/jbc.m803304200

Abstract

In a search for Polo-like kinase 1 (Plk1) interaction proteins, we have identified TRF1 (telomeric repeat binding factor 1) as a potential Plk1 target. In this communication we report further characterization of the interaction. We show that Plk1 associates with TRF1, and Plk1 phosphorylates TRF1 at Ser-435 in vivo. Moreover, Cdk1, serving as a priming kinase, phosphorylates TRF1 to generate a docking site for Plk1 toward TRF1. In the presence of nocodazole, ectopic expression of wild type TRF1 but not TRF1 with alanine mutation in the Plk1 phosphorylation site induces apoptosis in cells containing short telomeres but not in cells containing long telomeres. Unexpectedly, down-regulation of TRF1 by RNA interference affects cell proliferation and results in obvious apoptosis in cells with short telomeres but not in cells with long telomeres. Importantly, we observe that telomeric DNA binding ability of TRF1 is cell cycle-regulated and reaches a peak during mitosis. Upon phosphorylation by Plk1 in vivo and in vitro, the ability of TRF1 to bind telomeric DNA is dramatically increased. These results demonstrate that Plk1 interacts with and phosphorylates TRF1 and suggest that Plk1-mediated phosphorylation is involved in both TRF1 overexpression-induced apoptosis and its telomeric DNA binding ability.

Highlights

Composed of repetitive DNA sequences of TTAGGG arrays and telomere-binding proteins [1], telomeres are specialized DNA structures positioned at the termini of eukaryotic chromosomes [2]
We found that TRF1 is localized in the nuclear fraction, and its protein level in asynchronous cells is similar to that in mitotic cells, suggesting that TRF1 protein level is not cell cycle-regulated in HeLa cells (Fig. 1A)
In a search for Polo-like kinase 1 (Plk1)-interacting proteins, we observed the interaction between Plk1-PBD and TRF1

Summary

Introduction

Composed of repetitive DNA sequences of TTAGGG arrays (in vertebrates) and telomere-binding proteins [1], telomeres are specialized DNA structures positioned at the termini of eukaryotic chromosomes [2]. Upon phosphorylation by Plk1 in vivo and in vitro, the ability of TRF1 to bind telomeric DNA is dramatically increased. These results demonstrate that Plk1 interacts with and phosphorylates TRF1 and suggest that Plk1-mediated phosphorylation is involved in both TRF1 overexpression-induced apoptosis and its telomeric DNA binding ability.

Results

Conclusion