Rap1 is indispensable for TRF2 function in etoposide-induced DNA damage response in gastric cancer cell line.

X Li,Y Li,L Yang,W Liu,D Fan,H Ning,J Wang,L Zhang,H Wang,J Li,H Wen

doi:10.1038/oncsis.2015.1

Abstract

The telomeric protein TRF2, involving in telomeric and extratelomeric DNA damage response, has been previously reported to facilitate multidrug resistance (MDR) in gastric cancer cells by interfering ATM-dependent DNA damage response induced by anticancer drugs. Rap1 is the TRF2-interacting protein in the shelterin complex. Complex formation between Rap1 and TRF2 is essential for their function in telomere and end protection. Here we focus on the effects of Rap1 on TRF2 function in DNA damage response induced by anticancer drugs. Both Rap1 and TRF2 expression were upregulated in SGC7901 and its MDR variant SGC7901/VCR after etoposide treatment, which was more marked in SGC7901/VCR than in SGC7901. Rap1 silencing by siRNA in SGC7901/VCR partially reversed the etoposide resistance. And Rap1 silencing partially reversed the TRF2-mediated resistance to etoposide in SGC7901. Rap1 silencing did not affect the TRF2 upregulation induced by etoposide, but eliminated the inhibition effect of TRF2 on ATM expression and ATM phosphorylation at serine 1981 (ATM pS1981). Furthermore, phosphorylation of ATM targets, including γH2AX and serine 15 (S15) on p53, were increased in Rap1 silencing cells in response to etoposide. Thus, we confirm that Rap1, interacting with TRF2 in the shelterin complex, also has an important role in TRF2-mediated DNA damage response in gastric cancer cells treated by etoposide.

Highlights

The telomeric protein TRF2 has been evaluated to be a generalDNA-repair factor relevant with both telomeric and extratelomeric DNA damage response.[1,2] TRF2 accumulates at double-strand break sites in the first few seconds after irradiation as an early response to DNA damage.[3]
It showed that TRF2 promoted multidrug resistance (MDR) of gastric cancer cells by interfering DNA damage response induced by anticancer drugs.[7]
TRF2 and Rap[1] expression induced by etoposide treatment in gastric cancer cells In previous work, we reported that etoposide or adriamycin (ADR) treatment upregulated TRF2 expression in gastric cancer cells, which occurred at early stage of DNA damage response and showed dose-dependency

Summary

Introduction

DNA-repair factor relevant with both telomeric and extratelomeric DNA damage response.[1,2] TRF2 accumulates at double-strand break sites in the first few seconds after irradiation as an early response to DNA damage.[3] Phosphorylated by ataxia-telangiectasia mutated (ATM), TRF2 in turn inhibits activation of ATMdependent DNA damage response.[4,5] TRF2 interacts with doublestrand break repair proteins and involves in homologous recombination repair of nontelomeric double-strand breaks.[6] In our previous study, it showed that TRF2 promoted multidrug resistance (MDR) of gastric cancer cells by interfering DNA damage response induced by anticancer drugs.[7]. We aimed to investigate changes of Rap[1] and TRF2 expression in human gastric cells

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