DCTPP1 attenuates the sensitivity of human gastric cancer cells to 5-fluorouracil by up-regulating MDR1 expression epigenetically.

Li-Liang Xia,Yong Zhang,Tao-Tao Liu,Ying Wang,Fei-Fei Song,Ya-Bin Tang,Shu-Jun Wang,Ji-Min Zhu,Ling Xu,Guo-Ping Zhao,Ping Ji

doi:10.18632/oncotarget.11864

Li-Liang Xia, Yong Zhang + Show 9 more

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https://doi.org/10.18632/oncotarget.11864

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Abstract

Gastric cancer (GC) is among the most malignant cancers with high incidence and poor prognoses worldwide as well as in China. dCTP pyrophosphatase 1 (DCTPP1) is overexpressed in GC with a poor prognosis. Given chemotherapeutic drugs share similar structures with pyrimidine nucleotides, the role of DCTPP1 in affecting the drug sensitivity in GC remains unclear and is worthy of investigation. In the present study, we reported that DCTPP1-knockdown GC cell line BGC-823 exhibited more sensitivity to 5-fluorouracil (5-FU), demonstrated by the retardation of cell proliferation, the increase in cell apoptosis, cell cycle arrest at S phase and more DNA damages. Multidrug resistance 1 (MDR1) expression was unexpectedly down-regulated in DCTPP1-knockdown BGC-823 cells together with more intracellular 5-FU accumulation. This was in large achieved by the elevated methylation in promoter region of MDR1 gene. The intracellular 5-methyl-dCTP level increased in DCTPP1-knockdown BGC-823 cells as well. More significantly, the strong correlation of DCTPP1 and MDR1 expression was detectable in clinical GC samples. Our results thus imply a novel mechanism of chemoresistance mediated by the overexpression of DCTPP1 in GC. It is achieved partially through decreasing the concentration of intracellular 5-methyl-dCTP, which in turn results in promoter hypomethylation and hyper-expression of drug resistant gene MDR1. Our study suggests DCTPP1 as a potential indicative biomarker for the predication of chemoresistance in GC.

Highlights

Gastric cancer (GC) is of great threat to human worldwide due to its high incidence and mortality among cancers [1, 2]
Knockdown of dCTP pyrophosphatase 1 (DCTPP1) had no impact on the proliferation of BGC-823 cells in vitro (Figure 1C), it increased the sensitivity of both BGC-823-shRNA1 and BGC-823-shRNA2 cells to 5-FU in vitro with significant decrease in IC50(72h) of 5-FU when compared to BGC-823-negative control (NC) cells (Figure 1D)
The increased sensitivity to 5-FU induced by DCTPP1 knockdown could be partially rescued by transient expression of DCTPP1 in DCTPP1-knockdown BGC-823 cells (Figure 1E and 1F)

Summary

Introduction

Gastric cancer (GC) is of great threat to human worldwide due to its high incidence and mortality among cancers [1, 2]. The overall benefits of chemotherapy are limited due to drug resistance during treatment [5]. To identify new targets involved in drug resistance may foster opportunities to develop new strategies for the improvement of chemotherapy against GC. An array of NTP-PPases targeting non-canonical nucleotides have been identified from prokaryotes to mammalians. They are demonstrated to guarantee genome stability through preventing aberrant incorporation of non-canonical nucleotides into doublestrand DNA during replication, exerting “house-cleaning” function [6, 7]. Certain NTP-PPases are identified in mammalians with similar biological functions, such as dUTPase [11], ITPase [12] and MTH1 [13, 14]. DUTPase and MTH1 are reported to be associated with carcinogenesis and tumor progression [15,16,17,18], potentiating their significance in clinic [16, 19, 20]

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