04-07-2012, 12:59 PM
TRF2 Promotes Multidrug Resistance in Gastric Cancer Cells
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INTRODUCTION
Adriamycin (ADR) and etoposide are clinically important chemotherapeutic agents of
malignant tumors, including gastric cancer. The cytotoxic effects are exerted mainly by
inhibiting activity of nuclear DNA topoisomerase, resulting in accumulation of DNA
double-strand breaks (DSBs). Mechanisms of cellular resistance in cancer cells to these
DNA-damaging anticancer drugs have been broadly explored, yet have not been fully
characterized.1,2
Mammalian telomeres are specialized DNA-protein structures localized at the ends of
chromosomes. They are composed of repeated hexanucleotides TTAGGG bound by a
large number of telomere-binding proteins.3 TRF1 and TRF2 are two major telomeric
proteins which ensure proper maintenance of telomeres.4,5 Up to now, there have been
numerous papers focusing on the role of telomerase activity and telomere length in drug
resistance of cancer, but the findings remain controversial.6
MATERIALS AND METHODS
Cell lines and cell culture. Human gastric cancer cell line
SGC7901 was obtained from Academy of Military Medical Science
(Beijing, China). Its multidrug-resistant cell variants, SGC7901/
VCR and SGC7901/ADR, had been prepared and characterized in
our lab previously.10,11 All the cell lines were maintained in RPMI
1640 (GIBCO) supplemented with 10% heat-inactivated fetal calf
serum (GIBCO) and antibiotics at 37°C in a humidified atmosphere
consisting of 5% CO2.
RESULTS
Telomerase activity induced by drug-treatment.
It has been shown that upregulation of telomerase
activity might act as anti-apoptotic mechanisms in
DNA-damage response of malignant cells.7,15 To
test whether telomerase activation can be induced
by anticancer drugs in MDR gastric cancer cells, we
treated SGC7901 and MDR variants with 2 μg/ml,
20 μg/ml, 200 μg/ml, 1000 μg/ml of etoposide or
0.04 μg/ml, 0.4 μg/ml, 4 μg/ml, 20 μg/ml of
ADR. Telomerase activity was measured by
real-time quantitative TRAP assay at 3 h, 6 h, 12 h,
24 h and 36 h. Telomerase activity was found
increased as early as 3 h, and maintained until 12 h;
then decreased (Fig. 1). The upregulation was most
significant at 3 h and showed dose-dependency.