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Blood, Vol. 95 No. 10 (May 15), 2000:
pp. 3214-3218
NEOPLASIA
From the Cancer Chemotherapy Center, Japanese Foundation for Cancer
Research, Tokyo, and the Institute of Molecular and Cellular
Biosciences, The University of Tokyo, Tokyo, Japan.
Abnormality in the machinery of apoptosis is associated with a
resistant phenotype of the tumor cell to chemotherapy. To determine the
molecular basis of resistance to antitumor agent-induced apoptosis, we
performed a complementary DNA (cDNA) subtractive hybridization with
messenger RNA (mRNA) from human monocytic leukemia U937 and its variant
UK711, which is resistant to apoptosis induced by antitumor agents. We
found that glyoxalase I (GLO1), an enzyme that
detoxifies methylglyoxal, is selectively overexpressed in the
apoptosis-resistant UK711 cells. The GLO1 enzyme activity was
significantly elevated in UK711 and UK110 cells, another drug-resistant mutant, as well as in K562/ADM, adriamycin-resistant leukemia cells,
compared with their parental cells. When overexpressed in human Jurkat
cells, GLO1 inhibited etoposide- and adriamycin-induced caspase
activation and apoptosis, indicating the involvement of GLO1 in
apoptosis suppression caused by these drugs. Moreover, cotreatment with
S-p-bromobenzylglutathione cyclopentyl diester (BBGC),
a cell-permeable inhibitor of GLO1, enhanced etoposide-induced apoptosis in resistant UK711 cells but not in parental U937 cells. Taken together, these results indicate that GLO1 is a resistant factor
to antitumor agent-induced apoptosis in human leukemia cells and that
the GLO1 inhibitor could be a drug resistance-reversing agent.
(Blood. 2000;95:3214-3218)
Emergence of resistance to antitumor agents is a serious
problem in cancer chemotherapy. One mechanism of drug resistance is the
modulation of gene expression. Overexpression of drug transporter proteins, such as P-glycoprotein and multidrug resistance-associated protein (MRP), has been observed in a number of tumor cells resistant to antitumor agents.1,2 Other reports show that the
quantitative reduction of DNA topoisomerase I or II, molecular targets
of antitumor agents such as camptothecin (CPT) and etoposide (VP-16),
respectively, causes resistance to these agents to
develop.3,4 In clinical situations, however, many tumors
have been reported to acquire resistance to chemotherapy without
undergoing these changes, suggesting that another mechanism could be involved.
Apoptosis is an active cell death mechanism that plays a role in
several biologic processes. Various antitumor agents have been reported
to elicit apoptosis in tumor cells.5,6 This implies that a
blockade of the apoptosis signaling could be another mechanism for
multidrug resistance. We previously isolated UK711,5 a
mutant from human monocytic leukemia U937 cells, which showed resistance to apoptosis induced by such antitumor agents as VP-16, CPT,
adriamycin (ADM), mitomycin C, and 1-( To identify genes that are responsible for apoptosis resistance of the
mutant cells upstream of caspase protease activation, we used a
complementary (cDNA) subtraction approach using messenger (mRNA) from
U937 and UK711 cells. As a result of the screening, we found that the
glyoxalase I (GLO1) gene was overexpressed
in UK711 cells. Here, we report that GLO1 was involved in apoptosis resistance to antitumor agents in human leukemia cells. Moreover, we
demonstrated that the GLO1 inhibitor sensitized cells resistant to the
chemotherapeutic agent.
Materials
Cell lines and cell culture
Complementary DNA subtractive hybridization mRNA was prepared from 108 of U937 or UK711 cells using a Fast Track mRNA isolation kit (Invitrogen, Carlsbad, CA). Subtracted cDNA fragments were obtained from mRNA of both U937 and UK711 cells using a PCR-Select cDNA subtraction kit (Clontech Laboratories, Tokyo, Japan). The cDNA fragments were further tested for differential expression by dot-blot analysis. Finally, the expression was confirmed by Northern blot analysis, as described previously.14 Positive cDNA fragments were subcloned into pCRII vector (Invitrogen) and sequenced with an ABI PRISM Dye Primer Cycle Sequencing Kit (Applied Biosystems, Chiba, Japan) and an ABI PRISM 310 Genetic Analyzer (Applied Biosystems).Glyoxalase I assay Cytosolic fractions were prepared as previously described.15 Briefly, the cells were lysed in phosphate-buffered saline (PBS) containing 1 mmol/L phenylmethylsulfonyl fluoride (PMSF) by freezing and thawing and sonication, and then being centrifuged at 12 000g for 20 minutes. The supernatant was used as the cytosolic fraction. The GLO1 assay was performed in 7.9 mmol/L methylglyoxal, 1 mmol/L glutathione, 14.6 mmol/L magnesium sulfate, and 182 mmol/L imidazole-HCl (pH 7.0). An increase in absorbance at 240 nm due to the formation of S-D-lactoylglutathione was measured with each cytosolic fraction.Analysis of DNA fragmentation After treatment with the drugs, cells were suspended in 20 µL of 50 mmol/L Tris-HCl (pH8.0), 10 mmol/L ethylenediamine tetraacetic acid (EDTA), and 0.5 mg/mL proteinase K (Sigma). They were incubated at 50°C for 1.5 hours, then 10 µL of 2 µg/mL RNase A solution was added, and the suspension was incubated for another 1.5 hours. The sample was mixed with 10 µL of the preheated (70°C) solution containing 10 mmol/L EDTA (pH 8.0) 1% low-melting point agarose, 0.25% bromphenol blue, and 40% sucrose. DNA was analyzed by electrophoresis in 2% agarose gels, stained with ethidium bromide, and then photographed on an ultraviolet transilluminator.Assay of drug sensitivity The sensitivity of tumor cell lines to drugs was evaluated by the inhibition of cell growth after 24-hour incubation with various concentrations of drugs. The number of viable cells was estimated by the [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium] (MTS) method17 using CellTiter 96 AUueous 1 solution cell proliferation assay (Promega, Tokyo, Japan). The 50% inhibitory concentration (IC50) values were determined graphically from growth inhibition.Transfection of glyoxalase I cDNA of GLO1 open-reading frame was inserted into pFLAG (5a)-CMV expression vector. The pFLAG (5a)-CMV-GLO1 plasmid DNA was transiently transfected using DMRIE-C reagent (Gibco BRL), according to manufacturer's instructions, together with pHook-1 plasmid DNA (Invitrogen), which encodes a single-chain antibody fusion protein directed to the hapten phOx (4-ethoxymethlene-2-phenyl-2-oxazolin-5-1) and thereby allows the selective isolation of transfected cells with magnetic beads coated with phOx.18 GLO1-transfected cell populations were isolated on phOx-coated magnetic beads with the Capture-Teckit (Invitrogen). Cotransfection efficiency was more than 90%, as determined by -galactosidase staining.
Flow cytometry and nuclear staining assays After drug treatment, harvested cells were fixed in 70% ethanol. After treatment with 2 mg/mL RNase A solution, the cells were stained in 50 µg/mL of propidium iodide (PI) solution and then analyzed with a Becton Dickinson FACScan flow cytometer (Braintree, MA). To assay the nuclear morphology, harvested cells were washed with PBS and stained with 1 mmol/L Hechest 33342 for 15 minutes. The nuclear morphology of the cells was visualized using a fluorescene microscope (UFX-II A; Nikon, Tokyo, Japan).Measurement of caspase activity Drug-treated cell lysates were incubated with 20 mmol/L Acetyl-Asp-Glu-Val-Asp- -(4-methyl-coumaryl-7-amide) (Ac-DEVD-MCA) at
37°C for 120 minutes, and the release of AMC was monitored by a
spectrofluorometer (F-2500; Hitachi, Tokyo, Japan), using an excitation wavelength of 380 nm and an emission wavelength of 460 nm.
Western blot analysis Western blot analysis was performed using an anti-FLAG (M2) monoclonal antibody (Sigma) according to the instructions of the manufacturer. Briefly, cell lysates were electrophoresed by SDS-PAGE and then transferred to a nitrocellulose membrane. After blocking, the membrane was incubated with primary antibody for 2 hours at 25°C. Detection was accomplished using an antimouse Ig-peroxidase conjugated and the enhanced chemiluminescene detection system (Amersham, Tokyo, Japan).Statistics Values are reported as means ± SD in triplicate. Statistical analysis of the data were performed using an unpaired Student t test.
Overexpression of glyoxalase I in drug-induced apoptosis-resistant leukemia cells Previously, we isolated several mutants from U937 cells that showed resistance to multiple apoptosis inducers. Among them, UK711 showed significant resistance to apoptosis induced by several antitumor agents, including VP-16 and ADM (Figure 1A), but not by death-receptor stimulation such as TNF- or anti-Fas antibody (data not shown).5
Because the initial DNA damage caused by the drugs was comparable in
U937 and UK711 cells, cellular signaling leading to apoptosis could
differ between the 2 cell lines.5
Effect of overexpression of glyoxalase I on antitumor
agent-induced apoptosis
Reversal of apoptosis resistance to antitumor agents by glyoxalase I
inhibitor
Methylglyoxal is one of the side products of glycolysis that reacts
with such biologic compounds as DNA, RNA, and protein in
cells.19 Modifying DNA by means of methylglyoxal induced single-strand breaks and DNA-protein cross-link and
cytotoxity.19 GLO1 is ubiquitously distributed in all
mammalian cells and plays an important role in catalyzing the
formation of S-D-lactoylglutathione from methylglyoxal and
glutathione.20 Some groups have reported that tumor tissue
expressed higher GLO1 activity than normal tissue. In particular,
abnormal expression or activity of GLO1 has been demonstrated in human
colon, renal, and prostate cancers.21-24 Thus, the increase
of GLO1 expression has been shown to be associated with increased
proliferative activity of the tumor. In this study, we found that, in
antitumor agent-resistant leukemia cells, GLO1 was frequently
overexpressed (Figure 1, Tables 1 and 2). Further, we found that GLO1
activity was also higher in CPT-resistant human colon
cancer3 (HT-29/CPT) and CPT-resistant human gastric cancer cells3 (St-4/CPT) than their parental cell lines (data not shown). Because these mutant cell lines were cell populations that
survived after treatment with an anticancer agent, it is possible that
the development of drug resistance is accompanied by this
overexpression of GLO1. These results suggested that GLO1 could be not
only a tumor marker but also a drug resistance marker.
We thank Drs H. Seimiya, N. Fujita, and A. Tomida for helpful discussions.
Submitted September 7, 1999; accepted January 20, 2000.
Supported in part by the Program for Promotion of Fundamental Studies
in Health Sciences of the Organization for Pharmaceutical Safety and
Research of Japan, Grants-in-Aid for Cancer Research and Scientific
Research from the Ministry of Education, Culture and Science of Japan,
a grant from the Vehicle Racing Commemorative Foundation, and Public
Trust Haraguchi Memorial Cancer Research Fund.
Reprints: Takashi Tsuruo, Institute of Molecular and Cellular
Biosciences, The University of Tokyo, Tokyo, 1-1-1 Yayoi, Bunkyo-ku,
Tokyo 113-0032, Japan; e-mail: ttsuruo{at}iam.u-tokyo.ac.jp.
The publication costs of this
article were defrayed in part by
page charge payment. Therefore,
and solely to indicate this fact,
this article is hereby marked
"advertisement"
in accordance with 18 U.S.C.
section 1734.
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