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 Previous Article | Table of Contents | Next Article 
Blood, Vol. 92 No. 2 (July 15), 1998:
pp. 567-573
Telomerase Activity in Hodgkin's Disease
By
Karl-Fredrik Norrback,
Gunilla Enblad,
Martin Erlanson,
Christer Sundström, and
Göran Roos
From the Departments of Pathology and Oncology, Umeå University,
Umeå, Sweden; and the Departments of Oncology and Pathology, Uppsala
University, Uppsala, Sweden.
 |
ABSTRACT |
Telomere maintenance executed by the action of telomerase seems to
be a prerequisite for immortalization. Telomerase is found in most cell
lines and malignant tumors. A telomerase-independent mechanism for
telomere maintenance in Hodgkin's disease has been proposed in the
absence of detectable telomerase activity. In this study, telomerase
activity was detected in 31 of 77 Hodgkin's disease samples and a
strong correlation between eosinophilia and absence of detectable
telomerase activity was found. Purified eosinophils and specifically
eosinophil-derived neurotoxin and eosinophilic cationic protein, both
ribonucleases, were found to degrade telomerase. Purified neutrophils
also exhibited weak telomerase degradative activity. Reanalysis of
previously telomerase-negative Hodgkin's disease samples with
eosinophilia using ribonuclease inhibitors resulted in the detection of
telomerase activity. Ribonuclease-containing cells in vivo thus have a
considerable impact on the detectability of telomerase. In Hodgkin's
disease samples without eosinophilia, 24 of 27 exhibited telomerase
activity at decreased levels compared with non-Hodgkin's lymphomas and
at increased levels compared with reactive nodes indicative of a
telomerase positive tumor component in Hodgkin's disease. Telomerase
positivity of the Hodgkin's and Reed-Sternberg cells in vivo was also
supported by high levels of telomerase expression in Hodgkin's disease
cell lines. Based on our data, Hodgkin's lymphomas are potential
targets for antitelomerase therapy.
| |
INTRODUCTION |
THE TELOMERIC ENDS consist of DNA
repeats, in humans (TTAGGG)n, and associated proteins with
functional relevance for the integrity of chromosomes, chromosomal
localization, and gene expression.1-3 Because of the
properties of DNA-polymerase, lagging strand synthesis is incomplete,
leading to a subsequent shortening of the telomeres with each DNA
replication round, a phenomenon called the end replication problem.4 This problem precludes infinite growth unless the telomeric ends are reconstituted. At critical telomere shortening, normal somatic cells undergo senescence.5 In vitro, a
strong association between telomere length and induction of senescence has been demonstrated, and the telomere has been proposed to act as a
molecular clock for cell proliferation.5,6 In most
permanently growing cell lines, as well as in a majority of tumors,
telomerase activity seems to compensate for the telomere loss upon cell
division by adding new telomeric repeats to the chromosome
ends.7,8 The activity of telomerase seems to be a
prerequisite for an infinite life span, although other mechanisms for
telomere maintenance probably exist.7
Within the hematopoietic system, peripheral blood cells have been
demonstrated to express weak telomerase activity, whereas early
progenitor stem cells in the bone marrow seem to have stronger activity.9,10 In vitro activated T and B lymphocytes can
upregulate telomerase activity,9,11 and we have recently
found strong activity in normal germinal center B cells indicating
that, in vivo, a significant upregulation of telomerase can
occur.12
There are principally two ways that a tumor cell might acquire
telomerase activity.13,14 One is reactivation of telomerase through a process induced by critical telomere shortening. The second
pathway is through retention of the ability to express telomerase
activity from a normal cell competent to upregulate telomerase, like
bone marrow stem cells and lymphocytes. We believe that the latter is
the main pathway hematological malignancies use to acquire telomerase
activity.9 Retention of telomerase activity was supported
by data in non-Hodgkin's lymphomas that at diagnosis had significantly
increased telomerase activity levels compared with reactive lymph
nodes.12
Hodgkin's disease (HD) is subclassified into different subgroups based
on histopathological appearance and the number of Hodgkin's and
Reed-Sternberg (H-RS) cells. A typical feature of HD, although missing
in some cases, is infiltration of eosinophils. The tumor component of
HD, ie, the H-RS cells, constitutes only 1% to 2% of all
cells.15 Because of the proliferative demands on the clonal
H-RS cells, which are actively cycling, they are expected to exhibit
mechanisms for maintenance of telomere integrity.16,17 In a
previous study, a telomerase-independent maintenance mechanism of the
telomeres in HD was proposed in the absence of detectable telomerase
activity.18
In the current study, we have analyzed telomerase activity using a
quantitative technique in 77 HD lymph nodes and in HD-derived cell
lines. In contrast to the previous report, we could demonstrate telomerase positivity in 80% to 90% of the HD samples, and the level
of telomerase expression was increased compared with reactive lymph
nodes. All HD-derived cell lines expressed high levels of telomerase.
Eosinophilia, specifically the ribonuclease (RNase) content of the
eosinophils, was the probable reason for artifactual telomerase
negativity previously reported in HD.19
| |
MATERIALS AND METHODS |
Patient samples.
Seventy-seven lymph nodes with HD were obtained as frozen tissue stored
at  80°C. All samples were diagnostic lymph nodes and the patients
were untreated during the 3 months before sampling. The
histopathological diagnoses were reexamined in a blinded manner by one
of the authors (C.S.) using the Rye classification. Among the 77 Hodgkin's lymphomas, 45 cases were classified as nodular sclerosis
(NS), 24 cases as mixed cellularity (MC), 4 cases as lymphocytic
predominance (LP), and 1 case as lymphocytic depletion (LD) subtype.
Three cases were unclassifiable.
Four high-grade malignant and 5 low-grade malignant non-Hodgkin's
lymphomas classified according to the Kiel classification as well as 15 reactive lymph nodes were also added to the study as reference cases.
All reference samples were diagnostic and derived from lymph nodes.
Cell lines.
Primary foreskin fibroblasts and the following established cell lines
were used in the study: T47D1 (breast carcinoma), Hela (epitheloid
carcinoma of the cervix; obtained from the American Type Culture
Collection, Rockville, MD), and HDLM-2 (HD-derived), KM-H2
(HD-derived), and L-428 (HD-derived) obtained from the German Collection of Microorganisms and Cell Cultures (Braunschweig, Germany). The 1301 (T-cell lymphoblastic) cell line was a kind gift
from Prof Erik Lundgren (Department of Cell and Molecular Biology, Umeå University, Umeå, Sweden).
S-phase determination.
Fresh cells in suspension were used for DNA staining according to
Vindelov et al,20 and the flow cytometric analysis was performed using a FACScan instrument (Becton Dickinson Immunocytometry Systems, San José, CA). S-phase fractions were calculated by the
Cellfit software using the RFIT evaluation model (Becton Dickinson).
Purified cell populations.
Pure populations of eosinophilic and neutrophilic granulocytes were
prepared as described and were a kind gift from Dr Per Venge
(Department of Clinical Chemistry, Uppsala University, Uppsala, Sweden).21 Briefly, blood from normal donors
was centrifuged over an isotonic Percoll solution and the mononuclear
cell fraction was removed. The pellet containing neutrophils,
eosinophils, and erythrocytes was then resuspended and the red blood
cells were lysed. The remaining cells were incubated with anti-CD16
magnetic particles and separated using the Macs cell separation system (Miltenyi Biotec Inc, Auburn, CA). After the nonlabeled
CD16 eosinophils had been eluted, the separation column
was removed from the magnetic field and the CD16-labeled neutrophilic
granulocytes were eluted.
Purified RNases.
Purified eosinophil-derived neurotoxin (EDN) and eosinophil cationic
protein (ECP) were kind gifts from Dr Per Venge. EDN and ECP, which are
RNases found at high concentrations in eosinophilic granulocytes,19 were purified to homogeneity from buffy
coats obtained from healthy individuals, as previously
described.22,23
Counting of cells.
The number of eosinophils and H-RS cells was counted on
hematoxylin-eosin-stained paraffin sections by one of the authors (G.E.), as described.24,25 The cells were counted in 10 randomly selected high-power (×500) vision fields. To facilitate
counting, an eye-piece equipped with a lattice square net was used, and only cells falling within the lattice framework were counted. In cases
with nodular sclerosis, cellular regions were counted. The presence or
absence of germinal centers and necroses was also noted for each
specimen.
Telomerase assay.
Cellular extracts were prepared from tissue pieces or frozen sections
(3 × 40 µm) by adding an appropriate volume of lysis buffer. The
homogenate was stored on ice for 30 minutes and centrifuged at
13,000g for 20 minutes at 4°C. The supernatant was collected and snap-frozen in liquid nitrogen before storage at 80°C. Protein measurements were performed using the BCA protein assay kit (Pierce Chemical Co, Rockford, IL), and the extracts were diluted to a final
concentration of 0.14 µg/µL. A few reactive nodes and
non-Hodgkin's lymphomas were prepared as fresh samples from which cell
suspensions were made and extracts prepared at a cell number/microliter
corresponding to a protein concentration of 0.14 µg/µL, as
described.12
The TRAP (telomeric repeat amplification protocol) assay was performed
as described.26 Quantification of telomerase activity levels was made possible with inclusion of the internal telomerase assay standard (ITAS) used at 15 attograms/assay.27 The
polymerase chain reaction (PCR) products were resolved on a 10%
nondenaturating polyacrylamide gel with the ITAS separating above the
telomerase products. After fixation the gels were mounted on
Phosphorimager screens and were thereafter analyzed in a Molecular
Imager system GS-525 using the Phosphor Analyst version 1.4.1 (Bio-Rad
Laboratories, Hercules, CA). The telomerase activity level of a sample
is the mean of two or more analyses at 0.28 µg protein/assay
described to be within the linear range of the TRAP assay (Norrback et
al, unpublished data).27,28 The telomerase
activity was defined as the ratio between the telomerase products
formed and the ITAS product corrected for background. Lysis buffer
served as negative control and background. No marked differences were
observed if subtraction was performed for background levels within each
lane above the PCR products. A sample was considered telomerase
positive when a clear amplification of ITAS was observed and the
telomerase activity exhibited high processitivity. For an extract to be
considered telomerase negative, no telomerase products were visible,
and the ITAS had to be amplified greater than 90% of the ITAS in the lysis buffer to exclude the possibility of Taq inhibition or RNase activity in the sample. RNase incubation of selected samples verified that genuine RNA-dependent telomerase products were being formed.
Additional chemicals.
Additional chemicals used during the course of the study were rRNasin
(placental RNase inhibitor; Promega Corp, Madison, WI), dithiothreitol
(DTT; Sigma Chemical Co, St Louis, MO), high purity grade RNase
DNase-free (Boehringer Mannheim Gmbh, Mannheim, Germany), and RNase A
(US Biochemical, Cleveland, OH).
Statistical methods.
Correlation between different variables was tested according to
Spearman's test. Differences between groups were tested with Mann-Whitney's rank sum test or Kruskal-Wallis' test. The
 2 test was used when comparing the
proportions of different groups.
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RESULTS |
Thirty-one of 77 HD samples (40%) were found to be telomerase
positive. Thus, a majority of the samples were devoid of detectable telomerase activity. Storage time of the HD samples or preparation technique had no impact on the level of telomerase activity. Also, the
telomerase activity levels could not be shown to be affected by the
presence of necrosis or germinal centers. However, a striking correlation between the presence of eosinophilic granulocytes and the
absence of telomerase activity was found (P < .00001, Table
1). When extracts from telomerase-negative
HD cases with moderate eosinophilia were mixed with extracts from a
telomerase-positive cell line (T47D1, 0.28 µg/assay) at room
temperature (RT) before the TRAP assay, the telomerase activity of the
cell line was abolished.
To elucidate whether the telomerase-inhibitory activity of the HD
samples was due to the eosinophils per se or some other factor involved
in the eosinophilia, eosinophilic granulocytes were purified (purity,
99%). When Hela cell extracts were preincubated with an extract
corresponding to 50 eosinophils for 20 minutes at RT before the TRAP
assay, the telomerase activity of the cell line was almost completely
lost (Fig 1). An extract corresponding to
500 purified neutrophils (purity, 99.8%) was also shown to abolish the
telomerase activity of the Hela cell line but was much less potent than
the eosinophil extracts (Fig 1). Considering that EDN and ECP possess
RNase activity and are present in high amounts in eosinophils and to a
much lesser degree in neutrophils,19,29 we added placental
RNase inhibitor to the experiments described above.30 The
RNase inhibitor was used at a concentration of 1 U/µL or 10 U/µL
together with 1 mmol/L DTT. When the RNase inhibitor was present in
mixed extracts containing a telomerase-positive cell line and purified
eosinophils or neutrophils, the telomerase activity of the cell line
was always rescued (Fig 1).
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| Fig 1.
Eosinophils and neutrophils contain telomerase
degradative activity. Lane 1, an extract corresponding to 50 eosinophils was mixed with the Hela cell line (0.28 µg/assay) and
preincubated for 20 minutes at RT before the TRAP assay. Lanes 2 and 3, repeat experiment with 5 eosinophils or lysis mixed with the cell line. Lane 4, 50 eosinophils mixed with the Hela cell line (0.28 µg/assay) and preincubated for 40 minutes at RT before the TRAP assay. Lanes 5 and 6, repeat experiment with 5 eosinophils or lysis mixed with the
cell line. Lanes 7 and 8, 50 eosinophils mixed with the Hela cell line
(0.28 µg/assay) and preincubated for 150 minutes at RT before the
TRAP assay with or without placental RNase inhibitor (1 U/µL)
present. Lane 9, an extract corresponding to 500 neutrophils was mixed
with the Hela cell line (0.14 µg/assay) and preincubated for 5 hours
at RT before the TRAP assay. Lanes 10 and 11, repeat experiment with 1 U/µL and 10 U/µL placental RNase inhibitor present, respectively.
Notice that the rescue of the cell line-derived telomerase activity was
increased with increasing amounts of the RNase inhibitor present.
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To prove that EDN and ECP were the enzymes responsible for the
degradation of telomerase, we repeated similar experiments with
purified EDN and ECP. If 0.2 ng EDN was preincubated together with the
Hela cell line (0.28 µg/assay) for 20 minutes at RT before the TRAP
assay, the telomerase activity of the cell line was almost completely
lost. Ten times less EDN was needed to abrogate the telomerase activity
of the cell line if the preincubation time was extended (Fig
2). EDN was more potent than ECP at
degrading telomerase, reflecting the difference in potency of the
RNases.29 Commercially bought RNases showed roughly similar
kinetics of telomerase degradation. The presence of placental RNase
inhibitor in mixtures containing a telomerase-positive cell line and
pure RNases always rescued the telomerase activity (Fig 2). The
experiments investigating the telomerase degradative activity of
granulocyte extracts and purified RNases were verified using the cell
lines Hela, T47D1, and 1301.
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| Fig 2.
RNases abolish the amplification of ITAS only when mixed
with a cell extract. Lanes 1 and 2, positive controls (Hela cells, 0.28 µg/assay). Lanes 3 and 4, the Hela cell line (0.28 µg/assay) incubated for 5 hours at RT with 0.02 ng RNase DNase free before the
TRAP assay with or without placental RNase inhibitor (1 U/µL) present. Lanes 5 and 6, the Hela cell line (0.28 µg/assay) incubated for 5 hours at RT with 0.02 ng EDN before the TRAP assay with or
without placental RNase inhibitor (1 U/µL) present. Lane 7, 20 ng
RNase DNase free added to the TRAP assay without cell extract present.
Lanes 8 and 9, repeat experiment using 2 and 0.2 ng RNase DNase free,
respectively. Lane 10, 20 ng EDN added to the TRAP assay without cell
extract present. Lanes 11 and 12, repeat experiment using 2 and 0.2 ng
EDN, respectively.
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Finally, we prepared new extracts with the placental RNase inhibitor
present from 6 previously telomerase-negative HD samples exhibiting
moderate eosinophilia, and 5 samples expressed clearly detectable
telomerase activity (Fig 3). When purified
eosinophilic and neutrophilic granulocytes were reanalyzed using the
RNase inhibitor, they remained telomerase-negative.
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| Fig 3.
Demonstration of telomerase positivity when previously
telomerase-negative HD samples with eosinophilia were reanalyzed using RNase protection. All samples were analyzed with 10 U/µL placental RNase inhibitor present. Lanes 1 and 4, negative (lysis buffer) and
positive control (1301 cell line, 0.14 µg/assay), respectively. Lanes
2 and 3, sample A analyzed at 0.56 and 0.28 µg/assay, respectively. Lanes 5, 6, and 7, sample B analyzed at 0.14, 0.28, and 0.56 µg/assay, respectively. Lanes 8, 9, and 10, sample C analyzed at
0.14, 0.28, and 0.56 µg/assay, respectively. The amplification of
ITAS in sample A was not decreased, indicating that no free, unbound
RNases were present in the extract and supporting the idea that the
sample was truly telomerase-negative.
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Unexpectedly, when RNase-containing cell extracts were analyzed with
the TRAP assay, the amplification of ITAS was lost or diminished (Figs
1 and 4). The presence of the placental
RNase inhibitor in these extracts was found to always rescue the ITAS amplification. The pure RNases by themselves did not repress the amplification of ITAS. In contrast, when the RNases were preincubated with cell extracts of telomerase-positive cell lines or
telomerase-negative fibroblast cultures at RT before the TRAP assay,
the amplification of ITAS was lost (Fig 2). The presence of the RNase
inhibitor in the mixed extracts similarly rescued the ITAS
amplification. This effect of RNase-containing cell extracts or pure
RNases on the ITAS amplification was also seen at +37°C. We also
performed assays to evaluate the presence of Taq inhibitors or
deoxyribonuclease (DNase) activity without demonstrating positivity in
the extracts or in the purified RNases.
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| Fig 4.
Telomerase activity in HD samples and in an HD-derived
cell line. The level of telomerase activity was analyzed at 0.28 µg/assay. Lanes 1, 2, and 5, HD samples with eosinophilia that
exhibited undetectable telomerase activity. Lanes 3 and 4, 2 telomerase-positive HD samples without eosinophilia. Lane 6, the
HD-derived cell line KM-H2. The amplification of ITAS was almost
competed out by the telomerase products formed by KM-H2.
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Only the group of HD samples without eosinophilia was used for
quantitative estimates of telomerase activity, and 24 of 27 cases
(89%) clearly exhibited telomerase activity. All telomerase-positive HD cases had an undisturbed amplification of ITAS, and the 3 telomerase-negative cases fulfilled the conditions for true telomerase
negativity. The level of telomerase activity in the Hodgkin's
lymphomas was significantly higher than in 15 reactive lymph nodes
(P = .05, Table 2) and
significantly lower than in 9 non-Hodgkin's lymphomas (P = .001, Table 2). The H-RS cell counts did not correlate
with the level of telomerase, and only small differences with respect to telomerase activity levels were observed between the HD subgroups (Table 2).
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Table 2.
Levels of Telomerase Activity in HD-Affected Lymph
Nodes, Non-Hodgkin's Lymphomas, Reactive Lymph Nodes, and in
Permanent Cell Lines
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We also analyzed telomerase activity levels in the HD-derived cell
lines, HDLM-2, KM-H2, and L-428 (Table 2 and Fig 4).31 All
cell lines expressed significant levels of telomerase activity, but the
more slowly proliferating HDLM-2 (S phase, 13.5%) expressed decreased
levels compared with KM-H2 (S phase, 45.4%) and L-428 (S phase,
34.8%).31
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DISCUSSION |
In the present study, telomerase activity was detected in 31 of 77 HD
lymph nodes (40%), but a strong correlation between the presence of
eosinophilia and the absence of telomerase activity was found. Using
purified eosinophils, we could demonstrate that they harbored the
telomerase degradative activity observed in the HD samples with
eosinophilia. Extracts from purified neutrophils corresponding to high
cell numbers were also shown to contain weak degradative activity. The
telomerase degradative activity contained within both cell types could
be inhibited by the addition of placental RNase inhibitor. Purified EDN
and ECP, being our candidate enzymes, were shown to degrade telomerase
activity with a potency matching that of the eosinophil and neutrophil
extracts based on the content of these RNases in the cells. The
activity of both EDN and ECP could similarly be inhibited by the
addition of the RNase inhibitor. Reanalysis of previously
telomerase-negative HD samples with eosinophilia using RNase protection
resulted in detection of telomerase activity. Eosinophils thus have a
considerable impact upon the detectability of telomerase in HD and,
specifically, the activity of EDN and ECP was responsible for the
degradation of telomerase. However, we cannot exclude the possibility
that the eosinophils contained additional molecules that contributed to
the telomerase degradative activity observed, because immunodepletion of the extract with antibodies against EDN and ECP was not performed.
Because of the potency of eosinophils to quench the telomerase signal,
previous studies on materials in which the number of eosinophils could
be increased might have resulted in false-negatives. Similarly, the
RNase content in myeloid leukemias and large infiltrations of
neutrophils could have resulted in the detection of false telomerase activity values.32 We have also found that serum from
normal blood donors, when mixed with a telomerase-positive cell line, resulted in diminished telomerase activity that could be rescued in the
presence of the placental RNase inhibitor (Norrback et al, unpublished
data). EDN, also known as nonsecretory urinary RNase and
liver RNase,33,34 which is present in blood and
urine19,35 together with other RNases, could thus be a
source of false results when analyzing telomerase activity in these
fluids. It needs to be clarified to which cells/tissues addition of
exogenous RNase inhibitors is required to obtain standardized results
when analyzing telomerase activity. The addition of RNase inhibitors to
all assays detecting telomerase activity is, at present, highly
recommended.
Polymorphonuclear cells, including neutrophils, are considered to be
telomerase-negative based on a study not using RNase inhibitors.36 Even if neutrophils, which contain low levels of EDN and ECP, had active telomerase, it would be degraded upon extraction.19,33 We analyzed purified neutrophils using
RNase protection and, for the first time, found solid support for true telomerase negativity. Similarly, eosinophils were reanalyzed using the
RNase inhibitor and were found to be devoid of telomerase activity.
Thus, terminal differentiation with no further cell proliferation is
accompanied with downregulation of telomerase activity in these cells,
as previously suggested from in vitro differentiation of cell
lines.37,38
Another surprising finding was that the RNases affected the ITAS
amplification by an indirect mechanism requiring a cell extract. The
pure RNases were by themselves ineffective at abrogating the amplification of ITAS at a concentration 1,000-fold stronger than that
needed to abolish the amplification when they were mixed with a cell
extract. Possibly, the RNases released proteins with affinity for
sequences at the ITAS or the RNases activated DNase activity.
We decided to only analyze HD samples with no eosinophils for
quantitative estimates of telomerase activity due to the noncovalent binding of the placental RNase inhibitor to the RNases. Telomerase activity was detected in 89% (24/27) of the Hodgkin's lymphomas without eosinophilia not using RNase protection. The Hodgkin's lymphomas exhibited significantly higher levels of telomerase activity
than did reactive lymph nodes and significantly lower levels than
non-Hodgkin's lymphomas. We thus show that HD forms an intermediate
entity with respect to the level of telomerase expression. That the
telomerase activity levels of the HD samples were correct was supported
by the high fraction of positivity, the undisturbed amplification of
the ITAS, and the fact that all negative samples fulfilled the
conditions for true telomerase negativity. When previously
telomerase-negative HD samples with eosinophilia were reanalyzed using
RNase protection telomerase positivity (5 of 6) was observed,
indicating that most Hodgkin's lymphomas with eosinophilia were
telomerase positive as well.
The H-RS cell counts did not correlate to telomerase activity levels in
the HD cases without eosinophilia. The tumor component of HD
constitutes only 1% to 2% of all cells, and reactive lymph nodes also
express telomerase activity to a certain degree.12,15 Thus,
a correlation between telomerase activity levels and tumor cell density
might be difficult to find. The heterogeneity of the tumor component in
HD could also undermine a correlation between H-RS cell counts and
telomerase levels when all HD samples are studied as a
group.31,39
The H-RS cells, which are clonal and cycling, would be expected to
express telomerase activity to maintain the telomere
integrity.16,17 The increased telomerase activity found in
HD compared with reactive lymph nodes suggests that the H-RS cells
express telomerase activity in vivo. The support is emphasized knowing
that germinal centers, which are the sole source of high levels of
telomerase expression in lymph nodes,12,40 were almost
completely absent in the HD samples. The TRAP assay being PCR-based
easily detects telomerase activity from 0.1% to 1% of
telomerase-positive cells, making it reasonable to assume that the H-RS
cells in vivo could contribute to the telomerase activity levels
detected in the HD samples. The HD-derived cell lines chosen in this
study, generally accepted to be derived from H-RS cells based on
extensive characterization,31,39 all expressed significant
levels of telomerase activity. The telomerase positivity of the cell
lines, which were derived both from MC and NS subtypes, possibly
indicates a general ability of the H-RS cells to express the enzyme. It
also suggests that H-RS cells maintain the telomere integrity by the
action of telomerase and not by an alternative telomerase-independent
mechanism recently described to exist in a minority of tumors and
tumor-derived cell lines.7 There seemed to be a correlation
between cell proliferation and the expression level of telomerase in
the cell lines that would be expected because H-RS cells in many cases
are derived from lymphocytes. However, further studies are required to
prove the cell cycle connection to the expression of telomerase in H-RS cells.
An attractive future scenario within the field of hematology is a
first-line treatment with cytotoxic drug(s), followed by antitelomerase
treatment leading to telomere shortening of the tumor cells with
subsequent cell death. A resistance factor to the actions of
antitelomerase drug(s) would be the existence of an alternative
telomerase-independent mechanism to maintain the telomeres. Such a
mechanism was recently proposed to exist in HD in the absence of
detectable telomerase activity.18 There is currently no
support for the existence of a telomerase-independent mechanism for the
telomere maintenance in HD. To date, the findings that HD lymph nodes
and HD-derived cell lines express telomerase activity and the support
for telomerase positivity of the tumor component in vivo renders HD a
potential target for future antitelomerase therapy.
| |
FOOTNOTES |
Submitted October 20, 1997;
accepted March 6, 1998.
Supported by grants from the Swedish Cancer Society, the Medical
Faculty, Umeå University, and Lion's Cancer Research Foundation, Umeå University, and by a special grant from Västerbotten County Council.
Address reprint requests to Göran Roos, MD, PhD, Department of
Pathology, Umeå University, S-90187 Umeå, Sweden.
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" is accordance with 18 U.S.C. section 1734 solely to indicate this fact.
| |
ACKNOWLEDGMENT |
The authors are grateful to Pia Nilsson for valuable expertise and to
Dr Per Venge for providing purified eosinophils, neutrophils, and
purified EDN and ECP.
| |
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Abstract
Introduction
Abstract