The Journal of Clinical Endocrinology & Metabolism Vol. 82, No. 2 670-673
Copyright © 1997 by The Endocrine Society
Cyclooxygenase-Dependent Thyroid Cell Proliferation Induced by Immunoglobulins from Patients with Graves Disease1
Rosa Di Paola,
Claudia Menzaghi,
Vito De Filippis,
Daniela Corda and
Alfredo Di Cerbo
Division of Endocrinology (R.D.P., C.M., V.D.F., A.D.C.), Istituto
di Ricovero e Cura a Carattere Scientifico "Casa Sollievo della
Sofferenza" General Hospital, San Giovanni Rotondo (Foggia); and the
Department of Cell Biology and Oncology, Istituto di Ricerche
Farmacologiche "Mario Negri," Consorzio Mario Negri Sud (D.C.), S.
Maria Imbaro (Chieti), Italy
Address all correspondence and requests for reprints to: Dr. Alfredo Di Cerbo, Division of Endocrinology, Istituto di Ricovero e Cura a Carattere Scientifico "Casa Sollievo della Sofferenza," 71013 San Giovanni Rotondo (Foggia), Italy.
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Abstract
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IgG associated with Graves disease bind to the TSH receptor and alter
thyroid growth and function, mainly through the stimulation of adenylyl
cyclase. In addition, Graves IgG are able to interact with the
phospholipase C (PLC)/Ca2+ and phospholipase A2
(PLA2)/arachidonic acid (AA) cascades. The activation of
this latter pathway leads to thyroid cell growth in
vitro. The elucidation of additional mechanisms of action of
Graves IgG has made possible the identification of four subgroups of
patients, characterized by IgG with different biochemical activities
(extent of cAMP and AA release stimulation in in vitro
assays). On the basis of these results, a novel therapeutic approach
could be proposed based on the inhibition of PLA2 and AA
metabolism.
To test this hypothesis, the ability of IgG from 56 Graves patients
to stimulate [3H]thymidine incorporation in FRTL5 thyroid
cells in the presence and absence of the cyclooxygenase inhibitor
indomethacin (2.5 x 10-6 mol/L) was measured. A
significant reduction in [3H]thymidine incorporation was
found (33% inhibition; P < 0.0001) upon
pretreatment with indomethacin, suggesting that in vitro
thyroid cell growth is regulated by cyclooxygenase metabolites. This
strengthens the argument for involvement of the PLA2/AA
cascade in the pathophysiology of Graves disease and the proposal for
novel selective pharmacological treatments of these patients.
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Introduction
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TSH RECEPTOR- stimulating Igs play a
pathogenetic role in Graves disease. They are believed to act via the
TSH receptor to increase the cellular levels of cAMP and other second
messengers and thus alter thyroid growth and function (1, 2, 3).
We have previously demonstrated that the Igs (IgG) obtained from
Graves patients stimulate not only adenylyl cyclase (AC), but also
phospholipase A2 (PLA2) (4). This latter effect
is easily distinguished from the known effect on AC, as a subpopulation
of Graves IgG could be identified that induces arachidonic acid (AA)
release without affecting cAMP (5). Moreover, four subgroups of
Graves patients have been characterized on the basis of the different
biochemical activities of their IgG (extent of cAMP production and AA
release in in vitro assays) (5). Interestingly, we have
shown that the IgG able to stimulate both AC and PLA2
induced the highest levels of [3H]thymidine incorporation
in in vitro assays, and the corresponding patients were
those with more severe manifestations of the disease (5). The role of
AA in inducing thyroid growth led us to propose a novel therapeutic
approach in Graves disease based on the inhibition of
PLA2 and AA metabolism.
The regulation of growth has been well characterized in FRTL5 cells and
appears related to multiple transduction pathways including cAMP- and
Ca2+-dependent mechanisms activated by TSH, a
kinase-dependent pathway stimulated by insulin-like growth factor I,
and an AA-dependent pathway that produces PGE2 (6, 7, 8). PG
synthesis in FRTL-5 thyroid cells is under multihormonal control, as
insulin, insulin-like growth factor I, and serum are required for the
TSH-dependent activation of cyclooxygenase (9, 10). Furthermore, DNA
synthesis induced by TSH and the activity of monoclonal antibodies
against the TSH receptor are blocked in part by the cyclooxygenase
inhibitor indomethacin (1). AA and eicosanoid formation have been shown
to be involved in the control of cell growth in several cell systems
(11, 12, 13, 14). Similarly, AA and its metabolites might play a role in the
regulation of thyroid growth in Graves disease. We have analyzed this
possibility using the cyclooxygenase inhibitor indomethacin in FRTL5
thyroid cells stimulated to proliferate by IgG from Graves
patients.
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Materials and Methods
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Reagents and cells
Hormones used in the tissue culture media, Coons modified
Hams F-12 medium, ethyleneglycol-bis-(ß-aminoethyl
ether)-N,N,N',N'-tetraacetic
acid, Tris(hydroxymethyl) aminomethane, and indomethacin were obtained
from Sigma Chemical Co. (St. Louis, MO). Tissue culture materials were
purchased from Life Technologies (Grand Island, NY). Protein
A-Sepharose CL4B was obtained from Pharmacia LKB Biotechnology
(Uppsala, Sweden); glycine was purchased from Bio-Rad Laboratories
(Richmond, CA); Minicon B15 concentrators were obtained from Amicon
Division (W. R. Grace Co., Danvers, MA). [3H]Thymidine
was purchased from New England Nuclear Corp. (Boston, MA).
FRTL5 cells, a continuous line of functioning rat thyroid cells, were
cultured as previously described in Coons modified Hams F-12
medium, 5% calf serum, and a six-hormone mixture (TSH, insulin,
cortisol, transferrin,
glycyl-L-histidyl-L-lysine acetate, and
somatostatin; 6H medium) (15).
Patients
Sera were obtained from 88 patients with active Graves disease
randomly selected from the group of 104 enrolled for our previous study
(5) and from 54 normal subjects. The characteristics of patients have
been previously described (5).
IgG purification and [3H]thymidine
incorporation
IgG purification and [3H]thymidine
incorporation were performed as previously described (4, 5). To
evaluate the effect of the cyclooxygenase inhibition on
[3H]thymidine incorporation, FRTL5 cells were
preincubated with 2.5 x 10-6 mol/L indomethacin for
30 min before adding IgG. All determinations were made in triplicate
for each experimental point. The cut-off value discriminating between
[3H]thymidine incorporation due to pathological and
normal IgG was calculated using Receiver Operating Characteristic
Curves analysis (16).
Statistical analysis
For statistical analysis of the data, the Wilcoxon signed rank
test was used. Differences were considered statistically significant
for P < 0.05.
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Results
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IgG from 88 patients with Graves disease and 54 normal subjects
were characterized for their ability to stimulate
[3H]thymidine incorporation in FRTL5 thyroid cells. In
agreement with previous studies (17, 18) [3H]thymidine
incorporation was significantly higher in Graves patients
(P < 0.0001; Fig. 1
). On the basis of
the cut-off value (equal to a 116% increase over the basal value), IgG
from 88 patients with Graves disease were divided into 2 groups
according to whether their IgG were able to stimulate
[3H]thymidine incorporation in FRTL5 thyroid cells.
Fifty-six of 88 (63.6%) IgG gave values higher than the cut-off (Fig. 1
). [3H]Thymidine incorporation induced by these IgG was
then assayed in the presence or absence of 2.5 x
10-6 mol/L indomethacin, which is known to block
cyclooxygenase, a key enzyme leading to the synthesis of
PGE2 (19). In the entire group of patients, a significant
reduction of [3H]thymidine incorporation was found (33%
inhibition; P < 0.0001; range, 064% inhibition)
when cells were pretreated with 2.5 x 10-6 mol/L
indomethacin, indicating the ability of this cyclooxygenase inhibitor
to reduce thyroid cell growth in in vitro studies (Fig. 2
). Moreover, [3H]thymidine incorporation
was completely abolished after preincubation with 2.5 x
10-6 mol/L indomethacin in 38 of 56 IgG with elevated
[3H]thymidine incorporation in the absence of
indomethacin (Fig. 3
). To exclude a possible direct
toxic effect of indomethacin on FRTL5 cells, we also measured
[3H]thymidine incorporation induced by cholera toxin in
the presence and absence of the drug. We found that
[3H]thymidine incorporation is not modified by
pretreatment with the drug (data not shown). These data as well as the
finding that some IgG retained the ability to stimulate
[3H]thymidine incorporation in FRTL5 cells pretreated
with indomethacin (see Fig. 2
) rule out a possible toxic effect of the
drug. In conclusion, these data suggest that the AA/PGE2
pathway may contribute to thyroid growth in some patients with Graves
disease. Moreover, our findings confirm the existence of subgroups of
Graves IgG able to activate both cyclooxygenase- and
noncyclooxygenase-dependent pathways.

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Figure 1. Frequency distribution patterns of
[3H]thymidine incorporation induced by IgG from 88
patients with active Graves disease (shaded bars) and
54 normal subjects (open bars). The vertical
solid line indicates the sample cut-off value. See text for
details.
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Figure 2. [3H]Thymidine incorporation,
as measured before (closed circles) and after
(open circles) treatment with 2.5 x
10-6 mol/L indomethacin in 56 patients with active
Graves disease. Results are expressed as a percentage of basal
[3H]thymidine incorporation (Hanks Balanced Salt
Solution-BSA only). Individual data points represent the
means of triplicate determinations. The difference between the two
groups of data is statistically significant (P <
0.0001).
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Figure 3. Frequency distribution patterns of
[3H]thymidine incorporation induced by IgG from 56
patients with active Graves disease, measured before (shaded
bars) and after (open bars) treatment with
2.5 x 10-6 mol/L indomethacin. The vertical
solid line indicates the sample cut-off value. See text for
details.
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Discussion
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IgG produced by B lymphocytes infiltrating the thyroid are
believed to play a major role in the development of thyrotoxicosis and
goiter in Graves disease (20, 21). IgG bind the TSH receptor and
stimulate cAMP production in several thyroid systems, including human
thyroid slices and membranes (2, 3). Activation of the AC/cAMP pathway
is related to thyroid growth in Graves disease (6, 7, 22). Recently,
it has also been shown that the PLC (23, 24, 25, 26) and PLA2 (4, 5, 26) pathways are involved in the action of Graves IgG. This effect
and previous data showing that indomethacin blocks the mitogenic effect
of several monoclonal antibodies derived from Graves disease patients
(1) suggest a role for AA metabolites, particularly cyclooxygenase
products, in the regulation of thyroid growth in Graves disease.
Indeed, we found that indomethacin inhibits the mitogenic activity of
IgG from Graves patients in FRTL5 thyroid cells.
The molecular mechanism involved in the stimulation of the
PLA2/AA/PGE2 pathway has not been elucidated.
It has been reported that different regions of the TSH receptor are
involved in the activation of AC and PLC mediated by Graves IgG (24).
Likewise, Graves IgG that release AA could bind to specific regions
of the TSH receptor and, via activation of the
PLA2/AA/PGE2 pathway, regulate thyroid cell
growth.
The present results strengthen the argument that thyroid growth may
also depend on activation of the PLA2/AA/PGE2
pathway. We have previously shown that a subgroup of Graves IgG acts
mainly via the PLA2/AA cascade and that Graves patients
whose IgG are able to stimulate both AC/cAMP and PLA2/AA
pathways have a more severe form of the disease (5). These data and the
results of the present study could represent the molecular basis for a
clinical trial using inhibitors of AA metabolism, such as indomethacin
and acetylsalicylic acid, in association with the thionamide
antithyroid agents to improve management of some Graves patients.
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Acknowledgments
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We thank Dr. C. Checchia de Ambrosio for IgG purification, and
Dr. B. Dallapiccola for critical reading of the manuscript. We
acknowledge the gift of purified human TSH from the National Hormone
and Pituitary Program (NIH, Bethesda, MD).
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Footnotes
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1 Part of these data has been presented as an abstract at the 22nd
International Congress of Endocrinology, San Francisco, CA, June 1996
(Abstract P3-162). This work was supported in part by the Italian
Association for Cancer Research, the Italian National Research Council
(no. 95.00558.PF39-ACRO and Convenzione CNR-Consorzio Mario Negri Sud),
and the Italian Ministry of Health (EDRF 9201). 
Received June 27, 1996.
Revised September 16, 1996.
Accepted October 25, 1996.
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