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Molecular Oncology, Markers, Clinical Correlates |
Neurosurgical Laboratories, Brigham and Womens Hospital, Brain Tumor Center, Brigham and Womens Hospital, The Childrens Hospital, and Dana Farber Cancer Institute, Department of Surgery, Harvard Medical School [R. S. C., J. Z., P. M. B.], and Department of Medicine, Brigham and Womens Hospital, and Department of Adult Oncology, Dana-Farber Cancer Institute [M. B., J. D., J. F. D.], Boston, Massachusetts 02115
| ABSTRACT |
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| INTRODUCTION |
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Although many studies have attempted to define the role of these
hormones in meningioma growth, the specific activities of these
hormones in meningioma pathogenesis remain unknown. The potential role
of estrogen and progesterone on the growth of meningiomas has been
investigated several different ways with in vitro and
in vivo models. The first set of studies focused on the
expression of the receptors in meningiomas (9
, 10)
.
Secondly, studies were conducted to try to assess the mitogenic effects
of estrogen, progesterone agonists, and/or progesterone antagonists
both on meningioma cell cultures and spheroids and on tumors implanted
in vivo (11)
. Our laboratory demonstrated that
64% of meningiomas express mRNA for the PR and that its expression
correlates with nuclear localization of the receptor by
immunohistochemistry (12)
. Using reverse transcription and
PCR Southern blot analysis, we have demonstrated the presence of mRNA
for ER-
3
and
-ß in 68 and 44% of meningiomas, respectively (13)
.
Steroid hormone receptors belong to a large superfamily of nuclear receptors that bind DNA at specific sites to control gene transcription (14 , 15) . The mechanisms by which steroid receptors modulate the transcription of target genes are under extensive investigation. Once bound to ligand, the receptors undergo conformational changes and dimers of receptors recognize specific regulatory DNA sequences upstream of target genes. Activated receptors, through interactions with coactivator proteins, direct the assembly and the stabilization of a preinitiation complex that will ultimately conduct the transcription of these genes.
Recently, several coactivators that associate with these receptors in a ligand-dependent manner and enhance their ability to trans-activate target genes have been identified and characterized (16) . Therefore, to obtain a clear picture of the role of estrogen and progesterone in meningioma growth, it is likely to be to important to know not only the status of ER or PR expression in these tumors but also whether the coregulators of steroid hormone receptors are present. These additional regulatory layers may explain the heterogeneity of hormone responses that are observed in normal and malignant tissue. In this report, we studied the expression of three related 160-kDa proteins (17) , SRC-1, TIF2, and AIB1 (18, 19, 20, 21, 22) . Although the role of these coactivating proteins is being intensely studied in other hormonally influenced tumors such as breast cancer, the expression of these coactivators has yet to be examined in any type of brain tumors. The differential expression of steroid receptor cofactors may explain the differential response of these tumors to hormonal therapy.
| MATERIALS AND METHODS |
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Antibodies.
The AIB1 antibody is a polyclonal antibody generated against GST-AIB1
(amino acids 695933). The rabbit serum was affinity purified with the
use of GST-AIB1 which has been cleaved by thrombin and covalently
immobilized to Affi-Gel 15 (Bio-Rad). The specificity of the antibody
was confirmed by Western blot analysis (22)
. The TIF2
antibody is a monoclonal antibody against GST-TIF2 (amino acids
885-1122). The specificity of the antibody was confirmed by
immunoprecipitation with in vitro translated TIF2 followed
by Western blot analysis.
Western Blot Analysis.
Each frozen tissue specimen was crushed in a porcelain mortar and then
transferred to a Dounce tissue grinder containing 3 ml of cold NP40
lysis buffer [20 mM HEPES (pH 8.0), 1% NP40, 10%
glycerol, 2.5 mM EGTA, 2.5 mM EDTA, 10 µg/ml
leupeptin, 2 µg/ml aprotinin, 1 mM
phenylmethylsulfonyl fluoride, and 0.5 mM vanadate]. The
protein lysates were centrifuged at 10,000 x g for 30
min at 4°C to remove any cellular debris. The amount of protein was
quantified (Bio-Rad protein analysis), and stored at -70°C.
For all Western blots 100 µg of protein lysate from each sample were reconstituted in Laemmli sample buffer (23) , boiled for 5 min, and analyzed by SDS-polyacrylamide gel (7.5% acrylamide) electrophoresis.
After PAGE, the gels were transblotted to Immobilon-P (Millipore, Bedford MA) and blocked at RT with 5% nonfat milk in TBST for 1 h at RT. The first antibody was then diluted in TBST, and blots were incubated for 1 h at RT. The first antibodies included (a) the mouse monoclonal SRC-1 (1:100 in TBST) (24) , (b) the mouse monoclonal TIF2 (1:100 in TBST), and (c) the rabbit affinity-purified AIB1 (1:100 in TBST) (22) . After a rinsing in TBST, the blots were incubated with the secondary antimouse or antirabbit horseradish peroxidase-conjugated antibody (1:1500 in 5% nonfat milk-TBST) for 1 h at RT. The blots were again rinsed in TBST, and detection was conducted with the ECL-Plus Western detection system (Amersham Life Science, Arlington, IL) per manufacturers instructions. The blots were then exposed to Kodak XAR film for 160 min.
PR, ER, SRC-1, AIB1, and TIF2 Immunohistochemistry.
Sections of 6 µm were cut from formalin-fixed,
paraffin-embedded tissue blocks and mounted on polylysine-coated glass
slides. The sections were deparaffinized in a xylene bath and hydrated
in graded ethanol washes. To improve the staining pattern, antigen
retrieval with 10 mM sodium citrate (pH 6.0) at 100°C was
used for 30 min. Briefly, slides were incubated with the
peroxidase-blocking agent (0.3% hydrogen peroxide) for 30 min. They
were then incubated with the primary PR antibody (Biogenex PR 88;
diluted 1:40 in PBS containing horse serum), ER antibody (diluted 1:400
in PBS containing horse serum), SRC-1 antibody (diluted 1:3 in PBS
containing horse serum), TIF2 antibody (diluted 1:3 in PBS containing
horse serum), and AIB1 antibody (diluted 1:50 in PBS containing goat
serum) overnight at 4°C. The slides were then incubated with a mouse
or rabbit biotinylated secondary antibody provided in the Vectastain
ABC kit (Vector Laboratories, Burlington, CA) and ABC reagent for 30
min. Lastly, they were incubated with the substrate-chromagen
3,3'-diaminobenzidine for 25 min. Sections were counterstained with
methyl green for 5 min. All incubations except primary antibody were
conducted at RT. For each sample, an adjacent section was incubated
with horse serum as a negative control.
| RESULTS |
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Forty-three percent of the meningiomas were positive for ER expression
by immunohistochemistry (Fig. 1
; Table 1
). Of the specimens, which were
positive, sixty-seven percent were from female patients and
thirty-three percent were from male patients. These percentages are
similar to those we previously reported on a distinct set of tumors
(13)
. Normal brain tissue was negative for ER and PR
expression by immunohistochemistry. In contrast, the leptomeningeal
specimen was positive for PR.
The expression of SRC-1 and TIF2 are significantly related to the PR
but not ER expression in the meningiomas examined (P
0.05, Fishers exact test). Among those tumors, which are PR positive,
100% are SRC-1 positive and 92% are TIF2 positive. In contrast, among
the PR-negative tumors, 56% are SRC-1 positive and TIF2 positive. No
significant relationship was observed between AIBI and PR status.
| DISCUSSION |
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Our studies show that the expression of patterns of these genes varies
among the meningiomas examined, suggesting their expression may be
tissue dependent. The marked variation observed in the expression of
the coactivators examined promoted us to study the expression of the
steroid hormone receptors in the meningiomas. Our results show that the
expression of SRC-1 and TIF2 are significantly related to the PR
expression in the meningiomas examined. The majority of the
meningiomas, which were positive for PR, were also positive for SRC-1
and TIF2. In mammary epithelium, the expression of ER-
and SRC-1 was
segregated into distinct subsets of cells (24)
. By
immunohistochemistry, we were able to show that the steroid cofactors
and receptors are both expressed in meningioepithelial cells of
the tumor; it remains unclear whether they are in the same cell or
distinct subpopulations. Normal brain specimens were all positive for
SRC-1 and TIF2 and negative for ER, PR, and AIB1. In contrast, one
leptomeningeal specimen obtained from an autopsy was positive for
SRC-1, PR, and AIB1 but negative for TIF2 and ER. This raises the
possibility that TIF2 expression may be involved in meningioma
initiation. This is different from previous reports for breast cancer.
In breast tumors, AIB1 amplification was correlated with ER and PR
positively, as well as tumor size (20)
, suggesting that
AIB1 amplification may be related not only to ER activation but also to
PR activation.
In conclusion, we show tumor to tumor variation in the expression of SRC-1, AIB1, and TIF2 genes. These findings are consistent with our hypothesis that the relative expression of coactivators in meningiomas may contribute to the heterogeneity of hormonal responses observed in vitro and in vivo. Ultimately, an understanding of the function of these factors and their role in the pathways of steroid-mediated trans-activation will contribute to the development of new approaches in the prevention and treatment of meningiomas.
| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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1 M. B. is supported by NIH Grants CA57374 and
CA80111. R. C. is supported by the Boston Neurosurgical Foundation. ![]()
2 To whom requests for reprints should be
addressed, at Brigham and Womens Hospital, 221 Longwood Avenue, Room
121, Boston, MA 02115. Phone: (617) 278-0177; Fax: (617) 232-9029. ![]()
3 The abbreviations used are: ER, estrogen
receptor; PR progesterone receptor; SRC-1, steroid receptor cofactor;
TIF2, transcriptional intermediary factor 2; AIB1, amplified in breast
cancer protein; GST, glutathione S-transferase; RT, room
temperature; TBST, Tris-buffered saline [10 mM Tris (pH 8)
and 0.9% NaCl] containing 0.1% Tween 20. ![]()
Received 12/27/99; revised 6/12/00; accepted 6/12/00.
| REFERENCES |
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and ß in human meningiomas. J. Neuro-Oncol., 42: 109-116, 1999.[CrossRef][Medline]
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