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From the Childrens Hospital,*
and Departments of
Pathology
and Bacteriology and
Immunology,
The Haartman Institute,
University of Helsinki, Helsinki, Finland; and the Departments of
Pediatrics§
and Molecular Biology and
Pharmacology,¶
Washington University School of
Medicine, St. Louis, Missouri
| Abstract |
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-fetoprotein, which can
be detected in tumor tissue or serum. However,
additional markers of endoderm differentiation would be beneficial for
the classification of these tumors. Transcription factor GATA-4
regulates the differentiation and function of murine yolk sac
endoderm, and its expression correlates with proliferation and
cell survival in certain tissues. To see whether GATA-4 plays a role in
human YSTs, we surveyed its expression in human germ cell
tumors and cell lines. Northern analysis demonstrated expression of
GATA-4 mRNA in four human germ cell tumor lines exhibiting yolk sac
endoderm differentiation. GATA-4 protein was detected in eight of nine
pediatric YSTs by immunohistochemistry. Three of five immature
teratomas exhibited GATA-4 in neural blastematous cells and in
cylindrical epithelium, whereas all 16 mature teratomas were
devoid of GATA-4. We conclude that GATA-4 is a clinically useful marker
of human YSTs and speculate that it may play a role in the maintenance
of the malignant phenotype.
| Introduction |
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-fetoprotein (AFP), and
the serum AFP level is frequently elevated in patients with these
tumors.3
However, the histological appearance of YSTs can
vary, and small YST foci can be found mixed with other germ-cell tumor
histologies, such as teratomas or embryonal carcinomas, creating
diagnostic challenges.1 The molecular mechanisms involved in normal yolk sac development and malignant transformation are not fully understood. Recent studies have implicated transcription factor GATA-4 in the differentiation and function of murine yolk sac endoderm.4-7 GATA-4 belongs to a family of related zinc finger proteins that regulate gene expression in a variety of organs (reviewed in ref. 8 ). In addition to its role in yolk sac endoderm, GATA-4 appears to regulate transcription in cardiomyocytes,7,9 enterocytes,10 and hepatocytes.11 Within somatic cells of the mouse gonad (ie, granulosa, theca, Sertoli, and Leydig cells), expression of GATA-4 correlates with cell proliferation and survival.12-14 Given the established role of GATA-4 in murine endoderm differentiation and cellular proliferation, we have now examined the expression of GATA-4 in human YSTs and cell lines. We find that GATA-4 protein is expressed in YSTs originating from either gonadal or extragonadal sites, but not in mature teratomas. We suggest that GATA-4 may serve as a useful nuclear marker of malignant endoderm cells within YSTs.
| Materials and Methods |
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Paraffin-embedded, paraformaldehyde-fixed human tissue was
originally collected for diagnostic purposes. These samples included
nine yolk sac tumors (three gonadal and six extragonadal), one
embryonal carcinoma (vaginal), 16 benign teratomas (12 gonadal and four
sacrococcygeal), and five immature teratomas (two gonadal and three
extragonadal) (see Table 1
). Serial
sections (5 µm) were stained with hematoxylin-eosin or subjected to
immunohistochemistry for GATA-4 or AFP. All tumor histology was
reviewed by a designated pathologist (P. H.). The study was
approved by the ethical committees of both institutions.
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Mouse embryos were obtained by mating male and female B6DJLF1/J mice. For estimating embryonal age, noon of the day on which the copulation plug was found was considered as 0.5 days p.c. Precise staging of dissected embryos was performed using the Atlas of Mouse Development.15 The yolk sacs an placentas from 6 to 14 days p.c. were collected together with the embryos, fixed with 4% paraformaldehyde, and embedded in paraffin. All experiments on animals were performed according to the National Research Councils guide.
Human Germ Cell Tumor Lines
Two human germ cell tumor lines, originally derived from testicular yolk sac tumors,16 were kindly provided by Dr. Pera (Institute of Cancer Research, Surrey, UK). The GCT 72 cell line exhibits properties of visceral endoderm, whereas the GCT 44, GCT 46, and GCT 85 line resemble parietal endoderm.
In Situ Hybridization
Mouse embryos along with the extraembyonic membranes and placenta were washed briefly in phosphate-buffered saline, fixed in 4% paraformaldehyde in PBS, and embedded in paraffin. The sections were subjected to in situ hybridization as described.17 Tissue sections were incubated with 1 x 106 cpm of 33P-labeled (10003000 Ci/mmol; Amersham, Life Technologies, Arlington Heights, IL) antisense or sense riboprobe in a total volume of 80 µl. Antisense and sense riboprobes for GATA-4 were prepared as described elsewhere.4,17
Northern Hybridization
PolyA RNA was isolated from the lysed cells and analyzed for expression of GATA-4 and cyclophilin (used as a loading control) message, using Northern hybridization.4 One microgram of polyA RNA was subjected to electrophoresis on a 1% denaturing agarose gel and then transferred onto nylon membranes (Hybond N; Amersham, Arlington Heights, IL). To prepare the GATA-4 probe, a partial length human GATA-4 cDNA was used.18 The cDNA inserts were labeled with [32P]deoxy-CTP (3000 Ci/mmol; Amersham) and Prime-a-gene kit (Promega, Madison, WI). Hybridization and washing of the membranes were performed as previously described.4 A Fujifilm IP-Reader Bio-Imaging Analyzer BAS 1500 (Fuji Photo Co. Ltd., Tokyo, Japan) was used to analyze the hybridization signal with the MacBas software supplied by the manufacturer, using a Macintosh personal computer (Apple Computer, Cupertino, CA).
Immunohistochemistry
Tissue sections from paraffin-embedded human tissue samples were fixed in 4% paraformaldehyde and subjected to immunohistochemistry, using either a commercial polyclonal anti-mouse GATA-4 IgG (Santa Cruz Biotechnology, Santa Cruz, CA) or affinity-purified polyclonal rabbit anti-mouse GATA-44,17 or nonimmune IgG as the primary antibody. Earlier studies by us and others have demonstrated that these antibodies have no cross-reactivity with other GATA-binding proteins.4,13,17 Immunohistochemistry for AFP was performed using a commercial polyclonal antibody raised against human AFP (Dako, Glostrup, Denmark). A commercially available avidin-biotin immunoperoxidase system was used to visualize bound antibody (Vectastain Elite ABC Kit; Vector Laboratories, Burlingame, CA). 3-Amino-9-ethylcarbazole (Sigma Chemicals, St. Louis, MO) was used as the chromogen, and the development reaction occurred in the presence of 0.03% H202.
| Results |
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The histological similarities between human YSTs and the rodent
yolk sac/placenta have been appreciated for decades.2
In
light of these similarities, we explored whether GATA-4, a known marker
of yolk sac endoderm in the mouse, plays a role in human YSTs. To
illustrate the selective expression pattern of GATA-4 in yolk sac
endoderm, we first performed in situ hybridization studies
on the developing mouse embryo (Figure 1)
. Consistent with earlier
reports,4
abundant GATA-4 mRNA was observed in the
visceral and parietal endoderm of the postimplantation mouse embryo
(Figure 1, AF)
. These two layers of endoderm, derivatives of a
transient cell layer termed primitive endoderm, contribute to
extraembryonic tissues but not to the embryo proper.19
In
contrast, no GATA-4 mRNA was seen in embryonic ectoderm (Figure 1, AF)
. After gastrulation, GATA-4 mRNA was detected in nascent
mesoderm, including progenitors of the heart (Figure 1, B, C, E, F)
. We
found that expression of GATA-4 in the visceral endoderm layer persists
throughout gestation. Examination of the chorionic plate of a late
gestation mouse embryo (Figure 1, G and H)
demonstrated GATA-4 mRNA in
yolk sac endoderm cells within the crypts of Duval, structures
analogous to the Schiller-Duval bodies found in human YSTs; in
contrast, trophectoderm derivatives within the placenta were devoid of
this transcript.
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Previous studies have shown that murine cell lines exhibiting
visceral or parietal endoderm differentiation express
GATA-4.4,5
To see whether human tumor cell lines
exhibiting yolk sac endoderm differentiation also express this
transcription factor, we performed Northern analysis on RNA from a
series of human germ cell tumor lines. The cell line GCT 72 displays
properties of visceral endoderm, whereas the GCT 44, GCT 46, and GCT 85
cell lines resemble parietal endoderm.16
As shown in
Figure 2, a
4-kb GATA-4 transcript
comigrating with the transcript found in normal ovary RNA was detected
in each of these lines. In contrast, GATA-4 mRNA was not detected in a
variety of human tumor cell lines lacking endodermal differentiation,
such as HeLa (cervical carcinoma), K562 (erythroleukemia), or HL-60
(promyelocytic leukemia) (data not shown). We conclude that GATA-4
expression is evident in human tumor cell lines exhibiting yolk sac
endoderm differentiation.
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To explore the role of GATA-4 in human YSTs, we used
immunohistochemistry to compare the expression of GATA-4 and the
established marker, AFP, in a series of nine pediatric patients with
YSTs, including both gonadal and extragonadal tumors. The clinical,
laboratory, and pathological findings in these patients are summarized
in Table 2
. To detect GATA-4 antigen, we
used either a commercially available goat polyclonal anti-mouse GATA-4
IgG or, in selected cases, a rabbit polyclonal antibody produced in our
laboratory. Identical results were obtained with these antibodies.
Previous studies have shown that these antibodies react selectively
with GATA-4 and stain the nucleus of murine yolk sac endoderm,
cardiomyocytes, granulosa, Sertoli, and Leydig
cells.12,13,17
GATA-4 protein was detected in the nucleus
of malignant endoderm cells within the human YST specimens, but not in
fibrotic stroma or necrotic areas (Table 2
, Figure 3
). The majority of YSTs examined (eight
of nine) expressed GATA-4, and this antigen was detected in both
extragonadal (Figure 3B)
and gonadal (Figure 3E)
YSTs. Tumor regions
immunoreactive for GATA-4 often expressed cytoplasmic AFP (Figure 3C)
,
but the proportion of viable tumors cells staining for GATA-4 and AFP
varied among the specimens (Table 2)
. It should be noted that
GATA-4 antigen was detected in malignant cells in one YST specimen with
negative AFP immunohistochemistry but abundant AFP in the serum (Table 2
, Patient 3), suggesting that GATA-4 complements other markers. As
expected,13,14
GATA-4 antigen was detected in seminiferous
tubules of normal testicular tissue adjacent to foci of YST (Figure 3E)
.
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| Discussion |
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Although GATA-4 is a potentially useful marker for pathological classification of germ cell tumors, the presence of this antigen is not pathognomonic for YSTs. Some immature teratomas (three of five) were found to focally express GATA-4 within blastematous cells and cylindrical epithelium. In a similar fashion, AFP antigen, the traditional marker of malignant extraembryonic endoderm, can be detected in embryonal tissue within immature teratomas.20 Therefore, proper classification of YSTs and other germ cell malignancies continues to require judicious interpretation of both histopathology and tumor markers.20
GATA-4 has been implicated in the in vitro differentiation5 and in vivo function6 of visceral endoderm. Related GATA-binding proteins may also influence endoderm differentiation, based on studies in mouse19 and lower organisms such as Drosophila and C. elegans.21 It is tempting to speculate that GATA-binding proteins may have a role in the maintenance of the malignant phenotype in YSTs. It is of interest that recent data have linked GATA-binding proteins with antiapoptotic processes, which often operate in malignant cells. Specifically, down-regulation of GATA-1 is associated with apoptosis in proerythroblasts,22 and decreased expression of GATA-4 is associated with cardiomyocyte death9 and ovarian follicular atresia via apoptosis.12
Although there are limited data on the molecular events leading to the
formation of germ cell tumors, several molecules have been implicated
in the pathophysiology of these tumors. For example, the tumor
suppressor gene product p53 is detected in most adult testicular germ
cell tumors and in one-third of pediatric cases,23
and the
overexpression of p53 has been suggested to be a favorable prognostic
factor in testicular germ cell tumors. C-kit expression is common in
pediatric testicular germ cell tumors, and the c-kit/stem cell factor
signaling pathway was speculated to play a role in the initiation and
progression of these tumors.23
Likewise, the
platelet-derived growth factor
-receptor has been demonstrated
within in situ and occult testicular germ cell tumors, and
it may serve as a molecular marker for these tumors.24
The
clinical usefulness of this molecule, however, remains unclear because
of the low number of tumors studied. However, none of the
above-mentioned molecules has been specifically linked to yolk sac
tumors. The detection of GATA-4 mRNA and protein in human
endoderm-derived cell lines and YSTs suggests that this transcription
factor should be added to the list of molecules potentially involved in
the pathogenesis of germ cell malignancies.
Taken together, our results demonstrate that GATA-4 is expressed throughout mammalian yolk sac development. This factor is also expressed in readily detectable amounts in pediatric gonadal and extragonadal yolk sac tumors, providing a new nuclear marker for extraembyonic differentiation in germ cell tumors. Our unpublished studies have revealed that GATA-4 is also expressed in certain other types of gonadal tumors, such as Sertoli and Leydig cell tumors of the testis, and granulosa and theca cell tumors of the ovary, representing transformed counterparts for the cells expressing this transcription factor during mammalian development. Based on the these data and the results presented herein, GATA-4 transcription factor also plays a role in the pathophysiology of gonadal and extragonadal tumors.
| Acknowledgements |
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| Footnotes |
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Supported by the Sigrid Juselius Foundation (to D. B. W. and M. H.), the Finnish Pediatric Foundation (to S. S. and M. H.), the University Central Hospital in Helsinki (to S. S., M. A., M. L., O. R., and M. H.), Pediatric Cardiology SCOR HL61006 (to D. B. W.), the Washington University Monsanto-Searle Agreement (to D. B. W.), and an Established Investigator Award from the American Heart Association (to D. B. W.).
Accepted for publication August 24, 1999.
| References |
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-fetoprotein (AFP) in patients with germ cell tumors of the gonads and extragonadal sites: correlation between endodermal sinus (yolk sac) tumor and raised serum AFP. Cancer 1980, 46:380-385[Medline]
-receptor 1.5 kb transcript: target for molecular detection of testicular germ cell tumours of adolescents and adults. APMIS 1998, 106:207-213[Medline]
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