(American Journal of Pathology. 2001;158:1217-1222.)
© 2001 American Society for Investigative Pathology
Growth Hormone Receptor Is Expressed in Human Breast Cancer
Maria Gebre-Medhin*,
Lars-Gunnar Kindblom
,
Håkan Wennbo
,
Jan Törnell*
and
Jeanne M. Meis-Kindblom
From the Department of Physiology and
Pharmacology*
and the Department of
Pathology,
Lundberg Laboratory for Cancer
Research, Göteborg University, Göteborg; and
AstraZeneca,
R&D Mölndal,
Mölndal, Sweden
 |
Abstract
|
|---|
Several clinical observations and experimental studies indicate
that pituitary hormones, including growth hormone, play
a role in the development of human breast cancer. We analyzed 48 human
breast carcinomas using reverse transcription polymerase chain
reaction, immunohistochemistry, and Western blotting
techniques to assess growth hormone receptor expression. In 17 of these
cases, adjacent normal breast tissue was similarly analyzed.
These analyses revealed that growth hormone receptor (GHR) is expressed
in human breast cancer and appears to be up-regulated compared to
adjacent normal breast tissue. GHR expression correlated
inversely with tumor grade and MIB-1 index. Progesterone
receptor expression correlated positively with GHR expression. These
findings, along with our observation of GHR expression in
breast cancer stromal cells and previous reports of local production of
growth hormone in breast carcinoma, suggest that GHR-mediated
signaling pathways are involved in the development of human breast
cancer, possibly via autocrine or paracrine
mechanisms.
 |
Introduction
|
|---|
Breast cancer is by far the most
common malignancy in women, affecting one in eight in the United States
and Western Europe. An increased risk of breast cancer is associated
with early menarche, late menopause, and nulliparity. These
observations suggest that ovarian hormones play an important role not
only in normal breast development, but in the development of breast
cancer and its progression. Pituitary hormones are also essential for
normal breast development. Moreover, some observations suggest they are
also involved in the development of breast cancer. Administration of
growth hormone (GH) to aging primates
induces a marked increase in mammary gland size and epithelial
proliferation index.1
Conditions with increased GH levels,
such as acromegaly, are associated with an increased risk of
malignancy, including breast cancer.2-4
In the treatment
of advanced breast cancer, hypophysectomy has beneficial,
ovary-independent effects.5
Breast cancer cell lines grow
in response to both prolactin (PRL) and GH administration, and are
inhibited by PRL and GH antagonists.6-8
GH receptor (GHR)
expression in human breast cancer and breast cancer cell lines has
previously been detected using reverse transcription polymerase chain
reaction (RT-PCR), in situ hybridization, and
immunohistochemistry.9-11
However, quantitative analyses
for levels of GHR protein expression using Western blot techniques have
not been performed. We studied 48 human breast carcinomas as well as
adjacent normal mammary tissue using RT-PCR, Western blot, and
immunohistochemistry. Our results indicate that GHR expression is
up-regulated in breast cancer and suggest a role for GHR signaling in
this disease.
 |
Materials and Methods
|
|---|
The study included 48 breast carcinomas (47 primary tumors and one
lymph node metastasis) from 47 patients who had surgery at the
Sahlgrenska University Hospital in Göteborg, Sweden. Tumor size,
histological type, and tumor grade (Bloom-Richardson-Elston
score12
), as well as axillary lymph node status (positive
versus negative) were recorded in all cases. Material was
snap-frozen in liquid nitrogen for RT-PCR (36 cases) and Western
blotting (28 cases). Fresh frozen material of adjacent normal mammary
tissue was obtained in 17 cases. Immunohistochemical analyses were
performed in 47 cases; in all cases, the selected histological sections
included carcinoma as well as adjacent normal breast tissue.
Immunohistochemistry
All immunostains were performed according to standardized
protocols using the TechMate Horizon immunostainer (DAKO, Copenhagen,
Denmark). For detection of GHR, the mouse mAb 263 (AGEN
Biomedical, Brisbane, Australia) was used at a dilution of 1:500 with
application of tyramide signal amplification system (NEN Life Science
Products, Boston, MA). All primary tumors were also analyzed for
estrogen receptor (ER; clone 105, DAKO), progesterone receptor (PR;
clone PgR 636, DAKO), MIB-1 (Immunotech, Marseille, France), and p53
(D07, DAKO). The immunoreactions for mAb 263 were graded as negative
(0), weakly positive (1), moderately positive (2), or strongly positive
(3). For ER, PR, MIB-1, and p53, the estimated percentage of positive
tumor cell nuclei was recorded.
RT-PCR
Preparation of RNA was performed.13
cDNA
was synthesized from 0.5 µg RNA with 5 U avian myeloblastosis virus
reverse transcriptase (Promega, Madison, WI) and 0.5 µg oligo-(dt)
primer (Promega). For the PCR reaction, the following primers were
used: 5'-GCTGCTGTTGACCTTGGC-3' (sense) and 5'-ACCTCATCTGTCCAGTGG-3'
(antisense) (Scandinavian Gene Synthesis, Köping, Sweden) located
in exons 2 and 4, respectively. These primers will amplify a 201-bp
fragment corresponding to nucleotides 58258 of the human GHR cDNA. If
the GHR lacks the nucleotides corresponding to exon 3, the amplified
fragment will be 135 bp. PCR was performed following a standard
protocol. Samples were amplified for 30 cycles at an annealing
temperature of 55°C. Specificity of the PCR products was verified by
specific cleavage with the restriction enzyme Bsp 1286 I (Promega),
which cleaves the GHR in exon 3, rendering two fragments 119 and
82 bp in size when PCR products containing exon 3 are digested, whereas
PCR products without exon 3 are left intact. Specificity of PCR
products was also confirmed by Southern hybridization (not shown).
Western Blotting
The antibody used, GHR06, was a mouse monoclonal raised against
amino acids 396407 of the extracellular part of human GHR. It
recognizes the human GHR protein by Western blotting, by
immunoprecipitation, and by fluorescence-activated cell sorting
(G Norstedt, unpublished data).
Soluble tissues were prepared by homogenization in PE buffer (10 mmol/L
potassium phosphate buffer, pH 6.8 and 1 mmol/L EDTA) containing 6
mg/ml 3-(3-cholamidopropyl)dimethyl-ammonio 1-propane sulfate (CHAPS),
aprotinin (200 kallikrein inhibitory units per milliliter), leupeptin
(10 µg/ml), pepstatin (10 µg/ml), and Pefabloc (1 mg/ml; Boehringer
Mannheim, Mannheim, Germany). After sonication and centrifugation,
supernatants were collected and protein concentrations were determined
by the Bio-Rad method. Supernatants were stored at -70°C until
analysis. The samples were diluted in SDS sample buffer and denatured
before loading on a SDS-polyacrylamide gel (8% Tris-glycine; NOVEX,
San Diego, CA). Fifty micrograms of total protein were loaded into each
lane. A prestained standard (SeeBlue, NOVEX) was used as weight marker.
After electrophoresis, the proteins were transferred to a
polyvinyldifluoride (PVDF) membrane (Amersham, Buckinghamshire, UK)
using a standard electroblotting system, followed by incubation with
GHR06, diluted 1:1000. Immunoreactive protein was visualized by
chemiluminescence using an ALP-conjugated secondary antibody
(goat-anti-mouse, SIGMA), diluted 1:30000 and CDP Star (Tropix,
Bedford, MA) as substrate. Membranes were exposed to ECL film
(Amersham) for 10 seconds to 3 minutes and developed in a Curix 60
developing machine (AGFA). Autoradiograms were scanned and the bands
corresponding to GHR protein were analyze by densitometry. Quantitative
analyses were performed using ImageQuant software (Molecular Dynamics,
Sunnyvale, CA).
Statistical Analyses
Correlation between GHR expression as determined both by mAb 263
immunostaining and by Western blot analysis, and patient age, tumor
size, tumor grade, tumor type, axillary lymph node status, estrogen
receptor expression, progesterone receptor expression, MIB-1
immunoreactivity, and p53 immunoreactivity was evaluated using
Fishers permutation test. Differences in GHR expression between
tumors and adjacent normal mammary tissue as determined by Western blot
analysis were evaluated using a paired t-test. P
values <0.05 were considered significant.
 |
Results
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The patient and tumor characteristics are summarized in Table 1
. The 47 patients ranged in age from 34
to 90 years (median, 59 years). Tumors ranged from 15 to 110 mm in
greatest dimension. The vast majority of tumors were invasive ductal
carcinomas (n = 41); the remainder were invasive
lobular carcinomas (n = 3), atypical medullary
carcinomas (n = 2), and invasive tubular
carcinoma (n = 1). Axillary lymph nodes were
removed in 42 patients; 22 patients had metastases and 20 did not.
Immunohistochemistry
The GHR (mAb 263) immunostaining results are summarized in Table 1
. A variable degree of cytoplasmic staining of tumor cells was seen in
all but two of the 47 analyzed tumors (Figure 1, ac)
. Weak focal nuclear staining was
observed in a few instances. Weak or moderate cytoplasmic staining also
occurred in some stromal cells (Figure 1b)
. Adjacent normal breast
tissue was negative (Figure 1d)
, or weakly positive, sharply
contrasting with mostly strongly positive tumors. A significant inverse
correlation was found between GHR expression and tumor grade
(P < 0.05).

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Figure 1. GHR (mAb 263)
immunostaining of invasive ductal carcinomas of the breast
(a and
b) and an atypical medullary
carcinoma (c).
Strong cytoplasmic immunostaining of the epithelial component and weak
staining of some stromal cells are seen
(b and
c). Adjacent normal breast tissue is
negative (d)
or weakly positive.
|
|
Estrogen and progesterone receptor positivity, defined as >10%
positive tumor cell nuclei, was observed in 26/44 and 18/46 tumors,
respectively. MIB-1 positivity was
10% in 17/46 tumors, >10% and
<50% in 18/46, and
50% in 11/46 tumors. p53 immunostaining >20%
was seen in 14/47 tumors. There was a positive correlation between GHR
expression and progesterone receptor expression
(P < 0.01), and an inverse correlation between
GHR expression and level of MIB-1 immunoreactivity
(P < 0.05).
RT-PCR
Amplified fragments of the expected sizes (201 or 135 bp)
were detected in all 36 tumor samples examined (Figure 2a
and Table 1
). To verify their
identity, the PCR products were digested by the restriction enzyme Bsp
1286 I (Figure 2b)
. Twenty-one of 36 tumors expressed the GHR form
containing exon 3, seven tumors expressed the GHR form without exon 3,
and eight tumors expressed both forms. In 17 cases, GHR mRNA expression
was also assessed in adjacent normal mammary tissue. GHR mRNA was
detected in all normal mammary tissues and was always of the same form
as the corresponding tumor.

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Figure 2. a: RT-PCR of GHR expression in six breast cancer cases.
Lanes 2, 4, 6, 8,
10, and 12 represent RT-PCR of tumor tissues.
Lanes 3, 5, 7, 9,
11, and 13 represent no template controls.
Lane 1 shows a DNA marker (1 kb,
GIBCO BRL). The full-length GHR renders a
fragment of 201 bp (lanes 2,
4, 6, and 8).
The GHR without exon 3 renders a fragment of 135 bp
(lane 10).
Lane 12 represents a case in which both forms are expressed.
b: Digestion of the PCR fragment with Bsp 1286 I. Cleavage
occurs in the third exon, resulting in two fragments that are 119 and
82 bp in size (lanes
25) or, in the case of exon 3 deletion,
leaving the fragment undigested (lane
6). Lane 1 is the DNA marker
X174 HaeIII.
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Western Blotting
GHR protein was detected in all 28 tumors analyzed. The amount of
GHR varied between different tumors (Figure 3a
and Table 1
). The relative protein
levels ranged between 0.22 and 1.31 arbitrary units (median, 0.71). In
adjacent normal breast tissue (n = 17), the
relative protein levels ranged between 0.09 and 0.75 arbitrary units
(median, 0.26). Comparison of GHR expression levels in 16 tumors and
adjacent normal mammary tissues (Figure 3b)
revealed significantly
higher levels of GHR in tumors (P < 0.01,
paired t-test; Figure 3c
). No significant correlation was
found between GHR expression levels using Western blotting and any of
the clinical, morphological, or immunophenotypic parameters recorded.
However, there was a positive correlation between expression levels of
GHR detected by Western blotting and the intensity of GHR
immunoreactivity (P < 0.05).

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Figure 3. Western blots of GHR in human breast cancer tissues. a:
Representative blot of GHR expression in eight breast cancer cases.
b: Representative blot of GHR expression in tumor tissues
and adjacent normal breast tissues. c: Relative GHR
expression levels in breast cancer tissues are compared to relative GHR
expression levels of adjacent normal mammary tissues
(n = 16). Mean levels are
lower in normal mammary tissues compared to cancer tissues
(P < 0.01).
|
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 |
Discussion
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The RT-PCR, Western blotting, and immunohistochemistry results
clearly demonstrate that GHR is expressed in human breast cancer. These
findings agree with previous reports of GHR detected by RT-PCR in
surgically removed breast cancers and breast cancer cell
lines,9
or by using immunohistochemical10,11
and in situ hybridization techniques.11
Moreover, our immunohistochemical and Western blotting analyses
demonstrated greater GHR expression in tumors than normal breast
tissues. Thus, though adjacent normal breast tissues showed no or only
weak immunoreactivity for GHR, all but a few carcinomas showed strong
or moderate diffuse cytoplasmic staining. Also, the semiquantitative
Western blotting results showed significantly increased GHR expression
in tumors compared to adjacent normal breast tissues.
The predominantly cytoplasmic GHR immunoreactivity found in our study
supports previous observations.14-16
Weak nuclear
staining was occasionally seen; this has also been previously
reported17
and is of interest since nuclear translocation
of GHR may be induced by GH stimulation.18
Another
interesting observation was the detection of GHR in stromal cells of
the breast carcinomas. The stromal compartment of the normal mammary
gland is suggested to be the site of action for GH during normal
mammary development in rodents.19,20
GH, possibly via
local insulin-like growth factor (IGF)-I production, acts
synergistically with estradiol during normal mammary gland development
in rodents21,22
and primates.23
In this study of human breast cancer, there was an inverse correlation
between GHR expression as determined by immunohistochemistry and
proliferative activity (MIB-1 immunostaining) as well as tumor grade,
whereas there was a positive correlation between GHR expression and
progesterone receptor expression. These findings, as well as the
previous detection of GHR in benign epithelial proliferations of the
breast, all suggest that increased GHR expression does not correspond
to aggressive biological behavior per se. Additional points
of interest are the detection of GHR expression by RT-PCR and Western
blotting, and strong immunoreactivity for GHR in both stromal and
epithelial cells of a benign phyllodes tumor not included in this
series.
Despite the significant correlation between GHR expression levels
detected by Western blotting and immunostaining intensity, a
significant correlation between progesterone receptor expression, tumor
grade, and proliferative activity (MIB-1) was found only with
immunostaining intensity. This apparent discrepancy could be explained
by the relatively small number of cases analyzed using Western
blotting.
The detection of an additional GHR cDNA lacking exon 324
(in this series, seen as the sole form in 7/36 tumors; 21/36 tumors
expressed the full-length form; 8/36 expressed both forms) was
originally believed to be due to an alternative splicing event.
Subsequent studies suggested tissue-specific and individual-specific
expression patterns.25,26
The expression of GHR cDNA
without exon 3, however, has recently been shown to be the result of a
deletion of this part of the GHR gene, which, in turn, is due to a
recombination of two retro-elements flanking exon 3.27
Thus, our detection of the same GHR cDNA in tumors and normal breast
tissues from the same individual supports these findings.
Interestingly, the invasive ductal carcinomas of the breast with the
exon 3-deleted GHR occurred in patients who were significantly younger
than those who had full-length GHR (mean age 41 vs. 59
years). However, analysis of a larger series is required to draw any
conclusions.
This study indicates that GH and GHR play a role in human breast
cancer, but the exact mechanisms involved remain unclear.
Autocrine/paracrine mechanisms have been suggested based on the
detection of local GH production in normal breast tissue and
carcinoma,28
and transfection studies of GH expression
plasmids in MCF-7 breast cancer cells in which increased growth
response was recorded with autocrine/paracrine stimulation compared to
exogenous GH administration.8
Because GH-mediated
stimulation of IGF-I production occurs in normal breast development, a
similar phenomenon could occur in the development of breast cancer.
GH is closely related to PRL; although both hormones have specific
receptors, GH also activates PRL receptors (PRLR) in
primates.29
Thus, in many studies of GH action, it is not
possible to discriminate between GHR- and PRLR-mediated effects.
Tumor-promoting effects have been shown to be mediated via PRLR and not
GHR in mice.30
The situation in human breast cancer,
however, is probably more complex. Both GHR and PRLR are expressed in
most human breast carcinomas11,31
with higher expression
levels of PRLR and GHR in breast cancers compared to normal breast
tissues 32
(and this study). Local production of PRL, as
well as GH, has also been demonstrated in breast
carcinomas.28,33
More potent mitogenic signals are
suggested to be a result of PRLR activation rather than GHR
activation.7
In conclusion, this study, which provides evidence of GHR expression
and up-regulation in human breast cancer, indicates a role for GHR
signaling in human breast cancer. To further understand the mechanisms
involved, additional studies are necessary, including analyses of
benign breast lesions and precancerous conditions.
 |
Acknowledgements
|
|---|
We thank Gunnar Norstedt for providing the GHR antibody GHR06.
 |
Footnotes
|
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Address reprint requests to Maria Gebre-Medhin at her current address: Department of Physiology, Lund University, Sölvegatan 19, SE 223 62 Lund, Sweden. E-mail: Maria.gebre-medhin{at}medic.gu.se
Supported by grants from the Swedish Cancer Society, the Ingabritt and Arne Lundberg Foundation, the Assar Gabrielsson Foundation, the Syskonen Svensson Foundation, the Wilhelm and Martina Lundgren Foundation, and the Göteborg Medical Society.
Accepted for publication January 8, 2001.
 |
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