
Clinical Cancer Research Vol. 6, 3424-3429, September 2000
© 2000 American Association for Cancer Research
KAI1 Protein Is Down-Regulated during the Progression of Human Breast Cancer1
Xiaohong Yang,
Lisa Wei,
Careen Tang,
Rebecca Slack,
Elizabeth Montgomery2 and
Marc Lippman3
Lombardi Cancer Center, Georgetown University Medical Center, Washington, DC 20007
 |
ABSTRACT
|
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The
KAI1 gene was identified as a metastasis
suppressor gene for human prostate cancer. Recently, we showed that
KAI1 mRNA levels were higher in an immortal, normal-like
breast epithelial cell line and nonmetastatic breast cancer cell lines
but lower substantially in highly metastatic breast cancer cell lines.
In this study, we examined KAI1 protein expression in breast cancer
cell lines by Western blot and immunohistochemical study. KAI1 protein
levels paralleled KAI1 mRNA levels and were inversely
correlated with the metastatic potential of breast cancer cells.
Furthermore, we examined KAI1 protein expression immunohistochemically
in specimens from 81 patients with breast cancer and then correlated
the findings with the clinical and histopathological parameters of the
patients. High levels of KAI1 protein expression were found in normal
breast tissues and noninvasive breast cancer (ductal carcinoma
in situ). In contrast, KAI1 expression was reduced in
most of the infiltrating breast tumors. We found that, in general, more
malignant tumors demonstrated significantly lower KAI1 expression
(P = 0.004). Additionally, among 29 specimens
demonstrating multiple stages of malignancy within a single specimen,
23 demonstrated significant differences in KAI1 expression between
benign breast tissue, ductal carcinoma in situ, and
invasive carcinoma. The higher the incidence for malignancy within a
given specimen, the lower the KAI1 expression (P <
0.001). These data suggest that in advanced breast cancer, KAI1
expression is down-regulated. Therefore, KAI1 may be a potentially
useful indicator of human breast cancer progression.
 |
Introduction
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Breast cancer is the second most common cause of cancer-related
death among women in the United States (1)
. As with other
cancers, metastasis in breast cancer is the leading cause for
mortality. Breast cancer is genetically heterogeneous, and a variety of
genetic lesions have been identified that may contribute to disease
progression (2)
. Chromosome 11, in particular 11p, is one
of the most common regions undergoing genetic alterations in breast
cancer (3, 4, 5)
. Introduction of a normal human chromosome
11 into a highly metastatic breast cancer cell line, MDA-MB-435,
dramatically reduced the numbers of lung metastases in nude mice
(6)
. This suggests that human chromosome 11 harbors a
metastasis suppressor gene for human breast cancer.
KAI1, mapping to chromosome 11p11.2, was identified as a
metastasis suppressor gene for human prostate cancer (7)
.
Expression of KAI1 in a highly malignant prostate cancer cell line
resulted in a significant suppression of lung metastases. KAI1 encodes
a protein of 267 amino acids with a molecular weight of 29,610
(7)
. KAI1 is identical to CD82, which is a member of the
TM4SF4
(7)
. The TM4SF proteins share similar structures by
containing four highly conserved hydrophobic regions, presumed to be
transmembrane domains. The precise biochemical functions of TM4SF
proteins are not known; however, current data suggest largely that they
are involved in the regulation of cell development, proliferation,
activation, and motility (8)
. At least three different
TM4SF proteins, ME491/CD63, MRP-1/CD9, and KAI1/CD82, have been
implicated to play important roles in tumor progression and metastasis
(8)
. The role of KAI1 in cancer progression appears not to
be limited to prostate cancer only. After its initial identification,
KAI1 has been shown to be involved in the progression of human
pancreatic cancer, non-small cell lung cancer, bladder cancer, breast
cancer, and gastric cancer (9, 10, 11, 12, 13)
.
In our previous study, we compared the metastatic propensity and
invasive ability of a continuum of breast cancer cells with varying
degrees of progression toward malignancy and found that these
parameters appeared to correlate inversely with KAI1 mRNA
expression (14)
. The purpose of this study was to
determine whether there exists a correlation between the loss of KAI1
protein expression with advancing breast cancer disease. To test this,
we examined KAI1 protein levels by Western blot in four breast cancer
cell lines representing different stages of progression. In addition,
we performed immunohistochemical studies to assess KAI1 protein
expression in 81 human breast cancer specimens from patients with known
clinical outcome. Our results indicate that KAI1 protein expression
decreased in metastatic breast cancer cell lines and in patients with
highly malignant breast cancer.
 |
Materials and Methods
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Cell Lines and Culture Conditions.
The immortal, normal-like human breast MCF-10A cell line (provided by
Dr. Robert Soule, Karmanos Cancer Center, Detroit, MI) was grown
in DMEM/Hams F-12 media supplemented with 5% horse serum, 0.5
µg/ml hydrocortisone, 12 µg/ml insulin, 0.02 ng/ml epidermal growth
factor, and 1 ng/ml cholera toxin (15)
. Human breast
cancer cell lines MDA-MB-231 and T47D were obtained from The Lombardi
Cancer Center Tissue Culture Core Facility. MDA-MB-435 cells were a
gift from Dr Janet Price (University of Texas M. D. Anderson Cancer
Center; Ref. 16
). All breast cancer cell lines were
maintained in modified improved MEM containing 10% fetal bovine serum.
All cells were incubated at 37°C in 5% CO2 in
a humidified chamber. All cell lines were routinely tested and found to
be negative for Mycoplasma contamination.
Western Blot Analysis.
Cell proteins were solubilized in lysis buffer [50 mM
HEPES (pH 7.5), 150 mM NaCl, 1.5 mM MgCl, 1
mM EDTA, 1% Triton X-100, and 10% glycerol] containing
protease inhibitors (phenylmethylsulfonyl fluoride, leupeptin,
aprotinin, and trypsin inhibitor). Twenty µg of cell lysate were
mixed with Laemmlis sample buffer without 2-mercaptoethanol and
boiled for 5 min. After SDS-PAGE (17.5%; Norvex, San Diego, CA),
proteins were electrophoretically transferred to nitrocellulose
(Amersham, Arlington Heights, IL) and probed with C33, a specific
monoclonal antibody against KAI1 (a gift from Dr. Osamu Yoshie,
Shionogi Institute for Medical Science, Osaka, Japan; Ref.
17
). An enhanced chemiluminescence (ECL; Amersham) system
was used for signal detection.
Pathological Specimens.
Eighty-one surgically resected primary cancer tissues were obtained
from patients treated at The Lombardi Cancer Center. All tissues used
in this study are from the Lombardi tumor bank, and they include:
(a) normal breast tissue from patients with breast cancer;
(b) samples from patients with DCIS; and (c)
samples from patients with invasive breast carcinoma.
Immunohistochemistry.
Immunohistochemical staining was done on frozen tissue sections by a
typical immunoperoxidase method. Briefly, 6-µm frozen sections were
cut on a cryostat and fixed with acetone for 10 min at 4°C and
air-dried. All subsequent steps were performed at room temperature. The
sections were incubated with 10% fetal bovine serum for 1 h and
then treated with 10% H2O2
for 5 min to block the endogenous peroxidase activity. The sections
were then incubated with the mouse monoclonal antihuman KAI1 antibody
(anti-CD82; PharMingen, San Diego, CA) at a dilution of 1:150 for
2 h in a moist chamber. After treatment with biotinylated rabbit
antimouse immunoglobulin (1:250) for 1 h, the sections were
incubated with aminoethyl carbazole containing 0.1%
H2O2 for 1 h at
37°C. The sections were counterstained with hematoxylin, dehydrated
in graded ethanol, cleared in xylene, and mounted with Permount.
Staining intensity in the cancer cells was estimated as positive when
it appeared to be similar to that of normal breast duct cells and
benign fibroadenoma tumor cells. When the percentage of KAI1-positive
cells within a particular type of tissue was 51% or greater, the
specimen was classified as KAI1 abundant. When 550% or 04% of
cells were positively stained with KAI1, the sample was classified as
decreased or negative, respectively. Twenty-nine samples contained
multiple types of tissue within one specimen. Each tissue type was
scored for KAI1 expression separately, based on its staining intensity
and pattern.
Statistical Analysis.
To describe the relationship between pathological severity and
immunohistochemical detection of KAI1, the worst pathological
characteristic and its corresponding KAI1 expression level were used to
classify each individual. This relationship was assessed by The
Jonckheere-Terpstra test (18)
. For specimens with multiple
types of tissue present, the sign test was performed using the worst
and the best tumor characteristics to determine whether KAI1 expression
was related to tumor severity within the same person (19)
.
Because two statistical tests were performed with the same set of
specimens, a Bonferroni correction was used so that each test was
significant if P < 0.025. Survival status information
is available for 72 cases, including 27 deaths. Survival curves and the
median follow-up time among survivors were estimated according to the
methods of Kaplan and Meier (20)
. Log-rank tests were
performed to determine whether patients with negative KAI1 expression
demonstrated a different survival profile than patients with any KAI1
expression.
 |
Results
|
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Previously, we found that KAI1 mRNA levels were
inversely correlated with the metastatic potential of some breast
cancer cells (14)
. In this study, we performed Western
blot analysis and immunohistochemistry to examine KAI1 protein levels
in some of these breast cancer cells as well as an immortalized breast
epithelial cell line, MCF-10A. MCF-10A cells are not tumorigenic
(15)
. T47D, a breast cancer cell line, is neither invasive
in vitro nor metastatic in vivo. MDA-MB-231 and
MDA-MB-435 are highly malignant breast cancer cell lines
(21)
.
Western blot analysis was performed using a specific monoclonal
antibody (C33) against KAI1 (17)
. The molecular weight of
KAI1 protein in these cells ranged from 46,000 to 60,000, probably
because of its glycosylation (Fig. 1)
.
MDA-MB-435, which is highly metastatic, had an extremely low level of
KAI1 protein. MDA-MB-231 cells, reported to be highly invasive but
modestly metastatic in athymic nude mice (16)
, had higher
levels of KAI1 protein than MDA-MB-435 cells (Fig. 1)
. A nonmetastatic
breast cancer cell line, T47D, had much higher KAI1 protein than
metastatic MDA-MB-435 cells. In addition, MCF-10A, a nontumorigenic
breast epithelial cell line, had the highest protein levels among all
of these cells. Taken together, these studies indicated that KAI1
protein expression also was inversely correlated with the metastatic
potential of these breast cancer cells.

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Fig. 1. Western blot analysis of KAI1 protein expression
in some established breast cancer cells. Proteins were extracted from
subconfluent monolayer cell culture and separated by SDS-PAGE and
then transferred to nitrocellulose membrane. The blot was probed with
C33, a specific monoclonal antibody against KAI1 (a gift from Dr. Osamu
Yoshie, Osaka, Japan). Enhanced chemiluminescence (ECL) was used for
signal detection.
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To determine whether there is a correlation between the loss of KAI1
expression and breast cancer progression and to test the feasibility of
using KAI1 expression as a marker of breast cancer metastases, we
examined KAI1 expression immunohistochemically in specimens from 81
patients with breast cancer. All specimens were graded by pathologists
and classified into three groups: group 1, normal and benign lesions;
group 2, DCIS; and group 3, infiltrating cancer (including moderately
differentiated and poorly differentiated invasive cancers). Twenty-nine
specimens had two or more types of cells within one specimen. For
analysis, each specimen was graded by its most malignant cell type and
scored by KAI1 expression. Significantly high levels of KAI1 expression
were found in normal breast tissues and benign breast tumors from
patients with breast cancer. There also was abundant KAI1 staining in
the patients at the earlier malignant tumor stage (DCIS). However, KAI1
expression was dramatically reduced in most of the infiltrating breast
tumors (Table 1)
. Furthermore, poorly
differentiated tumors had much less KAI1 protein than well and
moderately differentiated ones (Fig. 2)
.
In general, more malignant tumors demonstrated significantly lower KAI1
expression (P = 0.004). Of the 29 specimens containing
a spectrum of tissue types, 23 demonstrated differences in KAI1
expression. The more malignant cells within individual specimens showed
significantly lower KAI1 expression than less or nonmalignant cells in
the same individual (P < 0.001). To avoid selection
bias, each slide was also graded by its least malignant cell type and
scored for KAI1 expression. The statistical analysis indicated the same
trends of lower KAI1 expression among increasingly malignant cells. The
effect of KAI1 on overall survival of these patients was analyzed to
determine whether KAI1 expression contributes to the prognosis of
breast cancer. Survival status information was available for 72
patients, including 27 deaths. The survival curves for individuals with
any KAI1 expression compared with negative KAI1 expression are shown in
Fig. 3
. KAI1 expression appears to be
associated with better survival. The survival estimates at 3 years are
80% (SE, 7%) and 74% (SE, 8%) for those individuals with any KAI1
expression versus negative expression, respectively. By 5
years, the survival estimates are 70% (SE, 8%) and 57% (SE, 9%) for
any and negative KAI1 expression groups, respectively. However, the
difference in the curves did not reach statistical significance
(P = 0.180). The median follow-up time among survivors
is 5.9 years.
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Table 1 Frequencies of KAI1 expression in breast cancer
patients
More malignant tumors demonstrated a significantly lower expression of
KAI1 (P = 0.004). Of 29 specimens demonstrating
multiple stages of malignancy, 23 displayed differences in KAI1
expression. The higher the incidence for malignancy within an
individual, the lower the KAI1 expression. Specimens with low or no
incidence for malignancy had higher KAI1 expression (P < 0.001).
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Fig. 2. Immunohistochemical staining of
KAI1 protein in tissues of breast cancer patients using a mouse
monoclonal antibody against KAI1 (anti-CD82; PharMingen) and aminoethyl
carbazole as the chromogen with hematoxylin counterstaining.
A, normal breast ducts showing abundant KAI1 protein at
the cell-to-cell border. B, DCIS expressing moderate
KAI1 protein. C, infiltrating breast cancer, which is
well to moderately differentiated, having very weak KAI1 staining.
D, negative staining of the tumor cells of the poorly
differentiated breast carcinoma x200.
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Fig. 3. Survival of patients with negative
KAI1 expression (04%) versus abundant or decreased
KAI1 expression (>4%). Survival estimates at 3 years and at 5 years
are provided with SEs in parentheses.
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Discussion
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Metastasis is a complicated multistage process that requires the
coordination of multiple genes, including both metastasis stimulating
genes and metastasis suppressor genes (22)
. Genomic
instability is one of the driving forces for tumor progression and
metastasis development. Among all genetic alterations, inactivation of
metastasis suppressor genes is one important factor contributing to the
formation of tumor metastasis. Chromosome 11, in particular 11p, is one
of the most common regions undergoing genetic alterations in human
breast cancer (3, 4, 5)
. A previous study demonstrated that a
breast cancer metastasis gene or genes exists on chromosome 11 by the
fact that the introduction of a normal copy of chromosome 11 into
malignant breast cancer cells significantly suppressed their metastatic
ability (6)
.
The KAI1 gene, located on human chromosome 11p11.2, was
initially identified as a metastasis suppressor gene for human prostate
cancer (7)
. Down-regulation of the KAI1 protein was
observed during the progression of prostate cancer (23)
.
However, the role of KAI1 in tumor progression may not be limited to
prostate cancer. KAI1 expression was reported to correlate with
favorable outcome in patients with non-small cell lung cancer
(10
, 24)
. KAI1 expression also was reported to be reduced
in metastatic human pancreatic cancers and high-grade bladder cancers
by in situ hybridization studies (9
, 11)
.
Recently, White et al. (25)
analyzed KAI1
protein in normal and cancer cells of a variety of tissues, and they
found that KAI1 protein was down-regulated in most of the cancer cell
lines analyzed. The role of KAI1 expression in gastric cancer seems to
be controversial. One study showed that KAI1 was unchanged in
metastatic and nonmetastatic gastric cancers (26)
, whereas
a more recent study demonstrated that KAI1 expression was decreased in
high-grade gastric cancer (13)
. In our previous study, we
observed that KAI1 mRNA levels were inversely correlated
with the metastatic potential of some breast cancer cell lines
(14)
. The present data showed that the expression of KAI1
protein was also down-regulated in highly malignant breast cancer cell
lines and specimens. Although most nonmalignant and DCIS tissues (9 of
14) tested were shown to be positive for the anti-KAI1 antibody, only
19% (13 of 67) of infiltrating tumor specimens retained strong KAI1
staining. Most strikingly, more pleomorphic tumor cells had
significantly lower levels of KAI1 protein as compared with lower grade
tumor or normal ductal cells in the same specimen. Therefore, within an
individual, the KAI1 expression was also inversely correlated with the
severity of tumor. In summary, our results, which are consistent with
most of the current literature, support the role of KAI1 as a favorable
prognostic factor for a variety of human cancers.
More recently, Huang et al. (12)
investigated the correlation of reduction in KAI1 expression with
recurrences in breast cancer patients. The results demonstrated that
the disease-free survival rate of patients with KAI1-negative tumors
was significantly lower than that of patients with KAI1-positive
tumors. In their other study, they showed that KAI1 expression in
non-small lung cancer is a favorable prognostic factor for both overall
and disease-free survival (24)
. In our study, we also
examined the relationship between KAI1 expression and overall survival
status of these patients with breast cancer. Our data indicated that
KAI1-positive patients tended to have better overall survival rate as
compared with KAI1-negative patients. However, the difference is not
statistically significant (Fig. 3)
. This result is consistent
with Huang et al., who demonstrated that KAI1 expression is
associated with disease-free survival (P = 0.0065) but
not with 5-year survival (P = 0.3080; Ref.
12
). Whether KAI1 is a better predictor for breast cancer
recurrences than overall survival remains to be seen in a much larger
study population. In addition, Huangs study examined the combined
effect of KAI1 and CD9 on breast cancer recurrences and survival. Their
results indicated that the disease-free survival and 5-year survival
rate of patients with either CD9-negative or KAI1-negative tumors were
both significantly lower than those for patients who expressed these
proteins. Multiple factors clearly contribute to breast cancer
survival. Further study of the alterations in these genes may
contribute more precise prognostication in breast cancer.
 |
ACKNOWLEDGMENTS
|
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We thank Drs. J. Carl Barrett, Osamu Yoshie, and Cheng-Long
Huang for generous gifts of KA11 cDNA and C33 antibody.
 |
FOOTNOTES
|
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by the Latham Trust Fund
(to L. W.) and Specialized Programs of Research Excellence Grant
5P50CA58185-08 (to M. L.). 
2 Present address: The Johns Hopkins
University, Department of Pathology, 632 Ross Building, 720 Rutland
Avenue, Baltimore, MD 21205-2196. 
3 To whom requests for reprints should be
addressed, at Lombardi Cancer Center, Georgetown University Medical
Center, 3970 Reservoir Road NW, Washington, DC 20007. Phone:
(202) 687-2110; Fax: (202) 687-6402. 
4 The abbreviations used are: TM4SF, transmembrane
4 protein superfamily; DCIS, ductal carcinoma in situ. 
Received 4/27/00;
accepted 6/23/00.
 |
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July 1, 2001;
61(13):
5284 - 5288.
[Abstract]
[Full Text]
[PDF]
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