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From the Departments of Pathology,*
Microbiology and
Immunology,
and
Surgery,
University of Texas Medical Branch,
Galveston, Texas; and the Department of
Pathology,
University of Chicago Hospitals,
Chicago, Illinois
| Abstract |
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-fetoprotein. Our results demonstrate that cDNA arrays can be
effectively used to identify new diagnostic markers, and that
CD10 is a reliable marker for identifying HCC, particularly
when used in conjunction with a panel of immunohistochemical markers
(polyclonal anti-carcinoembryonic antigen, CK7,
CK20, and
-fetoprotein) and in the distinction from
cholangiocarcinoma.
| Introduction |
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In conjunction with relevant clinical and laboratory information, such
as the presence or absence of cirrhosis and the serum
-fetoprotein
(AFP) level, a panel of immunohistochemical stains of biopsied or
resected liver specimens is often helpful in histological differential
diagnosis. Commonly used are a polyclonal antibody against
carcinoembryonic antigen (CEA-p), monoclonal antibodies specific for
cytokeratin (CK) 7 and CK20, and AFP. HCCs usually exhibit a
characteristic membranous staining pattern with CEA-p. The antibody
cross-reacts with the biliary glycoprotein I located at the bile
canalicular aspect of the hepatocyte surface.2
Most HCCs
do not express CK7 or CK20, but most primary and metastatic
adenocarcinomas express either or both antigens.3
When
performed in a well controlled setting, staining for AFP is relatively
specific for HCC, but with a low sensitivity, with only
20% of HCCs
being positive for this protein immunohistochemically.
The recent accumulation of genetic data derived from the human genome project has led to the development of new technologies and approaches to study gene expression profiles in a global setting. One such technology, cDNA arrays, allows large-scale gene expression profiling of human tissue to discover target genes that may be useful in the identification of potential therapeutic interventions and/or diagnostic probes. This technology has been used successfully in identifying many novel genes associated with neoplastic transformation,4-10 and more recently as an investigative tool in molecular pathology.11-13 Although genetic alterations in malignancies such as breast and colon cancers are relatively well explored, this is not the case with HCC. Furthermore, currently available diagnostic markers for HCC are not optimal, and thus more accurate immunohistochemical markers for HCC are needed.
In this study, we used cDNA array analysis to identify novel gene products that may serve as immunohistochemical markers for HCC. One such candidate identified is CD10, a cell surface protein. The potential usefulness of CD10 as a diagnostic marker in HCC was then examined immunohistochemically in archival tissue with hepatic tumors, which include HCC, CC, MC, and benign bile duct adenoma (BDA), using a monoclonal antibody for CD10. Several other antibodies were also included in this study for comparison. The results show that, used in combination with AFP, immunostaining for CD10 adds a significant sensitivity to the histological identification of HCC, while maintaining the specificity. In addition, the results presented in this report emphasize the effectiveness of using cDNA array technique to examine gene expression profiles in human tumors to identify potential diagnostic markers that are useful in surgical pathology.
| Materials and Methods |
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For molecular analysis, fresh tissue samples of HCC and
surrounding nonneoplastic liver were obtained at the time of resection.
They were snap-frozen in liquid nitrogen and stored at -80°C before
RNA extraction and protein analysis. For retrospective
immunohistochemical studies, samples were retrieved from the surgical
pathology archives at the University of Texas Medical Branch Hospitals
and University of Chicago Hospitals. Multiple sections were examined
microscopically to confirm the tumor type and the degree of
differentiation. One representative block was then selected for
immunohistochemical studies. The demographics of the patients and
histological classification of the tumors are summarized in Table 1
. Among the nine cases of MCs, four had
colorectal primaries (including one neuroendocrine carcinoma), two had
pancreatic head primaries, and three had unknown primaries.
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Total cellular RNA was isolated from HCC and the surrounding nonneoplastic liver tissue, using the RNAqueous-4-PCR RNA extraction kit (Ambion, Austin, TX), according to the manufacturers instructions. Briefly, 50 mg of liver tissue was pulverized under liquid nitrogen using a mortar and pestle and the powder used for extraction of RNA. After removal of contaminating DNA by treatment with DNase 1 (Ambion), the RNA was precipitated using 5 mol/L of ammonium acetate and absolute ethanol. The quality of RNA was monitored by agarose gel electrophoresis, as demonstrated by the presence of intact ribosomal RNAs (28S and 18S bands).
cDNA probes for array analysis were synthesized following the
manufacturers directions (Clontech, Palo Alto, CA). Briefly, 4 to 5
µg of total cellular RNA was used to generate cDNA probes in the
presence of [
-32P]dATP, 10x dNTP mix (5
mmol/L each of dCTP, dGTP, and dTTP), Human 1.2II 10x CDS
primer mix, 5x reaction buffer, Moloney-murine leukemia virus reverse
transcriptase (100 U/µl), and dithiothreitol (100 mmol/L). Probes
were then hybridized to Atlas Human Array 1.2II nylon membranes
(Clontech, Palo Alto, CA) that contain 1176 spotted human cDNAs (10
ng/spot), overnight at 68°C. Arrays were washed using the
manufacturers protocols and differential gene expression patterns
were detected by phosphorimaging. Data analysis was performed using the
AtlasImage software (Clontech). Arrays were performed in duplicate and
gene expression was normalized to overall global gene expression of
each array, as recommended by the manufacturer.
Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR)
Total cellular RNA was used in a RT-PCR reaction to confirm array data. cDNA synthesis was performed using the cDNA synthesis kit (Clontech) according to the manufacturers protocol. Briefly, 1 µg of total RNA was used in a 20-µl reaction mixture containing 5x reaction buffer (250 mmol/L Tris-HCl, pH 8.3, 375 mmol/L KCl, 15 mmol/L MgCl2), 10 mmol/L each dNTP, Moloney-murine leukemia virus reverse transcriptase (40 U/µl), RNase inhibitor (1 U), and an oligo (dT)18 primer. The reaction mix was incubated at 42°C for 1 hour to synthesize the first strand cDNA, and the reaction was then terminated at 94°C for 5 minutes and diluted to 100 µl with 80 µl of diethyl pyrocarbonate H2O. Subsequently, 5 to 10 µl of diluted reaction mixtures were subjected to 35 PCR cycles, using the AdvanTaq PCR kit (Clontech) according to the manufacturers suggested protocol. The primers used were as follows: CD10: sense, 5'-CTGGAGTTCATAATGGATCTTGTAAGC-3' and antisense 5'-CATCCAAGTGAGGTCATCTAAAGTCTG-3'; GAPDH: sense 5'-GGCTCTCCAGAACATCATCCCTGC-3' and antisense 5'-GGGTGTCGCTGTTGAAGTCAGAGG-3'.
Detection of CD10 by Western Immunoblotting Analysis
Soluble cell lysates from HCC and surrounding nonneoplastic liver were prepared by lysis in 200 µl of a buffer containing 50 mmol/L Tris-Cl (pH 7.5), 150 mmol/L NaCl, 1% Nonidet P-40, 0.1% sodium deoxycholate, and 25 mg/ml of aprotinin. Equal concentrations of protein were subjected to electrophoresis in a 12% sodium dodecyl sulfate-polyacrylamide gel, followed by transfer onto Hybond-N membranes (Amersham, Arlington Heights, IL). Nonspecific binding was blocked by incubation in phosphate-buffered saline (PBS) containing 0.1% Tween 20 (PBS-T) and 5% nonfat milk for 1 hour at room temperature. The membrane was incubated overnight at 4°C with anti-CD10/CALLA (clone 56C6; Neomarkers, Freemont, CA) at a 1:200 dilution in PBS-T containing 1% bovine serum albumin (PBS-T-BSA). After four washes in PBS-T, the membrane was incubated with anti-mouse IgG conjugated to horseradish peroxidase (Sigma Chemical Co. St. Louis, MO) diluted in PBS-T-BSA for 1 hour at room temperature. After four additional washes with PBS-T, the signals were visualized by enhanced chemiluminescence (ECL Plus; Amersham).
Antibodies and Immunohistochemical Staining
Multiple 3- to 4-µm sections were cut from a formalin-fixed, paraffin-embedded tissue block, and mounted on positively charged slides. Deparaffinization and quenching in 3% methanol H2O2 were performed as described previously.14
Primary antibodies used were purchased from various vendors. Most of these antibodies had been previously titrated and used routinely in our lab. These included rabbit anti-human CEA (1:1600), monoclonal mouse anti-human CK7 (isotype IgG1, kappa, 1:200), monoclonal mouse anti-human CK20 (IgG2a, kappa, 1:100), and rabbit anti-human AFP (1:1600), purchased from DAKO (Carpinteria, CA). CD10/CALLA (neutral endopeptidase) Ab-2 antibody (clone 56C6) is a mouse monoclonal antibody purchased from NeoMarkers. The Anti-CD10 was titrated and a dilution of 1:80 was chosen in our study.
Incubation condition for each primary antibody was 30 minutes at room temperature. Appropriate positive and negative controls were used for all of the stainings. For detection of the bound primary antibodies, the LSAB2 kit with horseradish peroxidase and diaminobenzidine as chromogen was used (DAKO), following the manufacturers instructions. All of the slides were counterstained with Harris hematoxylin (Fisher Scientific, Pittsburgh, PA).
Microscopic Examination
Immunohistochemical staining was evaluated microscopically and a complete absence of staining is recorded as negative. Presence of staining was further specified as membranous, luminal, or cytoplasmic. The intensity of staining was recorded at a subjective spectrum of 1 to 3, with 1 being minimal and 3 being strong. Staining of at least 5% of the tumor cells was considered to be positive for the antibody.
| Results |
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To search for potential diagnostic markers for HCC and to better
understand genetic changes involved in HCC, we used cDNA expression
arrays to simultaneously assess the expression patterns of 1176 human
genes. We have identified a number of genes that were differentially
expressed in HCC when compared with nonneoplastic liver tissues (MR
Beard, S-Y Xiao, D Fleming, manuscript in preparation). Among
these, CD10/CALLA mRNA level was consistently up-regulated in two of
four HCC samples examined. Compared to other identified genes, CD10 was
one of the most highly differentially regulated genes, which showed
40-fold increase in mRNA abundance in HCC, as compared to the
surrounding nontumor tissue (Figure 1A)
.
The increase in its mRNA level noted in arrays was confirmed by RT-PCR
using specific primers to CD10 (Figure 1B)
. Furthermore, Western
blotting analysis demonstrated that the protein expression of CD10 was
also markedly increased in HCC (Figure 1C)
, in concordance with the
array and RT-PCR data.
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The above results clearly demonstrate that in a subset of HCC
cases, CD10 is highly up-regulated and thus may be potentially a useful
diagnostic marker for HCC. To examine this possibility,
immunohistochemical analysis was performed using a monoclonal antibody
against CD10. The results showed that nonneoplastic hepatocytes and
bile duct epithelial cells both expressed CD10. In normal hepatocytes,
however, the expression was limited to the canalicular aspects of the
cell membrane (Figure 2A)
; whereas in
bile duct epithelium, it was present on the luminal surface of the
membranes (Figure 2A)
. Neoplastic hepatocytes in HCCs also exhibited
CD10 positivity on the canalicular aspect (Figure 2B)
. Benign BDAs
showed a CD10 expression pattern similar to that seen in normal bile
duct epithelium (Figure 2C)
, but their malignant counterpart, CCs, were
negative for CD10 expression (Figure 2D)
.
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| Discussion |
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Microarray analysis of gene expression profiles in normal and
neoplastic tissues is rapidly becoming a useful tool to identify
genetic alterations and potential diagnostic markers in cancer. In this
study we have used cDNA arrays containing 1176 genes to explore the
gene expression profiles in HCC and surrounding liver tissue to
identify novel genes differentially expressed in HCC, and to explore
their potential roles in clinical diagnosis. We identified CD10 to be
up-regulated at the mRNA level in two HCCs as compared to nonneoplastic
liver tissue. The up-regulation of CD10 mRNA level was among the
highest differentially regulated genes we found, with
40-fold
increase in mRNA abundance in both HCC samples. The reliability of our
array data was validated by semiquantitative RT-PCR that demonstrated
an increase in CD10 mRNA level in tumor cells. Further analysis by
Western blotting corroborated these findings by demonstrating an
increase in CD10 protein expression level in HCC, and thus suggested
the potential use of this antigen as a diagnostic marker for HCC.
By studying archival cases of HCC, CC, and MC immunohistochemically, we demonstrated the usefulness of CD10 in differential diagnosis among these tumors. Although 60% of HCCs in this series were positive for CD10 in a canalicular pattern, all of the CCs lacked the expression of this antigen, despite the fact that CD10 is normally expressed in bile duct epithelial cells and benign BDAs.
One of nine MCs examined in our study was positive for CD10, but in a diffuse cytoplasmic staining pattern. When interpreting the result of CD10-positive staining, one must be strict about the particular canalicular staining pattern in HCCs. CD10 may be expressed in various other types of adenocarcinomas, including clear cell or papillary renal cell carcinomas, and non-small cell carcinoma of the lung.20,21 It has been reported that in some well-differentiated adenocarcinomas, CD10 positivity is restricted to the apical surface of the malignant glandular cells, which may be confused with the canalicular pattern seen in HCC. However, because these tumors are well-differentiated adenocarcinomas, they do not pose the difficulty in differential diagnosis from HCCs by routine hematoxylin and eosin stain.22 On the other hand, poorly differentiated carcinomas may shows a diffuse cytoplasmic staining pattern22 in cases that express CD10. This should be readily distinguishable from the canalicular pattern seen in HCC. Nevertheless, caution should be exercised in interpreting the result of CD10 staining, and other immunomarkers should always be considered in conjunction.
There are several other immunohistochemical markers and special mucin stains currently available to aid in the differential diagnosis of intrahepatic tumors. The CEA-p cross-reacts with the biliary glycoprotein I at the bile canalicular aspects of the hepatocyte surface.2 Although it shows a characteristic canalicular staining pattern, the interpretation of the staining with this antibody is not always straightforward, because weak cell membrane staining and cytoplasmic staining can hinder interpretation. Staining for AFP produces a cytoplasmic pattern in HCC, but is present in a small proportion of cases23 (20% of HCCs in this series). Immunostains for CKs are sometimes helpful, because HCCs are consistently negative for CK20, and usually for CK7 as well. In contrast, most CCs are CK7+/CK20-. Another recently developed immunohistochemical marker, hepatocyte paraffin-1 (HepPar1), has a relatively higher sensitivity and specificity compared to those mentioned previously.23,24 However, a significant proportion of CCs can also be positive for this marker.23 Histochemical stains for apomucin expression, such as MUC3, MUC5AC, MUC6, and MUC7, have also been described.25
Among the 15 cases of HCCs examined in this study only 1 case concurrently expresses CD10 and AFP. However, 11 cases are positive for either AFP or CD10, resulting in a combined sensitivity of 73.3%. Therefore, if used in combination in routine practice, immunostaining for AFP and CD10 alone will give rise to an acceptable sensitivity and specificity in identifying HCC. The sensitivity and specificity will be further increased if other markers are also included (ie, CEA-p, CK7, CK20).
It is not known at the present whether the increased expression of CD10 in HCCs has any role in carcinogenesis or simply represents aberrant expression in transformed cells. Biochemically, CD10 is a neutral endopeptidase that functions to reduce cellular responses to specific peptide hormones.19 CD10 has also been found to be expressed on fetal liver cells17 and hepatoblastoma.26 Further studies using normal and neoplastic hepatocyte cell lines will be necessary to elucidate the roles of CD10 and its substrates, if any, in regulating hepatocyte growth, function, and neoplastic transformation.
In summary, the data presented in this report demonstrate for the first time that a canalicular staining pattern for CD10 expression can be used as a useful diagnostic marker for HCC. This new marker identification process is achieved by using the powerful cDNA array techniques in combination with immunohistochemical approaches.
| Acknowledgements |
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| Footnotes |
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Supported in part by an Institutional Research Grant from the American Cancer Society (to M. R. B.).
Presented in part at the 90th Annual Meeting of United States and Canadian Academy of Pathology, March 2001, Atlanta, GA.
Accepted for publication July 9, 2001.
| References |
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