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From the Department of Pathology,*
Division of
Gastrointestinal/Liver Pathology, and the Department of Internal
Medicine,
Division of Gastroenterology, The
Johns Hopkins University School of Medicine, Baltimore, Maryland
| Abstract |
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| Introduction |
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0.5% of head and
neck tumors.1
Although histologically benign, they have
been reported to recur after surgical therapy in 21 to 34% of patients
and can be locally aggressive.1,2
JNAs typically arise
from the posterolateral wall of the nasal cavity and grow by
erosion of bone and displacement of adjacent structures; eventually
these lesions can involve the nasopharynx, paranasal sinuses, orbit,
and skull base with intracranial extension.1
Histopathologically, JNAs are characterized by proliferating, irregular
vascular channels within a fibrous stroma. The stromal compartment
consists of plump cells that can be spindled or stellate in shape and
give rise to varying amounts of collagen
fibers.3 The pathogenesis of JNAs is unknown. However, a causal association between JNAs and familial adenomatous polyposis (FAP) has recently been suggested, with JNAs occurring 25 times more frequently in patients with FAP than in an age-matched population.4,5 FAP is an autosomal-dominant condition characterized by upper and lower gastrointestinal tract adenomas, a high tendency for the development of colorectal and periampullary adenocarcinomas, and by various extraintestinal manifestations including benign epidermal cysts, osteomas, desmoid tumors, and malignant tumors of the thyroid, liver, biliary tree, and brain.6-11
FAP results from germline mutations in the adenomatous polyposis coli (APC) gene on chromosome 5q. The APC gene product regulates the level of ß-catenin protein, which acts both as a submembranous component in cadherin-mediated cell-cell adhesion and as a downstream transcriptional activator in the Wnt signaling pathway.12,13 APC tumor suppressor protein, along with glycogen synthase kinase-3ß (GSK-3ß), promotes phosphorylation of serine/threonine residues encoded in exon 3 of the ß-catenin gene.12,14,15 Phosphorylation is then followed by ubiquitin-mediated degradation of ß-catenin protein.16,17 Loss of ß-catenin regulatory activity resulting in accumulation of ß-catenin protein can occur either by truncating APC gene mutations or by stabilizing ß-catenin gene mutations at GSK-3ß phosphorylation sites.15,18,19 A majority of colorectal adenomas and carcinomas can be shown to contain either bi-allelic inactivation of the APC gene or activating ß-catenin gene mutations.20,21
The increased incidence of JNA in patients with FAP raised the possibility that either APC or ß-catenin gene mutations affecting the APC/ß-catenin pathway might also be involved in the pathogenesis of sporadic JNAs. We therefore analyzed a series of JNAs from patients without FAP for mutations in both the APC and ß-catenin genes.
| Materials and Methods |
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The study population consisted of 16 primary JNAs and six recurrent JNAs from 16 patients who underwent surgical resection at The Johns Hopkins Hospital between 1984 and 1999. Tumor recurrences were resected from 4 months to 5 years after the original surgery (mean, 24 months). All patients were male and ranged in age from 10 to 24 years (mean, 14 years) at the time of initial surgery. None of the patients was known to have FAP and none was enrolled in The Johns Hopkins Polyposis Registry.
Immunohistochemistry for ß-Catenin
Immunoperoxidase stain using diaminobenzidine as the chromogen was performed on the Techmate 1000 automatic staining system (BioTek Solutions, Tucson, AZ). Deparaffinized sections of formalin-fixed tissue were stained with ß-catenin antibody (mouse monoclonal antibody; Becton Dickinson Transduction Laboratories, Lexington, KY) at 1:500 dilution after heat-induced antigen retrieval.22
DNA Extraction
Microdissection of JNAs from hematoxylin and eosin-stained slides for DNA extraction was performed from formalin-fixed, paraffin-embedded specimens. Genomic DNA was extracted as described previously.23 Corresponding normal control DNA was extracted from nonneoplastic nasopharyngeal mucosa in 15 of 16 patients (normal tissue was not available in the remaining case).
Mutation Analysis of the ß-Catenin Gene
Genomic DNA from each sample was amplified by polymerase
chain reaction (PCR) using the primer pair: 5'-ATGGAACCAGACAGAGGGGC-3'
and 5'-GCTACTTGTTCTGAGTGAAG-3'. These amplified a 200-bp fragment of
exon 3 of the ß-catenin gene that encompasses the
region for GSK-3ß phosphorylation. PCR reaction was performed under
standard conditions in a 50-µl volume using PCR Master [containing
1.25 U of Taq polymerase in Brij 35, 0.005% (v/v), dATP,
dCTP, dGTP, and dTTP at 0.2 mmol/L, 10 mmol/L Tris-HCl, 50 mmol/L KCl,
and 1.5 mmol/L MgCl2 (Boehringer Mannheim,
Mannheim, Germany)] and 1 µmol/L of both 5' and 3' oligonucleotides
with 40 cycles (94°C for 1 minute, 58°C for 1 minute, and 72°C
for 2 minutes). PCR products were treated with shrimp alkaline
phosphatase and exonuclease I (Amersham, Buckinghamshire, UK) before
sequencing. Treated PCR products were sequenced directly with
SequiTherm EXCEL II DNA sequencing kit (Epicentre, Madison, WI) using
the internal primers: 5'-AAAGCGGCTGTTAGTCACTFF-3' and
5'-GACTTGGGAGGTATCCACATCC-3'. Oligonucleotides were end-labeled with
(
-32P)-ATP (New England Nuclear-DuPont,
Boston, MA) using T4 polynucleotide kinase (New England Biolabs,
Beverly, MA). All mutations were verified in both sense and antisense
directions. Base substitutions in codons 32, 33, and the second
position of codon 34 were further confirmed by HinfI
restriction endonuclease (Promega, Madison, WI) assay. The 200-bp PCR
product for ß-catenin contains two HinfI
restriction endonuclease sites, which yield DNA fragments of 7 bp, 55
bp, and 138 bp after digestion of the wild-type allele.
ß-catenin mutations in codons 32 and 33 yield only
62-bp and 138-bp fragments after digestion because of ablation of the
first HinfI site. Mutations in the second position of codon
34 yield 55-bp and 145-bp fragments because of ablation of the other
HinfI site.
Mutation Analysis of the APC Gene
Mutation analysis of the APC gene was performed only on cases that did not show detectable ß-catenin mutations. Four sets of oligonucleotide primers (A1: 5'-CAGACTTATTGTGTAGAAGA-3' and A2: 5'-CTCCTGAAGAAAATTCAACA-3' for codons 1260 to 1359; B1: 5'-AGGGTTCTAGTTTATCTTCA-3' and B2: 5'-TCTGCTTGGTGGCATGGTTT-3' for codons 1339 to 1436; C1: 5'-GGCATTATAAGCCCCAGTGA-3' and C2: 5'-AAATGGCTCATCGAGGCTCA-3' for codons 1417 to 1516; D1: 5'-ACTCCAGATGGATTTTCTTG-3' and D2: 5'-GGCTGGCTTTTTTGCTTTAC-3' for codons 1497 to 1596) were used to amplify the mutation cluster region of the APC gene.24 PCR reaction was performed under standard conditions in a 50-µl volume using PCR Master (Boehringer Mannheim) and 1 µmol/L of both 5' and 3' oligonucleotides with 40 cycles (94°C for 1 minute, 55°C for 1 minute, and 68°C for 2 minutes for APC-B, -C, and -D primer pairs and 94°C for 1 minute, 52°C for 1 minute, and 68°C for 2 minutes for APC-A). PCR products were purified using shrimp alkaline phosphatase and exonuclease I. Purified PCR products were sequenced directly with SequiTherm EXCEL II DNA sequencing kit using the same primers as for DNA amplification.
| Results |
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All 16 primary JNAs and the six recurrent tumors showed strong,
diffuse nuclear staining for ß-catenin (Figure 1)
. In all cases the nuclear staining was
present only within stromal cell nuclei. Endothelial cell nuclei and
the nuclei of vascular smooth muscle cells showed faint cytoplasmic
staining but no nuclear ß-catenin accumulation.
Immunohistochemical staining of normal nasopharyngeal tissue was also
evaluated in a total of 14 cases that included this tissue on the
slides stained for evaluation of the JNAs (comprising 10 cases with
surface epithelium, eight cases with nonlesional fibrovascular stroma,
seven cases with subepithelial lamina propria, and one case with
cartilage). Strong membranous staining and light cytoplasmic staining
for ß-catenin was present within surface epithelium
and seromucinous glands of the lamina propria in all cases that
contained these elements. However, no nuclear accumulation of
ß-catenin was present in any nontumorous tissues.
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Mutations in exon 3 of the ß-catenin gene were
detected in 12 (75%) of 16 JNAs. The somatic nature of the mutations
was confirmed by finding no ß-catenin gene mutations
in the corresponding normal nasopharyngeal tissue from these patients
(available in 15 patients). In nine JNAs, mutations were 1-bp missense
mutations, predominantly in one of the serine/threonine residues at
GSK-3ß phosphorylation sites: codon 33 (five cases), codon 34 (two
cases), codon 35 (one case), and codon 37 (one case) (Figure 2)
. Three additional JNAs contained
deletions in exon 3 of ß-catenin (an 18-bp deletion
spanning codons 33 to 39, a 36-bp deletion spanning codons 28 to 40,
and a 27-bp deletion spanning codons 39 to 48) (Figure 3)
. In all tumors with
ß-catenin gene mutations, a mixture of wild-type and
mutant bands was present, as would be expected because of the
dominant-positive effect of ß-catenin gene
alterations. All five tumors with codon 33 mutations that could be
evaluated with HinfI restriction endonuclease digestion
showed the expected ablation of the HinfI recognition site.
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The four JNAs that did not show ß-catenin gene mutations were further evaluated for APC mutations by sequencing of the APC mutation cluster region. However, no APC gene mutations were detected.
ß-Catenin/APC Genes Mutations in Recurrent JNAs
Analysis of the six recurrent JNAs demonstrated identical genetic
status between the primary tumor and recurrence. In five cases,
identical ß-catenin gene mutations were present in
both primary and recurrent tumor, and in the remaining case no
alteration in either ß-catenin or APC
was detected in the primary or recurrent tumor. A summary of genetic
alterations in primary and recurrent JNAs is given in Table 1
.
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| Discussion |
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We identified mutations in exon 3 of the ß-catenin gene in 75% (12 of 16) sporadic JNAs from non-FAP patients. These mutations were predominantly 1-bp missense mutations in codons 33 and 37 (six cases total) leading to loss of serine/threonine sites for GSK-3ß phosphorylation. Other exon 3 mutations in codons 34 and 35 (three cases total) did not involve loss of a phosphorylation site but may still interfere with degradation of the ß-catenin gene product.21 Three cases contained deletion mutations ranging from 18 bp to 36 bp and would be expected to interfere with ß-catenin protein degradation. All six recurrent JNAs in our series showed ß-catenin gene status that was identical to that of the corresponding primary tumors (ß-catenin gene mutations in five cases and no ß-catenin or APC mutation in the remaining case).
This high frequency of ß-catenin gene mutations in sporadic JNAs, coupled with the increased frequency of JNAs among patients with FAP, suggests that these lesions arise through alterations of the APC/ß-catenin pathway. The presence of identical ß-catenin gene mutations in the primary and recurrent tumors further supports that these genetic alterations are important and are maintained through the temporal growth of the tumors.
Somatic alterations of the APC/ß-catenin pathway have now been demonstrated in the sporadic counterparts to most tumors that occur frequently in FAP patients, including gastrointestinal adenomas,20,21,28,29 desmoid tumors,30-32 medulloblastomas,33 childhood hepatoblastomas,34-35 and gastric fundic gland polyps.36 ß-catenin mutations have also been reported in a variety of other tumors such as anaplastic thyroid carcinoma,37 prostatic carcinoma,38 endometrial carcinoma,39-41 pilomatricoma,42 Wilms tumor,43 and hepatocellular carcinoma.44-46 Among patients with FAP, intestinal and extra-intestinal neoplasms typically arise through bi-allelic (germline then somatic) inactivation of the APC gene, whereas the corresponding tumors in non-FAP patients occur either through somatic bi-allelic APC inactivation or somatic mutation of a single ß-catenin allele. In contrast to the high frequency of ß-catenin gene mutations detected in JNAs in this study, APC mutations in the mutation cluster region were not found. However, we did not sequence the entire APC gene in this study and we did not analyze tumors from patients with FAP, and therefore it remains possible that a specific subset of JNAs would contain bi-allelic inactivation of the APC gene.
The demonstration of nuclear ß-catenin accumulation in all JNAs but ß-catenin mutations in only 75% of the JNAs is interesting. Nuclear ß-catenin accumulation can result from mutations in APC, ß-catenin, or AXIN1 (axis inhibitor 1) genes. The AXIN1 gene encodes a key factor for the WNT signaling pathway, and interacts with APC, ß-catenin, and GSK3ß, playing an important role in the degradation of ß-catenin.47 Somatic mutations of AXIN1 have been reported in three of six hepatocellular carcinoma (HCC) cell lines and five of 87 primary HCCs.48 In this study, we did not analyze for mutations in the AXIN1 gene. However, the role of AXIN1 in the pathogenesis of JNAs remains to be clarified.
All JNAs in our series showed strong immunohistochemical accumulation of ß-catenin protein within the nuclei of stromal cells, whereas endothelial cells and vascular smooth muscle cells showed only faint cytoplasmic staining without nuclear ß-catenin accumulation. JNAs are well known to be characterized histologically by proliferations of both vascular channels and spindled to stellate-shaped stromal cells that show ultrastructural features of fibroblasts,3 although the specific neoplastic cell has been debated. Some investigators have regarded JNAs as predominantly vasoproliferative malformations because of their tendency to bleed, their striking vascularity, and the presence of angiogenic growth factors within lesional endothelial cells.3,49 Schiff and colleagues49 demonstrated intense immunohistochemical staining for the angiogenic protein basic fibroblast growth factor or FGF within all endothelial cells of JNAs, whereas only some stromal cells were stained. In contrast, Hwang and colleagues27 found androgen receptor positivity by immunohistochemistry in both the endothelial cells and stromal cells of the majority of JNAs studied, although staining was typically more intense in the stromal cells. Our results indicate that JNAs are true neoplasms containing clonal alterations in the ß-catenin oncogene, and suggest that the stromal component is the key neoplastic element of JNAs.
| Footnotes |
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Accepted for publication November 29, 2000.
| References |
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