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The Journal of Clinical Endocrinology & Metabolism Vol. 92, No. 1 338-344
Copyright © 2007 by The Endocrine Society

Accumulation of Nonphosphorylated ß-Catenin and c-myc in Primary and Uremic Secondary Hyperparathyroid Tumors

Peyman Björklund, Göran Åkerström and Gunnar Westin

Department of Surgical Sciences, Endocrine Unit, Uppsala University Hospital, SE-751 85 Uppsala, Sweden

Address all correspondence and requests for reprints to: Gunnar Westin, Department of Surgical Sciences, Uppsala University Hospital, Klinisk forskningsavdelning 2, ingang 70, plan 3, lab 8, SE-751 85, Uppsala, Sweden. E-mail: gunnar.westin{at}surgsci.uu.se.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Context: Primary hyperparathyroidism (pHPT) resulting from parathyroid tumors is a common endocrine disorder with incompletely understood etiology, affecting about 1% of the adult population, with an even higher prevalence for elderly individuals. In renal failure, secondary hyperparathyroidism (sHPT) occurs with multiple tumor development as a result of calcium and vitamin D regulatory disturbance.

Objective: Aberrant Wnt/ß-catenin signaling with accumulation of ß-catenin in the cytoplasm/nucleus is involved in the development of a variety of neoplasms. The aim of this study was to evaluate whether the Wnt/ß-catenin signaling pathway is activated in parathyroid adenomas of pHPT and in hyperplastic glands from uremic patients with sHPT.

Design: Immunohistochemistry, Western blotting, real-time quantitative RT-PCR, and DNA sequencing were performed.

Results: ß-Catenin was accumulated in all analyzed parathyroid tumors (n = 47) from patients with pHPT and from patients with HPT secondary to uremia. The accumulation included nonphosphorylated, stabilized (transcriptionally active) ß-catenin. The overexpression was not related to increased ß-catenin mRNA levels. A protein-stabilizing mutation in exon 3 of ß-catenin (S37A) was detected in three of 20 pHPT tumors (15%). No mutation was detected in secondary hyperplastic glands (n = 20), and no evidence for truncated adenomatosis polyposis coli proteins was found in adenomas and secondary hyperplastic glands. Mutations in other Wnt signaling components leading to ß-catenin accumulation, other than in ß-catenin itself, are therefore anticipated. The ß-catenin target gene c-myc was overexpressed in a substantial fraction of the parathyroid tumors.

Conclusion: Our results strongly suggest that modifications in the Wnt/ß-catenin signaling pathway may be involved in the development of hyperparathyroidism.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
PATIENTS WITH PRIMARY hyperparathyroidism (pHPT) commonly (85%) have one enlarged hyperfunctioning parathyroid gland, a monoclonal or oligoclonal adenoma with an increased (right-shifted) set-point of the calcium-regulated PTH release. High serum PTH concentration and high serum ionized calcium concentration are diagnostic indications of this disease. In secondary HPT (sHPT), hyperplastic parathyroid glands develop in response to hypocalcemia and reduced level of 1,25-dihydroxyvitamin D3, commonly a result of renal failure. Approximately 85% of patients with the multiple endocrine neoplasia type 1 syndrome (MEN1) develop HPT. Mutation of the second MEN1 allele may result in uncontrolled growth of the cell and tumor development. Approximately 20% of sporadic parathyroid adenomas display somatic mutations in both copies of the MEN1 gene (1, 2, 3, 4). Furthermore, cyclin D1 protein overexpression has been reported in 20–40% of parathyroid tumors from patients with pHPT and in a substantial fraction of nodular hyperplasias from sHPT patients (5, 6, 7). Overexpression of cyclin D1 in the parathyroid glands of transgenic mice caused development of pHPT (8). In a small fraction of parathyroid adenomas, overexpression is a result of activation of the cyclin D1 gene by pericentromeric inversions of chromosome 11, involving the PTH promoter (9, 10).

The ubiquitously expressed multifunctional protein and protooncogene ß-catenin displays important functions in cell-cell adhesion by linking E-cadherin to the actin cytoskeleton and in the canonical Wnt signaling pathway by regulating cell proliferation and differentiation. It also plays an important role in interactions between cadherins and transmembrane proteins, such as the epidermal growth factor receptor.

In the absence of growth or differentiation signals, free cytoplasmic ß-catenin is rapidly turned over by phosphorylation of its amino terminus (Ser-33, Ser-37, Thr-41, Ser-45). A multiprotein complex consisting of glycogen synthase kinase-3ß (GSK-3ß)/adenomatosis polyposis coli (APC) /axin/casein kinase 1 regulates this phosphorylation and promotes subsequent binding of ß-transducin repeat-containing protein (ß-Trcp), ubiquitination, and degradation of ß-catenin by the proteasome pathway. Binding of Wnt ligands to the cell surface Frizzled receptors and low-density lipoprotein receptor-related protein 5/6 coreceptors leads to binding of axin to low-density lipoprotein receptor-related protein 6, blocking the GSK-3ß kinase activity together with the proteins Dishevelled and Frat, and accumulation of stabilized dephosphorylated ß-catenin and subsequent transport to the nucleus. In the nucleus, ß-catenin functions as a transcriptional cofactor by binding to transcription factor/lymphoid enhancer-binding factor (LEF) DNA-binding transcription factors or nuclear factor of kappa light polypeptide gene enhancer in B cells at target gene promoters. Over 90 target genes have been identified including c-myc, cyclin D1, E-cadherin, transcription factor-1, Ret, LEF1, ß-Trcp, c-Jun, Fra1, and RAR{gamma} (http://www.stanford.edu/~rnusse/wntwindow.html). Mutation of the ß-catenin phosphorylation sites in exon 3 (Ser-33, Ser-37, Thr-41, Ser-45) results in protein stabilization, cytoplasmic accumulation, and a constitutive ß-catenin/LEF-1 complex in melanoma cell lines (11, 12, 13, 14).

Aberrant activation of the Wnt signaling pathway, through the stabilizing ß-catenin mutations in exon 3 or inactivating APC mutations, is strongly implicated in the cause of approximately 95% of colorectal cancer. In addition, inappropriate activation of the Wnt pathway resulting from ß-catenin mutations or ß-catenin accumulation by other unknown mechanisms has recently been implicated in the development of solid-pseudopapillary tumors of the pancreas, human colonic aberrant crypt foci, hepatocellular carcinomas, esophageal, gastric, prostate, breast, liver, and colon cancers. Inactivating mutations in the AXIN and BTRC (ß-Trcp) genes have also been described in some tumors (12, 13). Here we have assessed a possible contribution of the Wnt/ß-catenin signaling pathway to parathyroid tumorigenesis.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Tissue specimens

Parathyroid adenomas and hyperplastic glands from patients with pHPT (n = 37) and sHPT (n = 20), respectively, were acquired from patients diagnosed and operated on in the clinical routine (Table 1Go). Tissues were intraoperatively snap-frozen. Normal parathyroid tissue (n = 6) was obtained from glands inadvertently removed in conjunction with thyroid surgery where autotransplantation was not required or as normal parathyroid gland biopsies in patients subjected to parathyroidectomy. Informed consent and approval of the institutional ethical committee were obtained.


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  		TABLE 1. Clinical data of the patients included in this study

 
Immunohistochemistry

Frozen tissue sections (6 µm) were stained as described previously (15) using an anti-ß-catenin goat polyclonal antibody (Santa Cruz Biotechnology, Inc., Santa Cruz, CA; catalog no. sc-1496). Control sections included use of primary antiserum preincubated with an excess of immunizing peptide (Santa Cruz Biotechnology; catalog no. sc-1496P). Most specimens were also stained with a mouse monoclonal anti-ß-catenin antibody (m1; Santa Cruz Biotechnology; catalog no. sc-7963) and some specimens with an anti-active-ß-catenin (Upstate Biotechnology, Lake Placid, NY; catalog no. 05-665) mouse monoclonal antibody (16), and a mouse anti-ß-catenin antibody (m2; BD Biosciences, Palo Alto, CA; catalog no. 610153) showing similar results. A rabbit polyclonal c-myc antibody (Santa Cruz Biotechnology; catalog no. sc-789) was used, and control sections included use of primary antiserum preincubated with an excess of immunizing peptide (Santa Cruz Biotechnology; catalog no. sc-789P). Three paraffin-embedded specimens (see Figs. 1CGo and 4CGo) were deparaffinized and subjected to antigen retrieval in 10 mM sodium citrate (pH 6.0) for 15 min in a microwave oven and thereafter stained for ß-catenin, c-myc, or proliferating cell nuclear antigen (PCNA) (Santa Cruz Biotechnology; catalog no. sc-56) as above. Sections were scored by their weak, medium, or strong staining intensity. Evaluations were made by two independent investigators.


Figure 1
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  		FIG. 1. Accumulation of ß-catenin in parathyroid tumors as revealed by immunohistochemistry and Western blotting analysis. A, Representative immunostainings of one normal parathyroid specimen and one parathyroid adenoma. An anti-ß-catenin goat polyclonal antibody was used, and as control, the antiserum was preabsorbed with an excess of immunizing peptide (magnification, x400). All 47 analyzed parathyroid tumors showed accumulation of cytoplasmic ß-catenin in comparison with normal tissue. B, Representative immunostainings with three additional anti-ß-catenin antibodies (magnification, x400). No staining was seen in the absence of primary antibodies (data not shown). C, Example of heterogenous ß-catenin staining of two secondary hyperplastic gland paraffin-embedded specimens (magnification, x20). Accumulation of ß-catenin in the cytoplasm and in the cell nucleus was evident. D, Western blotting analysis of five normal parathyroid tissue specimens and 16 HPT tumors. A longer exposure is shown in the upper panel. An anti-active (nonphosphorylated) ß-catenin monoclonal antibody (16 ) was used.

 

Figure 4
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  		FIG. 4. c-myc is overexpressed in parathyroid tumors. A, c-myc/GAPDH mRNA expression ratio for five normal parathyroid gland specimens, 17 parathyroid adenomas of pHPT, and 10 hyperplastic glands of sHPT by quantitative real-time RT-PCR. The 10log-transformed c-myc/GAPDH ratio for each specimen and the arithmetical mean values ± SEM and P values for each tumor group are shown. A circle represents the value for a single specimen. For some specimens, the values overlap or partially overlap. B, Representative immunostainings of one normal parathyroid specimen and one parathyroid adenoma. A rabbit polyclonal c-myc antibody was used, and as control, the antiserum was preabsorbed with an excess of immunizing peptide. C, Consecutive paraffin-embedded tissue sections from a hyperplastic secondary gland stained with antibodies to PCNA, ß-catenin, and c-myc. The arrow indicates an area with strong nuclear PCNA staining. ß-Catenin and c-myc stained variably overall and strongly in the depicted area.

 
Western blotting

Protein extracts for Western blotting were prepared from six to 20 consecutive frozen tissue sections (6 µm) in Cytobuster Protein Extract Reagent (Novagen Inc., Madison, WI) supplemented with Complete protease inhibitor cocktail (Roche Diagnostics GmbH, Penzberg, Germany). The anti-active (nonphosphorylated) ß-catenin (16) mouse monoclonal antibody (Upstate Biotechnology; catalog no. 05-665), the anti-APC mouse monoclonal antibody with the epitope mapping to the N terminus of APC (Santa Cruz Biotechnology; catalog no. sc-9998), and antiactin goat polyclonal antibody or anti-ß-tubulin rabbit polyclonal antibody (Santa Cruz Biotechnology) were used. After incubation with the appropriate secondary antibodies, bands were visualized using the enhanced chemiluminescence system (GE Healthcare Europe GmbH, Uppsala, Sweden).

Quantitative real-time RT-PCR

Total RNA was extracted with TriZol reagent (Life Technologies, Inc., Gaithersburg, MD) according to the manufacturer’s instructions, and the RNA was subsequently treated with RQ1 DNase I (Promega Corp., Madison, WI) and proteinase K. RT of total RNA was performed with hexamer random primers using the First-Strand cDNA synthesis kit (GE Healthcare Europe) according to the manufacturer’s instructions. The following mRNA-specific PCR primers and labeled probes (5'FAM-sequence-3'TAMRA) were used: ß-catenin (GenBank accession no. NM_001904) forward AGC CTG TTC CCC TGA GGG TAT TTG, reverse GAC TTG GGA GGT ATC CAC ATC CTC, and probe TGG CTA CTC AAG CTG ATT TGA TGG: c-myc (GenBank accession no. NM_002467) forward AAG ACT CCA GCG CCT TCT CTC CGT, reverse TGG GCT GTG AGG AGG TTT GCT GTG, and probe AGC GAC TCT GAG GAG GAA CAA GAA; GAPDH (GenBank accession no. NM_002046) forward GAA GGT GAA GGT CGG AGT C, reverse GAA GAT GGT GAT GGG ATT TC, and probe CAA GCT TCC CGT TCT CAG CC. All PCR were performed on the ABI PRISM 7700 Sequence Detection System using the TaqMan PCR core reagent kit (Applied Biosystems, Foster City, CA). Each cDNA sample was analyzed in triplicate. Standard curves for the expressed genes were established by amplifying a purified PCR fragment covering the sites for probes and primers.

Statistical analysis

Unpaired t test was used for all calculations. All data were calculated with Statistica 6 (StatSoft, Tulsa, OK). Values are presented as arithmetical mean ± SEM.

DNA sequencing of tumor DNA

DNA from parathyroid tumors (n = 40) was prepared by standard procedures including proteinase K treatment and phenol extraction. Blood DNA was prepared using the Wizard Genomic DNA purification kit (Promega). DNA was amplified by nested PCR with the following primers for exon 3 of ß-catenin (GenBank accession no. NM_001904): PCR forward primer, 5'-TGA TGG AGT TGG ACA TGG CC; forward nested, 5'-GGA ACC AGA CAG AAA AGC GG; and reverse, 5'-CTC ATA CAG GAC TTG GGA GG. Both strands of the PCR fragments were sequenced directly on ABI 373A or 3130xl Genetic Analyzer using the ABI Prism Dye Terminator Cycle Sequencing Ready Reaction kit (Applied Biosystems).


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Accumulation of ß-catenin in parathyroid tumors

To determine the ß-catenin protein expression level in normal and pathological parathyroid glands, we performed immunohistochemical analysis on frozen tissue sections with a specific goat polyclonal peptide antiserum. The analysis included six normal parathyroid gland specimens and a total of 47 parathyroid tumors from patients with pHPT (n = 37) or sHPT (n = 10). Clinical data of the patients with tumors included in the study are shown in Table 1Go. Tissue sections were incubated with the anti-ß-catenin antiserum and subsequently counterstained with hematoxylin. All six normal parathyroid specimens displayed weak but distinct membranous ß-catenin staining. All 37 adenomas and all 10 secondary hyperplastic glands stained with medium or strong intensity (Fig. 1AGo). In contrast to the normal parathyroid tissue, ß-catenin staining appeared dominantly in the cytoplasm/nucleus for the analyzed tumors. No immunoreactivity was observed when the ß-catenin antiserum was preincubated with the immunizing peptide (Fig. 1AGo). Similar aberrant accumulation of ß-catenin was also observed when using three additional anti-ß-catenin antibodies, namely a mouse monoclonal anti-ß-catenin antibody (m1), an anti-active (nonphosphorylated) ß-catenin mouse monoclonal antibody (16), and an additional mouse anti-ß-catenin antibody (m2) (Fig. 1BGo). Heterogeneous accumulation of ß-catenin was evident in some of the secondary hyperplastic glands (Fig. 1CGo). In agreement with the immunohistochemical results, Western blotting analysis revealed apparent accumulation of transcriptionally active nonphosphorylated ß-catenin in tumors (n = 16) compared with normal parathyroid (n = 5) tissues (Fig. 1DGo).

Stabilizing ß-catenin mutations in a fraction of parathyroid tumors

The observed augmented ß-catenin protein expression in the parathyroid tumors could be a result of increased transcription of the gene, protein-stabilizing mutations in exon 3, inactivation of APC, or other mechanisms. The overall ß-catenin mRNA expression levels of normal glands and the two tumor groups displayed small differences, with a considerable variation in mRNA level between individual specimens (Fig. 2Go). Thus, no relation of ß-catenin protein expression to ß-catenin mRNA expression could be demonstrated. To look for protein-stabilizing mutations, exon 3 of ß-catenin was PCR amplified from DNA of 20 adenomas and 20 secondary hyperplastic glands, and the sequence was determined of both strands. Homozygous mutations in exon 3 of ß-catenin were detected in three adenomas (15%), where serine 37 (TCT) was replaced by alanine (GCT). No mutations were found in the secondary hyperplastic glands. Constitutional DNA (blood) from two patients with mutation-associated tumor encoded the wild-type ß-catenin sequence.


Figure 2
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  		FIG. 2. Determination of ß-catenin/GAPDH mRNA expression ratio for five normal parathyroid gland specimens, 17 parathyroid adenomas of pHPT, and 10 hyperplastic glands of sHPT by quantitative real-time RT-PCR. The 10log-transformed ß-catenin/GAPDH ratio for each specimen and the arithmetical mean values ± SEM and P values for each tumor group are shown. A triangle represents the value for a single specimen. For some specimens, the values overlap or partially overlap. The variation among the ratios was due to differences of ß-catenin values and not of GAPDH.

 
Inactivation of APC, commonly by truncating mutations in sporadic colorectal cancers (17), disrupts the normal degradation of ß-catenin through the proteasomal pathway (12, 13). Western blotting analysis, using a mouse monoclonal antibody with the epitope mapping at the N terminus of APC, revealed no evidence for truncated APC proteins in parathyroid adenomas or secondary hyperplastic parathyroid glands (Fig. 3Go).


Figure 3
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  		FIG. 3. Wild-type APC is detected in parathyroid tumors. Western blotting analysis using an antibody with the epitope mapping at the N terminus of APC. Top, Lanes 1 and 2, normal parathyroid; lanes 3–12, parathyroid adenomas of pHPT. Bottom, Lane 1, normal liver; lane 2, normal breast; lanes 3–12, hyperplastic glands of sHPT. Coomassie blue-stained filters are shown as loading control.

 
c-myc is overexpressed in parathyroid tumors

c-myc constitutes a ß-catenin target gene (18) and plays a role in normal parathyroid cell cycle regulation (19). We therefore related the relative c-myc mRNA expression level of parathyroid tumors to that of normal parathyroid tissue and also investigated c-myc protein expression by immunohistochemistry. c-myc mRNA expression was significantly higher in parathyroid tumors from the two patient groups (Fig. 4AGo). The number of tumors displaying at least 2-fold increased relative c-myc mRNA expression was 10 of 17 (59%) for adenomas and three of 10 (30%) for secondary hyperplastic glands. A subset of the tumors (n = 19) was stained with a c-myc antibody, revealing distinct strong but variable specific cytoplasmic/nuclear staining in 15 parathyroid tumors (79%), compared with normal specimens displaying weak staining (Fig. 4BGo). Of the 19 stained parathyroid tumors, four showed normal c-myc mRNA and protein expression, whereas three tumors displayed strong c-myc immunoreactivity with mRNA expression levels within the normal range. Twelve tumors, including three adenomas with the ß-catenin S37A mutation, had both increased c-myc protein and mRNA expression. As stated above, all 27 tumors (Fig. 4AGo) showed aberrant accumulation of ß-catenin. Quantification of the nonphosphorylated ß-catenin protein relative to ß-tubulin of the tumors in Fig. 1DGo revealed a similar level among the specimens (within 1.5-fold). All these tumors overexpressed c-myc at the mRNA level (3- to 16-fold, data not shown), further substantiating a correlation of ß-catenin accumulation to c-myc overexpression. As shown in Fig. 1CGo, some hyperplastic glands displayed heterogeneous accumulation of ß-catenin. The immunohistochemical staining of consecutive tissue sections from hyperplastic glands with antibodies to the proliferation marker PCNA, ß-catenin, and c-myc overlapped in areas of evenly distributed as well as clusters of few strongly PCNA-positive (20) cells (Fig. 4CGo), further suggesting a role of ß-catenin accumulation in parathyroid hyperplasia. Many cells with overlapping ß-catenin and c-myc staining were apparently PCNA negative.


   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Our finding of ß-catenin protein accumulation in all analyzed parathyroid tumors of pHPT and hyperplastic parathyroid glands of HPT secondary to uremia strongly suggests activation of the Wnt signaling pathway as a major aberration common to these forms of HPT. Mutation (S37A) in exon 3 of ß-catenin was observed in three of 20 parathyroid adenomas (15%), whereas wild-type sequence was detected in the secondary hyperplastic glands (n = 20). The S37A mutations were homozygous as revealed by direct DNA sequencing and by sequencing of recombinant clones of the primary PCR fragment (data not shown). Homozygous mutation of ß-catenin seems to be uncommon in other tumor types but has been described in colorectal cancer (21). The level of Wnt/ß-catenin activity seems to regulate polyp multiplicity in a mouse intestinal tumor model and the dosage of ß-catenin signaling modulates embryonic stem cell differentiation (22, 23). In parathyroid cells, the combined Wnt/ß-catenin activity of two activating S37A ß-catenin alleles may be required for benign tumor growth. The S37A mutation is found at varying frequency in many different tumor types, and is particularly common in gastrointestinal carcinoid tumors (13, 24). The S37A mutant is resistant to ubiquitination and proteosomal degradation, with a longer half-life than wild-type ß-catenin (25, 26). Whether S37A represents the most frequent ß-catenin mutation in parathyroid tumors and whether it performs cell-type-specific functions remains to be determined. In agreement with our results, cytoplasmic ß-catenin immunoreactivity was reported in an analysis of 12 parathyroid tumor specimens (27). An additional study of 24 specimens found no evidence for ß-catenin accumulation (28). The reason for this discrepancy is unclear but could be explained by the experimental conditions used. In the present work, frozen tissues were used instead of paraffin-embedded material. Both studies failed to demonstrate stabilizing mutations of the ß-catenin gene (27, 28), likely explained by the low mutation frequency.

Accumulation of ß-catenin through stabilizing mutations or other mechanisms may result in deregulated transcription of Wnt signaling target genes and promotion of oncogenic signals that lead to tumor formation (11, 12, 13, 14). In colorectal cancer, aberrant accumulation of ß-catenin is caused by inactivating mutations in APC (85%) or stabilizing mutations in ß-catenin (10%). Most somatic mutations of APC lead to loss or truncations (17). We found no evidence for APC truncations in the parathyroid tumors analyzed here. Mutations in other Wnt signaling components leading to aberrant ß-catenin accumulation is therefore anticipated. Allelic loss on chromosome 5q where the APC gene is located has not been observed in parathyroid adenomas (29), but interestingly, accumulation of cytoplasmic ß-catenin has been demonstrated in the parathyroid tumors from a sporadic case with familial adenomatous polyposis- and MEN1-related tumors. The MEN1 gene was normal, whereas a germline mutation was found in the APC gene, and loss of the normal APC allele had occurred in the tumors (30).

The cyclin D1 oncogene, which constitutes a ß-catenin target gene in some tissues, is overexpressed at the protein level in 20–40% of parathyroid tumors from pHPT patients and in a substantial fraction of nodular hyperplasias from sHPT patients (5, 6, 7). In a small subset of parathyroid adenomas, overexpression is caused by an inversion event on chromosome 11, bringing the cyclin D1 gene under control of the PTH promoter (9, 10). It is likely that augmented cyclin D1 expression also could be caused by aberrant ß-catenin accumulation in a different subset of parathyroid tumors.

We found the ß-catenin target gene c-myc to be overexpressed in a substantial fraction of the analyzed parathyroid tumors. In 12 of 19 analyzed tumors, both protein and mRNA was found to be overexpressed, but three tumors showed strong c-myc protein overexpression with mRNA levels within the normal range. This observation raises a possibility of interference with the GSK-3ß-dependent degradation of c-myc, which may be regulated by a Wnt signaling pathway (31, 32). c-myc plays a role in normal parathyroid cell cycle regulation (19), and overexpression conceivably contributes to the enlarged hyperactive parathyroid glands characteristic of HPT. As has been suggested for cyclin D1 overexpression in pHPT (8), deregulated cell-growth control by c-myc or other factors may also be a primary cause of the abnormal control of PTH secretion by serum calcium.

A correlation between ß-catenin and tumorigenesis is well established (12, 13, 14). Small interfering RNAs or small molecule inhibitors directed against ß-catenin inhibit ß-catenin-dependent signaling and growth of colon cancer cells in vitro and in mouse models of colon cancer (33, 34, 35, 36). We have demonstrated aberrant accumulation of stabilized ß-catenin in parathyroid tumors of both pHPT and sHPT patients, possibly suggesting a common pathway of pathogenesis of the two conditions. Although mutation(s) leading to ß-catenin accumulation, other than in ß-catenin itself, remains to be identified in other Wnt signaling components, our findings suggest that ß-catenin may be a novel therapeutic target for HPT.


   Acknowledgments
 
We are grateful to B. Bondeson and P. Lillhager for skillful and extensive technical assistance.


   Footnotes
 
This work was supported by the Swedish Research Council, Swedish Cancer Society, and Lions Fund for Cancer Research.

Disclosure Statement: The authors have nothing to declare.

First Published Online October 17, 2006

Abbreviations: APC, Adenomatosis polyposis coli; GSK-3ß, glycogen synthase kinase-3ß; LEF, lymphoid enhancer-binding factor; MEN1, multiple endocrine neoplasia type 1 syndrome; PCNA, proliferating cell nuclear antigen; pHPT, primary hyperparathyroidism; sHPT, secondary hyperparathyroidism; ß-Trcp, ß-transducin repeat-containing protein.

Received June 2, 2006.

Accepted October 5, 2006.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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