HRPT2 mutations are associated with malignancy in sporadic parathyroid tumours

Non-functional parathyroid carcinoma: a review of the literature and report of a case requiring extensive surgery

Parathyroid carcinoma is a rare malignancy, and only accounts for 0.5-2% of cases of primary hyperparathyroidism. Less than 10% of parathyroid carcinomas are non-functional, and as such, they have been rarely reported in the literature. Importantly, margin status at resection is related to prognosis, and only a handful of case reports of non-functional carcinoma note this important parameter. Here we report the first case of non-functional parathyroid carcinoma with negative margins, and review the literature on this rare entity. Whether functional or non-functional, parathyroid carcinoma can often be difficult to differentiate from benign parathyroid adenoma. While diagnosis has been based on clinical and histological criteria, recent data concerning the molecular underpinnings of parathyroid carcinoma may allow for improved accuracy in distinguishing benign and malignant parathyroid tumors.

Defining a molecular phenotype for benign and malignant parathyroid tumors

BACKGROUND

It is frequently difficult to establish histologically whether a parathyroid tumor is a parathyroid carcinoma, parathyromatosis, or an atypical adenoma. The authors asked whether these tumors have a distinctive molecular profile, whether benign tumors could be distinguished from malignant tumors, and whether parathyromatosis is a low-grade parathyroid carcinoma or is benign tissue that can invade other organs.

METHODS

Samples of parathyroid carcinoma, atypical adenoma, parathyromatosis, parathyroid adenoma, and hyperplasia were obtained for tissue microarray studies. The molecular expression of genes involved in parathyroid tumor progression (HRPT2 ["parafibromin"], galectin-3, Ki-67, Rb, p27, and mdm-2) was investigated by immunohistochemistry.

RESULTS

Complete loss of parafibromin expression was seen in 5 of 16 (31.3%) parathyroid carcinomas; all parathyromatosis, atypical adenomas, adenomas, and hyperplasia stained positive for parafibromin. Loss of Rb expression was seen in 5 (33.3%) of 15 parathyroid carcinomas and 1 (7.1%) of 14 parathyroid hyperplasias; all parathyromatosis, atypical adenomas, and adenomas stained positive. Galectin-3 stained strongly positive in 14 (93.3%) of 15 parathyroid carcinomas, and positive in 3 (18.7%) of 16 cases of parathyromatosis, 2 (100%) of 2 atypical adenomas, 1 (5.6%) of 18 adenomas, and 2 (14.3%) of 14 hyperplasias. The Ki-67 proliferative index was high in 9 (60%) of 15 parathyroid carcinomas, 1 (6.7%) of 15 cases of parathyromatosis, 1 (5.6%) of 18 adenomas, and no atypical adenomas or hyperplasia. P27 and mdm-2 protein expression did not differ appreciably among the tumor types.

CONCLUSIONS

No single diagnostic marker currently determines whether a parathyroid tumor is a parathyroid carcinoma, but loss of parafibromin and Rb expression, and overexpression of galectin-3, generally distinguish parathyroid carcinoma from other parathyroid tumors. Parathyromatosis does not appear to be a low-grade parathyroid carcinoma.

Accuracy of combined protein gene product 9.5 and parafibromin markers for immunohistochemical diagnosis of parathyroid carcinoma

CONTEXT

Parafibromin, encoded by HRPT2, is the first marker with significant benefit in the diagnosis of parathyroid carcinoma. However, because parafibromin is only involved in up to 70% of parathyroid carcinomas and loss of parafibromin immunoreactivity may not be observed in all cases of HRPT2 mutation, a complementary marker is needed.

OBJECTIVE

We sought to determine the efficacy of increased expression of protein gene product 9.5 (PGP9.5), encoded by ubiquitin carboxyl-terminal esterase L1 (UCHL1) as an additional marker to loss of parafibromin immunoreactivity for the diagnosis of parathyroid carcinoma.

DESIGN

In total, 146 parathyroid tumors and nine normal tissues were analyzed for the expression of parafibromin and PGP9.5 by immunohistochemistry and for UCHL1 by quantitative RT-PCR. These samples included six hyperparathyroidism-jaw tumor syndrome-related tumors and 24 sporadic carcinomas.

RESULTS

In tumors with evidence of malignancy, strong staining for PGP9.5 had a sensitivity of 78% for the detection of parathyroid carcinoma and/or HRPT2 mutation and a specificity of 100%. Complete lack of nuclear parafibromin staining had a sensitivity of 67% and a specificity of 100%. PGP9.5 was positive in a tumor with the HRPT2 mutation L64P that expressed parafibromin. Furthermore, UCHL1 was highly expressed in the carcinoma/hyperparathyroidism-jaw tumor syndrome group compared to normal (P < 0.05) and benign specimens (P < 0.001).

CONCLUSION

These results suggest that positive staining for PGP9.5 has utility as a marker for parathyroid malignancy, with a slightly superior sensitivity (P = 0.03) and similar high specificity to that of parafibromin.

The tumor suppressor Cdc73 functionally associates with CPSF and CstF 3' mRNA processing factors

The CDC73 tumor suppressor gene is mutationally inactivated in hereditary and sporadic parathyroid tumors. Its product, the Cdc73 protein, is a component of the RNA polymerase II and chromatin-associated human Paf1 complex (Paf1C). Here, we show that Cdc73 physically associates with the cleavage and polyadenylation specificity factor (CPSF) and cleavage stimulation factor (CstF) complexes that are required for the maturation of mRNA 3' ends in the cell nucleus. Immunodepletion experiments indicate that the Cdc73-CPSF-CstF complex is necessary for 3' mRNA processing in vitro. Microarray analysis of CDC73 siRNA-treated cells revealed INTS6, a gene encoding a subunit of the Integrator complex, as an in vivo Cdc73 target. Cdc73 depletion by siRNA resulted in decreased INTS6 mRNA abundance, and decreased association of CPSF and CstF subunits with the INTS6 locus. Our results suggest that Cdc73 facilitates association of 3' mRNA processing factors with actively-transcribed chromatin and support the importance of links between tumor suppression and mRNA maturation.

[Indication and performance of endocrine surgery. The significance of molecular genetic examination]

The molecular genetic changes from certain endocrine tumors are already understood, reflecting as they do the etiology of these sporadic familial disorders. This already has clinical consequences to the treatment of familial endocrine tumors, which often appear in the course of syndromatic disorders. These consequences consist in slight changes to surgical technique, the search for other active and usually endocrinal tumors, and examination of family members for other gene carriers (of disease-specific mutations) and the most suitable prophylactic tumor therapy. In contrast, for sporadic endocrine tumors there exists far less clinically relevant knowledge. Starting with anamnesis and clinical findings of active endocrine tumors, we discuss the current possibilities for molecular genetic determination of disease-specific mutations (germline and tumor DNA) and their effect on surgical procedure.

The parafibromin tumor suppressor protein inhibits cell proliferation by repression of the c-myc proto-oncogene

Parafibromin is a tumor suppressor protein encoded by HRPT2, a gene recently implicated in the hereditary hyperparathyroidism-jaw tumor syndrome, parathyroid cancer, and a subset of kindreds with familial isolated hyperparathyroidism. Human parafibromin binds to RNA polymerase II as part of a PAF1 transcriptional regulatory complex. The physiologic targets of parafibromin and the mechanism by which its loss of function can lead to neoplastic transformation are poorly understood. We show here that RNA interference with the expression of parafibromin or Paf1 stimulates cell proliferation and increases levels of the c-myc proto-oncogene product, a DNA-binding protein and established regulator of cell growth. This effect results from both c-myc protein stabilization and activation of the c-myc promoter, without alleviation of the c-myc transcriptional pause. Chromatin immunoprecipitation demonstrates the occupancy of the c-myc promoter by parafibromin and other PAF1 complex subunits in native cells. Knockdown of c-myc blocks the proliferative effect of RNA interference with parafibromin or Paf1 expression. These experiments provide a previously uncharacterized mechanism for the anti-proliferative action of the parafibromin tumor suppressor protein resulting from PAF1 complex-mediated inhibition of the c-myc proto-oncogene.

[An historical case of malignant hyperparathyroidism with unusual metastatic sites]

We report a historical case of hyperparathyroidism in a young patient hospitalized for an array of osteolytic foci and incomplete fracture associated with a swollen neck, revealing a very special form of a metastatic parathyroid carcinoma with unusual multiple locations and exceptional medullary flooding. Carcinoma of the parathyroid gland produces a malignant hypersecreting tumor particularly difficult to diagnose. Treatment of this rare tumor is primarily surgical. The preoperative syndrome is unusually severe primary hyperparathyroidism. Intraoperatively, the size of the tumor and its local extension to surrounding tissue are highly suggestive. Confirmation requires pathological analysis of the operative specimens and can be further supported by the clinical course of local recurrence or metastasic spread. Specific immunohistochemical techniques have recently been shown to be contributive. The diagnosis is strengthened in the presence of associated Schantz and Castelman criteria. Foci of local extension can be identified preoperatively with ultrasound, (99m)Tc-sestamibi scintigraphy and MRI of the neck and mediastinum. The prognosis depends mainly on the possibility of achieving complete resection at the initial surgery. In some cases, very aggressive complementary postoperative radiotherapy is likely to improve locoregional control of the tumor. Chemotherapy alone or in combination with radiation has not demonstrated its effectiveness. The disease course and control can be monitored by regular assay of serum calcium and the parathormone.

Hyperparathyroidism 2 gene (HRPT2, CDC73) and parafibromin studies in two patients with primary hyperparathyroidism and uncertain pathological assessment

HRPT2 and parafibromin studies improved the diagnostic accuracy in two patients with primary hyperparathyroidism (PHPT) referred to us after surgery, in whom the clinical data were at variance with the pathological diagnosis of adenoma and carcinoma, respectively. Patients were referred to us after parathyroidectomy. Patient #1 had had a 1.5-cm tumor easily removed with a histological diagnosis of parathyroid carcinoma and normocalcemia for 2 years. Re-examination of the histology showed no cardinal signs of parathyroid cancer. Patient #2, with severe PHPT, had had the removal of a 3.5-cm tumor described histologically as adenoma. Ten years later PHPT recurred and persisted despite removal of two mildly enlarged parathyroid glands that were histologically normal. Re-review of the initial histology showed a trabecular pattern, fibrous bands, and atypical mitoses, suggesting an atypical adenoma. Because of the suspicion that case #1 could be an atypical adenoma and case #2 a carcinoma further molecular studies were performed. No HRPT2 and parafibromin abnormalities were identified in patient #1, strongly indicating a benign lesion. In patient #2, an HRPT2 germline mutation was found (E115X in exon 4) and associated with no parafibromin staining. These data, together with the clinical features, supported the suspicion of a parathyroid carcinoma that was confirmed by histological examination of further slides of the tumor, showing capsular and vascular invasion. A lung 1.5-cm nodule detected by computed tomography was excised. Histology showed a metastasis of parathyroid carcinoma. HRPT2 gene studies improved the diagnostic accuracy in 2 parathyroid tumors that are of uncertain type.

Human PAF complexes in endocrine tumors and pancreatic cancer

The human RNA polymerase II-associated factor (hPAF) complex is comprised of five subunits that include hPaf1, parafibromin, hLeo1, hCtr9 and hSki8. This multifaceted complex was first identified in yeast (yPAF) and subsequently in Drosophila and humans. Recent advances in the study on hPAF have revealed various functions of the complex in humans that are similar to yPAF, including efficient transcription elongation, mRNA quality control and cell cycle regulation. A major component of the hPAF complex, hPaf1, is amplified and overexpressed in pancreatic cancer. The parafibromin subunit of the hPAF complex is a product of the hereditary hyperparathyroidism type 2 (HRPT-2) tumor-suppressor gene, which is mutated in the germ line of hyperparathyroidism-jaw tumor patients. This review evaluates the role of the hPAF complex and its individual subunits in endocrine and pancreatic cancers. It focuses on the functions of the hPAF complex and its individual subunits and dysregulation of the complex, thus providing an insight into its potential involvement in the development of endocrine cancers and other tumor types.

Primary hyperparathyroidism: a current perspective

CONTEXT

Primary hyperparathyroidism (P-HPT) is one of the most common of all endocrine disorders. Eighty percent to 85% of cases are due to parathyroid adenomas while hyperplasia and carcinoma account for 10% to 15% and less than 1%, of cases, respectively. The past decade has witnessed remarkable advances in the understanding of the molecular basis of parathyroid hyperplasia and neoplasia. Additionally, imaging studies and the development of the intraoperative assay for parathyroid hormone have transformed the diagnosis and management of patients with these disorders.

OBJECTIVE

To review the pathology of parathyroid lesions associated with P-HPT, their molecular and genetic bases, including heritable hyperparathyroidism syndromes, and their clinical diagnosis and management.

DATA SOURCES

Review of pertinent epidemiology, pathology, radiology, and surgery literature on the diagnosis, classification, and treatment of P-HPT.

CONCLUSIONS

Although heritable causes of P-HPT including multiple endocrine neoplasia 1 and 2A and hyperparathyroidism-jaw tumor syndrome account for a minority of cases of P-HPT, advances in the characterization of the affected genes have provided insights into the genetic basis of sporadic parathyroid neoplasms. Alterations in cyclin D1 and loss of heterozygosity of chromosome 11q in adenomas and hyperplasias have provided support for clonality of these lesions. Parafibromin, the protein product of the HRPT2 gene responsible for hyperparathyroidism-jaw tumor syndrome, has been implicated in the development of sporadic parathyroid carcinomas and loss of immunohistochemical expression of this protein has been suggested to be of value in making the diagnosis of parathyroid carcinoma. Sestamibi scanning and ultrasound have revolutionized the planning of surgical approaches and the intraoperative parathyroid hormone assay has become the standard in guiding completion or extension of surgery.

The parafibromin tumor suppressor protein interacts with actin-binding proteins actinin-2 and actinin-3

Background

Germline and somatic inactivating mutations in the HRPT2 gene occur in the inherited hyperparathyroidism-jaw tumor syndrome, in some cases of parathyroid cancer and in some cases of familial hyperparathyroidism. HRPT2 encodes parafibromin. To identify parafibromin interacting proteins we used the yeast two-hybrid system for screening a heart cDNA library with parafibromin as the bait.

Results

Fourteen parafibromin interaction positive preys representing 10 independent clones encoding actinin-2 were isolated. Parafibromin interacted with muscle alpha-actinins (actinin-2 and actinin-3), but not with non-muscle alpha-actinins (actinin-1 and actinin-4). The parafibromin-actinin interaction was verified by yeast two-hybrid, GST pull-down, and co-immunoprecipitation. Yeast two-hybrid analysis revealed that the N-terminal region of parafibromin interacted with actinins. In actin sedimentation assays parafibromin did not dissociate skeletal muscle actinins from actin filaments, but interestingly, parafibromin could also bundle/cross-link actin filaments. Parafibromin was predominantly nuclear in undifferentiated proliferating myoblasts (C2C12 cells), but in differentiated C2C12 myotubes parafibromin co-localized with actinins in the cytoplasmic compartment.

Conclusion

These data support a possible contribution of parafibromin outside the nucleus through its interaction with actinins and actin bundling/cross-linking. These data also suggest that actinins (and actin) participate in sequestering parafibromin in the cytoplasmic compartment.

HRPT2 gene analysis and the diagnosis of parathyroid carcinoma

Parathyroid carcinoma is an uncommon cause of primary hyperparathyroidism (PHPT) and is usually associated with more severe clinical manifestations than its much more common benign counterpart, the parathyroid adenomas. The histopathological distinction between benign and malignant parathyroid tumors is difficult. Currently, pathological diagnosis of parathyroid carcinoma is restricted to lesions showing unequivocal growth, as evidenced by perineural invasion, full-thickness capsular invasion with growth into adjacent tissues, or metastasis. Major advances in the molecular pathogenesis of parathyroid carcinoma have been made by the cloning of the HRPT2 gene, which encodes parafibromin, a 531-amino acid putative tumor-suppressor protein. Germline mutations of HRPT2 confer susceptibility to the hyperparathyroidism-jaw tumor syndrome (HPT-JT), an autosomal dominant syndrome with high but incomplete penetrance. Somatic inactivating mutations of the HRPT2 gene have been reported in the majority of apparently sporadic parathyroid carcinomas but, unexpectedly, germline HRPT2 mutation have been found in up to 30% of these patients. Several studies have been performed to evaluate whether parafibromin immunostaining might have some diagnostic utility. Loss of parafibromin immunoreactivity has been found in the majority of parathyroid carcinomas, in 50% of equivocal carcinomas and, very rarely, in benign adenomas. On the other hand, with the exception of HPT-JT-related tumors, loss of parafibromin associated with HRPT2 mutations strongly predicts parathyroid malignancy. In clinical practice, parafibromin immunostaining and HRPT2 gene analysis could be particularly useful in the subset of parathyroid tumors with equivocal histology.

Loss of heterozygosity of 17p13, with possible involvement of ACADVL and ALOX15B, in the pathogenesis of adrenocortical tumors

OBJECTIVE

To determine the minimal common region of loss on 17p13 in a cohort of adrenocortical carcinomas (ACCs) (defined by a Weiss score > or =3) and adrenocortical adenomas (ACAs) (defined by a Weiss score <3) and subsequently to assess 3 genes in this region that could be involved in adrenocortical tumorigenesis.

SUMMARY BACKGROUND DATA

Loss of heterozygosity (LOH) of 17p13 has been demonstrated to occur more frequently in ACCs compared with ACAs.

METHODS

Using 12 microsatellite markers across 17p13, LOH analysis was performed on 37 paired blood and adrenocortical tumor samples (23 ACC and 14 ACA samples) to determine the minimal common region of loss for ACCs and ACAs. From this minimal region of loss, 3 genes were selected for quantitative real time reverse transcription polymerase chain reaction analysis on 20 ACCs and 30 ACAs.

RESULTS

LOH at 17p13 was found in 74% of ACCs compared with 14% of ACAs. There was a 10.4-Mb common minimal region of loss in ACCs whereas no minimal region of loss in ACAs could be demonstrated. Expression of Acyl coenzyme-A dehydrogenase very long chain (ACADVL) and Arachidonate 15-lipoxygenase second type (ALOX15B) was significantly down-regulated in ACCs compared with ACAs whereas there was no difference in expression of Potassium channel tetramerization domain containing 11 (KCTD11) in ACCs and ACAs.

CONCLUSIONS

We demonstrated a minimal common region of loss of 10.4-Mb on 17p13 in ACCs and within this region, we found that ACADVL and ALOX15B expression are good discriminators between ACCs and ACAs.

Aberrant methylation of the HRPT2 gene in parathyroid carcinoma

OBJECTIVES

The incidence of parathyroid carcinoma in hyperparathyroidism-jaw tumor syndrome (HPT-JT) is reported to be as high as 15%. We used a methylation-specific polymerase chain reaction (MS-PCR) technique to investigate whether hypermethylation is one mechanism of HRPT2 gene inactivation in parathyroid tumors.

METHODS

DNA was extracted from samples of parathyroid tumors embedded in paraffin. MS-PCR was performed on 11 parathyroid carcinomas, 37 sporadic parathyroid adenomas from control subjects, and 6 parathyroid adenomas from 3 patients with HPT-JT. Methylated and unmethylated PCR products from 2 tumors (Nos. 2 and 6) were cloned. Clones containing inserts were sequenced.

RESULTS

Two of 11 (18%) parathyroid carcinomas showed amplification patterns consistent with methylation, compared to 0 of 37 sporadic parathyroid adenomas, and 1 of 6 (17%) parathyroid tumor samples from 3 HPT-JT patients. These results were confirmed by sequencing multiple clones from each of these samples.

CONCLUSIONS

There is increasing evidence that loss of HRPT2 gene expression is strongly associated with parathyroid carcinomas. Our data indicate that methylation of the HRPT2 promoter may be another mechanism by which HRPT2 gene inactivation gives rise to parathyroid carcinomas.

Parafibromin, a component of the human PAF complex, regulates growth factors and is required for embryonic development and survival in adult mice

Parafibromin, a transcription factor associated with the PAF complex, is encoded by the HRPT2 gene, mutations of which cause the hyperparathyroidism-jaw tumor syndrome (OMIM145001). To elucidate the function of parafibromin, we generated conventional and conditional Hrpt2 knockout mice and found that Hrpt2(-/-) mice were embryonic lethal by embryonic day 6.5 (E6.5). Controlled deletion of Hrpt2 after E8.5 resulted in apoptosis and growth retardation. Deletion of Hrpt2 in adult mice led to severe cachexia and death within 20 days. To explore the mechanism underlying the embryonic lethality and death of adult mice, mouse embryonic fibroblasts (MEFs) were cultured and Hrpt2 was deleted in vitro. Hrpt2(-/-) MEFs underwent apoptosis, while Hrpt2(+/+) and Hrpt2(+/-) MEFs grew normally. To study the mechanism of this apoptosis, Hrpt2(+/+) and Hrpt2(-/-) MEFs were used in cDNA microarray, semiquantitative reverse transcription-PCR, and chromatin immunoprecipitation assays to identify genes regulated by parafibromin. These revealed that Hrpt2 expression and the parafibromin/PAF complex directly regulate genes involved in cell growth and survival, including H19, Igf1, Igf2, Igfbp4, Hmga1, Hmga2, and Hmgcs2. Thus, our results show that expression of Hrpt2 and parafibromin is pivotal in mammalian development and survival in adults and that these functions are likely mediated by the transcriptional regulation of growth factors.

Challenging lesions in the differential diagnosis of endocrine tumors: parathyroid carcinoma

Parathyroid neoplasms encompass a spectrum of proliferative lesions that include adenomas, atypical adenomas, and carcinomas. While the diagnosis of adenomas is usually straightforward, parathyroid carcinomas (PTCAs) often present considerable diagnostic challenges. Fibrosis and mitotic activity are common in PTCAs, but these features are not specific for malignancy. An unequivocal diagnosis of PTCA should be restricted to those tumors that invade adjacent soft tissues, thyroid gland, blood vessels, or perineural spaces or to those cases with documented metastases. Atypical adenomas include those tumors that share some of the features of PTCA but lack evidence of invasive growth. A variety of genetic abnormalities, including HRPT2 mutations, occur in PTCAs. Mutations of the HRPT2 gene, which encodes parafibromin, are responsible for the development of the hyperparathyroidism-jaw tumor syndrome and have also been implicated in the development of a high proportion of sporadic PTCAs. Correlative immunohistochemical studies have revealed nuclear parafibromin immunoreactivity in adenomas but absence or partial loss of staining in PTCAs. While parafibromin immunohistochemistry represents an important step in the ability to diagnose PTCA, additional studies will be required to test the validity of this approach and to determine the roles of other genes in the development of these tumors.

Downregulated parafibromin expression is a promising marker for pathogenesis, invasion, metastasis and prognosis of gastric carcinomas

Parafibromin is a protein encoded by the hyperparathyroidism 2 oncosuppressor gene and its downregulated expression is involved in pathogenesis of parathyroid carcinomas. To clarify the roles of parafibromin expression in tumourigenesis and progression of gastric carcinomas, it was examined by immunohistochemistry (IHC) on tissue microarray containing gastric carcinomas (n = 508), adenomas (n = 45) and gastritis (n = 49) with a comparison of its expression with clinicopathological parametres of carcinomas. Gastric carcinoma cell lines (MKN28, AGS, MKN45, KATO-III and HGC-27) were studied for parafibromin expression by IHC and western blot. Parafibromin expression was localised in the nucleus of gastric epithelial cells, adenoma, carcinoma cells and cell lines. Its expression was gradually decreased from gastritis to gastric carcinoma, through gastric adenomas (p < 0.05) and inversely correlated with tumour size, depth of invasion, lymphatic invasion, lymph node metastasis and Union Internationale Contre le Cancer (UICC) staging (p < 0.05) but not with sex or venous invasion (p > 0.05). Parafibromin was strongly expressed in older carcinoma patients compared with younger ones (p < 0.05). There was stronger positivity of parafibromin in intestinal-type than diffuse-type carcinomas (p < 0.05). Univariate analysis indicated cumulative survival rate of patients with positive parafibromin expression to be higher than without its expression (p < 0.05). Multivariate analysis showed that age, tumour size, depth of invasion, lymphatic invasion, lymph node metastasis, UICC staging and Lauren’s classification but not sex, venous invasion or parafibromin expression were independent prognostic factors for carcinomas(p < 0.05). Downregulated parafibromin expression possibly contributed to pathogenesis, growth, invasion and metastasis of gastric carcinomas. It was considered as a promising marker to indicate the aggressive behaviours and prognosis of gastric carcinomas.

Nucleolar localization of parafibromin is mediated by three nucleolar localization signals

Parafibromin is a putative tumor suppressor encoded by HRPT2 and implicated in parathyroid tumorigenesis. We previously reported a functional bipartite nuclear localization signal (NLS) at residues 125-139. We now demonstrate that parafibromin exhibits nucleolar localization, mediated by three nucleolar localization signals (NoLS) at resides 76-92, 192-194 and 393-409. These NoLS represent clusters of basic amino acids arginine and lysine, similar to those found in other nucleolar proteins, as well as being characteristic of NLSs. While parafibromin's bipartite NLS is the primary determinant of nuclear localization, it does not mediate nucleolar localization. In contrast, the three identified NoLSs play only a minor role in nuclear localization, but are critical for the nucleolar localization of parafibromin.

Identification of MEN1 and HRPT2 somatic mutations in paraffin-embedded (sporadic) parathyroid carcinomas

OBJECTIVE

Parathyroid carcinoma remains difficult to diagnose. Recently, it has been shown that mutations in the HRPT2 gene (encoding parafibromin) are associated with the development of parathyroid carcinoma. Although MEN1 is not typically thought to be involved in carcinoma formation, parathyroid carcinoma may be an extremely rare feature of the multiple endocrine neoplasia type 1 (MEN1) syndrome. We recently concluded that loss of heterozygosity (LOH) of the MEN1 gene is present in a relatively large number of parathyroid carcinomas, often in combination with LOH at the HRPT2 locus. The aim of this study was to evaluate the role of MEN1 and HRPT2 mutations in sporadic parathyroid tumours fulfilling histological criteria for malignancy.

PATIENTS AND DESIGN

Formalin-fixed, paraffin-embedded (FFPE) parathyroid carcinoma tissue from 28 cases identified in the period 1985-2000 in the Netherlands was studied. HRPT2 (27/28 cases) and MEN1 (23/28 cases) were analysed by direct sequencing.

RESULTS

Somatic MEN1 mutations were found in three of 23 (13%) sporadic parathyroid carcinoma cases; these consisted of one missense and two frameshift mutations. One of the latter two cases displayed lymph-node and lung metastases during follow-up. Six HRPT2 mutations were found in 4/27 cases (15%): five were truncating mutations and one was a missense mutation. Consistent with previously published reports, we found double mutations (2x) and germline mutations (2x) in apparently sporadic parathyroid carcinomas.

CONCLUSIONS

These results suggest that not only HRPT2 but also MEN1 mutations may play a role in sporadic parathyroid cancer formation.

Nuclear localization of the parafibromin tumor suppressor protein implicated in the hyperparathyroidism-jaw tumor syndrome enhances its proapoptotic function

Parafibromin is a tumor suppressor protein encoded by HRPT2, a gene recently implicated in the hereditary hyperparathyroidism-jaw tumor syndrome, parathyroid cancer, and a subset of kindreds with familial isolated hyperparathyroidism. Human parafibromin binds to RNA polymerase II as part of a PAF1 transcriptional regulatory complex. The mechanism by which loss of parafibromin function can lead to neoplastic transformation is poorly understood. Because the subcellular localization of parafibromin is likely to be critical for its function with the nuclear PAF1 complex, we sought to experimentally define the nuclear localization signal (NLS) of parafibromin and examine its potential role in parafibromin function. Using site-directed mutagenesis, we define a dominant bipartite NLS and a secondary NLS, both in the NH(2)-terminal region of parafibromin whose combined mutation nearly abolishes nuclear targeting. The NLS-mutant parafibromin is significantly impaired in its association with endogenous Paf1 and Leo1. We further report that overexpression of wild-type but not NLS-mutant parafibromin induces apoptosis in transfected cells. Inhibition of endogenous parafibromin expression by RNA interference inhibits the basal rate of apoptosis and apoptosis resulting from DNA damage induced by camptothecin, a topoisomerase I inhibitor. These experiments identify for the first time a proapoptotic activity of endogenous parafibromin likely to be important in its role as a tumor suppressor and show a functional role for the NLS of parafibromin in this activity.

Parafibromin tumor suppressor enhances cell growth in the cells expressing SV40 large T antigen

Parafibromin (PF) is a 531-amino acid protein encoded by HRPT2, a putative tumor suppressor gene recently implicated in the autosomal-dominant hyperparathyroidism-jaw tumor familial cancer syndrome and sporadic parathyroid carcinoma. To investigate effects of PF's overexpression on cell proliferation, we performed assays in four different cell lines. The transient overexpression of PF inhibited cell growth in HEK293 and NIH3T3 cells, but enhanced cell growth in the SV40 large T antigen-expressing cell lines such as 293FT and COS7 cells. In 293FT cells, PF was found to interact with SV40 large T antigen and its overexpression promoted entry into the S phase, implying that the interaction enhanced progression through the cell cycle. The tumor suppressor protein PF acts as a positive regulator of cell growth similar to an oncoprotein in the presence of SV40 large T antigen.

A case of hyperparathyroidism-jaw tumour syndrome found in the treatment of an ossifying fibroma in the maxillary bone

Hyperparathyroidism-jaw tumour (HPT-JT) syndrome is characterized by parathyroid tumours as well as by ossifying fibromas of the mandible and maxilla, renal cysts, or Wilms' tumours. Recently, the gene responsible for HPT-JT syndrome has been identified as the HRPT2 tumour suppressor gene. In an 18-year-old male, a tumour in the maxilla was first diagnosed as an ossifying fibroma. During biochemical screening before surgery, the patient received a diagnosis of primary hyperparathyroidism. Neck computed tomography scanning showed a parathyroid tumour. Surgical excisions to remove the jaw tumour and parathyroid adenoma were performed. The postoperative course has been uneventful and a follow up at 2 years revealed no evidence of recurrence. The HRPT2 germline mutation of 39delC was detected in the proband, but not in his unaffected parents. These results suggested that the germline mutation occurred de novo.

Rapid mutation screening for HRPT2 and MEN1 mutations associated with familial and sporadic primary hyperparathyroidism

Familial hyperparathyroidism, a disease of the parathyroid glands, may occur in conjunction with pituitary and pancreatic tumors (multiple endocrine neoplasia type I), kidney and bone tumors (hyperparathyroidism jaw tumor syndrome), or alone (familial isolated hyperparathyroidism). This study describes the development and validation of rapid scanning for mutations in two tumor suppressor genes linked to familial hyperparathyroidism-MEN1 and HRPT2. Denaturing high-performance liquid chromatography mutation scanning for MEN1 was performed using a set of 10 amplicons covering the nine coding exons and flanking intronic regions and for HRPT2 using a set of three amplicons for exons 1, 2, and 7 and flanking intronic regions, in which 80% of the mutations identified to date are located. All 52 MEN1 mutations or polymorphisms, 46 known and six unknown, were successfully detected. Mutation detection in exon 9 was not confounded by the presence of the common polymorphism D418D. In addition, all 10 HRPT2 mutations were successfully detected, and a two-step approach was able to distinguish IVS2 common polymorphisms from exon 2 mutations. The development of rapid denaturing high performance liquid chromatography mutation scanning of MEN1 and HRPT2 facilitates a molecular diagnosis of the associated familial syndromes for both clinically affected and at-risk family members.

Intrathyroidal Parathyroid Carcinoma as Cause of Hypercalcemia and Pitfall of Localization Techniques: Clinical and Biologic Features

OBJECTIVE

To describe an unusual case of intrathyroidal parathyroid carcinoma (PC), which was retrospectively diagnosed in a woman who underwent surgical treatment of a recurrent nodular goiter.

METHODS

We report the clinical and biologic features of an intrathyroidal PC, discuss the challenges with distinguishing PC from parathyroid adenoma, and review the related literature.

RESULTS

A 67-year-old woman sought medical attention for dysphagia attributable to the recurrence of a normal functioning multinodular goiter. Thyroid ultrasonography disclosed a 3-cm solid inferior nodule. Because she refused surgical treatment and a trial of levothyroxine was unsuccessful, periodic follow-up examinations were scheduled. At 1-year follow-up, hypercalcemia (12.1 to 12.6 mg/dL) and low phosphorus levels (2.0 to 2.3 mg/dL) were found, and parathyroid hormone (PTH) levels were profoundly increased (481 to 721 pg/mL). Neck ultrasonography showed a large hypoechogenic solid nodule, not clearly cleaved from the right thyroid lobe, which was possibly compatible with an enlarged parathyroid gland; however, a sestamibi scan was negative. During total thyroidectomy, intraoperative frozen sections of the intrathyroid nodule were compatible with nodular goiter with cellular pleomorphism. Final histologic examination showed cellular nests with nuclear pleomorphism and invasive behavior into the thyroid tissue and likely into the vessels, in conjunction with immunohistochemical negativity for thyroglobulin and strong positivity for PTH. These findings were highly suggestive of and supported the diagnosis of PC. Postoperatively, calcium levels normalized, and PTH values declined considerably but remained slightly increased. Vitamin D supplementation helped normalize the PTH levels. The patient has undergone follow-up for 5 years and has shown no morphologic or biochemical signs of tumor recurrence.

CONCLUSION

PC is a rare entity but should be suspected in patients with hypercalcemia, substantially increased PTH levels, and a neck mass. In such patients, techniques such as sestamibi scanning may fail to localize the neoplasm. Surgical treatment remains the preferred technique for an optimal outcome of the disease. Nevertheless, lifelong follow-up is necessary.

Sporadic human renal tumors display frequent allelic imbalances and novel mutations of the HRPT2 gene

Inactivation of the HRPT2 gene encoding parafibromin was recently linked to the familial hyperparathyroidism-jaw tumor syndrome. Patients with this syndrome carry an increased risk of parathyroid and renal tumors. To determine the relevance of HRPT2 for sporadic renal tumors, clear cell, papillary and chromophobe renal cell carcinomas as well as oncocytomas and Wilms tumors were analysed for HRPT2 gene alterations. Loss of heterozygosity (LOH) of HRPT2 was found in seven of 56 (12.5%) clear cell, three of 14 (21%) papillary, six of 10 (60%) chromophobe renal cell carcinomas, three of eight (38%) oncocytomas and four of 10 (40%) Wilms tumors. In addition, two novel HRPT2 point mutations, causing K34Q and R292K changes in parafibromin, were detected in one clear cell carcinoma and one Wilms tumor, respectively. These tumors displayed LOH of the remaining wild-type allele, but interestingly no von Hippel-Lindau (VHL) mutation. Functional analysis revealed that the K34Q mutant species of parafibromin is, unlike wild-type protein, defective in suppressing cyclin D1 expression in vivo. Taken together, these results suggest that renal cancer-associated mutations in parafibromin occur in the absence of VHL mutation, which in turn may contribute to constitutively elevated cyclin D1 expression and abnormal cell proliferation.

Loss of nuclear expression of parafibromin distinguishes parathyroid carcinomas and hyperparathyroidism-jaw tumor (HPT-JT) syndrome-related adenomas from sporadic parathyroid adenomas and hyperplasias

Parathyroid carcinoma is notoriously difficult to diagnose with confidence in borderline cases. Commonly there is a long lag time between diagnosis and clinical evidence of malignant behavior even in histopathologically straightforward lesions. There is therefore a need for a novel adjunctive marker to assist in the diagnosis of carcinoma. Parafibromin is the protein encoded by the putative tumor suppressor gene HRPT2. Mutations predicted to inactivate parafibromin were first detected in the germline of patients with hyperparathyroidism-jaw tumor (HPT-JT) syndrome. Subsequently, somatic mutations have been identified in the majority of sporadic carcinomas. We performed immunohistochemistry for parafibromin on 115 parathyroid tissues comprising 4 HPT-JT-related tumors (3 adenomas and 1 carcinoma), 11 sporadic parathyroid carcinomas, 79 sporadic adenomas, 3 multiple endocrine neoplasia 2A-related adenomas, 2 sporadic primary hyperplasias, 2 multiple endocrine neoplasia (MEN)-1-related hyperplasias, 6 secondary hyperplasias, 4 tertiary hyperplasias, and 4 normal parathyroid glands. There was complete absence of nuclear staining in 3 of 4 (75%) HPT-JT-related tumors and 8 of 11 (73%) sporadic parathyroid carcinomas and focal weak staining in 1 of 4 HPT-JT tumors and 2 of 11 sporadic parathyroid carcinomas. Only 1 parathyroid carcinoma exhibited diffuse strong nuclear expression of parafibromin. In contrast, 98 of 100 non-HPT-JT-related benign parathyroids showed diffuse strong nuclear positivity and 2 of 100 showed weak positive staining. We conclude that, in the correct clinical and pathologic context, complete absence of nuclear staining for parafibromin is diagnostic of parathyroid carcinoma or an HPT-JT-related tumor.

Surveillance for early detection of aggressive parathyroid disease: carcinoma and atypical adenoma in familial isolated hyperparathyroidism associated with a germline HRPT2 mutation

Familial hyperparathyroid syndromes involving mutations of HRPT2 (also CDC73), a tumor suppressor, are important to identify because the relatively high incidence of parathyroid malignancy associated with such mutations warrants a specific surveillance strategy. However, there is a dearth of reports describing experience with surveillance and early detection informed by genetic insight into this disorder.

INTRODUCTION

Familial isolated hyperparathyroidism (FIHP) is a rare cause of parathyroid (PT) tumors without other neoplasms or endocrinopathies. Germline mutations in CASR, MEN1, and rarely, HRPT2 have been identified in kindreds with FIHP. HRPT2 mutations may be enriched in FIHP families with PT carcinoma, underscoring the importance of identifying causative mutations.

MATERIALS AND METHODS

A 13-year-old boy, whose father had died of PT carcinoma, developed primary hyperparathyroidism. A left superior PT mass was identified by ultrasonography and removed surgically. Aggressive histological features of the boy's tumor included fibrous trabeculae, mitoses, and microscopic capsular infiltration. Two years later, under close biochemical surveillance, primary hyperparathyroidism recurred 5 months after documentation of normocalcemia and normal parathyroid status. Ultrasound and MRI identified a newly enlarged right superior PT gland but indicated no recurrent disease in the left neck. Histologic features typical of a benign adenoma were evident after surgical extirpation of the gland.

RESULTS

Leukocyte DNA analysis revealed a frameshift mutation in exon 2 of HRPT2. The initial tumor manifested the expected germline HRPT2 mutation, plus a distinct somatic frameshift mutation, consistent with the Knudson "two hit" concept of biallelic inactivation of a classic tumor suppressor gene. Genetic screening of the patient's 7 asymptomatic and previously normocalcemic siblings revealed three with the same germline HRPT2 mutation. One of the siblings newly identified as mutation-positive was noted to be hypercalcemic at the time of the genetic screening. He was found to have a PT adenoma with aggressive features. Two of the five children of another mutation-positive sibling also carry the same HRPT2 mutation.

CONCLUSIONS

Despite the reported rarity of HRPT2 mutations in FIHP, a personal or family history of PT carcinoma in FIHP mandates serious consideration of germline HRPT2 mutation status. This information can be used in diagnostic and management considerations, leading to early detection and removal of potentially malignant parathyroid tumors.

Parafibromin is a nuclear protein with a functional monopartite nuclear localization signal

Parafibromin is a nuclear protein with a tumour suppressor role in the development of non-hereditary and hereditary parathyroid carcinomas, and the hyperparathyroidism-jaw tumour (HPT-JT) syndrome, which is associated with renal and uterine tumours. Nuclear localization signal(s), (NLS(s)), of the 61 kDa parafibromin remain to be defined. Utilization of computer-prediction programmes, identified five NLSs (three bipartite (BP) and two monopartite (MP)). To investigate their functionality, wild-type (WT) and mutant parafibromin constructs tagged with enhanced green fluorescent protein or cMyc were transiently expressed in COS-7 cells, or human embryonic kidney 293 (HEK293) cells, and their subcellular locations determined by confocal fluorescence microscopy. Western blot analyses of nuclear and cytoplasmic fractions from the transfected cells were also performed. WT parafibromin localized to the nucleus and deletions or mutations of the three predicted BP and one of the predicted MP NLSs did not affect this localization. In contrast, deletions or mutations of a MP NLS, at residues 136-139, resulted in loss of nuclear localization. Furthermore, the critical basic residues, KKXR, of this MP NLS were found to be evolutionarily conserved, and over 60% of all parafibromin mutations lead to a loss of this NLS. Thus, an important functional domain of parafibromin, consisting of an evolutionarily conserved MP NLS, has been identified.

Parafibromin inhibits cancer cell growth and causes G1 phase arrest

The HRPT2 (hereditary hyperparathyroidism type 2) tumor suppressor gene encodes a ubiquitously expressed 531 amino acid protein termed parafibromin. Inactivation of parafibromin predisposes one to the development of HPT-JT syndrome. To date, the role of parafibromin in tumorigenesis is largely unknown. Here, we report that parafibromin is a nuclear protein that possesses anti-proliferative properties. We show that overexpression of parafibromin inhibits colony formation and cellular proliferation, and induces cell cycle arrest in the G1 phase. Moreover, HPT-JT syndrome-derived mutations in HRPT2 behave in a dominant-negative manner by abolishing the ability of parafibromin to suppress cell proliferation. These findings suggest that parafibromin has a critical role in cell growth, and mutations in HRPT2 can directly inhibit this role.

Diagnosis of parathyroid tumors in familial isolated hyperparathyroidism with HRPT2 mutation: implications for cancer surveillance

CONTEXT

Mutations of the HRPT2 gene have recently been implicated in the development of parathyroid carcinoma.

OBJECTIVE

The objective of this study was early diagnosis of parathyroid tumor in a family with germline HRPT2 mutation.

PATIENTS, METHODS, AND RESULTS

In a 40-yr-old male previously treated for parathyroid atypical adenoma, we screened the 17 translated HRPT2 exons and their exon-intron boundaries and found a germline frameshift mutation in exon 7 (685delAGAG) predicting a premature stop codon at nucleotides 767-769. Nine family members (age, 33.9 +/- 19.8 yr, mean +/- SD) also carry the mutation, but eight have had normal serum calcium. Biochemical and ultrasonographic evaluation uncovered a 27-yr-old hypercalcemic carrier niece with an atypical parathyroid adenoma, and a 43-yr-old normocalcemic carrier sister was found by ultrasonography to have an extrathyroidal nodule, which proved to be parathyroid carcinoma. The index case, 12 yr after surgery, was normocalcemic, but ultrasonography revealed an extrathyroidal nodule in the contralateral hemithyroid tissue that proved to be atypical adenoma.

CONCLUSIONS

Our report confirms that germline mutations of HRPT2 gene may be associated with multiple parathyroid neoplasms. Our experience suggests that longitudinal surveillance by serum biochemistry alone may not be 100% sensitive, and addition of routine neck ultrasonography is a readily accepted adjunct that may facilitate earlier disease detection in some families.

Parathyroid Cancer

Parathyroid cancer is a rare endocrine tumor and an uncommon cause of HPT. Advances have been made to identify a promising molecular diagnostic marker for the disease. The use of accurate preoperative imaging modalities would undoubtedly facilitate its management by making an accurate preoperative diagnosis by assessing its invasiveness, and by searching for nodal or distant metastases. The effectiveness of the application of intraoperative PTH assay in the management of this rare condition remains to be seen. Radical surgical treatment offers the best chance of cure, but for patients who have refractory unresectable disease or metastases, the availability of more effective targeted medical therapy may palliate the debilitating symptoms of hypercalcemia, reduce its metabolic complications, and potentially improve survival.

Metastatic calcifications and severe hypercalcemia in a patient with parathyroid carcinoma

Primary hyperparathyroidism is rarely produced by parathyroid carcinoma. We present the case of a 63-yr-old man who was admitted due to recent onset of constipation, weakness and progressive lethargy. At physical examination, a left cervical mass was palpated. Marked hypercalcemia (serum calcium 25 mg/dl) (6.22 mmol/l) complicated by renal insuficiency (serum creatinine 4.4 mg/dl) (388 micromol/l) was found, but both were unresponsive to conventional therapy and hemofiltration. Autopsy examination showed a carcinoma of the upper left parathyroid gland, multiple foci of metastatic calficications in the vessel walls and parenchyma of both lungs and kidneys, and the myocardium, which contributed to multi-organ failure and death. In addition to describing the clinical presentation, we review the mechanism of metastatic calcifications as well as the role of renal function and hyperphosphatemia, and the basis for therapy of hypercalcemic crisis.

Genetic analyses in patients with familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumour syndrome

BACKGROUND

A subset of familial isolated primary hyperparathyroidism (FIHP) is a variant of hyperparathyroidism-jaw tumour syndrome (HPT-JT). AIM/PATIENTS AND METHODS: We investigated the involvement of the HRPT2, MEN1 and CASR genes in 11 provisional FIHP families and two HPT-JT families.

RESULTS

Germline mutations of HRPT2 were found in two of the 11 FIHP families and one of the two HPT-JT families. One FIHP family with parathyroid carcinoma and atypical adenomas and another FIHP family with cystic parathyroid adenoma had novel frameshift mutations of 518-521del and 62-66del, respectively. In a patient with HPT-JT, a de novo germline mutation of 39delC was detected. Novel somatic HRPT2 mutations of 70-73del and 95-102del were found in two of five parathyroid tumours in a family with a 518-521del mutation. Biallelic inactivation of HRPT2 by a combination of germline and somatic mutation was confirmed in the parathyroid tumours. The finding that two families diagnosed with FIHP carried HRPT2 mutations suggests that they have occult HPT-JT. In the remaining 10 families, one family had a missense MEN1 mutation. No mutations of CASR were detected.

CONCLUSION

Our results confirm the need to test for HRPT2 in FIHP families, especially those with parathyroid carcinomas, atypical adenomas or adenomas with cystic change.

Parathyroid carcinoma

PURPOSE OF REVIEW

This article reviews current knowledge on the etiology, diagnosis and treatment of parathyroid carcinoma.

RECENT FINDINGS

Due to its rarity, research on the molecular etiology and treatment of parathyroid carcinoma has been slow. Mutations of the tumor suppressor gene, HRPT2, and resultant loss of expression of its gene product have been found in the majority of parathyroid cancers studied. Recent advances in the field have identified regions on several chromosomes that demonstrate loss of heterozygosity more commonly in parathyroid carcinoma than in benign parathyroid lesions. This has provided clues to the location and identity of additional tumor suppressor genes associated with the development of this cancer.

SUMMARY

Parathyroid carcinoma is an extremely rare cause of primary hyperparathyroidism, accounting for fewer than 1% of cases. The etiology of parathyroid cancer is largely unknown. Associations have been made with several inherited syndromes and with specific genetic lesions. Little is known about the most appropriate management of this disease. En bloc resection at the time of initial surgery appears to provide the best chance of cure. Anecdotal experience with adjuvant chemotherapy has shown a modest and short-lived effect. External beam radiation following surgical resection, however, may increase long-term survival compared with surgery alone. Bisphosphonates and a new class of drugs known as calcimimetics have been used effectively in some patients to control the symptoms of severe hypercalcemia in a palliative setting.

Parafibromin mutations in hereditary hyperparathyroidism syndromes and parathyroid tumours

OBJECTIVE

To investigate two patients with the hyperparathyroidism-jaw tumour (HPT-JT) syndrome and three patients with familial isolated hyperparathyroidism (FIHP), together with 31 parathyroid tumours (2 HPT-JT, 2 FIHP and 27 sporadic) for HRPT2 mutations. The HPT-JT syndrome and FIHP are autosomal dominant disorders that may be caused by abnormalities of the HRPT2 gene, located on chromosome 1q31.2. HRPT2 encodes a 531 amino acid protein, parafibromin, which interacts with human homologues of the yeast Paf1 complex.

DESIGN

Leukocyte and tumor DNA was used with HRPT2-specific primers for polymerase chain reaction amplification of the 17 exons and their splice junctions, and the DNA sequences of the polymerase chain reaction products determined.

RESULTS

Three heterozygous germline HRPT2 mutations, two in HPT-JT and one in FIHP patients, were identified. These consisted of one 1-bp duplication (745dup1bp), 1 nonsense (Arg234Stop) and 1 missense (Asp379Asn) mutation. One parathyroid tumour from an FIHP patient was demonstrated to harbour a germline deletion of 1 bp together with a somatic missense (Leu95Pro) mutation, consistent with a 'two-hit' model for hereditary cancer. The 27 sporadic benign parathyroid tumours did not harbour any HRPT2 somatic mutations. Six HRPT2 polymorphisms with allele frequencies ranging from 2% to 15% were detected.

CONCLUSIONS

Our results have identified three novel HRPT2 mutations (two germline and one somatic). The Asp379Asn mutation is likely to disrupt interaction with the human homologue of the yeast Paf1 complex, and the demonstration of combined germline and somatic HRPT2 mutations in a parathyroid tumour provide further evidence for the tumour suppressor role of the HRPT2 gene.

HRPT2 gene alterations in ossifying fibroma of the jaws

Ossifying fibroma (OF) is a benign neoplasm related to bone characterized by a progressive enlargement of the affected jaw. Recently, the candidate tumor suppressor gene HRPT2 was identified and alterations in this gene were related with the Hyperparathyroidism-jaw tumor syndrome that is characterized by parathyroid adenoma or carcinoma, fibro-osseous lesions (mainly OF) of the jaws, and renal lesions. The purpose of the present study was to evaluate the HRPT2 gene in OF. Tumour and blood samples were obtained from 3 patients with OF and one with juvenile ossifying fibroma (JOF). The results demonstrated three novel mutations in two out of three genotyped OF's. Interestingly, one of these patients showed a germ-line mutation after blood analysis. RT-PCR amplification was performed to analyze HRPT2 mRNA expression and only wild-type HRPT2 transcript was found in all tumours. Investigation of the parafibromin protein by immunohistochemistry showed a similar pattern of immunolocalization with strong nuclear and cytoplasmic staining in all cases. In conclusion, the present study shows for the first time mutations of HRPT2 gene in OF and suggests that OF may arise due to haploinsufficiency of the HRPT2 gene.

Genetic analyses in familial isolated hyperparathyroidism: implication for clinical assessment and surgical management

OBJECTIVE

Familial isolated primary hyperparathyroidism (FIPH) can result from either incomplete expression of a syndromic form of familial primary hyperparathyroidism [multiple endocrine neoplasia type 1 (MEN 1), hyperparathyroidism-jaw tumour syndrome (HPT-JT) or familial hypocalciuric hypercalcaemia (FHH)] or still unrecognized causes. Design Genetic analyses of MEN1, HRPT2 and CASR genes in FIHP.

PATIENTS

Seven well-characterized Italian kindreds with FIHP, with negative clinical features for MEN 1, HPT-JT and FHH. The mean age (+/- SD) at diagnosis was 45 +/- 17 years (range 18-70 years) in the probands and 42 +/- 18 years (range 15-69 years) in the other affected subjects.

MEASUREMENTS

Direct sequencing of germline DNA of the MEN1, HRPT2 and CASR genes from probands. The region of interest was amplified in some family members.

RESULTS

Germline MEN1 mutations were detected in three kindreds. Multiglandular involvement was found in all but one affected subject belonging to the three kindreds with MEN1 mutations. In these patients persistence/relapse of the disease was observed unless an extensive parathyroidectomy (excision of 3(1)/(2) glands) had been performed, with the exception of one patient, who is currently normocalcaemic 168 months after excision of two glands. No mutations of MEN1, HRPT2 and CASR genes were identified in the remaining four families.

CONCLUSIONS

MEN1 genotyping appears worthwhile in FIHP families, as the finding of mutation(s) may predict multiglandular involvement and therefore have practical surgical implications, and prompt further investigation in the family, with the possibility of identifying new cases and beginning a programme of periodic surveillance for emergence of tumours in all carriers.

Dental findings in a family with hyperparathyroidism–jaw tumor syndrome and a novel HRPT2 gene mutation

Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is an important diagnosis because of the possible involvement of other family members and risk of malignant disease. We report clinical and genetic studies in a previously undocumented Australian family with HPT-JT. The proband and his sister presented with bilateral or recurrent mandibular radiolucencies diagnosed histopathologically as cemento-ossifying fibromas. Mutation screening of the recently identified disease gene HRPT2 was performed by direct sequencing in 3 affected members. This revealed a novel mutation in exon 1 of HRPT2 (nt 20AGGACG --> GGGAG), which is predicted to inactivate the parafibromin protein through protein truncation and premature termination of translation. The terminology used for the jaw lesions in this syndrome warrants review to become more consistent. Cemento-ossifying fibroma is the preferred term to better reflect the pathologies found in most individuals and families,and to emphasize the significance of the jaw lesions in the diagnosis of the syndrome.

Monoubiquitination of human histone H2B: the factors involved and their roles in HOX gene regulation

In yeast, histone H2B monoubiquitination is a cotranscriptional event regulating histone H3 methylation at lysines 4 and 79. However, mammalian H2B monoubiquitination remains poorly understood. We report that in humans, the 600 kDa RNF20/40 complex is the E3 ligase and UbcH6 is the ubiquitin E2-conjugating enzyme for H2B-Lys120 monoubiquitination. RNF20 and RNF40 are both homologs of Bre1, the E3 ligase in the yeast case. UbcH6 physically interacts with RNF20/40 and with the hPAF complex. Formation of a trimeric complex with hPAF stimulates H2B monoubiquitination activity in vitro. Accordingly, UbcH6, RNF20/40, and the hPAF complex are recruited to transcriptionally active genes in vivo. RNF20 overexpression leads to elevated H2B monoubiquitination, subsequently higher levels of methylation at H3 lysines 4 and 79, and stimulation of HOX gene expression. In contrast, RNAi against the RNF20/40 complex or hPAF complex reduces H2B monoubiquitination, lowers methylation levels at H3 lysines 4 and 79, and represses HOX gene expression.

Das familiäre Nebenschilddrüsenkarzinom

In contrast to primary hyperparathyroidism, parathyroid carcinoma is a rare disease. In patients with hyperparathyroidism jaw tumor (HPT-JT) syndrome, caused by germline mutations in HRPT2, the development of parathyroid carcinoma is estimated to be 10-15%. This review summarizes the clinical and molecular genetic data of about 100 patients in the literature and three of our own cases. Unfortunately, osteofibromas, which might enable timely diagnosis of HPT-JT syndrome, occur in only about 30% of patients; about 80% have uniglandular disease. Based on the current data, a general recommendation to perform prophylactic parathyroidectomy cannot be given. However, thorough screening of patients at risk is mandatory. Of note in patients thought to have sporadic parathyroid carcinoma, germline HRPT2 mutations are found in up to 20%. Hence, any patient with parathyroid carcinoma should undergo HRPT2 mutation analysis.

Identification of a functional bipartite nuclear localization signal in the tumor suppressor parafibromin

Parafibromin is a putative tumor suppressor encoded by HRPT2, mutations in which have been implicated in the familial tumor syndrome hyperparathyroidism jaw tumor syndrome (HPT-JT), and sporadic parathyroid carcinoma. Recently, parafibromin has been shown to be an accessory factor for RNA polymerase II as part of the human Paf 1 complex, suggesting, as has been shown for its yeast homologue (Cdc 73), that it may have a role as an important regulator of transcription. Parafibromin has also been shown to interact with a histone methyltransferase complex that methylates histone H3 and to inhibit proliferation when overexpressed in mammalian cell lines. Despite these findings, the cellular localization of parafibromin has been controversial, with reports of both nuclear and nucleocytoplasmic localization. We have expressed wild-type and mutant parafibromin tagged with enhanced green fluorescent protein and have identified a functional bipartite nuclear localization signal (NLS) at residues 125-139 (nucleotides 373-417), KRAADEVLAEAKKPR, that is evolutionarily conserved and critical for the nuclear localization of parafibromin. We have also shown that the C-terminal arm of this bipartite NLS plays the primary role in nuclear localization. In support of these findings, specific HRPT2 mutations identified in HPT-JT or sporadic parathyroid carcinoma predicted to truncate parafibromin upstream of or within this NLS disrupt nuclear localization.