Cyclin D1 in parathyroid disease

Diagnosis, management, histology and genetics of sporadic primary hyperparathyroidism: old knowledge with new tricks

Primary hyperparathyroidism (pHPT) is a common endocrinopathy resulting from inappropriately high PTH secretion. It usually results from the presence of a single gland adenoma, multiple gland hyperplasia or rarely parathyroid carcinoma. All these conditions require different management, and it is important to be able to differentiate the underlined pathology, in order for the clinicians to provide the best therapeutic approach. Elucidation of the genetic background of each of these clinical entities would be of great interest. However, the molecular factors that control parathyroid tumorigenesis are poorly understood. There are data implicating the existence of specific genetic pathways involved in the emergence of parathyroid tumorigenesis. The main focus of the present study is to present the current optimal diagnostic and management protocols for pHPT as well as to review the literature regarding all molecular and genetic pathways that are to be involved in the pathophysiology of sporadic pHPT.

Molecular genetics in primary hyperparathyroidism: the role of genetic tests in differential diagnosis, disease prevention strategy, and therapeutic planning. A 2017 update

Primary hyperparathyroidism (PHPT) is one of the most frequent endocrine disease in developed countries. It mainly occurs as sporadic cases (about 90-95% of cases), while only the remaining 5-10% is represented by familial inherited parathyroid disorders due to causative mutations in specific target genes. Clinical variability among the different familial parathyroid syndromes is generally linked to the specific mutated gene and it can predispose subjects to different manifestations of parathyroid pathology, various degrees of PHPT severity, persistence and/or after-surgery recurrences. Genetic tests is helpful in differential diagnosis favouring the recognition of the specific familial PHPT syndrome and, subsequently, in planning the most suitable surgical procedures and/or pharmacological interventions. Moreover, genetic test is important to recognise mutation carriers, within PHPT familial forms, even before the appearance of biochemical and/or clinical symptoms. This review resumes general concepts about genetic diagnosis of PHPT in familial hereditary syndromes, specifically describing why, when, and which genetic screenings should be performed in every specific PHPT-associated parathyroid disease.

Cyclin D1 G870A polymorphism: Association with uterine leiomyoma risk and in silico analysis

Uterine leiomyoma (UL) is the most common benign tumor causing considerable morbidity during the reproductive years in women. Cyclin D1 (CCND1) is a cell cycle regulatory protein that is required for the G1 phase, and increased expression levels of this protein may affect tumorigenesis. The present study aimed to assess the possible effect of the CCND1 G870A polymorphism on UL susceptibility. A total of 154 women with UL and 197 healthy women who were age-, body mass index (BMI)- and ethnicity-matched were genotyped for the CCND1 G870A (rs9344) polymorphism using the polymerase chain reaction-restriction fragment length polymorphism method. The effects of G870A transition on the structure of mRNA and proteins of CCND1 was evaluated using bioinformatics tools. The frequency of the CCND1 870AA genotype was significantly higher in women with UL compared with the control subjects, and the risk of UL was 1.4-fold higher in women with the AA genotype when compared with the GG genotype before and after adjusting for age, BMI, and ethnicity [odds ratio (OR), 1.4; 95% confidence interval (CI), 1.1-2 (P=0.02)]. The frequency of CCND1 870GA genotype was not significantly different between the two groups. The frequency of the CCND1 870A allele was significantly higher in the women with UL when compared with the control subjects (57 vs. 48%; P=0.02). The in silico analysis revealed that the G870A transition may fundamentally alter the structure of the CCND1-mRNA. Thus, the CCND1 870AA genotype was associated with UL susceptibility in a sample of women from the southeast of Iran.

PTH and Vitamin D

PTH and Vitamin D are two major regulators of mineral metabolism. They play critical roles in the maintenance of calcium and phosphate homeostasis as well as the development and maintenance of bone health. PTH and Vitamin D form a tightly controlled feedback cycle, PTH being a major stimulator of vitamin D synthesis in the kidney while vitamin D exerts negative feedback on PTH secretion. The major function of PTH and major physiologic regulator is circulating ionized calcium. The effects of PTH on gut, kidney, and bone serve to maintain serum calcium within a tight range. PTH has a reciprocal effect on phosphate metabolism. In contrast, vitamin D has a stimulatory effect on both calcium and phosphate homeostasis, playing a key role in providing adequate mineral for normal bone formation. Both hormones act in concert with the more recently discovered FGF23 and klotho, hormones involved predominantly in phosphate metabolism, which also participate in this closely knit feedback circuit. Of great interest are recent studies demonstrating effects of both PTH and vitamin D on the cardiovascular system. Hyperparathyroidism and vitamin D deficiency have been implicated in a variety of cardiovascular disorders including hypertension, atherosclerosis, vascular calcification, and kidney failure. Both hormones have direct effects on the endothelium, heart, and other vascular structures. How these effects of PTH and vitamin D interface with the regulation of bone formation are the subject of intense investigation.

A systematic investigation based on microRNA-mediated gene regulatory network reveals that dysregulation of microRNA-19a/Cyclin D1 axis confers an oncogenic potential and a worse prognosis in human hepatocellular carcinoma

MicroRNAs (miRNAs) contribute to a wide variety of human diseases by regulating gene expression, leading to imbalances in gene regulatory networks. To discover novel hepatocellular carcinoma (HCC)-related miRNA-target axes and to elucidate their functions, we here performed a systematic investigation combining biological data acquisition and integration, miRNA-target prediction, network construction, functional assay and clinical validation. As a result, a total of 117 HCC differentially expressed miRNAs were identified, and 728 high confident target genes of these miRNAs were collected. Then, the interaction network of target genes was constructed and 221 key nodes with topological importance in the network were identified according to their topological features including degree, node-betweenness, closeness and K-coreness. Among these key nodes, Cyclin D1 had the highest node-betweenness, implying its bottleneck role in the network. Luciferase reporter assay confirmed that miRNA-19a, which was one of HCC downregulated miRNAs, directly targeted Cyclin D1 in HCC cells. Moreover, miR-19a might play inhibitory roles in HCC malignancy via regulating Cyclin D1 expression. Further clinical evidence also highlighted the prognostic potential of miR-19a/Cyclin D1 axis in HCC. In conclusion, this systematic investigation provides a framework to identify featured miRNAs and their target genes which are potent effectors in the occurrence and development of HCC. More importantly, miR-19a/Cyclin D1 axis might have promising applications as a therapeutic target and a prognostic marker for patients with HCC.

Complete genomic landscape of a recurring sporadic parathyroid carcinoma

Parathyroid carcinoma is a rare endocrine malignancy with an estimated incidence of less than 1 per million population. Excessive secretion of parathyroid hormone, extremely high serum calcium level, and the deleterious effects of hypercalcaemia are the clinical manifestations of the disease. Up to 60% of patients develop multiple disease recurrences and although long-term survival is possible with palliative surgery, permanent remission is rarely achieved. Molecular drivers of sporadic parathyroid carcinoma have remained largely unknown. Previous studies, mostly based on familial cases of the disease, suggested potential roles for the tumour suppressor MEN1 and proto-oncogene RET in benign parathyroid tumourigenesis, while the tumour suppressor HRPT2 and proto-oncogene CCND1 may also act as drivers in parathyroid cancer. Here, we report the complete genomic analysis of a sporadic and recurring parathyroid carcinoma. Mutational landscapes of the primary and recurrent tumour specimens were analysed using high-throughput sequencing technologies. Such molecular profiling allowed for identification of somatic mutations never previously identified in this malignancy. These included single nucleotide point mutations in well-characterized cancer genes such as mTOR, MLL2, CDKN2C, and PIK3CA. Comparison of acquired mutations in patient-matched primary and recurrent tumours revealed loss of PIK3CA activating mutation during the evolution of the tumour from the primary to the recurrence. Structural variations leading to gene fusions and regions of copy loss and gain were identified at a single-base resolution. Loss of the short arm of chromosome 1, along with somatic missense and truncating mutations in CDKN2C and THRAP3, respectively, provides new evidence for the potential role of these genes as tumour suppressors in parathyroid cancer. The key somatic mutations identified in this study can serve as novel diagnostic markers as well as therapeutic targets.

Role of the calcium-sensing receptor in extracellular calcium homeostasis

Maintaining a constant level of blood Ca(2+) is essential because of calcium's myriad intracellular and extracellular roles. The CaSR plays key roles in maintaining [Formula: see text] homeostasis by detecting small changes in blood Ca(2+) and modulating the production/secretion of the Ca(2+)-regulating hormones, PTH, CT, FGF23 and 1,25(OH)2D3, so as to appropriately regulate Ca(2+) transport into or out of blood via kidney, intestine, and/or bone. When Ca(2+) is high, the CaSR suppresses PTH synthesis and secretion, promotes its degradation, and inhibits parathyroid cellular proliferation. It has just the opposite effects on the C-cell, stimulating CT when [Formula: see text] is high. In bone, Ca(2+), acting via the CaSR, stimulates recruitment and proliferation of preosteoblasts, their differentiation to mature osteoblasts, and synthesis and mineralization of bone proteins. Conversely, [Formula: see text] inhibits the formation and activity and promotes apoptosis of osteoclasts, likely via the CaSR. These actions tend to mobilize skeletal Ca(2+) during [Formula: see text] deficiency and retain it when Ca(2+) is plentiful.

MEN1 intragenic deletions may represent the most prevalent somatic event in sporadic primary hyperparathyroidism

OBJECTIVE

Primary hyperparathyroidism (pHPT) is characterised by an inappropriate over production of parathyroid hormone and it is the most frequent pathological condition of the parathyroid glands. A minority of the cases belong to familial forms, but most of them are sporadic. The genetic alterations underlying the sporadic forms of pHPT remain poorly understood. The main goal of our study is to perform the molecular characterisation of a series of sporadic pHPT cases.

DESIGN AND METHODS

We have studied matched blood and tumour from 24 patients with pHPT, who went to a medical appointment in Hospital Pedro Hispano. Informed consent was obtained from all individuals. The MEN1, RET and CDKN1B molecular study was carried out in the germline DNA by PCR/SSCP and direct sequencing. Parathyroid tumours were further analysed by the same methods for MEN1, CDKN1B and CTNNB1 genetic alterations. The multiplex ligation-dependent probe amplification technique enabled the evaluation of MEN1 gene deletions. Protein expression for menin, cyclin D1, parafibromin, p27(Kip1), β-catenin and Ki-67 was conducted by immunohistochemistry.

RESULTS

The study of parathyroid tumours detected two somatic MEN1 mutations (c.249_252delGTCT and c.115_163del49bp) and revealed the presence of MEN1 intragenic deletions in 54% (13/24) of the tumours. In RET and CDKN1B genes only previously described, non-pathogenic variants were found. Cyclin D1 protein was overexpressed in 13% (3/24) of tumours.

CONCLUSIONS

These results suggest that MEN1 alterations, remarkably intragenic deletions, may represent the most prevalent genetic alteration in sporadic parathyroid tumours.

Calcium sensing receptor signalling in physiology and cancer

The calcium sensing receptor (CaSR) is a class C G-protein-coupled receptor that is crucial for the feedback regulation of extracellular free ionised calcium homeostasis. While extracellular calcium (Ca(2+)o) is considered the primary physiological ligand, the CaSR is activated physiologically by a plethora of molecules including polyamines and l-amino acids. Activation of the CaSR by different ligands has the ability to stabilise unique conformations of the receptor, which may lead to preferential coupling of different G proteins; a phenomenon termed 'ligand-biased signalling'. While mutations of the CaSR are currently not linked with any malignancies, altered CaSR expression and function are associated with cancer progression. Interestingly, the CaSR appears to act both as a tumour suppressor and an oncogene, depending on the pathophysiology involved. Reduced expression of the CaSR occurs in both parathyroid and colon cancers, leading to loss of the growth suppressing effect of high Ca(2+)o. On the other hand, activation of the CaSR might facilitate metastasis to bone in breast and prostate cancer. A deeper understanding of the mechanisms driving CaSR signalling in different tissues, aided by a systems biology approach, will be instrumental in developing novel drugs that target the CaSR or its ligands in cancer. This article is part of a Special Issue entitled: 12th European Symposium on Calcium.

Parathyroid carcinoma: challenges in diagnosis and treatment

Parathyroid carcinoma is a malignant neoplasm affecting 0.5% to 5.0% of all patients with primary hyperparathyroidism. Since it was first described by De Quervain in 1904 to this day, it continues to defy diagnosis and treatment because of its rarity, overlapping features with benign parathyroid disease, and lack of distinct characteristics. En bloc surgical extirpation of the tumor with clear margins remains the best curative treatment. Although prolonged survival is possible with recurrent or metastatic disease, cure is rarely achievable. Efficacy of adjuvant therapies, such as radiotherapy and chemotherapy, in management of persistent, recurrent, or metastatic disease has been disappointing.

Molecular alterations in sporadic primary hyperparathyroidism

Primary hyperparathyroidism (PHPT) is a frequent endocrine disorder characterized by an excessive autonomous production and release of parathyroid hormone (PTH) by the parathyroid glands. This endocrinopathy may result from the development of a benign lesion (adenoma or hyperplasia) or from a carcinoma. Most of the PHPT cases occur sporadically; however, approximately 10% of the patients present a familial form of the disease. The molecular mechanisms underlying the pathogenesis of sporadic PHPT are incompletely understood, even though somatic alterations in MEN1 gene and CCND1 protein overexpression are frequently observed. The MEN1 gene is mutated in about 30% of the parathyroid tumours and the protooncogene CCND1 is implicated in parathyroid neoplasia by rearrangements, leading to an overexpression of CCND1 protein in parathyroid cells. The aim of this work is to briefly update the molecular alterations underlying sporadic primary hyperparathyroidism.

Regulator of G protein signaling 5 is highly expressed in parathyroid tumors and inhibits signaling by the calcium-sensing receptor

The molecular mechanisms responsible for aberrant calcium signaling in parathyroid disease are poorly understood. The loss of appropriate calcium-responsive modulation of PTH secretion observed in parathyroid disease is commonly attributed to decreased expression of the calcium-sensing receptor (CaSR), a G protein-coupled receptor. However, CaSR expression is highly variable in parathyroid adenomas, and the lack of correlation between CaSR abundance and calcium-responsive PTH kinetics indicates that mechanisms independent of CaSR expression may contribute to aberrant calcium sensing in parathyroid disease. To gain a better understanding of parathyroid tumors and the molecular determinants that drive parathyroid adenoma development, we performed gene expression profiling on a panel of 64 normal and neoplastic parathyroid tissues. The microarray data revealed high-level expression of genes known to be involved in parathyroid biology (PTH, VDR, CGA, CaSR, and GCM2). Moreover, our screen identified regulator of G protein signaling 5 (RGS5) as a candidate inhibitor of CaSR signaling. We confirmed RGS5 to be highly expressed in parathyroid adenomas relative to matched-pair normal glands. Transient expression of RGS5 in cells stably expressing CaSR resulted in dose-dependent abrogation of calcium-stimulated inositol trisphosphate production and ERK1/2 phosphorylation. Furthermore, we found that RGS5-nullizygous mice display reduced plasma PTH levels, an outcome consistent with attenuated opposition to CaSR activity. Collectively, these data suggest that RGS5 can act as a physiological regulator of calcium sensing by CaSR in the parathyroid gland. The abnormally elevated expression of RGS5 observed in parathyroid adenomas could thus represent a novel mechanism of CaSR desensitization in patients with primary hyperparathyroidism.

Identification of differentially expressed microRNA in parathyroid tumors

BACKGROUND

The molecular factors that control parathyroid tumorigenesis are poorly understood. In the absence of local invasion or metastasis, distinguishing benign from malignant parathyroid neoplasm is difficult on histologic examination. We studied the microRNA (miRNA) profile in normal, hyperplastic, and benign and malignant parathyroid tumors to better understand the molecular factors that may play a role in parathyroid tumorigenesis and that may serve as diagnostic markers for parathyroid carcinoma.

METHODS

miRNA arrays containing 825 human microRNAs with four duplicate probes per miRNA were used to profile parathyroid tumor (12 adenomas, 9 carcinomas, and 15 hyperplastic) samples normalized to four reference normal parathyroid glands. Differentially expressed miRNA were validated by real-time quantitative TaqMan polymerase chain reaction (PCR).

RESULTS

One hundred fifty-six miRNAs in parathyroid hyperplasia, 277 microRNAs in parathyroid adenoma, and 167 microRNAs in parathyroid carcinomas were significantly dysregulated as compared with normal parathyroid glands [false discovery rate (FDR) < 0.05]. By supervised clustering analysis, all parathyroid carcinomas clustered together. Three miRNAs (miR-26b, miR-30b, and miR-126*) were significantly dysregulated between parathyroid carcinoma and parathyroid adenoma. Receiver-operating characteristic curve analysis showed mir-126* was the best diagnostic marker, with area under the curve of 0.776.

CONCLUSIONS

Most miRNAs are downregulated in parathyroid carcinoma, while in parathyroid hyperplasia most miRNAs are upregulated. miRNA profiling shows distinct differentially expressed miRNAs by tumor type which may serve as helpful adjunct to distinguish parathyroid adenoma from carcinoma.

Overexpression of degenerative spermatocyte homolog 1 up-regulates the expression of cyclin D1 and enhances metastatic efficiency in esophageal carcinoma Eca109 cells

Cyclin D1 plays a pivotal role in cell-cycle transition through G1 phase. In this article, we found that Degenerative Spermatocyte Homolog 1 (DEGS1) up-regulated the expression of cyclin D1 and the activation of transcription factor NF-kappaB was essential for DEGS1-induced cyclin D1 production. Forced expression of DEGS1 in Esophageal carcinoma cell line Eca109 cells increased their ability of cell migration and significantly induced tumor metastasis in nude mice, whereas RNA interference-mediated knockdown of DEGS1 cells significantly inhibited cell migration in vitro, as well as tumor metastasis in vivo. Our results demonstrated that expression of DEGS1 up-regulated the expression of cyclin D1 and enhanced the efficiency of tumor metastasis.

Cyclin D1 overexpression increases susceptibility to 4-nitroquinoline-1-oxide-induced dysplasia and neoplasia in murine squamous oral epithelium

The cyclin D1 oncogene is frequently amplified/overexpressed in oral squamous cell carcinomas. Mice with overexpression of cyclin D1 targeted to the stratified squamous epithelia of the tongue, esophagus, and forestomach develop a phenotype of epithelial dysplasia at these sites. In this study, we examined the effect of cyclin D1 overexpression on susceptibility of mice to carcinogen-induced tumorigenesis, using 4-nitroquinoline-1-oxide (4NQO), an established potent oral carcinogen in mice. Cyclin D1 overexpressing mice and nontransgenic littermates were administered 4NQO (20 or 50 parts per million (ppm) in the drinking water) for 8 wk and monitored for an additional 16 wk. Histopathological analyses of the tongue revealed significantly higher severity of dysplasia in the cyclin D1 overexpression mice, compared with nontransgenic controls and with untreated controls. Moreover, only the cyclin D1 overexpression mice developed neoplastic lesions in the oro-esophageal epithelia. Examination of the dysplastic and neoplastic lesions revealed abnormal proliferation. Our findings suggest that cyclin D1 overexpression enhances susceptibility to carcinogen-induced oral tumorigenesis. These results underscore the importance of cyclin D1 in the process of oral neoplastic development. Further, they emphasize the value of this transgenic model to study the pathogenesis of oral precancer and cancer and establish it as a model system to test candidate agents for chemoprevention of upper aero-digestive cancer.

Relation between menin expression and NF-kappaB activity in an intestinal cell line

In a previous study, we demonstrated that the Men1 gene is mainly expressed in the proliferative crypt compartment of the small intestine and that a reduction of menin expression in the crypt-like IEC-17 cell line induces an increase in proliferation rate concomitant with an increase in cyclin D1 expression. The aim of the present study was to test the hypothesis that the NF-kappaB pathway may be involved in cyclin D1 overexpression. Transcriptional activity of the cyclin D1 gene promoter was increased upon reduction of menin expression. Blockade of the NF-kappaB pathway restored proliferation, cell cycle, cyclin D1 gene transcription and cyclin D1 expression levels to those observed in the presence of menin. These data support a correlation between cyclin D1 expression, NF-kappaB activity and menin expression in this epithelial cell line and are relevant to the physiological function of menin in regulating proliferation in the intestinal epithelium.

Analysis of gene expression profile of TPM3-ALK positive anaplastic large cell lymphoma reveals overlapping and unique patterns with that of NPM-ALK positive anaplastic large cell lymphoma

Anaplastic large cell lymphoma (ALCL) comprises a group of non-Hodgkin lymphomas characterized by the expression of the CD30/Ki-1 antigen. A subset of ALCL is characterized by chromosomal translocations involving the anaplastic lymphoma kinase (ALK) gene on chromosome 2. While the most common translocation is the t(2;5)(p23;q35) involving the nucleophosmin (NPM) gene on chromosome 5, up to 12 other translocations partners of the ALK gene have been identified. One of these is the t(1;2)(q25;p23) which results in the formation of the chimeric protein TPM3-ALK. While several of the signaling pathways induced by NPM-ALK have been elucidated, those involved in ALCLs harboring TPM3-ALK are largely unknown. In order to investigate the expression profiles of ALCLs carrying the NPM-ALK and TPM3-ALK fusions, we carried out cDNA microarray analysis of two ALCL tissue samples, one expressing the NPM-ALK fusion protein and the other the TPM3-ALK fusion protein. RNA was extracted from snap-frozen tissues, labeled with fluorescent dyes and analyzed using cDNAs microarray containing approximately 9,200 genes and expressed sequence tags (ESTs). Quantitative fluorescence RT-PCR was performed to validate the cDNA microarray data on nine selected gene targets. Our results show a significant overlap of genes deregulated in the NPM-ALK and TPM-ALK positive lymphomas. These deregulated genes are involved in diverse cellular functions, such as cell cycle regulation, apoptosis, proliferation, and adhesion. Interestingly, a subset of the genes was distinct in their expression pattern in the two types of lymphomas. More importantly, many genes that were not previously associated with ALK positive lymphomas were identified. Our results demonstrate the overlapping and unique transcriptional patterns associated with the NPM-ALK and TPM3-ALK fusions in ALCL.

Cyclin D1 gene activation in human myeloma cells is independent of DNA hypomethylation or histone hyperacetylation

OBJECTIVE

Overexpression of cyclin D1 is a common event in solid and hematological cancers. In multiple myeloma (MM), a B-cell hemopathy, one mechanism responsible for cyclin D1 expression is the translocation t(11;14)(q13;q32). But this translocation does not account for cyclin D1 gene activation in all MM. We have hypothesized that epigenetic events could regulate cyclin D1 gene transcription.

METHODS

Using 6 MM cell lines representative of different cyclin D1 expression levels and exhibiting various chromosome 11 abnormalities, as well as normal B cells, we studied DNA methylation and histone acetylation of the cyclin D1 promoter.

RESULTS

With the bisulfite sequencing technique, we have studied the DNA methylation status of the core minimal cyclin D1 promoter containing Sp1- and CRE-binding sites. Our results show that this region is not methylated in 6 human MM cell lines as well as in normal B lymphocytes, independently of cyclin D1 expression. Treatment with the DNA methyltransferase inhibitor 5-aza-deoxycytidine (5-Aza) had no effect on cyclin D1 gene transcription. Chromatin immunoprecipitation (ChIP) experiments indicated that acetylated histones H4 are located at both the active and inactive cyclin D1 promoter. Treatment with a histone deacetylase inhibitor, trichostatin A (TSA), had no effect on gene transcription, nor had combined TSA plus 5-Aza treatment.

CONCLUSION

The cyclin D1 gene is silenced within the B lineage by a mechanism different from DNA methylation or histone deacetylation.

Parathyroid carcinoma

Parathyroid carcinoma is an uncommon malignancy. It accounts for less than 1% of cases of primary hyperparathyroidism (HPT). It is manifested by severe hypercalcemia and up to 50% of patients will have concomitant kidney or bone disease. The etiology of parathyroid carcinoma is unknown, however, the recently discovered HRPT2 gene, a tumor suppressor gene encoding for the protein parafibromin, has been implicated in the pathogenesis. Identification of inactivating germ-line mutations in HRPT2 has significant implications for diagnosis and management. This article summarizes the genetic aspects of parathyroid carcinoma, reviews its clinical manifestations, and outlines the principles of surgical therapy, the indications for adjuvant therapy, and the use of bisphosphonate and calcimimetic agents for management of hypercalcemia.

Minireview: Cyclin D1: normal and abnormal functions

Cyclin D1 encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the retinoblastoma protein and promotes progression through the G1-S phase of the cell cycle. Amplification or overexpression of cyclin D1 plays pivotal roles in the development of a subset of human cancers including parathyroid adenoma, breast cancer, colon cancer, lymphoma, melanoma, and prostate cancer. Of the three D-type cyclins, each of which binds cyclin-dependent kinase (CDK), it is cyclin D1 overexpression that is predominantly associated with human tumorigenesis and cellular metastases. In recent years accumulating evidence suggests that in addition to its original description as a CDK-dependent regulator of the cell cycle, cyclin D1 also conveys cell cycle or CDK-independent functions. Cyclin D1 associates with, and regulates activity of, transcription factors, coactivators and corepressors that govern histone acetylation and chromatin remodeling proteins. The recent findings that cyclin D1 regulates cellular metabolism, fat cell differentiation and cellular migration have refocused attention on novel functions of cyclin D1 and their possible role in tumorigenesis. In this review, both the classic and novel functions of cyclin D1 are discussed with emphasis on the CDK-independent functions of cyclin D1.

Update on genetic and clinical aspects of primary hyperparathyroidism

Primary hyperparathyroidism (pHPT) is a common endocrine disorder that predominantly affects postmenopausal women. It is mostly caused by solitary tumours within the parathyroid glands. Although the pathophysiology of pHPT is still incompletely understood, recent studies provide new clues on the development and cellular growth of tumours within the parathyroids associated with hypersecretion of parathyroid hormone and hypercalcaemia. The natural course of pHPT is rather benign. Nowadays, it has become an oligo- or asymptomatic disease often only detected by routine blood tests. These facts raise the question whether to perform parathyroidectomy on oligo- and asymptomatic patients with pHPT or whether it is possible to monitor these patients without surgery. The aim of this article is to review the literature as regards (i) the pathophysiological mechanisms that underlie parathyroid neoplasia and (ii) the defective calcium-sensing in patients with pHPT (iii) environmental and/or genetic risk factors that predispose to or promote parathyroid neoplasia, as well as (iv) alternative approaches to treat oligo- and asymptomatic patients with pHPT medically.

Mutational analyses of RB and BRCA2 as candidate tumour suppressor genes in parathyroid carcinoma

OBJECTIVE

Strong evidence indicates that at least one key tumour suppressor gene important for the development of malignant parathyroid tumours is located on chromosome 13, but the critical target gene remains unknown. Importantly, the region of acquired DNA loss includes two established tumour suppressor genes, the retinoblastoma gene, RB (RB1) and BRCA2. Resolution of whether RB or BRCA2 is the critical 13q tumour suppressor gene in parathyroid cancer requires analysis of these genes' sequences for intragenic inactivating mutations. Therefore, RB and BRCA2 were analysed in a group of parathyroid carcinomas in which mutations of these genes should be most readily detectable.

PATIENTS AND DESIGN

Six parathyroid carcinomas from four patients which showed loss of heterozygosity (LOH) at the RB locus and/or 13q loss by comparative genomic hybridazation (CGH) were selected from a CGH/LOH-screened panel of 16 carcinoma specimens from 10 patients. These tumours were examined for mutations by direct sequencing of the complete 27-exon coding region, intron-exon boundaries and promoter of RB. The 26 coding exons and intron-exon boundaries of BRCA2 were also directly sequenced in seven parathyroid carcinomas with loss in the BRCA2 region.

RESULTS

No microdeletions, insertions, or point mutations were detected in either RB or BRCA2 in any of the carcinomas.

CONCLUSION

The absence of tumour-specific somatic mutations in RB and BRCA2 suggests that they are unlikely to act as classic tumour suppressor genes in the pathogenesis of parathyroid carcinomas. While decreased expression of these genes might contribute to parathyroid carcinomatosis in a secondary fashion and 13q loss warrants further study as a diagnostic marker for parathyroid carcinoma, the putative 13q tumour suppressor awaits identification.

Cyclin D-dependent kinases, INK4 inhibitors and cancer

The Cyclin D-Cdk4,6/INK4/Rb/E2F pathway plays a key role in controlling cell growth by integrating multiple mitogenic and antimitogenic stimuli. The components of this pathway are gene families with a high level of structural and functional redundancy and are expressed in an overlapping fashion in most tissues and cell types. Using classical transgenic technology as well as gene-targeting in ES cells, a series of mouse models have been developed to study the in vivo function of individual components of this pathway in both normal homeostasis and tumor development. These models have proven to be useful to define specific as well as redundant roles among members of these cell cycle regulatory gene families. This pathway is deregulated in the vast majority of human tumors by genetic and epigenetic alterations that target at least some of its key members such as Cyclin D1, Cdk4, INK4a and INK4b, pRb etc. As a consequence, some of these molecules are currently being considered as targets for cancer therapy, and several novel molecules, such as Cdk inhibitors, are under development as potential anti-cancer drugs.

The NeiI polymorphism in the cyclin D1 gene and sporadic primary hyperparathyroidism

OBJECTIVES

The cell cycle regulator cyclin D1 plays an important role in parathyroid tumourigenesis. The NciI polymorphism in exon 4 has recently been associated with early onset of hereditary nonpolyposis colorectal cancer and is a prognostic indicator of nonsmall cell lung cancer and squamous cell carcinomas. Furthermore, a limited study of 28 primary hyperparathyroidism (pHPT) patients displayed a tendency of NciI influence on HPT development. We hypothesized that the NciI polymorphism may relate to a risk of developing pHPT.

DESIGN, SETTING AND SUBJECTS

We genotyped 182 patients with sporadic pHPT and matched controls for the cyclin D1 polymorphism. A total of 88 pHPT patients and controls were recruited via a health-screening.

RESULTS

The frequency distribution of the NciI genotypes NN, Ni, and ii were in pHPT patients and controls 22, 44 and 34%, and 26, 49 and 25%, respectively. The calculated allele frequencies were A = 0.56; G = 0.44 in cases and A = 0.49; G = 0.51 in controls. The frequency distributions did not differ comparing cases and controls when subgrouped after age and menopausal status. The NciI genotypes were not significantly associated with age of the individuals, serum (s)-calcium, s-parathyroid hormone (PTH), bone mineral density (BMD) or parathyroid tumour weight in any of the groups of pHPT patients or controls.

CONCLUSIONS

No significant differences in distribution of the genotypes could be detected between the groups, suggesting that the polymorphism has minor or no pathogenic importance in the development of pHPT. Our results suggest that determination of the NciI polymorphism in the cyclin D1 gene is not a clinically useful tool for prediction of pHPT.