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Journal of Clinical Endocrinology & Metabolism, doi:10.1210/jc.2005-2155
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The Journal of Clinical Endocrinology & Metabolism Vol. 91, No. 2 563-568
Copyright © 2006 by The Endocrine Society

Up-Regulation of the Gene Encoding Protein Kinase A Type I{alpha} Regulatory Subunit in Nodular Hyperplasia of Parathyroid Glands in Patients with Chronic Renal Failure

Yatsuka Hibi, Fukushi Kambe, Yoshihiro Tominaga, Yutaka Mizuno, Hironobu Kobayashi, Katsumi Iwase, Tsuneo Imai and Hisao Seo

Department of Endocrinology and Metabolism, Division of Molecular and Cellular Adaptation, Research Institute of Environmental Medicine, Nagoya University (Y.H., F.K., H.S.), Nagoya 464-8601, Japan; Department of Surgery, Renal Center, Nagoya Second Red Cross Hospital (Y.T.), Nagoya 466-8650, Japan; Department of Breast and Endocrine Surgery, Nagoya University Hospital (Y.H., Y.M., H.K., T.I.), Nagoya 466-8560, Japan; and Department of Endocrine Surgery, Fujita-Health University School of Medicine (K.I.), Toyoake 470-1192, Japan

Address all correspondence and requests for reprints to: Dr. Fukushi Kambe, Department of Endocrinology and Metabolism, Research Institute of Environmental Medicine, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. E-mail: kambe{at}riem.nagoya-u.ac.jp.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Context: Hyperplasia of parathyroid glands in patients with chronic renal failure is classified into diffuse (DH) and nodular (NH) types, and NH is often refractory to routine medical therapy.

Objective: Although it is considered that the parenchymal cells initially proliferate diffusely and then some of them are transformed to form nodules consisting of monoclonal cells, the underlying molecular mechanism for such a transformation is not fully understood. In this study we tried to identify the genes that are up-regulated in NH.

Design and Setting: The cDNA population prepared from DH was subtracted from that prepared from NH by a PCR-based cDNA subtraction method. The resultant cDNAs were cloned and sequenced. To confirm the up-regulation of the identified genes, a total of 35 parathyroid glands (18 DH, 16 NH, and one mixed) obtained from 21 patients were analyzed.

Results: One of the nuclear genes identified was the PRKAR1A gene, which encodes type I{alpha} regulatory subunit (RI{alpha}) of cAMP-dependent protein kinase (PKA). Immunohistochemical analysis demonstrated that RI{alpha} was abundantly expressed in the nodular region, whereas the adjacent diffuse region displayed relatively low expression. Northern and Western blot analyses demonstrated up-regulation of RI{alpha} expression in most NH tested. Determination of PKA activities revealed that free PKA activities measured in the absence of cAMP in the assay were inversely correlated with RI{alpha} expression, indicating the functional significance of RI{alpha} up-regulation.

Conclusions: These results suggest that the aberrant expression of RI{alpha} is involved in the diffuse to nodular transformation of hyperplasia of parathyroid glands by impairing cAMP/PKA signal transduction.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
A NUMBER OF pathogenic conditions, such as hypocalcemia, phosphate retention, deficiency of active vitamin D3, and decreased expression of vitamin D3 receptor and calcium-sensing receptor in parathyroid cells, have been reported to contribute to the development of hyperplasia of parathyroid glands in patients with chronic renal failure (1, 2). The four glands usually display asymmetric enlargements even in the same individuals despite the fact that the glands appear to be exposed to the same levels of external pathogenic factors. Histopathologically, hyperplasia of parathyroid glands can be classified into diffuse (DH) and nodular (NH) types. In DH, parenchymal cells proliferate diffusely by maintaining normal lobular structures, and fat cells usually coexist in the glands. In contrast, in NH, parenchymal cells proliferate and form at least one encapsulated nodule virtually devoid of fat cell accumulation. It was reported that the glands become heavier as the type changes from DH to NH (3), and that parenchymal cells in NH have a greater growth potential than the surrounding cells (4). Furthermore, we and others found that DH consists of polyclonal cells, whereas each nodule of NH is composed of monoclonal cells (5, 6).

Vitamin D3 pulse therapy has been shown to successfully decrease serum PTH levels and the size of hyperplastic parathyroid glands (7). However, a poor response to the therapy was shown in patients with NH, because it expresses less vitamin D3 receptor than DH (1). In addition, it was reported that the decreased expression of the receptor is associated with the reduced expression of cyclin-dependent kinase inhibitors, p21 and p27, which can lead to cell proliferation (8).

These findings indicate that in the secondary hyperparathyroidism due to chronic renal failure, the parathyroid glands initially proliferate diffusely and polyclonally in response to external pathogenic factors. Then the glands undergo transformation to NH, consisting of one or several monoclonal nodules that escape from vitamin D3 regulation. The autonomous and clonal proliferation suggests that a certain genetic abnormality occurs in a single parenchymal cell that makes the cell grow and divide exclusively. To determine this abnormality, studies of loss of heterozygosity of genes encoding multiple endocrine neoplasia type I, calcium-sensing receptor, vitamin D3 receptor, etc., and a genome-wide screening have been conducted (9, 10, 11, 12). However, it was found that the loss of heterozygosity of these genes is not a major genetic abnormality in NH, and that diverse molecular pathogenetic processes may exist for the clonal proliferation. In the present study we tried to identify the genes that are up-regulated in NH compared with the diffuse one by employing a PCR-based cDNA subtraction method.

One of the genes identified was the protein kinase A (PKA) regulatory subunit type I{alpha} (RI{alpha}) gene (PRKAR1A), which encodes the RI{alpha} of cAMP-dependent protein kinase (PKA). Various external physiological ligands increase intracellular cAMP levels by binding to their cognate G protein-coupled receptors present in plasma membrane, followed by activation of adenylate cyclase. The inactive holoenzyme of PKA is a tetramer composed of two regulatory (R) and two catalytic (C) subunits. Binding of the tetramer with cAMP dissociates the enzyme into a dimer of R subunit with four cAMPs and two free active C subunits. Most effects of cAMP are mediated by C subunit through phosphorylation of serine or threonine residues of target proteins. The inhibition of C subunit activity is the best-characterized function of R subunit. To date, four R subunit isoforms, RI{alpha}, RIß, RII{alpha}, and RIIß, and three C subunit isoforms, C{alpha}, Cß, and C{gamma}, have been identified. Type I PKA contains either RI{alpha} or RIß, and type II PKA contains either RII{alpha} or RIIß. All C subunits can form a complex with either RI or RII subunit. Because type I PKA is often overexpressed in growth-stimulated cells, whereas type II PKA is preferentially expressed in growth-arrested cells, the distinct functions of type I and type II PKA have been suggested in cell proliferation and differentiation (13). RI{alpha} is expressed ubiquitously, whereas RIß is expressed in limited tissues, such as brain and testis (14). RI{alpha} is therefore the main component of type I PKA in most cells and regulates PKA activity in response to cAMP (15). Our results show that RI{alpha} expression is up-regulated in most NH tested.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Case subjects and materials

As shown in Table 1Go, a total of 35 parathyroid glands obtained from 21 patients with secondary hyperparathyroidism due to chronic renal failure were analyzed in this study. All patients underwent total parathyroidectomy in Nagoya Second Red Cross Hospital or Nagoya University Hospital, followed by autotransplantation, in which the smallest glands showing diffuse hyperplasia were minced, and 30 pieces as large as 3 x 1 x 1 mm were implanted into the forearm without arteriovenous fistula. Informed consent for the analyses of tissue specimens was obtained from all patients. The types of DH and NH were diagnosed by histopathologists according to criteria described previously (16). Especially the diagnosis of a DH gland was strictly performed to minimize contamination by NH, and the smallest gland was used for transplantation, so that more than 400 hyperplastic parathyroid glands were required to obtain 18 DH glands.


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  		TABLE 1. Hyperplastic parathyroid glands used in this study and the analytical results

 
PCR-based cDNA subtractive hybridization

Total RNAs were extracted from five DH and five NH parathyroid glands obtained from nine patients (Table 1Go) using a RNA extraction kit (Qiagen, Valencia, CA). The total RNAs from DH and those from NH were pooled separately. The double-stranded cDNAs were synthesized from 1 µg total RNA of each group using a Smart PCR cDNA synthesis kit (BD Clontech, Mountain View, CA) and were used for suppression PCR-based cDNA subtractive hybridization using a PCR-select cDNA subtraction kit (BD Clontech). The procedures were described in our previous report (17). The cDNAs prepared from DH and NH were regarded as driver and tester, respectively, and the driver cDNA population was subtracted from the tester cDNA population. The resultant tester-specific cDNAs were amplified by PCR, and cloned into pGEM-T-easy vector (Promega Corp., Madison, WI). Approximately 1000 cDNA clones were subjected to the screening by dot-blot hybridization. The detailed procedures were described in the protocol of the PCR-select cDNA subtraction kit (BD Clontech). In brief, two sets of membranes onto which the cloned cDNA were blotted were prepared, and each was hybridized with a [32P]deoxy-CTP-labeled driver or tester cDNA population. The dots showing higher radioactivities with tester probe than with driver probe were determined by BAS 2000 Bioimage analyzing system (Fuji Photo Film, Tokyo, Japan), and the corresponding cDNAs were identified by sequencing.

Northern blot analysis

Fifteen micrograms of total RNA from DH and NH were subjected to Northern blot analysis as described previously (18). The membrane was hybridized with [32P]deoxy-CTP-labeled, human RI{alpha} cDNA, which was one of the clones identified by the cDNA subtractive hybridization. The same membrane was rehybridized with human ß-actin cDNA probe. Radioactivities of the bands were determined by BAS 2000. The cDNA probes were prepared by RT-PCR from human parathyroid total RNA: primers for human RI{alpha}: sense, 5'-GCTTGCTGTTTACTCCCTTC-3'; and antisense, 5'-AACGGTCCTTTCGCCATCTA-3'; and primers for human ß-actin: sense, 5'-ACCTTCAACACCCCAGCCATG-3'; and antisense, 5'-GGCCATCTCTTGCTCGAAGTC-3'.

Western blot analysis

The tissue samples were minced and washed in PBS, and dispersed in 5 vol ice-cold suspension buffer [100 mM NaCl, 10 mM Tris-HCl (pH 7.6), and 1 mM EDTA (pH 8.0) containing protease inhibitor cocktail tablets (Roche, Mannheim, Germany)]. After addition of an equal volume of 2x sodium dodecyl sulfate gel-loading buffer, the samples were placed in boiling water and sonicated to shear the chromosomal DNA. After centrifugation, the supernatants (50 µg protein/lane) were subjected to 12% PAGE. Detailed procedures for Western blot analysis were described in our previous report (19). A mouse monoclonal antibody specific for human RI{alpha} (BD Biosciences, Bedford, MA) and antimouse IgG goat antibody conjugated with horseradish peroxidase (Sigma- Aldrich Corp., St. Louis, MO) were used as first and second antibodies, respectively. The proteins were visualized by enhanced chemiluminescence reagents (Pierce Chemical Co., Rockford, IL). The densities of the bands were quantified using National Institutes of Health Image software (version 1.62, Bethesda, MD). The same membrane was then incubated with antiactin rabbit antibody (Sigma-Aldrich Corp.), followed by antirabbit IgG goat antibody conjugated with horseradish peroxidase (Sigma-Aldrich Corp.).

Immunohistochemistry

Immunohistochemistry was performed by a labeled streptavidin-biotin method using a commercial kit (SAB-PO kit, Nichirei, Tokyo, Japan). According to the instructions from the manufacturer, deparaffinization and rehydration were performed for paraffin-embedded, 3-µm-thick tissue sections mounted on silane-coated slides. Antigen retrieval was achieved by heating the sections in 10 mM citrate buffer (pH 6.0) in a microwave oven at 500 W for 1 min (heating to just before boiling) seven times. They were then treated with 1% hydrogen peroxide for 5 min to quench endogenous peroxidase activities and with 10% normal rabbit serum for 10 min to block nonspecific sites. The sections were then incubated overnight at 4 C with a mouse monoclonal antibody against human RI{alpha} (BD Biosciences), followed by incubation at room temperature for 10 min with a biotinylated antimouse IgG antibody and then for 5 min with horseradish peroxidase-conjugated streptavidin. After washing, a 3,3-diaminobenzidine chromogen solution was applied for 5 min. The sections were then counterstained with hematoxylin and mounted.

Determination of PKA activity

PKA activities in tissue lysates (30 µg protein) prepared from DH and NH were measured using a PKA assay kit (Upstate Biotechnology, Inc., New York, NY), which is based on phosphorylation of a specific substrate [Kemptide, a phosphorylation site in pyruvate kinase (20)] by PKA via transfer of a labeled phosphate from [{gamma}-32P]ATP to the substrate. The specificity of PKA activities was ensured by measuring the activities in the presence of inhibitors for protein kinase C, calcium calmodulin kinase, and PKA. We determined PKA activities in the presence and absence of 2 µM cAMP, which represent total and free PKA activities in tissues, respectively. The PKA activity ratio indicates free per total activity.

Statistics

Statistical analysis was performed by ANOVA, followed by Bonferroni’s multiple t test, and P < 0.05 was considered significant.


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
The PCR-based cDNA subtraction method allows isolation of differentially expressed cDNAs among two different cDNA populations, called tester and driver. The driver cDNA population is subtracted from the tester cDNA population by hybridization, and then the cDNAs present only in the tester population are enriched and amplified by PCR. In this study we employed the cDNAs prepared from NH as tester and those from DH as driver. The subtracted cDNAs amplified by PCR were cloned, and approximately 1000 clones were subjected to screening by dot-blot hybridization using tester and driver cDNAs as probes. The sequencing analysis of 100 clones that hybridized with tester cDNAs more preferentially than with driver cDNAs revealed that 21 cDNA clones were derived from mitochondrial genes, 10 clones from nuclear genes, and the others were unidentified or overlapped. One of the mitochondrial genes identified by this method was cytochrome b, which encodes a protein for complex III of the mitochondrial oxidative phosphorylation system (21). The up-regulation of cytochrome b may reflect the increased energy production in NH compared with DH. One of the nuclear genes identified was PRKAR1A. A Blast search of DDBJ (DNA databank of Japan) showed that the cloned nucleotide sequence was identical with region 3101–3517 nucleotides in PRKAR1A cDNA (accession no. M33336), which lies at the 3' end of the cDNA. PRKAR1A encodes RI{alpha}, which is a main component of type I PKA, and its overexpression has been reported in a number of transformed cell lines and cancers (22). We thus investigated the expression of RI{alpha} in DH and NH using specimens obtained from the patients with advanced chronic renal failure.

Six total RNAs prepared from each of DH and NH were subjected to Northern blot analysis using RI{alpha} and ß-actin cDNAs as probes. As shown in Fig. 1AGo, a single band of RI{alpha} mRNA, 3.7 kb in length, and a band of ß-actin mRNA, 2 kb, were detected. The expression level of RI{alpha} mRNA in each hyperplasia was evaluated after normalizing the RI{alpha} levels by ß-actin levels: the ratio of RI{alpha}/ß-actin. The ratio of the DH Dd could not be calculated, because of RNA degradation. All names of parathyroid glands tested in this study (Ad, An, Dd, etc.) and the meaning of the names are described in Table 1Go. The highest value among five DH samples was 0.39 of Bd, and five of six NH (Fn, An, Bn, Hn1 and Cn) exhibited a higher value than 0.39, suggesting up-regulation of RI{alpha} gene expression in NH. The only exception was Gn; its ratio was 0.32.


Figure 1
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  		FIG. 1. Abundant expression of RI{alpha} in NH. A, Total RNAs (15 µg/lane) prepared from DH and NH were subjected to Northern blot analysis using RI{alpha} and ß-actin cDNAs as probes. The names of the parathyroid glands are shown at the top of the image. Capital letters correspond to the patients, and lowercase letters attached to the capitals, d and n, indicate DH and NH, respectively (see Table 1Go). The radioactivities of the bands were determined using the BAS 2000 system, and RI{alpha} mRNA levels were normalized by ß-actin levels. The ratios are shown at the bottom of the image. ND, Not determined. B, Tissue lysates (50 µg protein/lane) prepared from DH and NH were subjected to Western blot analysis using anti-RI{alpha} and antiactin antibodies. The names of the parathyroid glands are shown at the top of the image. The densities of bands were quantified, and the ratios of RI{alpha}/actin are shown at the bottom of the image.

 
We next examined RI{alpha} expression by Western blot analysis using six whole-cell lysates prepared from each of DH and NH (Fig. 1BGo). The single bands of RI{alpha} and actin were detected with molecular weights of 49,000 and 42,000, respectively. The protein level of RI{alpha} in each hyperplasia was also evaluated by the ratio of RI{alpha}/actin. The highest value among six DH was 0.64 of Ed1, and four of six NH (Fn, An, Bn, and Hn1) exhibited a higher value than 0.64. Thus, the increased RI{alpha} expression in Fn, An, Bn, and Hn1 was confirmed by both Northern and Western blot analyses. In contrast, the lack of increased expression in Gn was observed by both methods. Cn displayed a relatively low level of RI{alpha} protein despite the increased expression at the mRNA level, probably due to the reduced translation efficiency.

Table 1Go summarizes the specimens used in this study and their analytical results. The weights of DH glands are less than 300 mg, whereas those of NH glands are more than 400 mg. Note the results of patients A, B, and C, from whom we obtained both DH and NH glands and analyzed them at both mRNA and protein levels. In all three patients, the NH glands expressed higher RI{alpha} than the DH glands at both levels. Although the protein level of Cn was relatively low among the nodular glands tested, its level was more than that of Cd.

When analyzed statistically, the mRNA levels (RI{alpha}/ß-actin ratios) of DH and NH were 0.25 ± 0.04 (mean ± SE) and 0.87 ± 0.20, respectively. The protein levels (RI{alpha}/actin ratios) were 0.36 ± 0.08 and 2.50 ± 1.08, respectively. For both levels, the values of NH were significantly higher than those of DH (P < 0.05).

The best-characterized function of RI{alpha} is inhibition of PKA kinase activity by binding with C subunit. To determine the functional significance of the up-regulation of RI{alpha} expression in NH, we measured PKA activities in the specimens including Cn (Table 1Go). Free PKA activity measured in the absence of cAMP in the assay indicated a steady-state PKA activity in tissues, whereas total activity determined in the presence of cAMP represented the total amount of PKA in the tissues. The ratio of PKA activities indicates free per total PKA activities. Approximately 80% of PKA was activated in DH of Ad and Bd. In contrast, only 6% of PKA was activated in NH of Bn and Cn, demonstrating that the higher expression of RI{alpha} induces the suppression of PKA activity. In Hn2, free PKA activity was also decreased to 25%. However, free PKA activity in Ed1 was reduced to 20%, which may reflect the relatively high RI{alpha} expression in Ed1 (RI{alpha}/actin protein, 0.64). Note that free PKA activities were markedly suppressed in NH.

The up-regulation of RI{alpha} in NH was also studied by immunohistochemical analysis of seven DH, four NH, and one mixed hyperplastic parathyroid glands. The representative images and the summarized results are presented in Fig. 2Go and Table 1Go, respectively. Six of seven DH glands showed a uniform and low level of RI{alpha} expression. The image of Id3 is shown in Fig. 2AGo. In contrast, RI{alpha} was abundantly expressed in all four NH glands tested. The image of Kn is shown in Fig. 2BGo. When the parathyroid gland including both DH and NH regions (Kdn) was stained (Fig. 2CGo), higher expression of RI{alpha} in the NH region and lower expression in the adjacent DH region were observed. Of note, the image of Kdn at higher magnification clearly indicates the cytoplasmic distribution of RI{alpha} protein (Fig. 2DGo). Furthermore, the expression levels of RI{alpha} appear to differ among the cells in NH, suggesting that RI{alpha} expression is not constitutive, but under some control.


Figure 2
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  		FIG. 2. Higher expression of RI{alpha} in the NH region and lesser expression in the adjacent DH region in mixed hyperplastic parathyroid gland. Immunohistochemistry was performed using DH, NH, and mixed hyperplastic parathyroid glands. RI{alpha} expression was visualized by a labeled streptavidin-biotin (LSAB) method. Representative images of DH (A; magnification, x40), NH (B; x40), and mixed (C, x40; D, x100) hyperplasia are shown. Di, No, and Cap indicate DH, NH, and capsular regions, respectively.

 
In the present study we analyzed 13 DH, 11 NH, and one mixed hyperplastic parathyroid glands. Up-regulation of RI{alpha} gene expression was demonstrated in 11 of 12 NH and mixed glands; the exception was Gn. In contrast, relatively low expression of RI{alpha} was found in 11 of 14 DH and mixed glands; the exceptions were Ed1, Ed2, and Kd. It can, therefore, be concluded that RI{alpha} gene expression is up-regulated in most NH parathyroid glands compared with DH glands.


   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
In the present study we demonstrate for the first time that the RI{alpha} gene expression is up-regulated in NH parathyroid glands in patients with advanced chronic renal failure. It is also shown that although total PKA activities are similar in DH and NH, free PKA activities are markedly reduced in NH. This is consistent with the primary function of RI{alpha}, the inhibition of kinase activity of the C subunit. Although the cAMP/PKA signaling pathway plays a regulatory role in proliferation, differentiation, and oncogenic transformation of various cell types, little is known about the involvement of this pathway in the proliferation of parathyroid cells.

Hypocalcemia, hyperphosphatemia, and vitamin D3 deficiency are three main causes of hyperplasia of parathyroid glands in chronic renal failure. Recent studies have revealed that using uremic rat models, the administration of high dietary calcium or vitamin D3 or the restriction of dietary phosphate prevents enlargement of parathyroid glands. This inhibition of the parathyroid cell growth is associated with the reduced expression of TGF-{alpha} and its receptor, epidermal growth factor receptor, and the increased expression of p21 cyclin-dependent kinase inhibitor (23, 24, 25, 26), demonstrating that TGF-{alpha} plays an important role as an autocrine/paracrine factor in the growth of parathyroid cells in uremia. In addition, the activation of calcium-sensing receptor is suggested to prevent hyperplasia of the parathyroid gland (27). The signaling induced by receptor activation involves intracellular calcium mobilization/oscillations as well as activation of various phospholipases and protein kinases and suppression of cAMP formation (28). However, how the cAMP/PKA signaling pathway regulates the proliferation of parathyroid cells remains to be addressed.

Apart from parathyroid cells, RI{alpha} overexpression has been reported in a variety of tumors, such as breast, renal, colorectal, and ovarian tumors and retinoblastoma (13, 22). The overexpression was also found in several cell lines and in virus- and oncogene-induced, transformed cells (22). The prevention of RI{alpha} expression by antisense oligonucleotide has become a possible single-gene-targeting approach for treatment of some cancers (13). However, the molecular mechanisms underlying RI{alpha}-dependent cell growth or transformation are poorly understood. RI{alpha} expression was found to promote G1 to S transition in some cells and to cause the cell to grow in the absence of serum (29, 30). It was also reported that RI{alpha} overexpression increases the amounts of type I PKA and stimulates the expression of transformation- and proliferation-related genes in prostate carcinoma PC3M cells (31). RI{alpha} function, apart from inhibiting the C subunit, was also reported (32). These reports thus indicate that RI{alpha} overexpression elicits multiple biological effects on cells, which include the stimulation of cell cycle progression and the suppression of apoptosis.

On the contrary, the inactivation of RI{alpha} has been shown to cause the Carney complex (33), which is a multiple neoplasia syndrome characterized by spotty skin pigmentation, cardiac and other myxomas, endocrine tumors, and Schwannomas. Endocrine tumors are often multiple and include adrenocortical, pituitary, thyroid, testicular, and ovarian tumors, but in this context, parathyroid tumors have not been described. The disease is inherited in an autosomal dominant fashion, and the haploinsufficiency appears to be sufficient for tumor development in certain tissues. Similar tumor developments were observed in the mouse model, in which endogenous RI{alpha} expression is suppressed by the antisense transgene (34). Interestingly, PKA activities appear to vary among tumors from Carney complex patients and mice, which is thought to be due to the difference in the compensatory responses of PKA subunit expression under decreased RI{alpha} conditions (35, 36). The fact that the haploinsufficiency of RI{alpha} can induce tumor development strongly suggests that PKA activities are strictly controlled in normal cells, and subtle dysregulation of PKA activities could cause tumorigenesis.

In conclusion, the present study demonstrates the possible involvement of up-regulation of RI{alpha} gene expression in DH to NH transformation of hyperplastic parathyroid glands in patients with chronic renal failure. It has been shown that the growth of RI{alpha}-overexpressing, transformed cells can be suppressed not only by antisense oligonucleotide, but also by some cAMP analogs (37). Considering that NH usually grows autonomously and is refractory to routine medical therapy using vitamin D3, the application of such types of drugs could become an alternative treatment for NH overexpressing RI{alpha}.


   Footnotes
 
This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science, Sports, and Culture, Japan.

First Published Online November 22, 2005

Abbreviations: C, Catalytic; DH, diffuse hyperplasia of parathyroid gland; NH, nodular hyperplasia of parathyroid gland; PKA, cAMP-dependent protein kinase; R, regulatory; RI{alpha}, type I{alpha} regulatory subunit.

Received September 29, 2005.

Accepted November 14, 2005.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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