Nucleotide sequence of cloned cDNAs encoding human preproparathyroid hormone

A potential kidney-bone axis involved in the rapid minute-to-minute regulation of plasma Ca2+

Background

Understanding the regulation of mineral homeostasis and function of the skeleton as buffer for Calcium and Phosphate has regained new interest with introduction of the syndrome “Chronic Kidney Disease-Mineral and Bone Disorder”(CKD-MBD). The very rapid minute-to-minute regulation of plasma-Ca²⁺ (p-Ca²⁺) takes place via an exchange mechanism of Ca²⁺ between plasma and bone. A labile Ca storage pool exists on bone surfaces storing excess or supplying Ca when blood Ca is lowered. Aim was to examine minute-to-minute regulation of p-Ca²⁺ in the very early phase of acute uremia, as induced by total bilateral nephrectomy and to study the effect of absence of kidneys on the rapid recovery of p-Ca²⁺ from a brief induction of acute hypocalcemia.

Methods

The rapid regulation of p-Ca²⁺ was examined in sham-operated rats, acute nephrectomized rats(NX), acute thyroparathyrectomized(TPTX) rats and NX-TPTX rats.

Results

The results clearly showed that p-Ca²⁺ falls rapidly and significantly very early after acute NX, from 1.23 ± 0.02 to 1.06 ± 0.04 mM (p < 0.001). Further hypocalcemia was induced by a 30 min iv infusion of EGTA. Control groups had saline. After discontinuing EGTA a rapid increase in p-Ca²⁺ took place, but with a lower level in NX rats (p < 0.05). NX-TPTX model excluded potential effect of accumulation of Calcitonin and C-terminal PTH, both having potential hypocalcemic actions. Acute TPTX resulted in hypercalcemia, 1.44 ± 0.02 mM and less in NX-TPTX rats,1.41 ± 0.02 mM (p < 0.05). Recovery of p-Ca²⁺ from hypocalcemia resulted in lower levels in NX-TPTX than in TPTX rats, 1.20 ± 0.02 vs.1.30 ± 0.02 (p < 0.05) demonstrating that absence of kidneys significantly affected the rapid regulation of p-Ca²⁺ independent of PTH, C-PTH and CT.

Conclusions

P-Ca²⁺ on a minute-to-minute basis is influenced by presence of kidneys. Hypocalcemia developed rapidly in acute uremia. Levels of p-Ca²⁺, obtained during recovery from hypocalcemia resulted in lower levels in acutely nephrectomized rats. This indicates that kidneys are of significant importance for the ‘set-point’ of p-Ca²⁺ on bone surface, independently of PTH and calcitonin. Our results point toward existence of an as yet unknown factor/mechanism, which mediates the axis between kidney and bone, and which is involved in the very rapid regulation of p-Ca²⁺.

Validation of a simple RP-HPLC method developed for the quantification of meta-cresol in parathyroid hormones formulation

Aim:

To develop and validate a rapid and sensitive reverse phase high performance liquid chromatography (RP-HPLC) method with UV detection for quantification of meta-cresol (m-cresol) in pharmaceutical preparation of parathyroid hormone (1–34) (PTH).

Materials and Methods:

Chromatography was performed on a Jupiter RP C-18 (4.6 mm ID × 250 mm L, porosity 300 Å, particle size 5 μm) with a guard column (reversed-phase C₁₈ column of 4.6 mm ID × 12.5 mm L, porosity 300 Å, particle size 5 μm) using a mobile phase containing 0.1% TFA in 60% methanol with isocratic program at 1.0 mL/min flow rate. Detection was carried out at 217 nm. The method was validated as per ICH guidelines for linearity (correlation coefficient = 0.99), range, accuracy, precision, and robustness (n = 9 during accuracy parameter whereas n =15 during linearity and range parameter and n = 6 during repeatability). Robustness was confirmed by considering two factors; age effect of the mobile phase and test sample and with different columns during method development.

Results:

The method was linear over the concentration range of 75–120 μg/mL. The precision of the method in terms of relative standard deviation was evaluated from intra- and inter-day replicate injections of system suitability standards of m-cresol using different equipment and different columns. Components of within- and between-batch variances were found to be below 2% (n = 30) and 3%, respectively, which constituted an acceptable level of variation. Retention time was found to be about 5.2 min and 10.9 min for m-cresol and PTH, respectively.

Conclusion:

The developed method thus has the potential of being useful for routine quality control of m-cresol.

Gastric acid, calcium absorption, and their impact on bone health

Calcium balance is essential for a multitude of physiological processes, ranging from cell signaling to maintenance of bone health. Adequate intestinal absorption of calcium is a major factor for maintaining systemic calcium homeostasis. Recent observations indicate that a reduction of gastric acidity may impair effective calcium uptake through the intestine. This article reviews the physiology of gastric acid secretion, intestinal calcium absorption, and their respective neuroendocrine regulation and explores the physiological basis of a potential link between these individual systems.

Development and validation of RP-HPLC and RP-UPLC methods for quantification of parathyroid hormones (1-34) in medicinal product formulated with meta-cresol

Rapid and sensitive reversed phase high performance liquid chromatography (RP-HPLC) and ultra performance liquid chromatography (RP-UPLC) method with UV detection has been developed and validated for quantification of parathyroid hormone (PTH) in presence of meta-cresol as a stabilizer in a pharmaceutical formulation. Chromatography was performed with mobile phase containing 0.1% Trifluoroacetic acid (TFA) in MilliQ water and 0.1% TFA in acetonitrile with gradient program and flow rate at 0.3 mL/min for HPLC and 0.4 mL/min for UPLC. Quantification was accomplished with internal reference standard (qualified against innovator product and National Institute for Biological Standards and Control (NIBSC) standard). The methods were validated for linearity (correlation coefficient=0.99), range, accuracy, precision and robustness. Robustness was confirmed by considering three factors; mobile phase composition, column temperature and flow rate/age of mobile phase. Intermediate precision was confirmed on different equipments, different columns and on different days. The relative standard deviation (RSD) (<2% for RP-HPLC and <1% for UPLC, n=30) indicated a good precision. Retention time was found about 17 min and 2 min by HPLC and UPLC methods, respectively. Both methods are simple, highly sensitive, precise and accurate and have the potential of being useful for routine quality control.

Tissue-specific regulatory regions of the PTH gene localized by novel chromosome 11 rearrangement breakpoints in a parathyroid adenoma

Parathyroid adenomas can contain clonal rearrangements of chromosome 11 that activate the cyclin D1 oncogene through juxtaposition with the PTH gene. Here we describe such a chromosomal rearrangement whose novel features provide clues to locating elusive cis-regulatory elements in the PTH gene and also expand the physical spectrum of pathogenetic breakpoints in the cyclin D1 gene region. Southern blot analyses of the parathyroid adenoma revealed rearrangement in the PTH gene locus. Analysis of rearranged DNA clones that contained the breakpoint, obtained by screening a tumor genomic library, pinpointed the breakpoint in the PTH locus 3.3 kb upstream of the first exon. Accordingly, highly conserved distal elements of the PTH 5' regulatory region were rearranged at the breakpoint approximately 450 kb upstream of the cyclin D1 oncogene, resulting in overexpression of cyclin D1 mRNA. Thus, PTH-cyclin D1 gene rearrangement breakpoints in parathyroid tumors can be located far from those previously recognized. In addition to expanding the molecular spectrum of pathogenetic chromosomal lesions in this disease, features of this specific rearrangement reinforce the existence of one or more novel cis-enhancer/regulatory elements for PTH gene expression and narrow their location to a 1.7-kb DNA segment in the distal PTH promoter.

Large scale preparation of recombinant human parathyroid hormone 1–84 from Escherichia coli

Human parathyroid hormone (hPTH) is a promising agent in the treatment of osteoporosis. The intact recombinant human parathyroid hormone [rhPTH(1-84)] was prepared in a large scale from Escherichia coli using a soluble fusion protein strategy. With degenerate codons, gene of hPTH(1-84) was synthesized, ligated with pET32a(+) vector, and then expressed in E. coli BL21(DE3) cells. The soluble fusion protein His(6)-thioredoxin-hPTH(1-84) was harvested after purification by immobilized metal affinity chromatography (IMAC). Following enterokinase cleavage, ion-exchange-chromatography (IEC) and size-exclusive-chromatography (SEC) were used, and finally, over 300mg/l intact hPTH(1-84) with high purity up to 99% was obtained. The purified rhPTH(1-84) was confirmed by mass spectrometry and N-terminal/C-terminal amino-acid sequence analysis. Additionally, this product stimulated adenylate cyclase in Rat Osteosarcoma Cell UMR-106 at the same extent as hPTH standards, indicating that the purified rhPTH(1-84) has full biological activity. The efficient procedure for expression and purification of rhPTH(1-84) may be useful for the mass production of this important protein.

The need for reliable serum parathyroid hormone measurements

Serum parathyroid hormone (PTH) is a recognized marker of bone remodeling in patients with renal osteodystrophy. However, identification of N-terminal truncated PTH fragments and a new form of PTH that interfere with second-generation PTH assays may be responsible for the great variability of PTH values and the difficulties of implementing the recommendations of the National Kidney Foundation/Kidney Disease Outcomes Quality Initiative.

Parathyroid hormone expression in a patient with metastatic nasopharyngeal rhabdomyosarcoma and hypercalcemia

Ectopic PTH secretion by tumor cells has been described as the cause of hypercalcemia associated with malignancy in the absence of osteolytic bone lesions. Although there have been case reports of elevated PTH and hypercalcemia in patients with rhabdomyosarcoma, to date ectopic PTH secretion by malignant cells has not been definitively shown. The possibility of PTH production by pleural-based metastatic nasopharyngeal rhabdomyosarcoma cells in a 62-yr-old Japanese male with hypercalcemia was investigated. The patient's serum PTH level was found to be elevated at 62.22 pmol/L, and pleural fluid PTH level was 47.28 pmol/L and PTHrP level was 3.7 pmol/L. RT-PCR of mRNA extracted from rhabdomyosarcoma cells in the pleural fluid was performed with the addition of PTH and PTHrP exonic primer sets yielded only a cDNA fragment of approx 150 bp consistent with the expected PTH fragment. Sequence analysis of a nested primer PCR fragment confirmed PTH mRNA sequence. We believe this patient to have had hypercalcemia secondary to ectopic PTH secretion, as we have identified the presence of PTH mRNA in tumor cells. We speculate that the overexpression of PTH in rhabdomyosarcoma cells results from molecular rearrangement of the PTH gene. The finding of a normal PTH DNA sequence of the PCR fragment suggests the likelihood of alterations in regulatory sequences.

Identification and characterization of cis-acting elements in the human and bovine PTH mRNA 3'-untranslated region

The human PTH mRNA 3'-UTR has a cis element homologous to the rat cis-acting instability element and a more proximal element identical to the single binding element identified in bovine PTH mRNA 3'-UTR. The function of the elements was shown in vitro.

INTRODUCTION

In the rat, Ca(2+) and phosphate regulate PTH mRNA stability by the interaction of trans-acting proteins with a defined cis-acting instability element in the distal region of the PTH mRNA 3'-untranslated region (UTR). This element has been characterized in the rat and is conserved in human, canine, feline, and murine 3'-UTRs but not in bovine and porcine 3'-UTRs.

MATERIALS AND METHODS

Parathyroid protein-binding assays to the PTH mRNA transcripts were performed. Functionality was studied in reporter genes that were transiently transfected into HEK293 cells.

RESULTS

Protein-RNA binding experiments identified an element in bovine PTH mRNA at the proximal end of the 3'-UTR that is different from the rat protein-binding element. The human 3'-UTR contains both elements, but only the distal element binds proteins. Functional studies with HEK293 cells transiently transfected with reporter genes containing the different elements and flanking nucleotides (nt) showed that the human distal element destabilized a reporter mRNA similar to the effect of this element in the rat. A reporter mRNA containing the single bovine PTH mRNA protein-binding element was also destabilized, and this was prevented by coexpression of AU-rich element binding factor 1 (AUF1).

CONCLUSION

Our results identify a new protein-binding element in the PTH mRNA 3'-UTR. In bovine PTH mRNA, it is the only element, and it is functional in destabilizing a reporter gene. It is also present in other species, including human PTH mRNA, where it is not functional, possibly because of differences in flanking sequences. The human PTH mRNA 3'-UTR distal element is highly homologous to the rat cis-acting instability element and destabilized a reporter gene, indicating its functionality. Therefore, different species have alternative cis-acting protein-binding elements that may determine the regulation of PTH mRNA stability in response to changes in serum calcium and phosphate.

Parathyroid hormone secretion and action: evidence for discrete receptors for the carboxyl-terminal region and related biological actions of carboxyl- terminal ligands

PTH is a major systemic regulator of the concentrations of calcium, phosphate, and active vitamin D metabolites in blood and of cellular activity in bone. Intermittently administered PTH and amino-terminal PTH peptide fragments or analogs also augment bone mass and currently are being introduced into clinical practice as therapies for osteoporosis. The amino-terminal region of PTH is known to be both necessary and sufficient for full activity at PTH/PTHrP receptors (PTH1Rs), which mediate the classical biological actions of the hormone. It is well known that multiple carboxyl-terminal fragments of PTH are present in blood, where they comprise the major form(s) of circulating hormone, but these fragments have long been regarded as inert by-products of PTH metabolism because they neither bind to nor activate PTH1Rs. New in vitro and in vivo evidence, together with older observations extending over the past 20 yr, now points strongly to the existence of novel large carboxyl-terminal PTH fragments in blood and to receptors for these fragments that appear to mediate unique biological actions in bone. This review traces the development of this field in the context of the evolution of our understanding of the "classical" receptor for amino-terminal PTH and the now convincing evidence for these receptors for carboxyl-terminal PTH. The review summarizes current knowledge of the structure, secretion, and metabolism of PTH and its circulating fragments, details available information concerning the pharmacology and actions of carboxyl-terminal PTH receptors, and frames their likely biological and clinical significance. It seems likely that physiological parathyroid regulation of calcium and bone metabolism may involve receptors for circulating carboxy-terminal PTH ligands as well as the action of amino-terminal determinants within the PTH molecule on the classical PTH1R.

The nucleotide sequences of the parathyroid gene in primates (suborder Anthropoidea)

Nucleotide sequences of the parathyroid (PTH) gene of 12 species of primates belonging to suborder Anthropoidea were examined. The PTH gene contains one intron that separates two exons that code the sequence of prepro and PTH, respectively. The intron of the PTH gene in Cebus apella, Callithrix jacchus, and Saguinus oedipus was 102 bp long, whereas a 103-bp intron was observed in the remaining species. Phylogenetic analysis using the nucleotide sequences of PTH revealed that these 12 species of primates of suborder Anthropoidea could be divided into two groups of the infraorder Platyrrhini (C. apella, C. jacchus, and S. oedipus) and the infraorder Catarrhini (Macaca fascicularis, Macaca fuscata, Cercopithecus aethiops, Papio hamadryas, Presbytes obscura, Hylobates lar, Pongo pygmaeus, Pan troglodytes, and Pan paniscus). The latter infraorder could be further subdivided into two subgroups belonging to the superfamily Cercopithecoidea (M. fascicularis, M. fuscata, C. aethiops, P. hamadryas, and P. obscura) and the superfamily Hominoidea (H. lar, P. pygmaeus, P. troglodytes, and P. paniscus). The deduced amino acid sequences of PTH gene between 12 species of nonhuman primates and human revealed no amino acid substitution in mature PTH among orangutans, chimpanzees, and humans. The results indicated that the PTH gene is very conserved among primates, especially between great apes and humans. The apes are the most suitable animals to be used for studying the bone metabolism and applying the knowledge to clinical use in humans.

A conserved cis-acting element in the parathyroid hormone 3'-untranslated region is sufficient for regulation of RNA stability by calcium and phosphate

Calcium and phosphate regulate parathyroid hormone (PTH) gene expression post-transcriptionally by changes in protein-PTH mRNA 3'-untranslated region (UTR) interactions, which determine PTH mRNA stability. We have identified the protein binding sequence in the PTH mRNA 3'-UTR and determined its functionality. The protein-binding element was identified by binding, competition, and antisense oligonucleotide interference. The sequence was preserved among species suggesting its importance. To study its functionality in the context of another RNA, a 63-base pair cDNA PTH sequence was fused to the growth hormone (GH) gene. There is no parathyroid (PT) cell line and therefore an in vitro degradation assay was used to determine the stability of transcripts for PTH, GH, and a chimeric GH-PTH 63 nucleotides with PT cytosolic proteins. The full-length PTH transcript was stabilized by PT proteins from rats fed a low calcium diet and destabilized by proteins from rats fed a low phosphate diet, correlating with PTH mRNA levels in vivo. These PT proteins did not affect the native GH transcript. However, the chimeric GH transcript was stabilized by low calcium PT proteins and destabilized by low phosphate PT proteins, similar to the PTH full-length transcript. Therefore, we have identified a PTH RNA-protein binding region and shown that it is sufficient to confer responsiveness to calcium and phosphate in a reporter gene. This defined element in the PTH mRNA 3'-UTR is necessary and sufficient for the regulation of PTH mRNA stability by calcium and phosphate.

Molecular mechanisms of primary hyperparathyroidism

Several advances have been achieved toward the goal of understanding the molecular basis of parathyroid tumorigenesis. The cyclin D1/PRAD1 oncogene has been identified, and is involved in the development of several different tumor types besides those of the parathyroid. The tumor suppressor RB gene has been linked to the pathogenesis of parathyroid carcinoma. The MEN-1 gene product has been identified and mutations in MENIN shown to contribute to sporadic tumors. An understanding of the functions of MENIN will provide further insights into parathyroid disease. Mutations in the RET gene have been identified as the causal agent in MEN-2 but this gene contributes rarely to development of sporadic parathyroid tumors. Ultimately, a description of parathyroid tumorigenesis will need to account for such features as the rarity of parathyroid carcinoma, the increased incidence of tumors after neck irradiation, and the increased frequency of hyperparathyroidism in postmenopausal women. In addition, the relationship between excessive cellular proliferation and an altered set-point in the mechanism linking extracellular calcium concentration to PTH secretion requires explanation. While mutations in the CASR gene itself play a critical role in familial disease, they do not appear to be involved in sporadic parathyroid tumorigenesis, and investigation of genes important for its expression is clearly warranted.

Identification of AUF1 as a parathyroid hormone mRNA 3'-untranslated region-binding protein that determines parathyroid hormone mRNA stability

Parathyroid hormone (PTH) mRNA levels are post-transcriptionally increased by hypocalcemia and decreased by hypophosphatemia, and this is mediated by cytosolic proteins binding to the PTH mRNA 3'-untranslated region (UTR). The same proteins are also present in other tissues, such as brain, but only in the parathyroid is their binding regulated by calcium and phosphate. The function of the PTH mRNA 3'-UTR-binding proteins was studied using an in vitro degradation assay. Competition for the parathyroid-binding proteins by excess unlabeled 3'-UTR destabilized the full-length PTH transcript in this assay, indicating that these proteins protect the RNA from RNase activity. The PTH RNA 3'-UTR-binding proteins were purified by RNA affinity chromatography of rat brain S-100 extracts. The eluate from the column was enriched in PTH RNA 3'-UTR binding activity. Addition of eluate to the in vitro degradation assay with parathyroid protein extracts stabilized the PTH transcript. A major band from the eluate at 50 kDa was sequenced and was identical to AU-rich binding protein (AUF1). Recombinant AUF1 bound the full-length PTH mRNA and the 3'-UTR. Added recombinant AUF1 also stabilized the PTH transcript in the in vitro degradation assay. Our results show that AUF1 is a protein that binds to the PTH mRNA 3'-UTR and stabilizes the PTH transcript.

Dynein light chain binding to a 3'-untranslated sequence mediates parathyroid hormone mRNA association with microtubules

The 3'-untranslated region (UTR) of mRNAs binds proteins that determine mRNA stability and localization. The 3'-UTR of parathyroid hormone (PTH) mRNA specifically binds cytoplasmic proteins. We screened an expression library for proteins that bind the PTH mRNA 3'-UTR, and the sequence of 1 clone was identical to that of the dynein light chain LC8, a component of the dynein complexes that translocate cytoplasmic components along microtubules. Recombinant LC8 binds PTH mRNA 3'-UTR, as shown by RNA electrophoretic mobility shift assay. We showed that PTH mRNA colocalizes with microtubules in the parathyroid gland, as well as with a purified microtubule preparation from calf brain, and that this association was mediated by LC8. To our knowledge, this is the first report of a dynein complex protein binding an mRNA. The dynein complex may be the motor that is responsible for transporting mRNAs to specific locations in the cytoplasm and for the consequent is asymmetric distribution of translated proteins in the cell.

Secretin, glucagon, gastric inhibitory polypeptide, parathyroid hormone, and related peptides in the regulation of the hypothalamus- pituitary-adrenal axis

Secretin, glucagon, gastric inhibitory polypeptide (GIP), and parathyroid hormone (PTH) belong, together with vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase (AC)-activating polypeptide, to a family of peptides (the VIP-secretin-glucagon family), which also includes growth hormone-releasing hormone and exendins. All the members of this peptide family possess a remarkable amino-acid sequence homology, and bind to G-protein-coupled receptors, whose signaling mechanism primarily involves AC/protein kinase A and phospholipase C/protein kinase C cascades. VIP and pituitary AC-activating polypeptide play a role in the regulation of the hypothalamus-pituitary-adrenal (HPA) axis, and in this review we survey findings that also other members of the VIP-secretin-glucagon family may have the same function. Secretin and secretin receptors are expressed in the hypothalamus and pituitary gland, and secretin inhibits adrenocorticotropic hormone (ACTH) release. No evidence is available for the presence of secretin receptors in adrenal glands, but secretin selectively depresses the glucocorticoid response to ACTH of dispersed zona fasciculata-reticularis (ZF/R) cells. Glucagon and glucagon-like peptide-1 are contained in the hypothalamus, and all the components of the HPA axis are provided with glucagon and glucagons-like-1 receptors. These peptides exert a short-term inhibitory effect on stress-induced pituitary ACTH release and depress the ZF/R cell response to ACTH by inhibiting the AC/protein kinase A cascade; they also stimulate hypothalamic arginine-vasopressin release. GIP receptors are present in the ZF/R of the normal adrenals, and are particularly abundant in some types of adrenocortical adenomas and hyperplasias. GIP, through the activation of the AC/protein kinase A cascade, evokes a sizeable glucocorticoid secretagogue effect, leading to the identification of a food/GIP-dependent Cushing's syndrome. PTH and PTH-related protein are expressed in the hypothalamus and pituitary gland, and PTH and PTH-related protein receptors in all the components of the HPA axis. Both peptides enhance ACTH and arginine-vasopressin release, as well as stimulate aldosterone and glucocorticoid secretion of dispersed zona glomerulosa and ZF/R cells, respectively. The involvement of growth hormone-releasing hormone and exendins in the functional regulation of the HPA axis has not yet been extensively investigated.

Proparathyroid hormone processing by the proprotein convertase-7: comparison with furin and assessment of modulation of parathyroid convertase messenger ribonucleic acid levels by calcium and 1,25-dihydroxyvitamin D3

We previously showed that the processing of proparathyroid hormone (proPTH) to PTH was accomplished most efficiently by furin (17). Colocalization studies demonstrated that furin is expressed in the parathyroid, whereas proprotein convertase (PC)1 and PC2 are not. Since that time, another member of the PC family, called PC7, has been identified. Here we show, using coinfection studies, that PC7, as well as furin, can appropriately cleave PTH from proPTH. ProPTH and PTH were purified from cell extracts by reversed-phase HPLC and were identified by Western blot analysis and delayed extraction matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Colocalization studies, using Northern blot and reverse transcriptase-PCR analyses, showed that PC7 messenger RNA (mRNA) is expressed in the parathyroid gland. Therefore, PC7, like furin, has the potential to be involved in the physiological processing of proPTH to PTH. The two major regulators of parathyroid cell synthetic and secretory activity are the extracellular fluid calcium and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels. We investigated whether either of these agents might modulate processing of proPTH to PTH by altering parathyroid convertase gene expression. In both in vitro and in vivo systems in which regulation of PTH mRNA levels were clearly apparent, there was no effect of either calcium or 1,25(OH)2D3 on parathyroid furin or PC7 mRNA levels. This is in contrast to the processing of proinsulin to insulin in the pancreatic beta-cell, which is up-regulated by glucose stimulation of PC1 and PC2 synthesis.

Vitamin D and the parathyroid

Vitamin D's biologically active metabolite, 1,25(OH)2D3, has important effects upon the parathyroid cell that are relevant to both the physiology of mineral metabolism and the regulation of the secondary hyperparathyroidism of chronic renal failure. 1,25(OH)2D3 markedly decreases parathyroid hormone (PTH) gene transcription and thus PTH synthesis and secretion. It also acts to decrease parathyroid cell proliferation. Nonhypercalemic analogs of 1,25(OH)2D3 are being developed that may have a wider therapeutic window than 1,25(OH)2D3 itself. In the situations of chronic hypocalcemia and hypophosphatemia, there are interesting interrelationships between 1,25(OH)2D3 and the post-transcriptional regulation of the PTH gene. In nodular secondary hyperparathyroidism, there is down-regulation of the vitamin D receptor in the parathyroid. Different vitamin D receptor genotypes may be associated with higher levels of serum PTH and a predisposition to autonomous hyperplasia.

Autotransplantation of rat parathyroid glands: a study on morphological changes

BACKGROUND

Autotransplantation of parathyroid glands in man is performed to preserve parathyroid function after surgery. In a rat model, we performed autotransplantation into the renal subcapsular space to examine reinnervation and changes in cell activity in the transplanted glands.

METHODS

Parathyroids grafted for 1-20 weeks were examined immunocytochemically for general and specific neuroendocrine markers to visualize nerve fibers and glandular cells and for bromodeoxyuridine to determine cell proliferation. In situ hybridization was used to localize and quantitate chromogranin A and parathyroid hormone (PTH) mRNA expression.

RESULTS

Reinnervation was observed as early as 1 week after transplantation in that nerve fibers containing the general neuronal marker protein gene product 9.5 appeared along blood vessels. During the following 20 weeks, the nerve fiber density increased gradually. One week after transplantation, the immunoreaction intensity for PTH, chromogranin A, and pancreastatin was lower than in control glands. Bromodeoxyuridine-labeled cells were fewer than in control glands at 1 week and at 5-10 weeks after transplantation. The density of PTH mRNA labeling was lower than in control glands during the whole time period studied and reached a minimum after 10 weeks. The density of chromogranin A mRNA labeling was unaffected at 1 and 3 weeks after transplantation and then decreased to a minimum at 10 weeks after transplantation; at 20 weeks, the chromogranin A mRNA labeling had again reached the level in control glands.

CONCLUSION

The changes in PTH and chromogranin A immunoreaction intensity and mRNA density indicate reduced hormone production for several weeks after transplantation. Our results using transmitter-specific markers indicate a rapid ingrowth of mostly sympathetic nerve fibers, preferentially around blood vessels. Later on, parasympathetic and sensory nerve fibers reached the grafts. The parathyroid innervation may be of importance for parathyroid hormone regulation, and the finding of an early reinnervation could be of clinical importance.

Lack of association between enhanced TRPM-2/clusterin expression and increased apoptotic activity in sex-hormone-induced prostatic dysplasia of the Noble rat

Although the functional role of TRPM-2/clusterin in the prostate remains controversial, it has been postulated that transcriptional activation of the gene is an important mechanism in castration-induced prostatic involution and perhaps is a means for prostatic cells to escape apoptotic induction. In the present study, we have measured expression levels of TRPM-2/clusterin and apoptotic activities in the prostates of castrated Noble (NBL) rats and those treated with testosterone (T) and estradiol-17beta (E2) for 16 weeks. We have previously shown that the combined sex hormone treatment (T+E2) induces dysplasia, a purported preneoplastic lesion, exclusively in the dorsolateral prostates (DLPs) of all treated rats. In the present study, we demonstrate that, as expected, castration readily induced enhanced TRPM-2/clusterin expression, which was accompanied by increased apoptotic activity in the epithelia of DLP and ventral prostate (VP). The increase in TRPM-2/clusterin expression appeared earlier and was more dramatic in the VP than in the DLP. In sharp contrast, treatment of rats with T+E2 for 16 weeks induced augmentation of TRPM-2/clusterin expression selectively in the dysplastic lesions of the DLP but not in the lesion-free VP. The enhanced expression of TRPM-2/clusterin in the dysplastic epithelium was, however, not attended by an increase in apoptotic activity within the lesion. Thus, the observed up-regulation of TRPM-2/clusterin expression in the dysplastic foci of T+E2-treated rats occurred in animals whose androgen status remained normal and, despite the increased level of expression of this gene, apoptotic activity in these lesions was unchanged from basal values measured in the DLPs of untreated rats. These findings suggest that TRPM-2/clusterin expression in dysplastic lesions was no longer repressed by androgen nor was it associated with apoptosis. We propose that overexpression of the gene is likely a phenotype of neoplastic transformation. In addition, we speculate that TRPM-2/clusterin may serve as a survival factor, which could favor accumulation of transformed cells in dysplastic foci and thus promote the carcinogenic process.

In vitro cleavage of internally quenched fluorogenic human proparathyroid hormone and proparathyroid-related peptide substrates by furin. Generation of a potent inhibitor

The cleavage of parathyroid hormone (PTH) from its precursor proparathyroid hormone (pro-PTH) is accomplished efficiently by the proprotein convertase furin (Hendy, G. N., Bennett, H. P. J., Gibbs, B. F., Lazure, C., Day, R., and Seidah, N. G. (1995) J. Biol. Chem. 270, 9517-9525). We also showed that a synthetic peptide comprising the -6 to +7 sequence of human pro-PTH is appropriately cleaved by purified furin in vitro. The human pro-PTH processing site Lys-Ser-Val-Lys-Lys-Arg differs from the consensus furin site Arg-Xaa-(Lys/Arg)-Arg that is represented by Arg-Arg-Leu-Lys-Arg in the cleavage site of pro-PTH-related peptide (pro-PTHrP). An earlier study demonstrated that an internally quenched fluorogenic substrate bearing an O-aminobenzoyl fluorescent donor at the NH2 terminus and an acceptor 3-nitrotyrosine near the COOH terminus was appropriately cleaved by the convertases furin and PC1 (Jean, F., Basak, A., DiMaio, J., Seidah, N. G., and Lazure, C. (1995) Biochem. J. 307, 689-695). Here, we have synthesized a series of internally quenched fluorogenic substrates based upon the pro-PTH and pro-PTHrP sequences to determine which residues are important for furin cleavage. Purified recombinant furin and PC1 cleaved the human pro-PTH internally quenched substrate at the appropriate site in an identical manner to that observed with the nonfluorescent peptide. Several substitutions in the P6-P3 sequence were well tolerated; however, replacement of the Lys at the P6 position with Gly and replacement of the P3 Lys by an acidic residue led to markedly compromised cleavage by furin. Furin activity was very sensitive to substitution in P' positions. Replacement of Ser at P1' with Gly and Val at P2' with Ala generated substrates that were less well cleaved. Substitution at the P1' position of Val for Ser in conjunction with Ala for Val at P2', as well as a single substitution of Lys for Val at P2', generated specific inhibitors of furin cleavage. The findings of this study open the way to the rational design of inhibitors of furin with therapeutic potential.

Persistence of Ca2+-sensing receptor expression in functionally active, long-term human parathyroid cell cultures

An original human parathyroid cell culture model from uremic patients with IIo hyperparathyroidism has been developed, with its main feature being long-term functionally active viability up to 5 months, as assessed by persistent responsiveness to changes of extracellular Ca2+ concentrations ([Ca2+]e). In addition to the inhibitory effect of increasing [Ca2+]e, increasing extracellular phosphate exerted a biphasic effect on parathyroid hormone (PTH) secretion. The presence of the Ca2+-sensing receptor (CaR), on which depends the response to [Ca2+]e and its persistence, has been demonstrated in our culture system both by direct detection and by inhibition of its activity. CaR protein was detected by Western blot analysis with a specific anti-CaR antibody. CaR gene transcripts have been identified by reverse transcription-polymerase chain reaction analysis. mRNA (by in situ hybridization) and protein (by immunocytochemistry) expression were detected for both CaR and PTH. Adding a specific anti-CaR antibody to the medium induced a marked reduction of low [Ca2+]e-stimulated PTH release, which decreased to levels equivalent to those obtained in high [Ca2+]e medium. The described long-term functionality could be due to several factors, including the clustered cell type of culture yielded by our preparation procedure, the growth characteristics of hyperplastic uremic tissue, and the use of a phosphate-rich medium. The present model, because of its long-term functionality, is a unique tool for the exploration of PTH synthesis and secretion and for studies of parathyroid cell growth in vitro.

The stability and degradation pathway of recombinant human parathyroid hormone: deamidation of asparaginyl residue and peptide bond cleavage at aspartyl and asparaginyl residues

PURPOSE

The stability of recombinant human parathyroid hormone (rhPTH) was examined under acidic to alkaline conditions; its degradation pathways were elucidated from resultant products.

METHODS

Degradation assay was performed in the pH range 2 to 10 at 40, 50 and 60 degrees C. The approximate molecular mass and pI values of the degradation products were estimated by electrophoresis. FAB-MS peptide mapping and amino acid composition analysis were used to determine these structures. The amount of each respective product was determined by HPLC.

RESULTS

At pH2, eight degradation products were found: 1-30rhPTH, 1-74rhPTH, 1-71rhPTH, 1-56rhPTH, 1-45rhPTH, 46-84rhPTH, 31-84rhPTH and Asp76-rhPTH; these were mainly as a consequence of peptide bond cleavage of the amide bond of Asp. At pH9, five products were found: isoAsp16-rhPTH, Asp16-rhPTH, Asp57-rhPTH, Asp76-rhPTH, 17-84rhPTH; the main degradation pathway was deamidation of Asn via a cyclic imide intermediate. Degradation products resulting from cleavage at Asp were increased in proportion to the extent that pH was lowered below 5. As pH was increased above 5, so were products resulting from deamidation of Asn. Correspondingly, levels of intact rhPTH were at a peak at pH5.

CONCLUSIONS

Degradation of rhPTH under acidic conditions predominantly occurs by cleavage at Asp, whereas, above pH5, deamidation of Asn is the more prominent, rhPTH is most stable at pH5.

The unique proline-rich domain of parotid proline-rich proteins functions in secretory sorting

When expressed in pituitary AtT-20 cells, parotid proline-rich proteins enter the regulated pathway. Because the short N-terminal domain of a basic proline-rich protein is necessary for efficient export from the ER, it has not been possible to evaluate the role of this polypeptide segment as a sorting signal for regulated secretion. We now show that addition of the six-amino acid propeptide of proparathyroid hormone to the proline-rich protein, and especially to a deletion mutant lacking the N-terminal domain, dramatically accelerates intracellular transport of these polypeptides. Under these conditions the chimeric deletion mutant is stored as effectively as the full-length protein in dense core granules. The propeptide does not function as a sorting signal in AtT-20 cells as it does not reroute a constitutively secreted reporter protein to the regulated pathway. During transit, the propeptide is cleaved from the chimeric polypeptides such that the original structures of the full-length and the deletion mutant proline-rich proteins are reestablished. We have also found that the percentage stimulated secretion of the proline-rich proteins increases incrementally (almost twofold) as their level of expression is elevated. The increase reflects an enrichment of these polypeptides in the granule pool and its incremental nature suggests that sorting of proline-rich proteins involves an aggregation-based process. Because we can now rule out contributions to sorting by both N- and C-terminal segments of the proline-rich protein, we deduce that the unique proline-rich domain is responsible for storage. Thus at least some of the determinants of sorting for regulated secretion are protein-specific rather than universal.

Overexpression of parathyroid hormone-related protein or parathyroid hormone in transgenic mice impairs branching morphogenesis during mammary gland development

Parathyroid hormone-related protein (PTHrP) was originally discovered as the tumor product that causes humoral hypercalcemia of malignancy. PTHrP is now known to be widely expressed in many normal fetal tissues where it may participate in the regulation of organogenesis. In this report, we document that overexpression of PTHrP in myoepithelial cells in the mammary glands of transgenic mice resulted in a form of breast hypoplasia characterized by a profound defect in branching morphogenesis of the developing mammary duct system. In addition, transgenic mice manifested a defect in lobuloalveolar development during pregnancy that seemed to be, in part, the consequence of an impaired ability to form terminal ducts in response to estrogen and progesterone stimulation. The effects of PTHrP on branching morphogenesis during breast development appeared to be the result of amino-terminal PTH-like sequences that signal through the PTH/PTHrP receptor, since overexpression of parathyroid hormone itself in the mammary glands of transgenic mice caused a similar development phenotype, and delivery of PTHrP (1–36) via locally implanted slow-release pellets impaired breast development in normal mice. These results suggest that PTHrP, which is a native product of mammary epithelial and myoepithelial cells may participate in normal breast development, perhaps as a locally secreted growth inhibitor.

Proparathyroid hormone is preferentially cleaved to parathyroid hormone by the prohormone convertase furin. A mass spectrometric study

Parathyroid hormone (PTH), an 84-amino acid peptide, is the major regulator of blood calcium homeostasis. Its mRNA, in addition to encoding the mature peptide, also encodes a "pre" sequence of 25 amino acids and a basic "pro" hexapeptide. To assess which of the subtilisin-like prohormone convertases can process proPTH to PTH we coinfected cells with a vaccinia virus construct expressing human preproPTH and vaccinia virus constructs expressing furin, PC1 or PC2. BSC-40 cells, having a constitutive secretory pathway, and GH4C1 cells, having a regulated secretory pathway, were used. PTH biosynthetic products in cell extracts and media were purified by high performance liquid chromatography, identified by radioimmunoassay, and unambiguously defined as either proPTH or PTH by ion-spray mass spectrometry. In both cell types, furin was the most effective in processing proPTH to PTH. In all cases only PTH was released into the medium. In addition, partially purified furin and PC1 were tested for their ability to appropriately cleave a tridecapeptide spanning the prohormone cleavage site found in proPTH. Here too furin was much more effective at cleaving at the correct site. Northern blot analysis and in situ hybridization showed that furin and preproPTH mRNA are co-expressed in the parathyroid, whereas PC1, PC2, and PC5 are not and PACE4 is expressed only at very low levels. Taken together these studies strongly suggest that furin is the enzyme responsible for the physiological processing of proPTH to PTH.

Peptide mapping of recombinant human parathyroid hormone by enzymatic digestion and subsequent fast-atom bombardment mass spectrometry

Peptide maps of recombinant human parathyroid hormone (rhPTH) were determined by both trypsin and V-8 protease digestion with subsequent fast-atom bombardment mass spectrometry (FAB-MS). Coverage of the sequence was 85% when using trypsin and 90% when using V-8 protease. Five rhPTH variants that were recombinantly produced as models of Asn deamidated type degradation products were measured, and molecular weight differences between their respective deamidated peptide fragments were completely detected. In the V-8 protease digests of some variants, characteristic peptide ions caused by the deamidation were observed and this greatly facilitated the assignment and recognition of the deamidated position. Our data suggest that FAB-mapping of rhPTH via the protease digestion methods used, appears to have great potential for structural investigations of the peptide.

Human parathyroid hormone: efficient synthesis in Escherichia coli using a synthetic gene, purification and characterization

Human parathyroid hormone is a peptide hormone consisting of 84 amino acid residues. Production of small proteins by direct expression in Escherichia coli is often unsuccessful owing to susceptibility of the mRNA and/or the product to endogenous enzymes. In this study, direct expression of the hormone at an excellent level (over 100 mg/L) has been achieved by using a suitably designed synthetic gene under the control of the T7 promoter. The protein produced in bacteria was extracted and easily purified in a good yield of 27 mg/L. The purified product was physico-chemically identified as intact human parathyroid hormone from the results of amino acid analysis, N-terminal sequencing, and peptide mapping using fast atom bombardment mass spectrometry. In biological assays the purified product stimulated adenylate cyclase in vitro, promoted bone growth and increased the serum osteocalcin in rats to the same extent as the authentic hormone.

Induction of graft-versus-host disease as immunotherapy for relapsed chronic myeloid leukemia

BACKGROUND

The ability of allogeneic bone marrow transplantation to cure chronic myeloid leukemia (CML) is due to both the conditioning regimen and the antileukemic effects of the lymphocytes in the grafted marrow. We studied the ability of interferon alfa-2b and infusions of mononuclear cells from the marrow donor to induce a graft-versus-leukemia reaction in patients with CML in relapse after bone marrow transplantation.

METHODS

Eleven patients with relapsed CML after allogeneic bone marrow transplantation were treated with interferon alfa-2b and infusions of mononuclear cells. The patients were monitored for toxic effects, for hematologic and cytogenetic responses, and, with use of the polymerase chain reaction, for elimination of cells containing the bcr/abl messenger RNA transcript characteristic of the leukemic cells.

RESULTS

Six of the eight patients with stable CML after relapse had complete remissions according to molecular genetic criteria, since no cells with bcr/abl messenger RNA transcripts were detected (the method can identify 1 leukemic cell among 1 million normal cells). The three patients with accelerated CML after relapse did not enter remission. Myelosuppression was prominent in eight patients. Grade I acute graft-versus-host disease (GVHD) occurred in six patients, and grade III acute GVHD occurred in three. Limited chronic GVHD developed in five patients.

CONCLUSIONS

The induction of a graft-versus-leukemia reaction with interferon alfa-2b and infusions of donor mononuclear cells in patients with CML in relapse after bone marrow transplantation is an effective antileukemic therapy that may offer an alternative to a second marrow transplantation.

Factors related to the recurrent hyperfunction of autografts after total parathyroidectomy in patients with severe secondary hyperparathyroidism

Total parathyroidectomy with autotransplantation has been widely accepted as the appropriate treatment for patients with hyperparathyroidism due to chronic renal failure on long term hemodialysis. However, recurrence has been an enigma and therefore, the factors involved in the recurrence of hyperparathyroidism were studied in 128 patients followed for more than 2 years after surgical treatment. The preoperative serum parathyroid hormone (PTH) concentrations correlated with the total weights of the parathyroid glands. When the original autotransplanted glands were divided into two groups, being diffuse and nodular, the rate of recurrent hyperparathyroidism due to graft hyperfunction was significantly higher in the patients who received nodular glands (24%) than in those who received diffuse glands (8.4%) (P < 0.05). To investigate whether PTH synthetic activity is different in diffuse and nodular glands, the amount of PTH mRNA was studied by in situ hybridization. There was no significant difference in the amount of PTH mRNA in the cells from either diffuse or nodular glands. These data suggest that the recurrence of hyperparathyroidism is not due to enhanced PTH synthetic activity of autotransplant grafts but to the abnormal growth rate of the transplanted gland.

Genetic mosaicism in normal tissues of Wilms' tumour patients

We describe the partial loss of heterozygosity (LOH) at chromosome 11p loci in normal tissues (normal kidney and/or blood) from four of 67 Wilms' tumour patients. Autologous tumour DNA showed complete loss of the same, maternally derived, alleles. These observations indicate that the normal tissues were mosaic for cells heterozygous and homozygous for 11p markers and that tumours subsequently developed from the homozygous cells that had undergone an 11p somatic recombination event. We suggest that LOH for 11p alleles is compatible with normal growth and differentiation and is significant pathologically only when accompanied by other genetic alterations.

Structural elements of human parathyroid hormone and their possible relation to biological activities

Human parathyroid hormone (hPTH) and several deletion analogues were examined for the presence of secondary structure using circular dichroism spectroscopy. The spectra of hPTH and the deletion analogues 8-84, 34-53, 53-84, 1-34, 13-34, 1-19, and 20-34, in neutral, aqueous buffer, gave no evidence for extensive secondary structure. An alpha-helical-like spectral contribution was found to arise from a region within peptide 13-34. This spectral contribution was speculated to arise from partial stability of a helix consisting of residues 17-29. Molecular dynamics simulations of peptide 1-34 suggested that this peptide tends to fold with a bend defined by residues 10-14, with the amino-terminal and carboxyl-terminal residues tending to be in more extended forms and the other residues in helical-like conformations. The addition of trifluoroethanol promoted the formation of alpha-helix, mainly in the 1-34 region. The putative helix comprised of residues 17-29 was stabilized by the addition of 10-20% TFE, while a second putative helix proximal to the amino terminus, and comprised of residues 3-11, was stabilized by slightly higher concentrations of TFE. An amphiphilic sequence was identified within the 20-34 fragment. The development of alpha-helix on binding this fragment, and other analogues containing this sequence, to palmitoyloleoylphosphatidylserine vesicles provided experimental evidence for the potential role of this amphiphilic sequence in binding to membranes or to a membrane receptor. The relationships between these alpha-helical regions in 1-34, either potentiated by trifluoroethanol or lipid vesicles, are discussed in terms of different receptor-binding regions within hPTH.

Interaction of nascent preproparathyroid hormone molecules with microsomal membranes

To characterize the early steps in the interaction of nascent chains of preproparathyroid hormone (prepro-PTH) with the secretory apparatus, such truncated nascent chains still attached to ribosomes were tested for binding to microsomal membranes and cleavage by signal peptidase. Nascent chains of 114, 97, 88, 81, 70, and 59 residues were tested for their ability to bind tightly to membranes and to undergo signal sequence cleavage. Chains of 81 residues and longer bound tightly to the membranes and were cleaved by signal peptidase. The 88- and 81-residue precursors and their corresponding pro-proteins were less efficiently associated with the membranes than were the 114- and 97-residue precursors and their corresponding pro-proteins. The 70-residue chain bound to the membrane but was not cleaved. When this peptide was subsequently released from the ribosome with puromycin, it was cleaved by signal peptidase. The 59-residue chain bound only slightly to the microsomal membrane and was not cleaved by signal peptidase, even when the nascent peptide was released from the ribosome with puromycin. Thus the critical length for productive binding to microsomal membranes is between 59 and 70 residues; the length required for signal cleavage is between 70 and 81 residues.

The expression of parathyroid hormone messenger RNA in normal and abnormal parathyroid tissue

The distribution and expression of preproparathyroid hormone (PTH) mRNA were investigated in parathyroid tissue from 57 parathyroidectomy specimens. PTH mRNA was detected by in situ hybridization using digoxigenin-labelled oligonucleotide probes. Cell morphology was seen to correlate with PTH mRNA expression. Strong expression of PTH mRNA was confined to cells which on haematoxylin and eosin staining had large vesicular nuclei. These included both vacuolated and non-vacuolated cells. Chief cells with small dark nuclei and scanty cytoplasm had little or no expression. In both adenoma and chief cell hyperplasia, the striking difference from normal was the greatly increased proportion of cells expressing PTH mRNA. In adenomas, the rim of uninvolved parathyroid tissue showed PTH mRNA expression similar to that of normal parathyroid. In hyperplasia, there was frequently concordance of staining within individual nodules. The findings establish morphological criteria for activity of parathyroid tissue and support current concepts of the different pathogenesis of hyperplasia and adenoma. The expression of PTH mRNA in oxyphil change and parathyroid carcinoma was also investigated.

A human bronchial epithelial cell strain with unusual in vitro growth potential which undergoes neoplastic transformation after SV40 T antigen gene transfection

Bronchial epithelial cells were cultured from an individual with no evidence of malignant disease. These cells, designated HB56B, had a greatly extended in vitro life-span, being able to undergo 50 passages and 200 population doublings in contrast to the usual 3 to 4 passages and 20 to 30 population doublings characteristic of normal human bronchial epithelial cells. HB56B cells had karyotypic evidence of an amplified region on the short arm of chromosome II. Unlike normal bronchial epithelial cells, which undergo terminal squamous differentiation in vitro in response to fetal bovine serum, HB56B cells were only minimally affected by serum. These cells were readily established as an immortalized cell line, HB56B/5T, following transfection with a plasmid containing SV40 early region DNA. HB56B cells were non-tumorigenic in athymic nude mice, but HB56B/5T cells within a few passages of transfection with the SV40 plasmid formed tumors of which 28/37 regressed. HB56B cells may offer an experimental system for the study of proliferation, differentiation, and senescence control in human bronchial epithelial cells.

Chicken parathyroid hormone-related protein and its expression during embryologic development

A parathyroid hormone-related protein (PTHrP) is the probable cause of humoral hypercalcemia in malignancy, but its normal physiologic role remains unknown. Since current evidence suggests that PTHrP may have a role in embryonic development, we cloned a genomic fragment that encodes chicken PTHrP (cPTHrP) and studied the expression of PTHrP in developing chick embryos. Blot hybridization of chicken genomic DNA with a cPTHrP genomic DNA probe showed a single band, suggesting that a single-copy gene encodes cPTHrP. By screening a chicken genomic library with the human probe an open reading frame was identified that corresponds to the human PTHrP (hPTHrP) exon IV. Compared to the human sequence the 5' splice junction is highly conserved and the two predicted propeptide residues are identical. The sequence predicts a mature peptide of 139 amino acids; all of the first 21 and 94 of the first 112, but only 8 of the final 27 residues of cPTHrP are identical to the human sequence. The structural features required for PTH receptor binding and activation are highly conserved between chicken and hPTHrP. Poly(A)-enriched RNA from 3-15 day chicken embryos was surveyed by hybridization to the chicken probe. A hybridizing band of 1.45 kb was found in tissues derived from all three germ layers, including brain, heart, lung, liver, gizzard, intestine, chorioallantoic membrane, yolk sac, and skeletal muscle. An additional 1.2 kb hybridizing band was found in some tissues. The conservation of the PTHrP sequence between chicken and mammals supports the view that PTHrP has an important physiologic role.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonenzymatic deamidation of asparaginyl and glutaminyl residues in proteins

Some asparagine and glutamine residues in proteins undergo deamidation to aspartate and glutamate with rates that depend upon the sequence and higher-order structure of the protein. Functional groups within the protein can catalyze this reaction, acting as general acids, bases, or stabilizers of the transition state. Information from specific proteins that deamidate and analysis of protein sequence and structure data bases suggest that asparagine and glutamine lability has been a selective pressure in the evolution of protein sequence and folding. Asparagine and glutamine deamidation can affect protein structure and function in natural and engineered mutant sequences, and may play a role in the regulation of protein folding, protein breakdown, and aging.

Mutation of the signal peptide-encoding region of the preproparathyroid hormone gene in familial isolated hypoparathyroidism

Preproparathyroid hormone (preproPTH) gene mutation has been proposed as a cause of familial isolated hypoparathyroidism (FIH). We cloned the preproPTH alleles of a patient with autosomal dominant FIH and sequenced the coding regions, 5' flanking regions, and splice junctions. The putatively abnormal (based on previous linkage studies) allele differed from the other allele's normal sequence at only one nucleotide. This T to C point mutation changes the codon for position 18 of the 31 amino acid prepro sequence from cysteine to arginine, disrupting the hydrophobic core of the signal sequence. Because the hydrophobic core is required by secreted proteins for efficient translocation across the endoplasmic reticulum, the mutant protein is likely to be inefficiently processed. Indeed, in vitro studies demonstrated dramatically impaired processing of the mutant preproPTH to proPTH. In summary, we observed a point mutation in the signal peptide-encoding region of a preproPTH gene in one FIH kindred and demonstrated a functional defect caused by the mutation. Mutation of the signal sequence constitutes a novel pathophysiologic mechanism in man, and further study may yield important insights both into this form of hormone deficiency and into the role of signal sequences in human physiology.

Abnormal expression and structural modification of the insulin-like growth-factor-II gene in human colorectal tumors

The insulin-like growth factor II (IGF-II) is a small protein implicated in fetal growth and development. It may play a role in the neoplastic process. The IGF-II gene is located on the short arm of chromosome II near insulin and c-Ha-ras I genes. Three distinct promoters control the transcription of this gene, leading to different IGF-II mRNA species. We have analyzed 21 human colorectal tumors and found overexpression of IGF-II in 6 of them (30%). When compared with expression in normal adjacent tissues, IGF-II mRNA increase in these tumors was either moderate (2- to 15-fold) or very marked (200- to 800-fold). In situ hybridization experiments confirmed that high IGF-II mRNA amounts were localized in cancer cells of the tumors overexpressing the IGF-II gene. In addition, DNA analysis revealed a structural modification of one IGF-II locus in one tumor characterized by very high IGF-II mRNA.

Parathyroid hormone-related protein and hypercalcemia in pancreatic neuro-endocrine tumors

We investigated the possible involvement of parathyroid hormone-related protein (PTHrP) in 2 cases of metastatic pancreatic neuro-endocrine tumors associated with severe hypercalcemia. Both patients displayed biochemical alterations in renal tubular reabsorption of calcium and phosphate, as well as in urinary cAMP excretion, similar to those encountered in primary hyperparathyroidism, although plasma levels of parathyroid hormone were within the normal range. Tumor protein extracts stimulated cAMP production, which was inhibited by the PTH-antagonist (8,18 Nle, 34 Tyr)bPTH-(3-34)amide, in the PTH-responsive osteoblastic cell line UMR-106. Northern blot analysis of tumor extracts revealed the presence of PTHrP mRNA transcripts, while PTH mRNA was undetectable. In contrast, neither PTHrP mRNA(s) nor cAMP-stimulating activity was detectable in other neuroendocrine tumors not accompanied by hypercalcemia. These results demonstrate that certain pancreatic neuroendocrine tumors associated with hypercalcemia can synthesize and release PTHrP.

Dexamethasone increases preproparathyroid hormone messenger RNA in human hyperplastic parathyroid cells in vitro

To determine if parathyroid hormone release in man is directly stimulated by glucocorticoids, dispersed human parathyroid cells from hyperplastic glands obtained from eight renal transplant recipients were studied in vitro. Dexamethasone (10(-11) to 10(-6) mol l-1) increased PTH release in a time- and dose-dependent manner. A plateau was reached at 10(-8) mol l-1 (1015 +/- 149 vs. 230 +/- 27 pg 10(-4) cells for control value, after 24 h incubation; P less than 0.0001). An interaction with a glucocorticoid receptor was suggested since 10(-6) mol l-1 RU 486 blunted the dexamethasone-induced PTH release. By Northern blot analysis, dexamethasone was found to increase the amount of preproPTH mRNA in these cells. The effect of dexamethasone was probably at the gene level since (1) 1,25 dihydroxy vitamin D3 inhibited both iPTH and preproPTH mRNA increases induced by dexamethasone and (2) alpha-amanitin (1,25 micrograms ml-1) also completely suppressed the dexamethasone-induced PTH release. Thus, for the first time, we demonstrate that dexamethasone induces an increase of PTH synthesis, probably by increasing PTH gene transcription. This effect may play an important pathogenic role in persisting hyperparathyroidism and steroid-induced bone complications in renal transplant recipients.