A second plasma calcium-lowering peptide from the human calcitonin precursor

“Statistics” is not a Sausage Machine: A Statistician's Viewpoint and Some Comments on Experimental Design

Any experiment involving the use of animals which is not well-planned, meticulously carried out, and scrupulously analysed, is unethical. Planning, or good experimental design, followed by analysis appropriate for the design, will help to ensure the optimal use of animals. Thus, collaboration between biologist and statistician, especially at the planning and analysis stages, is one of the best ways of achieving an ethical and successful experiment. However, genuine communication is necessary for any collaboration, and this requires time and patience, on the part of both biologist and statistician. Although the three fundamental principles of experimental design, replication, randomisation and local control, are straightforward in theory, there is substantial scope for misunderstanding and misinterpretation in practice. Each experiment presents unique and interacting biological and statistical problems, and both the right design and the correct analysis should be decided on a case-by-case basis.

Expression of the calcitonin gene family in medullary thyroid carcinoma

The regulatory peptide calcitonin was discovered in 1962. During the last decade it has been demonstrated to be part of a gene family. Calcitonin is synthesized in the parafollicular cells (C cells) of the thyroid gland. These cells give rise to an endocrine tumor, medullary thyroid carcinoma (MTC), which is found in a sporadic and an inherited form. Calcitonin is used as a tumor marker for MTC. The calcitonin gene was demonstrated in 1981 to give rise to an alternative peptide product, alpha-CGRP, and a second gene encoding a very similar peptide, beta-CGRP, has also been identified. A third CGRP-like peptide, amylin, was identified in 1986. This article summarizes the present knowledge about gene structure, regulation of gene expression, and expression of the calcitonin gene family in MTC and in MTC-derived cell lines. The methods employed for detection of gene expression and for measurement and characterized of peptide products are described, and finally the relevance of biochemical tumor markers is discussed in relation to the new diagnostic methods for inherited MTC based on molecular biological techniques.

Calcitonin and PDN-21 as tumour markers in MEN-2 family screening for medullary thyroid carcinoma

Calcitonin is expressed in medullary thyroid carcinomas (MTC). It is processed from a large molecular weight precursor and is flanked at its C-terminal end by a 21 aminoacid peptide (PDN-21) formed in equimolar concentrations to calcitonin by enzymatic cleavage of the prohormone. This investigation compared basal measurements of calcitonin and PDN-21 and the response of the two peptides following pentagastrin stimulation in normal controls and in family members with C-cell hyperplasia or early neoplasia. The results showed that calcitonin and PDN-21 may both be used in family screening for the MEN-2 syndrome, but the unstimulated circulating concentrations of calcitonin were higher and more influenced by C-cell hypersecretion than PDN-21 (P less than 0.01), and the increase in stimulated concentrations of calcitonin were significantly higher than for PDN-21 (P less than 0.01). These findings may be explained by differences with respect to secretion and metabolic clearance rate for the two peptides.

Evaluation of sensitive PDN-21 (katacalcin) determination as tumor marker in medullary thyroid carcinoma

PDN-21 (katacalcin), a peptide from the calcitonin (CT) gene, was measured in plasma from healthy persons and patients with medullary thyroid carcinoma (MTC). PDN-21 was detectable (greater than or equal to 10 ng/l) in 73% of normal persons (n = 40). In 17 normal persons with undetectable basal plasma levels, PDN-21 became detectable (greater than or equal to 10 ng/l) by stimulation with iv pentagastrin in 7 cases. Basal levels were more often detectable in men than in women. In 65 patients with MTC, PDN-21 levels were highly correlated with CT levels as determined by an "in house" RIA (r = 0.99); the mean ratio of CT/PDN-21, on a molar base, was 0.96 +/- 0.33 over the entire range. In iv stimulation tests with pentagastrin, PDN-21 and CT showed good parallelism (mean ratio of CT/PDN-21: 1.1 +/- 0.62); in MTC patients with normal basal levels, however, peak to basal ratios during iv pentagastrin testing were higher for PDN-21 than for CT, due to the more sensitive PDN-21 assay. In a selective venous catheter study of a patient with MTC, the mean CT/PDN-21 ratio for all samples was 1.04 +/- 0.12, but the peak to peripheral levels were higher for PDN-21 (4.1-fold) than for CT (2.8-fold). In conclusion, determination of PDN-21 by RIA is equivalent to determination of CT in diagnosing MTC patients. In few patients, it might be even slightly more sensitive. PDN-21 should be determined in all cases with borderline CT results.

The procalcitonin amino-terminal cleavage peptide (N-proCT) lacks biological activity on normal clonal rat osteoblastic and preosteoblastic cells in vitro

The human-derived procalcitonin amino-terminal cleavage peptide, N-proCT has previously been shown to act mitogenically on isolated chicken and human osteoblast-like cells and on the human osteosarcoma cell line U-2 OS. We have examined the effect of N-proCT on growth and phenotype of cloned rat osteoblastic and preosteoblastic cells. Neither cell growth nor the phenotype (ALP, PTH response) of either cell type was significantly changed by the procalcitonin cleavage peptide.

Procalcitonin's amino-terminal cleavage peptide is a bone-cell mitogen

The parafollicular-cell (C-cell) hormone calcitonin (CT) can preserve or even augment skeletal mass by inhibiting osteoclast-mediated bone resorption. The possibility of an additional anabolic skeletal influence has also been raised: C cells might, via CT or other secretory products, affect osteoblast-mediated bone formation. The 57-residue amino-terminal procalcitonin cleavage peptide, N-proCT, has recently been identified in human and rat C cells, where it is made and secreted in equimolar amounts with CT. The coelaboration of N-proCT and CT and N-proCT's sequence conservation during evolution prompted us to investigate the potential skeletal bioactivity of N-proCT. We found that synthetic human N-proCT, at nanomolar concentrations, stimulated proliferation of normal and neoplastic human osteoblasts. At maximally effective doses, human N-proCT caused more than a 100% increase above the control rate of DNA synthesis, an effect comparable to the maximal growth effect of insulin, a potent mitogen for osteoblasts. Human N-proCT exerted a similar maximal mitogenic effect in chicken osteoblast cultures but at 1000-fold greater concentrations than in human bone-cell cultures. The bone-cell action of N-proCT was potentiated with insulin with a greater than 200% increase in DNA synthesis at high insulin concentrations. In sharp contrast to these findings for N-proCT, the other bioactive C-cell peptides, CT and somatostatin, showed no mitogenic effects in human or chicken osteoblast cultures. Our results indicate that the action of N-proCT on cultured bone cells is separate from and potentiated by insulin, a known growth factor. Unlike insulin and related growth factors such as insulin-like growth factor I, N-proCT is not mitogenic in skin fibroblast cultures. We propose that N-proCT is a C-cell hormone that promotes bone formation via stimulatory actions on osteoblasts and preosteoblasts.

Effects of calcitonin, katacalcin, and calcitonin gene-related peptide on basal and TSH-stimulated thyroid hormone secretion in the mouse

It is known that transcripts of the calcitonin gene in the thyroid C cells are processed to mRNAs generating precursors for the three peptides, calcitonin, katacalcin, and calcitonin gene-related peptide (CGRP), and that these peptides are produced and secreted from the C cells. The present study investigated the effects of these three peptides on basal and TSH-stimulated thyroid hormone secretion in the mouse, according to the McKenzie technique. Mice were pre-treated with 125I and thyroxine. Calcitonin (3 nmol animal-1) reduced the basal blood radioiodine levels to 72 +/- 5% compared to 95 +/- 6% in controls (P less than 0.01). This effect is likely to be renal, since calcitonin significantly increased the renal excretion of a concomitantly injected 125I load. In contrast, katacalcin and CGRP were without effect on basal blood radioiodine levels. All three peptides (1 or 3 nmol animal-1) were without effect on TSH (70 microU animal-1)-induced increase in blood radiodine levels. However, when the peptides were given together (either two and two concomitantly, or all three together), the TSH-induced increase in blood radioiodine levels was inhibited. This inhibition of TSH-induced thyroid hormone secretion might represent an intrathyroidal regulatory mechanism of the follicular cell activity.

Calcitonin gene-related peptide inhibits osteoclastic bone resorption: a comparative study

Besides the calcitonin (CT) precursor, the calcitonin gene also encodes another peptide--calcitonin gene-related peptide (CGRP). We have previously reported that CGRP lowers plasma calcium in the rat. In the present study we have evaluated the effect of CGRP on resorption of bone by isolated rat osteoclasts and have compared these effects to those produced by calcitonins from three species (salmon, pig, and human calcitonins). There was a significant inhibition of bone resorption with rat calcitonin gene-related peptide (rCGRP) at a 1000-fold higher dose than that used for human CT. This effect well explains the CT-like effect of CGRP seen in the in vivo rat CT bioassay. Our results suggest that though CGRP may not be involved in the hormonal control of plasma calcium, the peptide may be an important local regulator of bone cell function.

[Katacalcin--a new tumor marker in C-cell cancer of the thyroid gland]

Katacalcin (KC) is situated on the C-terminal side of the procalcitonin molecule and is cleaved like calcitonin (CT) from this precursor peptide. Serum levels of KC were measured in 22 patients with C-cell carcinoma with a specific and sensitive radioimmunoassay (normal range, less than 0.1-0.15 ng/ml). Basal serum KC values in C-cell carcinoma patients were 0.32-290 ng/ml. There was a good correlation between KC and CT (r = 0.98, P less than 0.001). Serum KC, as well as CT, markedly increased after pentagastrin and calcium infusion. KC and CT were secreted in nearly equimolar amounts. During selective venous catheterization, KC and CT levels were increased in serum samples from veins draining tumor masses, which could be confirmed operatively. During the follow up, KC and CT measurements correlated well to the stage of disease. KC could be immunohistologically localized in C-cell carcinoma tissue. As a tumor marker, katacalcin is likely to be as useful as calcitonin in C-cell carcinoma.

Large forms of immunoreactive calcitonin in human seminal fluid exhibit PDN-21 immunoreactivity

Semen samples were obtained from 4 healthy males on two occasions. One of the samples was liquefied at room temperature for 20 min while the other was diluted immediately with buffer to suppress proteolysis. A pool of immunoextracted calcitonin from liquefied and diluted samples, respectively, was subjected to gel chromatography in a separate experiment. In lyophilized samples the majority of immunoreactive calcitonin (CT) had an approximate molecular weight (Mr) of 10 kilodaltons (Kd) and immunoreactive PDN-21 was also present in the fractions. In diluted ejaculates CT was composed of larger species as well as the 10 Kd form. PDN-21 was present in fractions containing the 10 Kd form but could not be detected in the peaks of larger molecular weight, probably because of lower sensitivity of the PDN-21 assay compared to the CT assay. Our finding of CT and PDN-21 in the same fractions after immunoextraction with CT antibodies suggests the presence of proforms of CT in human seminal fluid.

Binding of calcitonin and calcitonin gene-related peptide to calvarial cells and renal cortical membranes

Binding of calcitonin (CT) and calcitonin gene-related peptide (CGRP) to rat hemicalvariae and renal membranes was examined in an effort to determine whether CT and CGRP interact with the same bone cell binding site, and to see whether the binding pattern was similar for bone and renal cortex. Specific binding of 125I-salmon CT to rat calvariae was inhibited by unlabeled salmon, porcine, or human CT, but not by rat CGRP. Binding of 125I-rat CGRP to calvariae was inhibited by CGRP and high doses of salmon CT, but not by human or porcine CT. Binding of 125I-salmon CT to renal membranes was inhibited by unlabeled salmon CT or rat CGRP, but no specific binding of 125I-rat CGRP could be detected. The results suggest that separate bone cell receptors for CT and CGRP exist and that CGRP can interact with renal receptors for CT.

Medullary carcinoma of the thyroid. An immunocytochemical and histochemical study of 25 cases using eight separate markers

The current study was undertaken on 25 cases of thyroid medullary carcinoma to compare the diagnostic value of calcitonin with other peptides including PDN-21, the C-terminal flanking peptide of human calcitonin within the calcitonin precursor, and calcitonin gene-related peptide, CGRP. Antiserum raised to chromogranin, an acidic protein of 68,000 daltons, was also used to compare its diagnostic value as a general marker for neuroendocrine neoplasia with neuron-specific enolase (NSE) and Grimelius' argyrophil silver staining. Immunocytochemistry was performed using the peroxidase-antiperoxidase method at the light microscopic level and the immunogold staining procedure at the ultrastructural level. All tumors were reactive to calcitonin and CGRP antisera, whereas PDN-21 was present in 23 cases. It was also found that these peptides were colocalized in the majority of C-cells. The intensity and specificity of CGRP and PDN-21 immunoreaction was comparable to and in some cases even better than that obtained with calcitonin antiserum. In the majority of tumors, somatostatin and bombesin immunoreactivity was either absent, weak, or variable in intensity and distribution. The current study thus demonstrates that together with calcitonin, PDN and, in particular, CGRP antisera may be applied to corroborate immunocytochemical diagnosis in medullary carcinoma of the thyroid. With regard to general neuroendocrine markers, Grimelius' and chromogranin provided the most consistent results. NSE isoenzyme immunoreactivity, on the other hand, was more variable, probably reflecting the metabolic state of the tumor cells.

Calcitonin gene-related peptide: detailed immunohistochemical distribution in the central nervous system

With the use of an antiserum generated in rabbits against synthetic human calcitonin gene-related peptide (CGRP) the distribution of CGRP-like immunoreactive cell bodies and nerve fibers was studied in the rat central nervous system. A detailed stereotaxic atlas of CGRP-like neurons was prepared. CGRP-like immunoreactivity was widely distributed in the rat central nervous system. CGRP positive cell bodies were observed in the preoptic area and hypothalamus (medial preoptic, periventricular, anterior hypothalamic nuclei, perifornical area, medial forebrain bundle), premamillary nucleus, amygdala medialis, hippocampus and dentate gyrus, central gray and the ventromedial nucleus of the thalamus. In the midbrain a large cluster of cells was contained in the peripeduncular area ventral to the medial geniculate body. In the hindbrain cholinergic motor nuclei (III, IV, V, VI, VII XII) contained CGRP-immunoreactivity. Cell bodies were also observed in the ventral tegmental nucleus, the parabrachial nuclei, superior olive and nucleus ambiguus. The ventral horn cells of the spinal cord, the trigeminal and dorsal root ganglia also contained CGRP-immunoreactivity. Dense accumulations of fibers were observed in the amydala centralis, caudal portion of the caudate putamen, sensory trigeminal area, substantia gelatinosa, dorsal horn of the spinal cord (laminae I and II). Other areas containing CGRP-immunoreactive fibers are the septal area, nucleus of the stria terminalis, preoptic and hypothalamic nuclei (e.g., medial preoptic, periventricular, dorsomedial, median eminence), medial forebrain bundle, central gray, medial geniculate body, peripeduncular area, interpeduncular nucleus, cochlear nucleus, parabrachial nuclei, superior olive, nucleus tractus solitarii, and in the confines of clusters of cell bodies. Some fibers were also noted in the anterior and posterior pituitary and the sensory ganglia. As with other newly described brain neuropeptides it can only be conjectured that CGRP has a neuroregulatory action on a variety of functions throughout the brain and spinal cord.

Novel peptides from the calcitonin gene: expression, receptors and biological function

Calcitonin gene products include calcitonin and its carboxyl-terminal flanking peptide (in man PDN-21), and calcitonin gene-related peptide (CGRP). Alternative splicing of the initial gene transcripts results in the production of two distinct messenger RNA encoding precursors of CGRP and of calcitonin. CGRP messenger RNA is the predominant transcription product of the calcitonin gene in neural tissues, but it is also present in the pituitary and the C-cells of normal thyroid glands and in medullary thyroid carcinoma. Immunoreactive CGRP has, moreover, been recognized around blood vessels of the heart. Calcitonin and PDN-21 are cosecreted from thyroid C-cells, but they are also found in the brain and pituitary. CGRP receptors are present in the brain and the heart, and calcitonin receptors in bone and kidney cells and in the hypothalamus. Calcitonin administered peripherally and in vitro inhibits bone resorption and stimulates renal 1.25-dihydroxycholecalciferol production. CGRP used in the same manner has potent cardiovascular effects (vasodilation, hypotension, positive chronotropic and inotropic action in the heart). Intracerebroventricular administration of CGRP raises the blood pressure, and both CGRP and calcitonin inhibit gastric acid secretion and food intake. The distinct but overlapping effects of calcitonin and CGRP raise important regulatory and functional issues.

Amino terminal fragments of human progastrin from gastrinoma

Two peptides which copurified from a human gastrinoma were found to correspond to the amino acid sequence deduced for the amino terminal portion of human and porcine progastrin. The sequence of peptide A is Ser-Trp-Lys-Pro-Arg-Ser-Gln-Gln-Pro-Asp-Ala-Pro-Leu-Gly-Thr-Gly-Ala-Asn- Arg-Asp-Leu-Glu-Leu which is identical to an amino terminal portion of human progastrin. The sequence of peptide. B is identical to that of peptide A except it is missing the first five amino acids. If peptide A corresponds to the amino terminus of progastrin, the signal peptidase cleaves at an Ala-Ser bond.

Neuropeptides derived from prosomatostatin that do not contain the somatostatin-14 sequence

Two neuropeptides reacting with antibodies directed against the C-terminal region of somatostatin 28(1-12) were purified to homogeneity from rat brain extracts. Amino acid analysis revealed that the larger peptide (8 kdaltons) consisted of 76 amino acids. Microsequencing established its aminoterminal structure as: Ala-Pro-Ser-Asp-Pro-Arg-Leu-Arg-Gln-Phe-X-Gln-Lys. The 8 kdalton somatostatin 28(1-12)-like peptide corresponds to the whole prosomatostatin molecule without Arg-Lys-somatostatin-14. The smaller peptide (5 kdaltons) consists of 44 amino acids and is generated after cleavage of a Leu-Leu bond at position 56-57 of pre-prosomatostatin. Both 8 kdalton and 5 kdalton somatostatin 28(1-12)-like peptides contain somatostatin 28(1-12) at their C-termini. The 4 most abundant neuropeptides derived from pre-prosomatostatin (pre-proSS) and presently characterized are: somatostatin-14, somatostatin 28(1-12), somatostatin 28 and pre-proSS25-100.

Localization of the polymorphic human calcitonin gene on chromosome 11

A molecular probe containing a 584 base pairs sequence corresponding to part of the human calcitonin mRNA was used for the chromosomal assignment of the calcitonin gene. Restriction endonuclease analysis of DNA from human-Chinese hamster and human-mouse somatic cell hybrids, including some containing a translocation of human chromosomes, placed the calcitonin gene in the p14----qter region of chromosome 11. Analysis of human DNA showed that the calcitonin gene has a polymorphic site for restriction endonuclease TaqI.

The complete sequence of human preprocalcitonin

DNA complementary to mRNA extracted from the thyroid glands of patients suffering from medullary carcinoma of the thyroid (MCT), a calcitonin-producing tumour, was inserted in the Pst site of pBR 322 by G-C tailing. The recombinant plasmids were used to transform Escherichia coli DP 50. Ampicillin-resistant clones were screened using a 32P-labelled cDNA to mRNA extracted from a case of MCT particularly rich in calcitonin (CT) mRNA. Positive clones were subsequently rescreened using a 32P poly(T) probe. Eighty clones were thus purified, and the inserts obtained by digestion with PstI were subjected to positive hybridization selection with subsequent translation in vitro. An insert stimulating synthesis of the protein and containing restriction sites compatible with the previously published complete sequence of calcitonin mRNA from rat was sequenced. This cDNA insert contained the entire coding region of 426 bp, 70 bp at the 5'-end, and 295 bp upstream from the poly(A) tail. The complete amino acid sequence of human preprocalcitonin could thus be deduced.

Salmon and human calcitonin-like peptides in man

Calcitonin-like peptides have been identified in the serum of normal subjects and of medullary thyroid carcinoma (MTC) patients. Using specific homologous radioimmunoassays (RIA) in combination with reversed-phase high performance liquid chromatography and gel permeation chromatography under denaturing conditions, we have recognized major components which coeluted with human calcitonin-(1-32), PDN-21, a carboxyl-terminal flanking peptide derived from the calcitonin mRNA sequence, and salmon calcitonin-(1-32). An additional 12000 molecular weight peak possibly represents a human calcitonin-PDN-21 polyprotein. In both the human calcitonin-(1-32) (normal value less than 0.043 ngEq/ml; MTC 140 +/- 80 ngEq/ml, mean value +/- SEM) and the PDN-21 (normal value less than 0.050 ngEq/ml; MTC 33.6 +/- 16.5 ngEq/ml) RIAs, serum levels were increased in MTC patients. Circulating levels of the salmon calcitonin-like peptide were indistinguishable between normal subjects (0.038 +/- 0.006 ngEq/ml) and MTC patients (0.037 +/- 0.011 ngEq/ml).

Sequence of cDNA encoding human insulin-like growth factor I precursor

Somatomedins (SM) or insulin-like growth factors (IGF) constitute a heterogeneous group of peptides with important growth-promoting effects in vitro as well as in vivo. Amino acid sequences have been determined for only two of them, IGF-I and IGF-II, which are highly homologous. IGF-I, which is identical with SM-C, is composed of 70 amino acid residues and IGF-II contains 73 amino acids and may be identical with SM-A. Other peptides with different charge properties but with similar SM-like or insulin-like behaviour in biological and receptor assays, have been described but have not yet been fully characterized. The liver is known to be a major site of production of these peptides, but many other tissues--especially in the fetus--may synthesize them as well. We report here the nucleotide sequence of a human liver cDNA encoding the complete amino acid sequence of IGF-I. The IGF-I coding region is flanked by sequences encoding an amino-terminal peptide of at least 25 amino acid residues and a carboxyl-terminal peptide of 35 amino acids. This provides evidence that IGF-I is synthesized as a precursor protein and that formation of IGF-I from this precursor requires proteolytic processing at both ends.

Katacalcin: a new plasma calcium-lowering hormone

A second potent plasma calcium-lowering peptide, katacalcin (PDN-21), flanks calcitonin within the human calcitonin precursor. Plasma katacalcin was present in 57 healthy volunteers. Concentrations were higher in males than in females and approximately equimolar with calcitonin. Plasma katacalcin doubled within 5 min of calcium infusion. Plasma katacalcin was markedly raised in 20 patients with medullary carcinoma of the thyroid. Measurement of plasma katacalcin concentrations may prove useful in the diagnosis and follow-up of this condition. Katacalcin, like calcitonin, may be involved in both plasma calcium regulation and skeletal maintenance and thus may prove useful in the treatment of bone disease.