Salmon and human calcitonin-like peptides in man

A synthetic peptide derived from mouse pituitary calcitonin cDNA sequence exhibits potent inhibition of prolactin secretion and prolactin mRNA abundance in primary mouse pituitary cells

We have shown that gonadotrophs synthesize and secrete immunoreactive calcitonin (CT)-like peptide, and CT is a potent inhibitor of prolactin (PRL) secretion and gene transcription. CT cDNA cloned from LssT2 cells (pit-CT cDNA) exhibits 99% homology with mouse CT cDNA sequence, but exhibits four mismatches in the coding region of CT peptide (347-485 bp) with consequent changes in the amino acids at positions 5 and 17 of mouse CT. We have synthesized a putative 23 amino acid pit-CT peptide based on pit-CT cDNA sequence, and tested its effect on PRL secretion and mRNA abundance in primary mouse pituitary cells. The results suggest that synthetic pit-CT attenuates PRL mRNA abundance and inhibits PRL release from mouse anterior pituitary cells. Moreover, pit-CT is remarkably more potent than salmon (S)CT in attenuating PRL mRNA abundance. These results raise a possibility that this endogenous pituitary peptide may potentially serve as a therapeutic molecule for the treatment of prolactinomas.

Calcitonin Increases Tumorigenicity of Prostate Cancer Cells: Evidence for the Role of Protein Kinase A and Urokinase-Type Plasminogen Receptor

The expression of human (h) calcitonin (CT) and its receptor (CTR) is localized to basal epithelium in benign prostates but is distributed in whole epithelium of malignant prostates. Moreover, the abundance of hCT and CTR mRNA in primary prostate tumors positively correlates with the tumor grade. We tested the hypothesis that the modulation of endogenous hCT expression of prostate cancer (PC) cell lines alters their oncogenicity. The effect of modulation of hCT expression on oncogenic characteristics was examined in LNCaP and PC-3M cell lines. The endogenous hCT expression was modulated using either constitutively active expression vector containing hCT cDNA or anti-hCT hammerhead ribozymes. The changes in the oncogenicity of cell sublines was assessed with cell proliferation assays, invasion assays, colony formation assays, and in vivo growth in athymic nude mice. Up-regulation of hCT in PC-3M cells and or enforced hCT expression in LNCaP cells dramatically enhanced their oncogenic characteristics. In contrast, the down-regulation of hCT in PC-3M cells led to a dramatic decline in their oncogenicity. These results, when combined with our other results, that the expression of hCT in primary PCs increase with tumor grade, suggest an important role for hCT in the progression of PC to a metastatic phenotype.

Heterogeneity of circulating calcitonin levels: relations with calcitonin biosynthesis in medullary thyroid carcinomas

Calcitonin (CT), a hypocalcemic and hypophosphatemic hormone, is produced by the C-cells of the thyroid gland. It is the main tumoral marker of medullary thyroid carcinoma (MTC). Hypersecretion of CT is also associated with other types of tumors. Thus, heterogeneity of circulating CT can play an important role in the accurate determination of hormone levels in blood samples obtained from MTC patients. Further studies will be necessary to establish the predictive value of the several peptides coded by the calcitonin gene family. All of them specifically reflect the ways and the pattern of alternative splicing of the primary transcript of the Calc I gene. Such relations implicate further investigations concerning the relationship between calcitonin circulating levels, biosynthetic activity of C-cells and the expression of gene encoding for this hormone, in normal and neoplastic conditions.

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.

Presence of calcitonin-like immunoreactivity (iCT) in human prostate gland: evidence for iCT secretion by cultured prostate cells

Immunoreactive calcitonin (iCT) has been detected in human prostate tissue extracts as well as seminal plasma. The present studies were undertaken to examine whether iSCT (immunoreactive salmon CT-like human peptide) co-exists with iHCT (thyroid CT-like substance) in human prostate tissue extracts, and whether these substances are secreted by primary prostate cells in culture. Since the local secretion of these substances seems to increase in some neoplasms, a second objective of the study was to examine whether basal secretion of iCTs from primary prostate cells is increased in carcinoma. The present results have shown that both iHCT and iSCT were present in prostate tissue extracts. The mean iHCT levels in extracts of benign hyperplastic prostates (BPH) were 0.59 ng/g prostate, and these were significantly lower than iHCT concentrations in prostatic carcinoma (PC) (2.53 ng/g). No significant differences in their iSCT contents were observed. However, the results from culture of over 90 individual prostate tissue specimens from BPH or PC indicate that primary prostate cells secreted detectable quantities of iSCT and the basal release of this material from PC prostate cultures was almost four-fold higher than that from BPH prostate cultures. These results suggest that a CT-like immunoreactive material is secreted by primary prostate cells in culture, and the basal secretion of this material is significantly higher in PC cells as compared to BPH cells. Endogenous secretion of prostatic CT, and the elevation of its expression in PC suggest that it may serve as a regulatory factor in the pathophysiology of the prostate gland.

Diagnostic relevance of the amino-terminal cleavage peptide of procalcitonin (PAS-57), calcitonin and calcitonin gene-related peptide in medullary thyroid carcinoma patients

We have identified the amino-terminal cleavage peptide of procalcitonin (PAS-57) in the plasma of normal human subjects and of medullary thyroid carcinoma (MTC) patients together with calcitonin (CT) and CT gene-related peptide (CGRP). Major components on reversed-phase high-pressure liquid chromatography had the retention times of synthetic PAS-57, CT and CGRP as well as of precursor proteins. Plasma levels of PAS-57 (290 +/- 50 pgeq/ml; mean +/- S.E.M.), CT (27 +/- 8 pgeq/ml) and CGRP (8.4 +/- 0.8 pgeq/ml) were respectively 2.3-, 1.6- and 1.5-fold higher in normal men (n = 10) than in women (n = 8). In response to 1 min intravenous calcium infusions (2 mg per kilogram body weight) PAS-57 and CT were increased 3.5- and 2.7-fold (P less than 0.001), respectively, but CGRP remained unchanged. In MTC patients (n = 57) with raised levels of PAS-57 and CT, the molar ratio between PAS-57 and CT was 1.7-times higher than in normal subjects (P less than 0.01). We have found that PAS-57 is a predominant CT/CGRP gene derived product in the circulation of normal subjects and of MTC patients and a potential new MTC tumor marker.

Is helodermin-like immunoreactivity in human thyroid C cells due to a salmon calcitonin-like substance?

Helodermin-like and salmon calcitonin (sCT)-like immunoreactivities co-existed in a subset of human calcitonin (hCT)-containing cells in normal human thyroid tissue and medullary thyroid carcinomas. Helodermin/sCT-immunoreactive cells were mostly different from calcitonin gene-related peptide (CGRP)-positive cells. Helodermin and sCT immunoreactivities were not identified in pulmonary and pancreatic hCT-positive neuroendocrine tumors, except for a few lung tumor cells showing positive staining with one of two sCT antisera used. Helodermin immunoreactivity demonstrated by rabbit antiserum R0086 was completely abolished in the presence of synthetic sCT, while sCT immunoreactivity was not absorbed by synthetic helodermin. The carboxyl terminal Arg30-Thr31 sequence (and Pro35 amide structure) of helodermin would be the epitopic site recognized by this antiserum, since a similar amino acid sequence is present in sCT molecules but absent from hCT and CGRP.

A third human CALC (pseudo)gene on chromosome 11

A genomic locus in man (CALC-III) containing nucleotide sequences highly homologous to both exon 2 and exon 3 of the CALC-I and -II genes, is described in this paper. The CALC-I gene produces calcitonin (CT) (encoded by exon 4) or calcitonin gene-related peptide (CGRP) (encoded by exon 5) in a tissue-specific fashion. The CALC-II gene produces a second human CGRP, but probably not a second CT. The CALC-III gene does not seem to encode a CT- or CGRP-related polypeptide hormone and is probably a pseudogene. Like the other two CALC genes, the CALC-III gene is located on human chromosome 11.

The structure of procalcitonin of the salmon as deduced from its cDNA sequence

Oligonucleotide probes based on the known amino acid sequence of salmon calcitonin were used to screen a cDNA library obtained from ultimobranchial glands of salmon for clones encoding salmon calcitonin. From the cDNA sequence of strongly hybridizing clones the complete primary structure of the calcitonin precursor could be deduced. Its overall structure is identical with the structures of procalcitonins from other vertebrates and has the highest homology with the chicken precursor.

The calcitonin-like sequence of the beta CGRP gene

We have identified a region within the beta CGRP gene which has the potential to encode a novel calcitonin-like peptide. The gene is located on the short arm of chromosome 11 (11p 12-14.2) and we suggest that it resulted from a local duplication of the alpha gene. We have been unable to detect the corresponding mRNA in a variety of tissues which express alpha-calcitonin. It is not clear whether this sequence can be expressed in man.

Conformational and biological properties of partial sequences of salmon calcitonin

According to the Chou-Fasman rules for predicting the secondary structures of proteins, the 12-20 portion of salmon calcitonin should adopt an alpha helical conformation. These residues would form an amphipathic helix and contribute to the solubilization of certain phospholipids by the peptide. Circular dichroism was used to assess the extent that peptide segments of salmon calcitonin fold into structures of higher helical content in the presence of dimyristoylphosphatidylglycerol, lysolecithin or sodium dodecyl sulfate. All of the segments studied are carboxyl terminal amides as is the native, intact, salmon calcitonin. Salmon calcitonin segments 11-23 or 12-23 form no more helical structure in the presence of lipids or detergents than does a segment comprising the hydrophilic carboxyl terminal residues 22-32 which is not predicted to adopt a helical conformation. Even a larger segment containing residues 12-32 does not exhibit a great increase in helical content in the presence of lipids or detergents, and it causes only a small broadening of the phase transition of dimyristoylphosphatidylglycerol. In contrast, a preparation with an equivalent molar ratio of dimyristoylphosphatidylglycerol to the salmon calcitonin segment 1-23 exhibits a very marked broadening of the phase transition, similar to what is found with the 32 amino acid native hormone. This amino terminal segment also adopts a conformation of higher helical content than even the intact hormone. This 1-23 segment is the only one studied that showed significant interaction with lipids, and it is also the only one which exhibited any hypocalcemic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

A second human calcitonin/CGRP gene

The calcitonin (CT) gene is alternatively expressed in a tissue-specific fashion producing either the calcium regulatory hormone CT in the thyroid or the neuropeptide calcitonin gene related peptide (CGRP) in the brain. In medullary carcinoma of the thyroid both peptides are produced. We present here evidence for the existence in the human genome of a second CT gene, which is also expressed in human medullary thyroid carcinoma. This gene encodes a second human CGRP, differing from the known human CGRP in 3 of the 37 amino acids.

Salmon calcitonin inhibits human sperm motility in vitro

We have evaluated by a stroboscopic technique the in vitro effect of salmon calcitonin and human calcitonin on the motility of human migrated spermatozoa. We report here that human calcitonin is uneffective while salmon calcitonin is a potent inhibitor of the sperm motility. This salmon calcitonin action is abolished by the preincubation of the peptide with an anti-salmon calcitonin antiserum, demonstrating the specificity of the effect. In addition, we provide evidence that the release of intracellular calcium represents a necessary step for the action of the peptide. In fact, the salmon calcitonin effect is prevented in a dose-dependent way by dantrolene sodium which inhibits the release of calcium from intracellular stores while the calcium channel blocker verapamil is unefficacious. These results suggest a potential role for calcitonin in regulating human sperm motility.