Calcitonin COOH-terminal cleavage peptide as a model for identification of novel neuropeptides predicted by recombinant DNA analysis

Effects of streptozotocin-induced diabetes on taste buds in rat vallate papillae

Some studies have documented taste changes in patients with diabetes mellitus (DM). In order to understand the relationships between taste disorders caused by DM and the innervation and morphologic changes in the taste buds, we studied the vallate papillae and their taste buds in rats with DM. DM was induced in these rats with streptozotocin (STZ), which causes the death of beta cells of the pancreas. The rats were sacrificed and the vallate papillae were dissected for morphometric and quantitative immunohistochemical analyses. The innervations of the vallate papillae and taste buds in diabetic and control rats were detected using immunohistochemistry employing antibodies directed against protein gene product 9.5 (PGP 9.5) and calcitonin gene-related peptide (CGRP). The results showed that PGP 9.5- and CGRP-immunoreactive nerve fibers in the trench wall of diabetic vallate papillae, as well as taste cells in the taste buds, gradually decreased both intragemmally and intergemmally. The morphometry revealed no significant difference in papilla size between the control and diabetic groups, but there were fewer taste buds per papilla (per animal). The quantification of innervation in taste buds of the diabetic rats supported the visual assessment of immunohistochemical labeling, that the innervation of taste cells was significantly reduced in diabetic animals. These findings suggest that taste impairment in diabetic subjects may be caused by neuropathy defects and/or morphological changes in the taste buds.

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.

Expression in brain of a messenger RNA encoding a novel neuropeptide homologous to calcitonin gene-related peptide

As a consequence of alternative RNA processing events, a single rat gene can generate messenger RNA's (mRNA's) encoding either calcitonin or a neuropeptide referred to as alpha-type calcitonin gene-related peptide (alpha-CGRP). An mRNA product of a related gene has been identified in rat brain and thyroid encoding the protein precursor of a peptide differing from alpha-CGRP by only a single amino acid. The RNA encoding this peptide, which is referred to as beta-CGRP, appears to be the only mature transcript of the beta-CGRP gene. Hybridization histochemistry reveals a similar distribution of alpha- and beta-CGRP mRNA's, but their relative levels of expression vary in different cranial nerve nuclei. Thus beta-CGRP is a new member of a family of related genes with potential functions in regulating the transduction of sensory and motor information.

Calcitonin is a substrate for oligosaccharyltransferase in vitro

Tumor-derived, large molecular weight forms of calcitonin, have been postulated to result from glycosylation of the hormone. To address this question we have examined the glycosylation of calcitonin in vitro and in cultured thyroidal C-cells. We show that native, undenatured calcitonin is an active substrate for oligosaccharyltransferase and that glycosylation of calcitonin by the transferase is inhibited by tunicamycin. In addition, calcitonin is an effective competitive inhibitor of the glycosylation of a known peptide substrate for oligosaccharyltransferase. Pulse-labelling of cultured medullary thyroid carcinoma cells with [3H]-mannose indicate that detectable quantities of carbohydrate-containing forms of calcitonin are produced in these cells. These data indicate that glycosylation of calcitonin is one mechanism whereby tumor cells could produce higher molecular weight forms of the hormone.

Interaction of calcitonin and calcitonin gene-related peptide at receptor sites in target tissues

Discrete receptor sites for calcitonin (CT) and calcitonin gene-related peptide (CGRP) were found in the nervous system and in peripheral tissues. Each peptide was capable of cross-reacting with the specific receptor of the other. In contrast to CT receptors, CGRP receptors were not linked to adenylate cyclase. However, CGRP could stimulate adenylate cyclase in CT target tissues apparently by interacting with CT receptors. The relative abilities of CGRP and mammalian CT to inhibit CT binding suggest that CGRP could serve as an endogenous ligand for CT receptors in the central nervous system.

Alternative RNA processing: determining neuronal phenotype

On the basis of an analysis of the human and rat calcitonin genes and of a related gene, alternative RNA processing represents a developmental strategy of the brain to dictate tissue-specific patterns of polypeptide synthesis. This regulation allows the calcitonin gene to generate two messenger RNA's, one encoding the precursor of a novel neuropeptide, referred to as CGRP, which predominates in the brain, and the second encoding the precursor to the hormone calcitonin which predominates in thyroid C cells. The distribution of CGRP in the central and peripheral nervous system and in endocrine and other organ systems suggests potential functions in nociception, ingestive behavior, cardiovascular homeostasis, and mineral metabolism.

Multiple endocrine neoplasia syndromes

The multiple endocrine neoplasia (MEN) syndromes are characterized by autosomal dominant inheritance with a high degree of penetrance but varying expression. This review gives a classification of these syndromes and a short summary of the historical background. The pathogenesis of the disease and its possible origin in the APUD cell system are discussed together with the mechanisms underlying normal and ectopic hormone production by MEN tumors on the basis of recent findings in molecular endocrinology. The natural history and the clinical manifestations of the different syndromes are described. The sensitivity and discriminative capacity of the tests used to detect the syndromes in an early stage are compared. The choice of therapy and criteria for the timing and extensiveness of treatment are also considered. Lastly, problems associated with the ethical and legal aspects of screening, central registration, and monitoring of relatives at risk are described.

Production of a novel neuropeptide encoded by the calcitonin gene via tissue-specific RNA processing

Alternative processing of the RNA transcribed from the calcitonin gene appears to result in the production of a messenger RNA in neural tissue distinct from that in thyroidal 'C' cells. The thyroid mRNA encodes a precursor to the hormone calcitonin whereas that in neural tissues generates a novel neuropeptide, referred to as calcitonin gene-related peptide (CGRP). The distribution of CGRP-producing cells and pathways in the brain and other tissues suggests functions for the peptide in nociception, ingestive behaviour and modulation of the autonomic and endocrine systems. The approach described here permits the application of recombinant DNA technology to analyses of complex neurobiological systems in the absence of prior structural or biological information.

Tapping the immunological repertoire to produce antibodies of predetermined specificity

We understand the structure of antibodies in detail, but know little about the molecular basis of the immunogenicity of proteins. Recent experiments have shown that chemically synthesized peptides representative of virtually any part of the surface of a protein can elicit antibodies reactive with the native molecule. Such peptides can serve as synthetic vaccines, and antibodies, useful in the study of changes in protein structure, can be generated. As these antibodies react with regions of the protein known in advance to the experimenter, they can be said to be of predetermined specificity.

Alternative RNA processing in calcitonin gene expression generates mRNAs encoding different polypeptide products

Alternative processing of RNA transcripts from the calcitonin gene results in the production of distinct mRNAs encoding the hormone calcitonin or a predicted product referred to as calcitonin gene-related peptide (CGRP). The calcitonin mRNA predominates in the thyroid while the CGRP-specific mRNA appears to predominate in the hypothalamus. These observations lead us to propose a model in which developmental regulation of RNA processing is used to increase the diversity of neuroendocrine gene expression.

RNA processing regulation of neuroendorcrine gene expression

Alternative RNA processing events account for biological polymorphism in the endocrine, immune, and other systems; these may have possible widespread significance in the regulation of eukaryotic gene expression. The selective use of alternative hormone-encoding exons can produce multiple mRNAs generating different protein products. The resultant "peptide switching" is a previously unrecognized mechanism allowing a single gene to encode different hormones in different tissues and thus increases the diversity of endocrine gene expression.