Calcitonin Messenger RNA Encodes Multiple Polypeptides in a Single Precursor

Abstract

Recombinant DNA techniques were used to analyze the structure of the messenger RNA encoding a precursor of calcitonin, a small calcium-regulating hormone of 32 amino acids. Analyses of the nucleotide sequences of cloned complementary DNA's comprising the entire coding sequence of the messenger RNA revealed that calcitonin is flanked at both its amino and carboxyl termini by peptide extensions linked to the hormone by short sequences of basic amino acids. The location of glycine next to the carboxyl terminal prolinamide of calcitonin is consistent with indications that glycine is required for the enzymatic amidation of proline to the prolinamide. During cellular biosynthesis, calcitonin arises from a large precursor protein by cleavages at both amino and carboxyl terminal residues of the hormone. These findings raise questions concerning the regulation of these cleavages and the potential biological functions of the precursor extensions derived from these cleavages.

Calcitonin/calcitonin gene-related peptide transcription unit: tissue-specific expression involves selective use of alternative polyadenylation sites.

“…This use of alternative donor sites within a single exon generates mRNAs with polymorphism of the 5' noncoding exon but occurs in a fixed ratio in both CGRP-and calcitonin-producing tissues. The sequence of the shorter, more frequently observed 5' end corresponds to that found at the end of the insert in the cDNA clone pCal (4), whereas the longer extension product is identical to that described for another calcitonin cDNA clone (25). Similar stochastic variations in RNA splicing patterns have been observed for human growth hormone (16,53) and -y-fibrinogen (12).…”

Ectopic synthesis of high‐Mr calcitonin by the BEN lung carcinoma cell line reflects aberrant proteolytic processing

“…The unexpectedly high iK as judged by gel filtration of some of the large calcitonin secreted by the BEN cell line (Mr 40000) may reflect molecular asymmetry or glycosylation, both of which can lead to disparities in Mr estimations. Since glycosylation of the rat calcitonin polyprotein has been demonstrated [37,38], it is likely that glycosylation in addition to aberrant proteolytic processing may well contribute to the heterogeneous nature of large calcitonins secreted by the BEN cell line, other cell lines and tumours.…”

Elucidation of the nucleotide sequence of chicken calcitonin mRNA: direct evidence for the expression of a lower vertebrate calcitonin-like gene in man and rat.

“…This could result from the expression of a gene coding for a salmon-like hormone or from the presence of a molecule sharing only common antigenic determinants with salmon calcitonin. The human (Craig et al, 1982; Le Moullec et al, 1984) and murine (Jacobs et al, 1981;Amara et al, 1982) calcitonin mRNAs show a high homology in nucleotide sequence and consequently a strong conservation of amino acids present in the precursor. Elucidating the nucleotide sequence of a lower vertebrate calcitonin mRNA would be of great help in studying the evolution of the calcitonin gene and in searching for a gen expressing a salmon-like molecule.…”