title: Identification of procalcitonin in a rat medullary thyroid carcinoma cell line.
abstract: As a first step in studying the biosynthesis of the peptide hormone calcitonin, we have identified procalcitonin species in CA-77 cells, a newly developed rat medullary thyroid carcinoma cell line. mRNA extracted from the cells directed the synthesis of a putative procalcitonin in a reticulocyte lysate translation system containing microsomal membranes. Both this species and a radiolabeled form of immunoreactive calcitonin from intact cells had the same retention time during reverse phase high performance liquid chromatography. The putative cellular procalcitonin was also immunoprecipitated by antiserum to a synthetic peptide whose sequence constitutes the COOH-terminal 16 residues of preprocalcitonin. The polypeptide had a Mr = 13,400, as estimated by gel filtration chromatography under denaturing conditions. Microsequencing of the [35S]methionine-labeled polypeptide indicated that residues 13, 32, and 34 of procalcitonin were methionine. Similar analysis of the peptide labeled with [3H]proline indicated that residues 2 and 11 of the precursor were proline. The positions of methionine and proline could be aligned in a unique manner with the NH2-terminal half of the preprocalcitonin sequence inferred from cDNA analyses. These results indicate that procalcitonin consists of 111 amino acids and suggest that a 25-residue signal sequence is cotranslationally cleaved from preprocalcitonin. From the procalcitonin sequence we can now predict the sequence of likely biosynthetic intermediates and mature secretory products derived from the NH2-terminal as well as COOH-terminal regions of the precursor.
mesh_terms: D000595:Amino Acid Sequence; D002116:Calcitonin / Q000235:genetics* / Q000302:isolation & purification; D015740:Calcitonin Gene-Related Peptide; D002460:Cell Line; D006023:Glycoproteins / Q000235:genetics*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D011061:Poly A / Q000235:genetics; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics* / Q000302:isolation & purification; D012313:RNA / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D012156:Reticulocytes / Q000378:metabolism; D013964:Thyroid Neoplasms / Q000378:metabolism*
chemical_list: C000606589:CALCA protein, human; C000606591:Calca protein, rat; D006023:Glycoproteins; D011498:Protein Precursors; D012333:RNA, Messenger; D011061:Poly A; D012313:RNA; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide