Processing of thyrotropin-releasing hormone prohormone (pro-TRH) in the adult rat pancreas: identification and localization of pro-TRH-related peptides in beta-cells of pancreatic islets.
Rat TRH prohormone (pro-TRH) contains five separate copies of the TRH progenitor sequence, Gln-His-Pro-Gly. All five sequences are flanked by paired basic amino acid cleavage sites and linked together by connecting sequences. RIAs to synthetic TRH and prepro-TRH-(178-199) were used to investigate pro-TRH processing in the endocrine pancreas of adult rats. HPLC analysis of adult rat pancreatic extracts showed the presence of a major immunoreactive peptide eluting at the position of prepro-TRH-(178-199). An additional peak coeluting with [less than Glu172]prepro-TRH-(172-199) (less than Glu = pyroglutamyl) revealed the presence of a C-terminally extended form of TRH. Quantification of TRH in pancreatic extracts indicated the presence of 22 mol TRH/mol prepro-TRH-(178-199) and 17 mol TRH/mol [less than Glu172]prepro-TRH-(172-199). Treatment of rats with streptozotocin markedly reduced the pancreatic content of both immunoreactive TRH (-84%) and immunoreactive prepro-TRH-(178-199) (-62%). Light microscopic immunocytochemistry showed that prepro-TRH-(178-199)-like immunoreactivity was exclusively located within insulin-containing cells of the pancreatic islets. At the electron microscopic level, prepro-TRH-(178-199) immunoreactivity appeared to be concentrated in secretory granules. The present study demonstrates that processing of pro-TRH generates both non-TRH- and TRH-related peptides in the adult rat pancreas. Our data also indicate that beta-cells of the endocrine pancreas are the major source of TRH- and pro-TRH-derived peptides.
Leduque
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Laboratoire d'Histologie-Embryologie, CNRS URA 559, Faculté de Médecine Lyon-Sud, Oullins, France.
Bulant
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Dubois
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Nicolas
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Vaudry
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D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D007150:Immunohistochemistry; D007515:Islets of Langerhans / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000032:analysis / Q000235:genetics*; D011499:Protein Processing, Post-Translational; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D011863:Radioimmunoassay; D051381:Rats; D011919:Rats, Inbred Strains; D015183:Restriction Mapping; D013973:Thyrotropin-Releasing Hormone / Q000032:analysis / Q000235:genetics*
D011498:Protein Precursors; D013973:Thyrotropin-Releasing Hormone; C046418:pro-thyrotropin releasing hormone; D011761:Pyrrolidonecarboxylic Acid