Elevated proenkephalin-derived peptide levels in ACTH-producing adenomas: nucleus and cytoplasm localization.
The biosynthesis of met-enkephalin in human pituitary and human pituitary adenomas is still not well known. In this work, we studied the processing of proenkephalin-derived peptides in postmortem human pituitary (PMHP), ACTH-producing adenomas (ACTH-PA), nonfunctioning adenomas (NFA), and GH-producing adenomas (GH-PA). ACTH-PA contained at least 10 times more proenkephalin-derived peptides than PMHP, NFA,and GH-PA. Proenkephalin processing was different in the four tested tissues. In ACTH-PA, proenkephalin was processed to high-, intermediate-, and low-mol-wt products. The highest met-enkephalin-containing peptides levels corresponded to intermediate and low-mol-wt materials, although met-enkephalinArg-Phe and synenkephalin immunoreactivity appeared only in high-mol-wt peptides. In PMHP and NFA, met-enkephalin-Arg-Phe immunoreactivity was detected in intermediate- and low-mol-wt materials, and it was absent in GH-PA. Immunoblotting of ACTH-PA showed that met-enkephalin-Arg-Phe immunoreactivity corresponded to peptides of 44, 32-30, 27, and 17 kDa. The 32-30 and 17-kDa molecules were localized in the nuclear fraction where they were extracted after enzymatic digestion with DNase I. Plasmatic met-enkephalin levels did not increase in patients with Cushing's disease, suggesting that the pentapeptide stored in ACTH-PA was not released to the general circulation. In conclusion, we demonstrated that only ACTH-PA contained high levels of proenkephalin peptides, which were stored in cytoplasm organelles and in the nucleus, probably bound to chromatin. These results suggest an adenoma-specific physiological role of proenkephalin products.
Vindrola
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O
Instituto de Fisiologia, Laboratorio de Bioquimica, Universidad Autonoma de Puebla, Mexico. ovindrol@siu.cen.buap.mx
Chervin
A
A
Vitale
M
M
Mella
A N
AN
Aloyz
R
R
Basso
A
A
D000236:Adenoma / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000378:metabolism*; D000328:Adult; D000368:Aged; D043424:Carboxypeptidase B; D002268:Carboxypeptidases / Q000378:metabolism; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003850:Deoxyribonuclease I / Q000378:metabolism; D004744:Enkephalin, Methionine / Q000378:metabolism; D004745:Enkephalins / Q000378:metabolism*; D005260:Female; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D008970:Molecular Weight; D010902:Pituitary Gland / Q000378:metabolism; D010911:Pituitary Neoplasms / Q000378:metabolism*; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D014357:Trypsin / Q000378:metabolism
D004745:Enkephalins; D011498:Protein Precursors; C029992:proenkephalin; D019382:Human Growth Hormone; D004744:Enkephalin, Methionine; C036693:synenkephalin; D000324:Adrenocorticotropic Hormone; D003850:Deoxyribonuclease I; D002268:Carboxypeptidases; D043424:Carboxypeptidase B; D014357:Trypsin