Elevated proenkephalin-derived peptide levels in ACTH-producing adenomas: nucleus and cytoplasm localization

• Published in: Endocrine Vol. 8; no. 3; pp. 231 - 240
• Main Authors: Vindrola, O, Chervin, A, Vitale, M, Mella, A N, Aloyz, R, Basso, A
• Format: Journal Article
• Language: English
• Published: United States 01.06.1998
• Subjects: Adenoma - metabolism; Adrenocorticotropic Hormone - metabolism; Adult; Aged; Carboxypeptidase B; Carboxypeptidases - metabolism; Chromatography, Gel; Chromatography, High Pressure Liquid; Deoxyribonuclease I - metabolism; Enkephalin, Methionine - metabolism; Enkephalins - metabolism; Female; Human Growth Hormone - metabolism; Humans; In Vitro Techniques; Male; Middle Aged; Molecular Weight; Pituitary Gland - metabolism; Pituitary Neoplasms - metabolism; Protein Precursors - metabolism; Protein Processing, Post-Translational; Trypsin - metabolism
• ISSN: 1355-008X
• DOI: 10.1385/ENDO:8:3:231

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.