Effect of tunicamycin on the synthesis, processing, and secretion of pro-opiomelanocortin peptides in mouse pituitary cells.
Pro-opiomelanocortin (POMC) is glycosylated and proteolytically cleaved to produce a number of smaller peptide hormones including adrenocorticotropic hormone (ACTH) and endorphin in mammalian pituitary and the mouse pituitary cell line AtT-20/D16v. When glycosylation of POMC is inhibited in AtT-20 cells with the drug tunicamycin, a 26,000-dalton protein appears in place of the glycosylated 29,000- and 32,000-dalton forms of POMC. The 26,000-dalton form found in tunicamycin-treated cells has the same [35S]methionine tryptic peptides as 29,000- and 32,000-dalton POMC, indicating that the decrease in apparent mass is most likely due to loss of carbohydrate and not to changes in the peptide backbone. The 4,500-dalton form of alpha(1-39)ACTH and the 3,000- and 11,000-dalton forms of endorphin are all present in tunicamycin-treated cells. The glycosylated form of alpha(1-39)ACTH, however, is missing and the glycosylated ACTH intermediates are replaced by unglycosylated ACTH intermediates. Pulse-chase studies demonstrate that the 26,000-dalton unglycosylated POMC is the precursor of the smaller ACTH and endorphin molecules in tunicamycin-treated cells. Furthermore, all of the forms of ACTH and endorphin found in tunicamycin-treated cells are secreted. Thus, it appears that glycosylation is not an essential step for correct cleavage or secretion of POMC or its products.
D000324:Adrenocorticotropic Hormone / Q000096:biosynthesis*; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D005944:Glucosamine / Q000031:analogs & derivatives*; D051379:Mice; D008970:Molecular Weight; D010446:Peptide Fragments / Q000096:biosynthesis / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D010907:Pituitary Hormones / Q000096:biosynthesis / Q000378:metabolism*; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D011333:Pro-Opiomelanocortin; D011498:Protein Precursors / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology*
D010446:Peptide Fragments; D010907:Pituitary Hormones; D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; C028182:proopiocortin fragments; D014415:Tunicamycin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D005944:Glucosamine