Evidence for intragranular processing of pro-opiocortin in the mouse pituitary intermediate lobe.
Mouse pituitary neurointermediate lobes were pulse-incubated in [3H] arginine or [3H] lysine for 10 min and then chase-incubated for periods 0 to 4h. The labeled peptides from the lobes were analysed by immunoprecipitation with specific antisera, and thereafter, by acid-urea polyacrylamide gel electrophoresis. Using this paradigm, the synthesis of a prohormone common to adrenocorticotropin (ACTH) and endorphin was detected in 10 min pulse labeled lobes. Following a chase period, processing of the prohormone to several forms of ACTH (mol. wt. 25000, 23000, and 13000), beta-lipotropin and beta-endorphin was observed. To determine the intracellular site of processing of the prohormone, subcellular fractionation studies of labeled lobes were carried out. Analysis of the fractions from the pulse-labeled lobes revealed that the newly synthesized labeled prohormone was primarily localized in a granule-enriched fraction. In lobes that were pulsed and then chase-incubated for 1 h, there was a decrease in the amount of prohormone and an appearance of processed products in the granule-enriched fraction. In another paradigm, where the secretory granule-fraction was isolated from pulse-labeled lobes and then incubated in vitro for 6 h at pH 5.5, processing of the endogenous labeled prohormone within the isolated granule fraction was observed. These data suggest, that in the mouse neurointermediate lobe, the ACTH/endorphin prohormone (pro-opiocortin) is rapidly packaged into secretory granules after synthesis and processed intragranularly.
D000324:Adrenocorticotropic Hormone / Q000096:biosynthesis; D000818:Animals; D002458:Cell Fractionation; D003594:Cytoplasmic Granules / Q000378:metabolism*; D004723:Endorphins / Q000096:biosynthesis; D008297:Male; D051379:Mice; D008861:Microsomes / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism* / Q000648:ultrastructure; D010908:Pituitary Hormones, Anterior / Q000378:metabolism*; D011333:Pro-Opiomelanocortin; D011498:Protein Precursors / Q000378:metabolism*; D001615:beta-Endorphin; D008083:beta-Lipotropin / Q000096:biosynthesis
D004723:Endorphins; D010908:Pituitary Hormones, Anterior; D011498:Protein Precursors; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin; D000324:Adrenocorticotropic Hormone; D008083:beta-Lipotropin