Dopaminergic regulation of secretory granule-associated proteins in rat intermediate pituitary.
The biosynthesis of peptides requires the synthesis of the prohormone, several biosynthetic processing enzymes, and other granule constituents. We have investigated the regulated expression of proopiomelanocortin (POMC) and five enzymes essential for the processing of POMC to smaller, bioactive peptides in intermediate pituitary melanotropes. Rats were treated with a dopaminergic agonist (bromocriptine) or antagonist (haloperidol) for periods ranging from 1 h to 5 days, followed by analyses of mRNA levels and protein biosynthetic rates. Multiplex RNase protection assays showed that bromocriptine treatment caused a striking decrease in POMC mRNA levels, and significant decreases in mRNA levels for prohormone convertase 2 (PC2), carboxypeptidase H (CPH), and peptidylglycine alpha-amidating monooxygenase (PAM). Smaller increases in mRNA levels were seen after haloperidol stimulation. Protein biosynthetic rates changed more profoundly than mRNA levels at short drug treatment times, indicating a role for translational effects after treatment with bromocriptine and with haloperidol. The homogeneous population of melanotropes in the intermediate lobe of the pituitary allows a quantitative analysis of transcript levels and biosynthetic rates. POMC mRNA levels are 200-1,000-fold higher than levels of any of the processing enzyme mRNAs, and POMC biosynthetic rates exceed those of PC2, PC1, and PAM by 1,000-10,000-fold.
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Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205-2185, USA.
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D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001971:Bromocriptine / Q000494:pharmacology; D003573:Cytochrome b Group / Q000235:genetics / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000201:enzymology*; D004298:Dopamine / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006220:Haloperidol / Q000494:pharmacology; D006727:Hormone Antagonists / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism* / Q000648:ultrastructure; D011233:Precipitin Tests; D011333:Pro-Opiomelanocortin / Q000235:genetics / Q000378:metabolism; D045706:Proprotein Convertase 2; D043484:Proprotein Convertases; D014176:Protein Biosynthesis / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013381:Subtilisins / Q000235:genetics / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology
D003573:Cytochrome b Group; D018492:Dopamine Antagonists; D006727:Hormone Antagonists; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C023646:cytochrome b561; D001971:Bromocriptine; D011333:Pro-Opiomelanocortin; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D043484:Proprotein Convertases; D013381:Subtilisins; D045706:Proprotein Convertase 2; D016282:Aspartic Acid Endopeptidases; D006220:Haloperidol; D004298:Dopamine