Differential effects of a phorbol ester on carboxypeptidase E in cultured astrocytes and AtT-20 cells, a neuroendocrine cell line

Differential effects of temperature blockade on the proteolytic processing of three secretory granule-associated proteins

Vesicular transport within the secretory pathway can be arrested by incubating cells at 15 degrees C or 20 degrees C to block exit from the endoplasmic reticulum or trans-Golgi network, respectively. Using this powerful tool we have compared the intracellular sites of endoproteolytic processing of proopiomelanocortin and two prohormone processing enzymes in AtT-20 mouse pituitary corticotrope tumor cells. For comparison, proopiomelanocortin processing was also evaluated in primary neurointermediate pituitary cultures. AtT-20 cells synthesize and store endogenous proopiomelanocortin and prohormone convertase 1; AtT-20 cells expressing high levels of integral membrane or soluble peptidylglycine alpha-amidating monooxygenase were generated by stable transfection. Cells were incubated with [35S]methionine and chased at 4 degrees C, 15 degrees C, 20 degrees C or 37 degrees C. The endoproteolytic processing of peptidylglycine alpha-amidating mono-oxygenase, prohormone convertase 1, and proopiomelanocortin was compared following immunoprecipitation. Endoproteolytic processing of integral membrane and soluble peptidylglycine alpha-amidating monooxygenase proteins was completely blocked by incubation of cells at 20 degrees C. In contrast, prohormone convertase 1 processing from the 87 kDa precursor to the 81 kDa intermediate proceeded to completion at both 15 degrees C and 20 degrees C, while cleavage to generate the 63 kDa prohormone convertase 1 protein was completely blocked at 20 degrees C. In AtT-20 cells and neurointermediate pituitary cultures, generation of beta-lipotropin from proopiomelanocortin continued at a slow but significant rate at 20 degrees C, while processing of beta-lipotropin to beta-endorphin was blocked. Thus prohormone convertase 1 processing begins in the endoplasmic reticulum and is not completed until after the trans-Golgi network, while peptidylglycine alpha-amidating monooxygenase processing begins after the trans-Golgi network. Selected proopiomelanocortin cleavages begin before entry into immature granules.

Dopamine antagonist haloperidol increases carboxypeptidase E mRNA in rat neurointermediate pituitary but not in various other rat tissues

Carboxypeptidase E (CPE) is involved with the biosynthesis of many neuropeptides, including several whose genes are regulated by haloperidol treatments. In this study, we examined whether haloperidol alters CPE mRNA levels in a variety of tissues. Rats were treated for either 1, 3, 7, 14, or 21 days with 2 mg/kg haloperidol, and then Northern blot analysis performed on RNA from neurointermediate pituitary, anterior pituitary, hypothalamus, striatum, cerebellum, and adrenal. The 14 and 21 day treatments produced a significant 90-110% elevation of CPE mRNA in neurointermediate pituitary. However, the levels of CPE mRNA in the other tissues were not significantly influenced by the haloperidol treatments. This finding indicates that CPE is not co-regulated with peptide hormone mRNAs in all tissues.