Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01189 (beta-endorphin)
 21,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Neuropeptide precursors synthesized at the rough endoplasmic reticulum are transported and sorted at the trans-Golgi network (TGN) to the granules of the regulated secretory pathway (RSP) of neuroendocrine cells. They are then processed into active peptides and stored in large dense-core granules (LDCGs) until secreted upon stimulation. We have studied the regulation of biogenesis of the LDCGs and the mechanism by which neuropeptide precursors, such as pro-opiomelanocortin (POMC), are sorted into these LDCGs of the RSP in neuroendocrine and endocrine cells. We provide evidence that chromogranin A (CgA), one of the most abundant acidic glycoproteins ubiquitously present in neuroendocrine/endocrine cells, plays an important role in the regulation of LDCG biogenesis. Specific depletion of CgA expression by antisense RNAs in PC12 cells led to a profound loss of secretory granule formation. Exogenously expressed POMC was neither stored nor secreted in a regulated manner in these CgA-deficient PC12 cells. Overexpression of CgA in a CgA- and LDCG-deficient endocrine cell line, 6T3, restored regulated secretion of transfected POMC and the presence of immunoreactive CgA at the tips of the processes of these cells. Unlike CgA, CgB, another granin protein, could not substitute for the role of CgA in regulating LDCG biogenesis. Thus, we conclude that CgA is a key player in the regulation of the biogenesis of LDCGs in neuroendocrine cells. To examine the mechanism of sorting POMC to the LDCGs, we carried out site-directed mutagenesis, transfected the POMC mutants into PC12 cells, and assayed for regulated secretion. Our previous molecular modeling studies predicted a three-dimensional sorting motif in POMC that can bind to a sorting receptor, membrane carboxypeptidase E (CPE). The sorting signal consists of four conserved residues at the N-terminal loop structure of POMC: two acidic residues and two hydrophobic residues. The two acidic residues were predicted to bind to a domain on CPE (CPE254-273) containing two basic residues (R255 and K260) to effect sorting into immature secretory granules. Site-directed mutagenesis of the motif on POMC resulted in accumulation of the mutant in the Golgi, as well as high basal secretion, indicating that the mutant POMC was inefficiently sorted to the RSP. These results support the model that POMC is actively sorted to the RSP granules for processing and secretion by a sorting signal-mediated mechanism.
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PMID:Secretory granule biogenesis and neuropeptide sorting to the regulated secretory pathway in neuroendocrine cells. 1474 11

The formation of secretory granules and regulated secretion are generally assumed to occur only in specialized endocrine, neuronal, or exocrine cells. We discovered that regulated secretory proteins such as the hormone precursors pro-vasopressin, pro-oxytocin, and pro-opiomelanocortin, as well as the granins secretogranin II and chromogranin B but not the constitutive secretory protein alpha(1)-protease inhibitor, accumulate in granular structures at the Golgi and in the cell periphery in transfected COS-1 fibroblast cells. The accumulations were observed in 30-70% of the transfected cells expressing the pro-hormones and for virtually all of the cells expressing the granins. Similar structures were also generated in other cell lines believed to be lacking a regulated secretory pathway. The accumulations resembled secretory granules morphologically in immunofluorescence and electron microscopy. They were devoid of markers of the endoplasmic reticulum, endosomes, and lysosomes but in part stained positive for the trans-Golgi network marker TGN46, consistent with their formation at the trans-Golgi network. When different regulated proteins were coexpressed, they were frequently found in the same granules, whereas alpha(1)-protease inhibitor could not be detected in accumulations formed by secretogranin II, demonstrating segregation of regulated from constitutive secretory proteins. In pulse-chase experiments, significant intracellular storage of secretogranin II and chromogranin B was observed and secretion of retained secretogranin II was stimulated with the calcium ionophore A23187. The results suggest that expression of regulated cargo proteins is sufficient to generate structures that resemble secretory granules in the background of constitutively secreting cells, supporting earlier proposals on the mechanism of granule formation.
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PMID:Expression of regulated secretory proteins is sufficient to generate granule-like structures in constitutively secreting cells. 1499 40

Neuroendocrine tumors are usually slow-growing tumors. Many of these are capable of secreting peptide hormones or biogenic amines that may lead to endocrine syndromes. Nonfunctioning tumors can either secrete no hormones at all, or secrete hormones not giving rise to endocrine symptoms, such as chromogranin A, chromogranin B or pancreatic polypeptide. Chromogranin A is produced by the majority of endocrine tumors, both functioning and nonfunctioning, and is the best available marker for diagnosis, follow-up and treatment monitoring of patients with differentiated neuroendocrine tumors. Examples of endocrine syndromes are classical carcinoid syndrome caused by serotonin (measured in the urine as its metabolite 5-HIAA), insulinoma syndrome caused by insulin or proinsulin, Zollinger-Ellison syndrome resulting from gastrin secretion, glucagonoma syndrome caused by glucagon, WDHA syndrome caused by vasoactive intestinal peptide, or Cushing's syndrome resulting from ectopic production of adrenocorticotropic hormone or corticotropin-releasing hormone. In case there is uncertainty about the diagnosis, specific tests can be applied, such as the secretin test for diagnosis of gastrinomas and the 72-hour fast for diagnosis of an insulinoma. In patients with suspicion of an inherited syndrome, such as multiple endocrine neoplasia (MEN) 1 and MEN2 syndromes, genetic testing is indicated.
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PMID:Biochemical Testing in Patients with Neuroendocrine Tumors. 2630 2


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