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Ramzy A, Kieffer TJ. Altered islet prohormone processing: A cause or consequence of diabetes? Physiol Rev 2021; 102:155-208. [PMID: 34280055 DOI: 10.1152/physrev.00008.2021] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Peptide hormones are first produced as larger precursor prohormones that require endoproteolytic cleavage to liberate the mature hormones. A structurally conserved but functionally distinct family of nine prohormone convertase enzymes (PCs) are responsible for cleavage of protein precursors of which PC1/3 and PC2 are known to be exclusive to neuroendocrine cells and responsible for prohormone cleavage. Differential expression of PCs within tissues define prohormone processing; whereas glucagon is the major product liberated from proglucagon via PC2 in pancreatic α-cells, proglucagon is preferentially processed by PC1/3 in intestinal L cells to produce glucagon-like peptides 1 and 2 (GLP-1, GLP-2). Beyond our understanding of processing of islet prohormones in healthy islets, there is convincing evidence that proinsulin, proIAPP, and proglucagon processing is altered during prediabetes and diabetes. There is predictive value of elevated circulating proinsulin or proinsulin : C-peptide ratio for progression to type 2 diabetes and elevated proinsulin or proinsulin : C-peptide is predictive for development of type 1 diabetes in at risk groups. After onset of diabetes, patients have elevated circulating proinsulin and proIAPP and proinsulin may be an autoantigen in type 1 diabetes. Further, preclinical studies reveal that α-cells have altered proglucagon processing during diabetes leading to increased GLP-1 production. We conclude that despite strong associative data, current evidence is inconclusive on the potential causal role of impaired prohormone processing in diabetes, and suggest that future work should focus on resolving the question of whether altered prohormone processing is a causal driver or merely a consequence of diabetes pathology.
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Affiliation(s)
- Adam Ramzy
- Laboratory of Molecular and Cellular Medicine, Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada
| | - Timothy J Kieffer
- Laboratory of Molecular and Cellular Medicine, Department of Cellular and Physiological Sciences, Life Sciences Institute, University of British Columbia, Vancouver, BC, Canada.,Department of Surgery, University of British Columbia, Vancouver, BC, Canada.,School of Biomedical Engineering, University of British Columbia, Vancouver, BC, Canada
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Bonnemaison M, Bäck N, Lin Y, Bonifacino JS, Mains R, Eipper B. AP-1A controls secretory granule biogenesis and trafficking of membrane secretory granule proteins. Traffic 2014; 15:1099-121. [PMID: 25040637 DOI: 10.1111/tra.12194] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 02/06/2023]
Abstract
The adaptor protein 1A complex (AP-1A) transports cargo between the trans-Golgi network (TGN) and endosomes. In professional secretory cells, AP-1A also retrieves material from immature secretory granules (SGs). The role of AP-1A in SG biogenesis was explored using AtT-20 corticotrope tumor cells expressing reduced levels of the AP-1A μ1A subunit. A twofold reduction in μ1A resulted in a decrease in TGN cisternae and immature SGs and the appearance of regulated secretory pathway components in non-condensing SGs. Although basal secretion of endogenous SG proteins was unaffected, secretagogue-stimulated release was halved. The reduced μ1A levels interfered with the normal trafficking of carboxypeptidase D (CPD) and peptidylglycine α-amidating monooxygenase-1 (PAM-1), integral membrane enzymes that enter immature SGs. The non-condensing SGs contained POMC products and PAM-1, but not CPD. Based on metabolic labeling and secretion experiments, the cleavage of newly synthesized PAM-1 into PHM was unaltered, but PHM basal secretion was increased in sh-μ1A PAM-1 cells. Despite lacking a canonical AP-1A binding motif, yeast two-hybrid studies demonstrated an interaction between the PAM-1 cytosolic domain and AP-1A. Coimmunoprecipitation experiments with PAM-1 mutants revealed an influence of the luminal domains of PAM-1 on this interaction. Thus, AP-1A is crucial for normal SG biogenesis, function and composition.
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Affiliation(s)
- Mathilde Bonnemaison
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, 06030, USA
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Hung WL, Hwang C, Gao S, Liao EH, Chitturi J, Wang Y, Li H, Stigloher C, Bessereau JL, Zhen M. Attenuation of insulin signalling contributes to FSN-1-mediated regulation of synapse development. EMBO J 2013; 32:1745-60. [PMID: 23665919 DOI: 10.1038/emboj.2013.91] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Accepted: 03/27/2013] [Indexed: 01/07/2023] Open
Abstract
A neuronal F-box protein FSN-1 regulates Caenorhabditis elegans neuromuscular junction development by negatively regulating DLK-mediated MAPK signalling. In the present study, we show that attenuation of insulin/IGF signalling also contributes to FSN-1-dependent synaptic development and function. The aberrant synapse morphology and synaptic transmission in fsn-1 mutants are partially and specifically rescued by reducing insulin/IGF-signalling activity in postsynaptic muscles, as well as by reducing the activity of EGL-3, a prohormone convertase that processes agonistic insulin/IGF ligands INS-4 and INS-6, in neurons. FSN-1 interacts with, and potentiates the ubiquitination of EGL-3 in vitro, and reduces the EGL-3 level in vivo. We propose that FSN-1 may negatively regulate insulin/IGF signalling, in part, through EGL-3-dependent insulin-like ligand processing.
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Affiliation(s)
- Wesley L Hung
- Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada
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Cawley NX, Sridhar M, Hong H, Loh P. Exploring the membrane topology of prohormone convertase 1 in AtT20 Cells: in situ analysis by immunofluorescence microscopy. F1000Res 2012; 1:9. [PMID: 24163733 PMCID: PMC3799554 DOI: 10.12688/f1000research.1-9.v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/03/2012] [Indexed: 11/20/2022] Open
Abstract
Prohormone convertase 1 (PC1) was previously characterized as a partially transmembrane protein in purified chromaffin granules of bovine adrenal medulla1. This was challenged with experiments on transfected PC1 in COS1 cells, a non-endocrine cell line2. To address this issue, we undertook to analyze its extraction properties in vitro and its immunocytochemical localization in situ in AtT20 cells, an endocrine cell line that expresses PC1. Most of the 87 kDa form of PC1 was resistant to carbonate extraction suggesting that it had properties of a transmembrane protein. Under semi-permeabilized conditions whereby only the plasma membrane was permeabilized, the carboxy-terminus of PC1 was specifically immunostained whereas the amino-terminus was not. These results indicate that the amino-terminus of PC1 was within the lumen of the Golgi and granules, and some of the C-terminus was exposed to the cytosol. Thus, endogenous PC1 can assume a transmembrane orientation in situ in AtT20 cells.
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Affiliation(s)
- Niamh X Cawley
- Section on Cellular Neurobiology, Program in Developmental Neuroscience, Eunice Shriver Kennedy National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA ; National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA
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Suckale J, Solimena M. The insulin secretory granule as a signaling hub. Trends Endocrinol Metab 2010; 21:599-609. [PMID: 20609596 DOI: 10.1016/j.tem.2010.06.003] [Citation(s) in RCA: 135] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/06/2010] [Revised: 06/01/2010] [Accepted: 06/03/2010] [Indexed: 02/06/2023]
Abstract
The insulin granule was previously thought of as merely a container, but accumulating evidence suggests that it also acts as a signaling node. Regulatory pathways intersect at but also originate from the insulin granule membrane. Examples include the small G-proteins Rab3a and Rab27a, which influence granule movement, and the transmembrane proteins (tyrosine phosphatase receptors type N) PTPRN and PTPRN2, which upregulate β-cell transcription and proliferation. In addition, many cosecreted compounds possess regulatory functions, often related to energy metabolism. For instance, ATP and γ-amino butyric acid (GABA) modulate insulin and glucagon secretion, respectively; C-peptide protects β-cells and kidney cells; and amylin reduces gastric emptying and food intake via the brain. In this paper, we review the current knowledge of the insulin granule proteome and discuss its regulatory functions.
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Affiliation(s)
- Jakob Suckale
- Molecular Diabetology, Paul Langerhans Institute Dresden, School of Medicine and University Clinic Carl Gustav Carus, Dresden University of Technology, Dresden 01307, Germany
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Stevens A, White A. ACTH: cellular peptide hormone synthesis and secretory pathways. Results Probl Cell Differ 2009; 50:63-84. [PMID: 19888563 DOI: 10.1007/400_2009_30] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Adrenocorticotrophic hormone (ACTH) is derived from the prohormone, pro-opiomelanocortin (POMC). This precursor undergoes proteolytic cleavage to yield a number of different peptides which vary depending on the tissue. In the anterior pituitary, POMC is processed to ACTH by the prohormone convertase, PC1 and packaged in secretory granules ready for stimulated secretion. In response to stress, corticotrophin releasing hormone (CRH), stimulates release of ACTH from the pituitary cell which in turn causes release of glucocorticoids from the adrenal gland. In tissues, such as the hypothalamus and skin, ACTH is further processed intracellularly to alpha melanocyte stimulating hormone (alphaMSH) which has distinct roles in these tissues. The prohormone, POMC, is itself released from cells and found in the human circulation at concentrations greater than ACTH. While much is known about the tightly regulated synthesis of POMC, there is still a lot to learn about the mechanisms for differentiating secretion of POMC, and the POMC-derived peptides. Understanding what happens to the POMC released from cells will provide new insights into its function.
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Affiliation(s)
- Adam Stevens
- Endocrine Sciences, Faculty of Medical and Human Sciences, University of Manchester, Manchester, M13 9PT, UK.
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Rabah N, Gauthier D, Dikeakos JD, Reudelhuber TL, Lazure C. The C-terminal region of the proprotein convertase 1/3 (PC1/3) exerts a bimodal regulation of the enzyme activity in vitro. FEBS J 2007; 274:3482-91. [PMID: 17565604 DOI: 10.1111/j.1742-4658.2007.05883.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The proprotein convertase PC1/3 preferentially cleaves its substrates in the dense core secretory granules of endocrine and neuroendocrine cells. Similar to most proteinases synthesized first as zymogens, PC1/3 is synthesized as a larger precursor that undergoes proteolytic processing of its signal peptide and propeptide. The N-terminally located propeptide has been shown to be essential for folding and self-inhibition. Furthermore, PC1/3 also possesses a C-terminal region (CT-peptide) which, for maximal enzymatic activity, must also be cleaved. To date, its role has been documented through transfection studies in terms of sorting and targeting of PC1/3 and chimeric proteins into secretory granules. In this study, we examined the properties of a 135-residue purified bacterially produced CT-peptide on the in vitro enzymatic activity of PC1/3. Depending on the amount of CT-peptide used, it is shown that the CT-peptide increases PC1/3 activity at low concentrations (nm) and decreases it at high concentrations (microm), a feature typical of an activator. Furthermore, we show that, contrary to the propeptide, the CT-peptide is not further cleaved by PC1/3 although it is sensitive to human furin activity. Based on these results, it is proposed that PC1/3, through its various domains, is capable of controlling its enzymatic activity in all regions of the cell that it encounters. This mode of self-control is unique among members of all proteinases families.
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Affiliation(s)
- Nadia Rabah
- Neuropeptides Structure and Metabolism Laboratory, Institut de recherches cliniques de Montréal, Québec, Canada
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Lou H, Smith AM, Coates LC, Cawley NX, Peng Loh Y, Birch NP. The transmembrane domain of the prohormone convertase PC3: a key motif for targeting to the regulated secretory pathway. Mol Cell Endocrinol 2007; 267:17-25. [PMID: 17240044 PMCID: PMC1892588 DOI: 10.1016/j.mce.2006.11.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 11/17/2006] [Accepted: 11/28/2006] [Indexed: 10/23/2022]
Abstract
The biosynthesis of hormones and neuropeptides involves post-translational cleavage of precursors at basic amino acids by prohormone convertases (PCs) predominantly in secretory granules that bud from the trans-Golgi Network. This study reports that the amino acid sequence of PC3 (aa617-638), previously identified as a novel transmembrane (TM) domain, confers lipid raft association and facilitates sorting of the enzyme to the secretory granules of Neuro2A cells for prohormone cleavage. Floatation analysis on sucrose density gradients showed that a proportion of full length (PC3-FL) and carboxyl terminus-truncated PC3(1-638) (PC3-638) containing the TM domain were associated with lipid rafts in Neuro2A cells, while PC3(1-616) (PC3-616) and PC3-DeltaTM lacking the TM domain were not. Secondly, PC3-FL and PC3-638 underwent stimulated secretion and were shown to be colocalized with a secretory granule marker, chromogranin A, by immunocytochemistry. In contrast, PC3-616 and PC3-DeltaTM were constitutively secreted and primarily localized in the Golgi. These data indicate that the transmembrane domain of PC3 plays a key role in sorting the enzyme to the regulated secretory pathway.
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Affiliation(s)
- Hong Lou
- Section on Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | | | - Leigh C. Coates
- Laboratory of Molecular Neuroendocrinology, School of Biological Sciences, University of Auckland, Auckland, New Zealand
| | - Niamh X. Cawley
- Section on Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Y. Peng Loh
- Section on Cellular Neurobiology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA
- *To whom correspondence should be addressed: Dr. Y. Peng Loh, Building 49/Room 5A22 National Institutes of Health Bethesda, Maryland 20892, USA Tel: 301-496-3239 Fax: 301-496-9938 E-mail:
| | - Nigel P. Birch
- Laboratory of Molecular Neuroendocrinology, School of Biological Sciences, University of Auckland, Auckland, New Zealand
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