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Diabetes, Obesity & Metabolism Sep 2018Insulin synthesis in pancreatic β-cells is initiated as preproinsulin. Prevailing glucose concentrations, which oscillate pre- and postprandially, exert major dynamic... (Review)
Review
Insulin synthesis in pancreatic β-cells is initiated as preproinsulin. Prevailing glucose concentrations, which oscillate pre- and postprandially, exert major dynamic variation in preproinsulin biosynthesis. Accompanying upregulated translation of the insulin precursor includes elements of the endoplasmic reticulum (ER) translocation apparatus linked to successful orientation of the signal peptide, translocation and signal peptide cleavage of preproinsulin-all of which are necessary to initiate the pathway of proper proinsulin folding. Evolutionary pressures on the primary structure of proinsulin itself have preserved the efficiency of folding ("foldability"), and remarkably, these evolutionary pressures are distinct from those protecting the ultimate biological activity of insulin. Proinsulin foldability is manifest in the ER, in which the local environment is designed to assist in the overall load of proinsulin folding and to favour its disulphide bond formation (while limiting misfolding), all of which is closely tuned to ER stress response pathways that have complex (beneficial, as well as potentially damaging) effects on pancreatic β-cells. Proinsulin misfolding may occur as a consequence of exuberant proinsulin biosynthetic load in the ER, proinsulin coding sequence mutations, or genetic predispositions that lead to an altered ER folding environment. Proinsulin misfolding is a phenotype that is very much linked to deficient insulin production and diabetes, as is seen in a variety of contexts: rodent models bearing proinsulin-misfolding mutants, human patients with Mutant INS-gene-induced Diabetes of Youth (MIDY), animal models and human patients bearing mutations in critical ER resident proteins, and, quite possibly, in more common variety type 2 diabetes.
Topics: Animals; Diabetes Mellitus; Disease Models, Animal; Endoplasmic Reticulum; Humans; Insulin; Insulin-Secreting Cells; Mice; Mutation; Proinsulin; Protein Folding; Protein Precursors; Protein Translocation Systems
PubMed: 30230185
DOI: 10.1111/dom.13378 -
Cellular and Molecular Life Sciences :... Jul 1998Proinsulin has generally been regarded as an inert precursor to insulin. However, over the past few years, proinsulin has established itself as a useful research tool... (Review)
Review
Proinsulin has generally been regarded as an inert precursor to insulin. However, over the past few years, proinsulin has established itself as a useful research tool for understanding how cells synthesize and secrete peptide hormones. Last year, proinsulin attracted renewed interest for its role as the precursor to C peptide, which may prove useful in the treatment of patients suffering from insulin-dependent diabetes mellitus. This mini-review focuses on three aspects of proinsulin, each of which attracted attention in 1997. These three aspects illustrate how this peptide hormone precursor may yet prove to be more important than its primary role as a prohormone, with only one bioactive product, would suggest.
Topics: Amino Acid Sequence; C-Peptide; Carboxypeptidases; Diabetes Mellitus; Molecular Sequence Data; Proinsulin; Protein Processing, Post-Translational
PubMed: 9711235
DOI: 10.1007/s000180050196 -
Protein Science : a Publication of the... Apr 2024Primary defects in folding of mutant proinsulin can cause dominant-negative proinsulin accumulation in the endoplasmic reticulum (ER), impaired anterograde proinsulin...
Primary defects in folding of mutant proinsulin can cause dominant-negative proinsulin accumulation in the endoplasmic reticulum (ER), impaired anterograde proinsulin trafficking, perturbed ER homeostasis, diminished insulin production, and β-cell dysfunction. Conversely, if primary impairment of ER-to-Golgi trafficking (which also perturbs ER homeostasis) drives misfolding of nonmutant proinsulin-this might suggest bi-directional entry into a common pathological phenotype (proinsulin misfolding, perturbed ER homeostasis, and deficient ER export of proinsulin) that can culminate in diminished insulin storage and diabetes. Here, we've challenged β-cells with conditions that impair ER-to-Golgi trafficking, and devised an accurate means to assess the relative abundance of distinct folded/misfolded forms of proinsulin using a novel nonreducing SDS-PAGE/immunoblotting protocol. We confirm abundant proinsulin misfolding upon introduction of a diabetogenic INS mutation, or in the islets of db/db mice. Whereas blockade of proinsulin trafficking in Golgi/post-Golgi compartments results in intracellular accumulation of properly-folded proinsulin (bearing native disulfide bonds), impairment of ER-to-Golgi trafficking (regardless whether such impairment is achieved by genetic or pharmacologic means) results in decreased native proinsulin with more misfolded proinsulin. Remarkably, reversible ER-to-Golgi transport defects (such as treatment with brefeldin A or cellular energy depletion) upon reversal quickly restore the ER folding environment, resulting in the disappearance of pre-existing misfolded proinsulin while preserving proinsulin bearing native disulfide bonds. Thus, proper homeostatic balance of ER-to-Golgi trafficking is linked to a more favorable proinsulin folding (as well as trafficking) outcome.
Topics: Mice; Animals; Proinsulin; Protein Folding; Insulin; Endoplasmic Reticulum; Diabetes Mellitus; Insulin-Secreting Cells; Homeostasis; Disulfides
PubMed: 38511500
DOI: 10.1002/pro.4949 -
Horumon To Rinsho. Clinical... Jul 1973
Review
Topics: Amino Acid Sequence; Animals; Antibody Formation; Chemical Phenomena; Chemistry; Humans; Models, Chemical; Proinsulin
PubMed: 4588456
DOI: No ID Found -
Journal of Chromatography May 1993Proinsulin is synthesized in the beta-cells of the endocrine pancreas, one of the four cell types found in the islets of Langerhans. Specific enzymatic cleavage of... (Review)
Review
Proinsulin is synthesized in the beta-cells of the endocrine pancreas, one of the four cell types found in the islets of Langerhans. Specific enzymatic cleavage of proinsulin results in the formation of equimolar amounts of insulin and C-peptide, via several intermediate split-proinsulin forms. Most mammals produce a single insulin, but in rodents two non-allelic insulin genes are expressed. There is an inverse ratio between the two insulins in rats and mice, the reason for this being unknown. It has been suggested that differences in transcription, translation (biosynthesis) and/or posttranslational processes (enzymatic conversion, intracellular degradation) could be possible explanations. Elevated amounts of proinsulin-immunoreactive material (PIM) have been described to occur in various conditions/diseases, suggesting alterations in beta-cell function, but the composition of the secreted PIM (intact proinsulin or its intermediates) has been incompletely determined. Studies of the biosynthesis of proinsulins and their conversion with the purpose of revealing some of these points depend on accessible reversed-phase high-performance liquid chromatographic (RP-HPLC) analyses capable of separating all the relevant, closely related polypeptides involved. This review will deal with the optimization of the RP-HPLC separations as well as sample preparation and recovery. Applications of the selected methods in the study of proinsulin biosynthesis and its conversion will also be presented.
Topics: Animals; C-Peptide; Chromatography, High Pressure Liquid; Humans; Insulin; Islets of Langerhans; Mice; Proinsulin; Rats
PubMed: 8314931
DOI: 10.1016/0378-4347(93)80309-r -
The Medical Clinics of North America Jul 1978The availability of C-peptide measurement continues to provide new and useful information about the state of beta cell secretory function and the natural history of... (Review)
Review
The availability of C-peptide measurement continues to provide new and useful information about the state of beta cell secretory function and the natural history of diabetes. Measurement of proinsulin is of value in the diagnosis of insulin-secreting tumors.
Topics: C-Peptide; Cross Reactions; Diabetes Mellitus; Diabetic Ketoacidosis; Humans; Immunoassay; Peptides; Proinsulin
PubMed: 98676
DOI: 10.1016/s0025-7125(16)31768-0 -
Clinical Biochemistry Dec 1991Insulin, like other secretory peptides, is synthesized via a larger and less active precursor, proinsulin, converted in the beta cell by sequential limited proteolysis... (Review)
Review
Insulin, like other secretory peptides, is synthesized via a larger and less active precursor, proinsulin, converted in the beta cell by sequential limited proteolysis to insulin and C-peptide which are stored in secretory granules. Since this process is incomplete, some intact and partially processed proinsulins with variable biological and immunological activities remain trapped in the granules and enter the circulation with insulin, resulting in the heterogeneity of plasma immunoreactive insulin (IRI). Whereas methods measuring proinsulin from corrected IRI in sera fractionated by gel chromatography were not sufficiently sensitive and specific, immunoradiometric assays (IRMA) now allow reliable determinations of proinsulin, split proinsulins and true insulin and thereby the monitoring of the dynamics of conversion in various diabetic states. The recent finding of increased 32,33-split proinsulin associated with absolute true insulin deficiency, correlated with cardiovascular risk factors in Type II diabetics, sheds new light on the molecular pathology of noninsulin-dependent diabetes.
Topics: Chemistry Techniques, Analytical; Diabetes Mellitus; Humans; Proinsulin; Protein Biosynthesis; Protein Processing, Post-Translational; Transcription, Genetic
PubMed: 1773484
DOI: 10.1016/s0009-9120(05)80001-3 -
Annals of Clinical Biochemistry Sep 1999
Review
Topics: C-Peptide; Humans; Immunoassay; Insulin; Proinsulin; Quality Control; Reference Standards
PubMed: 10505204
DOI: 10.1177/000456329903600501 -
Recent Progress in Hormone Research 1976
Review
Topics: Adenoma, Islet Cell; Amino Acid Sequence; C-Peptide; Diabetes Mellitus; Humans; Hypokalemia; Immunoassay; Insulin; Insulin Antibodies; Kidney; Pancreatic Neoplasms; Peptides; Proinsulin
PubMed: 198859
DOI: 10.1016/b978-0-12-571133-3.50017-9 -
FEBS Letters Jun 2013Dominant mutations in the human insulin gene can lead to pancreatic β-cell dysfunction and diabetes mellitus due to toxic folding of a mutant proinsulin. Analogous to a... (Review)
Review
Dominant mutations in the human insulin gene can lead to pancreatic β-cell dysfunction and diabetes mellitus due to toxic folding of a mutant proinsulin. Analogous to a classical mouse model (the Akita mouse), this monogenic syndrome highlights the susceptibility of human β-cells to endoreticular stress due to protein misfolding and aberrant aggregation. The clinical mutations directly or indirectly perturb native disulfide pairing. Whereas the majority of mutations introduce or remove a cysteine (leading in either case to an unpaired residue), non-cysteine-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the evolution of insulin has been constrained not only by its structure and function, but also by the susceptibility of its single-chain precursor to impaired foldability.
Topics: Animals; Cystine; Diabetes Mellitus; Humans; Models, Molecular; Mutation; Proinsulin; Protein Folding; Protein Structure, Tertiary; Proteostasis Deficiencies
PubMed: 23669362
DOI: 10.1016/j.febslet.2013.04.044