RESUMO
Biosynthesis of peptide hormones by pancreatic islet endocrine cells is a tightly orchestrated process that is critical for metabolic homeostasis. Like neuroendocrine peptides, insulin and other islet hormones are first synthesized as larger precursor molecules that are processed to their mature secreted products through a series of proteolytic cleavages, mediated by the prohormone convertases Pc1/3 and Pc2, and carboxypeptidase E. Additional posttranslational modifications including C-terminal amidation of the ß-cell peptide islet amyloid polypeptide (IAPP) by peptidyl-glycine α-amidating monooxygenase (Pam) may also occur. Genome-wide association studies (GWAS) have showed genetic linkage of these processing enzymes to obesity, ß-cell dysfunction, and type 2 diabetes (T2D), pointing to their important roles in metabolism and blood glucose regulation. In both type 1 diabetes (T1D) and T2D, and in the face of metabolic or inflammatory stresses, islet prohormone processing may become impaired; indeed elevated proinsulin:insulin (PI:I) ratios are a hallmark of the ß-cell dysfunction in T2D. Recent studies suggest that genetic or acquired defects in proIAPP processing may lead to the production and secretion of incompletely processed forms of proIAPP that could contribute to T2D pathogenesis, and additionally that impaired processing of both PI and proIAPP may be characteristic of ß-cell dysfunction in T1D. In islet α-cells, the prohormone proglucagon is normally processed to bioactive glucagon by Pc2 but may express Pc1/3 under certain conditions leading to production of GLP-1(7-36NH2 ). A better understanding of how ß-cell processing of PI and proIAPP, as well as α-cell processing of proglucagon, are impacted by genetic susceptibility and in the face of diabetogenic stresses, may lead to new therapeutic approaches for improving islet function in diabetes.
Assuntos
Carboxipeptidase H/fisiologia , Ilhotas Pancreáticas/metabolismo , Pró-Proteína Convertase 1/fisiologia , Pró-Proteína Convertase 2/fisiologia , Amidina-Liases/metabolismo , Células Secretoras de Glucagon/metabolismo , Humanos , Insulina/biossíntese , Células Secretoras de Insulina/metabolismo , Oxigenases de Função Mista/metabolismo , Proinsulina/metabolismoRESUMO
The proprotein convertases (PCs) are serine proteases responsible for the proteolytic maturation of many precursor proteins involved in upper airway remodelling during nasal polyposis. We have previously found that PC1/3 is expressed in human nasal mucosa. However, whether PC1/3 is related to nasal polyp formation has not been investigated. To gain insight into the functional role of PC1/3 in nasal polyps, we determined PC1/3 expression in nasal polyps by immunostaining, Western blotting and enzyme assays and generated stable cells expressing PC1/3 using airway epithelial cell line NCI-H292. Nasal polyps exhibit increased PC1/3 expression compared to normal nasal mucosa. PC1/3 was expressed in neuroendocrine cells in normal nasal mucosa and it was also expressed in goblet and ciliated cells in nasal polyps. NCI-H292 cells stably expressing PC1/3 displayed morphological changes, enhanced cell proliferation and migration, downregulation of E-cadherin and cytokeratins and upregulation of N-cadherin, vimentin, matrix metalloproteinase-2, collagen-I, snail and twist. Importantly, PC1/3 expression was positively correlated with epithelial-mesenchymal transition in cultured human nasal epithelial cells and in nasal polyps. Taken together, our data suggest that PC1/3 overexpression induces morphological and phenotypic epithelial-mesenchymal transition changes of airway epithelial cells and these changes may contribute to the pathogenesis of nasal polyps.
Assuntos
Células Epiteliais/citologia , Transição Epitelial-Mesenquimal , Epitélio/metabolismo , Regulação da Expressão Gênica , Pólipos Nasais/metabolismo , Pró-Proteína Convertase 1/fisiologia , Animais , Linhagem Celular , Perfilação da Expressão Gênica , Células Caliciformes/metabolismo , Humanos , Inflamação , Camundongos , Mucosa Nasal/metabolismo , Células Neuroendócrinas/citologia , Fenótipo , Sistema Respiratório/citologia , Sinusite/metabolismo , CicatrizaçãoRESUMO
Treatment of cultured bovine adrenal chromaffin cells with the catecholamine transport blocker reserpine was shown previously to increase enkephalin levels severalfold. To explore the biochemical mechanism of this effect, we examined the effect of reserpine treatment on the activities of three different peptide precursor processing enzymes: carboxypeptidase E (CPE) and the prohormone convertases (PCs) PC1/3 and PC2. Reserpine treatment increased both CPE and PC activity in extracts of cultured chromaffin cells; total protein levels were unaltered for any enzyme. Further analysis showed that the increase in CPE activity was due to an elevated V(max), with no change in the K(m) for substrate hydrolysis or the levels of CPE mRNA. Reserpine activation of endogenous processing enzymes was also observed in extracts prepared from PC12 cells stably expressing PC1/3 or PC2. In vitro experiments using purified enzymes showed that catecholamines inhibited CPE, PC1/3, and PC2, with dopamine quinone the most potent inhibitor (IC(50) values of â¼50-500 µM); dopamine, norepinephrine, and epinephrine exhibited inhibition in the micromolar range. The inhibition of purified CPE with catecholamines was time-dependent and, for dopamine quinone, dilution-independent, suggesting covalent modification of the protein by the catecholamine. Because the catecholamine concentrations found to be inhibitory to PC1/3, PC2, and CPE are well within the physiological range found in chromaffin granules, we conclude that catecholaminergic transmitter systems have the potential to exert considerable dynamic influence over peptidergic transmitter synthesis by altering the activity of peptide processing enzymes.
Assuntos
Carboxipeptidase H/fisiologia , Catecolaminas/fisiologia , Células Cromafins/enzimologia , Neuropeptídeos/metabolismo , Pró-Proteína Convertase 1/fisiologia , Pró-Proteína Convertase 2/fisiologia , Processamento de Proteína Pós-Traducional/fisiologia , Animais , Carboxipeptidase H/antagonistas & inibidores , Catecolaminas/farmacologia , Bovinos , Células Cultivadas , Células Cromafins/efeitos dos fármacos , Células PC12 , Pró-Proteína Convertase 1/antagonistas & inibidores , Pró-Proteína Convertase 2/antagonistas & inibidores , Processamento de Proteína Pós-Traducional/efeitos dos fármacos , Ratos , Reserpina/farmacologiaRESUMO
Most peptide hormone genes are, in addition to endocrine cells, also expressed in neurons. The peptide hormone cholecystokinin (CCK) is expressed in different molecular forms in cerebral neurons and intestinal endocrine cells. To understand this difference, we examined the roles of the neuroendocrine prohormone convertases (PC) 1/3, PC2, and PC5/6 by measurement of proCCK, processing intermediates and bioactive, alpha-amidated, and O-sulfated CCK peptides in cerebral and jejunal extracts of null mice, controls, and in the PC5/6-expressing SK-N-MC cell-line. In PC1/3 null mice, the synthesis of bioactive CCK peptide in the gut was reduced to 3% of the translational product, all of which was in the form of alpha-amidated and tyrosine O-sulfated CCK-22, whereas the neuronal synthesis in the brain was largely unaffected. This is opposite to the PC2 null mice in which only the cerebral synthesis was affected. SK-N-MC cells, which express neither PC1/3 nor PC2, synthesized alone the processing intermediate, glycine-extended CCK-22. Immunocytochemistry confirmed that intestinal endocrine CCK cells in wild-type mice express PC1/3 but not PC2. In contrast, cerebral CCK neurons contain PC2 and only little, if any, PC1/3. Taken together, the data indicate that PC1/3 governs the endocrine and PC2 the neuronal processing of proCCK, whereas PC5/6 contributes only to a modest endocrine synthesis of CCK-22. The results suggest that the different peptide patterns in the brain and the gut are due to different expression of PCs.
Assuntos
Encéfalo/metabolismo , Colecistocinina/biossíntese , Células Enteroendócrinas/metabolismo , Neurônios/metabolismo , Pró-Proteína Convertase 1/fisiologia , Pró-Proteína Convertase 2/fisiologia , Pró-Proteína Convertase 5/fisiologia , Animais , Linhagem Celular Tumoral , Humanos , Camundongos , Especificidade de Órgãos , Fragmentos de Peptídeos/biossínteseRESUMO
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.
Assuntos
Regulação Enzimológica da Expressão Gênica , Regulação da Expressão Gênica , Pró-Proteína Convertase 1/fisiologia , Animais , Linhagem Celular , Relação Dose-Resposta a Droga , Furina/química , Humanos , Insetos , Cinética , Camundongos , Peptídeos/química , Estrutura Terciária de Proteína , Proteínas Recombinantes/químicaRESUMO
Neural apoptosis-regulated convertase-1/proprotein convertase subtilisin-kexin like-9 (NARC-1/PCSK9) is a proprotein convertase recently described to play a major role in cholesterol homeostasis through enhanced degradation of the low-density lipoprotein receptor (LDLR) and possibly in neural development. Herein, we investigated the potential involvement of this proteinase in the development of the CNS using mouse embryonal pluripotent P19 cells and the zebrafish as models. Time course quantitative RT-PCR analyses were performed following retinoic acid (RA)-induced neuroectodermal differentiation of P19 cells. Accordingly, the mRNA levels of NARC-1/PCSK9 peaked at day 2 of differentiation and fell off thereafter. In contrast, the expression of the proprotein convertases subtilisin kexin isozyme 1/site 1 protease and Furin was unaffected by RA, whereas that of PC5/6 and PC2 increased within and/or after the first 4 days of the differentiation period respectively. This pattern was not affected by the cholesterogenic transcription factor sterol regulatory element-binding protein-2, which normally up-regulates NARC-1/PCSK9 mRNA levels in liver. Furthermore, in P19 cells, RA treatment did not affect the protein level of the endogenous LDLR. This agrees with the unique expression pattern of NARC-1/PCSK9 in the rodent CNS, including the cerebellum, where the LDLR is not significantly expressed. Whole-mount in situ hybridization revealed that the pattern of expression of zebrafish NARC-1/PCSK9 is similar to that of mouse both in the CNS and periphery. Specific knockdown of zebrafish NARC-1/PCSK9 mRNA resulted in a general disorganization of cerebellar neurons and loss of hindbrain-midbrain boundaries, leading to embryonic death at approximately 96 h after fertilization. These data support a novel role for NARC-1/PCSK9 in CNS development, distinct from that in cholesterogenic organs such as liver.
Assuntos
Sistema Nervoso/enzimologia , Sistema Nervoso/crescimento & desenvolvimento , Pró-Proteína Convertase 1/fisiologia , Serina Endopeptidases/fisiologia , Animais , Diferenciação Celular/fisiologia , Linhagem Celular Tumoral , Colesterol/biossíntese , Colesterol/genética , Humanos , Fígado/enzimologia , Camundongos , Sistema Nervoso/citologia , Sistema Nervoso/embriologia , Pró-Proteína Convertase 1/biossíntese , Pró-Proteína Convertase 1/genética , Pró-Proteína Convertase 9 , Pró-Proteína Convertases , Serina Endopeptidases/biossíntese , Serina Endopeptidases/deficiência , Serina Endopeptidases/genética , Peixe-ZebraRESUMO
The physiology of the incretin hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), and their role in type 2 diabetes currently attract great interest. Recently we reported an essential role for prohormone convertase (PC) 1/3 in the cleavage of intestinal proglucagon, resulting in formation of GLP-1, as demonstrated in PC1/3-deficient mice. However, little is known about the endoproteolytic processing of the GIP precursor. This study investigates the processing of proGIP in PC1/3 and PC2 null mice and in cell lines using adenovirus-mediated overexpression. Supporting a role for PC1/3 in proGIP processing, we found co-localization of GIP and PC1/3 but not PC2 in intestinal sections by immunohistochemistry, and analysis of intestinal extracts from PC1/3-deficient animals demonstrated severely impaired processing to GIP, whereas processing to GIP was unaltered in PC2-deficient mice. Accordingly, overexpression of preproGIP in the neuroendocrine AtT-20 cell line that expresses high levels of endogenous PC1/3 and negligible levels of PC2 resulted in production of GIP. Similar results were obtained after co-expression of preproGIP and PC1/3 in GH4 cells that express no PC2 and only low levels of PC1/3. In addition, studies in GH4 cells and the alpha-TC1.9 cell line, expressing PC2 but not PC1/3, indicate that PC2 can mediate processing to GIP but also to other fragments not found in intestinal extracts. Taken together, our data indicate that PC1/3 is essential and sufficient for the production of the intestinal incretin hormone GIP, whereas PC2, although capable of cleaving proGIP, does not participate in intestinal proGIP processing and is not found in intestinal GIP-expressing cells.
Assuntos
Polipeptídeo Inibidor Gástrico/fisiologia , Glucose/metabolismo , Insulina/metabolismo , Pró-Proteína Convertase 1/fisiologia , Adenoviridae/genética , Adenoviridae/metabolismo , Animais , Células COS , Linhagem Celular , Células Cultivadas , Chlorocebus aethiops , Cromatografia em Gel , Cromatografia Líquida de Alta Pressão , AMP Cíclico/metabolismo , DNA Complementar/metabolismo , Relação Dose-Resposta a Droga , Citometria de Fluxo , Polipeptídeo Inibidor Gástrico/metabolismo , Vetores Genéticos , Imuno-Histoquímica , Mucosa Intestinal/metabolismo , Camundongos , Camundongos Transgênicos , Modelos Genéticos , Peptídeos/química , Reação em Cadeia da Polimerase , Pró-Proteína Convertases/metabolismo , RNA/metabolismo , RNA Mensageiro/metabolismo , Radioimunoensaio , Ratos , Receptores dos Hormônios Gastrointestinais/metabolismo , Proteínas Recombinantes/químicaRESUMO
Agouti-related protein (AGRP) plays a key role in energy homeostasis. The carboxyl-terminal domain of AGRP acts as an endogenous antagonist of the melanocortin-4 receptor (MC4-R). It has been suggested that the amino-terminal domain of AGRP binds to syndecan-3, thereby modulating the effects of carboxyl-terminal AGRP at the MC4-R. This model assumes that AGRP is secreted as a full-length peptide. In this study we found that AGRP is processed intracellularly after Arg(79)-Glu(80)-Pro(81)-Arg(82). The processing site suggests cleavage by proprotein convertases (PCs). RNA interference and overexpression experiments showed that PC1/3 is primarily responsible for cleavage in vitro, although both PC2 and PC5/6A can also process AGRP. Dual in situ hybridization demonstrated that PC1/3 is expressed in AGRP neurons in the rat hypothalamus. Moreover, hypothalamic extracts from PC1-null mice contained 3.3-fold more unprocessed full-length AGRP, compared with wild-type mice, based on combined HPLC and RIA analysis, demonstrating that PC1/3 plays a role in AGRP cleavage in vivo. We also found that AGRP(83-132) is more potent an antagonist than full-length AGRP, based on cAMP reporter assays, suggesting that posttranslational cleavage is required to potentiate the effect of AGRP at the MC4-R. Because AGRP is cleaved into distinct amino-terminal and carboxyl-terminal peptides, we tested whether amino-terminal peptides modulate food intake. However, intracerebroventricular injection of rat AGRP(25-47) and AGRP(50-80) had no effect on body weight, food intake, or core body temperature. Because AGRP is cleaved before secretion, syndecan-3 must influence food intake independently of the MC4-R.
Assuntos
Glicoproteínas de Membrana/fisiologia , Fragmentos de Peptídeos/metabolismo , Pró-Proteína Convertase 1/fisiologia , Processamento de Proteína Pós-Traducional , Proteoglicanas/fisiologia , Receptor Tipo 4 de Melanocortina/fisiologia , Proteína Relacionada com Agouti , Animais , Metabolismo Energético/efeitos dos fármacos , Hipotálamo/metabolismo , Peptídeos e Proteínas de Sinalização Intercelular , Masculino , Hormônios Peptídicos/farmacologia , Ratos , Ratos Sprague-Dawley , Sindecana-3RESUMO
Rat prothyrotropin-releasing hormone (pro-TRH) is endoproteolyzed within the regulated secretory pathway of neuroendocrine cells yielding five TRH peptides and seven to nine other unique peptides. Endoproteolysis is performed by two prohormone convertases, PC1 and PC2. Proteolysis of pro-TRH begins in the trans-Golgi network and forms two intermediates that are then differentially processed as they exit the Golgi and are packaged into immature secretory granules. We hypothesized that this initial endoproteolysis may be necessary for downstream sorting of pro-TRH-derived peptides as it occurs before Golgi exit and thus entry into the regulated secretory pathway. We now report that when pro-TRH is transiently expressed in GH4C1 cells, a neuroendocrine cell line lacking PC1, under pulse-chase conditions release is constitutive and composed of more immature processing intermediates. This is also observed by radioimmunoassay under steady-state conditions. When a mutant form of pro-TRH, which has the dibasic sites of initial processing mutated to glycines, is expressed in AtT20 cells, a neuroendocrine cell line endogenously expressing PC1, both steady-state and pulse-chase experiments revealed that peptides derived from this mutant precursor are secreted in a constitutive fashion. A constitutively secreted form of PC1 does not target pro-TRH peptides to the constitutive secretory pathway but results in sorting to the regulated secretory pathway. These results indicated that initial processing action of PC1 on pro-TRH in the trans-Golgi network, and not a cargo-receptor relationship, is important for the downstream sorting events that result in storage of pro-TRH-derived peptides in mature secretory granules.
Assuntos
Complexo de Golgi/metabolismo , Peptídeos/química , Pró-Proteína Convertase 1/fisiologia , Precursores de Proteínas/química , Hormônio Liberador de Tireotropina/química , Animais , Anticorpos Monoclonais/química , Linhagem Celular , Meios de Cultivo Condicionados/farmacologia , Epitopos/química , Glicina/química , Imuno-Histoquímica , Imunoprecipitação , Microscopia Confocal , Modelos Genéticos , Mutação , Sistemas Neurossecretores/metabolismo , Plasmídeos/metabolismo , Pró-Proteína Convertase 1/química , Pró-Proteína Convertase 2/química , Radioimunoensaio , Ratos , Vesículas Secretórias/química , Vesículas Secretórias/metabolismo , Transfecção , Rede trans-Golgi/metabolismoRESUMO
Islet amyloid polypeptide (IAPP; amylin) is a peptide hormone that is cosecreted with insulin from beta-cells. Impaired processing of proIAPP, the IAPP precursor, has been implicated in islet amyloid formation in type 2 diabetes. We previously showed that proIAPP is processed to IAPP by the prohormone convertases PC1/3 and PC2 at its carboxyl (COOH) and amino (NH(2)) termini, respectively. In this study, we investigated the role of carboxypeptidase E (CPE) in the processing of proIAPP using mice lacking active CPE (Cpe(fat)/Cpe(fat)) and NIT-2 cells, a beta-cell line derived from their islets. Western blot analysis demonstrated that an approximately 6-kDa NH(2)-terminally unprocessed form of proIAPP was elevated approximately 86% in islets from Cpe(fat)/Cpe(fat) mice, compared with wild type. This increase was independent of the development of hyperglycemia (8 wk male) or obesity (18 wk female). Impaired proIAPP processing was associated with a decrease in PC2 (but not PC1/3) and both the 21- and 27-kDa forms of the PC2 chaperone protein 7B2, suggesting that PC2-mediated processing of proIAPP at its NH(2) terminus was impaired in the absence of CPE. Formation of COOH-terminally amidated (pro)IAPP was reduced approximately 75% in NIT-2, compared with NIT-1 beta-cells, supporting a direct role for CPE in maturation of IAPP by removal of its COOH-terminal dibasic residues, the step essential for IAPP amidation. We conclude that lack of CPE in islet beta-cells results in a marked decrease in processing of proIAPP at its NH(2) (but not COOH) terminus that is associated with attenuated levels of PC2 and (pro)7B2 and a great reduction in formation of mature amidated IAPP.
Assuntos
Amiloide/metabolismo , Carboxipeptidase H/fisiologia , Ilhotas Pancreáticas/metabolismo , Animais , Linhagem Celular , Feminino , Masculino , Camundongos , Pró-Proteína Convertase 1/fisiologia , Pró-Proteína Convertase 2/fisiologiaRESUMO
Islet amyloid polypeptide (IAPP) (amylin), the major component of islet amyloid, is produced by cleavage at the COOH- and NH(2)-termini of its precursor, proIAPP, likely by the beta-cell prohormone convertases (PC) 1/3 and PC2. Mice lacking PC2 can process proIAPP at its COOH- but not its NH(2)-terminal cleavage site, suggesting that PC1/3 is capable of initiating proIAPP cleavage at its COOH-terminus. To determine the precise role of PC1/3 in proIAPP processing, Western blot analysis was performed on islets isolated from mice lacking PC1/3 (PC1/3(-/-)). These islets contained not only fully processed IAPP as in PC1/3(+/+) islets, but also elevated levels of a COOH-terminally unprocessed intermediate form, suggesting impaired processing at the COOH-terminus. Next, GH3 cells that do not normally express proIAPP or detectable levels of PC1/3 or PC2 were cotransduced with adenoviruses expressing rat proIAPP and either PC2 or PC1/3. As expected, in GH3 cells transduced to express only proIAPP, no processing was observed. Coexpression of proIAPP and PC2 resulted in production of mature IAPP, whereas in cells that coexpressed proIAPP and PC1/3 only a 6-kDa intermediate was produced. We conclude that PC1/3 is important for processing of proIAPP at the COOH-terminus, but in its absence, PC2 can initiate complete processing of proIAPP to IAPP by cleaving the precursor at either its NH(2)- or COOH-terminal cleavage sites.