Cloning and sequence analysis of cDNA for bovine carboxypeptidase E

Peptides derived from growth factors: Exploring their diverse impact from antimicrobial properties to neuroprotection

Growth factor-derived peptides are bioactive molecules that play a crucial role in various physiological processes within the human body. Over the years, extensive research has revealed their diverse applications, ranging from antimicrobial properties to their potential in neuroprotection and treating various diseases. These peptides exhibit innate immune responses and have been found to possess potent antimicrobial properties against a wide range of pathogens. Growth factor-derived peptides have demonstrated the ability to promote neuronal survival, prevent cell death, and stimulate neural regeneration. As a result, they hold immense promise in the treatment of various neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis, as well as in the management of traumatic brain injuries. Moreover, growth factor-derived peptides have shown potential for supporting tissue repair and wound healing processes. By enhancing cell proliferation and migration, these peptides contribute to the regeneration of damaged tissues and promote a more efficient healing response. The applications of growth factor-derived peptides extend beyond their therapeutic potential in health; they also have a role in various disease conditions. For example, researchers have explored their influence on cancer cells, where some peptides have demonstrated anti-cancer properties, inhibiting tumor growth and promoting apoptosis in cancer cells. Additionally, their immunomodulatory properties have been investigated for potential applications in autoimmune disorders. Despite the immense promise shown by growth factor-derived peptides, some challenges need to be addressed. Nevertheless, ongoing research and advancements in biotechnology offer promising avenues to overcome these obstacles. The review summarizes the foundational biology of growth factors and the intricate signaling pathways in various physiological processes as well as diseases such as cancer, neurodegenerative disorders, cardiovascular ailments, and metabolic syndromes.

Peptidomic Analysis Reveals Seasonal Neuropeptide and Peptide Hormone Changes in the Hypothalamus and Pituitary of a Hibernating Mammal

During the winter, hibernating mammals undergo extreme changes in physiology, which allow them to survive several months without access to food. These animals enter a state of torpor, which is characterized by decreased metabolism, near-freezing body temperatures, and a dramatically reduced heart rate. The neurochemical basis of this regulation is largely unknown. Based on prior evidence suggesting that the peptide-rich hypothalamus plays critical roles in hibernation, we hypothesized that changes in specific cell-cell signaling peptides (neuropeptides and peptide hormones) underlie physiological changes during torpor/arousal cycles. To test this hypothesis, we used a mass spectrometry-based peptidomics approach to examine seasonal changes of endogenous peptides that occur in the hypothalamus and pituitary of a model hibernating mammal, the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). In the pituitary, we observed changes in several distinct peptide hormones as animals prepared for torpor in October, exited torpor in March, and progressed from spring (March) to fall (August). In the hypothalamus, we observed an overall increase in neuropeptides in October (pre-torpor), a decrease as the animal entered torpor, and an increase in a subset of neuropeptides during normothermic interbout arousals. Notable changes were observed for feeding regulatory peptides, opioid peptides, and several peptides without well-established functions. Overall, our study provides critical insight into changes in endogenous peptides in the hypothalamus and pituitary during mammalian hibernation that were not available from transcriptomic measurements. Understanding the molecular basis of the hibernation phenotype may pave the way for future efforts to employ hibernation-like strategies for organ preservation, combating obesity, and treatment of stroke.

Mice heterozygous for a null mutation of Cpe show reduced expression of carboxypeptidase E mRNA and enzyme activity but normal physiology, behavior, and levels of neuropeptides

Carboxypeptidase E (CPE) is an essential enzyme that contributes to the biosynthesis of the vast majority of neuropeptides and peptide hormones. There are several reports claiming that small decreases in CPE activity cause physiological changes in animals and/or cultured cells, but these studies did not provide evidence that neuropeptide levels were affected by decreased CPE activity. In the present study, we tested if CPE is a rate-limiting enzyme in neuropeptide production using CpeNeo mice, which contain a neomycin cassette within the Cpe gene that eliminates enzyme expression. Homozygous CpeNeo/Neo mice show defects found in Cpe^fat/fat and/or Cpe global knockout (KO) mice, including greatly decreased levels of most neuropeptides, severely impaired fertility, depressive-like behavior, adult-onset obesity, and anxiety-like behavior. Removal of the neomycin cassette with Flp recombinase under a germline promoter restored expression of CPE activity and resulted in normal behavioral and physiological properties, including levels of neuropeptides. Mice heterozygous for the CpeNeo allele have greatly reduced levels of Cpe mRNA and CPE-like enzymatic activity. Despite the decreased levels of Cpe expression, heterozygous CpeNeo mice are behaviorally and physiologically identical to wild-type mice, with normal levels of most neuropeptides. These results indicate that CPE is not a rate-limiting enzyme in the production of most neuropeptides, casting doubt upon studies claiming small decreases in CPE activity contribute to obesity or other physiological effects.

BDV Syndrome: An Emerging Syndrome With Profound Obesity and Neurodevelopmental Delay Resembling Prader-Willi Syndrome

CONTEXT

CPE encodes carboxypeptidase E, an enzyme that converts proneuropeptides and propeptide hormones to bioactive forms. It is widely expressed in the endocrine and central nervous system. To date, 4 individuals from 2 families with core clinical features including morbid obesity, neurodevelopmental delay, and hypogonadotropic hypogonadism, harboring biallelic loss-of-function (LoF) CPE variants, have been reported.

OBJECTIVE

We describe 4 affected individuals from 3 unrelated consanguineous families, 2 siblings of Syrian, 1 of Egyptian, and 1 of Pakistani descent, all harboring novel homozygous CPE LoF variants.

METHODS

After excluding Prader-Willi syndrome (PWS), exome sequencing was performed in both Syrian siblings. The variants identified in the other 2 individuals were reported as research variants in a large-scale exome study and in the ClinVar database. Computational modeling of all possible missense alterations allowed assessing CPE tolerance to missense variants.

RESULTS

All affected individuals were severely obese with neurodevelopmental delay and other endocrine anomalies. Three individuals from 2 families shared the same CPE homozygous truncating variant c.361C > T, p.(Arg121*), while the fourth carried the c.994del, p.(Ser333Alafs*22) variant. Comparison of clinical features with previously described cases and standardization according to the Human Phenotype Ontology terms indicated a recognizable clinical phenotype, which we termed Blakemore-Durmaz-Vasileiou (BDV) syndrome. Computational analysis indicated high conservation of CPE domains and intolerance to missense changes.

CONCLUSION

Biallelic truncating CPE variants are associated with BDV syndrome, a clinically recognizable monogenic recessive syndrome with childhood-onset obesity, neurodevelopmental delay, hypogonadotropic hypogonadism, and hypothyroidism. BDV syndrome resembles PWS. Our findings suggest missense variants may also be clinically relevant.

Identifying Receptors for Neuropeptides and Peptide Hormones: Challenges and Recent Progress

Intercellular signaling events mediated by neuropeptides and peptide hormones represent important targets for both basic science and drug discovery. For many bioactive peptides, the protein receptors that transmit information across the receiving cell membrane are not known, severely limiting these signaling pathways as potential therapeutic targets. Identifying the receptor(s) for a given peptide of interest is complicated by several factors. Most notably, cell-cell signaling peptides are generated through dynamic biosynthetic pathways, can act on many different families of receptor proteins, and can participate in complex ligand-receptor interactions that extend beyond a simple one-to-one archetype. Here, we discuss recent methodological advances to identify signaling partners for bioactive peptides. Recent efforts have centered on methods to identify candidate receptors via transcript expression, methods to match peptide-receptor pairs through high throughput screening, and methods to capture direct ligand-receptor interactions using chemical probes. Future applications of the receptor identification approaches discussed here, as well as technical advancements to address their limitations, promise to lead to a greater understanding of how cells communicate to deliver complex physiologies. Importantly, such advancements will likely provide novel targets for the treatment of human diseases within the central nervous and endocrine systems.

Brain-Derived Neurotrophic Factor (BDNF): Novel Insights into Regulation and Genetic Variation

Since its discovery, brain-derived neurotrophic factor (BDNF) has spawned a literature that now spans 35 years of research. While all neurotrophins share considerable overlap in sequence homology and their processing, BDNF has become the most widely studied neurotrophin because of its broad roles in brain homeostasis, health, and disease. Although research on BDNF has produced thousands of articles, there remain numerous long-standing questions on aspects of BDNF molecular biology and signaling. Here we provide a comprehensive review, including both a historical narrative and a forward-looking perspective on advances in the actions of BDNF within the brain. We specifically review BDNF’s gene structure, peptide composition (including domains, posttranslational modifications and putative motif sites), mechanisms of transport, signaling pathway recruitment, and other recent developments including the functional effects of genetic variation and the discovery of a new BDNF prodomain ligand. This body of knowledge illustrates a highly conserved and complex role for BDNF within the brain, that promotes the idea that the neurotrophin biology of BDNF is diverse and that any disease involvement is likely to be equally multifarious.

Mass Spectrometry Profiling of Pituitary Glands

Many chronic diseases are associated with hypothalamic-pituitary-adrenal axis dysfunction. Therefore, proteomic profiling of the pituitary gland has potential to uncover new information on the underlying pathways affected in these conditions. This could lead to identification of new biomarkers or drug targets for development of novel therapeutics. Here we present a protocol for preparation of pituitary protein extracts and analysis of the major hormones and accessory proteins using liquid chromatography tandem mass spectrometry (LC-MS/MS). The same methods can be applied in the study of other tissues of the diffuse neuroendocrine system.

Computational and structural evidence for neurotransmitter-mediated modulation of the oligomeric states of human insulin in storage granules

Human insulin is a pivotal protein hormone controlling metabolism, growth, and aging and whose malfunctioning underlies diabetes, some cancers, and neurodegeneration. Despite its central position in human physiology, the in vivo oligomeric state and conformation of insulin in its storage granules in the pancreas are not known. In contrast, many in vitro structures of hexamers of this hormone are available and fall into three conformational states: T6, T3Rf3, and R6 As there is strong evidence for accumulation of neurotransmitters, such as serotonin and dopamine, in insulin storage granules in pancreatic β-cells, we probed by molecular dynamics (MD) and protein crystallography (PC) if these endogenous ligands affect and stabilize insulin oligomers. Parallel studies independently converged on the observation that serotonin binds well within the insulin hexamer (site I), stabilizing it in the T3R3 conformation. Both methods indicated serotonin binding on the hexamer surface (site III) as well. MD, but not PC, indicated that dopamine was also a good site III ligand. Some of the PC studies also included arginine, which may be abundant in insulin granules upon processing of pro-insulin, and stable T3R3 hexamers loaded with both serotonin and arginine were obtained. The MD and PC results were supported further by in solution spectroscopic studies with R-state-specific chromophore. Our results indicate that the T3R3 oligomer is a plausible insulin pancreatic storage form, resulting from its complex interplay with neurotransmitters, and pro-insulin processing products. These findings may have implications for clinical insulin formulations.

Dissecting carboxypeptidase E: properties, functions and pathophysiological roles in disease

Since discovery in 1982, carboxypeptidase E (CPE) has been shown to be involved in the biosynthesis of a wide range of neuropeptides and peptide hormones in endocrine tissues, and in the nervous system. This protein is produced from pro-CPE and exists in soluble and membrane forms. Membrane CPE mediates the targeting of prohormones to the regulated secretory pathway, while soluble CPE acts as an exopeptidase and cleaves C-terminal basic residues from peptide intermediates to generate bioactive peptides. CPE also participates in protein internalization, vesicle transport and regulation of signaling pathways. Therefore, in two types of CPE mutant mice, Cpe^fat/Cpe^fat and Cpe knockout, loss of normal CPE leads to a lot of disorders, including diabetes, hyperproinsulinemia, low bone mineral density and deficits in learning and memory. In addition, the potential roles of CPE and ΔN-CPE, an N-terminal truncated form, in tumorigenesis and diagnosis were also addressed. Herein, we focus on dissecting the pathophysiological roles of CPE in the endocrine and nervous systems, and related diseases.

Unraveling the aggregation propensity of human insulin C-peptide

Over the last 20 years, proinsulin C-peptide emerged as an important player in various biological events. Much time and effort has been spent in exploring all functional features of C-peptide and recording its implications in Diabetes mellitus. Only a few studies, though, have addressed C-peptide oligomerization and link this procedure with Diabetes. The aim of our work was to examine the aggregation propensity of C-peptide, utilizing Transmission Electron Microscopy, Congo Red staining, ATR-FTIR, and X-ray fiber diffraction at a 10 mg ml^-1 concentration. Our experimental work clearly shows that C-peptide self-assembles into amyloid-like fibrils and therefore, the aggregation propensity of C-peptide is a characteristic novel feature that should be related to physiological and also pathological conditions. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 108: 1-8, 2017.

Proteomic Profiling of the Pituitary Gland in Studies of Psychiatric Disorders

Psychiatric disorders have been associated with perturbations of the hypothalamic-pituitary-adrenal axis. Therefore, proteomic studies of the pituitary gland have the potential to provide new insights into the underlying pathways affected in these conditions as well as identify new biomarkers or targets for use in developing improved medications. This chapter describes a protocol for preparation of pituitary protein extracts followed by characterization of the pituitary proteome by label-free liquid chromatography-tandem mass spectrometry in expression mode (LC-MS^E). The main focus was on establishing a method for identifying the major pituitary hormones and accessory proteins as many of these have already been implicated in psychiatric diseases.

Genome-Wide Association Study between Single Nucleotide Polymorphisms and Flight Speed in Nellore Cattle

Introduction

Cattle temperament is an important factor that affects the profitability of beef cattle enterprises, due to its relationship with productivity traits, animal welfare and labor safety. Temperament is a complex phenotype often assessed by measuring a series of behavioral traits, which result from the effects of multiple environmental and genetic factors, and their interactions. The aims of this study were to perform a genome-wide association study and detect genomic regions, potential candidate genes and their biological mechanisms underlying temperament, measured by flight speed (FS) test in Nellore cattle.

Materials and Methods

The genome-wide association study (GWAS) was performed using a single-step procedure (ssGBLUP) which combined simultaneously all 16,600 phenotypes from genotyped and non-genotyped animals, full pedigree information of 162,645 animals and 1,384 genotyped animals in one step. The animals were genotyped with High Density Bovine SNP BeadChip which contains 777,962 SNP markers. After quality control (QC) a total of 455,374 SNPs remained.

Results

Heritability estimated for FS was 0.21 ± 0.02. Consecutive SNPs explaining 1% or more of the total additive genetic variance were considered as windows associated with FS. Nine candidate regions located on eight different Bos taurus chromosomes (BTA) (1 at 73 Mb, 2 at 65 Mb, 5 at 22 Mb and 119 Mb, 9 at 98 Mb, 11 at 67 Mb, 15 at 16 Mb, 17 at 63 Kb, and 26 at 47 Mb) were identified. The candidate genes identified in these regions were NCKAP5 (BTA2), PARK2 (BTA9), ANTXR1 (BTA11), GUCY1A2 (BTA15), CPE (BTA17) and DOCK1 (BTA26). Among these genes PARK2, GUCY1A2, CPE and DOCK1 are related to dopaminergic system, memory formation, biosynthesis of peptide hormone and neurotransmitter and brain development, respectively.

Conclusions

Our findings allowed us to identify nine genomic regions (SNP windows) associated with beef cattle temperament, measured by FS test. Within these windows, six promising candidate genes and their biological functions were identified. These results may contribute to a better comprehension into the genetic control of temperament expression in Nellore cattle.

INS-gene mutations: from genetics and beta cell biology to clinical disease

A growing list of insulin gene mutations causing a new form of monogenic diabetes has drawn increasing attention over the past seven years. The mutations have been identified in the untranslated regions of the insulin gene as well as the coding sequence of preproinsulin including within the signal peptide, insulin B-chain, C-peptide, insulin A-chain, and the proteolytic cleavage sites both for signal peptidase and the prohormone convertases. These mutations affect a variety of different steps of insulin biosynthesis in pancreatic beta cells. Importantly, although many of these mutations cause proinsulin misfolding with early onset autosomal dominant diabetes, some of the mutant alleles appear to engage different cellular and molecular mechanisms that underlie beta cell failure and diabetes. In this article, we review the most recent advances in the field and discuss challenges as well as potential strategies to prevent/delay the development and progression of autosomal dominant diabetes caused by INS-gene mutations. It is worth noting that although diabetes caused by INS gene mutations is rare, increasing evidence suggests that defects in the pathway of insulin biosynthesis may also be involved in the progression of more common types of diabetes. Collectively, the (pre)proinsulin mutants provide insightful molecular models to better understand the pathogenesis of all forms of diabetes in which preproinsulin processing defects, proinsulin misfolding, and ER stress are involved.

Proinsulin entry and transit through the endoplasmic reticulum in pancreatic beta cells

Insulin is an essential hormone for maintaining metabolic homeostasis in the body. To make fully bioactive insulin, pancreatic beta cells initiate synthesis of the insulin precursor, preproinsulin, at the cytosolic side of the endoplasmic reticulum (ER), whereupon it undergoes co- and post-translational translocation across the ER membrane. Preproinsulin is cleaved by signal peptidase to form proinsulin that folds on the luminal side of the ER, forming three evolutionarily conserved disulfide bonds. Properly folded proinsulin forms dimers and exits from the ER, trafficking through Golgi complex into immature secretory granules wherein C-peptide is endoproteolytically excised, allowing fully bioactive two-chain insulin to ultimately be stored in mature granules for insulin secretion. Although insulin biosynthesis has been intensely studied in recent decades, the earliest events, including proinsulin entry and exit from the ER, have been relatively understudied. However, over the past 5 years, more than 20 new insulin gene mutations have been reported to cause a new syndrome termed Mutant INS-gene-induced Diabetes of Youth (MIDY). Although these mutants have not been completely characterized, most of them affect proinsulin entry and exit from the ER. Here, we summarize our current knowledge about the early events of insulin biosynthesis and review recent advances in understanding how defects in these events may lead to pancreatic beta cell failure.

Studies on the regioselectivity and kinetics of the action of trypsin on proinsulin and its derivatives using mass spectrometry

Human M-proinsulin was cleaved by trypsin at the R(31)R(32)-E(33) and K(64)R(65)-G(66) bonds (B/C and C/A junctions), showing the same cleavage specificity as exhibited by prohormone convertases 1 and 2 respectively. Buffalo/bovine M-proinsulin was also cleaved by trypsin at the K(59)R(60)-G(61) bond but at the B/C junction cleavage occurred at the R(31)R(32)-E(33) as well as the R(31)-R(32)E(33) bond. Thus, the human isoform in the native state, with a 31 residue connecting C-peptide, seems to have a unique structure around the B/C and C/A junctions and cleavage at these sites is predominantly governed by the structure of the proinsulin itself. In the case of both the proinsulin species the cleavage at the B/C junction was preferred (65%) over that at the C/A junction (35%) supporting the earlier suggestion of the presence of some form of secondary structure at the C/A junction. Proinsulin and its derivatives, as natural substrates for trypsin, were used and mass spectrometric analysis showed that the k(cat.)/K(m) values for the cleavage were most favourable for the scission of the bonds at the two junctions (1.02±0.08×10(5)s(-1)M(-1)) and the cleavage of the K(29)-T(30) bond of M-insulin-RR (1.3±0.07×10(5)s(-1)M(-1)). However, the K(29)-T(30) bond in M-insulin, insulin as well as M-proinsulin was shielded from attack by trypsin (k(cat.)/K(m) values around 1000s(-1)M(-1)). Hence, as the biosynthetic path follows the sequence; proinsulin→insulin-RR→insulin, the K(29)-T(30) bond becomes shielded, exposed then shielded again respectively.

New roles of carboxypeptidase E in endocrine and neural function and cancer

Carboxypeptidase E (CPE) or carboxypeptidase H was first discovered in 1982 as an enkephalin-convertase that cleaved a C-terminal basic residue from enkephalin precursors to generate enkephalin. Since then, CPE has been shown to be a multifunctional protein that subserves many essential nonenzymatic roles in the endocrine and nervous systems. Here, we review the phylogeny, structure, and function of CPE in hormone and neuropeptide sorting and vesicle transport for secretion, alternative splicing of the CPE transcript, and single nucleotide polymorphisms in humans. With this and the analysis of mutant and knockout mice, the data collectively support important roles for CPE in the modulation of metabolic and glucose homeostasis, bone remodeling, obesity, fertility, neuroprotection, stress, sexual behavior, mood and emotional responses, learning, and memory. Recently, a splice variant form of CPE has been found to be an inducer of tumor growth and metastasis and a prognostic biomarker for metastasis in endocrine and nonendocrine tumors.

Adventures with insulin in the islets of Langerhans

Insulin is a small but beautifully organized protein with a unique two-chain structure, the first protein to be sequenced. The mechanism of its biosynthesis invited much initial speculation but was finally clarified by the discovery of proinsulin, its single-chain precursor. The rich present-day field of protein precursor processing via post-translational proteolysis within the secretory pathway arose in the early 1970s as an offshoot of studies on insulin biosynthesis, which provided a novel paradigm for the generation of many other small neuroendocrine peptides. Before long, this mechanism was also found to play a role in the production of a much wider spectrum of proteins traversing the secretory pathway (receptors, growth factors, blood-clotting components, and even many viral envelope proteins) occurring in almost all eukaryotic cells. Indeed, yeast provided a key clue in the search for the proprotein convertases, the endoproteases that work along with carboxypeptidases and other modifying enzymes, such as the amidating enzyme complex (PAM), in converting inactive or less active precursor proteins into their fully active peptide products. In this "Reflections" article, I have tried to recount the people and events in my life that led to my involvement first in basic biochemical research and then on to insulin, proinsulin, and many relevant related areas that continue to fascinate and challenge my colleagues and me, as well as many other biomedical scientists today, as diabetes mellitus increasingly threatens human health throughout our contemporary world.

On the discovery of precursor processing

Studies of the biosynthesis of insulin in a human insulinoma beginning in 1965 provided the first evidence for a precursor of insulin, the first such prohormone to be identified. Further studies with isolated rat islets then confirmed that the precursor became labeled more rapidly than insulin and later was converted to insulin by a proteolytic processing system located mainly within the secretory granules of the beta cell and was then stored or secreted. The precursor was designated "proinsulin" in 1967 and was isolated and sequenced from beef and pork sources. These structural studies confirmed that the precursor was a single polypeptide chain which began with the B chain of insulin, continued through a connecting segment of 30-35 amino acids and terminated with the A chain. Paired basic residues were identified at the sites of excision of the C-peptide. Human proinsulin and C-peptide were then similarly obtained and sequenced. The human C-peptide assay was developed and provided a useful tool for measuring insulin levels indirectly in diabetics treated with insulin. The discovery of other precursor proteins for a variety of peptide hormones, neuropeptides, or plasma proteins then followed, with all having mainly dibasic cleavage sites for processing. The subsequent discovery of a similar biosynthetic pathway in yeast led to the identification of eukaryotic families of specialized processing subtilisin-like endopeptidases coupled with carboxypeptidase B-like exopeptidases. Most neuroendocrine peptides are processed by two specialized members of this family - PC2 and/or PC1/3 - followed by carboxypeptidase E (CPE). This brief report concentrates mainly on the role of insulin biosynthesis in providing a useful early paradigm of precursor processing in the secretory pathway.

Neurotensin and neuromedin N are differentially processed from a common precursor by prohormone convertases in tissues and cell lines

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six amino acid NT-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by specialized endoproteases that belong to the family of proprotein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Processing gives rise mainly to NT and NN in the brain, NT and a large peptide with a C-terminal NN moiety (large NN) in the gut, and NT, large NN, and a large peptide with a C-terminal NT moiety (large NT) in the adrenals. Recent evidence indicates that PC1, PC2, and PC5-A are the prohormone convertases responsible for the processing patterns observed in the gut, brain, and adrenals, respectively. As NT, NN, large NT, and large NN are all endowed with biological activity, the evidence reviewed here supports the idea that posttranslational processing of pro-NT/NN in tissues may generate biological diversity of pathophysiological relevance.

Carboxypeptidase E knockout mice exhibit abnormal dendritic arborization and spine morphology in central nervous system neurons

Carboxypeptidase E (CPE) is involved in maturation of neuropeptides and sorting of brain-derived neurotrophic factor (BDNF) to the regulated pathway for activity-dependent secretion from CNS neurons. CPE knockout (CPE-KO) mice have many neurological deficits, including deficits in learning and memory. Here, we analyzed the dendritic arborization and spine morphology of CPE-KO mice to determine a possible correlation of defects in such structures with the neurological deficits observed in these animals. Analysis of pyramidal neurons in layer V of cerebral cortex and in hippocampal CA1 region in 14-week-old CPE-KO mice showed more dendritic complexity compared with wild type (WT) mice. There were more dendritic intersections and more branch points in CPE-KO vs. WT neurons. Comparison of pyramidal cortical neurons in 6- vs. 14-week-old WT mice showed a decrease in dendritic arborization, reflecting the occurrence of normal dendritic pruning. However, this did not occur in CPE-KO neurons. Furthermore, analysis of spine morphology demonstrated a significant increase in the number of D-type spines regarded as nonfunctional in the cortical neurons of CPE-KO animals. Our findings suggest that CPE is an important, novel player in mediating appropriate dendritic patterning and spine formation in CNS neurons.

(Pro)Insulin processing: a historical perspective

Insulin, the major secreted product of the beta-cells of the islets of Langerhans, is initially synthesized as a precursor (preproinsulin), from which the mature hormone is excised by a series of proteolytic cleavages. This review provides a personal narrative of some of the key research projects leading to the identification of the central processing enzymes as proprotein convertase 1, proprotein convertase 2, and carboxypeptidase E. It also discusses the central roles of the intragranular environment and chaperone-like proteins in modulating processing activity.

Characterization of gene expression profiles for different types of mast cells pooled from mouse stomach subregions by an RNA amplification method

Background

Mast cells (MCs) play pivotal roles in allergy and innate immunity and consist of heterogenous subclasses. However, the molecular basis determining the different characteristics of these multiple MC subclasses remains unclear.

Results

To approach this, we developed a method of RNA extraction/amplification for intact in vivo MCs pooled from frozen tissue sections, which enabled us to obtain the global gene expression pattern of pooled MCs belonging to the same subclass. MCs were isolated from the submucosa (sMCs) and mucosa (mMCs) of mouse stomach sections, respectively, 15 cells were pooled, and their RNA was extracted, amplified and subjected to microarray analysis. Known marker genes specific for mMCs and sMCs showed expected expression trends, indicating accuracy of the analysis.

We identified 1,272 genes showing significantly different expression levels between sMCs and mMCs, and classified them into clusters on the basis of similarity of their expression profiles compared with bone marrow-derived MCs, which are the cultured MCs with so-called 'immature' properties. Among them, we found that several key genes such as Notch4 had sMC-biased expression and Ptgr1 had mMC-biased expression. Furthermore, there is a difference in the expression of several genes including extracellular matrix protein components, adhesion molecules, and cytoskeletal proteins between the two MC subclasses, which may reflect functional adaptation of each MC to the mucosal or submucosal environment in the stomach.

Conclusion

By using the method of RNA amplification from pooled intact MCs, we characterized the distinct gene expression profiles of sMCs and mMCs in the mouse stomach. Our findings offer insight into possible unidentified properties specific for each MC subclass.

Characterization of the porcine carboxypeptidase E cDNA: comparative analysis and investigation of a non-synonymous SNP

Carboxypeptidase E (CPE) is an important enzyme responsible for the proteolytic processing of prohormone intermediates. A naturally occurring point mutation, leading to an accumulation of many neuroendocrine peptides has been characterized within exon 5 of the CPE gene in mice. In the present study the sequence of the cDNA for the porcine CPE gene including all the coding region and the 3'-UTR region was generated. Comparisons with bovine, human, mouse, and rat CPE cDNA sequences showed that the coding regions of the gene are highly conserved both at the nucleotide and at the amino acid level. A very low nonsynonymous/synonymous substitution ratios between the proteins was found indicating that purifying selection is acting on the CPE gene. A nonsynonymous SNP identified at position 1272 in the transcript resulting in a codon change from TCA (Serine) to TTA (Leucine) was genotyped in the Danish pig populations. However, the mutated allele was only identified in one particular family. Exon 5 was sequenced in 45 unrelated pigs. No evidence of variation was found in this region. In accordance with previous results and in accordance with comparative mapping information the gene was accurately mapped to porcine chromosome 8 using the ImpRH panel.

Differential processing of pro-neurotensin/neuromedin N and relationship to pro-hormone convertases

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six amino acid neurotensin-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by endoproteases that belong to the recently identified family of pro-protein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Pro-NT/NN processing gives rise mainly to NT and NN in the brain, to NT and a large peptide ending with the NN sequence at its C-terminus (large NN) in the gut and to NT, large NN and a large peptide ending with the NT sequence (large NT) in the adrenals. Recent evidence indicates that PC1, PC2 and PC5-A are the pro-hormone convertases responsible for the processing patterns observed in the gut, brain and adrenals, respectively. As NT, NN, large NT and large NN are all endowed with biological activity, the evidence reviewed here supports the idea that post-translational processing of pro-NT/NN in tissues may generate biological diversity.

Prohormone convertases differentially process pro-neurotensin/neuromedin N in tissues and cell lines

Neurotensin (NT) is synthesized as part of a larger precursor that also contains neuromedin N (NN), a six-amino acid neurotensin-like peptide. NT and NN are located in the C-terminal region of the precursor (pro-NT/NN) where they are flanked and separated by three Lys-Arg sequences. A fourth dibasic sequence is present in the middle of the precursor. Dibasics are the consensus sites recognized and cleaved by specialized endoproteases that belong to the family of proprotein convertases (PCs). In tissues that express pro-NT/NN, the three C-terminal Lys-Arg sites are differentially processed, whereas the middle dibasic is poorly cleaved. Processing gives rise mainly to NT and NN in the brain, to NT and a large peptide with a C-terminal NN moiety (large NN) in the gut, and to NT, large NN, and a large peptide with a C-terminal NT moiety (large NT) in the adrenals. Recent evidence indicates that PC1, PC2, and PC5-A are the prohormone convertases responsible for the processing patterns observed in the gut, brain, and adrenals, respectively. As NT, NN, large NT, and large NN are all endowed with biological activity, the evidence reviewed in this paper supports the idea that posttranslational processing of pro-NT/NN in tissues may generate biological diversity of pathophysiological relevance.

Investigation of changes in global gene expression in the frontal cortex of early-weaned and socially isolated piglets using microarray and quantitative real-time RT-PCR

We hypothesize that early-weaned piglets experience aberrant expression of stress-responsive genes in the frontal cortex, a key brain area involved in cognitive function and behavior organization. To test this hypothesis, female early-weaned piglets (EW; n = 6) were weaned 10 days after birth, while non-weaned piglets (NW; n = 6) were left with their dams. Half of EW (n = 3) and NW (n = 3) animals were socially isolated (SI) for 15 min at 12 days of age, when all animals (n = 12) were euthanized and tissue collected. The effects of EW and SI were examined by gene expression profiling using cDNA microarray hybridizations, generated from a porcine brain cDNA library. A total of 103 genes were differentially expressed (P < 0.05, fold change >1.25) among four direct comparisons. Forty-two genes had known functions, from which 24 showed relevant brain-related functions. Quantitative real-time polymerase chain reaction (Q-RT-PCR) was used to confirm regulation of expression of a subset of 6 genes with important brain functions, selected from the microarray outcomes. In non-weaned animals, a significant suppression of mRNA abundance for carboxypeptidase E, 14-3-3 protein and phosphoprotein enriched in astrocytes 15 kDa was observed in response to SI. Also, in early-weaned animals, diazepam binding inhibitor and actin-related protein 2/3 complex mRNA levels were suppressed in response to SI. Results suggest that social isolation of non- and early-weaned piglets may impact expression of genes involved in regulation of neuronal function, development, and protection in the frontal cortex of young pigs.

Obesity and post-prandial lipid metabolism. Feast or famine?

Both in Western countries and in third world countries there is an increasing incidence of obesity. Obesity per se or insulin resistance associated with obesity may increase cardiovascular risk factors including dyslipidemia, hypertension and Type 2 diabetes. Over the past decade the understanding has increased of specific mediators in the hypothalamus that are involved in regulating food intake and body weight. In obese humans fasting plasma lipids can be normal but postprandial lipid metabolism is abnormal with an accumulation of triglyceride-rich remnant lipoproteins. In viscerally obese men chylomicron remnant catabolism was markedly decreased when compared with lean individuals. The decreased clearance of chylomicron remnants in viscerally obese subjects may be explained by competition between chylomicron remnants and the increased hepatic production of VLDL for clearance by low density lipoprotein receptors. Increased food intake in rodent models of obesity was shown to be associated with a delay in the catabolism of remnant lipoprotein particles. Prevention of hyperphagia was found to correct the impairment in the metabolism of remnant lipoproteins. Under fasting and food restricted conditions the improvement of remnant metabolism was associated with an increased oxidation of remnant lipids as determined by a novel stable isotope breath test. Anti-obesity and lipid lowering drugs have been used for the treatment of obesity. Inhibitors of cholesterol synthesis inhibitors (statins) have been shown to be effective in treating dyslipidemia. Inhibition of cholesterol synthesis with Atorvastatin was shown to improve chylomicron metabolism by increasing chylomicron remnant catabolism in obese subjects as assessed by the newly developed stable isotope breath test.

Effect of mutation of two critical glutamic acid residues on the activity and stability of human carboxypeptidase M and characterization of its signal for glycosylphosphatidylinositol anchoring

Human carboxypeptidase (CP) M was expressed in baculovirus-infected insect cells in a glycosylphosphatidylinositol-anchored form, whereas a truncated form, lacking the putative signal sequence for glycosylphosphatidylinositol anchoring, was secreted at high levels into the medium. Both forms had lower molecular masses (50 kDa) than native placental CPM (62 kDa), indicating minimal glycosylation. The predicted glycosylphosphatidylinositol-anchor attachment site was investigated by mutation of Ser(406) to Ala, Thr or Pro and expression in HEK-293 and COS-7 cells. The wild-type and S406A and S406T mutants were expressed on the plasma membrane in glycosylphosphatidylinositol-anchored form, but the S406P mutant was not and was retained in a perinuclear location. The roles of Glu(260) and Glu(264) in CPM were investigated by site-directed mutagenesis. Mutation of Glu(260) to Gln had minimal effects on kinetic parameters, but decreased heat stability, whereas mutation to Ala reduced the k(cat)/ K(m) by 104-fold and further decreased stability. In contrast, mutation of Glu(264) to Gln resulted in a 10000-fold decrease in activity, but the enzyme still bound to p-aminobenzoylarginine-Sepharose and was resistant to trypsin treatment, indicating that the protein was folded properly. These results show that Glu(264) is the critical catalytic glutamic acid and that Glu(260) probably stabilizes the conformation of the active site.

Altered expression of the neuropeptide-processing enzyme carboxypeptidase E in the rat brain after global ischemia

Carboxypeptidase E, an exoprotease involved in the processing of bioactive peptides released by a regulated secretory pathway, was identified in a subtractive complementary DNA library derived from an ischemic rat brain by differential screening. In situ hybridization and immunocytochemical analysis showed the presence of carboxypeptidase E messenger RNA and protein in the cerebral cortex, thalamus, striatum, and hippocampus of a healthy rat brain. After 15 minutes of transient global ischemia followed by 8 hours of reperfusion, increased levels of carboxypeptidase E messenger RNA and protein were observed in the hippocampal CA1 and CA3 regions and in the cortex, as detected by Northern and Western blot analyses and in situ hybridization. After extended reperfusion (24 to 72 hours), both carboxypeptidase E messenger RNA and protein levels were decreased. The ischemia-induced changes in carboxypeptidase E expression suggest that this enzyme may play a role in modulating the brain's response to ischemia.

The crystal structure of the inhibitor-complexed carboxypeptidase D domain II and the modeling of regulatory carboxypeptidases

The three-dimensional crystal structure of duck carboxypeptidase D domain II has been solved in a complex with the peptidomimetic inhibitor, guanidinoethylmercaptosuccinic acid, occupying the specificity pocket. This structure allows a clear definition of the substrate binding sites and the substrate funnel-like access. The structure of domain II is the only one available from the regulatory carboxypeptidase family and can be used as a general template for its members. Here, it has been used to model the structures of domains I and III from the former protein and of human carboxypeptidase E. The models obtained show that the overall topology is similar in all cases, the main differences being local and because of insertions in non-regular loops. In both carboxypeptidase D domain I and carboxypeptidase E slightly different shapes of the access to the active site are predicted, implying some kind of structural selection of protein or peptide substrates. Furthermore, emplacement of the inhibitor structure in the active site of the constructed models showed that the inhibitor fits very well in all of them and that the relevant interactions observed with domain II are conserved in domain I and carboxypeptidase E but not in the non-active domain III because of the absence of catalytically indispensable residues in the latter protein. However, in domain III some of the residues potentially involved in substrate binding are well preserved, together with others of unknown roles, which also are highly conserved among all carboxypeptidases. These observations, taken together with others, suggest that domain III might play a role in the binding and presentation of proteins or peptide substrates, such as the pre-S domain of the large envelope protein of duck hepatitis B virus.

Processing and sorting of the prohormone convertase 2 propeptide

The prohormone convertases (PCs) are synthesized as zymogens whose propeptides contain several multibasic sites. In this study, we investigated the processing of the PC2 propeptide and its function in the regulation of PC2 activity. By using purified pro-PC2 and directed mutagenesis, we found that the propeptide is first cleaved at the multibasic site separating it from the catalytic domain (primary cleavage site); the intact propeptide thus generated is then sequentially processed at two internal sites. Unlike the mechanism described for furin, our mutagenesis studies show that internal cleavage of the propeptide is not required for activation of pro-PC2. In addition, we identified a point mutation in the primary cleavage site that does not prevent the folding nor the processing of the zymogen but nevertheless results in the generation of an inactive PC2 species. These data suggest that the propeptide cleavage site is directly involved in the folding of the catalytic site. By using synthetic peptides, we found that a PC2 propeptide fragment inhibits PC2 activity, and we identified the inhibitory site as the peptide sequence containing basic residues at the extreme carboxyl terminus of the primary cleavage site. Finally, our study supplies information concerning the intracellular fate of a convertase propeptide by providing evidence that the PC2 propeptide is generated and is internally processed within the secretory granules. In agreement with this localization, an internally cleaved propeptide fragment could be released by stimulated secretion.

Processing of proenkephalin-A in bovine chromaffin cells. Identification of natural derived fragments by N-terminal sequencing and matrix-assisted laser desorption ionization-time of flight mass spectrometry

A large variety of proenkephalin-A-derived peptides (PEAPs) are present in bovine adrenal medulla secretory granules that are cosecreted with catecholamines upon stimulation of chromaffin cells. In the present paper, after reverse phase high performance liquid chromatography of intragranular soluble material, PEAPs were immunodetected with antisera raised against specific proenkephalin-A (PEA) sequences (PEA63-70 and PEA224-237) and analyzed by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. Thirty PEAPs were characterized in addition to enkephalins and whole PEA, indicating that preferential proteolytic attacks occurred at both N- and C-terminal regions. A similar approach was used to characterize PEA-derived fragments exocytotically released into the extracellular space that showed five additional minor PEAPs. Among all these naturally generated peptides, enkelytin, the antibacterial bisphos- phorylated C-terminal peptide (PEA209-237), was predominantly generated, as shown by MALDI-TOF mass spectrometry analysis, which constituted an efficient method for its identification. Finally, the data on PEA intragranular and extracellular processing in adrenal medulla are discussed in regard to the known enzymatic processing mechanisms. We note the high conservation of the cleavage points in evolutionarily diverse organisms, highlighting an important biological function for the released PEAPs.

Glu300 of rat carboxypeptidase E is essential for enzymatic activity but not substrate binding or routing to the regulated secretory pathway

Several recently discovered members of the carboxypeptidase E (CPE) gene family lack critical active site residues that are conserved in other family members. For example, three CPE-like proteins contain a Tyr in place of Glu300 (equivalent to Glu270 of carboxypeptidase A and B). To investigate the importance of this position, Glu300 of rat CPE was converted into Gln, Lys, or Tyr, and the proteins expressed in Sf9 cells using the baculovirus system. All three mutants were secreted from the cells, but the media showed no enzyme activity above background levels. Wild-type CPE and the Gln300 point mutant bound to a p-aminobenzoyl-Arg-Sepharose affinity resin, and this binding was competed by an active site-directed inhibitor, guanidinoethylmercaptosuccinic acid. The affinity purified mutant CPE protein showed no detectable enzyme activity (<0.004% of wild-type CPE) toward dansyl-Phe-Ala-Arg. Expression of the Gln300 and Lys300 mutant CPE proteins in the NIT3 mouse pancreatic beta-cell line showed that these mutants are routed into secretory vesicles and secreted via the regulated pathway. Taken together, these results indicate that Glu300 of CPE is essential for enzyme activity, but not required for substrate binding or for routing into the regulated secretory pathway.

Purification and characterization of human metallocarboxypeptidase Z

Carboxypeptidase Z (CPZ) is a recently discovered member of the metallocarboxypeptidase gene family that has an N-terminal domain related to the Wnt/wingless binding domain of frizzled receptors and other proteins. To further characterize the enzymatic properties of CPZ, the enzyme was purified using Arg- and heparin-affinity columns. CPZ has a neutral pH optimum, and is inhibited by chelating agents and several divalent cations (Zn2+, Mn2+, Cd2+, Cu2+, Hg2+). Active site-directed inhibitors of several other metallocarboxypeptidases also inhibit CPZ activity with moderate potency. CPZ cleaves substrates with C-terminal Arg residues, preferring peptides with an Ala in the penultimate position. No activity is detected toward substrates with an Ile-Arg or a Pro-Arg sequence. The Km for dansyl-Phe-Ala-Arg and dansyl-Pro-Ala-Arg are both approximately 2 mM. Taken together, these data suggests a selective role for CPZ in the processing of extracellular peptides or proteins.

Identification of mouse CPX-1, a novel member of the metallocarboxypeptidase gene family with highest similarity to CPX-2

The recent finding that Cpe(fat)/Cpe(fat) mice, which lack carboxypeptidase E (CPE) activity because of a point mutation, are still capable of a reduced amount of neuroendocrine peptide processing suggested that additional carboxypeptidases (CPs) participate in this processing reaction. Searches for novel members of the CPE gene family led to the discovery of CPD, CPZ, AEBP1, and CPX-2. In the present report, we describe mouse CPX-1, another novel member of this gene family. Like AEBP1 and CPX-2, CPX-1 contains an N-terminal region of 160 amino acids with sequence similarity to the discoidin domain of a variety of proteins. The 410-residue CP-like domain of CPX-1 has 54% to 62% amino acid sequence identity with AEBP1 and CPX-2 and 33% to 49% amino acid identity with other members of the CPE subfamily. However, several active-site residues that are important for catalytic activity of other CPs are not conserved in CPX-1. Furthermore, CPX-1 expressed in either the baculovirus system or the mouse AtT-20 cell line does not cleave standard CP substrates. Northern blot analysis showed the highest levels of CPX-1 mRNA in testis and spleen and lower levels in salivary gland, brain, heart, lung, and kidney. In situ hybridization of CPX-1 mRNA in embryonic and fetal mouse tissue showed expression throughout the head and thorax, with abundance in primordial cartilage and skeletal structures. In the head, high levels of CPX-1 mRNA were associated with the nasal mesenchyme, primordial cartilage structures in the ear, and the meninges. In the thorax, CPX-1 mRNA was expressed in multiple developing skeletal structures, including chondrocytes and perichondrial cells of the rib, vertebral, and long-bone primordia. Taken together, these findings suggest that it is unlikely that CPX-1 functions in the processing of neuroendocrine peptides. Instead, CPX-1 may have a role in development, possibly mediating cell interactions via its discoidin domain.

Cloning and expression of Aplysia carboxypeptidase D, a candidate prohormone-processing enzyme

Many peptide hormones in a variety of species are produced from larger precursors by limited proteolysis at basic amino acid-containing sites. The marine mollusc Aplysia has homologs of mammalian peptide-processing enzymes, including furin, prohormone convertase 1 (PC1), PC2, and carboxypeptidase E (CPE). A novel neuronal Aplysia enzyme was recently identified that was most closely related to carboxypeptidase D (CPD; Fan and Nagle, DNA Cell Biol. 15, 937-945, 1996), a second carboxypeptidase thought to be present in the secretory pathway and to contribute to peptide hormone processing. We have identified and cloned multiple overlapping bag-cell neuron cDNAs that encode two proteins that are members of the CPD family. Sequence analyses demonstrate that the longer CPD protein (1446 residues) contains an N-terminal signal peptide and four carboxypeptidase-like domains; the third and fourth domains are not predicted to form active enzymes, as several critical residues are absent. The shorter CPD protein is predicted to contain two active carboxypeptidase-like domains. Northern blot analysis identified a major Aplysia CPD mRNA (5.3 kb) and several smaller minor transcripts in central nervous system tissue. The CPD was purified from Aplysia ovotestis using a method previously developed for mammalian CPD. The purified Aplysia CPD binds antisera raised against regions of the protein encoded by the Aplysia cDNA clone, as well as an antiserum raised against duck CPD. The enzymatic properties of purified Aplysia CPD are generally similar to those of mammalian CPD. Aplysia CPD is a candidate prohormone-processing enzyme that may play a role in the processing of Aplysia prohormones in the secretory pathway.

Identification of mouse CPX-2, a novel member of the metallocarboxypeptidase gene family: cDNA cloning, mRNA distribution, and protein expression and characterization

A novel member of the metallocarboxypeptidase gene family was identified from its homology with carboxypeptidase E and has been designated CPX-2. The cDNA of 2500 nucleotides encodes a protein of 764 amino acids that contains an N-terminal signal peptide-like sequence, a 158-residue discoidin domain, and a 400-residue carboxypeptidase domain. The 400-residue metallocarboxypeptidase domain has 59% amino acid identity with a protein designated AEBP-1; 44% to 46% identity with carboxypeptidases E, N, and Z; and lower homology with other members of the metallocarboxypeptidase gene family. The discoidin domain of CPX-2 has 22% amino acid identity with the carbohydrate-binding domain of discoideum-I, 29% to 34% identity with the phospholipid-binding domain of human factors V and VIII, and 59% identity with the discoidin-like domain on AEBP-1. CPX-2 is missing several of the predicted active-site residues that are conserved in most other members of the metallocarboxypeptidase gene family and which are thought to be required for enzyme activity. Expression of CPX-2 using the baculovirus system produced several forms of protein, from 80 to 105 kDa, but no detectable activity toward a variety of carboxypeptidase substrates. A shorter 50-kDa form of CPX-2, which contains the carboxypeptidase domain but not the discoidin domain, was also inactive when expressed in the baculovirus system. CPX-2 is able to bind to Sepharose-Arg; this binding is blocked by 10 mM Arg. Northern blot analysis showed CPX-2 mRNA in mouse brain, liver, kidney, and lung. In situ hybridization analysis of brain revealed a broad distribution. Areas that are enriched in CPX-2 include the hippocampus, cerebral cortex, median eminence, and choroid plexus. Taken together, these data suggest a widespread function for CPX-2, possibly as a binding protein rather than an active carboxypeptidase.

Cloning, sequence analysis, and distribution of rat metallocarboxypeptidase Z

A cDNA encoding human carboxypeptidase Z (CPZ), a novel metallocarboxypeptidase, was recently cloned (Song and Fricker, J. Biol. Chem., 272, 1054, 1997). In the present study, a cDNA encoding the rat homolog of CPZ was identified. As with the human form, rat CPZ contains an N-terminal domain of 120 amino acids that has 20% to 30% amino acid identity with the "frizzled" domain found on proteins that interact with Wnt, a protein involved in tissue polarity in early embryogenesis. Sequence analysis showed rat and human CPZ to be highly conserved within the frizzled domain (77% amino acid identity), the carboxypeptidase domain (91%), and the C-terminal 28 residues (78%). The entire rat CPZ protein has high sequence similarity with human CPZ (81% amino acid identity), moderate sequence similarity to human carboxypeptidase N (45%), human carboxypeptidase E (41%), and human carboxypeptidase M (33%), and less sequence similarity with other metallocarboxypeptidases. Northern blot analysis showed rat CPZ mRNA to be abundant in the placenta, with low to moderate levels in the brain, lung, thymus, and kidney. The BRL3A rat liver cell line and the PC12 rat adrenal cell line express high levels of CPZ mRNA. In situ hybridization analysis indicated that CPZ is expressed only in specific cell types. For example, in the brain, CPZ mRNA is present in leptomeningeal cells, but not in the majority of other cell types. This distribution in leptomeningeal cells is shared by AEBP1, a recently reported member of the metallocarboxypeptidase gene family. However, the distribution of CPZ and AEBP1 differ in pituitary and thyroid. Taken together, these studies suggest that CPZ functions in a range of cell types.

Defective prohormone processing and altered pancreatic islet morphology in mice lacking active SPC2

The prohormone convertase SPC2 (PC2) participates in the processing of proinsulin, proglucagon, and a variety of other neuroendocrine precursors, acting either alone or in conjunction with the structurally related dense-core granule convertase SPC3 (PC3/PC1). We have generated a strain of mice lacking active SPC2 by introducing the neomycin resistance gene (Neor) into the third exon of the mSPC2 gene. This gene insertion results in the synthesis of an exon 3-deleted form of SPC2 that does not undergo autoactivation and is not secreted. The homozygous mutant mice appear to be normal at birth. However, they exhibit a small decrease in rate of growth. They also have chronic fasting hypoglycemia and a reduced rise in blood glucose levels during an intraperitoneal glucose tolerance test, which is consistent with a deficiency of circulating glucagon. The processing of proglucagon, prosomatostatin, and proinsulin in the alpha, delta, and beta cells, respectively, of the pancreatic islets is severely impaired. The islets in mutant mice at 3 months of age show marked hyperplasia of alpha and delta cells and a relative diminution of beta cells. SPC2-defective mice offer many possibilities for further delineating neuroendocrine precursor processing mechanisms and for exploring more fully the physiological roles of many neuropeptides and peptide hormones.

Characterization of Aplysia carboxypeptidase E

Carboxypeptidase E (CPE) is involved in the biosynthesis of peptide hormones and neurotransmitters. To determine whether a recently reported Aplysia californica cDNA encodes a CPE-like enzyme, this cDNA was expressed in the baculovirus system. The Aplysia CPE is optimal at pH 5.5-6.5 and is inhibited by chelating agents and by the sulfhydryl reagent p-chloromercuriphenyl sulfonate. The effect of divalent cations and active site-directed inhibitors on enzyme activity are generally similar for Aplysia and rat CPE. Western blot analysis using antisera to the N- and C-terminal regions of the Aplysia CPE show that the Aplysia CPE is present in atrial glands and ovotestis. This Aplysia CPE is purified on a p-aminobenzoyl-Arg Sepharose affinity column under conditions that selectively purify rat CPE. Taken together, these results suggest that the previously cloned cDNA represents a CPE-like enzyme that is expressed in Aplysia tissue.

The pro region is not required for the expression or intracellular routeing of carboxypeptidase E

Carboxypeptidase E (CPE) is initially synthesized as a larger precursor containing an additional 14-residue propeptide that is highly conserved between human and rat. Previous studies have established that the proenzyme is enzymically active and that deletion of the pro region does not affect the expression of the active enzyme. In the present study the function of the pro region was examined both by deleting this region from CPE and by attaching this region to the N-terminus of albumin. CPE lacking the pro region is sorted into the regulated secretory pathway in AtT-20 cells, based on confocal microscopy and examination of the stimulated secretion of the protein. Stimulation of AtT-20 cells with either forskolin or phorbol 12-myristate 13-acetate induces the secretion of wild-type CPE and of CPE lacking the pro region to similar extents, indicating a similar efficiency of sorting of the mutant. When the pro region of proalbumin is replaced with the pro region of CPE followed by expression in AtT-20 cells, the protein is not sorted into the regulated pathway, based on the lack of stimulated secretion. Confocal microscopy suggests that the proCPE/albumin protein is retained in the endoplasmic reticulum to a greater extent than is proalbumin. Pulse-chase analysis indicates that the pro region of CPE is not efficiently removed from the N-terminus of albumin, and the small amount of propeptide cleavage that does occur takes place soon before secretion of the protein. In contrast, confocal microscopy indicates that the majority of the propeptide is removed from CPE, and that this cleavage occurs in the trans-Golgi network or soon after sorting into the secretory vesicles. Taken together, these results suggest that the pro region of CPE is not required for the expression or intracellular routeing of this protein.

Carboxypeptidase E is a regulated secretory pathway sorting receptor: genetic obliteration leads to endocrine disorders in Cpe(fat) mice

A proposed mechanism for sorting secretory proteins into granules for release via the regulated secretory pathway in endocrine-neuroendocrine cells involves binding the proteins to a sorting receptor at the trans-Golgi network, followed by budding and granule formation. We have identified such a sorting receptor as membrane-associated carboxypeptidase E (CPE) in pituitary Golgi-enriched and secretory granule membranes. CPE specifically bound regulated secretory pathway proteins, including prohormones, but not constitutively secreted proteins. We show that in the Cpe(fat) mutant mouse lacking CPE, the pituitary prohormone, pro-opiomelanocortin, was missorted to the constitutive pathway and secreted in an unregulated manner. Thus, obliteration of CPE, the sorting receptor, leads to multiple endocrine disorders in these genetically defective mice, including hyperproinsulinemia and infertility.

Distinct properties of neuronal and astrocytic endopeptidase 3.4.24.16: a study on differentiation, subcellular distribution, and secretion processes

Endopeptidase 3.4.24.16 belongs to the zinc-containing metalloprotease family and likely participates in the physiological inactivation of neurotensin. The peptidase displays distinct features in pure primary cultured neurons and astrocytes. Neuronal maturation leads to a decrease in the proportion of endopeptidase 3.4.24.16-bearing neurons and to a concomitant increase in endopeptidase 3.4.24.16 activity and mRNA content. By contrast, there is no change with time in endopeptidase 3.4.24.16 activity or content in astrocytes. Primary cultured neurons exhibit both soluble and membrane-associated endopeptidase 3.4.24.16 activity. The latter behaves as an ectopeptidase on intact plated neurons and resists treatments with 0.2% digitonin and Na2CO3. Further evidence for an association of the enzyme with plasma membranes was provided by cryoprotection experiments and electron microscopic analysis. The membrane-associated form of endopeptidase 3.4.24.16 increased during neuronal differentiation and appears to be mainly responsible for the overall augmentation of endopeptidase 3.4.24.16 activity observed during neuronal maturation. Unlike neurons, astrocytes only contain soluble endopeptidase 3.4.24.16. Astrocytes secrete the enzyme through monensin, brefeldin A, and forskolin-independent mechanisms. This indicates that endopeptidase 3.4.24.16 is not released by classical regulated or constitutive secreting processes. However, secretion is blocked at 4 degrees C and by 8 bromo cAMP and is enhanced at 42 degrees C, two properties reminiscent of that of other secreted proteins lacking a classical signal peptide. By contrast, neurons appear unable to secrete endopeptidase 3.4.24.16.