The cDNA structure of the porcine pro-hormone convertase PC2 and the comparative processing by PC1 and PC2 of the N-terminal glycopeptide segment of porcine POMC

Multiple Neuropeptide-Coding Genes Involved in Planarian Pharynx Extension

Planarian feeding behavior involves three steps: moving toward food, extending the pharynx from their planarian's ventral side after arriving at the food, and ingesting the food through the pharynx. Although pharynx extension is a remarkable behavior, it remains unknown what neuronal cell types are involved in its regulation. To identify neurons involved in regulating pharynx extension, we quantitatively analyzed pharynx extension and sought to identify these neurons by RNA interference (RNAi) and in situ hybridization. This assay, when performed using planarians with amputation of various body parts, clearly showed that the head portion is indispensable for inducing pharynx extension. We thus tested the effects of knockdown of brain neurons such as serotonergic, GABAergic, and dopaminergic neurons by RNAi, but did not observe any effects on pharynx extension behavior. However, animals with RNAi of the Prohormone Convertase 2 (PC2, a neuropeptide processing enzyme) gene did not perform the pharynx extension behavior, suggesting the possible involvement of neuropeptide(s in the regulation of pharynx extension. We screened 24 neuropeptide-coding genes, analyzed their functions by RNAi using the pharynx extension assay system, and identified at least five neuropeptide genes involved in pharynx extension. These was expressed in different cells or neurons, and some of them were expressed in the brain, suggesting complex regulation of planarian feeding behavior by the nervous system.

Transcriptomic analysis of Rongchang pig brains and livers

Recent developments in high-throughput RNA sequencing (RNA-seq) technology have led to a dramatic impact on our understanding of the structure and expression profiles of the mammalian transcriptome. To gain insights into the usefulness of swine production and biomedical model, the transcriptome profiling of Rongchang pig brains and livers was characterized using RNA-seq technology to uncover functional candidate molecules. In the study, total RNAs from brains and livers of Rongchang pig were sequenced and 8.6Gb sequencing data was obtained. This analysis revealed tissue specificity through the identification of 5575 and 4600 differentially expressed genes (DEGs) in brains and livers, respectively and the functional analysis of DEGs. Furthermore, 83 neuropeptide gene transcripts, 69 neuropeptide receptor gene transcripts, 10 pro-neuropeptide convertase gene transcripts and many other neuropeptide related protein gene transcripts were identified. Totally, the major characteristics of the transcriptional profiles of Rongchang pig brains and livers were present.

α-MSH overexpression in the nucleus tractus solitarius decreases fat mass and elevates heart rate

The POMC pathway is involved in the regulation of energy and cardiovascular homeostasis in the hypothalamus and the brain stem. Although the acute effects of POMC-derived peptides in different brain locations have been elucidated, the chronic site-specific effects of distinct peptides remain to be studied. To this end, we used a lentiviral gene delivery vector to study the long-term effects of α-MSH in the nucleus tractus solitarius (NTS) of the brain stem. The α-MSH vector (LVi-α-MSH-EGFP) based on the N-terminal POMC sequence and a control vector (LVi-EGFP) were delivered into the NTS of C57BL/6N male mice fed on a western diet. Effects on body weight and composition, feeding, glucose metabolism, and hemodynamics by telemetric analyses were studied during the 12-week follow-up. The LVi-α-MSH-EGFP-treated mice had a significantly smaller gain in the fat mass compared with LVi-EGFP-injected mice. There was a small initial decrease in food intake and no differences in the physical activity. Glucose metabolism was not changed compared with the control. LVi-α-MSH-EGFP increased the heart rate (HR), which was attenuated by adrenergic blockade suggesting an increased sympathetic activity. Reduced response to muscarinic blockade suggested a decreased parasympathetic activity. Fitting with sympathetic activation, LVi-α-MSH-EGFP treatment reduced urine secretion. Thus, the results demonstrate that long-term α-MSH overexpression in the NTS attenuates diet-induced obesity. Modulation of autonomic nervous system tone increased the HR and most probably contributed to an anti-obesity effect. The results underline the key role of NTS in the α-MSH-induced long-term effects on adiposity and in regulation of sympathetic and parasympathetic activities.

Lentivirus-mediated α-melanocyte-stimulating hormone overexpression in the hypothalamus decreases diet induced obesity in mice

Melanocyte stimulating hormone (MSH) derived from the pro-hormone pro-opiomelanocortin (POMC) has potent effects on metabolism and feeding that lead to reduced body weight in the long-term. To determine the individual roles of POMC derived peptides and their sites of action, we created a method for the delivery of single MSH peptides using lentiviral vectors and studied the long-term anti-obesity effects of hypothalamic α-MSH overexpression in mice. An α-MSH lentivirus (LVi-α-MSH-EGFP) vector carrying the N'-terminal part of POMC and the α-MSH sequence was generated and shown to produce bioactive peptide in an in vitro melanin synthesis assay. Stereotaxis was used to deliver the LVi-α-MSH-EGFP or control LVi-EGFP vector to the arcuate nucleus (ARC) of the hypothalamus of male C57Bl/6N mice fed on a high-fat diet. The effects of 6-week-treatment on body weight, food intake, glucose tolerance and organ weights were determined. Additionally, a 14-day pairfeeding study was conducted to assess whether the weight decreasing effect of the LVi-α-MSH-EGFP treatment is dependent on decreased food intake. The 6-week LVi-α-MSH-EGFP treatment reduced weight gain (8.4 ± 0.4 g versus 12.3 ± 0.6 g; P < 0.05), which was statistically significant starting from 1 week after the injections. The weight of mesenteric fat was decreased and glucose tolerance was improved compared to LVi-EGFP treated mice. Food intake was decreased during the first week in the LVi-α-MSH-EGFP treated mice but subsequently increased to the level of LVi-EGFP treated mice. The LVi-EGFP injected control mice gained more weight even when pairfed to the level of food intake by LVi-α-MSH-EGFP treated mice. We demonstrate that gene transfer of α-MSH, a single peptide product of POMC, into the ARC of the hypothalamus, reduces obesity and improves glucose tolerance, and that factors other than decreased food intake also influence the weight decreasing effects of α-MSH overexpression in the ARC. Furthermore, viral MSH vectors delivered stereotaxically provide a novel tool for further exploration of chronic site-specific effects of POMC peptides.

First survey and functional annotation of prohormone and convertase genes in the pig

Background

The pig is a biomedical model to study human and livestock traits. Many of these traits are controlled by neuropeptides that result from the cleavage of prohormones by prohormone convertases. Only 45 prohormones have been confirmed in the pig. Sequence homology can be ineffective to annotate prohormone genes in sequenced species like the pig due to the multifactorial nature of the prohormone processing. The goal of this study is to undertake the first complete survey of prohormone and prohormone convertases genes in the pig genome. These genes were functionally annotated based on 35 gene expression microarray experiments. The cleavage sites of prohormone sequences into potentially active neuropeptides were predicted.

Results

We identified 95 unique prohormone genes, 2 alternative calcitonin-related sequences, 8 prohormone convertases and 1 cleavage facilitator in the pig genome 10.2 assembly and trace archives. Of these, 11 pig prohormone genes have not been reported in the UniProt, UniGene or Gene databases. These genes are intermedin, cortistatin, insulin-like 5, orexigenic neuropeptide QRFP, prokineticin 2, prolactin-releasing peptide, parathyroid hormone 2, urocortin, urocortin 2, urocortin 3, and urotensin 2-related peptide. In addition, a novel neuropeptide S was identified in the pig genome correcting the previously reported pig sequence that is identical to the rabbit sequence. Most differentially expressed prohormone genes were under-expressed in pigs experiencing immune challenge relative to the un-challenged controls, in non-pregnant relative to pregnant sows, in old relative to young embryos, and in non-neural relative to neural tissues. The cleavage prediction based on human sequences had the best performance with a correct classification rate of cleaved and non-cleaved sites of 92% suggesting that the processing of prohormones in pigs is similar to humans. The cleavage prediction models did not find conclusive evidence supporting the production of the bioactive neuropeptides urocortin 2, urocortin 3, torsin family 2 member A, tachykinin 4, islet amyloid polypeptide, and calcitonin receptor-stimulating peptide 2 in the pig.

Conclusions

The present genomic and functional characterization supports the use of the pig as an effective animal model to gain a deeper understanding of prohormones, prohormone convertases and neuropeptides in biomedical and agricultural research.

Effects of maternal dexamethasone treatment in early pregnancy on pituitary-adrenal axis in fetal sheep

Fetal exposure to elevated levels of bioactive glucocorticoids early in gestation, as in suspected cases of congenital adrenal hyperplasia, may result in adverse neurological events. Fetal hypothalamic-pituitary-adrenal development and function may be involved. We investigated immediate and long-term effects of maternal dexamethasone (DEX) administration early in pregnancy on fetal growth and pituitary-adrenal activity in sheep. Pregnant ewes carrying singleton fetuses (total n = 119) were randomized to control (2 ml saline/ewe) or DEX-treated groups (im injections of 0.14 mg/kg ewe weight . 12 h) at 40-41 d gestation (dG). At 50, 100, 125, and 140 dG, fetal plasma and tissues were collected. DEX-exposed fetuses were lighter than controls at 100 dG (P < 0.05) but not at any other times. Fetal plasma ACTH levels and pituitary POMC and PC-1 mRNA levels were similar between groups. Fetal plasma cortisol levels were significantly reduced after DEX exposure in both male and female fetuses at 50 dG (P < 0.05), were similar at 100 and 125 dG, but were significantly higher than controls at 140 dG. At 140 dG, there was increased adrenal P450C(17) and 3beta-HSD mRNA in female fetuses and reduced expression of ACTH-R mRNA in males. Fetal hepatic CBG mRNA levels mimicked plasma cortisol patterns. DEX exposure reduced CBG only in males at 50 dG (P < 0.05). Placental mRNA levels of 11beta-HSD2 were increased after DEX in males (P < 0.05). Therefore, in sheep, early DEX may alter the developmental trajectory of the fetal hypothalamic-pituitary-adrenal axis, directly increasing fetal adrenal activation but not anterior pituitary function. In females, this effect may be attributed, in part, to increased fetal adrenal steroidogenic activity.

Combined acromegaly and subclinical Cushing disease related to high-molecular-weight adrenocorticotropic hormone

A 36-year-old man with a 1-year history of diabetes mellitus was referred to the authors' hospital for further endocrinological evaluation of acromegaly. On physical examination, typical acromegalic features but no typical cushingoid features were observed. The clinical diagnosis of growth hormone (GH)-producing pituitary adenoma was confirmed by MR imaging findings, nonsuppression of serum GH levels during a 75-g oral glucose tolerance test (trough GH 6.33 ng/ml), and elevated serum insulin-like growth factor-I levels (1361.3 ng/ml). Moreover, autonomic adrenocorticotropic hormone (ACTH) secretion was suspected, based on inadequate suppression of ACTH or cortisol levels by an 0.5-mg overnight dexamethasone suppression test. Analysis of the patient's plasma by using the gel filtration method revealed the presence of a high-molecular-weight (HMW) form of ACTH known to exhibit low biological activity. Transsphenoidal adenomectomy was performed for the pituitary tumor. Immunohistochemical investigation of the resected specimen showed strong and diffuse immunoreactivity to GH and focal immunoreactivity to ACTH. Although there have been a few cases of pituitary adenoma that produced GH and ACTH concomitantly, this is the first report of the detection of HMW ACTH in patients with GH- and ACTH-producing adenomas. Furthermore, the previous cases also did not exhibit typical cushingoid features. It is suggested that the secretion of ACTH in patients with concurrent GH- and ACTH-secreting adenomas might consist of the HMW form and that the HMW ACTH is consequently associated with a subclinical Cushing state.

The role of proopiomelanocortin (POMC) neurones in feeding behaviour

The precursor protein, proopiomelanocortin (POMC), produces many biologically active peptides via a series of enzymatic steps in a tissue-specific manner, yielding the melanocyte-stimulating hormones (MSHs), corticotrophin (ACTH) and β-endorphin. The MSHs and ACTH bind to the extracellular G-protein coupled melanocortin receptors (MCRs) of which there are five subtypes. The MC3R and MC4R show widespread expression in the central nervous system (CNS), whilst there is low level expression of MC1R and MC5R. In the CNS, cell bodies for POMC are mainly located in the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius of the brainstem. Both of these areas have well defined functions relating to appetite and food intake. Mouse knockouts (ko) for pomc, mc4r and mc3r all show an obese phenotype, as do humans expressing mutations of POMC and MC4R. Recently, human subjects with specific mutations in β-MSH have been found to be obese too, as have mice with engineered β-endorphin deficiency. The CNS POMC system has other functions, including regulation of sexual behaviour, lactation, the reproductive cycle and possibly central cardiovascular control. However, this review will focus on feeding behaviour and link it in with the neuroanatomy of the POMC neurones in the hypothalamus and brainstem.

Periconceptional undernutrition in sheep accelerates maturation of the fetal hypothalamic-pituitary-adrenal axis in late gestation

We investigated the effects of moderate maternal periconceptional undernutrition from 60 d before to 30 d after mating on fetal hypothalamic-pituitary-adrenal axis function in late gestation. Ewes were sampled regularly during the period of undernutrition for circulating hormone levels. Vascular catheters were inserted into ewes and their singleton fetuses at 112 d gestation (term, 145 d), and fetal ACTH(1-24) and metyrapone challenge tests were performed at 127 and 128 d. Postmortems were performed at 132 d. Fetuses of undernourished ewes (UN, n = 12) had elevated baseline cortisol concentrations (P < 0.05), compared with fetuses of ad libitum-fed ewes (n = 10). There were no differences between groups in fetal responses to ACTH challenge, but only UN fetuses demonstrated ACTH and 11-deoxycortisol responses to metyrapone (P < 0.05). UN fetuses had increased mRNA levels for proopiomelanocortin and prohormone convertase-1, but not -2, in the pars intermedia of the pituitary gland (P < 0.05). Glucocorticoid receptor mRNA levels were not different between groups in pituitary or hypothalamus. Maternal cortisol and ACTH levels during undernutrition were profoundly suppressed (P < 0.001), rather than elevated, in UN ewes. Furthermore, the normal pregnancy rise in maternal serum progesterone concentrations was delayed in undernourished mothers. These data demonstrate that events around the time of conception have profound effects on fetal hypothalamic-pituitary-adrenal development in late gestation and that factors other than fetal exposure to excess glucocorticoids may be important.

Immunohistochemical evidence for the involvement of protein convertases 5A and 2 in the processing of pro-neurotensin in rat brain

The neuropeptides/neurotransmitters neurotensin (NT) and neuromedin (NN) are synthesized by endoproteolytic cleavage of a common inactive precursor, pro-NT/NN. In vitro studies have suggested that the prohormone convertases PC5A and PC2 might both be involved in this process. In the present study, we used dual immunohistochemical techniques to determine whether either one or both of these two convertases were co-localized with pro-NT/NN maturation products and could therefore be involved in the physiological processing of this propeptide in rat brain. PC2-immunoreactive neurons were present in all regions immunopositive for NT. All but three regions expressing NT were also immunopositive for PC5A. Dual localization of NT with either convertase revealed that NT was extensively co-localized with both PC5A and PC2, albeit with regional differences. These results strongly suggest that PC5A and PC2 may play a key role in the maturation of pro-NT/NN in mammalian brain. The regional variability in NT/PC co-localization patterns may account for the region-specific maturation profiles previously reported for pro-NT/NN. The high degree of overlap between PC5A and PC2 in most NT-rich areas further suggests that these two convertases may act jointly to process pro-NT/NN. At the subcellular level, PC5A was largely co-localized with the mid-cisternae Golgi marker MG-160. By contrast, PC2 was almost completely excluded from MG-160-immunoreactive compartments. These results suggest that PC5A, which is particularly efficient at cleaving the two C-terminal-most dibasics of pro-NT/NN, may be acting as early as in the Golgi apparatus to release NT, whereas PC2, which is considerably more active than PC5A in cleaving the third C-terminal doublet, may be predominantly involved further distally along the secretory pathway to release NN.

Corticotropin releasing hormone and proopiomelanocortin involvement in the cutaneous response to stress

The skin is a known target organ for the proopiomelanocortin (POMC)-derived neuropeptides alpha-melanocyte stimulating hormone (alpha-MSH), beta-endorphin, and ACTH and also a source of these peptides. Skin expression levels of the POMC gene and POMC/corticotropin releasing hormone (CRH) peptides are not static but are determined by such factors as the physiological changes associated with hair cycle (highest in anagen phase), ultraviolet radiation (UVR) exposure, immune cytokine release, or the presence of cutaneous pathology. Among the cytokines, the proinflammatory interleukin-1 produces important upregulation of cutaneous levels of POMC mRNA, POMC peptides, and MSH receptors; UVR also stimulates expression of all the components of the CRH/POMC system including expression of the corresponding receptors. Molecular characterization of the cutaneous POMC gene shows mRNA forms similar to those found in the pituitary, which are expressed together with shorter variants. The receptors for POMC peptides expressed in the skin are functional and include MC1, MC5 and mu-opiate, although most predominant are those of the MC1 class recognizing MSH and ACTH. Receptors for CRH are also present in the skin. Because expression of, for example, the MC1 receptor is stimulated in a similar dose-dependent manner by UVR, cytokines, MSH peptides or melanin precursors, actions of the ligand peptides represent a stochastic (predictable) nonspecific response to environmental/endogenous stresses. The powerful effects of POMC peptides and probably CRH on the skin pigmentary, immune, and adnexal systems are consistent with stress-neutralizing activity addressed at maintaining skin integrity to restrict disruptions of internal homeostasis. Hence, cutaneous expression of the CRH/POMC system is highly organized, encoding mediators and receptors similar to the hypothalamic-pituitary-adrenal (HPA) axis. This CRH/POMC skin system appears to generate a function analogous to the HPA axis, that in the skin is expressed as a highly localized response which neutralizes noxious stimuli and attendant immune reactions.

Evolution of the prohormone convertases: identification of a homologue of PC6 in the protochordate amphioxus

Many of the protein precursors traversing the secretory pathway undergo cleavage at multibasic sites to generate their bioactive forms. The proprotein convertases (PCs), a family of subtilisin-like proteases, are the major endoproteases that serve this function. Genes encoding seven distinct members of this family have so far been characterized in vertebrates: furin, PC2, PC1/PC3, PC4, PACE4, PC5/PC6 and PC7/PC8/LPC. Multiple PC genes have also been cloned from a number of invertebrates, including Drosophila melanogaster and Caenorhabditis elegans. These findings suggest that gene duplication and diversification of the PCs have occurred throughout metazoan evolution. To investigate the structural and functional changes which have occurred during vertebrate development, we have analyzed the expression of PC genes in the protochordate amphioxus. We have previously shown that amphioxus express homologous PC2 and PC1/PC3 genes [Proc. Natl. Acad. Sci. USA 92 (1995) 3591]. Here we report the characterization of amphioxus cDNAs encoding proteases with a high degree of similarity to mammalian PC6. Three cDNAs encoding three PC6 isoforms differing only in their carboxy-terminal sequences were found, derived by alternative splicing. Two isoforms appear to be soluble enzymes, whereas the third contains a transmembrane hydrophobic segment and thus is likely to be membrane-bound. All three variants contain many repeats of a cysteine-rich motif that is found in several other PC family members. Thus, amphioxus, like the vertebrates, expresses two types of PCs, e.g., PC2 and PC1/PC3 which function in the regulated secretory pathway in neuroendocrine cells, and the more widely expressed PC6 which functions mainly in the constitutive pathway.

Activation and routing of membrane-tethered prohormone convertases 1 and 2

Many peptide hormones and neuropeptides are processed by members of the subtilisin-like family of prohormone convertases (PCs), which are either soluble or integral membrane proteins. PC1 and PC2 are soluble PCs that are primarily localized to large dense core vesicles in neurons and endocrine cells. We examined whether PC1 and PC2 were active when expressed as membrane-tethered proteins, and how tethering to membranes alters the biosynthesis, enzymatic activity, and intracellular routing of these PCs. PC1 and PC2 chimeras were constructed using the transmembrane domain and cytoplasmic domain of the amidating enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The membrane-tethered PCs were rerouted from large dense core vesicles to the Golgi region. In addition, the chimeras were transiently expressed at the cell surface and rapidly internalized to the Golgi region in a fashion similar to PAM. Membrane-tethered PC1 and PC2 exhibited changes in pro-domain maturation rates, N-glycosylation, and in the pH and calcium optima required for maximal enzymatic activity against a fluorogenic substrate. In addition, the PC chimeras efficiently cleaved endogenous pro-opiomelanocortin to the correct bioactive peptides. The PAM transmembrane domain/cytoplasmic domain also prevented stimulated secretion of pro-opiomelanocortin products in AtT-20 cells.

Proopiomelanocortin (POMC) mRNA and POMC-derived peptides immunolocalization in the skin of Protopterus annectens, an African lungfish

Antisera against adrenocorticotropic hormone (ACTH), alpha-melanocyte stimulating hormone (alpha-MSH) and beta-endorphin were used to localize, by immunohistochemistry, proopiomelanocortin (POMC)-derived peptides in the skin excised from different regions of the African lungfish Protopterus annectens. Immunoreactivity was observed in the epidermis mainly in the germinal layer. Using human POMC cDNA as hybridization probe, POMC-like mRNA was identified in situ in epidermal cells. The demonstration in the same cells of POMC mRNA and POMC-related peptides immunoreactivity indicates a local production of opiate hormones.

Hair cycle-dependent production of ACTH in mouse skin

We investigated the functional determinants of the cutaneous expression of elements of the hypothalamic-pituitary-adrenal axis. In the present work, the presence of adrenocorticotropin (ACTH) peptide in skin of C57/BL6 mouse was demonstrated by reversed-phase HPLC analysis combined with specific radioimmunoassay. ACTH concentration that was low in telogen, increased during anagen in two steps: a rapid phase in anagen I, and a slower rise that reached its peak in anagen VI. Immunofluorescence localized the ACTH antigen to the basal layer of epidermis, outer root sheath of hair follicle and subcutaneous muscle of anagen VI skin. At physiological plasma concentration (10-9 M), ACTH selectively stimulated DNA synthesis in dermis, while pharmacological doses (10-7-10-6 M) inhibited DNA synthesis in both dermis and epidermis. In conclusion, we suggest that local production of ACTH may represent a regulatory element in the control of skin functions including hair growth.

Cutaneous immunomodulation and coordination of skin stress responses by alpha-melanocyte-stimulating hormone

The capacity of the skin immune system to mount various types of immune responses is largely dependent on their ability to release and respond to different signals provided by immunoregulatory mediators such as cytokines. There is recent evidence that neuropeptides such as alpha-melanocyte-stimulating hormone (alpha MSH), upon stimulation, are released by epidermal cells including keratinocytes, Langerhans cells, and melanocytes as well as immunocompetent cells. Moreover, alpha MSH recently has been recognized as a potent immunomodulating agent, which inhibits the production and activity of immunoregulatory and proinflammatory cytokines such as IL-1, IL-2, interferon-gamma, downregulates the expression of costimulatory molecules (B7) on antigen-presenting cells; and recently turned out to be a potent inducer of inhibitory mediators such as cytokine synthesis inhibitory factor interleukin-10. Recently, it also was discovered that monocytes among the five known melanocortin (MC) receptors only express MC-1, which is specific for alpha MSH. The expression of MC-1 on monocytes is upregulated by mitogens, endotoxins, and proinflammatory cytokines. There is also recent evidence for the in vivo relevance of the immunosuppressing capacity of alpha MSH. Accordingly, in animals alpha MSH has been shown to inhibit the induction of contact hypersensitivity reactions and to induce hapten-specific tolerance. These findings indicate that, in addition to the cytokine network, neurohormones within the cutaneous microenvironment are a crucial element for the induction, elicitation, and regulation of cutaneous immune and inflammatory responses.

Processing of pro-opiomelanocortin in GH3 cells: inhibition by prohormone convertase 2 (PC2) antisense mRNA

The processing of pro-opiomelanocortin (POMC) was examined in GH3 cells, a rat sommatomammotrope cell line, by transiently-transfecting the cells with mouse POMC cDNA. The peptide products were extracted, chromatographed on HPLC and identified by specific radioimmunoassay. POMC was processed to generate ACTH-related peptides, beta-endorphin and Lys-gamma 3- MSH, with complete disappearance of the POMC precursor. The ACTH-related molecules were identified as ACTH1-14, ACTH1-15, ACTH1-17, as well as ACTH1-39. GH3 cells which were not transfected with POMC cDNA did not contain endogenous POMC-related peptides. RT-PCR demonstrated that GH3 cells contain prohormone convertase 2 (PC2) mRNA but no PC1 mRNA. To determine if PC2 was the enzyme responsible for POMC processing in this cell line, GH3 cells were stably-transfected with PC2 antisense cDNA. A cell line was obtained which showed an absence of PC2 protein compared to control untransfected GH3 cells, indicating successful hybridization of PC2 antisense mRNA to the endogenous PC2 mRNA. When this cell line was then transiently-transfected with POMC cDNA, POMC was not processed. The results from these experiments suggest that PC2 alone can correctly process POMC to biologically active smaller peptides in vivo. Additionally, the GH3 cell line with and without incorporation of PC2 antisense cDNA can be used as a model system to study the role of PC2 in the post-translational processing of other prohormones and proproteins in vivo.

Characterization of multiple prohormone convertase PC1/3 transcripts in porcine ovary

Overlapping cDNAs encoding porcine prohormone convertase, PC1/3, have been isolated from a pregnant sow ovary cDNA library using a mouse PC1/3 cDNA as a probe. Nucleotide sequence analysis of these cDNAs predicts a PC1/3 precursor protein of 753 amino acid residues, which shares an overall sequence homology of 96, 92, and 92% with the human, rat, and mouse counterparts, respectively. Furthermore, five different polyadenylation sites have been observed. The utilization of these polyadenylation sites results in a length difference of 40-440 bp in the 3' untranslated regions of the transcripts.

Frog prohormone convertase PC2 mRNA has a mammalian-like expression pattern in the central nervous system and is colocalized with a subset of thyrotropin-releasing hormone-expressing neurons

The prohormone convertase (PC2) is expressed in the mammalian central nervous system (CNS) and has been shown to play an important role in the processing of certain neuropeptide precursors and prohormones at paired basic residues. Amphibian PC2 cDNA was recently cloned for the frog Xenopus laevis, and both its sequence and its pituitary expression pattern were shown to be very similar to those of mammalian PC2. To investigate further the function of PC2 in the vertebrate CNS, we used in situ hybridization histochemistry to localize the distribution of cells expressing PC2 mRNA in the frog brain and the spinal cord. The distribution of PC2-expressing cells was also compared with that of cells expressing thyrotropin-releasing hormone (TRH) mRNA or peptide. PC2-expressing cells were detected in specific nuclei that were widely distributed in the frog CNS. In forebrain, telencephalic PC2 mRNA was found in the olfactory bulb, pallium, striatum, amygdala, and septum, and diencephalic PC2 mRNA was seen in the preoptic area, thalamus, and hypothalamus. More posteriorly, PC2 cells were localized to midbrain tegmentum, the torus semicircularis, and the optic tectum, as well as the cerebellum, brainstem, and spinal cord. Despite this wide distribution steady-state levels of PC2 mRNA were clearly different in various brain nuclei. Regions with higher levels showed good correspondence to areas shown by others in frog to contain large numbers of neuropeptide-expressing cells, including TRH cells. On the other hand, not all brain areas with high levels of TRH mRNA had high levels of PC2 mRNA. Localization studies combining in situ hybridization and immunocytochemistry showed that, at least in optic tectum and brainstem, PC2 mRNA and pro-TRH peptide coexist. These findings suggest that pro-TRH is processed by PC2 in some, but possibly not all, brain regions. Thus, different converting enzymes may be involved in pro-TRH processing in different brain regions.

Isolation and in situ localization of a cDNA encoding a Kex2-like prohormone convertase in the nematode Caenorhabditis elegans

1. A cDNA that encodes a Kex2-like prohormone convertase (PC) containing an active site similar to that of mammalian PC2 has been isolated from C. elegans. Total RNA was isolated from a mixed population of strain BA713 worms. After poly-(A)-selection and reverse transcription, degenerate/nested polymerase chain reactions (PCR) were performed using primers based on conserved regions within the active sites of the known vertebrate and invertebrate endoproteases. 2. Two distinct 300-bp PCR products that shared homologies with the active sites of known Kex2-like endoproteases were isolated. These two PCR products were used to screen a C. elegans cDNA library. 3. The complete cDNA for a Kex2-like endoprotease, designated CELPC2, was isolated and determined to be 2527 bp in length. This size was confirmed by northern analysis. The deduced amino acid sequence for the CELPC2 cDNA is very similar to the known Kex2-like endoproteases, especially at conserved regions within the active sites, but not identical to any one of them. The strongest structural homology was to vertebrate and invertebrate PC2 sequences. 4. In situ hybridization suggests that CELPC2 is synthesized primarily in cells associated with the circumpharyngeal nerve ring and the dorsorectal ganglion.

cDNA structure and in situ localization of the Aplysia californica pro-hormone convertase PC2

The complete cDNA structure of the Aplysia californica pro-protein and pro-hormone convertase PC2 (aPC2) was obtained from a cDNA library of the nervous system. The deduced amino acid sequence revealed that aPC2 exhibits an 85%, 61% and 62% sequence identity to the Lymnaea stagnalis, Xenopus laevis and mouse PC2 homologues, respectively. The deduced stagnalis, Xenopus laevis and mouse PC2 homologues, respectively. The deduced primary sequence suggested a protein of 653 amino acids which includes a 27- and 88-amino acid signal peptide and pro-segment. The signal peptide and the C-terminal segments are the least conserved regions. On Northern blots of nervous system we detected a transcript of 6.8 kb. The in situ hybridization histochemistry on the abdominal ganglion revealed intense labeling of the bag cells. Large peptidergic cells and clusters of sensory and motor neurons also contained high levels of aPC2 mRNA.

Comparative biosynthesis, covalent post-translational modifications and efficiency of prosegment cleavage of the prohormone convertases PC1 and PC2: glycosylation, sulphation and identification of the intracellular site of prosegment cleavage of PC1 and PC2

We present herein the pulse-chase analysis of the biosynthesis of the prohormone convertases PC1 and PC2 in the endocrine GH4C1 cells infected with vaccinia virus recombinants expressing these convertases. Characterization of the pulse-labelled enzymes demonstrated that pro-PC1 (88 kDa) is cleaved into PC1 (83 kDa) and pro-PC2 (75 kDa) into PC2 (68 kDa). Secretion of glycosylated and sulphated PC1 (84 kDa) occurs about 30 min after the onset of biosynthesis, whereas glycosylated and sulphated PC2 (68 kDa) is detected in the medium after between 1 and 2 h. Furthermore, in the case of pro-PC2 only, we observed that a fraction of this precursor escapes glycosylation. A small proportion (about 5%) of the intracellular glycosylated pro-PC2 (75 kDa) is sulphated, and it is this glycosylated and sulphated precursor that is cleaved into the secretable 68 kDa form of PC2. Major differences in the carbohydrate structures of PC1 and PC2 are demonstrated by the resistance of the secreted PC1 to endoglycosidase H digestion and sensitivity of the secreted PC2 to this enzyme. Inhibition of N-glycosylation with tunicamycin caused a dramatic intracellular degradation of these convertases within the endoplasmic reticulum, with the net effect of a reduction in the available activity of PC1 and PC2. These results emphasize the importance of N-glycosylation in the folding and stability of PC1 and PC2. Pulse-labelling experiments in uninfected mouse beta TC3 and rat Rin m5F insulinoma cells, which endogenously synthesize PC2, showed that, as in infected GH4C1 cells, pro-PC2 predominates intracellularly. In order to define the site of prosegment cleavage, pulse-chase analysis was performed at low temperature (15 degrees C) or after treatment of GH4C1 cells with either brefeldin A or carbonyl cyanide m-chlorophenylhydrazone. These results demonstrated that the onset of the conversions of pro-PC1 into PC1 and non-glycosylated pro-PC2 into PC2 (65 kDa) occur in a pre-Golgi compartment, presumably within the endoplasmic reticulum. In contrast, pulse labelling in the presence of Na(2)35SO4 demonstrated that the processing of glycosylated and sulphated pro-PC2 occurs within the Golgi apparatus. In order to test the possibility that zymogen processing is performed by furin, we co-expressed this convertase with either pro-PC1 or pro-PC2. The data demonstrated the inability of furin to cleave either proenzyme.

cDNA structure of the mouse and rat subtilisin/kexin-like PC5: a candidate proprotein convertase expressed in endocrine and nonendocrine cells

By using reverse transcriptase/PCR and oligonucleotide sequences derived from conserved segments (including the conserved RRGDL sequence) of the known proprotein convertases (PCs) PC1, PC2, furin, and PC4, we identified a subtilisin/kexin-like PC called PC5 in both mouse and rat tissues. The composite structure (2.85 kb) was deduced from the analysis of the reverse transcription/PCR products combined with the sequence from a clone isolated from a cDNA library made from corticotropin-activated mouse adrenocortical Y1 cells. The deduced cDNA structures of mouse PC5 and rat PC5 showed that the closest homologue is PACE4. Furthermore, like furin, Drosophila melanogaster (d) dfurin2, and PACE4, PC5 shows the presence of a C-terminal Cys-rich domain containing either 5 (PC5 and PACE4) or 10 (dfurin2) repeats of the consensus motif Cys-Xaa2-Cys-Xaa3-Cys-Xaa(5-7)-Cys-Xaa2-Cys-Xaa (8-15)-Cys-Xaa3-Cys-Xaa(9-16). The richest sources of rat PC5 mRNA (3.8 kb) are the adrenal and gut, but it can also be detected in many endocrine and nonendocrine tissues. Corticotropin-stimulated adrenocortical Y1 cells showed an increased expression of PC5 mRNA, suggesting an upregulation by cAMP. In situ hybridization of rat brain sections demonstrated a unique distribution of PC5 compared to PC1, PC2, and furin.

Ontogeny of the prohormone convertases PC1 and PC2 in the mouse hypophysis and their colocalization with corticotropin and alpha-melanotropin

In the adult pituitary, anterior lobe corticotrophs and intermediate lobe melanotrophs differentially process proopiomelanocortin (POMC). Within the corticotrophs, POMC is processed mainly to corticotropin (ACTH) and beta-lipotropin, while alpha-melanotropin (alpha MSH) and beta-endorphin are the major end products in the melanotrophs. The observed transient presence of alpha MSH-like immunoreactivity during ontogeny suggested an age-dependent variation in POMC processing in the adenohypophysis. In this tissue, cell-specific POMC products are likely the result of differential expression of the two known prohormone convertases PC1 and PC2. In the present ontogeny study done in the mouse intermediate and anterior pituitary, we examined how the expression pattern of PC1 and PC2 mRNA transcripts correlates with that of ACTH and alpha MSH-like immunoreactivities. Our data demonstrated that both PC1 and PC2 transcripts can be detected in the presumptive adenohypophysis starting on embryonic day 15 (E15). In the intermediate lobe, PC1 and PC2 mRNAs appear on E18 and E16, respectively, and their levels increased during ontogeny, reaching maximal expression in the adult. Similarly, PC1 expression in the anterior pituitary increased from E15 to adulthood. However, PC2 mRNA expression peaked between postnatal days 1 (P1) and 14 (P14) and then decreased to adult levels. The distribution of PC1 and PC2 immunoreactivity is nicely correlated with the in situ hybridization data. In the anterior lobe, during the P1-P14 postnatal period, PC2 immunoreactivity was detected within cells synthesizing an alpha MSH-like peptide(s). This observation substantiates our earlier biochemical data suggesting that PC2 is the important convertase in the processing of POMC into alpha MSH. Furthermore, the demonstrated variation in the relative ratio of PC1/PC2 expression during ontogeny rationalizes the observed plasticity of POMC processing in the adenohypophysis. It is expected that beta-endorphin processing will follow that of alpha MSH.

On the potential role of proopiomelanocortin in skin physiology and pathology

Pro-opiomelanocortin (POMC) is the precursor of ACTH, alpha-MSH and beta-endorphin, neuropeptides with multiple regulatory functions. Both the pituitary gland and peripheral tissues such as mammalian skin are capable of generating POMC-derived neuropeptides. Mammalian skin is also a target for POMC products; their possible roles in skin physiology and pathology are discussed in this communication.