Nucleobindins and encoded peptides: From cell signaling to physiology

Deciphering the dual nature of nesfatin-1: a tale of zinc ion's Janus-faced influence

BACKGROUND

Nucleobindin-2 (Nucb2) and nesfatin-1 (N1) are widely distributed hormones that regulate numerous physiological processes, from energy homeostasis to carcinogenesis. However, the role of nesfatin-2 (N2), the second product of Nucb2 proteolytic processing, remains elusive. To elucidate the relationship between the structure and function of nesfatins, we investigated the properties of chicken and human homologs of N1, as well as a fragment of Nucb2 consisting of N1 and N2 conjoined in a head-to-tail manner (N1/2).

RESULTS

Our findings indicate that Zn(II) sensing, in the case of N1, is conserved between chicken and human species. However, the data presented here reveal significant differences in the molecular features of the analyzed peptides, particularly in the presence of Zn(II). We demonstrated that Zn(II) has a Janus effect on the M30 region (a crucial anorexigenic core) of N1 and N1/2. In N1 homologs, Zn(II) binding results in the concealment of the M30 region driven by a disorder-to-order transition and adoption of the amyloid fold. In contrast, in N1/2 molecules, Zn(II) binding causes the exposure of the M30 region and its destabilization, resulting in strong exposure of the region recognized by prohormone convertases within the N1/2 molecule.

CONCLUSIONS

In conclusion, we found that Zn(II) binding is conserved between chicken and human N1. However, despite the high homology of chicken and human N1, their interaction modes with Zn(II) appear to differ. Furthermore, Zn(II) binding might be essential for regulating the function of nesfatins by spatiotemporally hindering the N1 anorexigenic M30 core and concomitantly facilitating N1 release from Nucb2.

Calnuc-derived nesfatin-1-like peptide is an activator of tumor cell proliferation and migration

Calnuc (nucleobindin-1, nucb1) is a Ca2+ -binding protein involved in the etiology of many human diseases. To understand the functions of calnuc, we have identified a nesfatin-1-like peptide (NLP) in its N terminus that is proteolyzed by a convertase enzyme in the secretory granules of cells. Mutational studies confirm the presence of a proteolytic cleavage site for proprotein convertase subtilisin/kexin type 1 (PCSK1). We demonstrate that NLP regulates Gαq-mediated intracellular Ca2+ dynamics, likely via a G-protein-coupled receptor. NLP treatment to carcinoma cell lines (SCC131 cells) promotes the expression of regulators of cell cycle, proliferation, and clonogenicity by the AKT/mTOR pathway. NLP is causative of augmented migration and epithelial-mesenchymal transition (EMT), illustrating its metastatic propensity and establishing its tumor promotion ability.

Antioxidant and Anti-Inflammatory Activity on LPS-Stimulated RAW 264.7 Macrophage Cells of White Mulberry (Morus alba L.) Leaf Extracts

The white mulberry (Morus alba L.) is widely used as a medicinal plant in Asia. In this study, the bioactive compounds of ethanolic extracts of white mulberry leaves from the Sakon Nakhon and Buriram cultivars were evaluated. The ethanolic extracts of mulberry leaves from the Sakon Nakhon cultivar showed the highest total phenolic content of 49.68 mg GAE/g extract and antioxidant activities of 4.38 mg GAE/g extract, 4.53 mg TEAC/g extract, and 92.78 mg FeSO₄/g extract using 2,2 diphenyl-1-picrylhydrazyl (DPPH), 2,20-azinobis-(3-ethylbenzothiazolin-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays, respectively. The resveratrol and oxyresveratrol compounds in mulberry leaves were also investigated by high-performance liquid chromatography (HPLC). The mulberry leaf extracts from the Sakon Nakhon and Buriram cultivars showed oxyresveratrol contents of 1.20 ± 0.04 mg/g extract and 0.39 ± 0.02 mg/g extract, respectively, whereas resveratrol was not detected. It was also found that the potent anti-inflammatory properties of mulberry leaf extracts and its compounds, resveratrol and oxyresveratrol, suppressed the LPS-stimulated inflammatory responses in RAW 264.7 macrophage cells by significantly reducing nitric oxide production in a concentration-dependent manner. These compounds further inhibited interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) production and suppressed the mRNA and protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-stimulated RAW 264.7 macrophage cells. Therefore, it is established that mulberry leaf extract and its bioactive compounds contribute to its anti-inflammatory activity.

Expression of phoenixin-14 and nesfatin-1 in the hypothalamo-pituitary-gonadal axis in the phases of the estrous cycle

Phoenixin-14 (PNX-14) and nucleobindin 2 (NUCB2)/nesfatin-1 are regulatory neuropeptides expressed in the hypothalamus. These neuropeptides can be effective in hormonal regulation of the hypothalamo-pituitary-gonadal (HPG) axis and reproductive functions. In the present study, the distribution of PNX-14 and NUCB2/nesfatin-1 in the hypothalamus, pituitary, ovary, and uterus tissues during the phases of the estrous cycle in female rats was investigated. Eighteen Wistar Albino rats determined among animals showing regular estrous cycle by vaginal smear method were divided into three groups: proestrus (Group I), estrus (Group II) and diestrus (Group III). Serum gonadotropin-releasing hormone (GnRH), plasma PNX-14, and NUCB2/nesfatin-1 concentrations were the highest, moderate, and lowest in estrus, diestrus, and proestrus phases, respectively. PNX-14 immunoreactivity in the supraoptic and arcuate nuclei of the hypothalamus and NUCB2/nesfatin-1 immunoreactivity in the paraventricular nuclei were particularly evident in the estrus phase. These neuropeptide immunoreactivities were decreased in different cells of anterior pituitary during proestrus compared with those during estrus and diestrus. PNX-14 immunoreactivity in the ovary, especially during the estrus phase, was diffuse and intense in the granulosa and luteal cells and oocytes, and it was few and weak in theca cells. In addition, NUCB2/nesfatin-1 immunoreactivity was abundant and strong in granulosa and luteal cells, theca and interstitial cells, and oocytes during estrus. In the estrus phase, PNX-14 immunoreactivity was strong in the glandular epithelial cells and stromal cells of the endometrium, also NUCB2/nesfatin-1 immunoreactivity was strong in the epithelial and glandular epithelial cells. As a result, when the estrous cycle was evaluated, it was concluded that the changes in the distribution of PNX-14 and NUCB2/nesfatin-1 at all phases were related to GnRH and that these neuropeptides showed the highest immunoreactivity especially in the HPG axis and uterus tissues of estrus rats.

Zinc Supplementation Improved Neuropeptide Y, Nesfatin-1, Leptin, C-reactive protein, and HOMA-IR of Diet-Induced Obese Rats

Obesity is a mild chronic inflammation that causes many metabolic diseases. It was aimed to investigate some parameters affective on the energy metabolism by adding zinc (Zn, ZnSO4) to drinking water of diet-induced obese rats. Five-week aged, male Sprague Dawley rats divided into as control group, consuming standard rat diet, and high-fat diet (HFD) group. After obesity induced by feeding HFD for 8 weeks, the obese rats were divided into Zn-supplemented obese group (HFD + obese + Zn; 150 mg Zn/L (for 6 weeks), 235 mg Zn/L (7th week), 250 mg Zn/L (8th week) in drinking water) and obese group (HFD + obese). Mean body weight, serum concentrations of C-reactive protein, neuropeptide-Y, leptin, insulin fasting blood glucose, and HOMA-IR were statistically decreased by given Zn in HFD + obese + Zn group compared to HFD + obese rats. It was observed that the total cholesterol, LDL, and HDL cholesterol levels of HFD + obese + Zn group became closer to the control group level, and Zn supplementation caused a statistically significant decrease in cholesterol profile than HFD + obese rats. Also, increased mean serum nesfatin-1 level, an effective protein for the formation of satiety, was analyzed in HFD + obese + Zn group when compared to HFD + obese ones. Serum triglyceride concentration tended to decrease with the effect of Zn in obese rats. In conclusion, it can be said that oral use of Zn could improve energy balance and prevent the occurrence of metabolic diseases related to obesity depending on the anti-inflammatory effect of Zn.

Application of solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) and comparison of both detection techniques (DAD and FLD) to analyse nesfatin-1 in fetal bovine serum samples

In this study, we propose a simple, cost-effective, and sensitive high-performance liquid chromatography with both detection techniques such as diode-array detection and fluorescence detection (HPLC-DAD-FLD) for the determination of nesfatin-1 in fetal bovine serum samples. The limit of detection (LOD) and limit of quantification (LOQ) for nesfatin-1 were set at satisfactory values in the range 0.22–0.35 mg mL−1 and in the range 0.67–1.05 mg mL−1, respectively (at two different wavelengths (DAD) and at four different wavelengths (FLD)). Analyte concentrations were determined as the average value from fetal bovine serum matrix samples. The preliminary results show that the SPE procedure on Isolute Si-TsOH (SCX-3) could be used for further nesfatin-1 analyses in human serum samples. Both the SPE technique, chromatographic analysis with gradient elution mode and detection technique are fast and convenient.

Nucleobindin-derived nesfatin-1 and nesfatin-1-like peptide stimulate pro-opiomelanocortin synthesis in murine AtT-20 corticotrophs through the cAMP/PKA/CREB signaling pathway

Nucleobindin (NUCB)-derived peptides, nesfatin-1 (NES-1) and nesfatin-1-like peptide (NLP) have several physiological roles in vertebrates. While NES-1 is implicated in stress, whether NUCB1/NLP and NUCB2/NES-1 have any effect on proopiomelanocortin (POMC) remains unknown. The main aim of this study was to determine if NES-1 and/or NLP affect POMC synthesis in mouse corticotrophs. Immunocytochemistry was employed to target NUCB colocalization with POMC in immortalized mouse tumoral corticotrophs (AtT-20 cells). The ability of NES-1 and NLP to modulate POMC mRNA and protein in AtT-20 cells was assessed by qPCR and Western blot, respectively. Moreover, cell-signaling molecules mediating the effect of NES-1 and NLP on POMC synthesis in mouse tumoral corticotrophs were studied using pharmacological blockers. Mouse tumoral corticotrophs showed immunoreactivity for both NUCB1/NLP and NUCB2/NES-1. Both NES-1 and NLP exerted a stimulatory effect on POMC transcript abundance and protein expression in a dose- and time-dependent manner. This effect was comparable to corticotropin-releasing factor (CRF, positive control) stimulation of POMC. Incubation of mouse tumoral corticotrophs with NES-1 or NLP upregulated the phosphorylation of protein kinase A (PKA) and cAMP-response element-binding protein (CREB). The stimulatory effect of these peptides on POMC transcript abundance and protein expression was blocked by the PKA inhibitor, H89, and an adenylate cyclase inhibitor, 2',3'-dideoxyadenosine (DDA). These pharmacological studies indicate that NES-1 and NLP act through the cAMP/PKA/CREB cellular pathway to stimulate POMC synthesis. Our results provide molecular evidence to support a stimulatory role for nucleobindin-derived peptides on POMC synthesis from corticotrophs. Collectively, this research indicates that corticotrophs produce NUCBs, and the encoded peptides NES-1 and NLP could elicit a direct action to stimulate the pituitary stress hormone. This stimulatory effect is mediated by an uncharacterized G protein-coupled receptor (GPCR) that utilizes the cAMP/PKA/CREB pathway.

A comparative account of nesfatin-1 in vertebrates

Nesfatin-1 was discovered as an anorexigenic peptide derived from proteolytic cleavage of the prepropeptide, nucleobindin 2 (NUCB2). It is widely expressed in central as well as peripheral tissues and is known to have pleiotropic effects such as regulation of feeding, reproduction, cardiovascular functions and maintenance of glucose homeostasis. In order to execute its multifaceted role, nesfatin-1 employs diverse signaling pathways though its receptor has not been identified till date. Further, nesfatin-1 is reported to be under the regulatory effect of feeding state, nutritional status as well as several metabolic and reproductive hormones. This peptide has also been associated with variety of human diseases, especially metabolic, reproductive, cardiovascular and mental disorders. The current review is aimed to present a consolidated picture and highlight lacunae for further investigation in order to develop a deeper comprehensive understanding on physiological significance of nesfatin-1 in vertebrates.

Nesfatin-1 in lipid metabolism and lipid-related diseases

Nesfatin-1, an anorexic neuropeptide discovered in 2006, is widely distributed in the central nervous system and peripheral tissues. It has been shown to be involved in the regulation of food intake and lipid metabolism, inhibiting fat accumulation, accelerating lipid decomposition, and in general, inhibiting the development of lipid-related diseases, such as obesity and metabolic syndrome. Potential mechanisms of Nesfatin-1 action in lipid metabolism and lipid-related diseases will be discussed as well as its role as a biomarker in cardiovascular disease. This review expected to provide a new strategy for the diagnosis and prevention of clinically related diseases.

Aberrant environment and PS-binding to calnuc C-terminal tail drives exosomal packaging and its metastatic ability

The characteristic features of cancer cells are aberrant (acidic) intracellular pH and elevated levels of phosphatidylserine. The primary focus of cancer research is concentrated on the discovery of biomarkers directed towards early diagnosis and therapy. It has been observed that azoxymethane-treated mice demonstrate an increased expression of calnuc (a multi-domain, Ca2+- and DNA-binding protein) in their colon, suggesting it to be a good biomarker of carcinogenesis. We show that culture supernatants from tumor cells have significantly higher amounts of secreted calnuc compared to non-tumor cells, selectively packaged into exosomes. Exosomal calnuc is causal for epithelial-mesenchymal transition and atypical migration in non-tumor cells, which are key events in tumorigenesis and metastasis. In vitro studies reveal a significant affinity for calnuc towards phosphatidylserine, specifically to its C-terminal region, leading to the formation of 'molten globule' conformation. Similar structural changes are observed at acidic pH (pH 4), which demonstrates the role of the acidic microenvironment in causing the molten globule conformation and membrane interaction. On a precise note, we propose that the molten globule structure of calnuc caused by aberrant conditions in cancer cells to be the causative mechanism underlying its exosome-mediated secretion, thereby driving metastasis.

Nesfatin-1 and Nesfatin-1-like peptide suppress basal and TRH-Induced expression of prolactin and prolactin regulatory element-binding protein mRNAs in rat GH3 somatolactotrophs

Prolactin (PRL), mainly synthesized and secreted by the lactotrophs and somatolactotrophs of the anterior pituitary, is a pleiotropic hormone that regulates lactation. In the last decade, nesfatin-1 (NESF) and NESF-like peptide (NLP), encoded in nucleobindin 1 and 2 (NUCB1 and NUCB2), respectively, were characterized as metabolic factors with a potential role in the control of pituitary hormones. We hypothesized that NUCBs and their encoded peptides (NESF and NLP) suppress PRL transcription in the pituitary. The main objective of this research was to determine whether exogenous NESF and NLP, and/or endogenous NUCB1 and NUCB2 regulate the expression of prl and preb mRNAs. Using immortalized rat somatolactotrophs (GH3 cells), dose-response studies were performed to test whether NESF and NLP affect prl and preb. Moreover, the ability of these peptides to modulate the effects of the PRL stimulator thyrotropin releasing hormone (TRH) was studied. Besides, the effects of siRNA-mediated knockdown of endogenous NUCBs on prl and preb mRNAs were determined. NESF and NLP reduced the transcription of prl and preb in GH3 cells. Both NESF and NLP also prevented the stimulatory effects of TRH prl and preb expression. The knockdown of endogenous NUCB1 attenuates both basal prl and TRH-induced expression of prl and preb, while the silencing of NUCBs did not affect the actions of exogenous NESF or NLP. Overall, this work reveals that NUCBs and encoded-peptides are novel regulators of PRL. Future research should test whether the effects observed here in GH3 cells are preserved both in vivo and at the post-transcriptional level.

Localization of Nucleobindin2/Nesfatin-1-Like Immunoreactivity in Human Lungs and Neutrophils

Nucleobindin2 (NUCB2)/nesfatin-1 expression in human plasma positively correlates with the expression of pro-inflammatory cytokines in patients with chronic obstructive pulmonary disease (COPD), implicating its potential role in neutrophilic lung inflammation. There are no data on the localization of nucleobindin2 (NUCB2)/nesfatin-1 in human lungs and inflammatory cells. We examined the localization of NUCB2/nesfatin-1-immunoreactivity in normal and inflamed human lungs obtained from COPD patients and neutrophils with light and immunoelectron microscopy. Immunohistology showed localization of NUCB2/nesfatin-1-like immunoreactivity in the bronchiolar epithelium, alveolar septa, vascular endothelium and various immune cells of normal and inflamed lungs. Further, NUCB2/nesfatin-1-like immunoreactivity accumulated within 0.5 μm of the plasma membrane in human neutrophils following 90 min. of 1 ng/mL LPS stimulation. NUCB2/nesfatin-1-like immunoreactivity was also found to localize in euchromatic portions of neutrophilic nuclei at five times the mean concentration compared to heterochromatin. Finally, our results indicate that NUCB2/nesfatin-1-like immunoreactivity is predominantly cytoplasmic including that in the Golgi complex and vesicles as it localizes at two times the concentration in neutrophilic cytoplasm compared to nucleus. Our study is the first to detail the localization of NUCB2/nesfatin-1-like immunoreactivity in lungs and neutrophils, and nuclear localization of NUCB2/nesfatin-1 also implicates its potential role in transcriptional regulation.

The Complex World of Regulation of Pituitary Growth Hormone Secretion: The Role of Ghrelin, Klotho, and Nesfatins in It

The classic concept of how pituitary GH is regulated by somatostatin and GHRH has changed in recent years, following the discovery of peripheral hormones involved in the regulation of energy homeostasis and mineral homeostasis. These hormones are ghrelin, nesfatins, and klotho. Ghrelin is an orexigenic hormone, released primarily by the gastric mucosa, although it is widely expressed in many different tissues, including the central nervous system and the pituitary. To be active, ghrelin must bind to an n-octanoyl group (n = 8, generally) on serine 3, forming acyl ghrelin which can then bind and activate a G-protein-coupled receptor leading to phospholipase C activation that induces the formation of inositol 1,4,5-triphosphate and diacylglycerol that produce an increase in cytosolic calcium that allows the release of GH. In addition to its direct action on somatotrophs, ghrelin co-localizes with GHRH in several neurons, facilitating its release by inhibiting somatostatin, and acts synergistically with GHRH stimulating the synthesis and secretion of pituitary GH. Gastric ghrelin production declines with age, as does GH. Klotho is an anti-aging agent, produced mainly in the kidneys, whose soluble circulating form directly induces GH secretion through the activation of ERK1/2 and inhibits the inhibitory effect that IGF-I exerts on GH. Children and adults with untreated GH-deficiency show reduced plasma levels of klotho, but treatment with GH restores them to normal values. Deletions or mutations of the Klotho gene affect GH production. Nesfatins 1 and 2 are satiety hormones, they inhibit food intake. They have been found in GH3 cell cultures where they significantly reduce the expression of gh mRNA and that of pituitary-specific positive transcription factor 1, consequently acting as inhibitors of GH production. This is a consequence of the down-regulation of the cAMP/PKA/CREB signaling pathway. Interestingly, nesfatins eliminate the strong positive effect that ghrelin has on GH synthesis and secretion. Throughout this review, we will attempt to broadly analyze the role of these hormones in the complex world of GH regulation, a world in which these hormones already play a very important role.

Nesfatin-1 and nesfatin-1-like peptide suppress growth hormone synthesis via the AC/PKA/CREB pathway in mammalian somatotrophs

Nesfatin-1 (NESF) and NESF-like peptide (NLP), encoded in nucleobindin 2 and 1 (NUCB2 and NUCB1), respectively, are orphan ligands and metabolic factors. We hypothesized that NESF and NLP suppress growth hormone (GH) synthesis, and aimed to determine whether mammalian somatotrophs are a source and site of action of these peptides. Using immortalized rat somatotrophs (GH3 cells), NUCB expression was determined by qPCR, immunofluorescence and Western blot. NESF and NLP binding to GH3 cells was tested using fluorescence imaging. Both time- and concentration-dependent studies were performed to test whether NESF and NLP affect GH. Moreover, the ability of these peptides to modulate the effects of ghrelin, and cell-signaling pathways were studied. GH3 cells express NUCB mRNAs and protein. Labeled NESF and NLP bind to the surface of GH3 cells, and incubation with either NESF or NLP decreased GH mRNA and protein expression, downregulated pit-1 mRNA, and blocked the GH stimulatory effects of ghrelin. Pre-incubation with either of these peptides reduced CREB phosphorylation by an AC-activator, but not when PKA was directly activated by a cAMP analog. Our results indicate that rat somatotrophs are a source of NUCBs, and that NESF and NLP downregulate GH synthesis through the AC/PKA/CREB signaling pathway.

Nucleobindin-1 regulates ECM degradation by promoting intra-Golgi trafficking of MMPs

Matrix metalloproteinases (MMPs) degrade several ECM components and are crucial modulators of cell invasion and tissue organization. Although much has been reported about their function in remodeling ECM in health and disease, their trafficking across the Golgi apparatus remains poorly understood. Here we report that the cis-Golgi protein nucleobindin-1 (NUCB1) is critical for MMP2 and MT1-MMP trafficking along the Golgi apparatus. This process is Ca2+-dependent and is required for invasive MDA-MB-231 cell migration as well as for gelatin degradation in primary human macrophages. Our findings emphasize the importance of NUCB1 as an essential component of MMP transport and its overall impact on ECM remodeling.

A Comparative Update on the Neuroendocrine Regulation of Growth Hormone in Vertebrates

Growth hormone (GH), mainly produced from the pituitary somatotrophs is a key endocrine regulator of somatic growth. GH, a pleiotropic hormone, is also involved in regulating vital processes, including nutrition, reproduction, physical activity, neuroprotection, immunity, and osmotic pressure in vertebrates. The dysregulation of the pituitary GH and hepatic insulin-like growth factors (IGFs) affects many cellular processes associated with growth promotion, including protein synthesis, cell proliferation and metabolism, leading to growth disorders. The metabolic and growth effects of GH have interesting applications in different fields, including the livestock industry and aquaculture. The latest discoveries on new regulators of pituitary GH synthesis and secretion deserve our attention. These novel regulators include the stimulators adropin, klotho, and the fibroblast growth factors, as well as the inhibitors, nucleobindin-encoded peptides (nesfatin-1 and nesfatin-1-like peptide) and irisin. This review aims for a comparative analysis of our current understanding of the endocrine regulation of GH from the pituitary of vertebrates. In addition, we will consider useful pharmacological molecules (i.e. stimulators and inhibitors of the GH signaling pathways) that are important in studying GH and somatotroph biology. The main goal of this review is to provide an overview and update on GH regulators in 2020. While an extensive review of each of the GH regulators and an in-depth analysis of specifics are beyond its scope, we have compiled information on the main endogenous and pharmacological regulators to facilitate an easy access. Overall, this review aims to serve as a resource on GH endocrinology for a beginner to intermediate level knowledge seeker on this topic.

Ontogenetic Pattern Changes of Nucleobindin-2/Nesfatin-1 in the Brain and Intestinal Bulb of the Short Lived African Turquoise Killifish

Nesfatin-1 (Nesf-1) was identified as an anorexigenic and well conserved molecule in rodents and fish. While tissue distribution of NUCB2 (Nucleobindin 2)/Nesf-1 is discretely known in vertebrates, reports on ontogenetic expression are scarce. Here, we examine the age-related central and peripheral expression of NUCB2/Nesf-1 in the teleost African turquoise killifish Nothobranchius furzeri, a consolidated model organism for aging research. We focused our analysis on brain areas responsible for the regulation of food intake and the rostral intestinal bulb, which is analogous of the mammalian stomach. We hypothesize that in our model, the stomach equivalent structure is the main source of NUCB2 mRNA, displaying higher expression levels than those observed in the brain, mainly during aging. Remarkably, its expression significantly increased in the rostral intestinal bulb compared to the brain, which is likely due to the typical anorexia of aging. When analyzing the pattern of expression, we confirmed the distribution in diencephalic areas involved in food intake regulation at all age stages. Interestingly, in the rostral bulb, NUCB2 mRNA was localized in the lining epithelium of young and old animals, while Nesf-1 immunoreactive cells were distributed in the submucosae. Taken together, our results represent a useful basis for gaining deeper knowledge regarding the mechanisms that regulate food intake during vertebrate aging.