RESP18, a novel endocrine secretory protein transcript, and four other transcripts are regulated in parallel with pro-opiomelanocortin in melanotropes

In Cerebellar Atrophy of 12-Month-Old ATM-Null Mice, Transcriptome Upregulations Concern Most Neurotransmission and Neuropeptide Pathways, While Downregulations Affect Prominently Itpr1, Usp2 and Non-Coding RNA

The autosomal recessive disorder Ataxia-Telangiectasia is caused by a dysfunction of the stress response protein, ATM. In the nucleus of proliferating cells, ATM senses DNA double-strand breaks and coordinates their repair. This role explains T-cell dysfunction and tumour risk. However, it remains unclear whether this function is relevant for postmitotic neurons and underlies cerebellar atrophy, since ATM is cytoplasmic in postmitotic neurons. Here, we used ATM-null mice that survived early immune deficits via bone-marrow transplantation, and that reached initial neurodegeneration stages at 12 months of age. Global cerebellar transcriptomics demonstrated that ATM depletion triggered upregulations in most neurotransmission and neuropeptide systems. Downregulated transcripts were found for the ATM interactome component Usp2, many non-coding RNAs, ataxia genes Itpr1, Grid2, immediate early genes and immunity factors. Allelic splice changes affected prominently the neuropeptide machinery, e.g., Oprm1. Validation experiments with stressors were performed in human neuroblastoma cells, where ATM was localised only to cytoplasm, similar to the brain. Effect confirmation in SH-SY5Y cells occurred after ATM depletion and osmotic stress better than nutrient/oxidative stress, but not after ATM kinase inhibition or DNA stressor bleomycin. Overall, we provide pioneer observations from a faithful A-T mouse model, which suggest general changes in synaptic and dense-core vesicle stress adaptation.

Mechanisms of ag85a/b DNA vaccine conferred immunotherapy and recovery from Mycobacterium tuberculosis-induced injury

Our previous research developed a novel tuberculosis (TB) DNA vaccine ag85a/b that showed a significant therapeutic effect on the mouse tuberculosis model by intramuscular injection (IM) and electroporation (EP). However, the action mechanisms between these two vaccine immunization methods remain unclear. In a previous study, 96 Mycobacterium tuberculosis (MTB) H37 Rv-infected BALB/c mice were treated with phosphate-buffered saline, 10, 50, 100, and 200 μg ag85a/b DNA vaccine delivered by IM and EP three times at 2-week intervals, respectively. In this study, peripheral blood mononuclear cells (PBMCs) from three mice in each group were isolated to extract total RNA. The gene expression profiles were analyzed using gene microarray technology to obtain differentially expressed (DE) genes. Finally, DE genes were validated by real-time reverse transcription-quantitive polymerase chain reaction and the GEO database. After MTB infection, most of the upregulated DE genes were related to the digestion and absorption of nutrients or neuroendocrine (such as Iapp, Scg2, Chga, Amy2a5), and most of the downregulated DE genes were related to cellular structural and functional proteins, especially the structure and function proteins of the alveolar epithelial cell (such as Sftpc, Sftpd, Pdpn). Most of the abnormally upregulated or downregulated DE genes in the TB model group were recovered in the 100 and 200 μg ag85a/b DNA IM groups and four DNA EP groups. The pancreatic secretion pathway downregulated and the Rap1 signal pathway upregulated had particularly significant changes during the immunotherapy of the ag85a/b DNA vaccine on the mouse TB model. The action targets and mechanisms of IM and EP are highly consistent. Tuberculosis infection causes rapid catabolism and slow anabolism in mice. For the first time, we found that the effective dose of the ag85a/b DNA vaccine immunized whether by IM or EP could significantly up-regulate immune-related pathways and recover the metabolic disorder and the injury caused by MTB.

Regulated Endocrine-Specific Protein-18, an Emerging Endocrine Protein in Physiology: A Literature Review

Regulated endocrine-specific protein-18 (RESP18), a novel 18-kDa protein, was first identified in neuroendocrine tissue. Subsequent studies showed that Resp18 is expressed in the adrenal medulla, brain, pancreas, pituitary, retina, stomach, superior cervical ganglion, testis, and thyroid and also circulates in the plasma. Resp18 has partial homology with the islet cell antigen 512, also known as protein tyrosine phosphatase, receptor type N (PTPRN), but does not have phosphatase activity. Resp18 might serve as an intracellular signal; however, its function is unclear. It is regulated by dopamine, glucocorticoids, and insulin. We recently reported that the targeted disruption of the Resp18 locus in Dahl salt-sensitive rats increased their blood pressure and caused renal injury. The aim of the present review was to provide a comprehensive summary of the reported data currently available, especially the expression and proposed organ-specific function of Resp18.

Stability of proICA512/IA-2 and its targeting to insulin secretory granules require β4-sheet-mediated dimerization of its ectodomain in the endoplasmic reticulum

The type 1 diabetes autoantigen ICA512/IA-2/RPTPN is a receptor protein tyrosine phosphatase of the insulin secretory granules (SGs) which regulates the size of granule stores, possibly via cleavage/signaling of its cytosolic tail. The role of its extracellular region remains unknown. Structural studies indicated that β2- or β4-strands in the mature ectodomain (ME ICA512) form dimers in vitro. Here we show that ME ICA512 prompts proICA512 dimerization in the endoplasmic reticulum. Perturbation of ME ICA512 β2-strand N-glycosylation upon S508A replacement allows for proICA512 dimerization, O-glycosylation, targeting to granules, and conversion, which are instead precluded upon G553D replacement in the ME ICA512 β4-strand. S508A/G553D and N506A/G553D double mutants dimerize but remain in the endoplasmic reticulum. Removal of the N-terminal fragment (ICA512-NTF) preceding ME ICA512 allows an ICA512-ΔNTF G553D mutant to exit the endoplasmic reticulum, and ICA512-ΔNTF is constitutively delivered to the cell surface. The signal for SG sorting is located within the NTF RESP18 homology domain (RESP18-HD), whereas soluble NTF is retained in the endoplasmic reticulum. Hence, we propose that the ME ICA512 β2-strand fosters proICA512 dimerization until NTF prevents N506 glycosylation. Removal of this constraint allows for proICA512 β4-strand-induced dimerization, exit from the endoplasmic reticulum, O-glycosylation, and RESP18-HD-mediated targeting to granules.

Regulated endocrine-specific protein 18 (RESP18) is localized to and regulated in A-like cells and G-cells in rat stomach

The regulated endocrine-specific protein 18 (RESP18) has previously been localized to different endocrine cells and neurons, in particular the pituitary gland and hypothalamus. It is found in the lumen of the endoplasmic reticulum and is degraded at the post-ER pre-Golgi compartment, and a role in processing of secreted peptides has been hypothesized. The present study examines localization of RESP18 in the gastrointestinal mucosa of rats by immunohistochemistry, and expression and regulation in response to hypergastrinemia induced by acid inhibition (pantoprazole), gastrin antagonism (YF476), fasting-refeeding and octreotide by mRNA measurements. RESP18 was mainly found in the gastric mucosa, but could also be detected in a few, scattered cells in the lower small intestine and in colon. In the antral mucosa, all RESP18 immunoreactivity was localized to ghrelin-producing A-like cells and gastrin-producing G-cells. In the corpus mucosa, a significant fraction, but not all of the RESP18 immunoreactive cells, were A-like cells. In both antrum and corpus, Resp18 mRNA seemed to vary similarly with the activation of the A-like cells, and in the antrum also with stimulation of the G-cells. This study demonstrates, for the first time, the localization of RESP18 to specific neuroendocrine cells of the gastrointestinal mucosa and that it seems to be regulated synchronously with the peptides secreted from these cells. This suggests that Resp18 may indeed have a functional role in the synthesis or storage of these gastrointestinal peptides.

Locating a Blood Pressure Quantitative Trait Locus Within 117 kb on the Rat Genome

Previously, a blood pressure (BP) quantitative trait locus (QTL) on rat chromosome 9 (RNO9) was localized to a <2.4 cM interval using congenic strains generated by introgressing segments of RNO9 from the Dahl salt-resistant (R) rat into the background of the Dahl salt-sensitive (S) rat. Renal gene expression using Affymetrix gene chips was profiled on S and a congenic strain spanning the 2.4-cM BP QTL interval. This analysis identified 20 differentially expressed genes/expressed sequence tags. Of these, the locus with the greatest differential expression (30- to 35-fold) was regulated endocrine-specific protein 18 ( Resp18 ), which also mapped in the 2.4-cM BP QTL interval. Additional substitution mapping located the QTL to <0.4 cM or ≈493 kb. This newly defined QTL region still included Resp18 . Nucleotide variants were identified between S and R genomic DNA of Resp18 in the coding, 5′ regulatory and 3′ untranslated regions. The coding sequence variation (T/C) occurs in exon 2 and predicts an amino acid change (Ile/Val) in the protein product. Resp18 was considered a differentially expressed positional candidate for the QTL. To fine-map the BP QTL, we constructed a congenic strain with a smaller introgressed region. Compared with the S rat, this strain (1) had significantly lower BP, (2) did not contain the R form of Resp18 , and (3) did not retain the rather spectacular differential expression of Resp18. Together, these results demonstrate that a BP QTL independent of Resp18 exists within the newly defined 117-kb QTL region on RNO9.

Extensive oligonucleotide microarray transcriptome analysis of the rat cerebral artery and arachnoid tissue

Cerebral vessels have certain distinct anatomical and developmental characteristics which are well known, but their characteristic genetic expression profile remains as yet only poorly understood. We investigated gene expression in the rat cerebral artery in comparison with the rat descending aorta, two locations which have obviously different anatomical and developmental characteristics. Since the contamination of cerebral small arteries by arachnoid tissue is to a certain extent inevitable, we also performed a gene expression analysis of arachnoid tissue as a background. In an effort to obtain the necessary quality and quantity of total RNA, a novel freeze-fracture apparatus minimizing the time required for the entire procedure from tissue separation to RNA preparation was used. With the material obtained, a group of genes highly expressed in each tissue was detected by oligonucleotide microarray analysis. In the circle of Willis, peptide-19 (PEP-19), connexin-37 (CXN-37), growth arrest-and DNA damage-inducible gene (GADD45), and the putative G protein coupled receptor RA1c, Notch-1, and jagged-1 were predominantly expressed. In arachnoid tissue, bone morphologic protein (BMP)-7, BMP-6, beta defensin-1, neuroendocrine protein 7B2, thiol-specific antioxidant protein, IL-18, beta-chain clathrin-associated protein complex AP-1, and angiopoietin-2 were highly expressed. In the aorta, most of the abundantly expressed genes related to lipid metabolism. By means of oligonucleotide microarray analysis, the distinct gene expression profiles in the circle of Willis arachnoid tissue, and aorta were made evident. From these findings it is reasonable to conclude that a functional interaction exists between the circle of Willis and arachnoid tissue.

Post-translational modifications of ICA512, a receptor tyrosine phosphatase-like protein of secretory granules

The autoantigen of type I diabetes ICA512 is a receptor tyrosine phosphatase-like protein enriched in the secretory granule membranes of neurons and peptide secreting endocrine cells. While the function of ICA512 remains unknown, it is thought to link regulated neuropeptide and peptide hormone secretion with signal transduction pathways involving tyrosine phosphorylation/dephosphorylation. To characterize further its biochemical properties, we conducted studies in the bovine pituitary, an abundant source of native ICA512, as well as in fibroblasts transfected with various human ICA512 cDNA constructs. Based on these studies we have established that the signal peptide of ICA512 encompasses residues 1-34 and that the ectodomain of ICA512 undergoes multiple post-translation modifications, including N-glycosylation. Newly synthesized ICA512 appears first as a pro-protein of 110 kDa that is then converted by post-translational modifications into a 130-kDa species. Cleavage of pro-ICA512 at a consensus for furin-like convertases generates a 60-66-kDa ICA512 transmembrane fragment (amino acids 449-979). Such processing ICA512 is not restricted to neuroendocrine cells, as it can also occur in transfected fibroblasts. Finally, the predicted N-terminal fragment of ICA512 resulting from this cleavage (amino acids 35-448) or parts thereof are present in the neurosecretosomes of posterior pituitary, raising the possibility that they may be secreted upon exocytosis of secretory granules.

The expression of endothelin-1 and endothelin-converting enzyme-1 (ECE-1) are independently regulated in bovine aortic endothelial cells

The endopeptidase called endothelin-converting enzyme-1 (ECE-1) is thought to play a physiological role in endothelin-1 (ET-1) biosynthesis. For human ECE-1, differential splicing of messenger RNA (mRNA) results in the synthesis of three isoforms, termed ECE-1a, ECE-1b, and ECE-1c. The isoform(s) responsible for the hydrolysis of the biosynthetic intermediate big ET-1 in endothelial cells have yet to be assigned. To investigate whether the expression of mRNAs for preproET-1 and ECE-1 are regulated in parallel, a variety of conditions were used to compare levels of ET-1 synthesis by bovine aortic endothelial cells (BAECs) with levels of mRNA for preproET-1, ECE-1a, ECE-1c, and the combined ECE-1 isoforms (ECE-1a/b/c). Stimulation of BAECs with tumor necrosis factor-alpha or transforming growth factor-beta increased ET-1 synthesis, and treatment of BAECs with 2-chloroadenosine or staurosporine caused concentration-dependent reductions in ET-1 synthesis. Estimates of mRNA levels by reverse transcription-polymerase chain reaction (RT-PCR) with linear cycling conditions showed changes in preproET-1 expression to correlate well with ET-1 secretion. In contrast, RT-PCR analysis of ECE-1 expression by using primer pairs to measure ECE-1a, ECE-1c, or all the ECE-1 isoforms simultaneously showed no correlation between their mRNA levels and those of preproET-1. This indicates that under the conditions investigated, expression of ECE-1 is not coordinated with ET-1 synthesis in BAECs.

A novel neuroendocrine intracellular signaling pathway

Expression of many components of the secretory pathway in peptidergic neuroendocrine cells is precisely controlled in response to secretagogues. Regulated endocrine-specific protein (RESP18) was identified as a dopamine-regulated intermediate pituitary transcript. Although the amino acid sequence of RESP18 initially suggested that it might be a novel preprohormone, its widespread expression in peptide-producing neurons and endocrine cells and its localization to the lumen of the endoplasmic reticulum suggested that it subserves a unique function. Subtractive hybridization of a pituitary corticotrope AtT-20 cell line engineered for inducible RESP18 expression demonstrated a RESP18-dependent induction of several transcripts. Regulation of RESP18 expression in vitro and in vivo was accompanied by changes in the same transcripts. Several cDNAs encoding transcripts up-regulated by RESP18 were analyzed by DNA sequencing, searching the GenBank databases for homologous proteins, and Northern blotting. One novel clone showed a tissue distribution nearly identical to that of RESP18. One clone was identical to rat LIMK2, a protein kinase containing modular protein-protein interaction LIM (lin-11, isl-1, mec-3) domains. Another clone was similar to monomeric bacterial isocitrate dehydrogenases. Like the unfolded protein response, these data demonstrate a novel signaling pathway from the secretory pathway lumen to the nucleus. RESP18 acts as a lumicrine peptide (an intracellular luminal autocrine hormone) inducing this pathway.

Paradoxical behavioral response to apomorphine in tenascin-gene knockout mouse

Tenascin is a large extracellular matrix glycoprotein which is highly expressed in the developing nervous system. To examine the role of tenascin in vivo, we have produced mice in which the tenascin-gene is inactivated. These animals did not easily habituate to unfamiliar circumstances and displayed hyperlocomotion. A dopamine receptor agonist, apomorphine, reduced this hyperlocomotion dose dependently, but this phenomenon was not due to the appearance of apomorphine-induced stereotypic behavior, suggesting that tenascin-gene mutant mice have a paradoxical behavioral response to apomorphine compared to wild-type mice.

Expression of RESP18 in peptidergic and catecholaminergic neurons

We examined the expression of regulated endocrine-specific protein of 18-kD (RESP18) in selected peptidergic and catecholaminergic neurons of adult rat brain. In the hypothalamic paraventricular, supraoptic, and accessory nuclei, RESP18 mRNA was highly expressed in neurons immunostained for oxytocin and vasopressin. RESP18 mRNA was also highly expressed in paraventricular nucleus neurons immunostained for corticotropin-releasing hormone, thyrotropin-releasing hormone, and somatostatin. RESP18 mRNA was expressed in POMC cells of the arcuate nucleus, in neuropeptide Y cells of the dorsal tegmental nucleus, lateral reticular nucleus, and hippocampus, and in brainstem catecholaminergic neurons. RESP18 mRNA expression was high in all paraventricular and arcuate neurons, but RESP18 protein was detectable in the perikarya of a subset of these neurons, suggesting an important post-transcriptional component to the regulation of RESP18 expression. RESP18 antisera immunostained perikarya but not axon fibers or terminals. Sub-cellular fractionation of homogenates of several hypothalamic nuclei identified RESP18 protein in fractions enriched in endoplasmic reticulum. The presence of 22- and 24-kD RESP18 isoforms in the neural lobe of the pituitary indicated that some RESP18 protein exited the endoplasmic reticulum. The post-transcriptional regulation of RESP18 expression and localization of RESP18 protein primarily to the endoplasmic reticulum suggests that RESP18 plays a regulatory role in peptidergic neurons.

Cloning, human chromosomal assignment, and adipose and hepatic expression of the CL-6/INSIG1 gene

Rat CL-6 is the most highly insulin-induced gene in a liver cell line and is expressed in proliferating liver during regeneration and development. CL-6 is now denoted INSIG1 (insulin-induced gene 1). Human INSIG1 was isolated and found to be 80% identical to the rat gene within the translated region. It was located on human chromosome 7 within band q36. The human INSIG1 promoter conferred a high level of expression in both liver and fibroblast cell lines. INSIG1 expression was upregulated at the transcriptional level in rat regenerating liver and induced in a model of murine adipocyte differentiation, suggesting that INSIG1 may play a role in growth and differentiation of tissues involved in metabolic control.

Differential expression of tenascin by astrocytes associated with the supraoptic nucleus (SON) of hydrated and dehydrated adult rats

The present study evaluated the expression of tenascin by astrocytes in the supraoptic nucleus and associated ventral glial limitans (SON-VGL) under conditions that induce reversible changes in neuronal organization (dehydration and rehydration). Immunostaining of astroglia cultured from rat neonatal SON-VGL confirmed that these cells are capable of both expressing and secreting tenascin. Observations of immunostained tissue sections from adult rats revealed tenascin immunoreactivity primarily in the VGL and dendritic zone, subjacent to SON neuronal somata. Comparison of immunostained tissues from hydrated and dehydrated animals showed an apparent decrease in the intensity of immunostaining with dehydration. Subsequent Western blots of similar tissues confirmed the presence of the 210-220-kDa tenascin protein in the SON-VGL. SON-VGL tissues from control, dehydrated, and rehydrated rats were then studied by using SDS-PAGE and quantitative gel densitometry. A consistent decrease in tenascin concentration was observed by 6 days of dehydration that, with rehydration, reversed back toward or beyond control levels. Together, these observations indicate that SON-VGL astrocytes variably express tenascin and that this protein may play a role in adult SON plasticity.

Location of neurons that express regulated endocrine-specific protein-18 in the rat diencephalon

In situ hybridization for regulated endocrine-specific protein-18 messenger RNA showed a distinct and limited pattern of expression in the hypothalamus, midline thalamus, amygdala and hippocampus of the rat. High levels of regulated endocrine-specific protein-18 messenger RNA were found in the magnocellular neurons of the hypothalamic paraventricular, supraoptic and accessory nuclei, in the neurons of the periventricular, medial tuberal, arcuate, lateral and perifornical nuclei, infundibular stalk, and in the ventrolateral division of the ventromedial nucleus and compact division of the dorsomedial nucleus. Lower levels of regulated endocrine-specific protein-18 messenger RNA were found in the parvocellular divisions of the paraventricular nucleus as well as in the bed nucleus of the stria terminalis, median preoptic nucleus, medial preoptic nucleus, medial and lateral preoptic areas, subfornical organ, suprachiasmatic nucleus, anterior hypothalamic area, zona incerta, ventromedial nucleus, dorsomedial nucleus and tuber cinereum. Regulated endocrine-specific protein-18 messenger RNA was also found in thalamic structures including the paraventricular, central medial, intermediodorsal, anterodorsal, rhomboid and reticular nuclei. Signal was also identified in the medial and lateral habenula, in the central, medial, basomedial and anterior cortical nuclei of the amygdala, and in the CA1-CA3 and dentate gyrus of the hippocampus. Dopamine may regulate regulated endocrine-specific protein-18 expression in the CNS because (i) regulated endocrine-specific protein-18 was originally identified in melanotropes based on its regulation by dopaminergic agents and (ii) many of the nuclei that contain regulated endocrine-specific protein-18 also receive dopaminergic input. The localization of regulated endocrine-specific protein-18 in the diencephalon suggests that regulated endocrine-specific protein-18 is involved in regulation of limbic and autonomic function, neuroendocrine control of salt and water balance, reproductive function and feeding behavior.

A neuroendocrine-specific protein localized to the endoplasmic reticulum by distal degradation

Regulated endocrine-specific protein, 18-kDa (RESP18), was previously cloned from rat neurointermediate pituitary based on its coordinate regulation with proopiomelanocortin and neuroendocrine specificity. RESP18 has no homology to any known protein. Although RESP18 is translocated across microsomal membranes after in vitro translation, AtT-20 pituitary tumor cells, which endogenously synthesize RESP18, do not release it into the culture medium. In this work, immunostaining and subcellular fractionation have identified RESP18 as an endoplasmic reticulum (ER) protein. Biosynthetic labeling and temperature block studies of AtT-20 cells demonstrated the localization of RESP18 to the ER lumen by a unique mechanism, degradation by proteolysis in a post-ER pre-Golgi compartment. Proteases in this compartment were saturated by exogenous RESP18 overexpression in AtT-20 cells. Furthermore, a calpain protease inhibitor enhanced secretion of RESP18 from AtT-20 cells overexpressing RESP18. Saturation and inhibition of the RESP18 degrading proteases allowed RESP18 to enter secretory granules and acquire a post-translational modification, likely O-glycosylation; this modified 21-kDa RESP18 isoform was the only RESP18 secreted. Rat anterior pituitary extracts contain 18-kDa and O-glycosylated RESP18 with similar properties. Exogenous RESP18 expression in hEK-293 cells demonstrated ER localization and RESP18 metabolism similar to AtT-20 cells, indicating that the cellular machinery involved in localizing RESP18 is not specific to neuroendocrine cells. The data implicate a novel ER localization mechanism for this neuroendocrine-specific luminal ER resident.

Molecular probing of the secretory pathway in peptide hormone-producing cells

The biosynthetic machinery in the melanotrope cells of the Xenopus intermediate pituitary is primarily dedicated to the generation of proopiomelanocortin (POMC)-derived, melanophore-stimulating peptides. Transfer of the animal to a black background stimulates the production of these peptides and causes a dramatic increase in POMC mRNA levels. To identify genes involved in the biosynthesis and regulated release of peptide hormones, we differentially screened an intermediate pituitary cDNA library of toads adapted to a black background with cDNA probes derived from intermediate pituitary mRNA of black- and white-adapted animals. Here we report the identification of twelve distinct genes whose expression levels in the melanotropes are regulated in coordination with that of POMC. Four of these genes are novel while the others code for translocon-associated proteins, a lumenal cysteine protease of the endoplasmic reticulum, prohormone-processing enzymes, members of the granin family and a transmembrane protein presumably involved in the assembly and/or specific functioning of vacuolar H(+)-ATPase from secretory granules. Our results indicate that a wide variety of both soluble and membrane-associated components of the secretory pathway is recruited in physiologically activated, peptide hormone-producing cells.