The cysteine-rich with EGF-like domains 2 (CRELD2) protein interacts with the large cytoplasmic domain of human neuronal nicotinic acetylcholine receptor alpha4 and beta2 subunits

Molecular characterization of the ER stress-inducible factor CRELD2

Previously, we found by constructing various luciferase reporters that a well-conserved ATF6-binding element in the CRELD2 promoter is activated by transient ATF6 overexpression. In this study, we established ATF6-deficient and ATF4-deficient cell lines to analyze CRELD2 mRNA and protein expression together with that of other ER stress-inducible factors. Our results showed that ATF6 deficiency markedly suppressed tunicamycin (Tm)-induced expression of unglycosylated CRELD2. This reduction reflected a decrease in the CRELD2 transcription level. On the other hand, a putative ATF4-binding site in the mouse CRELD2 promoter did not respond to Tm stimulation, but ATF4 loss resulted in reductions in CRELD2 mRNA and protein expression, accompanied by a decrease in Tm-induced ATF6 expression. In contrast, transient suppression of GADD34, an ATF4 downstream factor, suppressed Tm-induced CRELD2 protein expression without a decrease in ATF6 protein expression. Furthermore, we investigated the association of CRELD2 with a well-known ERAD substrate, namely, an α1-antitripsin truncation mutant, NHK, by generating various CRELD2 and NHK constructs. Coimmunoprecipitation of these proteins was observed only when the cysteine in the CXXC motif on the N-terminal side of CRELD2 was replaced with alanine, and the interaction between the two was found to be disulfide bond-independent. Taken together, these findings indicate that CRELD2 expression is regulated by multiple factors via transcriptional and posttranscriptional mechanisms. In addition, the N-terminal structure of CRELD2, including the CXXC motif, was suggested to play a role in the association of the target proteins. In the future, the identification and characterization of factors interacting with CRELD2 will be useful for understanding protein homeostasis under various ER stress conditions.

CRELD2, endoplasmic reticulum stress, and human diseases

CRELD2, a member of the cysteine-rich epidermal growth factor-like domain (CRELD) protein family, is both an endoplasmic reticulum (ER)-resident protein and a secretory factor. The expression and secretion of CRELD2 are dramatically induced by ER stress. CRELD2 is ubiquitously expressed in multiple tissues at different levels, suggesting its crucial and diverse roles in different tissues. Recent studies suggest that CRELD2 is associated with cartilage/bone metabolism homeostasis and pathological conditions involving ER stress such as chronic liver diseases, cardiovascular diseases, kidney diseases, and cancer. Herein, we first summarize ER stress and then critically review recent advances in the knowledge of the characteristics and functions of CRELD2 in various human diseases. Furthermore, we highlight challenges and present future directions to elucidate the roles of CRELD2 in human health and disease.

CRELD2 is a novel modulator of calcium release and calcineurin-NFAT signalling during osteoclast differentiation

Cysteine rich with epidermal growth factor (EGF)-like domains 2 (CRELD2) is an endoplasmic reticulum (ER) resident chaperone protein with calcium binding properties. CRELD2 is an ER-stress regulated gene that has been implicated in the pathogenesis of skeletal dysplasias and has been shown to play an important role in the differentiation of chondrocytes and osteoblasts. Despite CRELD2 having an established role in skeletal development and bone formation, its role in osteoclasts is currently unknown. Here we show for the first time that CRELD2 plays a novel role in trafficking transforming growth factor beta 1 (TGF-β1), which is linked to an upregulation in the expression of Nfat2, the master regulator of osteoclast differentiation in early osteoclastogenesis. Despite this finding, we show that overexpressing CRELD2 impaired osteoclast differentiation due to a reduction in the activity of the calcium-dependant phosphatase, calcineurin. This in turn led to a subsequent block in the dephosphorylation of nuclear factor of activated T cells 1 (NFATc1), preventing its nuclear localisation and activation as a pro-osteoclastogenic transcription factor. Our exciting results show that the overexpression of Creld2 in osteoclasts impaired calcium release from the ER which is essential for activating calcineurin and promoting osteoclastogenesis. Therefore, our data proposes a novel inhibitory role for this calcium-binding ER-resident chaperone in modulating calcium flux during osteoclast differentiation which has important implications in our understanding of bone remodelling and the pathogenesis of skeletal diseases.

Multidimensional Intersection of Nicotine, Gene Expression, and Behavior

The cholinergic system plays a crucial role in nervous system function with important effects on developmental processes, cognition, attention, motivation, reward, learning, and memory. Nicotine, the reinforcing component of tobacco and e-cigarettes, directly acts on the cholinergic system by targeting nicotinic acetylcholine receptors (nAChRs) in the brain. Activation of nAChRs leads to a multitude of immediate and long-lasting effects in specific cellular populations, thereby affecting the addictive properties of the drug. In addition to the direct actions of nicotine in binding to and opening nAChRs, the subsequent activation of circuits and downstream signaling cascades leads to a wide range of changes in gene expression, which can subsequently alter further behavioral expression. In this review, we provide an overview of the actions of nicotine that lead to changes in gene expression and further highlight evidence supporting how these changes can often be bidirectional, thereby inducing subsequent changes in behaviors associated with further drug intake.

GREB1L, CRELD2 and ITGA10 expression in the human developmental and postnatal kidneys: an immunohistochemical study

BACKGROUND

Aim of our study is to provide an insight into the genetic expression landscape of GREB1L, ITGA10 and CRELD2 which are important in human genitourinary tract development which might help elucidate the critical stages for the onset of kidney anomalies.

METHODS

Morphological parameters were analyzed using immunohistochemistry on human foetal (13-38 w) and postnatal (1.5 and 7.5y) human kidney samples.

RESULTS

GREB1L marker had a strong intensity and the highest rate in proximal tubules (PTC) of 1.5 years' kidney (90.25%). In the distal tubules (DCT) there were statistically significant differences in 13 w, 15 w, 16 w, 21 w, 38 w and 7.5y regarding 1.5y (Kruskal-Wallis test, p < 0.001). There was significantly more GREB1L in the glomeruli at 21 w and 38 w in regard to all other stages (Kruskal-Wallis test, p < 0.01). ITGA10 staining intensity was strongest in PCT with the highest rate in 13 w (92.75%), while the lowest rate was found in glomeruli and DCT (Kruskal-Wallis test, p < 0.001). CRELD2 had the strongest staining intensity in PCT with the highest rate in 13 w and 1.5y (92.25%) and lowest in the glomeruli of 7.5 years (24.3 %). In DCT there were statistically significant differences in CRELD2 positive cells in 13 w, 15 w, 16 w, 21 w, 38 w and 7.5y regarding 1.5y (Kruskal-Wallis test, p < 0.01). ITGA10 and CRELD2 co-localised in the postnatal period in DCT.

CONCLUSION

High kidney expressions of GREB1L, ITGA10 and CRELD2 even in the postnatal period implicate their importance not only for the onset of CAKUT in the case of their mutation but also for maintenance of kidney homeostasis.

CRELD2 Is a Novel LRP1 Chaperone That Regulates Noncanonical WNT Signaling in Skeletal Development

Cysteine-rich with epidermal growth factor (EGF)-like domains 2 (CRELD2) is an endoplasmic reticulum (ER)-resident chaperone highly activated under ER stress in conditions such as chondrodysplasias; however, its role in healthy skeletal development is unknown. We show for the first time that cartilage-specific deletion of Creld2 results in disrupted endochondral ossification and short limbed dwarfism, whereas deletion of Creld2 in bone results in osteopenia, with a low bone density and altered trabecular architecture. Our study provides the first evidence that CRELD2 promotes the differentiation and maturation of skeletal cells by modulating noncanonical WNT4 signaling regulated by p38 MAPK. Furthermore, we show that CRELD2 is a novel chaperone for the receptor low-density lipoprotein receptor-related protein 1 (LRP1), promoting its transport to the cell surface, and that LRP1 directly regulates WNT4 expression in chondrocytes through TGF-β1 signaling. Therefore, our data provide a novel link between an ER-resident chaperone and the essential WNT signaling pathways active during skeletal differentiation that could be applicable in other WNT-responsive tissues. © 2020 American Society for Bone and Mineral Research. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research..

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

BACKGROUND

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

RESULTS

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23-50.72 fold changes), while only 36 were predicted to be secreted (1.35-66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

CONCLUSIONS

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

Identification and functional study of three nAChR regulators, ubiquilin-1, PICK1, and CRELD2, in Locusta migratoria manilensis dorsal unpaired median neurons

Insect nicotinic acetylcholine receptors (nAChRs) are not only important neurotransmitter receptors but also effective insecticide targets. The regulation of nAChRs has been mainly studied in vertebrates, especially in mammals. Here, two types of nAChRs were found present in the locust Locusta migratoria manilensis dorsal unpaired median (DUM) neurons, α-bungarotoxin (α-Bgt)-sensitive nAChRs and α-Bgt-resistant nAChRs, responding to acetylcholine (ACh) at different concentrations. The homologs to three mammalian nAChR regulators, ubiquilin-1, CRELD2 (cysteine-rich with EFG-like domain 2), and PICK1 (protein interacting with PRKCA 1), were characterized in L. migratoria, and their functions on regulating native nAChRs were investigated via RNAi followed by membrane potential measurement with DiBAC₄ (3) and agonist-evoked macroscopic current recording in cultured L. migratoria DUM neurons. Ubiquilin-1 and PICK1 negatively regulated nAChRs because silencing of ubiquilin-1 and PICK1 both resulted in increased membrane potential and increased inward currents in DUM neurons, while CRELD2 positively regulated nAChRs as decreased membrane potential and inward currents were observed in DUM neurons. In addition, ubiquilin-1 regulated both α-Bgt-sensitive and α-Bgt-resistant types of nAChRs whereas PICK1 and CRELD2 regulated only the α-Bgt-resistant nAChRs. The present study broadened our understanding on the regulation of insect nAChRs and will benefit pest management given the important role of nAChRs in insect neurons and insecticide science. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Expression analysis and functional characterization of the mouse cysteine-rich with EGF-like domains 2

We have previously identified a novel endoplasmic reticulum (ER) stress-inducible protein, namely, cysteine-rich with EGF-like domains 2 (CRELD2), which is predominantly regulated by ATF6. However, few studies on intrinsic CRELD2 have been published. In the present study, we elucidated the expression of intrinsic CRELD2 in mouse tissues and ER stress- treated Neuro2a cells. Among nine tissues we tested, CRELD2 protein in the heart and skeletal muscles was negligible. CRELD2 expression in Neuro2a cells was induced at the late phase after treatment with tunicamycin (Tm) compared with rapid induction of growth arrest and DNA damage inducible gene 153 (GADD153). On the other hand, another ER stress inducer, thapsigargin, increased the intrinsic CRELD2 secretion from Neuro2a cells. We furthermore established CRELD2-deficient Neuro2a cells to evaluate their features. In combination with the NanoLuc complementary reporter system, which was designed to detect protein-protein interaction in living cells, CRELD2 interacted with not only CRELD2 itself but also with ER localizing proteins in Neuro2a cells. Finally, we investigated the responsiveness of CRELD2-deficient cells against Tm-treatment and found that CRELD2 deficiency did not affect the expression of genes triggered by three canonical ER stress sensors but rendered Neuro2a cells vulnerable to Tm-stimulation. Taken together, these findings provide the novel molecular features of CRELD2, and its further characterization would give new insights into understanding the ER homeostasis and ER stress-induced cellular dysfunctions.

Characterization of the Role of MANF in Regulating the Secretion of CRELD2

We recently demonstrated that the secretion of two novel endoplasmic reticulum (ER) stress-inducible proteins, cysteine-rich with epidermal growth factor (EGF)-like domains 2 (CRELD2) and mesencephalic astrocyte-derived neurotrophic factor (MANF), are oppositely regulated by the overexpression of 78 kDa glucose-regulated protein (GRP78). In the present study, we found that the co-transfection of CRELD2 and MANF remarkably enhanced the secretion of CRELD2 without affecting the expression level of GRP78. To identify the structural features of CRELD2 and MANF involved in this process, we generated several CRELD2 and MANF expression constructs. The deletion of the four C-terminal amino acids, either REDL in CRELD2 or RTDL in MANF, abolished the increased secretion of CRELD2 induced by the co-expression of MANF. The deleted mutation of MANF partially abolished the increased secretion of wild type CRELD2 (wtCRELD2) as a positive action of wild type MANF (wtMANF), even when we added the amino acid sequence RTDL at the C-terminus of each mutated MANF construct. Enhanced green fluorescent protein (EGFP), which was tagged with the signal peptide sequence at the N-terminus and four C-terminal amino acids (KEDL, REDL or RTDL), were retained intracellularly, but they did not enhance the secretion of wtCRELD2. Taken together, our data demonstrate that MANF is a factor in regulating the secretion of CRELD2 through four C-terminal amino acids, RTDL and REDL, and the fluctuation of intracellular MANF seems to potentiate the secretion of CRELD2.

Selective actions of Lynx proteins on different nicotinic acetylcholine receptors in the locust, Locusta migratoria manilensis

Nicotinic acetylcholine receptors (nAChRs) are major neurotransmitter receptors and targets of neonicotinoid insecticides in the insect nervous system. The full function of nAChRs is often dependent on associated proteins, such as chaperones, regulators and modulators. Here, three Lynx (Ly-6/neurotoxin) proteins, Loc-lynx1, Loc-lynx2 and Loc-lynx3, were identified in the locust, Locusta migratoria manilensis. Co-expression with Lynx resulted in a dramatic increase in agonist-evoked macroscopic currents on nAChRs Locα1/β2 and Locα2/β2 in Xenopus oocytes, but no changes in agonist sensitivity. Loc-lynx1 and Loc-lynx3 only modulated nAChRs Locα1/β2 while Loc-lynx2 modulated Locα2/β2 specifically. Meanwhile, Loc-lynx1 induced a more significant increase in currents evoked by imidacloprid and epibatidine than Loc-lynx3, and the effects of Loc-lynx1 on imidacloprid and epibatidine were significantly higher than those on acetylcholine. Among three lynx proteins, only Loc-lynx1 significantly increased [(3) H]epibatidine binding on Locα1/β2. The results indicated that Loc-lynx1 had different modulation patterns in nAChRs compared to Loc-lynx2 and Loc-lynx3. Taken together, these findings indicated that three Lynx proteins were nAChR modulators and had selective activities in different nAChRs. Lynx proteins might display their selectivities from three aspects: nAChR subtypes, various agonists and different modulation patterns. Insect Lynx (Ly-6/neurotoxin) proteins act as the allosteric modulators on insect nicotinic acetylcholine receptors (nAChRs), the important targets of insecticides. We found that insect lynx proteins showed their selectivities from at least three aspects: nAChR subtypes, various agonists and different modulation patterns.

Characterization of V-ATPase inhibitor-induced secretion of cysteine-rich with EGF-like domains 2

We previously demonstrated that cysteine-rich with EGF-like domains 2 (CRELD2), a novel ER stress-inducible factor, is a secretory glycoprotein; however, the stimuli that induce CRELD2 secretion have not yet been characterized. In this study, we found that the perturbation of intravesicular acidification of cytoplasmic organelles in HEK293 cells stably expressing wild-type (wt) CRELD2 induced its secretion. In particular, Concanamycin A (CMA) and Bafilomycin A1 (Baf), inhibitors of vacuolar ATPase (V-ATPase), increased the secretion of CRELD2 without relying on its C-terminal structure. The levels of secretion of EGFP-fused CRELD2 (SP-EGFP-CRELD2), which consists of EGFP following the putative signal peptide (SP) sequence of CRELD2, from COS7 cells transiently transfected with this construct were also increased after each of the treatments, but their intracellular localization was barely affected by CMA treatment. Transient overexpression of 78-kDa glucose-regulated protein (GRP78) and protein disulfide isomerase (PDI) also increased the secretion of CRELD2 from HEK293 cells expressing wt CRELD2, whereas the perturbation of intravesicular acidification did not alter the expression of GRP78 and PDI in the HEK293 cells. We further studied the roles of intracellular calcium ions and the Golgi apparatus in the secretion of CRELD2 from HEK293 cells in which intravesicular acidification was perturbed. The treatment with calcium ionophore increased the secretion of wt CRELD2, while that with BAPTA-AM, an intracellular calcium chelator, did not reduce the CMA-induced CRELD2 secretion. By contrast, treatment with brefeldin A (BFA), which inhibits the transportation of proteins from the ER to the Golgi apparatus, almost completely abolished the secretion of wt CRELD2 from the HEK293 cells. In conclusion, we demonstrated that the intravesicular acidification by V-ATPase regulates the secretion of CRELD2 without relying on the balance of intracellular calcium ions and the expression of ER chaperones such as GRP78 and PDI. These findings concerning the role of V-ATPases in modulating the secretion of CRELD2, a novel ER stress-inducible secretory factor, may provide new insights into the prevention and treatment of certain ER stress-related diseases.

The predicted secretomes of Monosiga brevicollis and Capsaspora owczarzaki, close unicellular relatives of metazoans, reveal new insights into the evolution of the metazoan extracellular matrix

The extracellular matrix (ECM) is a major mediator of multi-cellularity in the metazoa. Multiple ECM proteins are conserved from sponges to human, raising questions about the evolutionary origin of ECM. Choanoflagellates are the closest unicellular relatives of the metazoa and proteins with domains characteristic of metazoan ECM proteins have been identified from the genome-predicted proteome of the choanoflagellate Monosiga brevicollis. However, a systematic analysis of M. brevicollis secretory signal peptide-containing proteins with ECM domains has been lacking. We analysed all predicted secretory signal-peptide-containing proteins of M. brevicollis for ECM domains. Nine domains that are widespread in metazoan ECM proteins are represented, with EGF, fibronectin III, laminin G, and von Willebrand Factor_A domains being the most numerous. Three proteins contain more than one category of ECM domain, however, no proteins correspond to the domain architecture of metazoan ECM proteins. The fibronectin III domains are all present within glycoside hydrolases and none contain an integrin-binding motif. Glycosaminoglycan-binding motifs identified in animal thrombospondin type 1 domains are conserved in some M. brevicollis representatives of this domain, whereas there is little evidence of conservation of glycosaminoglycan-binding motifs in the laminin G domains. The identified proteins were compared with the predicted secretory ECM domain-containing proteins of the integrin-expressing filasterean, Capsaspora owczarzaki. C. owczarzaki encodes a smaller number of secretory, ECM domain-containing proteins and only EGF, fibronectin type III and laminin G domains are represented. The M. brevicollis and C. owczarzaki proteins have distinct domain architectures and all proteins differ in their domain architecture to metazoan ECM proteins. These identifications provide a basis for future experiments to validate the extracellular location of these proteins and uncover their functions in choanoflagellates and C. owczarzaki. The data strengthen the model that ECM proteins are metazoan-specific and evolved as innovations in the last common metazoan ancestor.

Endoplasmic reticulum (ER) stress inducible factor cysteine-rich with EGF-like domains 2 (Creld2) is an important mediator of BMP9-regulated osteogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitors that can undergo osteogenic differentiation under proper stimuli. We demonstrated that BMP9 is one of the most osteogenic BMPs. However, the molecular mechanism underlying BMP9-initiated osteogenic signaling in MSCs remains unclear. Through gene expression profiling analysis we identified several candidate mediators of BMP9 osteogenic signaling. Here, we focus on one such signaling mediator and investigate the functional role of cysteine-rich with EGF-like domains 2 (Creld2) in BMP9-initiated osteogenic signaling. Creld2 was originally identified as an ER stress-inducible factor localized in the ER-Golgi apparatus. Our genomewide expression profiling analysis indicates that Creld2 is among the top up-regulated genes in BMP9-stimulated MSCs. We confirm that Creld2 is up-regulated by BMP9 in MSCs. ChIP analysis indicates that Smad1/5/8 directly binds to the Creld2 promoter in a BMP9-dependent fashion. Exogenous expression of Creld2 in MSCs potentiates BMP9-induced early and late osteogenic markers, and matrix mineralization. Conversely, silencing Creld2 expression inhibits BMP9-induced osteogenic differentiation. In vivo stem cell implantation assay reveals that exogenous Creld2 promotes BMP9-induced ectopic bone formation and matrix mineralization, whereas silencing Creld2 expression diminishes BMP9-induced bone formation and matrix mineralization. We further show that Creld2 is localized in ER and the ER stress inducers potentiate BMP9-induced osteogenic differentiation. Our results strongly suggest that Creld2 may be directly regulated by BMP9 and ER stress response may play an important role in regulating osteogenic differentiation.

Armet/Manf and Creld2 are components of a specialized ER stress response provoked by inappropriate formation of disulphide bonds: implications for genetic skeletal diseases

Mutant matrilin-3 (V194D) forms non-native disulphide bonded aggregates in the rER of chondrocytes from cell and mouse models of multiple epiphyseal dysplasia (MED). Intracellular retention of mutant matrilin-3 causes endoplasmic reticulum (ER) stress and induces an unfolded protein response (UPR) including the upregulation of two genes recently implicated in ER stress: Armet and Creld2. Nothing is known about the role of Armet and Creld2 in human genetic diseases. In this study, we used a variety of cell and mouse models of chondrodysplasia to determine the genotype-specific expression profiles of Armet and Creld2. We also studied their interactions with various mutant proteins and investigated their potential roles as protein disulphide isomerases (PDIs). Armet and Creld2 were up-regulated in cell and/or mouse models of chondrodysplasias caused by mutations in Matn3 and Col10a1, but not Comp. Intriguingly, both Armet and Creld2 were also secreted into the ECM of these disease models following ER stress. Armet and Creld2 interacted with mutant matrilin-3, but not with COMP, thereby validating the genotype-specific expression. Substrate-trapping experiments confirmed Creld2 processed PDI-like activity, thus identifying a putative functional role. Finally, alanine substitution of the two terminal cysteine residues from the A-domain of V194D matrilin-3 prevented aggregation, promoted mutant protein secretion and reduced the levels of Armet and Creld2 in a cell culture model. We demonstrate that Armet and Creld2 are genotype-specific ER stress response proteins with substrate specificities, and that aggregation of mutant matrilin-3 is a key disease trigger in MED that could be exploited as a potential therapeutic target.

Characterization of the 5'-flanking region of the mouse asparagine-linked glycosylation 12 homolog gene

Recently, we characterized multiple roles of the endoplasmic reticulum stress responsive element (ERSE) in the promotion of a unique headto-head gene pair: mammalian asparagine-linked glycosylation 12 homolog (ALG12) and cysteine-rich with EGF-like domains 2 (CRELD2). This bidirectional promoter, which consists of fewer than 400 base pairs, separates the two genes. It has been demonstrated that the ALG12 promoter shows less transcriptional activity through ERSE, but its basic regulatory mechanism has not been characterized. In this study, we focused on well-conserved binding elements for the transcription factors for ATF6, NF-Y and YY1 and the Sp1 and Ets families in the 5’-flanking region of the mouse ALG12 gene. We characterized their dominant roles in regulating ALG12 promoter activities using several deletion and mutation luciferase reporter constructs. The ALG12 gene is expressed in three distinct cell lines: Neuro2a, C6 glioma and HeLa cells. The reporter activity in each cell line decreased similarly with serial deletions of the mouse ALG12 promoter. Mutations in the ERSE and adjacent NF-Y-binding element slightly affected reporter activity. Each of the mutations in the GC-rich sequence and YY1-binding element reduced ALG12 promoter activity, and the combination of these mutations additively decreased reporter activity. Each mutation in the tandem-arranged Ets-family consensus sequences partially attenuated ALG12 promoter activity, and mutations of all three Ets-binding elements decreased promoter activity by approximately 40%. Mutation of the three conserved regulatory elements (GC-rich, YY1 and Ets) in the ALG12 promoter decreased reporter activity by more than 90%. Our results suggest that the promoter activity of the mouse ALG12 gene is regulated in a similar manner in the three cell lines tested in this study. The well-conserved consensus sequences in the promoter of this gene synergistically contribute to maintaining basal gene expression.

Impact of human D398N single nucleotide polymorphism on intracellular calcium response mediated by α3β4α5 nicotinic acetylcholine receptors

The human CHRNA5 D398N polymorphism (rs16969968) causes an aspartic acid to asparagine change in the nicotinic acetylcholine receptor (nAChR) α5 subunit gene. The N398 variant of CHRNA5 is linked to increased risk for nicotine dependence. In this study, we explored the effect of the CHRNA5 D398N polymorphism on the properties of human α3β4* nicotinic acetylcholine receptors in human embryonic kidney (HEK) cells. Addition of either D398 or N398 variant of α5 subunit in the α3β4* receptor did not affect total [(125)I]-epibatidine binding or surface expression of the receptor. However, addition of α5(D398) into α3β4* receptor decreased the maximal response to agonist without significantly affecting EC(50) in aequorin intracellular calcium assay. α3β4α5(N398) nAChRs showed further decreased maximal response. The differences in agonist efficacy between the receptor subtypes were found to be dependent upon the concentration of external calcium but independent of external sodium. Moreover, activation of α3β4α5 nAChRs led to significantly greater intracellular calcium release from IP(3) stores relative to α3β4 nAChRs although no effect of the α5 polymorphism was observed. Finally, inclusion of the α5 variant caused a small shift to the left in IC(50) for some of the antagonists tested, depending upon α5 variant but did not affect sensitivity of α3β4* receptors to desensitization in response to incubation with nicotine. In conclusion, addition of either variant of α5 into an α3β4α5 receptor similarly effects receptor pharmacology and function. However, the N398 variant exhibits a reduced response to agonists when extracellular calcium is high and it may lead to distinct downstream cellular signaling.

Transcriptional profiling of chondrodysplasia growth plate cartilage reveals adaptive ER-stress networks that allow survival but disrupt hypertrophy

Metaphyseal chondrodysplasia, Schmid type (MCDS) is characterized by mild short stature and growth plate hypertrophic zone expansion, and caused by collagen X mutations. We recently demonstrated the central importance of ER stress in the pathology of MCDS by recapitulating the disease phenotype by expressing misfolding forms of collagen X (Schmid) or thyroglobulin (Cog) in the hypertrophic zone. Here we characterize the Schmid and Cog ER stress signaling networks by transcriptional profiling of microdissected mutant and wildtype hypertrophic zones. Both models displayed similar unfolded protein responses (UPRs), involving activation of canonical ER stress sensors and upregulation of their downstream targets, including molecular chaperones, foldases, and ER-associated degradation machinery. Also upregulated were the emerging UPR regulators Wfs1 and Syvn1, recently identified UPR components including Armet and Creld2, and genes not previously implicated in ER stress such as Steap1 and Fgf21. Despite upregulation of the Chop/Cebpb pathway, apoptosis was not increased in mutant hypertrophic zones. Ultrastructural analysis of mutant growth plates revealed ER stress and disrupted chondrocyte maturation throughout mutant hypertrophic zones. This disruption was defined by profiling the expression of wildtype growth plate zone gene signatures in the mutant hypertrophic zones. Hypertrophic zone gene upregulation and proliferative zone gene downregulation were both inhibited in Schmid hypertrophic zones, resulting in the persistence of a proliferative chondrocyte-like expression profile in ER-stressed Schmid chondrocytes. Our findings provide a transcriptional map of two chondrocyte UPR gene networks in vivo, and define the consequences of UPR activation for the adaptation, differentiation, and survival of chondrocytes experiencing ER stress during hypertrophy. Thus they provide important insights into ER stress signaling and its impact on cartilage pathophysiology.

Biosynthesis and secretion of mouse cysteine-rich with EGF-like domains 2

In this study, we found that Cysteine-rich with EGF-like domains 2 (CRELD2), a novel endoplasmic reticulum stress-inducible protein, is not only localized in the ER-Golgi apparatus but also spontaneously secreted. Deletion of four C-terminal amino acids from mouse CRELD2 or addition of tag-peptides to its C-terminus dramatically enhanced CRELD2 secretion. Intra- and extra-cellular CRELD2 is differentially glycosylated and its spontaneous secretion was significantly prevented by overexpression of a dominant negative mutant Sar1 and treatment with brefeldin A. Overexpression of wild-type GRP78 remarkably enhanced the secretion of wild-type but not mutant CRELD2. Our results demonstrate both that CRELD2 is a novel secretory glycoprotein regulated by Sar1 and GRP78 and that the C-terminal of CRELD2 plays a crucial role in its secretion.

Role of an ER stress response element in regulating the bidirectional promoter of the mouse CRELD2 - ALG12 gene pair

BACKGROUND

Recently, we identified cysteine-rich with EGF-like domains 2 (CRELD2) as a novel endoplasmic reticulum (ER) stress-inducible gene and characterized its transcriptional regulation by ATF6 under ER stress conditions. Interestingly, the CRELD2 and asparagine-linked glycosylation 12 homolog (ALG12) genes are arranged as a bidirectional (head-to-head) gene pair and are separated by less than 400 bp. In this study, we characterized the transcriptional regulation of the mouse CRELD2 and ALG12 genes that is mediated by a common bidirectional promoter.

RESULTS

This short intergenic region contains an ER stress response element (ERSE) sequence and is well conserved among the human, rat and mouse genomes. Microarray analysis revealed that CRELD2 and ALG12 mRNAs were induced in Neuro2a cells by treatment with thapsigargin (Tg), an ER stress inducer, in a time-dependent manner. Other ER stress inducers, tunicamycin and brefeldin A, also increased the expression of these two mRNAs in Neuro2a cells. We then tested for the possible involvement of the ERSE motif and other regulatory sites of the intergenic region in the transcriptional regulation of the mouse CRELD2 and ALG12 genes by using variants of the bidirectional reporter construct. With regards to the promoter activities of the CRELD2-ALG12 gene pair, the entire intergenic region hardly responded to Tg, whereas the CRELD2 promoter constructs of the proximal region containing the ERSE motif showed a marked responsiveness to Tg. The same ERSE motif of ALG12 gene in the opposite direction was less responsive to Tg. The direction and the distance of this motif from each transcriptional start site, however, has no impact on the responsiveness of either gene to Tg treatment. Additionally, we found three putative sequences in the intergenic region that antagonize the ERSE-mediated transcriptional activation.

CONCLUSIONS

These results show that the mouse CRELD2 and ALG12 genes are arranged as a unique bidirectional gene pair and that they may be regulated by the combined interactions between ATF6 and multiple other transcriptional factors. Our studies provide new insights into the complex transcriptional regulation of bidirectional gene pairs under pathophysiological conditions.

An unfolded protein response is the initial cellular response to the expression of mutant matrilin-3 in a mouse model of multiple epiphyseal dysplasia

Multiple epiphyseal dysplasia (MED) can result from mutations in matrilin-3, a structural protein of the cartilage extracellular matrix. We have previously shown that in a mouse model of MED the tibia growth plates were normal at birth but developed a progressive dysplasia characterised by the intracellular retention of mutant matrilin-3 and abnormal chondrocyte morphology. By 3 weeks of age, mutant mice displayed a significant decrease in chondrocyte proliferation and dysregulated apoptosis. The aim of this current study was to identify the initial post-natal stages of the disease. We confirmed that the disease phenotype is seen in rib and xiphoid cartilage and, like tibia growth plate cartilage is characterised by the intracellular retention of mutant matrilin-3. Gene expression profiling showed a significant activation of classical unfolded protein response (UPR) genes in mutant chondrocytes at 5 days of age, which was still maintained by 21 days of age. Interestingly, we also noted the upregulation of arginine-rich, mutated in early stage of tumours (ARMET) and cysteine-rich with EGF-like domain protein 2 (CRELD2) are two genes that have only recently been implicated in the UPR. This endoplasmic reticulum (ER) stress and UPR did not lead to increased chondrocyte apoptosis in mutant cartilage by 5 days of age. In an attempt to alleviate ER stress, mutant mice were fed with a chemical chaperone, 4-sodium phenylbutyrate (SPB). SPB at the dosage used had no effect on chaperone expression at 5 days of age but modestly decreased levels of chaperone proteins at 3 weeks. However, this did not lead to increased secretion of mutant matrilin-3 and in the long term did not improve the disease phenotype. We performed similar studies with a mouse model of Schmid metaphyseal chondrodysplasia, but again this treatment did not improve the phenotype.

Gene regulation of alpha4beta2 nicotinic receptors: microarray analysis of nicotine-induced receptor up-regulation and anti-inflammatory effects

alpha4beta2 Nicotinic acetylcholine receptors play an important role in the reward pathways for nicotine. We investigated whether receptor up-regulation of alpha4beta2 nicotinic acetylcholine receptors involves expression changes for non-receptor genes. In a microarray analysis, 10 muM nicotine altered expression of 41 genes at 0.25, 1, 8 and 24 h in halpha4beta2 SH-EP1 cells. The maximum number of gene changes occurred at 8 h, around the initial increase in (3)[H]-cytisine binding. Quantitative RT-PCR corroborated gene induction of endoplasmic reticulum proteins CRELD2, PDIA6, and HERPUD1, and suppression of the pro-inflammatory cytokines IL-1beta and IL-6. Nicotine suppresses IL-1beta and IL-6 expression at least in part by inhibiting NFkappaB activation. Antagonists dihydro-beta-erythroidine and mecamylamine blocked these nicotine-induced changes showing that receptor activation is required. Antagonists alone or in combination with nicotine suppressed CRELD2 message while increasing alpha4beta2 binding. Additionally, small interfering RNA knockdown of CRELD2 increased basal alpha4beta2 receptor expression, and antagonists decreased CRELD2 expression even in the absence of alpha4beta2 receptors. These data suggest that endoplasmic reticulum proteins such as CRELD2 can regulate alpha4beta2 expression, and may explain antagonist actions in nicotine-induced receptor up-regulation. Further, the unexpected finding that nicotine suppresses inflammatory cytokines suggests that nicotinic alpha4beta2 receptor activation promotes anti-inflammatory effects similar to alpha7 receptor activation.

CRELD2 is a novel endoplasmic reticulum stress-inducible gene

Recently, endoplasmic reticulum (ER) stress responses have been suggested to play important roles in maintaining various cellular functions and to underlie many tissue dysfunctions. In this study, we first identified cysteine-rich with EGF-like domains 2 (CRELD2) as an ER stress-inducible gene by analyzing a microarray analysis of thapsigargin (Tg)-inducible genes in Neuro2a cells. CRELD2 mRNA is also shown to be immediately induced by treatment with the ER stress-inducing reagents tunicamycin and brefeldin A. In the genomic sequence of the mouse CRELD2 promoter, we found a typical ER stress responsible element (ERSE), which is well conserved among various species. Using a luciferase reporter analyses, we demonstrated that the ERSE in mouse CRELD2 is functional and responds to Tg and ATF6-overexpression. Each mutation of ATF6- or NF-Y-binding sites in the ERSE of the mouse CRELD2 promoter dramatically decreased both the basal activity and responsiveness toward the ER stress stimuli. Our study suggests that CRELD2 could be a novel mediator in regulating the onset and progression of various ER stress-associated diseases.

ATF6 is a transcription factor specializing in the regulation of quality control proteins in the endoplasmic reticulum

Eukaryotic cells cope with endoplasmic reticulum (ER) stress by activating the unfolded protein response (UPR), a coordinated system of transcriptional and translational controls, which ensures the integrity of synthesized proteins. Mammalian cells express three UPR transducers in the ER, namely IRE1, PERK and ATF6. The IRE1 pathway, which is conserved from yeast to humans, mediates transcriptional induction of not only ER quality control proteins (molecular chaperones, folding enzymes and components of ER-associated degradation) but also proteins working at various stages of secretion. The PERK pathway, conserved in metazoan cells, is responsible for translational control and also participates in transcriptional control in mammals. ATF6 is an ER-membrane-bound transcription factor activated by ER stress-induced proteolysis which consists of two closely related factors, ATF6alpha and ATF6beta, in mammals. ATF6alpha but not ATF6beta plays an important role in transcriptional control. In this study, we performed a genome-wide search for ATF6alpha-target genes in mice. Only 30 of the 14,729 analyzable genes were identified as specific targets, of which 40% were ER quality control proteins, 20% were ER proteins, while the rest had miscellaneous functions. The negative effects of the absence of PERK on transcriptional induction of ER quality control proteins could be explained by its inhibitory effect on ATF6alpha activation. Further, proteins involved in transport from the ER are not regulated by ATF6alpha, and transport of folded cargo molecules from the ER was not affected by the absence of ATF6alpha. Based on these results, we propose that ATF6 is a transcription factor specialized in the regulation of ER quality control proteins.

Identification of novel androgen receptor target genes in prostate cancer

BACKGROUND

The androgen receptor (AR) plays critical roles in both androgen-dependent and castrate-resistant prostate cancer (PCa). However, little is known about AR target genes that mediate the receptor's roles in disease progression.

RESULTS

Using Chromatin Immunoprecipitation (ChIP) Display, we discovered 19 novel loci occupied by the AR in castrate resistant C4-2B PCa cells. Only four of the 19 AR-occupied regions were within 10-kb 5'-flanking regulatory sequences. Three were located up to 4-kb 3' of the nearest gene, eight were intragenic and four were in gene deserts. Whereas the AR occupied the same loci in C4-2B (castrate resistant) and LNCaP (androgen-dependent) PCa cells, differences between the two cell lines were observed in the response of nearby genes to androgens. Among the genes strongly stimulated by DHT in C4-2B cells--D-dopachrome tautomerase (DDT), Protein kinase C delta (PRKCD), Glutathione S- transferase theta 2 (GSTT2), Transient receptor potential cation channel subfamily V member 3 (TRPV3), and Pyrroline-5-carboxylate reductase 1 (PYCR1)--most were less strongly or hardly stimulated in LNCaP cells. Another AR target gene, ornithine aminotransferase (OAT), was AR-stimulated in a ligand-independent manner, since it was repressed by AR siRNA knockdown, but not stimulated by DHT. We also present evidence for in vivo AR-mediated regulation of several genes identified by ChIP Display. For example, PRKCD and PYCR1, which may contribute to PCa cell growth and survival, are expressed in PCa biopsies from primary tumors before and after ablation and in metastatic lesions in a manner consistent with AR-mediated stimulation.

CONCLUSION

AR genomic occupancy is similar between LNCaP and C4-2B cells and is not biased towards 5' gene flanking sequences. The AR transcriptionally regulates less than half the genes nearby AR-occupied regions, usually but not always, in a ligand-dependent manner. Most are stimulated and a few are repressed. In general, response is stronger in C4-2B compared to LNCaP cells. Some of the genes near AR-occupied regions appear to be regulated by the AR in vivo as evidenced by their expression levels in prostate cancer tumors of various stages. Several AR target genes discovered in the present study, for example PRKCD and PYCR1, may open avenues in PCa research and aid the development of new approaches for disease management.

CRELD2: Gene mapping, alternate splicing, and comparative genomic identification of the promoter region

CRELD2 is the second member of the CRELD family of proteins. The only other CRELD family member, encoded by CRELD1, is also known as the AVSD2 gene as mutations in CRELD1 are associated with cardiac atrioventricular septal defects (AVSD). Like CRELD1, CRELD2 is ubiquitously expressed during development and by mature tissues. Recently, a specific CRELD2 isoform (CRELD2beta) was implicated as a regulator of alpha4beta2 nicotinic acetylcholine receptor expression, suggesting that the CRELD family has widely diverse biological roles in both developmental events and subsequent cell function. Here we report additional characterization of CRELD2, which was undertaken to further our understanding of this important family. Mapping of CRELD2 by FISH shows that it maps to 22q13 rather than the GenBank reported locus of 22p13. Comparative genomic analysis of upstream sequences shows a discrete region that is highly conserved among diverse species with hallmark features indicative of a promoter region. Functional analysis demonstrates that this region has promoter activity. Consistent with widespread expression of CRELD2, this region is GC-rich and lacks a TATA box. Overall, the highest levels of CRELD2 expression occur in adult endocrine tissues. However, alternative splicing of CRELD2 is extensive with positive identification of several splice variants expressed by most normal fetal and adult tissues. Confirmed splice variants encode 5 different CRELD2 isoforms that differ significantly in composition indicating that CRELD2 function is varied and as yet poorly understood.