Down syndrome candidate region-1 protein interacts with Tollip and positively modulates interleukin-1 receptor-mediated signaling

Rcn1, the fission yeast homolog of human DSCR1, regulates arsenite tolerance independently from calcineurin

Calcineurin (CN) is a conserved Ca2+/calmodulin-dependent phosphoprotein phosphatase that plays a key role in Ca2+ signaling. Regulator of calcineurin 1 (RCAN1), also known as Down syndrome critical region gene 1 (DSCR1), interacts with calcineurin and inhibits calcineurin-dependent signaling in various organisms. Ppb1, the fission yeast calcineurin regulates Cl--homeostasis, and Ppb1 deletion induces MgCl2 hypersensitivity. Here, we characterize the conserved and novel roles of the fission yeast RCAN1 homolog rcn1+. Consistent with its role as an endogenous calcineurin inhibitor, Rcn1 overproduction reproduced the calcineurin-null phenotypes, including MgCl2 hypersensitivity and inhibition of calcineurin signaling upon extracellular Ca2+ stimuli as evaluated by the nuclear translocation and transcriptional activation of the calcineurin substrate Prz1. Notably, overexpression of rcn1+ causes hypersensitivity to arsenite, whereas calcineurin deletion induces arsenite tolerance, showing a phenotypic discrepancy between Rcn1 overexpression and calcineurin deletion. Importantly, although Rcn1 deletion induces modest sensitivities to arsenite and MgCl2 in wild-type cells, the arsenite tolerance, but not MgCl2 sensitivity, associated with Ppb1 deletion was markedly suppressed by Rcn1 deletion. Collectively, our findings reveal a previously unrecognized functional collaboration between Rcn1 and calcineurin, wherein Rcn1 not only negatively regulates calcineurin in the Cl- homeostasis, but also Rcn1 mediates calcineurin signaling to modulate arsenite cytotoxicity.

Down Syndrome Candidate Region 1 Isoform 1L regulated tumor growth by targeting both angiogenesis and tumor cells

Angiogenesis is critical for solid tumor growth beyond its minimal size. Previously, we reported that Down Syndrome Candidate Region 1 isoform 1L (DSCR1-1L) was one of the most up-regulated genes in endothelial cells induced by VEGF and histamine, and regulated endothelial cell proliferation, migration and angiogenesis. However, it was not known whether DSCR1-1L played a role in tumor growth. In this study, we found that DSCR1-1L shRNAs significantly inhibited the growth of transplanted melanoma in mice and its associated tumoral angiogenesis. In the gain of function assay, overexpression of DSCR1-1L cDNA in mouse endothelium is sufficient to significantly increase the tumor initiation induced by carcinogen, the growth of xenografted tumor, and the tumor metastasis in our endothelially-expressed DSCR1-1L transgenic mice, in which angiogenesis was induced. It was the first time to find that DSCR1-1L was also expressed in various tumor cells. DSCR1-1L shRNAs inhibited, but overexpression of DSCR1-1L cDNA increased, the tumor cell proliferation and migration. Most recently, we reported that DSCR1-1L modulated angiogenesis by down-regulation of VE-cadherin expression. Here, we found that DSCR1-1L down-regulated the expression of E-cadherin. Hence, DSCR1-1L is an excellent therapeutic target for cancers by regulation of both the endothelial and tumor cells through down-regulating (V)E-cadherin. DSCR1-1L shRNAs have the potential to be developed for clinical application.

Methylation of RCAN1.4 mediated by DNMT1 and DNMT3b enhances hepatic stellate cell activation and liver fibrogenesis through Calcineurin/NFAT3 signaling

Background: Liver fibrosis is characterized by extensive deposition of extracellular matrix (ECM) components in the liver. RCAN1 (regulator of calcineurin 1), an endogenous inhibitor of calcineurin (CaN), is required for ECM synthesis during hypertrophy of various organs. However, the functional role of RCAN1 in liver fibrogenesis has not yet been addressed. Methods: We induced experimental liver fibrosis in mice by intraperitoneal injection of 10 % CCl4 twice a week. To investigate the functional role of RCAN1.4 in the progression of liver fibrosis, we specifically over-expressed RCAN1.4 in mice liver using rAAV8-packaged RCAN1.4 over-expression plasmid. Following the establishment of the fibrotic mouse model, primary hepatic stellate cells were isolated. Subsequently, we evaluated the effect of RCAN1.4 on hepatic fibrogenesis, hepatic stellate cell activation, and cell survival. The biological role and signaling events for RCAN1 were analyzed by protein-protein interaction (PPI) network. Bisulfite sequencing PCR (BSP) was used to predict the methylated CpG islands in the RCAN1.4 gene promoter. We used the chromatin immunoprecipitation (ChIP assay) to investigate DNA methyltransferases which induced decreased expression of RCAN1.4 in liver fibrosis. Results: Two isoforms of RCAN1 protein were expressed in CCl4-induced liver fibrosis mouse model and HSC-T6 cells cultured with transforming growth factor-beta 1 (TGF-β1). RCAN1 isoform 4 (RCAN1.4) was selectively down-regulated in vivo and in vitro. The BSP analysis indicated the presence of two methylated sites in RCAN1.4 promoter and the downregulated RCAN1.4 expression levels could be restored by 5-aza-2'-deoxycytidine (5-azadC) and DNMTs-RNAi transfection in vitro. ChIP assay was used to demonstrate that the decreased RCAN1.4 expression was associated with DNMT1 and DNMT3b. Furthermore, we established a CCl4-induced liver fibrosis mouse model by injecting the recombinant adeno-associated virus-packaged RCAN1.4 (rAAV8-RCAN1.4) over-expression plasmid through the tail vein. Liver- specific-over-expression of RAN1.4 led to liver function recovery and alleviated ECM deposition. The key protein (a member of the NFAT family of proteins) identified on PPI network data was analyzed in vivo and in vitro. Our results demonstrated that RCAN1.4 over-expression alleviates, whereas its knockdown exacerbates, TGF-β1-induced liver fibrosis in vitro in a CaN/NFAT3 signaling-dependent manner. Conclusions: RCAN1.4 could alleviate liver fibrosis through inhibition of CaN/NFAT3 signaling, and the anti-fibrosis function of RCAN1.4 could be blocked by DNA methylation mediated by DNMT1 and DNMT3b. Thus, RCAN1.4 may serve as a potential therapeutic target in the treatment of liver fibrosis.

Leucine-Rich Repeat Kinase 2 (LRRK2) Stimulates IL-1β-Mediated Inflammatory Signaling through Phosphorylation of RCAN1

Leucine-rich repeat kinase 2 (LRRK2) is a Ser/Thr kinase having mixed lineage kinase-like and GTPase domains, controlling neurite outgrowth and neuronal cell death. Evidence suggests that LRRK2 is involved in innate immune response signaling, but the underlying mechanism is yet unknown. A novel protein inhibitor of phosphatase 3B, RCAN1, is known to positively regulate inflammatory signaling through modulation of several intracellular targets of interleukins in immune cells. In the present study, we report that LRRK2 phosphorylates RCAN1 (RCAN1-1S) and is markedly up-regulated during interleukin-1β (IL-1β) treatment. During IL-1β treatment, LRRK2-mediated phosphorylation of RCAN1 promoted the formation of protein complexes, including that between Tollip and RCAN1. LRRK2 decreased binding between Tollip and IRAK1, which was accompanied by increased formation of the IRAK1-TRAF6 complex. TAK1 activity was significantly enhanced by LRRK2. Furthermore, LRRK2 enhanced transcriptional activity of NF-κB and cytokine IL-8 production. These findings suggest that LRRK2 might be important in positively modulating IL-1β-mediated signaling through selective phosphorylation of RCAN1.

Brief Communication: Maternal Plasma Autoantibodies Screening in Fetal Down Syndrome

Imbalance in the metabolites levels which can potentially be related to certain fetal chromosomal abnormalities can stimulate mother's immune response to produce autoantibodies directed against proteins. The aim of the study was to determine the concentration of 9000 autoantibodies in maternal plasma to detect fetal Down syndrome. Method. We performed 190 amniocenteses and found 10 patients with confirmed fetal Down syndrome (15th–18th weeks of gestation). For the purpose of our control we chose 11 women without confirmed chromosomal aberration. To assess the expression of autoantibodies in the blood plasma, we used a protein microarray, which allows for simultaneous determination of 9000 proteins per sample. Results. We revealed 213 statistically significant autoantibodies, whose expression decreased or increased in the study group with fetal Down syndrome. The second step was to create a classifier of Down syndrome pregnancy, which includes 14 antibodies. The predictive value of the classifier (specificity and sensitivity) is 100%, classification errors, 0%, cross-validation errors, 0%. Conclusion. Our findings suggest that the autoantibodies may play a role in the pathophysiology of Down syndrome pregnancy. Defining their potential as biochemical markers of Down syndrome pregnancy requires further investigation on larger group of patients.

Salmonella Virulence Factor SsrAB Regulated Factor Modulates Inflammatory Responses by Enhancing the Activation of NF-κB Signaling Pathway

Effector proteins encoded by Salmonella pathogenicity islands play a key role in promoting bacterial intracellular survival, colonization, and pathogenesis. In this study, we investigated the function of the virulence-associated effector SrfA (SsrAB regulated factor) both in macrophages in vitro and in infected mice in vivo. SrfA was secreted into the cytoplasm during S. Typhimurium infection and disassociated IL-1R-associated kinase-1 (IRAK-1) from the IRAK-1-Toll interacting protein (Tollip) complex by interacting with Tollip. The released IRAK-1 was phosphorylated and subsequently activated the NF-κB signaling pathway, which enhanced the LPS-induced expression of inflammatory cytokines, such as IL-8, IL-1β, and TNF-α. The coupling of ubiquitin to endoplasmic reticulum degradation aa 183-219 domain of Tollip is the binding region for SrfA, and both the MDaa207-226 and CTaa357-377 regions of SrfA mediate binding to Tollip and NF-κB signaling activation. Deletion of SrfA in S. Typhimurium had no notable effects on its replication but impaired the induction of NF-κB activation in infected macrophages. The mice infected with srfA-deficient bacteria exhibited a decreased inflammatory response and an increased survival rate compared with those infected with wild-type S. Typhimurium. We conclude that SrfA is a novel Salmonella virulence effector that helps modulate host inflammatory responses by promoting NF-κB signaling activation.

RCAN 1 and 3 proteins regulate thymic positive selection

Cooperation between calcineurin (CN)-NFATc and RAF-MEK-ERK signaling pathways is essential in thymocyte positive selection. It is known that the Regulators of Calcineurin (RCAN) proteins can act either facilitating or suppressing CN-dependent signaling events. Here, we show that RCAN genes are expressed in lymphoid tissues, and address the role of RCAN proteins in T cell development. Overexpression of human RCAN3 and RCAN1 can modulate T cell development by increasing positive selection-related surface markers, as well as the "Erk(hi) competence state" in double positive thymocytes, a characteristic molecular signature of positive selection, without affecting CN activity. We also found that RCAN1/3 interact with RAF kinases and CN in a non-exclusive manner. Our data suggests that the balance of RCAN interactions with CN and/or RAF kinases may influence T cell positive selection.

Histone deacetylase 3 promotes RCAN1 stability and nuclear translocation

Regulator of calcineurin 1 (RCAN1; also referred as DSCR1 or MCIP1) is located in close proximity to a Down syndrome critical region of human chromosome 21. Although RCAN1 is an endogenous inhibitor of calcineurin signaling that controls lymphocyte activation, apoptosis, heart development, skeletal muscle differentiation, and cardiac function, it is not yet clear whether RCAN1 might be involved in other cellular activities. In this study, we explored the extra-functional roles of RCAN1 by searching for novel RCAN1-binding partners. Using a yeast two-hybrid assay, we found that RCAN1 (RCAN1-1S) interacts with histone deacetylase 3 (HDAC3) in mammalian cells. We also demonstrate that HDAC3 deacetylates RCAN1. In addition, HDAC3 increases RCAN1 protein stability by inhibiting its poly-ubiquitination. Furthermore, HDAC3 promotes RCAN1 nuclear translocation. These data suggest that HDAC3, a new binding regulator of RCAN1, affects the protein stability and intracellular localization of RCAN1.

The vertebrate RCAN gene family: novel insights into evolution, structure and regulation

Recently there has been much interest in the Regulators of Calcineurin (RCAN) proteins which are important endogenous modulators of the calcineurin-NFATc signalling pathway. They have been shown to have a crucial role in cellular programmes such as the immune response, muscle fibre remodelling and memory, but also in pathological processes such as cardiac hypertrophy and neurodegenerative diseases. In vertebrates, the RCAN family form a functional subfamily of three members RCAN1, RCAN2 and RCAN3 whereas only one RCAN is present in the rest of Eukarya. In addition, RCAN genes have been shown to collocate with RUNX and CLIC genes in ACD clusters (ACD21, ACD6 and ACD1). How the RCAN genes and their clustering in ACDs evolved is still unknown. After analysing RCAN gene family evolution using bioinformatic tools, we propose that the three RCAN vertebrate genes within the ACD clusters, which evolved from single copy genes present in invertebrates and lower eukaryotes, are the result of two rounds of whole genome duplication, followed by a segmental duplication. This evolutionary scenario involves the loss or gain of some RCAN genes during evolution. In addition, we have analysed RCAN gene structure and identified the existence of several characteristic features that can be involved in RCAN evolution and gene expression regulation. These included: several transposable elements, CpG islands in the 5′ region of the genes, the existence of antisense transcripts (NAT) associated with the three human genes, and considerable evidence for bidirectional promoters that regulate RCAN gene expression. Furthermore, we show that the CpG island associated with the RCAN3 gene promoter is unmethylated and transcriptionally active. All these results provide timely new insights into the molecular mechanisms underlying RCAN function and a more in depth knowledge of this gene family whose members are obvious candidates for the development of future therapies.

PINK1 positively regulates IL-1β-mediated signaling through Tollip and IRAK1 modulation

Background

Parkinson disease (PD) is characterized by a slow, progressive degeneration of dopaminergic neurons in the substantianigra. The cause of neuronal loss in PD is not well understood, but several genetic loci, including PTEN-induced putative kinase 1 (PINK1), have been linked to early-onset autosomal recessive forms of familial PD. Neuroinflammation greatly contributes to PD neuronal degeneration and pathogenesis. IL-1 is one of the principal cytokines that regulates various immune and inflammatory responses via the activation of the transcription factors NF-κB and activating protein-1. Despite the close relationship between PD and neuroinflammation, the functional roles of PD-linked genes during inflammatory processes remain poorly understood.

Methods

To explore the functional roles of PINK1 in response to IL-1β stimulation, HEK293 cells, mouse embryonic fibroblasts derived from PINK1-null (PINK1^−/−) and control (PINK1^+/+) mice, and 293 IL-1RI cells stably expressing type 1 IL-1 receptor were used. Immunoprecipitation and western blot analysis were performed to detect protein–protein interaction and protein ubiquitination. To confirm the effect of PINK1 on NF-κB activation, NF-κB-dependent firefly luciferase reporter assay was conducted.

Results

PINK1 specifically binds two components of the IL-1-mediated signaling cascade, Toll-interacting protein (Tollip) and IL-1 receptor-associated kinase 1 (IRAK1). The association of PINK1 with Tollip, a negative regulator of IL-1β signaling, increases upon IL-1β stimulation, which then facilitates the dissociation of Tollip from IRAK1 as well as the assembly of the IRAK1–TNF receptor-associated factor 6 (TRAF6) complex. PINK1 also enhances Lys63-linked polyubiquitination of IRAK1, an essential modification of recruitment of NF-κB essential modulator and subsequent IκB kinase activation, and increases formation of the intermediate signalosome including IRAK1, TRAF6, and transforming growth factor-β activated kinase 1. Furthermore, PINK1 stimulates IL-1β-induced NF-κB activity via suppression of Tollip inhibitory action.

Conclusions

These results suggest that PINK1 upregulates IL-1β-mediated signaling through the functional modulation of Tollip and IRAK1. These results further suggest that PINK1 stimulates the ubiquitination of proximal molecules and increases signalosome formation in the IL-1β-mediated signaling pathway. The present study therefore supports the idea of the close relationship between neuroinflammation and PD.

Covalent NEDD8 conjugation increases RCAN1 protein stability and potentiates its inhibitory action on calcineurin

Similar to ubiquitin, regulatory roles for NEDD8 (neural precursor cell-expressed developmentally down-regulated 8) are being clarified during cell growth, signal transduction, immune response, and development. However, NEDD8 targets and their functional alterations are not well known. Regulator of calcineurin 1 (RCAN1/DSCR1P1) is located near the Down syndrome critical region on the distal part of chromosome 21, and its gene product is an endogenous inhibitor of calcineurin signaling. RCAN1 is modified by ubiquitin and consequently undergoes proteasomal degradation. Here we report that NEDD8 is conjugated to RCAN1 (RCAN1-1S) via three lysine residues, K96, K104, and K107. Neddylation enhances RCAN1 protein stability without affecting its cellular location. In addition, we found that neddylation significantly inhibits proteasomal degradation of RCAN1, which may underlie the ability of NEDD8 to enhance RCAN1 stability. Furthermore, neddylation increases RCAN1 binding to calcineurin, which potentiates its inhibitory activity toward downstream NFAT signaling. The present study provides a new regulatory mechanism of RCAN1 function and highlights an important role for diverse RCAN1-involved cellular physiology.

Regulator of Calcineurin 1 Isoform 4 (RCAN1.4) Is Overexpressed in the Glomeruli of Diabetic Mice

Calcineurin (CaN) is activated in diabetes and plays a role in glomerular hypertrophy and extracellular matrix (ECM) accumulation. Here, kidneys from diabetic model mice were investigated for the expression of the regulator of CaN 1 (RCAN1) isoform 4 (RCAN1.4) which had been shown to be transcriptionally upregulated by CaN activation. We found the increased immunoreactivity for RCAN1 in the glomerular cells of db/db mice and streptozotocin-induced diabetic mice. In concordance, the expression of RCAN1 protein and RCAN1.4 mRNA were elevated in the whole kidney sample from db/db mice. Interleukin-1β (IL-1β), tumor necrosis factor-α, and glycated albumin (AGE-BSA) were identified as inducers of RCAN1.4 in mesangial cells. Pretreatment of cyclosporine A blocked the increases of RCAN1.4 stimulated by IL-1β or AGE-BSA, suggesting that activation of CaN is required for the RCAN1.4 induction. Stable transfection of RCAN1.4 in Mes-13 mesangial cells upregulated several factors relevant to ECM production and degradation. These results suggested that RCAN1.4 might act as a link between CaN activation and ECM turnover in diabetic nephropathy.