Aspartyl beta -hydroxylase (Asph) and an evolutionarily conserved isoform of Asph missing the catalytic domain share exons with junctin

Ethanol inhibition of aspartyl-asparaginyl-beta-hydroxylase in fetal alcohol spectrum disorder: potential link to the impairments in central nervous system neuronal migration

Fetal alcohol spectrum disorder (FASD) is caused by prenatal exposure to alcohol and associated with hypoplasia and impaired neuronal migration in the cerebellum. Neuronal survival and motility are stimulated by insulin and insulin-like growth factor (IGF), whose signaling pathways are major targets of ethanol neurotoxicity. To better understand the mechanisms of ethanol-impaired neuronal migration during development, we examined the effects of chronic gestational exposure to ethanol on aspartyl (asparaginyl)-beta-hydroxylase (AAH) expression, because AAH is regulated by insulin/IGF and mediates neuronal motility. Pregnant Long-Evans rats were pair-fed isocaloric liquid diets containing 0, 8, 18, 26, or 37% ethanol by caloric content from gestation day 6 through delivery. Cerebella harvested from postnatal day 1 pups were used to examine AAH expression in tissue, and neuronal motility in Boyden chamber assays. We also used cerebellar neuron cultures to examine the effects of ethanol on insulin/IGF-stimulated AAH expression, and assess the role of GSK-3beta-mediated phosphorylation on AAH protein levels. Chronic gestational exposure to ethanol caused dose-dependent impairments in neuronal migration and corresponding reductions in AAH protein expression in developing cerebella. In addition, prenatal ethanol exposure inhibited insulin and IGF-I-stimulated directional motility in isolated cerebellar granule neurons. Ethanol-treated neuronal cultures (50mMx96h) also had reduced levels of AAH protein. Mechanistically, we showed that AAH protein could be phosphorylated on Ser residues by GSK-3beta, and that chemical inhibition of GSK-3beta and/or global Caspases increases AAH protein in both control- and ethanol-exposed cells. Ethanol-impaired neuronal migration in FASD is associated with reduced AAH expression. Because ethanol increases the activities of both GSK-3beta and Caspases, the inhibitory effect of ethanol on neuronal migration could be mediated by increased GSK-3beta phosphorylation and Caspase degradation of AAH protein.

Minor sarcoplasmic reticulum membrane components that modulate excitation-contraction coupling in striated muscles

In striated muscle, activation of contraction is initiated by membrane depolarisation caused by an action potential, which triggers the release of Ca(2+) stored in the sarcoplasmic reticulum by a process called excitation-contraction coupling. Excitation-contraction coupling occurs via a highly sophisticated supramolecular signalling complex at the junction between the sarcoplasmic reticulum and the transverse tubules. It is generally accepted that the core components of the excitation-contraction coupling machinery are the dihydropyridine receptors, ryanodine receptors and calsequestrin, which serve as voltage sensor, Ca(2+) release channel, and Ca(2+) storage protein, respectively. Nevertheless, a number of additional proteins have been shown to be essential both for the structural formation of the machinery involved in excitation-contraction coupling and for its fine tuning. In this review we discuss the functional role of minor sarcoplasmic reticulum protein components. The definition of their roles in excitation-contraction coupling is important in order to understand how mutations in genes involved in Ca(2+) signalling cause neuromuscular disorders.

Junctin and the histidine-rich Ca2+ binding protein: potential roles in heart failure and arrhythmogenesis

Contractile dysfunction and ventricular arrhythmias associated with heart failure have been attributed to aberrant sarcoplasmic reticulum (SR) Ca(2+) cycling. The study of junctin (JCN) and histidine-rich Ca(2+) binding protein (HRC) becomes of particular importance since these proteins have been shown to be critical regulators of Ca(2+) cycling. Specifically, JCN is a SR membrane protein, which is part of the SR Ca(2+) release quaternary structure that also includes the ryanodine receptor, triadin and calsequestrin. Functionally, JCN serves as a bridge between calsequestrin and the Ca(2+) release channel, ryanodine receptor. HRC is a SR luminal Ca(2+) binding protein known to associate with both triadin and the sarcoplasmic reticulum Ca(2+)-ATPase, and may thus mediate the crosstalk between SR Ca(2+) uptake and release. Indeed, evidence from genetic models of JCN and HRC indicate that they are important in cardiophysiology as alterations in these proteins affect SR Ca(2+) handling and cardiac function. In addition, downregulation of JCN and HRC may contribute to Ca(2+) cycling perturbations manifest in the failing heart, where their protein levels are significantly reduced. This review examines the roles of JCN and HRC in SR Ca(2+) cycling and their potential significance in heart failure.

Prognostic value of aspartyl (asparaginyl)-beta-hydroxylase/humbug expression in non-small cell lung carcinoma

Despite improvements in the detection and use of biomarkers, including epidermal growth factor receptor, ERCC1, and p16, the 5-year survival rate with non-small cell lung cancer remains at 15%. This suggests that additional biomarkers are needed to better prognosticate clinical course and guide therapeutic approaches. Previous studies showed that increased levels of aspartyl (asparaginyl)-beta-hydroxylase and a highly related molecule, humbug, correlate with clinical course and survival with hepatic, biliary, pancreatic, and colon carcinomas. We now characterize the prognostic use of aspartyl (asparaginyl)-beta-hydroxylase/humbug immunoreactivity in different subtypes of non-small cell lung cancer. Tissue microarrays including 375 paraffin-embedded non-small cell lung cancers (195 adenocarcinomas; 18 bronchioloalveolar carcinomas; 113 squamous cell carcinomas; and 49 large cell carcinomas) were immunostained with FB50 monoclonal antibody, which recognizes human aspartyl (asparaginyl)-beta-hydroxylase/humbug. Immunoreactivity (intensity and distribution) in neoplastic cells were scored under code, and data were subjected to univariate and Cox multivariate analyses, adjusting for age, stage, and treatment. High levels of FB50 immunoreactivity were more often detected in adenocarcinomas (28% for adenocarcinoma, 17% for bronchioloalveolar carcinoma), compared with squamous cell carcinomas (10%) and large cell carcinomas (10%). Univariate analysis demonstrated inverse relationships between intensity of FB50 immunoreactivity and survival with squamous cell carcinoma (P = .004), and a strong trend with respect to large cell carcinoma (P = .057). Cox multivariate test showed that FB50 immunoreactivity (P = .025), clinical stage (P = .029), and tumor size (P = .0001) were all independent predictors of survival with squamous cell carcinoma. High levels of FB50 immunohistochemical staining correlate with poor prognosis in non-small cell lung cancer, particularly squamous cell carcinoma subtype. Therefore, FB50 immunoreactivity may be useful in defining patient subsets that are likely to benefit from adjuvant therapy.

Upstream stimulatory factors are involved in the P1 promoter directed transcription of the A beta H-J-J locus

BACKGROUND

Alternative splicing of the locus A beta H-J-J generates functionally distinct proteins: the enzyme aspartyl (asparaginyl) beta-hydroxylase (AAH), truncated homologs of AAH with a role in calcium homeostasis humbug and junctate and a structural protein of the sarcoplasmic reticulum membranes junctin. AAH and humbug are over expressed in a broad range of malignant neoplasms. We have previously reported that this locus contains two promoters, P1 and P2. While AAH and humbug are expressed in most tissues under the regulation of the P1 promoter, AAH, junctin and junctate are predominantly expressed in excitable tissues under the control of the P2 promoter. We previously demonstrated that Sp transcription factors positively regulate the P1 promoter.

RESULTS

In the present study, we extended the functional characterization of the P1 promoter of the A beta H-J-J locus. We demonstrated by quantitative Real-time RT-PCR that mRNAs from the P1 promoter are actively transcribed in all the human cell lines analysed. To investigate the transcription mechanism we transiently transfected HeLa cells with sequentially deleted reporter constructs containing different regions of the -661/+81 P1 nucleotide sequence. Our results showed that (i) this promoter fragment is a powerful activator of the reporter gene in HeLa cell line, (ii) the region spanning 512 bp upstream of the transcription start site exhibits maximal level of transcriptional activity, (iii) progressive deletions from -512 gradually reduce reporter expression. The region responsible for maximal transcription contains an E-box site; we characterized the molecular interactions between USF1/2 with this E-box element by electrophoretic mobility shift assay and supershift analysis. In addition, our USF1 and USF2 chromatin immunoprecipitation results demonstrate that these transcription factors bind the P1 promoter in vivo. A functional role of USF1/USF2 in upregulating P1-directed transcription was demonstrated by analysis of the effects of (i) in vitro mutagenesis of the P1/E-box binding site, (ii) RNA interference targeting USF1 transcripts.

CONCLUSION

Our results suggest that USF factors positively regulate the core of P1 promoter, and, together with our previously data, we can conclude that both Sp and USF DNA interaction and transcription activity are involved in the P1 promoter dependent expression of AAH and humbug.

Regulatory roles of junctin in sarcoplasmic reticulum calcium cycling and myocardial function

Junctin (JCN), a 26-kd sarcoplasmic reticulum (SR) transmembrane protein, forms a quaternary protein complex with the ryanodine receptor, calsequestrin, and triadin in the SR lumen of cardiac muscle. Within this complex, calsequestrin, triadin, and JCN appear to be critical for normal regulation of ryanodine receptor-mediated calcium (Ca) release. Junctin and triadin exhibit 60% to 70% amino acid homology in their transmembrane domains, including repeated KEKE motifs important for macromolecular protein-protein interactions within their SR luminal tails. Recent studies have uncovered functional roles of both JCN and triadin in the mouse heart, using transgenic overexpression strategies, which exhibit varying phenotypes including mild SR structural alterations, prolongation of Ca transient decay, impaired relaxation, and cardiac hypertrophy and/or heart failure. More specifically, both in vitro adenoviral gene transfer and in vivo gene-targeting techniques to manipulate JCN expression levels have shown that JCN is an essential factor in maintaining normal cardiac Ca handling and cardiac function. This article reviews the new findings on the regulatory roles of JCN in cardiac SR Ca cycling and contractility, with special emphasis on the effects of JCN ablation on delayed after depolarization-induced arrhythmias and premature mortality in mouse models.

Overexpression of junctate induces cardiac hypertrophy and arrhythmia via altered calcium handling

Junctate-1 is a newly identified integral endoplasmic/sarcoplasmic reticulum Ca2+ binding protein. However, its functional role in the heart is unknown. In the present study, the consequences of constitutively overexpressed junctate in cardiomyocytes were investigated using transgenic (TG) mice overexpressing junctate-1. TG mice (8 weeks old) showed cardiac remodeling such as marked bi-atrial enlargement with intra-atrial thrombus and biventricular hypertrophy. The TG mice also showed bradycardia with atrial fibrillation, reduced amplitude and elongated decay time of Ca2+ transients, increased L-type Ca2+ current and prolonged action potential durations. Time-course study (2-8 weeks) showed an initially reduced SR function due to down-regulation of SERCA2 and calsequestrin followed by sarcolemmal protein expression and cardiac hypertrophy at later age. These sequential changes could well be correlated with the physiological changes. Adrenergic agonist treatment and subsequent biochemical study showed that junctate-1 TG mice (8 weeks old) were under local PKA signaling that could cause increased L-type Ca2+ current and reduced SR function. Junctate-1 in the heart is closely linked to the homeostasis of E-C coupling proteins and a sustained increase of junctate-1 expression leads to a severe cardiac remodeling and arrhythmias.

Increased Ca2+ storage capacity of the skeletal muscle sarcoplasmic reticulum of transgenic mice over-expressing membrane bound calcium binding protein junctate

Junctate is an integral sarco(endo)plasmic reticulum protein expressed in many tissues including heart and skeletal muscle. Because of its localization and biochemical characteristics, junctate is deemed to participate in the regulation of the intracellular Ca2+ concentration. However, its physiological function in muscle cells has not been investigated yet. In this study we examined the effects of junctate over-expression by generating a transgenic mouse model which over-expresses junctate in skeletal muscle. Our results demonstrate that junctate over-expression induced a significant increase in SR Ca2+ storage capacity which was paralleled by an increased 4-chloro-m-cresol and caffeine-induced Ca2+ release, whereas it did not affect SR Ca2+-dependent ATPase activity and SR Ca2+ loading rates. In addition, junctate over-expression did not affect the expression levels of SR Ca2+ binding proteins such as calsequestrin, calreticulin and sarcalumenin. These findings suggest that junctate over-expression is associated with an increase in the SR Ca2+ storage capacity and releasable Ca2+ content and support a physiological role for junctate in intracellular Ca2+ homeostasis.

Multiple functions of junctin and junctate, two distinct isoforms of aspartyl beta-hydroxylase

The single genomic locus, AbetaH-J-J, encodes three functionally distinct proteins aspartyl beta-hydroxylase, junctin and junctate by alternative splicing. Among these three proteins, junctin and junctate could play important roles in the regulation of intracellular Ca(2+) by regulating either Ca(2+) release from intracellular Ca(2+) stores or Ca(2+) influx in various biological processes. Here we review recent findings concerning the expressional regulations and the proposed functions of junctin and junctate.

Transcriptional activity and Sp 1/3 transcription factor binding to the P1 promoter sequences of the human AbetaH-J-J locus

Alternative splicing of the locus AbetaH-J-J generates functionally distinct proteins: the enzyme aspartyl (asparaginyl) beta-hydroxylase, humbug and junctate (truncated homologs of aspartyl (asparaginyl) beta-hydroxylase with a role in calcium regulation), and junctin (a structural protein of the sarcoplasmic reticulum membrane). Aspartyl (asparaginyl) beta-hydroxylase and humbug are overexpressed in a broad range of malignant neoplasms. We have previously reported the gene structure of this locus, showing the presence of two putative promoters, P1 and P2, and characterized the P2 sequences, directing tissue-specific transcription of junctin, aspartyl (asparaginyl) beta-hydroxylase and junctate. In addition, aspartyl (asparaginyl) beta-hydroxylase and humbug are expressed from exon 1 by the P1 promoter. The present study identifies and functionally characterizes the P1 promoter activity of the AbetaH-J-J locus. We demonstrate that mRNAs from the P1 promoter are actively transcribed in all the human tissues and cell lines analyzed, and define the transcription start point in HeLa and RD cells. To investigate the transcription mechanism we cloned 1.7 kb upstream of exon 1 from a human BAC clone, and produced progressively deleted reporter constructs. Our results showed that: (a) the 1.7 kb fragment was a powerful activator of the reporter gene in human hepatoblastoma (HepG2) and human embryonic rhabdomyosarcoma (RD) cell lines; (b) 512 bp upstream of the transcription start site were essential for maximal promoter activity; and (c) progressive deletions from -512 resulted in gradually decreased reporter expression. The region responsible for maximal transcription contains at least 12 GC boxes homologous to binding sequences of specific transcription factor 1 (Sp1); by electrophoretic mobility shift assay and supershift analysis, we identified three GC-rich elements that bind Sp transcription factor family nuclear factors with very high efficiency. A functional role of Sp transcription factors in upregulating P1-directed transcription was demonstrated by analysis of the effects of: (a) in vitro mutagenesis of the Sp1 transcription factor binding sites; (b) transfection with Sp transcription factor 1/3 expression vectors; and (c) treatment with decoy oligonucleotides targeting Sp transcription factors. In addition, Sp1 and Sp3 transcription factor chromatin immunoprecipitation demonstrated in vivo binding of these proteins to P1 promoter. Our results suggest that Sp transcription factors positively regulate the core of the P1 promoter, and the comparison of the two promoters of the AbetaH-J-J locus demonstrates that they are very different with regard to transcriptional efficiency and ability to direct tissue-specific transcription.

Binding of proprotein convertase subtilisin/kexin type 9 to epidermal growth factor-like repeat A of low density lipoprotein receptor decreases receptor recycling and increases degradation

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes degradation of hepatic low density lipoprotein receptors (LDLR), the major route of clearance of circulating cholesterol. Gain-of-function mutations in PCSK9 cause hypercholesterolemia and premature atherosclerosis, whereas loss-of-function mutations result in hypocholesterolemia and protection from heart disease. Recombinant human PCSK9 binds the LDLR on the surface of cultured hepatocytes and promotes degradation of the receptor after internalization. Here we localized the site of binding of PCSK9 within the extracellular domain of the LDLR and determined the fate of the receptor after PCSK9 binding. Recombinant human PCSK9 interacted in a sequence-specific manner with the first epidermal growth factor-like repeat (EGF-A) in the EGF homology domain of the human LDLR. Similar binding specificity was observed between PCSK9 and purified EGF-A. Binding to EGF-A was calcium-dependent and increased dramatically with reduction in pH from 7 to 5.2. The addition of PCSK9, but not heat-inactivated PCSK9, to the medium of cultured hepatocytes resulted in redistribution of the receptor from the plasma membrane to lysosomes. These data are consistent with a model in which PCSK9 binding to EGF-A interferes with an acid-dependent conformational change required for receptor recycling. As a consequence, the LDLR is rerouted from the endosome to the lysosome where it is degraded.

Multiple levels of control of the expression of the human A beta H-J-J locus encoding aspartyl-beta-hydroxylase, junctin, and junctate

The human AbetaH-J-J locus is a genomic sequence which generates three functionally distinct proteins, the enzyme aspartyl-beta-hydroxylase (AbetaH), the structural protein of sarcoplasmic reticulum junctin, and the membrane-bound calcium binding protein junctate. The first and second exons are mutually exclusive when mature mRNAs are produced. Moreover, the use of different splice donors has been shown to be involved in the generation of protein diversity by alternative splicing. As to transcriptional regulation, two promoters (P1 and P2) were identified. When the P1 and P2 promoter sequences are compared, important differences are clearly detectable. The most interesting result emerging from studies focused on the P2 promoter is that the calcium-dependent transcriptional factor MEF-2 activates the transcription of junctin, junctate, and AbetaH in excitable tissues and, to a lesser extent, in kidney. No Sp1 binding sites are present in the P2 promoter. In contrast, P1 promoter contains GC-rich sequences, which have homologies with the Sp1 consensus binding site.

Induced and repressed genes after irradiation sensitizing by pentoxyphylline

Aim in cancer therapy is to increase the therapeutic ratio eliminating the disease while minimizing toxicity to normal tissues. Radiation therapy is a main component in targeting cancer. Radiosensitizing agents like pentoxyphylline (PTX) have been evaluated to improve radiotherapy. Commonly, cells respond to radiation by the activation of specific early and late response genes as well as by inhibition of genes, which are expressed under normal conditions. A display of the genetic distinctions at the level of transcription is given here to characterize the molecular events underlying the radiosensitizing mechanisms. The method of suppression subtractive hybridization allows the visualization of both induced and repressed genes in irradiated cells compared with cells sensitized immediately after irradiation. The genes were isolated by cDNA-cloning, differential analysis and sequence similarity search. Genes involved in protein synthesis, metabolism, proteolysis and transcriptional regulation were detected. It is important that genes like KIAA280, which were only known as unidentified EST sequences before without function, but inaccessible by array technology were recovered as functional genes. Database searches for PTX-induced genes detected a human mRNA completely unknown. In case of suppressed genes, we detected several mRNAs; one thereof shows homology to a hypothetical protein possibly involved in signal transduction. A further mRNA encodes the protein BM036 supposed to associate with the E2F transcription factor. A hypothetical protein H41 was detected, which may repress the Her-2/neu receptor influencing breast cancer, gliomas and prostate tumors. Radiation combined with PTX may lead to a better prognosis by down regulation of the Her-2/neu, which will be proven by clinical studies in the near future.

Differential growth factor regulation of aspartyl-(asparaginyl)-beta-hydroxylase family genes in SH-Sy5y human neuroblastoma cells

Background

Aspartyl (asparaginyl)-β-hydroxylase (AAH) hydroxylates Asp and Asn residues within EGF-like domains of Notch and Jagged, which mediate cell motility and differentiation. This study examines the expression, regulation and function of AAH, and its related transcripts, Humbug and Junctin, which lack catalytic domains, using SH-Sy5y neuroblastoma cells.

Results

Real time quantitative RT-PCR demonstrated 8- or 9-fold higher levels of Humbug than AAH and Junctin, and lower levels of all 3 transcripts in normal human brains compared with neuroblastic tumor cells. AAH and Humbug expression were significantly increased in response to insulin and IGF-I stimulation, and these effects were associated with increased directional motility. However, over-expression of AAH and not Humbug significantly increased motility. Treatment with chemical inhibitors of Akt, Erk MAPK, or cyclin-dependent kinase 5 (Cdk-5) significantly reduced IGF-I stimulated AAH and Humbug expression and motility relative to vehicle-treated control cells. In addition, significantly increased AAH and Humbug expression and directional motility were observed in cells co-transfected with Cdk-5 plus its p35 or p25 regulatory partner. Further studies demonstrated that activated Cdk-5 mediated its stimulatory effects on AAH through Erk MAPK and PI3 kinase.

Conclusion

AAH and Humbug are over-expressed in SH-Sy5y neuroblastoma cells, and their mRNAs are regulated by insulin/IGF-1 signaling through Erk MAPK, PI3 kinase-Akt, and Cdk-5, which are known mediators of cell migration. Although AAH and Humbug share regulatory signaling pathways, AAH and not Humbug mediates directional motility in SH-Sy5y neuroblastoma cells.

The tallysomycin biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 unveiling new insights into the biosynthesis of the bleomycin family of antitumor antibiotics

The tallysomycins (TLMs) belong to the bleomycin (BLM) family of antitumor antibiotics. The BLM biosynthetic gene cluster has been cloned and characterized previously from Streptomyces verticillus ATCC 15003, but engineering BLM biosynthesis for novel analogs has been hampered by the lack of a genetic system for S. verticillus. We now report the cloning and sequencing of the TLM biosynthetic gene cluster from Streptoalloteichus hindustanus E465-94 ATCC 31158 and the development of a genetic system for S. hindustanus, demonstrating the feasibility to manipulate TLM biosynthesis in S. hindustanus by gene inactivation and mutant complementation. Sequence analysis of the cloned 80.2 kb region revealed 40 open reading frames (ORFs), 30 of which were assigned to the TLM biosynthetic gene cluster. The TLM gene cluster consists of nonribosomal peptide synthetase (NRPS) genes encoding nine NRPS modules, a polyketide synthase (PKS) gene encoding one PKS module, genes encoding seven enzymes for deoxysugar biosynthesis and attachment, as well as genes encoding other biosynthesis, resistance, and regulatory proteins. The involvement of the cloned gene cluster in TLM biosynthesis was confirmed by inactivating the tlmE glycosyltransferase gene to generate a TLM non-producing mutant and by restoring TLM production to the DeltatlmE::ermE mutant strain upon expressing a functional copy of tlmE. The TLM gene cluster is highly homologous to the BLM cluster, with 25 of the 30 ORFs identified within the two clusters exhibiting striking similarities. The structural similarities and differences between TLM and BLM were reflected remarkably well by the genes and their organization in their respective biosynthetic gene clusters.

Prognostic value of humbug gene overexpression in stage II colon cancer

Overexpression of aspartyl (asparaginyl) beta-hydroxylase (AAH) has been demonstrated in hepatocellular carcinoma, cholangiocarcinoma, and pancreatic carcinoma. AAH has an important role in regulating cell motility and invasiveness. Humbug is a truncated homolog of AAH, with a role in calcium regulation. The present study examines the prognostic use of AAH and humbug gene expression in stage II colon cancer. One hundred thirty cases of TNM stage II colon carcinoma were retrieved from the Rhode Island Hospital pathology archives. Tissue microarrays were immunostained with the FB50 and 15C7 monoclonal antibodies generated to recombinant AAH. However, FB50 also recognizes humbug. In addition, AAH and humbug expression was analyzed in samples of colon cancer and adjacent normal mucosa by real-time quantitative reverse transcriptase-polymerase chain reaction. Humbug (FB50) expression was localized to the tumor cytoplasm, whereas normal colonic epithelium did not exhibit significant immunoreactivity. Humbug staining was detected in 85% of the neoplasms, 23% of which stained strongly. Strong humbug immunoreactivity positively correlated with nuclear grade (P = .006) and inversely with survival (P = .027). In contrast to humbug, AAH (15C7) immunoreactivity was seen in normal and neoplastic epithelium. There was no correlation between AAH immunoreactivity and tumor grade, or survival. Correspondingly, reverse transcriptase-polymerase chain reaction studies demonstrated up-regulation of humbug but not AAH in 95% of colon carcinomas relative to adjacent colon cancer-free mucosa (P < .0001). This study demonstrates that high levels of humbug immunoreactivity in colon carcinomas correlate with histologic grade and tumor behavior, suggesting that humbug can serve as a prognostic biomarker of TNM stage II colon cancers. In addition, molecular studies demonstrated that the increased levels of FB50 detected were due to humbug, as opposed to AAH overexpression.

Chondrocyte secreted CRTAC1: a glycosylated extracellular matrix molecule of human articular cartilage

Cartilage acidic protein 1 (CRTAC1), a novel human marker which allowed discrimination of human chondrocytes from osteoblasts and mesenchymal stem cells in culture was so far studied only on the RNA-level. We here describe its genomic organisation and detect a new brain expressed (CRTAC1-B) isoform resulting from alternate last exon usage which is highly conserved in vertebrates. In humans, we identify an exon sharing process with the neighbouring tail-to-tail orientated gene leading to CRTAC1-A. This isoform is produced by cultured human chondrocytes, localized in the extracellular matrix of articular cartilage and its secretion can be stimulated by BMP4. Of five putative O-glycosylation motifs in the last exon of CRTAC1-A, the most C-terminal one is modified according to exposure of serial C-terminal deletion mutants to the O-glycosylation inhibitor Benzyl-alpha-GalNAc. Both isoforms contain four FG-GAP repeat domains and an RGD integrin binding motif, suggesting cell-cell or cell-matrix interaction potential. In summary, CRTAC1 acquired an alternate last exon from the tail-to-tail oriented neighbouring gene in humans resulting in the glycosylated isoform CRTAC1-A which represents a new extracellular matrix molecule of articular cartilage.

Aspartyl-asparagyl beta hydroxylase over-expression in human hepatoma is linked to activation of insulin-like growth factor and notch signaling mechanisms

Aspartyl-(asparagyl)-beta-hydroxylase (AAH) is overexpressed in various malignant neoplasms, including hepatocellular carcinomas (HCCs). The upstream regulation of AAH and its functional role in Notch-mediated signaling and motility in HCC cells was accessed. The mRNA transcript levels of AAH, insulin receptor substrate (IRS), insulin and insulin-like growth factor (IGF) receptors and polypeptides, Notch, Jagged, and HES were measured in 15 paired samples of HCC and adjacent HCC-free human liver biopsy specimens using real-time quantitative RT-PCR and Western blot analysis. Overexpression of AAH was detected in 87% of the HCC relative to the paired HCC-free liver tissue. IRS-1, IRS-2, and IRS-4 were each overexpressed in 80% of the HCC samples, and IGF-I and IGF-2 receptors were overexpressed in 40% and 100% of the HCCs, respectively. All HCC samples had relatively increased levels of Notch-1 and HES-1 gene expression. Overexpression of AAH led to increased levels of Notch, and co-immunoprecipitation experiments demonstrated a direct interaction between AAH and Notch as well as its ligand Jagged. In conclusion, contributions to the malignant phenotype of HCC is due to activation of IGF-I and IGF-II signaling that results in over-expression of both AAH and Notch. The functional role of AAH in relation to cell motility has been linked to increased activation of the Notch signaling pathway.

Conservation of intrinsic disorder in protein domains and families: II. functions of conserved disorder

Regions of conserved disorder prediction (CDP) were found in protein domains from all available InterPro member databases, although with varying frequency. These CDP regions were found in proteins from all kingdoms of life, including viruses. However, eukaryotes had 1 order of magnitude more proteins containing long disordered regions than did archaea and bacteria. Sequence conservation in CDP regions varied, but was on average slightly lower than in regions of conserved order. In some cases, disordered regions evolve faster than ordered regions, in others they evolve slower, and in the rest they evolve at roughly the same rate. A variety of functions were found to be associated with domains containing conserved disorder. The most common were DNA/RNA binding, and protein binding. Many ribosomal proteins also were found to contain conserved disordered regions. Other functions identified included membrane translocation and amino acid storage for germination. Due to limitations of current knowledge as well as the methodology used for this work, it was not determined whether these functions were directly associated with the predicted disordered region. However, the functions associated with conserved disorder in this work are in agreement with the functions found in other studies to correlate to disordered regions. We have established that intrinsic disorder may be more common in bacterial and archaeal proteins than previously thought, but this disorder is likely to be used for different purposes than in eukaryotic proteins, as well as occurring in shorter stretches of protein. Regions of predicted disorder were found to be conserved within a large number of protein families and domains. Although many think of such conserved domains as being ordered, in fact a significant number of them contain regions of disorder that are likely to be crucial to their functions.

Expression of aspartyl beta-hydroxylase and its clinicopathological significance in hepatocellular carcinoma

The human aspartyl beta-hydroxylase is a highly conserved enzyme that hydroxylates epidermal growth factor-like domains in transformation-associated proteins. The aspartyl beta-hydroxylase gene is upregulated in many human malignancies. The purpose of this study was to investigate the expression of aspartyl beta-hydroxylase in hepatocellular carcinoma. Aspartyl beta-hydroxylase mRNA levels were measured in 161 hepatocellular carcinomas and paired nontumorous liver tissues by conventional and real-time RT-PCR. Immunohistochemical staining of aspartyl beta-hydroxylase was performed using EnVision Plus system. The results showed that aspartyl beta-hydroxylase was overexpressed in 150 of 161 hepatocellular carcinomas (93%), including 45 of 48 unifocal small hepatocellular carcinomas (94%). Aspartyl beta-hydroxylase was highly expressed in hepatocellular carcinoma cells in contrast to its low level of expression in non-neoplastic liver cells. The protein expression level of aspartyl beta-hydroxylase in the hepatocellular carcinoma was parallel with the mRNA expression level (r=0.6594, P<0.0001). A significantly higher tumor aspartyl beta-hydroxylase overexpression level was associated with the presence of intrahepatic metastasis and the progression of histological grades. In conclusion, aspartyl beta-hydroxylase is overexpressed frequently in hepatocellular carcinoma, including early-stage small hepatocellular carcinoma, indicating that overexpression of aspartyl beta-hydroxylase plays a role in the development and progression of hepatocellular carcinoma.

Novel sarco(endo)plasmic reticulum proteins and calcium homeostasis in striated muscles

The impact of calcium signaling on many cellular functions is reflected by the tight regulation of the intracellular Ca(2+) concentration that is ensured by diverse pumps, channels, transporters and Ca(2+) binding proteins. In this review, we present recently identified novel sarco(endo)plasmic reticulum proteins that may have a potential involvement in the regulation of Ca(2+) homeostasis in striated muscles.

Junctate, an inositol 1,4,5-triphosphate receptor associated protein, is present in rodent sperm and binds TRPC2 and TRPC5 but not TRPC1 channels

The acrosome reaction, the first step of the fertilization, is induced by calcium influx through Canonical Transient Receptor Potential channels (TRPC). The molecular nature of TRPC involved is still a debated question. In mouse, TRPC2 plays the most important role and is responsible for the calcium plateau. However, TRPC1 and TRPC5 are also localized in the acrosomal crescent of the sperm head and may participate in calcium signaling, especially in TRPC2-deficient mice. Activation of TRPC channels is an unresolved question in germ and somatic cells as well. In particular, in sperm, little is known concerning the molecular events leading to TRPC2 activation. From the discovery of IP3R binding domains on TRPC2, it has been suggested that TRPC channel activation may be due to a conformational coupling between IP3R and TRPC channels. Moreover, recent data demonstrate that junctate, an IP3R associated protein, participates also in the gating of some TRPC. In this study, we demonstrate that junctate is expressed in sperm and co-localizes with the IP3R in the acrosomal crescent of the anterior head of rodent sperm. Consistent with its specific localization, we show by pull-down experiments that junctate interacts with TRPC2 and TRPC5 but not with TRPC1. We focused on the interaction between TRPC2 and junctate, and we show that the N-terminus of junctate interacts with the C-terminus of TRPC2, both in vitro and in a heterologous expression system. We show that junctate binds to TRPC2 independently of the calcium concentration and that the junctate binding site does not overlap with the common IP3R/calmodulin binding sites. TRPC2 gating is downstream phospholipase C activation, which is a key and necessary step during the acrosome reaction. TRPC2 may then be activated directly by diacylglycerol (DAG), as in neurons of the vomeronasal organ. In the present study, we investigated whether DAG could promote the acrosome reaction. We found that 100 microM OAG, a permeant DAG analogue, was unable to trigger the acrosome reaction. Altogether, these results provide a new hypothesis concerning sperm TRPC2 gating: TRPC2 activation may be due to modifications of its interaction with both junctate and IP3R, induced by depletion of calcium from the acrosomal vesicle.

Genetic and phenotypic analysis of Tcm, a mutation affecting early eye development

Tcm (total cataract with microphthalmia) is an autosomal dominant mouse eye mutation. Heterozygous Tcm/+ mice are born with several eye malformations including microphthalmia, retinal and iris dysplasia, total lens cataract, and ventral coloboma. The Tcm mutation was previously mapped to a 26-Mb region on Chr 4 between D4Mit235 and D4Mit106. In this study, we characterize the Tcm/ Tcm homozygous mutant and find they are viable but severely microphthalmic. The developing eye in the Tcm/Tcm homozygote shows defects during early eye development, before formation of the optic cup. Further genetic mapping reduced the Tcm critical region to a 1.3-Mb region bordered by SNPs rs3666764 and rs3713818. This critical region contains two known genes (Asph and Gfd6) and three predicted genes, all of which are positional candidates for Tcm. Sequence analysis of Tcm genomic DNA revealed no mutations in the coding regions and splice site junctions of the five candidate genes. These results indicate that the causitive Tcm mutation falls within a noncoding regulatory region of one of the five candidate genes or in an undescribed gene.

Myocyte enhancer factor 2 activates promoter sequences of the human AbetaH-J-J locus, encoding aspartyl-beta-hydroxylase, junctin, and junctate

Alternative splicing of the locus AbetaH-J-J generates three functionally distinct proteins: an enzyme, AbetaH (aspartyl-beta-hydroxylase), a structural protein of the sarcoplasmic reticulum membrane (junctin), and an integral membrane calcium binding protein (junctate). Junctin and junctate are two important proteins involved in calcium regulation in eukaryotic cells. To understand the regulation of these two proteins, we identified and functionally characterized one of the two promoter sequences of the AbetaH-J-J locus. We demonstrate that the P2 promoter of the AbetaH-J-J locus contains (i) a minimal sequence localized within a region -159 bp from the transcription initiation site, which is sufficient to activate transcription of both mRNAs; (ii) sequences which bind known transcriptional factors such as those belonging to the myocyte enhancer factor 2 (MEF-2), MEF-3, and NF-kappaB protein families; and (iii) sequences bound by unknown proteins. The functional characterization of the minimal promoter in C2C12 cells and in the rat soleus muscle in vivo model indicates the existence of cis elements having positive and negative effects on transcription. In addition, our data demonstrate that in striated muscle cells the calcium-dependent transcription factor MEF-2 is crucial for the transcription activity directed by the P2 promoter. The transcription directed by the AbetaH-J-J P2 promoter is induced by high expression of MEF-2, further stimulated by calcineurin and Ca2+/calmodulin-dependent protein kinase I, and inhibited by histone deacetylase 4.

Complementary DNA cloning, genomic characterization and expression analysis of a mammalian gene encoding histidine-rich calcium binding protein

A protein complex present at the junctional sarcoplasmic reticulum (SR) membrane is implicated in the Ca(2+) release process during muscle contraction. The histidine-rich Ca(2+)-binding protein (HRC) is an emerging component associated into the SR protein complex. We cloned cDNAs for rat and monkey HRCs, showing a conserved sequence organization in common with other mammalian HRCs. Genomic analysis revealed that each mammalian HRC gene is present as a single copy in the genome, consisting of 6 exons and 5 introns. Developmental expression analysis using mouse embryos and postnatal hearts demonstrated that Hrc transcription begins at 12.5 days postcoitum and its level increases gradually, reaching an adult level in the range 5-20 days after birth. Comparing the Hrc gene and other SR genes, we found that the timing and pattern of gene expression vary among the SR genes and the full-level expression of these genes is achieved in the heart after postnatal day 20. Collectively, our study provides comprehensive information about the structure and expression of the mammalian HRC gene, together with the comparative expression data of the related SR genes.

Junctate is a key element in calcium entry induced by activation of InsP3 receptors and/or calcium store depletion

In many cell types agonist-receptor activation leads to a rapid and transient release of Ca(2+) from intracellular stores via activation of inositol 1,4,5 trisphosphate (InsP(3)) receptors (InsP(3)Rs). Stimulated cells activate store- or receptor-operated calcium channels localized in the plasma membrane, allowing entry of extracellular calcium into the cytoplasm, and thus replenishment of intracellular calcium stores. Calcium entry must be finely regulated in order to prevent an excessive intracellular calcium increase. Junctate, an integral calcium binding protein of endo(sarco)plasmic reticulum membrane, (a) induces and/or stabilizes peripheral couplings between the ER and the plasma membrane, and (b) forms a supramolecular complex with the InsP(3)R and the canonical transient receptor potential protein (TRPC) 3 calcium entry channel. The full-length protein modulates both agonist-induced and store depletion-induced calcium entry, whereas its NH(2) terminus affects receptor-activated calcium entry. RNA interference to deplete cells of endogenous junctate, knocked down both agonist-activated calcium release from intracellular stores and calcium entry via TRPC3. These results demonstrate that junctate is a new protein involved in calcium homeostasis in eukaryotic cells.

Substrate Requirements of the Oxygen-sensing Asparaginyl Hydroxylase Factor-inhibiting Hypoxia-inducible Factor

The hypoxia-inducible factor alpha subunits 1 and 2 (HIF-1alpha and HIF-2alpha) are subjected to oxygen-dependent asparaginyl hydroxylation, a modification that represses the carboxyl-terminal transactivation domain (CAD) at normoxia by preventing recruitment of the p300/cAMP-response element-binding protein coactivators. This hydroxylation is performed by the novel asparaginyl hydroxylase, factor-inhibiting HIF-1' (FIH-1), of which HIF-1alpha and HIF-2alpha are the only reported substrates. Here we investigated the substrate requirements of FIH-1 by characterizing its subcellular localization and by examining amino acids within the HIF-1alpha substrate for their importance in recognition and catalysis by FIH-1. Using immunohistochemistry, we showed that both endogenous and transfected FIH-1 are primarily confined to the cytoplasm and remain there under normoxia and following treatment with the hypoxia mimetic, dipyridyl. Individual alanine mutations of seven conserved amino acids flanking the hydroxylated asparagine in HIF-1alpha revealed the importance of the valine (Val-802) adjacent to the targeted asparagine. The HIF-1alpha CAD V802A mutant exhibited a 4-fold lower V(max) in enzyme assays, whereas all other mutants were hydroxylated as efficiently as the wild type HIF-1alpha CAD. Furthermore, in cell-based assays the transcriptional activity of V802A was constitutive, suggesting negligible normoxic hydroxylation in HEK293T cells, whereas the wild type and other mutants were repressed under normoxia. Molecular modeling of the HIF-1alpha CAD V802A in complex with FIH-1 predicted an alteration in asparagine positioning compared with the wild type HIF-1alpha CAD, providing an explanation for the impaired catalysis observed and confirming the importance of Val-802 in asparaginyl hydroxylation by FIH-1.

Glycosylation regulates Notch signalling

Intracellular post-translational modifications such as phosphorylation and ubiquitylation have been well studied for their roles in regulating diverse signalling pathways, but we are only just beginning to understand how differential glycosylation is used to regulate intercellular signalling. Recent studies make clear that extracellular post-translational modifications, in the form of glycosylation, are essential for the Notch signalling pathway, and that differences in the extent of glycosylation are a significant mechanism by which this pathway is regulated.

Antisense oligodeoxynucleotides directed against aspartyl (asparaginyl) beta-hydroxylase suppress migration of cholangiocarcinoma cells

BACKGROUND

Aspartyl (asparaginyl) beta-hydroxylase (AAH) is an alpha-ketoglutarate-dependent dioxygenase that hydroxylates aspartate and asparagine residues in EGF-like domains of proteins. The consensus sequence for AAH beta-hydroxylation occurs in signaling molecules such as Notch and Notch homologs, which have roles in cell migration.

AIM

This study evaluated the potential role of AAH in cell migration using cholangiocarcinoma cell lines as models due to their tendency to widely infiltrate the liver.

METHODS

Five human cholangiocarcinoma cell lines established from human tumors were examined for AAH expression and motility. The effect of antisense oligodeoxynucleotide inhibition of AAH on cholangiocarcinoma cell migration was investigated.

RESULTS

Western blot analysis detected the approximately 86 kDa AAH protein in all five cholangiocarcinoma cell lines, and higher levels of AAH in cell lines derived from moderately or poorly differentiated compared with well-differentiated tumors. Immunocytochemical staining and fluorescence activated cell sorting analysis revealed both surface and intracellular AAH immunoreactivity. Using the phagokinetic non-directional migration assay and a novel ATPLite luminescence-based directional migration assay, we correlated AAH expression with motility. Correspondingly, antisense and not sense or mutated antisense AAH oligodeoxynucleotides significantly inhibited AAH expression and motility in cholangiocarcinoma cells.

CONCLUSIONS

AAH over-expression may contribute to the infiltrative growth pattern of cholangiocarcinoma cells by promoting motility.

Antisense oligonucleotides selectively regulate aspartyl beta-hydroxylase and its truncated protein isoform in vitro but distribute poorly into A549 tumors in vivo

Alternative splicing of the human beta-aspartyl (asparaginyl) hydroxylase (BAH) gene results in the expression of humbug, a truncated form of BAH that lacks the catalytic domain of the enzyme. Overexpression of BAH and humbug has been associated with a variety of human cancers, and although humbug lacks enzymatic activity, it is expressed at levels comparable with that of BAH in various cancer cell lines. Phosphorothioate antisense oligonucleotides (ONs) were designed to dissect out the function of these hydroxylase protein isoforms. In A549 cells, these ONs differentially down-regulated BAH and humbug at the mRNA and protein level. Phosphorothioate ON uptake and antisense studies were conducted in parallel in nude mice bearing A549 tumor xenografts. Microscopic examination of the tumor after administration of a fluorescein-labeled ON showed strong labeling of the outer layers of the tumor connective tissue but cells within the interior of the tumor were sparsely labeled. A modest but significant effect on tumor growth was observed in animals treated with an antisense ON directed against both BAH and humbug transcripts. However, Northern analysis of tumor RNA did not indicate a down-regulation of the targeted mRNA species. These results demonstrate the successful development of antisense ONs that selectively differentiate between the closely related beta-hydroxylase protein isoforms. However, determination of the biological function of these proteins in vivo was limited by the poor uptake properties of phosphorothioate ONs in A549 tumors.

Role of the aspartyl-asparaginyl-beta-hydroxylase gene in neuroblastoma cell motility

Aspartyl (asparaginyl) beta-hydroxylase (AAH) is overexpressed in various malignant neoplasms, and high levels of immunoreactivity mainly occur in infiltrating or metastasized tumors. In addition, AAH is abundantly expressed in normally invasive placental trophoblastic cells. These observations led to the hypothesis that AAH may have a role in motility and aggressive behavior of tumor cells. The present study demonstrates that AAH is overexpressed in primary human malignant neuroectodermal tumors, including medulloblastomas and neuroblastomas, and that AAH expression is at a low level or undetectable in the normal mature brain. In the Sy5y neuroblastoma cell line, endogenous expression of the approximately 86-kd AAH protein was demonstrated by Western blot analysis, and immunoreactivity predominantly localized to the cell surface by immunocytochemical staining and FACS analysis. Sy5y cells that were stably transfected with the human AAH cDNA had increased levels of proliferating cell nuclear antigen and Bcl-2, and reduced levels of p21/Waf1 and p16. In addition, increased AAH expression enhanced Sy5y cell motility, whereas antisense oligodeoxynucleotide inhibition of AAH significantly reduced Sy5y cell motility and increased the levels of p21/Waf1 and p16. The findings suggest that AAH overexpression contributes to the malignant phenotype of neuroectodermal tumor cells by increasing motility and enhancing proliferation, survival, and cell cycle progression. Because AAH expression is at a low level or undetectable in normal brain, the AAH gene may be a target for treating primitive neuroectodermal tumors.

Absence of post-translational aspartyl beta-hydroxylation of epidermal growth factor domains in mice leads to developmental defects and an increased incidence of intestinal neoplasia

The BAH genomic locus encodes three distinct proteins: junctin, humbug, and BAH. All three proteins share common exons, but differ significantly based upon the use of alternative terminal exons. The biological roles of BAH and humbug and their functional relationship to junctin remain unclear. To evaluate the role of BAH in vivo, the catalytic domain of BAH was specifically targeted such that the coding regions of junctin and humbug remained undisturbed. BAH null mice lack measurable BAH protein in several tissues, lack aspartyl beta-hydroxylase activity in liver preparations, and exhibit no hydroxylation of the epidermal growth factor (EGF) domain of clotting Factor X. In addition to reduced fertility in females, BAH null mice display several developmental defects including syndactyly, facial dysmorphology, and a mild defect in hard palate formation. The developmental defects present in BAH null mice are similar to defects observed in knock-outs and hypomorphs of the Notch ligand Serrate-2. In this work, beta-hydroxylation of Asp residues in EGF domains is demonstrated for a soluble form of a Notch ligand, human Jagged-1. These results along with recent reports that another post-translational modification of EGF domains in Notch gene family members (glycosylation by Fringe) alters Notch pathway signaling, lends credence to the suggestion that aspartyl beta-hydroxylation may represent another post-translational modification of EGF domains that can modulate Notch pathway signaling. Previous work has demonstrated increased levels of BAH in certain tumor tissues and a role for BAH in tumorigenesis has been proposed. The role of hydroxylase in tumor formation was tested directly by crossing BAH KO mice with an intestinal tumor model, APCmin mice. Surprisingly, BAH null/APCmin mice show a statistically significant increase in both intestinal polyp size and number when compared with BAH wild-type/APCmin controls. These results suggest that, in contrast to expectations, loss of BAH catalytic activity may promote tumor formation.

Asparagine hydroxylation of the HIF transactivation domain a hypoxic switch

The hypoxia-inducible factors (HIFs) 1alpha and 2alpha are key mammalian transcription factors that exhibit dramatic increases in both protein stability and intrinsic transcriptional potency during low-oxygen stress. This increased stability is due to the absence of proline hydroxylation, which in normoxia promotes binding of HIF to the von Hippel-Lindau (VHL tumor suppressor) ubiquitin ligase. We now show that hypoxic induction of the COOH-terminal transactivation domain (CAD) of HIF occurs through abrogation of hydroxylation of a conserved asparagine in the CAD. Inhibitors of Fe(II)- and 2-oxoglutarate-dependent dioxygenases prevented hydroxylation of the Asn, thus allowing the CAD to interact with the p300 transcription coactivator. Replacement of the conserved Asn by Ala resulted in constitutive p300 interaction and strong transcriptional activity. Full induction of HIF-1alpha and -2alpha, therefore, relies on the abrogation of both Pro and Asn hydroxylation, which during normoxia occur at the degradation and COOH-terminal transactivation domains, respectively.

Molecular cloning and characterization of mouse cardiac junctate isoforms

Junctate is a newly identified integral ER/SR membrane calcium binding protein, which is an alternative splicing form of the same gene generating aspartyl beta-hydroxylase and junctin. Screening a mouse heart cDNA library using canine junctin cDNA as a probe yielded three complete mouse heart cDNAs. One of the cDNAs is homologous to the previously reported human junctate. The three mouse junctate proteins are composed of 270, 259, and 215 amino acids (we named them junctate-1, -2, and -3). The apparent molecular masses of the mouse junctates in SDS-PAGE were in the range between 40 and 53 kDa. Northern and Western blot analyses indicate that mouse junctates are expressed in heart, brain, spleen, lung, liver, kidney, and stomach, but not in skeletal muscle. The apparent molecular weights of junctates from heart and brain were somewhat different from those from the other tissues tested, suggesting that there are tissue-specific expression patterns of the different junctate isoforms. Immunohistochemical studies showed that junctates were expressed both in ventricular and atrial tissues. This is the first study that shows the presence of 3 distinct cardiac junctate isoforms expressed in various mammalian tissues.