The mouse Fused locus encodes Axin, an inhibitor of the Wnt signaling pathway that regulates embryonic axis formation

Mutations at the mouse Fused locus have pleiotropic developmental effects, including the formation of axial duplications in homozygous embryos. The product of the Fused locus, Axin, displays similarities to RGS (Regulators of G-Protein Signaling) and Dishevelled proteins. Mutant Fused alleles that cause axial duplications disrupt the major mRNA, suggesting that Axin negatively regulates the response to an axis-inducing signal. Injection of Axin mRNA into Xenopus embryos inhibits dorsal axis formation by interfering with signaling through the Wnt pathway. Furthermore, ventral injection of an Axin mRNA lacking the RGS domain induces an ectopic axis, apparently through a dominant-negative mechanism. Thus, Axin is a novel inhibitor of Wnt signaling and regulates an early step in embryonic axis formation in mammals and amphibians.

Identification of a domain of Axin that binds to the serine/threonine protein phosphatase 2A and a self-binding domain

Axin is a negative regulator of embryonic axis formation in vertebrates, which acts through a Wnt signal transduction pathway involving the serine/threonine kinase GSK-3 and beta-catenin. Axin has been shown to have distinct binding sites for GSK-3 and beta-catenin and to promote the phosphorylation of beta-catenin and its consequent degradation. This provides an explanation for the ability of Axin to inhibit signaling through beta-catenin. In addition, a more N-terminal region of Axin binds to adenomatous polyposis coli (APC), a tumor suppressor protein that also regulates levels of beta-catenin. Here, we report the results of a yeast two-hybrid screen for proteins that interact with the C-terminal third of Axin, a region in which no binding sites for other proteins have previously been identified. We found that Axin can bind to the catalytic subunit of the serine/threonine protein phosphatase 2A through a domain between amino acids 632 and 836. This interaction was confirmed by in vitro binding studies as well as by co-immunoprecipitation of epitope-tagged proteins expressed in cultured cells. Our results suggest that protein phosphatase 2A might interact with the Axin.APC.GSK-3.beta-catenin complex, where it could modulate the effect of GSK-3 on beta-catenin or other proteins in the complex. We also identified a region of Axin that may allow it to form dimers or multimers. Through two-hybrid and co-immunoprecipitation studies, we demonstrated that the C-terminal 100 amino acids of Axin could bind to the same region as other Axin molecules.

Hepatic IL-17 responses in human and murine primary biliary cirrhosis

The emergence of new regulatory and pro-inflammatory immune cell subsets and cytokines dictates the need to re-examine the role of these subsets in various diseases involving the immune system. IL-17 has been recently identified as a key cytokine involved in numerous autoimmune processes. However, its role in liver autoimmune diseases remains unclear. Primary biliary cirrhosis (PBC) is characterized histologically by autoreactive CD4 and CD8 T cells surrounding damaged bile ducts. CD4(+) T cells are a major source of IL-17, which compose a distinct T helper subset (Th17). Thus we set out to determine the role of IL-17 in both human and a murine model of PBC in a liver-targeted manner. Our data demonstrate an increase in the frequency of IL-17(+) lymphocytic infiltration in liver tissues from PBC patients and those with other liver dysfunctions as compared to healthy livers. IL-2 receptor alpha knockout mice, a recently identified murine model of human PBC, also demonstrate marked aggregations of IL-17-positive cells within portal tracts and increased frequencies of Th17 cells in the liver compared to the periphery. Interestingly, CD4(+) T cells from livers of normal C57BL/6J mice also secreted higher levels of IL-17 relative to those from spleens, indicating a preferential induction of Th17 cells in liver tissues. Importantly, C57BL/6J cocultures of splenic CD4(+) T cells and liver non-parenchymal cells increased IL-17 production approximately 10-fold compared to T cells alone, suggesting a role of the liver microenvironment in Th17 induction in cases of liver autoimmunity and other liver inflammatory diseases.

Genetic analysis of organ fusion in Arabidopsis thaliana

Postgenital organ fusion occurs most commonly during reproductive development and is important in many angiosperms during genesis of the carpel. Although a number of mutants have been described that manifest ectopic organ fusion, little is known about the genes involved in regulating this process. In this article we describe the characterization of a collection of 29 Arabidopsis mutants showing an organ fusion phenotype. Mapping and complementation analyses revealed that the mutant alleles define nine different loci distributed throughout the Arabidopsis genome. Multiple alleles were isolated for the four complementation groups showing the strongest organ fusion phenotype while the remaining five complementation groups, all of which show only weak floral organ fusion, have a single representative allele. In addition to fusion events between aerial parts of the shoot, some mutants also show abnormal ovule morphology with adjacent ovules joined together at maturity. Many of the fusion mutants isolated have detectable differences in the rate at which chlorophyll can be extracted; however, in one case no difference could be detected between mutant and wild-type plants. In three mutant lines pollen remained unresponsive to contact with the mutant epidermis, demonstrating that organ fusion and pollen growth responses can be genetically separated from one another.

Impaired mammary gland and lymphoid development caused by inducible expression of Axin in transgenic mice

Axin is a component of the canonical Wnt pathway that negatively regulates signal transduction by promoting degradation of beta-catenin. To study the role of Axin in development, we developed strains of transgenic mice in which its expression can be manipulated by the administration of doxycycline (Dox). Animals carrying both mouse mammary tumor virus (MMTV)-reverse tetracycline transactivator and tetracycline response element (TRE)2-Axin-green fluorescent protein (GFP) transgenes exhibited Dox-dependent Axin expression and, when induced from birth, displayed abnormalities in the development of mammary glands and lymphoid tissues, both sites in which the MMTV promoter is active. The transgenic mammary glands underwent normal ductal elongation and side branching during sexual maturation and early pregnancy, but failed to develop lobulo-alveoli, resulting in a defect in lactation. Axin attenuated the expression of cyclin D1, a Wnt target that promotes the growth and differentiation of mammary lobulo-alveoli. Increased apoptosis occurred in the mammary epithelia, consistent with the inhibition of a Wnt/cyclin D1 survival signal by Axin. High levels of programmed cell death also occurred in the thymus and spleen. Immature thymocytes underwent massive apoptosis, indicating that the overexpression of Axin blocks the normal development of T lymphocytes. Our data imply that the Axin tumor suppressor controls cell survival, growth, and differentiation through the regulation of an apoptotic signaling pathway.

NF-IL6, a member of the C/EBP family, regulates E1A-responsive promoters in the absence of E1A

A cDNA encoding NF-IL6, an interleukin-6 (IL-6)-regulated human nuclear factor of the C/EBP family, is demonstrated to complement the transactivation function of E1A. The endogenous NF-IL6 level varies according to cell type and correlates positively with an IL-6-regulated cellular E1A-substituting activity that was described recently (J.M. Spergel and S. Chen-Kiang, Proc. Natl. Acad. Sci. USA 88:6472-6476, 1991). When expressed by transfection in cells which contain low levels of NF-IL6 and are incapable of complementing the function of E1A proteins, NF-IL6 also transactivates the E1A-responsive E2ae and E1B promoters, to the same magnitude as E1A. Activation by NF-IL6 is concentration dependent and sequence specific: mutational studies of the E2ae promoter suggest that the promoter-proximal NF-IL6 recognition site functions as a dominant negative regulatory site whereas the promoter-distal NF-IL6 recognition site is positively regulated at low NF-IL6 concentrations and negatively regulated when the NF-IL6 level is high. Consistent with these functions, NF-IL6 alone is sufficient to complement an E1A deletion mutant dl312 in viral infection, when expressed at appropriate concentrations. These results identify NF-IL6 as a sequence-specific cellular nuclear factor which regulates E1A-responsive genes in the absence of E1A.

Fos and Jun repress transcription activation by NF-IL6 through association at the basic zipper region

NF-IL6 and AP-1 family transcription factors are coordinately induced by interleukin-6 (IL-6) in a cell-type-specific manner, suggesting that they mediate IL-6 signals in the nucleus. We show that the basic leucine zipper (bZIP) region of NF-IL6 mediates a direct association with the bZIP regions of Fos and Jun in vitro. This interaction does not depend on the presence of their cognate recognition DNA elements or the posttranslational modification of either partner. NF-IL6 homodimers can bind to both NF-IL6 and AP-1 sites, whereas Fos and Jun cannot bind to most NF-IL6 sites. Cross-family association with Fos or with Jun alters the DNA binding specificity of NF-IL6 and reduced its binding to NF-IL6 sites. NF-IL6 isoforms that differ in the site of translation initiation have distinct transcriptional activities. Activation of a reporter gene linked to the NF-IL6 site by NF-IL6 is repressed by Fos and by Jun in transient transfection assays. Thus, association with AP-1 results in repression of transcription activation by NF-IL6. The repression is NF-IL6 site dependent and may have a role in determining the promoter and cell type specificity in IL-6 signaling.

Tyrosine sulfation is prevalent in human chemokine receptors important in lung disease

Post-translational sulfation of tyrosines affects the affinity and binding of at least some chemokine receptors to their ligand(s) and has been hypothesized to be a feature in all chemokine receptors. This binding initiates downstream signaling cascades. By this mechanism, tyrosine sulfation can influence the cells involved in acute and chronic events of cellular immunity. These events include leukocyte trafficking and airway inflammation important in asthma and chronic obstructive pulmonary disease (COPD). We are using computational methods to convert the poorly defined hypothesis of more widespread sulfation of chemokine receptors to more specific assessments of how closely the sequence environment of each tyrosine residue resembles the sequence environment of tyrosine residues proven to be sulfated. Thus, we provide specific and readily tested hypotheses about the tyrosine residues in all of the chemokine receptors. Tyrosine sulfation was predicted with high scores in the N-terminus domain of 13 out of 18 human chemokine receptor proteins using a position-specific scoring matrix, which was determined to be 94.2% accurate based on Receiver Operating Characteristic analysis. The remaining chemokine receptors have sites exhibiting features of tyrosine sulfation. These putative sites demonstrate clustering in a manner consistent with known tyrosine sulfation sites and conservation both within the chemokine receptor family and across mammalian species. Human chemokine receptors important in asthma and COPD, such as CXCR1, CXCR2, CXCR3, CXCR4, CCR1, CCR2, CCR3, CCR4, CCR5, and CCR8, contain at least one known or predicted tyrosine sulfation site. Recognition that tyrosine sulfation is found in most clinically relevant chemokine receptors could help the development of specific receptor-ligand antagonists to modulate events important in airway diseases.

Differential mechanisms in the pathogenesis of autoimmune cholangitis versus inflammatory bowel disease in interleukin-2Ralpha(-/-) mice

Interleukin-2 (IL-2) receptor alpha knockout (IL-2Ralpha(-/-)) mice have a deficiency of CD25 and a corresponding functional defect in T regulatory cells (Tregs). These mice spontaneously develop portal inflammation with biliary ductular damage and colitis with features similar to human inflammatory bowel disease with T cell infiltrates in both the liver and colon. In humans, inflammatory bowel disease may be accompanied by primary sclerosing cholangitis (PSC), but seldom primary biliary cirrhosis (PBC). We hypothesized that the effector mechanism responsible for T cell infiltrates would differ for colon versus liver. To address this thesis, we developed three colonies of double-knockout mice including IL-2Ralpha(-/-) CD4(-/-), IL-2Ralpha(-/-) CD8(-/-), and IL-2Ralpha(-/-) T cell receptor (TCR)-beta(-/-). Tissue immunopathology, body weight, and serum levels of cytokines, immunoglobulins, and anti-mitochondrial antibodies (AMA) were assayed at 3 months of age. Relative to IL-2Ralpha(-/-) mice, IL-2Ralpha(-/-) CD4(-/-) mice had increased biliary ductular damage but reduced inflammation in the colon. In contrast, IL-2Ralpha(-/-) CD8(-/-) mice had increased colon inflammation but markedly attenuated biliary ductular damage. Both IL-2Ralpha(-/-) CD4(-/-) and IL-2Ralpha(-/-) CD8(-/-) mice demonstrated elevated serum levels of tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma), interleukin-12p40 (IL-12p40), and interleukin-2 (IL-2) compared with C57BL/6J controls, but only IL-2Ralpha(-/-) CD8(-/-) mice had increased serum levels of immunoglobulin A (IgA), AMA and interleukin-17 (IL-17). Finally, and of importance, IL-2Ralpha(-/-) TCR-beta(-/-) mice had abrogation of liver and colon pathological conditions and lacked AMA. In conclusion, on loss of Treg function in mice, CD8 T cells mediate biliary ductular damage whereas CD4 T cells mediate induction of colon-specific autoimmunity.

Domains of axin and disheveled required for interaction and function in wnt signaling

Disheveled blocks the degradation of beta-catenin in response to Wnt signal by interacting with the scaffolding protein, Axin. To define this interaction in detail we undertook a mutational and binding analysis of the murine Axin and Disheveled proteins. The DIX domain of Axin was found to be important for association with Disheveled and two other regions of Axin (between residues 1-168 and 600-810) were identified that can promote the association of Axin and Disheveled. We found that the DIX domain of Disheveled is critical for association with Axin in vivo and for Disheveled activity. The Disheveled DIX domain controlled the ability of Disheveled to induce the accumulation of cytosolic beta-catenin whereas the PDZ domain was not essential to this function.

Hearing loss and pneumococcal meningitis: an animal model

Clinical studies of predisposing factors in the development of hearing loss secondary to bacterial meningitis have produced conflicting results. An animal model of meningogenic labyrinthitis was developed for more precise study of these parameters. Rabbits were inoculated intrathecally with 10(5) pneumococci to induce meningitis. Hearing thresholds were measured using auditory-evoked responses to 1 kHz, 10 kHz, and click stimuli before infection and every 12 hours thereafter. Profound deafness occurred in all subjects at an average of 48 hours following infection. The incidence and severity of hearing loss was strongly correlated with the duration of meningitis. Temporal bone histology revealed acute inflammation of all perilymphatic spaces including the cochlear aqueduct. This model demonstrated that the risk and severity of hearing loss increase with the duration of meningitis and suggested that the cochlear aqueduct is an anatomic pathway for the extension of infection from the cerebrospinal fluid to the cochlea. The implications for therapy in humans is discussed.

Nuclear signaling by interleukin-6

The molecular analysis of the regulation of nuclear proteins induced by interleukin-6 has provided new insights into this largely unknown signal transduction pathway. Transcription factors of the CCAAT/enhancer-binding protein and AP-1 families, as well as the octamer-binding proteins and the tumor suppressor gene product pRB, are regulated by interleukin-6 in a cell type specific manner, suggesting that they may play a role in the nuclear signaling by interleukin-6.

Rheology of Mobility-Control Foams

Abstract

Enhanced oil recovery (EOR) studies have consistently demonstrated the need to mitigate gas channeling in processes involving use of gas to displace crude oil. The use of foam for gas mobility control was first investigated in 1955, and an early field test by Union Oil Co. of California indicated significant merit in the concept. Work was undertaken at New Mexico State U. to provide rheological data of in-situ-generated foam in an attempt to define the mobility-lowering mechanism.

A capillary viscometer was constructed to measure the rheological properties of the most promising foams made with commercially available additives. Data collected at different shear rates show that foams are pseudoplastic in nature and several orders of magnitude more viscous, 10 to 100 cp (0.01 to 0.1 Pa·s) than their gas or liquid fractions. Significantly, foam viscosities are generally an inverse function of foam density, which is very advantageous in oil-displacement processes. In areas where gas fingering is pronounced, foam viscosity would be expected to increase with gas saturation and, thereby, would tend to mitigate further gas channeling.

The spontaneous generation of a viscous foam phase may also serve to reduce the flowing gas saturation and, thus, lower gas mobility because of the relative permeability effect. This technology is easily adapted to the water-alternating-gas (WAG) process involving CO2 or rich-gas displacement of oil.

Introduction

Interest in the use of CO2 for EOR is increasing rapidly. This increase is a result of both the increased price of oil, which makes the use of CO2 economically feasible, and the unique ability of CO2 to displace oil in reservoir formations.

A major problem in the use of gases including CO2 for oil displacement is the severe gas channeling that occurs in the formation as a consequence of the high mobility of the gas phase. To alleviate this problem, CO2 has been injected alternately with water (WAG). This process is good but limited in applicability because water is also quite mobile.

The use of foam for mobility control shows considerable promise. Early work was done by Bond and Holbrook1 and by Fried.2 These and later studies suggest that foam injectivity is considerably different from that of either water or gas.

In previous studies, varied results were obtained because of the extreme variability in flow properties of the various foams used. The extrapolation of the results of available tests to a particular reservoir formation would be hazardous without more specific insight into foam rheology. Our study was conducted for the specific purpose of expanding knowledge in this important area.

The flow properties were studied by passing foams through capillary tubes of various sizes and then analyzing the shear-stress and shear-rate data. The foams were generated in a porous matrix. The liquid phase consisted of brine containing calcium and an ethoxylated alcohol sulfate. This solution has been shown capable of producing excellent foam under usual oil reservoir conditions.3 The gaseous phase consisted of nitrogen, which was considered typical of possible displacing gases.

The foams were found to be pseudoplastic. The apparent viscosities were identified as a strong function of the foam density; drier foams typically had higher apparent viscosities than wet ones at the same shear rate. Also, the foams had much higher viscosities than those of the fluids from which they were made.

Capillary-tube dimensions, both length and diameter, affected the measured apparent viscosities. These results are attributed to wall effects, shear-induced coalescence, and unusual shear gradients in the flowing foam.

Autoimmunity and tyrosine sulfation

Homeostasis of the immune system is achieved through refined regulation and communication between immunologically relevant receptor and their cognate ligands amongst mononuclear cells during ontogeny and day to day immune responses. An aberrance in not only the kinetics of receptor expression but also the relative diversity of expression alter these events. More importantly, improper modulation of ligand binding affinity can be a triggering event that results in autoimmunity. As one of the most common post-translational modifications, tyrosine sulfation possesses the ability to regulate mononuclear cell function at various stages of the immune response. For example, removal of sulfated tyrosine residues consistently decreases the binding affinity of the ligand to its corresponding receptor as exemplified by studies of several tyrosine sulfated proteins such as PSGL-1, CD44v5, CCR5, and CXCR4, all known to play a role in a variety of autoimmune diseases. This review defines possible roles that tyrosine sulfated proteins may play in the pathogenesis of autoimmune diseases.

Posttransplantation lymphoproliferative disorder of the head and neck: imaging features in seven adults

PURPOSE

To determine the cross-sectional imaging findings of posttransplantation lymphoproliferative disorder (PTLD) of the head and neck.

MATERIALS AND METHODS

Computed tomographic (CT) scans (n = 6) and magnetic resonance (MR) images (n = 2) in seven patients with histopathologically proved PTLD of the Waldeyer (lymphoid) ring or cervical lymph nodes were retrospectively reviewed for abnormalities.

RESULTS

The interval between transplantation and PTLD onset was 3.5-108 months (mean, 30 months). All patients had imaging abnormalities involving the Waldeyer ring, and focal 2.0-4. 5-cm masses were present in six patients (unilateral oropharyngeal tonsil in two, bilateral oropharyngeal tonsils in one, nasopharyngeal adenoids in three, unilateral pharyngeal tonsil and ipsilateral nasopharynx in one). In three patients, the mass was centrally low attenuating at CT or isointense to fluid at MR imaging, with enhancing solid peripheral lymphoid tissue. Three patients also had nodal findings: one with a 7-cm low-attenuating nodal mass in the right neck and two with numerous bilateral lymph nodes (mostly normal sized) in the anterior and posterior cervical lymph chains. One patient also had a small mass in the upper mediastinum.

CONCLUSION

In the setting of organ transplantation, findings of masses in the Waldeyer ring or an excessive number of cervical nodes should increase the index of suspicion of PTLD.

Ursodeoxycholic acid reduces CpG-induced IgM production in patients with primary biliary cirrhosis

AIM

Ursodeoxycholic acid (UDCA) treatment reduces IgM serum levels in patients with primary biliary cirrhosis (PBC) without affecting serum antimitochondrial antibody (AMA) titers. We previously reported that PBC-associated hyper-IgM is secondary to a disease-specific hyperproduction following bacterial stimulation by B cells.

METHODS

We isolated peripheral blood mononuclear cells (PBMC) from patients with PBC and controls and evaluated whether bacterial CpG challenge in the presence of UDCA at concentrations consistent with those achieved in treated patients led to changes in total IgM, IgG-AMA, and IgM-AMA production. Further, p65 phosphorylation and CD38 cell expression were analyzed as measures of activation of the NF-kB signaling pathway and B cell subsets, respectively.

RESULTS

UDCA significantly reduced CpG-induced total IgM and IgM-AMA production, but had no impact on IgG-AMA production. UDCA also significantly reduced the activation ofnaïve and IgM memory, but not IgG memory, B cells, as represented by CD38 expression levels. Further, p65 phosphorylation was significantly reduced in the presence of UDCA.

CONCLUSION

UDCA reduces total and IgM-AMA production in PBMC from patients with PBC by downregulating B cell activation and NF-kB signaling. These data ultimately suggest novel mechanisms of action for UDCA in chronic autoimmune cholestasis.

A new defibrillator discrimination algorithm utilizing electrogram morphology analysis

Inappropriate therapies delivered by implantable cardioverter defibrillators (ICDs) for supraventricular arrhythmias remain a common problem, particularly in the event of rapidly conducted atrial fibrillation or marked sinus tachycardia. The ability to differentiate between ventricular tachycardia and supraventricular arrhythmias is the major goal of discrimination algorithms. Therefore, we developed a new algorithm, SimDis, utilizing morphological features of the shocking electrograms. This algorithm was developed from electrogram data obtained from 36 patients undergoing ICD implantation. An independent test set was evaluated in 25 patients. Recordings were made in sinus rhythm, sinus tachycardia, and following the induction of ventricular tachycardia and atrial fibrillation. The arrhythmia complex is defined as wide if the duration is at least 30% greater than the template in sinus rhythm. For narrow complexes, four maximum and minimum values were measured to form a 4-element feature vector, which was compared with a representative feature vector during normal sinus rhythm. For each rhythm, any wide complex was classified as ventricular tachycardia. For narrow complexes, the second step of the algorithm compared the electrogram with the template, computing similarity and dissimilarity values. These values were then mapped to determine if they fell within a previously established discrimination boundary. On the independent test set, the SimDis algorithm correctly classified 100% of ventricular tachycardias (27/27), 98% of sinus tachycardias (54/55), and 100% of episodes of atrial fibrillation (37/37). We conclude that the SimDis algorithm yields high sensitivity (100%) and specificity (99%) for arrhythmia discrimination, using the computational capabilities of an ICD system.

Prediction of tyrosine sulfation sites in animal viruses

Post-translational modification of proteins by tyrosine sulfation enhances the affinity of extracellular ligand-receptor interactions important in the immune response and other biological processes in animals. For example, sulfated tyrosines in polyomavirus and varicella-zoster virus may help modulate host cell recognition and facilitate viral attachment and entry. Using a Position-Specific-Scoring-Matrix with an accuracy of 96.43%, we analyzed the possibility of tyrosine sulfation in all 1517 animal viruses available in the Swiss-Prot database. From a total of 97,729 tyrosines, we predicted 5091 sulfated tyrosine sites from 1024 viruses. Our site predictions in hemagglutinin of influenza A, VP4 of rotavirus, and US28 of cytomegalovirus strongly suggest an important link between tyrosine sulfation and viral disease mechanisms. In each of these three viral proteins, we observed highly conserved amino acid sequences surrounding predicted sulfated tyrosine sites. Tyrosine sulfation appears to be much more common in animal viruses than is currently recognized.