Diverse substrate recognition mechanisms for rhomboids; thrombomodulin is cleaved by Mammalian rhomboids

The rhomboids are a recently discovered family of intramembrane proteases that are conserved across evolution. Drosophila was the first organism in which they were characterized, where at least Rhomboids 1-3 activate EGF receptor signaling by releasing the active forms of EGF-like growth factors. Subsequent work has begun to shed light on the role of these proteases in bacteria and yeast, but nothing is known about the function of rhomboids in vertebrates beyond evidence that the subclass of mitochondrial rhomboids is conserved. Here, we report that the anticoagulant cell-surface protein thrombomodulin is the first mammalian protein to be a rhomboid substrate in a cell culture assay. The thrombomodulin transmembrane domain (TMD) is cleaved only by vertebrate RHBDL2-like rhomboids. Thrombomodulin TMD cleavage is directed not by sequences within the TMD, as is the case with Spitz but by its cytoplasmic domain, which, at least in some contexts, is necessary and sufficient to determine cleavage by RHBDL2. These data suggest that thrombomodulin could be a physiological substrate for rhomboid. Moreover, the discovery of a second mode of substrate recognition by rhomboids implies mechanistic diversity in this family of intramembrane proteases.     

K+ depolarization induces RhoA kinase translocation to caveolae and Ca2+ sensitization of arterial muscle

KCl causes smooth muscle contraction by elevating intracellular free Ca2+, whereas receptor stimulation activates an additional mechanism, termed Ca2+ sensitization, that can involve activation of RhoA-associated kinase (ROK) and PKC. However, recent studies support the hypothesis that KCl may also increase Ca2+ sensitivity. Our data showed that the PKC inhibitor GF-109203X did not, whereas the ROK inhibitor Y-27632 did, inhibit KCl-induced tonic (5 min) force and myosin light chain (MLC) phosphorylation in rabbit artery. Y-27632 also inhibited BAY K 8644- and ionomycin-induced MLC phosphorylation and force but did not inhibit KCl-induced Ca2+ entry or peak ( approximately 15 s) force. Moreover, KCl and BAY K 8644 nearly doubled the amount of ROK colocalized to caveolae at 30 s, a time that preceded inhibition of force by Y-27632. Colocalization was not inhibited by Y-27632 but was abolished by nifedipine and the calmodulin blocker trifluoperazine. These data support the hypothesis that KCl caused Ca2+ sensitization via ROK activation. We discuss a novel model for ROK activation involving translocation to caveolae that is dependent on Ca2+ entry and involves Ca2+-calmodulin activation.     

The role of OX40 ligand interactions in the development of the Th2 response to the gastrointestinal nematode parasite Heligmosomoides polygyrus

In these studies, we examined the effects of OX40 ligand (OX40L) deficiency on the development of Th2 cells during the Th2 immune response to the intestinal nematode parasite Heligmosomoides polygyrus. Elevations in IL-4 production and total and Ag-specific serum IgE levels were partially inhibited during both the primary and memory immune responses to H. polygyrus in OX40L(-/-) mice. The host-protective memory response was compromised in OX40L(-/-) mice, as decreased worm expulsion and increased egg production were observed compared with H. polygyrus-inoculated OX40L(+/+) mice. To further examine the nature of the IL-4 defect during priming, adoptively transferred DO11.10 T cells were analyzed in the context of the H. polygyrus response. Although Ag-specific T cell IL-4 production was reduced in the OX40L(-/-) mice following immunization with OVA peptide plus H. polygyrus, Ag-specific T cell expansion, cell cycle progression, CXCR5 expression, and migration were comparable between OX40L(+/+) and OX40L(-/-) mice inoculated with OVA and H. polygyrus. These studies suggest an important role for OX40/OX40L interactions in specifically promoting IL-4 production, as well as associated IgE elevations, in Th2 responses to H. polygyrus. However, OX40L interactions were not required for serum IgG1 elevations, increases in germinal center formation, and Ag-specific Th2 cell expansion and migration to the B cell zone.     

Angiopoietin-1 and angiopoietin-2 share the same binding domains in the Tie-2 receptor involving the first Ig-like loop and the epidermal growth factor-like repeats

Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) have been identified as ligands with different effector functions of the vascular assembly and maturation-mediating receptor tyrosine kinase Tie-2. To understand the molecular interactions of the angiopoietins with their receptor, we have studied the binding of Ang-1 and Ang-2 to the Tie-2 receptor. Enzyme-linked immunosorbent assay-based competition assays and co-immunoprecipitation experiments analyzing the binding of Ang-1 and Ang-2 to truncation mutants of the extracellular domain of Tie-2 showed that the first Ig-like loop of Tie-2 in combination with the epidermal growth factor (EGF)-like repeats (amino acids 1-360) is required for angiopoietin binding. The first Ig-like domain or the EGF-like repeats alone are not capable of binding Ang-1 and Ang-2. Concomitantly, we made the surprising finding that Tie-2 exon-2 knockout mice do express a mutated Tie-2 protein that lacks 104 amino acids of the first Ig-like domain. This mutant Tie-2 receptor is functionally inactive as shown by the lack of ligand binding and receptor phosphorylation. Collectively, the data show that the first 104 amino acids of the Tie-2 receptor are essential but not sufficient for angiopoietin binding. Conversely, the first 360 amino acids (Ig-like domain plus EGF-like repeats) of the Tie-2 receptor are necessary and sufficient to bind both Ang-1 and Ang-2, which suggests that differential receptor binding is not likely to be responsible for the different functions of Ang-1 and Ang-2.     

Charting the Drosophila neuropile: a strategy for the standardised characterisation of genetically amenable neurites

Insect neurons are individually identifiable and have been used successfully to study principles of the formation and function of neuronal circuits. In the fruitfly Drosophila, studies on identifiable neurons can be combined with efficient genetic approaches. However, to capitalise on this potential for studies of circuit formation in the CNS of Drosophila embryos or larvae, we need to identify pre- and postsynaptic elements of such circuits and describe the neuropilar territories they occupy. Here, we present a strategy for neurite mapping, using a set of evenly distributed landmarks labelled by commercially available anti-Fasciclin2 antibodies which remain comparatively constant between specimens and over developmental time. By applying this procedure to neurites labelled by three Gal4 lines, we show that neuritic territories are established in the embryo and maintained throughout larval life, although the complexity of neuritic arborisations increases during this period. Using additional immunostainings or dye fills, we can assign Gal4-targeted neurites to individual neurons and characterise them further as a reference for future experiments on circuit formation. Using the Fasciclin2-based mapping procedure as a standard (e.g., in a common database) would facilitate studies on the functional architecture of the neuropile and the identification of candiate circuit elements.     

A microscope-based screening platform for large-scale functional protein analysis in intact cells

A modular microscope-based screening platform, with applications in large-scale analysis of protein function in intact cells is described. It includes automated sample preparation, image acquisition, data management and analysis, and the genome-wide automated retrieval of bioinformatic information. The modular nature of the system ensures that it is rapidly adaptable to new biological questions or sets of proteins. Two automated functional assays addressing protein secretion and the integrity of the Golgi complex were developed and tested. This shows the potential of the system in large-scale, cell-based functional proteomic projects.     

Stage-specific inductive signals in the Drosophila neuroectoderm control the temporal sequence of neuroblast specification

One of the initial steps of neurogenesis in the Drosophila embryo is the delamination of a stereotype set of neural progenitor cells (neuroblasts) from the neuroectoderm. The time window of neuroblast segregation has been divided into five successive waves (S1-S5) in which subsets of neuroblasts with specific identities are formed. To test when identity specification of the various neuroblasts takes place and whether extrinsic signals are involved, we have performed heterochronic transplantation experiments. Single neuroectodermal cells from stage 10 donor embryos (after S2) were transplanted into the neuroectoderm of host embryos at stage 7 (before S1) and vice versa. The fate of these cells was uncovered by their lineages at stage 16/17. Transplanted cells adjusted their fate to the new temporal situation. Late neuroectodermal cells were able to take over the fate of early (S1/S2) neuroblasts. The early neuroectodermal cells preferentially generated late (S4/S5) neuroblasts, despite their reduced time of exposure to the neuroectoderm. Furthermore, neuroblast fates are independent from divisions of neuroectodermal progenitor cells. We conclude from these experiments that neuroblast specification occurs sequentially under the control of non-cell-autonomous and stage-specific inductive signals that act in the neuroectoderm.     

Dopamine and alcohol relapse: D1 and D2 antagonists increase relapse rates in animal studies and in clinical trials

A considerable number of animal studies on the effects of dopaminergic agents on alcohol intake behavior have been performed. Acute alcohol administration in rats induces dopamine release in the caudate nucleus and in the nucleus accumbens, an effect related among others to reinforcement. It has been repeatedly suggested that D1 and D2 receptor activation mediates reward. As alcohol consumption and dopaminergic transmission seem to have a close relationship, all kinds of dopaminergic agents may be regarded as putative therapeutics for preventing relapse. In a prospective European double-blind multicenter clinical trial, comparing the D1, D2, D3 antagonist flupenthixol and placebo in 281 chronic alcohol-dependent patients (27.4% women), the application of the Lesch typology made an outcome differentiation possible. It could be shown in which patients flupenthixol administration was followed by a significantly higher relapse rate and in which patient groups no differences were found when compared to placebo.     

Intragastric ethanol infusion model for cellular and molecular studies of alcoholic liver disease

The intragastric alcohol infusion rat model (IAIRM) of alcoholic liver disease (ALD) has been utilized in various laboratories to study various aspects of ALD pathogenesis including oxidative stress, cytokine upregulation, hypoxic damage, apoptosis, ubiquitin-proteasome pathway and CYP2E1 induction. The basic value of the model is that it produces pathologic changes which resemble ALD including microvesicular and macrovesicular fat, megamitochondria, apoptosis, central lobular and pericellular fibrosis, portal fibrosis, bridging fibrosis, central necrosis, and mixed inflammatory infiltrate including PMNs and lymphocytes. The model is valuable because the diet and ethanol intake are totally under the control of the investigator. A steady state can be maintained with high or low blood alcohol levels for long periods. The cycling of the blood alcohol levels, when a constant infusion rate of alcohol is maintained, simulates binge drinking. Using this model the importance of dietary fat, especially the degree of saturation of the fatty acids on the induction of liver pathology, has been documented. The role of endotoxin, the Kupffer cell, TNFalpha, and NADPH oxidase have been demonstrated. The importance of 2E1 in oxidative stress induction has been shown using inhibitors of the isozyme. The importance of dietary iron in the pathogenesis of cirrhosis has been documented. Acetaldehyde has been shown to play a role in preventing liver pathology by preventing NFkappaB activation. Using the model, to maintain high blood alcohol levels is found to be necessary to demonstrate proteasomal peptidase inhibition. Ubiquitin synthesis is also inhibited at high blood alcohol levels in the IAIRM model. Oxidized proteins accumulate in the liver at high blood alcohol levels. Neoantigens derived from protein adducts formed with products of oxidation induce autoimmune mechanisms of liver injury. Thus, in many ways the model has revolutionized our understanding of the pathogenesis of ALD.