Axon extension and guidance require a coordinated assembly of F-actin and microtubules as well as regulated translation. The molecular basis of how the translation of mRNAs encoding guidance proteins could be closely tied to the pace of cytoskeletal assembly is poorly understood. Previous studies have shown that the F-actin-microtubule crosslinker Short stop (Shot) is required for motor and sensory axon extension in the Drosophila embryo. Here, we provide biochemical and genetic evidence that Shot functions with a novel translation inhibitor, Krasavietz (Kra, Exba), to steer longitudinally directed CNS axons away from the midline. Kra binds directly to the C-terminus of Shot, and this interaction is required for the activity of Shot to support midline axon repulsion. shot and kra mutations lead to weak robo-like phenotypes, and synergistically affect midline avoidance of CNS axons. We also show that shot and kra dominantly enhance the frequency of midline crossovers in embryos heterozygous for slit or robo, and that in kra mutant embryos, some Robo-positive axons ectopically cross the midline that normally expresses the repellent Slit. Finally, we demonstrate that Kra also interacts with the translation initiation factor eIF2␤ and inhibits translation in vitro. Together, these data suggest that Kra-mediated translational regulation plays important roles in midline axon repulsion and that Shot functions as a direct physical link between translational regulation and cytoskeleton reorganization.

Although mainly expressed in neuronal cells, lipocalin-type PGD synthase (L-PGDS) is detected in the macrophages infiltrated to atherosclerotic plaques. However, the regulation and significance of L-PGDS expression in macrophages are unknown. Here, we found that treatment of macrophages with bacterial endotoxin (LPS) or Pseudomonas induced L-PGDS expression. Epigenetic suppression of L-PGDS expression in macrophages blunted a majority of PGD2 produced after LPS treatment. Chromatin immunoprecipitation assays show that L-PGDS induction was regulated positively by AP-1, but negatively by p53. L-PGDS expression was detected in whole lung and alveolar macrophages treated with LPS or Pseudomonas. L-PGDS overexpressing transgenic mice improved clearance of Pseudomonas from the lung compared with nontransgenic mice. Similarly, intratracheal instillation of PGD2 enhanced removal of Pseudomonas from the lung in mice. In contrast, L-PGDS knockout mice were impaired in their ability to remove Pseudomonas from the lung. Together, our results identify induction of L-PGDS expression by inflammatory stimuli or bacterial infection, the regulatory mechanism of L-PGDS induction, and the protective role of L-PGDS expression in host immune response. Our study suggests a potential therapeutic usage of L-PGDS or PGD2 against Pseudomonas pneumonia.

In addition to hepatocytes, hepatitis C virus (HCV) infects immune cells, including macrophages. However, little is known concerning the impact of HCV infection on cellular functions of these immune effector cells. Lipopolysaccharide (LPS) activates IB kinase (IKK) signalsome and NF-B, which leads to the expression of cyclooxygenase-2 (COX-2), which catalyzes production of prostaglandins, potent effectors on inflammation and possibly hepatitis. Here, we examined whether expression of HCV core interferes with IKK signalsome activity and COX-2 expression in activated macrophages. In reporter assays, HCV core inhibited NF-B activation in RAW 264.7 and MH-S murine macrophage cell lines treated with bacterial LPS. HCV core inhibited IKK signalsome and IKK␤ kinase activities induced by tumor necrosis factor alpha in HeLa cells and coexpressed IKK␥ in 293 cells, respectively. HCV core was coprecipitated with I⌲⌲␤ and prevented nuclear translocation of IKK␤. NF-B activation by either LPS or overexpression of IKK␤ was sufficient to induce robust expression of COX-2, which was markedly suppressed by ectopic expression of HCV core. Together, these data indicate that HCV core suppresses IKK signalsome activity, which blunts COX-2 expression in macrophages. Additional studies are necessary to determine whether interrupted COX-2 expression by HCV core contributes to HCV pathogenesis.Hepatitis C virus (HCV), a flavivirus, causes hepatitis, cirrhosis, and hepatocellular carcinoma (18). Currently, almost 3% of the world population is infected by HCV, and these numbers seem to be increasing (3). One of the most remarkable features of HCV infection is that more than 85% of acutely infected patients become chronically infected (4). Although CD4 ϩ and CD8 ϩ T-cell responses are crucial for controlling HCV infection in acute HCV patients, these T-cell responses are significantly impaired in chronic HCV patients (16). Thus, this suggests that HCV evades host immune responses. While hepatocytes are a major target of HCV infection, recent studies showed that HCV can replicate in immune cells such as B and T lymphocytes and monocytes that express HCV receptors, such as CD81 and low-density lipoprotein receptor (1, 2, 52). Thus, it is possible that HCV infects immune effector cells, which contributes to evasion of host immune surveillance.

Recently, a new member of the ABC transporter superfamily of Arabidopsis, AtMRP5, was identified and characterized. In the present work, we found that AtMRP5 can bind specifically to sulfonurea when it is expressed in HEK293 cells. We also present evidence for a new role of AtMRP5 in the salt stress response of Arabidopsis. We used reverse genetics to identify an Arabidopsis mutant (atmrp5-2) in which the AtMRP5 gene was disrupted by transferred DNA insertion. In root-bending assays using Murashige and Skoog medium supplemented with 100 mm NaCl, root growth of atmrp5-2 was substantially inhibited in contrast to the almost normal growth of wild-type seedlings. This hypersensitive response of the atmrp5-2 mutant was not observed during mannitol treatment. The root growth of the wild-type plant grown in Murashige and Skoog medium supplemented with the MRP inhibitor glibenclamide and NaCl was inhibited to a very similar extent as the root growth of atmrp5-2 grown in NaCl alone. The Na ϩ -dependent reduction of root growth of the wild-type plant in the presence of glibenclamide was partially restored by diazoxide, a known K ϩ channel opener that reverses the inhibitory effects of sulfonylureas in animal cells. Moreover, the atmrp5-2 mutant was defective in 86 Rb ϩ uptake. When seedlings were treated with 100 mm NaCl, atmrp5-2 seedlings accumulated less K ϩ and more Na ϩ than those of the wild type. These observations suggest that AtMRP5 is a putative sulfonylurea receptor that is involved in K ϩ homeostasis and, thus, also participates in the NaCl stress response.The ATP-binding cassette (ABC) transporter superfamily is the largest known membrane transporter protein family, and its members are capable of a multitude of transport functions (Higgins, 1992(Higgins, , 1995. These proteins are highly interesting because of their involvement in numerous pathologies, such as cystic fibrosis, diabetes, and multidrug resistance (Demolombe and Escande, 1996). In animals, two ABC proteins are directly involved in regulating ion channels in the plasma membrane, specifically ATPsensitive potassium channels (K ATP channels) and the cystic fibrosis transmembrane conductance regulator (CFTR). K ATP channels were initially identified in the heart (Noma, 1983) and are complexes composed of an inward rectifier K ϩ channel and an ABC protein, the sulfonylurea receptor (Babenko et al., 1998; Miki et al., 1999). K ATP channels are highly specific for K ϩ and are inhibited by micromolar concentrations of intracellular ATP. CFTR is a chloride channel expressed by a variety of secreting epithelial cells that is regulated by cAMP-dependent phosphorylation and ATP (Anderson et al., 1991; Bear et al., 1992). These channels serve to link the electrical activity of cell membranes with cellular metabolism.The presence of ABC proteins in plants was established by the cloning of several genes encoding members of this group in Arabidopsis and other species (Dudler and Hertig, 1992; Smart and Fleming, 1996; Davies et al., 1997; Lu et al., 1997 Lu...

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