The heterotrimeric influenza virus polymerase, containing the PA, PB1 and PB2 proteins, catalyses viral RNA replication and transcription in the nucleus of infected cells. PB1 holds the polymerase active site and reportedly harbours endonuclease activity, whereas PB2 is responsible for cap binding. The PA amino terminus is understood to be the major functional part of the PA protein and has been implicated in several roles, including endonuclease and protease activities as well as viral RNA/complementary RNA promoter binding. Here we report the 2.2 ångström (A) crystal structure of the N-terminal 197 residues of PA, termed PA(N), from an avian influenza H5N1 virus. The PA(N) structure has an alpha/beta architecture and reveals a bound magnesium ion coordinated by a motif similar to the (P)DX(N)(D/E)XK motif characteristic of many endonucleases. Structural comparisons and mutagenesis analysis of the motif identified in PA(N) provide further evidence that PA(N) holds an endonuclease active site. Furthermore, functional analysis with in vivo ribonucleoprotein reconstitution and direct in vitro endonuclease assays strongly suggest that PA(N) holds the endonuclease active site and has critical roles in endonuclease activity of the influenza virus polymerase, rather than PB1. The high conservation of this endonuclease active site among influenza strains indicates that PA(N) is an important target for the design of new anti-influenza therapeutics.

The recent emergence of highly pathogenic avian influenza A virus strains with subtype H5N1 pose a global threat to human health. Elucidation of the underlying mechanisms of viral replication is critical for development of anti-influenza virus drugs. The influenza RNA-dependent RNA polymerase (RdRp) heterotrimer has crucial roles in viral RNA replication and transcription. It contains three proteins: PA, PB1 and PB2. PB1 harbours polymerase and endonuclease activities and PB2 is responsible for cap binding; PA is implicated in RNA replication and proteolytic activity, although its function is less clearly defined. Here we report the 2.9 ångström structure of avian H5N1 influenza A virus PA (PA(C), residues 257-716) in complex with the PA-binding region of PB1 (PB1(N), residues 1-25). PA(C) has a fold resembling a dragon's head with PB1(N) clamped into its open 'jaws'. PB1(N) is a known inhibitor that blocks assembly of the polymerase heterotrimer and abolishes viral replication. Our structure provides details for the binding of PB1(N) to PA(C) at the atomic level, demonstrating a potential target for novel anti-influenza therapeutics. We also discuss a potential nucleotide binding site and the roles of some known residues involved in polymerase activity. Furthermore, to explore the role of PA in viral replication and transcription, we propose a model for the influenza RdRp heterotrimer by comparing PA(C) with the lambda3 reovirus polymerase structure, and docking the PA(C) structure into an available low resolution electron microscopy map.

Although technically challenging, surgery for HCC with IVC/RA tumor thrombus can be safely performed and should be considered in patients with resectable primary tumor and sufficient hepatic reservoir because compared with transcatheter arterial chemoembolization or symptomatic treatment, it significantly improved patient survival.

The canonical transient receptor potential channels (TRPCs) are Ca2+-permeable nonselective cation channels with various physiological functions. Here, we report that TRPC6, a member of the TRPC family, promotes hippocampal neuron dendritic growth. The peak expression of TRPC6 in rat hippocampus was between postnatal day 7 and 14, a period known to be important for maximal dendritic growth. Overexpression of TRPC6 increased phosphorylation of Ca2+/calmodulin-dependent kinase IV (CaMKIV) and cAMP-response-element binding protein (CREB) and promoted dendritic growth in hippocampal cultures. Downregulation of TRPC6 by short hairpin RNA interference against TRPC6 suppressed phosphorylation of both CaMKIV and CREB and impaired dendritic growth. Expressing a dominant-negative form of CaMKIV or CREB blocked the TRPC6-induced dendritic growth. Furthermore, inhibition of Ca2+ influx suppressed the TRPC6 effect on dendritic growth. Finally, in TRPC6 transgenic mice, the phosphorylation of CaMKIV and CREB was enhanced and the dendritic growth was also increased. In conclusion, TRPC6 promoted dendritic growth via the CaMKIV-CREB pathway. Our results thus revealed a novel role of TRPC6 during the development of the central nervous system (CNS).

Vascular endothelial growth factor (VEGF, VEGF-A), a selective mitogen for endothelial cells is a critical factor for vascular development. Two isoforms that differ in the presence of exons 6 and 7, Vegf(165) and Vegf(121), are the dominant forms expressed in zebrafish embryo. Simultaneous overexpression of both isoforms in the embryo results in increased production of flk1, tie1, scl, and gata1 transcripts, indicating a stimulation of both endothelial and hematopoietic lineages. We also demonstrate that vegf can stimulate hematopoiesis in zebrafish by promoting the formation of terminally differentiated red blood cells. Simultaneous overexpression of both isoforms also causes ectopic vasculature and blood cells in many of the injected embryos as well as pericardial edema in later stage embryos. Overexpression of vegf also resulted in earlier onset of flk1, tie1, scl, and gata1 expression in the embryo, indicating a possible role of vegf in stimulating the differentiation of both vascular and hematopoietic lineages. Co-injection of RNAs for both isoforms results in increased expression of three of these markers over and above that observed when either RNA is singly injected and analysis of vegf expression in the notochord mutants no tail and floating head suggests that the notochord patterns the formation of the dorsal aorta by stimulating adjacent somite cells to express vegf, which in turn functions as a signal in dorsal aorta patterning. Finally, studies of vegf expression in cloche mutant indicate that vegf expression is generally independent of cloche function. These results show that in the zebrafish embryo, vegf can not only stimulate endothelial cell differentiation but also hematopoiesis. Moreover, these effects are most dramatic when both vegf isoforms are co-expressed, indicating a synergistic effect of the expression of the two forms of the VEGF protein.

Histone deacetylases (HDACs) are key transcription regulators that function by deacetylating histones/transcription factors and modifying chromatin structure. In this work, we showed that chemical inhibition of HDACs by valproic acid (VPA) led to impaired liver development in zebrafish mainly by inhibiting specification, budding, and differentiation. Formation of exocrine pancreas but not endocrine pancreas was also inhibited. The liver defects induced by VPA correlate with suppressed total HDAC enzymatic activity, but are independent of angiogenesis inhibition. Gene knockdown by morpholino demonstrated that hdac3 is specifically required for liver formation while hdac1 is more globally required for multiple development processes in zebrafish including liver/exocrine pancreas formation. Furthermore, overexpression of hdac3 but not hdac1 partially rescued VPA induced small liver. One mechanism by which hdac3 regulates zebrafish liver growth is through inhibiting growth differentiation factor 11 (gdf11), a unique target of hdac3 and a member of the transforming growth factor beta family. Simultaneous overexpression or morpholino knockdown showed that hdac3 and gdf11 function antagonistically in zebrafish liver development. These results revealed a novel and specific role of hdac3 in liver development and the distinct functions between hdac1 and hdac3 in zebrafish embryonic development.

Cancer is a complex organ whose behavior is not only influenced by genetic and epigenetic changes in cancer cells but also by stromal cells, local extracellular matrix and specific tissue architecture. Intercellular communications within the cancer microenvironment are critical to coordinate the assembly of multiple cell types for an amalgamated form and function of a cancer. Exosomes are small membrane vesicles with an endosome origin that are released by cells into the extracellular environment. They carry a cargo of proteins, lipids, and nucleic acids and transfer their cargo to recipient cells and altering the recipient cells' biochemical composition, signaling pathways, and gene regulation. Exosomes can thus serve as extracellular messengers mediating cell-cell communication. Both cancer cells and stromal cells release exosomes not only into the cancer microenvironment but also into the circulation. In this review, we summarize the research done so far on cancer-derived exosomes and assess their roles as extracellular messengers facilitating cancer progression and metastasis.

Channels formed by the canonical transient receptor potential (TRPC) subfamily of proteins are Ca 21 -permeable, nonselective cation channels with various functions. Through a phospholipase C (PLC)-dependent mechanism TRPC6, a member of TRPC subfamily, can be activated by receptor tyrosine kinases (RTK) or G protein-coupled receptors (GPCR), which are implicated in cell proliferation and human malignancies. Here, we report that TRPC6 has a critical role in human gastric cancer development. Expression of TRPC6 was greatly upregulated in human gastric cancer epithelial cells compared with that in normal gastric epithelial cells. Treatment of AGS or MKN45 cells, human gastric cancer cell lines, with SKF96365, an agent known to inhibit TRPC channels, arrested cell cycle in G2/M phase and suppressed cell growth. Importantly, expressing a dominant negative mutant of TRPC6 (DNC6) in these cells also arrested cell cycle in G2/M phase and inhibited cell growth. Transient receptor potential (TRP) channels are a large family of nonselective cation channels and initially characterized in the photoreceptor of Drosophila as a light sensor. 5,6 Canonical transient receptor potential (TRPC) channels, which share the highest homology to Drosophila TRP, are one subfamily of TRP channels in mammalian cells.7,8 TRPC channels include 7 members, TRPC1-7, which are mainly permeable to Ca 21 . The role of TRPC channels in cell proliferation has been revealed in artery smooth muscle cells 9 and in several types of cancer cells. 10,11We thus asked whether TRPC6 channels contribute to cell cycle progression of gastric cancer cells and to gastric cancer development. In this study, we found that TRPC6 expression was upregulated in human gastric cancer samples and blockade of TRPC6 induced G2/M phase arrest and growth retardation in gastric cancer cells. Furthermore, blockade of TRPC6 channels inhibited development of xenografted gastric tumor. These results support the idea that Ca 21 elevation regulated by TRPC6 was critical for G2/M phase transition in gastric cancer cells and contributed to the development of human gastric cancer. Material and methods Materials and cell cultureAntibody for TRPC6 was purchased from Alomone (Israel), antibodies for Cdc2 and pTyr15 Cdc2 from Cell Signaling (Danvers, MA), and for SKF96365 from Calbiochem (Darmstadt, Germany). Other reagents were from Sangon (Shanghai, China), unless otherwise noted. The AGS and MKN45 cells were cultured in Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% heat-inactivated fetal bovine serum in a humidified cell incubator with an atmosphere of 5% CO 2 at 37°C. Adenoviral vectorsThe GFP, DNC6 (human) and WTC6 (mouse) were constructed into an adenoviral vector with the CMV promoter. The adenovirus contained an internal ribosome entry site (IRES)-GFP tag. The AGS and MKN45 cells were infected at multiplicity of infection (MOI) 5 10 and HEK293 cells at MOI 5 2. Clinical specimens, immunohistology and in situ hybridizationA total of 25 primary gastric cancer samples a...