Augmentation of antigen-specific immune responses using DNA-fusogenic liposome vaccine

In an attempt to enhance the immunological efficacy of genetic immunization, we investigated a new biological means for delivering antigen gene directly to the cytoplasm via membrane fusion. In this context, we investigated fusogenic liposome (FL) encapsulating DNA as a possible genetic immunization vehicle. RT-PCR analysis indicated that a FL could introduce and express encapsulating OVA gene efficiently and rapidly in vitro. Consistent with this observation, an in vitro assay showed that FL-mediated antigen-gene delivery can induce potent presentation of antigen via the MHC class I-dependent pathway. Accordingly, immunization with FL containing the OVA-gene induced potent OVA-specific Th1 and Th2 cytokine production. Additionally, OVA-specific CTL responses and antibody production were also observed in systemic compartments including the spleen, upon immunization with the OVA-gene encapsulating FL. These findings suggest that FL is an effective genetic immunization carrier system for the stimulation of antigen-specific immune responses against its encoding antigen.     

Generation of highly stable IL-18 based on a ligand-receptor complex structure

Human interleukin-18 (hIL-18), initially cloned as an IFN-gamma-inducing factor, has a key role in many inflammatory diseases. We have previously developed a high production system for correctly folded active hIL-18 protein, leading to the revelation of the 3D-structure and the receptor binding mode. These findings can strongly indicate the experimental and medical applications of IL-18; however, the recombinant protein is prone to be inactivated forming multimers. Recently, therapeutic approaches using recombinant IL-18 have shown the effectiveness for treatment of cancer; indicating the necessity of a more stable protein for therapy with intertrial reliability. Here we have generated a highly stable hIL-18 with replacement of cysteine by serine based on the tertiary structure and the binding mechanism, retaining the biological activity. Similar rational designs can be applied to develop new therapeutic molecules of other cytokines.     

Restricted expression of tumor necrosis factor-related apoptosis-inducing ligand receptor 4 in human peripheral blood lymphocytes

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumor but not normal cells, thus providing therapeutic possibilities for human cancers. However, it is not fully clear how widespread TRAIL receptors are, or how TRAIL signaling is modulated in normal cells. We characterized cell surface expression of TRAIL receptors in normal healthy donor peripheral blood and report that each of the TRAIL receptors are characteristically expressed on restricted cell populations. TRAIL-R1 is distinctively expressed on B-lymphocytes, TRAIL-R2 on monocytes, TRAIL-R3 on neutrophils and most impressively, CD8+ lymphocytes and NKT lymphocytes but not CD4+ lymphocytes express TRAIL-R4.     

Regulation of SNAREs by tomosyn and ROCK: implication in extension and retraction of neurites

Extension of neurites requires the SNARE-dependent fusion of plasmalemmal precursor vesicles with the plasma membrane of growth cones. Here, we show that tomosyn localizes at the palm of growth cones and inhibits the fusion of the vesicles there, thus promoting transport of the vesicles to the plasma membrane of the leading edges of growth cones. Tomosyn localizes because ROCK activated by Rho small G protein phosphorylates syntaxin-1, which increases the affinity of syntaxin-1 for tomosyn and forms a stable complex with tomosyn, resulting in inhibition of the formation of the SNARE complex. In retraction of neurites, tomosyn localizes all over the edges of the neurites and inhibits fusion of the vesicles with the plasma membrane. Thus, tomosyn demarcates the plasma membrane by binding to syntaxin-1 phosphorylated by ROCK, and thereby regulates extension and retraction of neurites.     

Endocytosis of E-cadherin regulated by Rac and Cdc42 small G proteins through IQGAP1 and actin filaments

E-cadherin is a key cell-cell adhesion molecule at adherens junctions (AJs) and undergoes endocytosis when AJs are disrupted by the action of extracellular signals. To elucidate the mechanism of this endocytosis, we developed here a new cell-free assay system for this reaction using the AJ-enriched fraction from rat liver. We found here that non-trans-interacting, but not trans-interacting, E-cadherin underwent endocytosis in a clathrin-dependent manner. The endocytosis of trans-interacting E-cadherin was inhibited by Rac and Cdc42 small G proteins, which were activated by trans-interacting E-cadherin or trans-interacting nectins, which are known to induce the formation of AJs in cooperation with E-cadherin. This inhibition was mediated by reorganization of the actin cytoskeleton by Rac and Cdc42 through IQGAP1, an actin filament-binding protein and a downstream target of Rac and Cdc42. These results indicate the important role of the Rac/Cdc42-IQGAP1 system in the dynamic organization and maintenance of the E-cadherin-based AJs.     

Targeted disruption of the mouse 3-phosphoglycerate dehydrogenase gene causes severe neurodevelopmental defects and results in embryonic lethality

D-3-Phosphoglycerate dehydrogenase (Phgdh; EC 1.1.1.95) is the first committed enzyme of L-serine biosynthesis in the phosphorylated pathway. To determine the physiological importance of Phgdh-dependent L-serine biosynthesis in vivo, we generated Phgdh-deficient mice using targeted gene disruption in embryonic stem cells. The absence of Phgdh led to a drastic reduction of L-serine metabolites such as phosphatidyl-L-serine and sphingolipids. Phgdh null embryos have small bodies with abnormalities in selected tissues and died after days post-coitum 13.5. Striking abnormalities were evident in the central nervous system in which the Phgdh null mutation culminated in hypoplasia of the telencephalon, diencephalon, and mesencephalon; in particular, the olfactory bulbs, ganglionic eminence, and cerebellum appeared as indistinct structures. These observations demonstrate that the Phgdh-dependent phosphorylated pathway is essential for normal embryonic development, especially for brain morphogenesis.     

Activation of Cdc42 by trans interactions of the cell adhesion molecules nectins through c-Src and Cdc42-GEF FRG

Nectins, Ca2+ -independent immunoglobulin-like cell-cell adhesion molecules, initiate cell-cell adhesion by their trans interactions and recruit cadherins to cooperatively form adherens junctions (AJs). In addition, the trans interactions of nectins induce the activation of Cdc42 and Rac small G proteins, which increases the velocity of the formation of AJs. We examined here how nectins induce the activation of Cdc42 in MDCK epithelial cells and L fibroblasts. Nectins recruited and activated c-Src at the nectin-based cell-cell adhesion sites. FRG, a GDP/GTP exchange factor specific for Cdc42, was then recruited there, tyrosine phosphorylated by c-Src, and activated, causing an increase in the GTP-bound active form of Cdc42. Inhibition of the nectin-induced activation of c-Src suppressed the nectin-induced activation of FRG and Cdc42. Inhibition of the nectin-induced activation of FRG or depletion of FRG by RNA interference suppressed the nectin-induced activation of Cdc42. These results indicate that nectins induce the activation of Cdc42 through c-Src and FRG locally at the nectin-based cell-cell adhesion sites.     

Multivariate analysis of noise in genetic regulatory networks

Stochasticity is an intrinsic property of genetic regulatory networks due to the low copy numbers of the major molecular species, such as, DNA, mRNA, and regulatory proteins. Therefore, investigation of the mechanisms that reduce the stochastic noise is essential in understanding the reproducible behaviors of real organisms and is also a key to design synthetic genetic regulatory networks that can reliably work. We use an analytical and systematic method, the linear noise approximation of the chemical master equation along with the decoupling of a stoichiometric matrix. In the analysis of fluctuations of multiple molecular species, the covariance is an important measure of noise. However, usually the representation of a covariance matrix in the natural coordinate system, i.e. the copy numbers of the molecular species, is intractably complicated because reactions change copy numbers of more than one molecular species simultaneously. Decoupling of a stoichiometric matrix, which is a transformation of variables, significantly simplifies the representation of a covariance matrix and elucidates the mechanisms behind the observed fluctuations in the copy numbers. We apply our method to three types of fundamental genetic regulatory networks, that is, a single-gene autoregulatory network, a two-gene autoregulatory network, and a mutually repressive network. We have found that there are multiple noise components differently originating. Each noise component produces fluctuation in the characteristic direction. The resulting fluctuations in the copy numbers of the molecular species are the sum of these fluctuations. In the examples, the limitation of the negative feedback in noise reduction and the trade-off of fluctuations in multiple molecular species are clearly explained. The analytical representations show the full parameter dependence. Additionally, the validity of our method is tested by stochastic simulations.     

Poly(A)- and primer-independent RNA polymerase of Norovirus

Replication of positive-strand caliciviruses is mediated by a virus-encoded RNA-dependent RNA polymerase (RdRp). To study the replication of Norovirus (NV), a member of the family Caliciviridae, we used a recombinant baculovirus system to express an enzymatically active RdRp protein from the 3D region of the NV genome and defined conditions for optimum enzymatic activity. Using an RNA template from the NV 3' genomic region, we observed similar levels of enzymatic activity in assays with and without a poly(A) tail. RdRp activity was not significantly affected by the addition of an RNA primer to the reaction mixture. Thus, the NV RdRp exhibited primer- and poly(A)-independent RNA polymerase activity. While the RdRp inhibitor phosphonoacetic acid inhibited NV RdRp activity, another gliotoxin did not. The active recombinant NV RdRp will be of benefit to studies of NV replication and will facilitate the development of specific inhibitors of NV proliferation.