Tumor necrosis factor-α inducing protein (Tipα) is a unique carcinogenic factor released from Helicobacter pylori (H. pylori). Tipα specifically binds to cells and is incorporated into cytosol and nucleus, where it strongly induces expression of TNF-α and chemokine genes mediated through NF-κB activation, resulting in tumor development. To elucidate mechanism of action of Tipα, we studied a binding protein of Tipα in gastric epithelial cells.

Stomach cancer is strongly associated with infection by Helicobacter pylori. In 2005, we identified a new H. pylori gene encoding a TNF-alpha inducing protein (Tipalpha) that acts as a carcinogenic factor. Tipalpha is secreted from H. pylori as a homodimer whose subunits are linked by disulfide bonds. We also characterized a Tipalpha deletion mutant (del-Tipalpha) that lacks the N-terminal six amino acid residues (LQACTC), including two cysteines (C5 and C7) that form disulfide bonds, but nonetheless shows a weak ability to induce TNF-alpha expression. Here we report that del-Tipalpha has a novel elongated structure containing a 40-A-long alpha helix, and forms a heart-shaped homodimer via non-covalent bonds. Moreover, their circular dichroism spectra strongly suggest that the structures of the del-Tipalpha and Tipalpha homodimers are very similar. del-Tipalpha's unique mode of dimer formation provides important insight into protein-protein interactions and into the mechanism underlying the carcinogenicity of H. pylori infection.

Because the influenza A virus has an RNA genome, its RNA-dependent RNA polymerase, comprising the PA, PB1, and PB2 subunits, is essential for viral transcription and replication. The binding of RNAprimers/promoters to the polymerases is an initiation step in viral transcription. In our current study, we reveal the 2.7 A tertiary structure of the C-terminal RNA-binding domain of PB2 by x-ray crystallography. This domain incorporates lysine 627 of PB2, and this residue is associated with the high pathogenicity and host range restriction of influenza A virus. We found from our current analyses that this lysine is located in a unique "phi"-shaped structure consisting of a helix and an encircled loop within the PB2 domain. By electrostatic analysis, we identified a highly basic groove along with this phi loop and found that lysine 627 is located in the phi loop. A PB2 domain mutant in which glutamic acid is substituted at position 627 shows significantly lower RNA binding activity. This is the first report to show a relationship between RNA binding activity and the pathogenicity-determinant lysine 627. Using the Matras program for protein three-dimensional structural comparisons, we further found that the helix bundles in the PB2 domain are similar to that of activator 1, the 40-kDa subunit of DNA replication clamp loader (replication factor C), which is also an RNA-binding protein. This suggests a functional and structural relationship between the RNA-binding mechanisms underlying both influenza A viral transcription and cellular DNA replication. Our present results thus provide important new information for developing novel drugs that target the primer/promoter RNA binding of viral RNA polymerases.

The C-terminal domain protein (amino-acid residues 535-759) of the PB2 subunit of the RNA-dependent RNA polymerase from the highly pathogenic influenza A virus was expressed as a soluble protein in Escherichia coli and crystallized using sodium formate as a precipitant. Data sets were collected from crystals of native and selenomethionine-substituted protein on the KEK NW12 beamline at the Photon Factory and the crystals diffracted to a maximum resolution of 2.44 A for the SeMet-derivative crystal. The native crystals were found to belong to space group P3(2)21, with unit-cell parameters a = b = 52.5, c = 156.3 A. The Matthews value (V(M)) was 2.7 A(3) Da(-1), assuming the presence of one molecule in the asymmetric unit. The SeMet-derivative crystals were found to belong to the same space group, with unit-cell parameters a = b = 52.6, c = 156.4 A. Attempts are being made to solve the structure by multi-wavelength anomalous dispersion phasing.

Green tea is an acknowledged cancer preventive in Japan, and the main constituent of green tea catechins is (-)-epigallocatechin gallate (EGCG). To investigate the bioavailability of EGCG in humans, we generated a monoclonal antibody against EGCG in BALB/c mice by immunizing thyroglobulin-conjugated EGCG. Out of 32 hybridoma cell lines, three hybridomas were selected by enzyme-linked immunosorbent assay (ELISA), and then determined by surface plasmon resonance assay: One hybridoma TG38 produced a specific monoclonal antibody against EGCG. The primary structure of TG38 light chain was then deduced from DNA sequence of the light chain gene. The NCBI-BLAST search showed the uniqueness of TG38 monoclonal antibody, and three amino acid residues specific for TG38 were aligned on two loops and one beta-sheet of the tertiary structure of the antibody. The TG38 antibody is the first monoclonal antibody against EGCG and catechins, since it bound to four green tea catechins with a galloyl group.

A116 Green tea is now an acknowledged cancer preventive beverage, and its active constituents are green tea catechins, such as (-)-epigallocatechin gallate (EGCG). The study of the strucure-function relationship of green tea catechins has revealed that the galloyl group of EGCG is essential for cancer preventive activity. To develop new cancer preventive drugs, we thus focused on alkyl gallates with various lengths of fatty acid chains. Eleven alkyl gallates were kindly provided by Dr. Tomihiko Higuchi, The University of Tokushima. We found that inhibitory activities of cancer cell growth with the alkyl gallates increased associated with length of fatty acid chains: Specifically, octyl gallate (C=8), nonyl gallates (C=9), and lauryl gallate (C=12) showed the strongest inhibitory activities among the 11 compounds. These alkyl gallates also inhibited growth of Bhas 42 cells (BALB/3T3 cells transfected with v-H-ras gene, a standard model of initiated cells) 100-fold stronger than EGCG did: IC50 values were 0.6 μM for lauryl gallate, 0.8 μM for octyl gallate, 130 μM for EGCG and 140 μM for gallic acid. Furthermore, lauryl and octyl gallates inhibited in vitro transformation of Bhas 42 cells induced by okadaic acid, a tumor promoter, suggesting that they are anti-tumor promoters. We have previously shown that strong expressions of growth-arrest and DNA damage-inducible gene (GADD153) and p21WAF1 are essential mechanisms for synergistic induction of cancer preventive activity with EGCG and cancer preventive agents such as COX-2 inhibitors and retinoids. Interestingly, treatment with octyl, nonyl and lauryl gallates alone strongly induced GADD153 gene expression in human lung cancer cell line PC-9 without any use of cancer preventive agents. Moreover, the analysis of cell cycles of PC-9 cells treated with lauryl gallate by flow cytometry revealed inhibition of G1/S transition. All these results strongly suggest that alkyl gallates with long fatty acid chains are new candidates for cancer preventive agents.