Specific purification of elongation factor 2 and isolation of its antibody

Intratumor administration of fusogenic liposomes containing fragment A of diphtheria toxin suppresses tumor growth

Previously, we reported that experimental i.p. administration of fusogenic liposomes containing fragment A of diphtheria toxin (DTA) completely regressed ascites tumors without any severe side effects. In this study, we examined the therapeutic effects of intratumor injection of fusogenic liposomes using ddY mice implanted with Sarcoma-180 (S-180) cells intradermally. Intratumor injections of fusogenic liposomes containing DTA significantly inhibited the tumor growth as assessed by the relative mean tumor volume, and by the survival time of mice. No therapeutic effects were observed when simple liposomes containing DTA or empty fusogenic liposomes were administered. Using [3H]inulin encapsulated in fusogenic liposomes as a marker, we demonstrated that fusogenic liposomes delivered their contents into the solid tumor cells about 15 times more efficiently than simple liposomes. These results suggest that intratumor administration of fusogenic liposomes containing DTA is a highly effective approach to the local treatment of solid tumors.

Application of fusogenic liposomes containing fragment A of diphtheria toxin to cancer therapy

Previously we reported that fusogenic liposomes, prepared by fusing simple liposomes with Sendai virus particles, could introduce their contents directly and efficiently into the cytoplasm. In this study, we examined the anti-tumour activity of fusogenic liposomes containing fragment A of diphtheria toxin (DTA). Fusogenic liposomes containing DTA showed high cytotoxicity against sarcoma-180 (S-180) cells in vitro. When these liposomes were administered into the abdominal cavity of ddY mice carrying S-180, tumour cells completely disappeared in four of six tumour-bearing mice without decrease in body weight. Neither simple liposomes containing DTA nor empty fusogenic liposomes had any effect on tumour suppression. We conclude that fusogenic liposomes containing DTA are new and potentially effective tools for the treatment of ascites tumours without any severe side-effects.

Binding of monoclonal antibody specific for domain Ia/II of Pseudomonas aeruginosa exotoxin A at pH 4 strongly neutralizes exotoxin A-induced cytotoxicity in cell culture and in vivo

Mouse monoclonal antibodies (MAbs) against Pseudomonas aeruginosa exotoxin A (Ex-A) were established, and 4 of 20 MAbs were extensively studied for analysis of the structure-function relationship of Ex-A. IN vivo experiments demonstrated that MAb Ex-3C7 protected mice either injected with Ex-A or infected with Ex-A-producing P. aeruginosa from death caused by Ex-A at the highest rate, followed by MAbs Ex-4F2 and Ex-8H5, in that order. MAb Ex-2A10 failed to rescue the mice. MAb Ex-3C7 (immunoglobulin G1 [IgG1]) inhibited incorporation of Ex-A into target cells and strongly neutralized cytotoxicity in cell culture but did not inhibit an enzymatic activity of Ex-A, ADP-ribosyltransferase, at all. The MAb also bound Ex-A, even at a low pH of 4, and recognized amino acid residues 241 to 297 (domain Ia/II), suggesting that MAb Ex-3C7 can interfere with the conformational change and/or processing of Ex-A by keeping a complex of Ex-A and antibody stable at low pH in the phagolysosome. MAb Ex-4F2 (IgG1), which recognizes residues 550 to 590 (domain III), strongly inhibited Ex-A incorporation and neutralized cytotoxicity in cell culture but only weakly inhibited ADP-ribosyltransferase. MAb Ex-8H5 (IgG1), which recognizes residues 591 to 613 (domain III), also inhibited cytotoxicity in cell culture, but weakly. In contrast to the above three MAbs, MAb Ex-2A10 (IgG2b) greatly inhibited ADP-ribosyltransferase but showed no inhibition of Ex-A incorporation and no neutralizing activity against cell toxicity. A line of evidence indicates that (i) domain Ia/II plays an important role in the pathogenesis of Ex-A and (ii) MAbs that inhibit an intracellular postbinding process, such as conformational change, processing, and translocation of Ex-A in target cells, can display potent inhibitory activity against cytotoxicity in vivo, as well as in cell culture, and would be a good candidate for therapy of pseudomonal infections.

The carboxyl terminal amino acid residues of Pseudomonas aeruginosa exotoxin A involved in cell toxicity and pathogenesis, characterized by a neutralizing human monoclonal antibody

Human monoclonal antibody HI-1A4 (IgG3, lambda) neutralized a toxicity caused by pseudomonal exotoxin A (Ex-A) in cell culture and in vivo, and was effective in experimental Pseudomonas aeruginosa infections in mice. HI-1A4 inhibited an Ex-A catalyzed ADP-ribosylation of elongation factor 2 but did not inhibit an incorporation of toxin into a target cell at all. One molecule of HI-1A4 neutralized at least 2 molecules of Ex-A. HI-1A4 retained its binding activity at pH 4.0. The epitope region for HI-1A4 was demonstrated to be a carboxyl terminal end of amino acid residues 591-613 of Ex-A. HI-1A4 might bind to Ex-A carboxyl terminal region outside a target cell, be incorporated into cells as a complex with Ex-A, and inhibit the intracellular function in which the carboxyl terminal part of Ex-A was involved, resulting in the interruption of intoxication of Ex-A.

Molecular cloning and characterization of the Caenorhabditis elegans elongation factor 2 gene (eft-2)

A Caenorhabditis elegans lambda ZAP cDNA library was screened using a fragment amplified from highly conserved regions of the mammalian and Drosophila elongation factor 2 (EF-2). Two types of cDNA clones were obtained, corresponding to two mRNA species with 3'-untranslated regions of 60 and 115 nucleotides, both encoding identical polypeptides. Sequence analysis of these clones and comparisons with hamster and Drosophila EF-2 sequences suggests that they encode C. elegans EF-2. Clone pCef6A, encoding the entire C. elegans EF-2 mRNA sequence including 45 nucleotides of 5'-untranslated region, contains a 2,556-bp open reading frame which predicts a polypeptide of 852 amino acid residues (Mr 94,564). The deduced amino acid sequence is greater than 80% identical to that of mammalian and Drosophila EF-2. Conserved sequence segments shared among a variety of GTP-binding proteins are found in the amino-terminal region. The carboxy-terminal half contains segments unique to EF-2 and its prokaryotic homolog, EF-G, as well as the histidyl residue which is ADP-ribosylated by diphtheria toxin. The C. elegans protein contains a 12-amino-acid insertion between positions 90 and 100, and a 13-amino-acid deletion between positions 237 and 260, relative to hamster EF-2. Partial sequencing of a genomic clone encoding the entire C. elegans EF-2 gene (named eft-2) has so far revealed two introns of 48 and 44 bp following codons Gln-191 and Gln-250, respectively. Southern and Northern blot analyses indicate that eft-2 is a single-copy gene and encodes a 3-kb mRNA species which is present throughout nematode development.

Complete sequence of the coding region of human elongation factor 2 (EF-2) by enzymatic amplification of cDNA from human ovarian granulosa cells

The use of two primers allowed the specific enzymatic amplification of elongation factor 2 starting with total double-stranded cDNA from human ovarian granulosa cells. The amplified DNA fragment with a length of 1765 bp was restricted and sequenced by the shot gun approach. From the sequences obtained from the amplified fragment and the cDNA insert of pHGR81 [Rapp et al. (1988) Biol. Chem. Hoppe-Seyler 369, 247-250] respectively, the DNA sequence containing the complete coding as well as the 3'-untranslated region was assembled.

Identification of Nsp100 as elongation factor 2 (EF-2)

The nerve growth factor-sensitive phosphoprotein from PC12 cells, previously designated Nsp100, has been shown to be elongation factor 2 (EF-2). The criteria used for this identification include: (i) similarity of N-terminal sequence; (ii) phosphorylation by the same kinase; (iii) ADP-ribosylation mediated by diphtheria toxin; (iv) comparable function in cell-free protein synthesis. According to these criteria, Nsp100 and EF-2 are identical and the kinase that phosphorylates Nsp100 in PC12 cells is calcium/calmodulin kinase III.

Amino acid sequence of mammalian elongation factor 2 deduced from the cDNA sequence: homology with GTP-binding proteins

Complementary DNA clones, pHEW1 and pRE2, coding for hamster and rat polypeptide chain elongation factor 2 (EF-2), respectively, were isolated and sequenced. It was shown that the cDNA insert in pHEW1 contains a 2574-base-pair open reading frame coding for an 857-amino acid polypeptide with Mr 95,192, excluding the initiation methionine. Comparative studies of sequence homology among EF-2 and several GTP-binding proteins show that five regions in the amino-terminal position of EF-2, corresponding to about 160 amino acids, show homology with GTP-binding proteins, including protein synthesis elongation and initiation factors, mammalian ras proteins, and transducin. The carboxyl-terminal half of EF-2 contains several regions that have 34-75% homology with bacterial elongation factor G. These results suggest that the amino-terminal region of EF-2 participates in the GTP-binding and GTPase activity whereas the carboxyl-terminal region interacts with ribosomes. Finally, the sequence provides direct evidence that diphthamide (2-[3-carboxy-amido-3-(trimethylammonio)propyl]histidine), the site of ADP-ribosylation by diphtheria toxin, is produced by post-translational modification of a histidine residue in the primary translational product.