Diphtheria Resistant cells

Aullo, P., Alcami, J., Popoff, M. R Klatzmann, D. R., Murphy, J. R., and Boquet, P. (1992) A recombinant diphtheria toxin related human CD4 fusion protein specifically kills HIV infected cells which express gpl20 but selects fusion toxin resistant cells which carry HIV. EMBO J. 11, 575-583. 

Diphtheria toxin, an exotoxin of Corynebacterium diphtheriae infected with a specific lysogenic phage, catalyzes the ADP-ribosylation of EF-2 on the unique amino acid diphthamide in mammalian cells. This modification inactivates EF-2 and thereby specifically inhibits mammalian protein synthesis. Many animals (eg, mice) are resistant to diphtheria toxin. This resistance is due to inability of diphtheria toxin to cross the cell membrane rather than to insensitivity of mouse EF-2 to diphtheria toxin-catalyzed ADP-ribosylation by NAD. 

Terreri AM, Rocchi P, Capucci A, et al. 1983. Induction of diphtheria toxin-resistant mutatants in human cells by halogenated compounds. J Cancer Res Clin Oncol 105 111-112. 

Diphtheria toxin-resistant mutants were obsened in human epithelial type EUE cells but not in human lung fibroblasts exposed to epichlorohydrin in vitro. Epichlorohydrin... 

CIR, Chromosomal aberrations, rat liver cell line (RLi ) in vitro GIH, Gene mutation, human fibroblasts, diphtheria toxin resistance... 

The enzymatic specificity of diphtheria toxin deserves special comment. The toxin ADP-ribosylates EF-2 in all eukaryotic cells in vitro whether or not they are sensitive to the toxin in vivo, but it does not modify any other protein, including the bacterial counterpart of EF-2. This narrow enzymatic specificity has called attention to an unusual posttranslational derivative of histidine, diphthamide, that occurs in EF-2 at the site of ADP-ribosylation (see fig. 1). Although the unique occurrence of diphthamide in EF-2 explains the specificity of the toxin, it raises questions about the functional significance of this modification in translocation. Interestingly, some mutants of eukaryotic cells selected for toxin resistance lack one of several enzymes necessary for the posttranslational synthesis of diphthamide in EF-2 that is necessary for toxin recognition, but these cells seem perfectly competent in protein synthesis. Thus, the raison d etre of diphthamide, as well as the biological origin of the toxin that modifies it, remains a mystery. 

Pyrolysis products were also found to induce prophage X in lysogenic E. ooli K12, strain GY5027 (30), by Inductest III, which was developed by Moreau et al, (31) (Figure 2). The genotoxic effects of pyrolysis products on cultured mammalian cells were also investigated. Trp-P-1, Trp-P-2, IQ and MelQ were found to induce diphtheria toxin-resistant mutants of Chinese hamster lung cells in the presence of S9 mix. The mutation frequencies were 33, 160, 40 and 38 per 106 survivors per Mg of Trp-P-1, Trp-P-2,... 

Both regular and caffeine-free instant coffees, without S9 mix, also induced diphtheria toxin-resistant mutants of Chinese hamster lung cells (44). It is urgent that carcinogenicity of methylglyoxal be tested with animals. 

In the mammalian cell mutation test CHL cells are exposed to the test compound for 3 h with and without the metabolic activation system. After 7 days of culture, diphtheria toxine is added and the cells are left again to culture for another 7 days until the nmnber of diphteria toxin resistent colonies are scored. 

Moehring JM, Moehring TJ, Donley DE (1980) Posttranslational modification of elongation factor 2 in diphtheria-toxin-resistant mutants of CHO-Kl cells. Proc Natl Acad Sci USA 77 1010-1014. 

Iglewski WJ, Lee H (1983) Purification and properties of an altered form of elongation factor 2 from mutant cells resistant to intoxication by diphtheria toxin. Eur J Biochem 134 237-240... 

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