Toxin-resistant Cell Mutants

The toxins mentioned above have the disadvantage as targeting vehicles that they can only be used on toxin-resistant cells as they will kill normal cells. It is possible to make mutant toxins with highly reduced toxicity, but so far such mutants have proved to be less active in translocation than the wild-type toxins. In future work it may therefore be necessary to look for other toxins that do not kill the cells. 

Ferreri, A.M., Rocchi, P, Capucci, A. Prodi, G. (1983) Induction of diphtheria toxin-resistant mutants in human cells by halogenated compounds. J. Cancer Res. din. 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... 

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. 

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. 

Rocchi P, Ferreri AM, Borgia R, et al. 1980. Polycyclic hydrocarbons induction of diptheria toxin-resistant mutants in human cells. Carcinogenesis 1 765-767. 

The bacterial RNase, barnase, linked to Pseudomonas aeruginosa exotoxin A or to a non-toxic deletion mutant of the toxin lacking the enzymatic domain, was found to be toxic to cells to a greater extent than either component alone (Prior et al., 1991 1992). A C-terminal KDEL sequence was required for toxicity. Cells resistant to the intracellular action of the toxin were also sensitive to the fusion protein. This... 

Teter, K., Jobling, M.G. and Holmes, R.K. (2003) A class of mutant CHO cells resistant to cholera toxin rapidly degrades the catalytic polypeptide of cholera toxin and exhibits increased endoplasmic reticulum-associated degradation. Traffic, 4, 232-242. 

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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