O6-Methylguanine-DNA methyltransferase in human cells

The role of O6-methylguanine-DNA methyltransferase in cell survival, mutagenesis and carcinogenesis

“…The reaction was equally as rapid with the rodent O6-MT (Bogden et al, 1981;Scicchitano and Pegg, 1982). Once the O6-MT in a cell has reacted, only RNA and protein synthesis restored the original levels of 06-MT (Robins and Cairns, 1979;Warren and Lawley, 1980;Waldstein et al, 1982b;Yarosh et al, 1984a), demonstrating that the O6-MT is not rejuvenated after its reaction with a methyl group, and remains as a dead end complex.…”

“…The O6-MT in crude extracts of mouse cells was 22 kd (Yagi et al, 1983) and the human O6-MT from cells in culture and tissue has been reported to be between 21 kd and 24 kd (Myrnes et al, 1982;Harris et al, 1983;Yarosh et al, 1984a). No evidence has been reported of cleavage of a mammalian O6-MT protein.…”

“…The purified E. coli O6-MT was very heat-resistant, with a half-life of 45 min at 95 ° . Partially purified human O6-MT from placenta (Yarosh et al, 1984a) or lymphocytes (Brent, 1984) has been reported to rapidly lose activity at 45 °, while another laboratory has reported that O6-MT partially purified from human lymphoid cells retained 54% of its activity after 10 min at 95 ° . This difference may be resolved when the human O6-MT is available in pure form.…”

“…Rapid production of O6-MeGua in DNA and rapid demethylation by O6-MT resulted in depletion of cellular levels of the protein because of its stoichiometric and not catalytic activity (Schendel and Robins, 1978;Robins and Cairns, 1979;Waldstein et al, 1982b;Zlotogorski and Erickson, 1983;Yarosh et al, 1984a). Restoration of the original level required RNA and protein synthesis as noted before, and the net rate of O6-MT production was about 6000 molecules per hour in adapted E. coli (Robins and Cairns, 1979) and between 750 and 4500 molecules per hour in human tumor cells (Yarosh et al, 1984a;Foote and Mitra, 1984).…”

The 1987 Walter Hubert lecture: Regulation and deficiencies in DNA repair

“…There is, however, no evidence for the occurrence of a similar mechanism of inducible antimutagenic DNA repair in eukaryotic cells. Treatment of human cells in tissue culture with direct-acting alkylating agents does not give rise to an increased resistance to the same agents (Karran et al, 1982b;Frosina et al, 1984;Yarosh et al, 1984). Moreover, it has been difficult to obtain human tumour cell lines with markedly increased resistance to simple alkylating agents (Teicher et al, 1986) and the moderately improved resistance observed in certain lines after prolonged exposure to alkylating agents is very likely due to a mechanism different from that defined for inducible bacteria.…”