Adaptive response in mammalian cells: crossreactivity of different pretreatments on cytotoxicity as contrasted to mutagenicity.

Abstract

Pretreatment of H4 (rat hepatoma) cells for 48 hr with low nontoxic doses of alkylating agents [methyl methanesulfonate (MMS), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and N-methyl-N-nitrosoureal renders the cells more resistant to the toxic effect of these compounds. Cross When Escherichia coli cells are continuously exposed to nontoxic levels of a simple alkylating agent, such as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or N-methyl-N-nitrosourea (MNU), an adaptative DNA repair pathway is induced. It protects the bacteria against the killing and mutagenic effects of high toxic doses of alkylating agents (1-3). This adaptive response is also observed in Micrococcus luteus (4).In Escherichia coli, different processes are implicated in the adaptive response. Adaptation to killing by alkylating agents is attributed to the induction of high levels of a DNA glycosylase, coded by the alk gene (5), which excises 3-methyladenine, 3-methylguanine (6), and 7-methylguanine (6, 7). Resistance to mutagenesis has been attributed to the induction of high levels of an 06-alkylguanine methyltransferase (8-10).Evidence for an adaptive response in mammals comes from the experiments of Montesano et al. (ref. 11; reviewed in ref. 12), showing that the livers of rats continuously exposed to low levels of dimethylnitrosamine and then challenged with high doses of dimethylnitrosamine, accumulate 7-methylguanine but not 06-methylguanine (O6MeGua) in their DNA. Of the several animal species used for such studies, only the rat shows an increase in methyltransferase.In vitro, it has been shown that chronic treatment of Chinese hamster ovary (CHO) cells with nontoxic doses of MNNG renders the cells resistant to both killing and formation of sister chromatid exchanges upon further treatment with high toxic levels of MNNG or MNU (13). A single incubation of V79 Chinese hamster cells with a subtoxic dose of MNNG or MNU also modifies the cell sensitivity towards these agents (14).In mammalian cells, 7-alkylguanine, 3-alkyladenine, and 3-alkylguanine are enzymatically excised through a DNA glycosylase pathway that creates an apurinic site (15-17), whereas O6MeGua is repaired by a transalkylase (18). Therefore, mammalian cells contain the potential proteins that could mimic the situation observed in adapted E. coli.The aim of our work was to determine whether mammalian cells could be adapted for killing and mutagenesis by repeated treatment with low nontoxic concentrations of alkylating agents and whether these effects could be related to the type of damage induced by the drugs. We used simple alkylating agents [methyl methanesulfonate (MMS) and MNNG] that differ in their mutagenicity and give different spectra of methylated bases (19)(20)(21). The results show that adaptation to killing and mutagenesis are two independent processes and that adaptation to mutagenesis, in contrast to carcinogenesis, can be correlated with the amount of O6MeGua produced in cellular DNA during the adaptive treatment. MATERIALS AND METHODSChemical R...

Biological Complexities in Radiation Carcinogenesis and Cancer Radiotherapy: Impact of New Biological Paradigms

“…A similar adaptive response has also been observed in some higher mammalian systems [97] and in lymphocytes exposed to a low dose of ionizing radiation [98,99]. Most of these studies were performed in in vitro conditions and there is now little doubt that the in vitro pretreatment of human lymphocytes with tritiated thymidine or with low doses of X-rays makes these cells less susceptible to cytogenetic damage by subsequent high acute doses of X- or gamma-rays [4,5,6,99].…”

Prostate tumor-stroma interaction: molecular mechanisms and opportunities for therapeutic targeting

“…Using the laser capture microdissection (LCM) technique, genetic aberrations were detected in the fibromuscular stromal compartment surrounding tumor epithelium, further supporting the reciprocal nature of the tumorstroma interaction (Moinfar et al, 2000). Although the mechanisms of the genetic and phenotypic response of stroma to adjacent tumor epithelium are currently unclear, possible mechanisms include: a) Transition or interconversion of epithelium to stroma (Wernert et al, 2001); b) Irreversible induction of stromal changes, both at the morphologic and the biochemical levels, by soluble and insoluble factors secreted by tumor epithelium; c) Selection of previous existing clones of stromal cell populations and preferential expansion of these clones based on their proliferative and survival advantages (Singer et al, 1995;Tso et al, 2000); d) The combination of b and c above; that is, after prolonged ''adaptation'' to a tumorassociated stromal microenvironment, permanent genetic changes may occur in the stromal cell population through a poorly understood ''adaptive mutation'' mechanism (Laval and Laval, 1984;Chung, 1995).…”

Determination of DNA sequence changes induced by ethyl methanesulfonate in human cells, using a shuttle vector system.

“…However, there is an adaptive response when alkylation damage occurs in which enzymes that remove the damage are induced (6,10,22). Similar systems may operate in mammalian cells (12,17,23).…”