Induction of SOS response, cellular efflux and oxidative stress response genes by chlorambucil in DNA repair-deficient Escherichia coli cells (ada, ogt and mutS).

Chlorambucil (CLB) is a bifunctional alkylating drug widely used as an anticancer agent and as an immunosuppressant. It is known to be mutagenic, teratogenic and carcinogenic. The cellular actions of CLB have remained poorly investigated. It is very likely that DNA damage and its repair are the key elements determining the destiny of CLB-exposed cells. We investigated the role of two specific DNA repair pathways involved in CLB-induced mutagenicity and gene expression changes by using Escherichia coli strains lacking either (i) two DNA methyltransferase functions (O(6)-methylguanine-DNA methyltransferase I (ada) and II (ogt)), or (ii) mismatch repair (MutS (mutS)). Mutagenicity was determined as the development of ciproxin and rifampicin resistance and the gene expression changes were assessed using expression profiling of all E. coli 4290 open reading frames (ORFs) by cDNA array. Chlorambucil-induced mutants in mutS cells, implying the importance of mismatch repair in preventing CLB-induced mutations. It also induced mutants in the ada, ogt strain, but to a lesser extent than in the wild-type strain. The simultaneous upregulation of several genes of the SOS response, cellular efflux and oxidative stress response, was demonstrated in both of the DNA repair-deficient strains but not in the wild-type cells. These and our previous results show that single-gene knock-out cells use specific gene regulation strategies to avoid mutations and cell death induced by agents such as chlorambucil.

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