Alkyltransferase-mediated toxicity of bis-electrophiles in mammalian cells

作者：Kalapila Aley G; Pegg Anthony E^*

来源：Mutation Research-Fundamental and Molecular Mechanisms of Mutagenesis, 2010, 684(1-2): 35-42.

DOI：10.1016/j.mrfmmm.2009.11.006

• Dihaloalkanes
• Epihalohydrins
• Butadiene diepoxide
• Alkyltransferase
• DNA-protein cross-links

The primary function of O(6)-alkylguanine-DNA alkyltransferase(AGT) is to maintain genomic integrity in the face of damage by both endogenous and exogenous alkylating agents. However, paradoxically, bacteria[ and mammalian AGTs have been shown to increase cytotoxicity and mutagenicity of dihaloalkanes and other bis-electrophiles when expressed in bacterial cells. We have extended these studies to mammalian cells using CHO cells that lack ACT expression and CHO cells stably transfected with a plasmid that expresses human ACT. The cytotoxicity of 1,2-dibromoethane, dibrornomethane and epibromohydrin was significantly increased by the presence of ACT but cytotoxicity of butadiene diepoxide was not affected. Mutations caused by these agents were assessed using hypoxanthine-guanine phosphoribosyltransferase (HPRT) as a reporter gene. There was a small (c. 2-3-fold) but statistically significant AGT-mediated increase in mutations caused by 1,2-dibromoethane, dibromomethane and epibromohydrin. Analysis of the mutation spectrum induced by 1,2-dibromoethane showed that the presence of ACT also altered the types of mutations with an increase in total base substitution mutants due to a rise in transversions at both G:C and A:T sites. ACT expression also led to mutations arising from the transcribed strand, which were not seen in cells lacking ACT. Although the frequency of deletion mutations was decreased by ACT expression, the formation of large deletions (>= 3 exons) was increased. This work demonstrates that interaction of ACT with some bis-electrophiles can cause mutagenicity and diminished cell survival in mammalian cells. It is consistent with the hypothesis that DNA-AGT cross-links, which have been characterized in experiments with purified ACT protein and such bis-electrophiles, can be formed in mammalian cells.

• 出版日期2010-2-3