P IV.10 - P IV.10 Stable yeast but not human apurinic/apyrimidinic en-donuclease transfectants of Chinese hamster cells are more resistant to genotoxic agents

Abstract

Apurinic/apyrimidinic (AP) endonucleases play a main role in excisiion repair of either spontaneously arisen or induced abasic sites. In order to examine the biological significance of Ap endonucleases in protection of mammalian cells against genotocix agents, we have generated stable transfectants of Chinese hamster ovary (CHO) cells harbouring human (APE) and yeast (APN1) Ap endonuclease, and compared their effects as to protection against mutagen-induced cell killing and formation of chromosomal aberrations. Although APE was markedly expressed on RNA and protein level, nuclear extracts of human APE transfectants showed an activity equal to that of the parental cell line and did not become more resistant to the cell killing and clastogenic effect of methyl methanesulfonate and hydrogen peroxide. On the other hand, CHO cells stably transfected with the yeast APN1 gene expressed higher Ap endonuclease activity and became more resistant tot the cytotoxic and clastogenic effect of the agents. From the resulsts the conclusions have been drawn that i) excision repair capacity as well as mutagen resistance in mammalian cells can be enhanced by introducing the yeast APN1 gene and ii) Ap sites are both cytotoxic and clastogenic lesions.