Abstract
Metnase (also known as SETMAR) is a fusion gene expressed only in anthropoid or higher primates that contains a histone methyltranferase (SET) and a transposase domain derived from the Mariner transposase (MAR). Metnase improves the integration of foreign DNA, enhances DSB repair via the NHEJ pathway potentially through interaction with DNA Ligase IV, promotes replication-fork restart through interaction with PCNA, interacts with and stimulates TopoII alpha-dependent chromosome decatenation and suppresses chromosomal translocations Metnase is expressed higher levels in several cancer cell lines. To explore the role of Metnase in response to equitoxic doses of photon (2Gy 137Cs) or hadron particle (1Gy carbon and iron ion) radiation we constructed normal (BJ1 hTERT) and cancer (HT1080) human fibroblast cell lines bearing stably-integrated Metnase shRNA expression vectors. We examined replication recovery over time after irradiation by monitoring the incorporation of the nucleoside analog EdU in wild type and Metnase knockdown cells. We found that carbon and iron ion treatment suppressed replication recovery in both normal and cancer fibroblasts regardless of Metnase expression levels. Interestingly, Metnase knockdown promoted replication recovery in normal fibroblasts in response to gamma treatment suggesting that Metnase may have, as yet undetermined roles in cell cycle checkpoint in response to gamma radiation. These data also suggest that hadron-particle radiation evokes a stronger checkpoint response that may not be influenced by Metnase.
