Does the translocation of human ribosomal protein S3 (hS3) to the nucleus under conditions of oxidative stress pose a threat to the efficient repair of damaged DNA bases

3140 The human ribosomal protein S3 (hS3) possesses roles in extra ribosomal activities that influence DNA repair, cancer metastasis and apoptosis beyond its participation in protein synthesis. One example of such activity is the processing of oxidative DNA damage. Several DNA modifications are formed under conditions of oxidative stress, most common being 7, 8-dihydro-8-oxoguanine (8-oxoG), which if not repaired, results in G:C to T:A transversion mutations. The removal of 8-oxoG in humans is not as robust as seen in other organisms as the specific 8-oxoG DNA glycosylase/AP lyase (hOGG1) that initiates the base excision repair (BER) of 8-oxoG is relatively inefficient because of high affinity for the product of the reaction it catalyses. Our in vitro studies using surface plasmon resonance (SPR) technology have shown that hS3 has an extraordinarily high binding affinity for 8-oxoG and abasic sites in DNA. Additionally, pre-incubation of hS3 with a 37mer oligonucleotide containing 8-oxoG inhibited the removal of this lesion by OGG1, thereby suggesting that hS3 is creating an obstacle to the efficient repair of 8-oxoG. In agreement with this hypothesis are studies that show that the knockdown of hS3 expression by RNA interference in HEK293 cells resulted in increased cell survival in the presence of DNA damaging agents. Recent data from our lab also demonstrated a significant portion of cytoplasmic hS3 is translocated to the nucleus in cells exposed to genotoxic agents, showing that in fact hS3 is poised to carry out a role involving BER.
 The ability of hS3 to presumably block the liberation of 8-oxoG has led us to question what effect hS3 expression has in vivo on the whole animal. We have created mice that over express hS3 and are testing the hypothesis that, “Under conditions of oxidative stress cytoplasmic hS3 translocates to the nucleus and binds to 8-oxoG residues in DNA, blocks its repair and affects cell survival and/or tumorigenesis in vivo”. Observations made in these mice should be informative to understand the role of this protein in the oxidative stress induced DNA damage response pathway and its potential involvement in cancer etiology.