An evaluation of siRNA screening in identification of targets in PTEN deficient tumor cells.

Abstract

e13569 Background: PTEN is frequently lost in cancer cells through genetic mutation or epigenetic silencing. Loss of PTEN function has been widely reported to result in up-regulation of PI3K and consequently AKT signalling, therefore promoting cell survival and proliferation. More recently a role for PTEN in maintaining genomic integrity was suggested by the finding that PTEN deficient cells demonstrate chromosomal instability and are sensitive to ionising radiation induced DNA damage. Methods: We utilised a siRNA screening approach with a human ‘druggable’ genome siRNA library to identify novel drug targets for PTEN associated cancers. The library contained 2 individual siRNAs directed against 6,961 druggable targets of the human genome, including 691 kinases, 206 phosphatases, 230 DNA repair genes. Bioinformatics analysis identified 981 genes as being synthetically lethal with loss of PTEN. The Ingenuity knowledgebase tool was then used to define the biological processes which were represented by these genes. Results: Twenty-one statistically significant processes were identified as being synthetically lethal with loss of PTEN, including the response to cellular stress. We show that PTEN deficient cells have an increase in endogenous DNA damage due to elevated ROS Furthermore we identify a specific requirement for the DNA damage response kinase ataxia telangiectasia mutated in response to ROS in PTEN deficient cells. Inhibition of ATM caused DNA damage, cell cycle arrest and apoptosis. The dependence on ATM was shown to be the result of a loss of a nuclear function for PTEN and independent of AKT deregulation. Conclusions: This study highlights the utility of siRNA screening in target identification and in uncovering novel biological functions. Furthermore, these observations suggest that ATM may represent a therapeutic target in PTEN deficient tumours.