Abstract 772: Rap2b, a novel p53 downstream target, promotes cell survival after DNA damage.

Abstract

Abstract The tumor suppressor p53 is a critical regulator of apoptosis and cell survival. It evokes both pro-survival and pro-apoptosis programs upon DNA damage. However, the mechanisms underlying this cell fate decision are largely unclear. To identify p53 targets in a global and unbiased manner, we performed gene expression microarray and ChIP-chip assays using mouse embryonic fibroblasts (MEFs) and mouse embryonic stem (mES) cells. I treated MEFs and mES cells with adriamycin, a DNA damage agent, for 8 hours. Comparing to the untreated cells (negative controls), I obtained common genes that were dramatically induced both in MEFs and mES cells. Subsequently, we further analyzed these genes and obtained a list of 90 common genes. Then, I compared these 90 genes with published p53 targets in human cell lines U2OS and HCT116, and found 10 genes (Alox5, Eda2r, Btg2, Mdm2, Adrb2, Cdkn1a, Tnfrsf10b, Rap2b, Ddit4, Bbc3) that are conserved p53 targets between mouse and human. Most of these genes have been well studied except for Rap2b. Both mouse and human Rap2b share the same amino acid residue sequence, which indicating Rap2b might have important conserved functions both in human and in mouse. Using conventional chromatin immunoprecipitation (ChIP) assay and luciferase reporter assay, I identified one p53 binding motif in Rap2b promoter region. After DNA damage, p53 binds to the promoter of Rap2b and activates its transcription. The reduction of Rap2b levels by small interference RNA increases the apoptosis of cells under the damaged condition, suggesting that Rap2b helps cell survive upon DNA damage. This pro-survival role of Rap2b is very similar to the function of another well-known p53 target, Mdm2. Bioinformatic analysis revealed that Rap2b is over-expressed in many types of tumors, consistent with its pro-survival function. Anchorage independent growth assay showed that Rap2b only has weak transformation activity, suggesting that it is not a typical oncogene. Importantly, Rap2b activates RalGDS-Ral survival pathway after DNA damage. Therefore, our results identified a novel player, Rap2b, in the pro-survival program conducted by p53 and revealed a connection between the p53 signaling and the RalGDS-Ral cell survival pathway. Future studies will focus on investigating whether the inhibition of Rap2b may increase the apoptosis of tumor cells. Citation Format: Yunlong He, Mangmang Li, Wendy Dubois, Alexander Kovalchuk, Xiaolin Wu, Jing Huang. Rap2b, a novel p53 downstream target, promotes cell survival after DNA damage. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 772. doi:10.1158/1538-7445.AM2013-772