Abstract 2989: Depletion of the Topoisomerase I binding proteins BTBD1 and BTBD2 alters the DNA damage response in tumor cells treated with camptothecin

Abstract

Abstract The Topoisomerase I (Top1) binding proteins BTBD1 and BTBD2 belong to a family of structurally related proteins of diverse function. BTBD1 and BTBD2 are highly homologous (>80% identity) and are comprised of an N-terminal BTB/POZ domain, typically involved in protein-protein interactions, followed by a related BACK (BTB and C-terminal Kelch) domain. The carboxy-terminal half of these proteins have been shown to be the Top1 binding portion (Xu et al., 2002) and contain a PHR domain found in certain E3 ubiquitin ligases. Understanding the role of BTBD1 and 2 proteins, with an emphasis on the effects of their depletion by RNAi and concomitant treatment of cells with the Top1 specific camptothecin (CPT) family of chemotherapeutic agents, is the focus of this present study. Treatment of cells with CPT and related analogues results in Top1 mediated DNA damage that was assayed by detection of the phosphorylation of DNA damage response elements (DDRE), including ATM, ATR, Chk1 and H2A.X, by Western blot. We have observed a >5-fold activation of the basal levels of DDRE in cells in which BTBD1 and BTBD2 have been depleted by RNAi. Furthermore, the response to CPT in these cells is temporally accelerated compared to cells treated with a non-specific control siRNA and CPT. In addition, immunofluorescent studies have revealed that there is a clearing of Top1 from the nucleoli of BTBD1 and 2-depleted cells even in the absence of CPT treatment. Recently characterized members of the BTB family of proteins have been shown to be involved in the repair of DNA damage (Munoz et al., 2009). It appears that BTBD1 and 2 proteins are involved in the response to DNA damage induced by Top1 specific drugs and as such open a new area of study with potential for development of novel combination therapies. Xu L, et al., BMC Genomics. 2002. 3(1). Muñoz IM, et al., Mol Cell. 2009. 35:116-27. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2989.