Abstract SY15-03: Systems biology of DNA damage and repair

Abstract

Abstract Post-translational modifications such as protein phosphorylation and acetylation, together with binding of the modified proteins to modular signaling domains (i.e. 14-3-3 proteins, WW domains, FHA domains, Polo-box domains, and BRCT domains) function together within signaling networks to control the cellular response to DNA damage. How signals emerging from these pathways are integrated and processed as a network is unclear. To address this, we have been developing systems models of signaling where kinase activities, protein phosphorylation, binding of substrates to phosphoserine/threonine binding domains, and cellular responses including cell cycle arrest and apoptosis are quantitatively measured at densely sampled points in time, and correlated mathematically using partial least squares regression/principal components analysis, or step-wise regression methods. We have used this to approach to map context-dependent signaling events that control the fate of individual cells after genotoxic stress. In addition to the ATM/Chk2 and ATR/Chk1 pathways that contribute to these responses, we have used this approach to identify a third DNA damage signaling pathway mediated by p38 MAPK-activation of MAPKAP Kinase-2 that is required for p53-deficient, but not for p53-proficient, tumor cell survival after DNA damage. In response to cisplatin exposure, MAPKAP Kinase-2 is required for Cdc25A destabilization and activation of the G1 and intra-S checkpoints, while in response to doxorubicin or camptothecin treatment, MAPKAP Kinase-2 is required for targeting of Cdc25B to 14-3-3, and activation of the G2/M checkpoint. MAPKAP Kinase-2 depletion abolishes these cell cycle checkpoints in p53-defective tumor cells, sensitizes them to chemotherapy in culture, and induces dramatic tumor regression after low-dose chemotherapy in a murine xenograft tumor model. No such MAPKAP Kinase-2 dependence is seen in p53-proficient tumors. Chk1 responds to the same genotoxic stresses that activate MAPKAP Kinase-2, and Chk1 is activated normally in the MAPKAP Kinase-2-depleted cells that display aberrant checkpoint function. Thus, MAPKAP Kinase-2 and Chk1 function together as a molecular ‘AND’ gate that is required to integrate DNA damage signals to control cell cycle progression and prevent mitotic catastrophe within tumors. The biological basis for the ‘AND’ gate function of Chk1 and MAPKAP Kinase-2 is directly related to the subcellular context in which each kinase functions. ATM is second molecular target whose inhibition has been postulated to sensitize tumors to chemotherapy. Using in vitro cell culture models together with murine xenografts and Eμ-myc driven lymphomas, we show that ATM inhibition can result in either pronounced tumor resistance or sensitization to DNA damaging chemotherapy, determined solely by the underlying state of the p53 pathway. We show that ATM-deficient p53-wild type tumors that are resistant to chemotherapy can be re-sensitized by inhibition of DNA-PK. These findings for MAPKAP Kinase-2 , ATM and DNA-PK demonstrate how signals from the DNA damage network are re-routed in p53-defective tumor cells, and show how pathway- and network-focused diagnostics can be used to successfully predict therapeutic outcome in human cancer treatment. Citation Format: Michael B. Yaffe. Systems biology of DNA damage and repair [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr SY15-03