Abstract 2468: ATM signaling to mTORC1 in response to DNA damage independent of AMPK activation

Abstract

Abstract When DNA becomes damaged either as a result of endogenous processes or exposure to radiation or chemicals, the DNA damage response is rapidly engaged. DNA damage response pathways have been well-characterized at the molecular level, and are known to involve a large network of proteins that trigger cell cycle checkpoints to allow time for DNA repair or trigger apoptosis via p53-dependent mechanisms if the damage is too severe to be repaired. However in addition to these classic damage responses, our previous work on ROS-induced pathways indicated that an additional aspect of the cellular damage response to many types of damage or stress could be induction of autophagy via repression of mTORC1. We found previously that ROS could activate ATM in the cytoplasm, independently of the DNA damage produced by ROS, and subsequently activate the LKB1-AMPK energy-sensing pathway to activate TSC2 and repress mTOR, therefore inducing autophagy. We next asked whether a similar pathway could be induced in response to DNA damage, since there have been a few reports of AMPK activation by DNA damage in some cell lines, and ATM has been shown to activate AMPK via both LKB1-dependent and LKB1-independent mechanisms. In a panel of cancer cell lines, including MCF7 breast carcinoma cells and SKOV3 ovarian carcinoma and other cells such as MEFs and HEK293, we profiled the signaling events in response to classic double-strand break agents such as etoposide, ionizing radiation or radiomimetic neocarzinostatin, as well as the intrastrand crosslinking agent cisplatin. In a cell-line and damage-specific manner, mTORC1 could be repressed, but unlike the previously identified ROS-induced signaling pathway, AMPK was not activated. In addition, in contrast to the rapid ROS-induced signaling pathway, DNA damage induced mTORC1 suppression occurred over a period of hours (6-24 hours), suggesting that additional mechanisms may be involved in signaling to mTORC1. Using Tsc2-deficient MEFs, we demonstrated that mTORC1 suppression requires TSC2, a negative regulator of mTORC1. This dichotomous response between ROS-induced mTORC1 suppression via AMPK activation of TSC2, and DNA damage, which does not require AMPK, indicates that mTORC1 regulation by DNA damage is complex and context-dependent, which may have implications for understanding mechanisms of action of DNA damaging cancer therapeutics. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2468. doi:10.1158/1538-7445.AM2011-2468