Abstract 2535: Regulation of Chk1 by the mTOR pathway is essential for cancer cells to complete DNA replication in response to replication stress

Abstract

Abstract Oncogenic signaling leads to DNA replication stress, DNA damage and consequently DNA damage response (DDR), a barrier for tumorigenesis. For survival and proliferation, cancer cells must overcome this oncogene-induced DDR, but the molecular mechanism by which this is achieved is largely unknown. Here we report that the mTOR pathway prevents either spontaneous or drug induced DNA damage by sustaining ATR-Chk1 checkpoint in pediatric rhabdomyosarcoma (RMS) both in vivo and in vitro. Pharmacological inhibition of mTOR signaling by the selective TOR kinase inhibitor AZD8055 lead to spontaneous DNA damage and apoptosis as demonstrated by the induction of H2AX phosphorylation and PARP1 cleavage both in cell culture and tumor xenografts of RMS. Treatment RMS Rh30 cells with AZD8055 enhanced hydroxyurea induced H2AX phosphorylation and attenuated ATR-Chk1 checkpoint activation, as shown by decreased levels of phospho-Chk1(S345). We further found that mTOR signaling controls CHK1 expression at the transcriptional level via enhancing the activity of cyclin dependent kinases (CDKs). Consistent with its essential role for cells to survive DNA replication stress, siRNA-mediated knockdown of Chk1, or inhibition of Chk1 function by a Chk1 kinase inhibitor resulted in H2AX phosphorylation, while ectopic increase of Chk1 attenuated the DNA damage induced by mTOR kinase inhibition. Most importantly, the mTOR kinase inhibitor prevented the slow S-phase progression following DNA replication stress, which was accompanied with a decrease of Chk1 protein levels and phospho-Chk1(S345). Our data suggest that the TORC1/TORC2 pathway promotes RMS tumorigenesis by enhancing the cell survival functions of the ATR-Chk1 checkpoint in response to DNA replication stress. Our findings discovered an important unexpected functional linkage between TOR signaling and the ATR-Chk1 checkpoint signaling cascade and may impact targeting these two prominent cancer cell signaling pathways. Supported by CA77776. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2535. doi:1538-7445.AM2012-2535