Abstract 497: Higher nucleolar index of nucleolin as an indicator of aberrant cellular DNA damage response (DDR)
Authors: Nadeem Iqra , Aslam Amna , Wang Jingyuan , Kozlova Anna , Gordon Danielle , Javed Rumsha , Steinberg Ruchama , Rameau Rachele Dolce , Jiang Xinyin , Saxena Anjana D. 
Published: July 2017

Nucleoli provide a survival advantage for various tumor types, exemplified in prostate neoplasia, leukemia, lung, and breast carcinomas. Unregulated expression and increased nucleolar localization of many stress-responsive factors often correlate with hyper-proliferative status. Therefore, nucleolar changes in cancer cells are the first cytological indicators that can serve as an index for diagnostic and prognostic purposes. In this study, we examine an abundant nucleolar stress factor, nucleolin (NCL) for its sub-nuclear localization under normal and DNA damage conditions. NCL is a multifunctional RNA-binding phosphoprotein that plays critical role/s in many cellular processes including regulation of gene expression during normal cell cycle as well as in the cellular DNA damage response (DDR). NCL-mediated DDR involves changes in its phosphorylation status, sub-nuclear translocation and a multi-level regulation of p53-checkpoint signaling. However, the role/s of p53 status and the signaling pathways triggered during NCL-mediated stress response remain elusive, and forms the focus of this study. Taking advantage of two human ductal breast epithelial tumor cell lines with different genetic backgrounds (wild type, wt-p53 and mutant, mut-p53 L194F), we demonstrate that NCL is predominantly nucleolar in unstressed conditions irrespective of the p53 status. Upon genotoxic stress, however, wt-p53 is required for NCL to mobilize from nucleoli to the nucleoplasmic region. We observed a significant increase in nucleoplasmic index for NCL that is wt-p53 dependent and specific to the type of DNA damage. In contrast, in the presence of mut-p53, NCL failed to translocate even under various DNA damage conditions, resulting in a higher nucleolar index. Interestingly, another nucleolar factor, nucleophosmin (NPM) remained unaltered upon stress conditions even in the presence of wt-p53. This study corroborates the previous research that suggests NCL translocation requires wt-p53 and provides new insights into the role of p53-mutations (e.g. the zinc finger mutation in the central DNA binding region-L194F) in NCL-mediated DDR. Further, we also assessed the role of NCL and p53 (wt vs. mut) in regulating stress signaling (ATM/ATR and p38-kinase) pathways and gene expression in apoptosis. Together, our study elaborates a novel approach that correlates NCL sub-nuclear localization, downstream signaling pathways and gene expression during the cellular DDR.

Citation Format: Iqra Nadeem, Amna Aslam, Jingyuan Wang, Anna Kozlova, Danielle Gordon, Rumsha Javed, Ruchama Steinberg, Rachele Dolce Rameau, Xinyin Jiang, Anjana D. Saxena. Higher nucleolar index of nucleolin as an indicator of aberrant cellular DNA damage response (DDR) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 497. doi:10.1158/1538-7445.AM2017-497