Abstract 14: Nucleolin phosphorylation by CK2 is important for its role in regulating apoptosis

Abstract

Abstract Nucleolar phosphoprotein nucleolin integrates critical cellular processes including gene expression, ribosome biogenesis, proliferation and the cellular response to stress. Elevated levels of nucleolin are found in a variety of tumors. Nucleolin has distinct mechanisms in p53 regulation to influence cell survival: In “normal unstressed” cells (with hyper-proliferative signals but no obvious DNA damage), nucleolin stabilizes p53 and induces apoptosis. Under DNA-damage however, nucleolin can cause translational repression. The translational repression is overcome upon DNA damage in part, possibly due to nucleolin translocation to the nucleoplasm, altered interactions with ribosomal protein, RPL26 and/or p53-antagonist, HDM2. In contrast, nucleolin binding to AU rich elements (AREs) of anti-apoptotic BCL2-mRNA stabilizes BCL2, leading to cell survival. Importantly, increased nucleolin phosphorylation by the interphase kinase CK2 is finely regulated in exponentially dividing cells; however, role of nucleolin phosphorylation remains largely unexplored in cell survival. We recently demonstrated that phosphorylation deficient nucleolin mutant confers dominant negative effect on cell proliferation. In this study, we dissect the role of nucleolin phosphorylation in regulating p53-signaling pathway. Our pathway specific qRT-PCR-array analyses indicate that expression of phosphorylation-deficient nucleolin mutant resulted in an increased gene expression in the apoptosis, DNA damage and repair pathways that are downstream to p53 activation. We further elucidate that targeting nucleolin phosphorylation by CK2 initiates an increased expression of BH3-only proteins: p53-transcriptional targets e.g. BID and PUMA. Interestingly, an increased expression of BIM, a p53-independent target that is required during DNA damage induced cell death is evident with NCL expression regardless of its phosphorylation status. This is the first step in understanding nucleolin-phosphorylation mediated regulation of gene expression in the p53-pathway to control cell proliferation. This information will be useful in identifying new targets that can be either directly (via RNA binding) or indirectly (through other proteins or gene expression) regulated by nucleolin phosphorylation. Citation Format: Esther Akinwunmi, Shu Xiao, Yuqi Guo, Xin Li, Anjana D. Saxena. Nucleolin phosphorylation by CK2 is important for its role in regulating apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 14. doi:10.1158/1538-7445.AM2015-14