Abstract 593: Rb association with Bax is regulated by phosphorylation

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA The Retinoblastoma protein (Rb) is important in the control of cell proliferation and apoptosis. Its activity is controlled by reversible phosphorylation on several serine and threonine residues that mediate binding to various cellular proteins. The role of Rb phosphorylation in the control of apoptosis is largely unknown, although several apoptotic stimuli result in dephosphorylation of Rb. Our previous work identified Rb (threonine-821) dephosphorylation as required for induction of apoptosis caused by UV light and inhibitions of cyclin dependent kinases. These studies led to the identification of proteins that bind to Rb under apoptotic conditions. One such Rb binding protein is the pro-apoptotic protein Bax. Bax, a member of the Bcl-2 family, undergoes a conformational change during apoptosis that is associated with the permeabilization of the outer mitochondrial membrane. In this study, we examined the role of Rb phosphorylation in the regulation of binding to Bax. In MCF7 cells, by activating the phosphatase responsible for dephosphorylating Rb, PP1, apoptotic death is triggered. We utilize siRNA to block the expression of PNUTS (Phosphatase Nuclear Targeting Subunit) which causes Rb dephosphorylation, and cell death. We have found that Bax binds to Rb under normal cell conditions, but when Rb becomes dephosphorylated on specific amino acid sites, Bax dissociates from Rb. Our cell fractionation studies have shown that phosphorylated Rb co-localizes with the mitochondrial fraction. Further examination of the specific sites of Rb phosphorylation required for binding to Bax is underway. Citation Format: Lisa Antonucci, Jacklynn V. Egger, Nancy A. Krucher. Rb association with Bax is regulated by phosphorylation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 593. doi:10.1158/1538-7445.AM2014-593