Abstract LB-321: Cytoplasmic DEDD promotes G1- to S-phase cell cycle transition

Death Effector Domain-Containing DNA-binding protein (DEDD), a highly conserved and ubiquitous protein, has been studied primarily for its role as a scaffold protein in cell death pathways. DEDD resides predominantly in the cytoplasm, but translocates to the nucleus to propagate the terminal apoptotic signal. Overexpression of nuclear DEDD, not cytoplasmic DEDD, has been shown to be sufficient to induce cytotoxic effects. This suggests that DEDD may have functional importance beyond directing apoptotic signals. Further, the cytoplasmic function of DEDD has yet to be characterized. Other DED-containing proteins, such as FADD, have been shown to interact with cyclin/cyclin-dependent kinase cell cycle regulatory molecules. Here, we show that DEDD is implicated in cell cycle regulation and can assume a pro- proliferative function when overexpressed in the cytoplasm. To glean phenotypic changes in cell cycle transitions, we utilized a two-dimensional approach with an EdU proliferation label and a propidium iodine DNA content label differentiated via flow cytometry analysis. Based on these labels, it can be determined whether a cell is in the G1-, S-, or G2-phase of the cell cycle. We have identified that overexpression of DEDD leads to an increase in S-phase cells when compared to control suggesting an easier transition through the G1/S checkpoint. Conversely, a knockdown of DEDD leads to a decrease in S-phase cells and an increase in G1-phase cells when compared to control indicating G1 arrest. Gain-of-function flow cytometry analysis was repeated by overexpressing a DEDD construct with disrupted nuclear localization sequences. The resulting phenotype mirrored that of the overexpressed wild-type DEDD construct. Thus, these results suggest that DEDD may be interacting with regulatory molecules regulating the G1/S checkpoint of the cell cycle and that the change in G1- to S-phase transition dynamics in response to manipulated DEDD expression is not attributable to the nuclear function of DEDD. Further studies will focus on elucidating the specific molecular interactions through which DEDD can carry out this novel cell cycle regulatory function. Citation Format: Keon R. Schmidt, Yingjia Ni, Siyuan Zhang. Cytoplasmic DEDD promotes G1- to S-phase cell cycle transition [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 LB-321. doi:10.1158/1538-7445.AM2017-LB-321