Talk Abstracts

Talk on Wednesday 09:30-09:45am submitted by JT Greene

Par-4 Overexpression Impedes Leukemogenesis the Eµ-TCL1 Leukemia Model through Inhibition of NF-kB Signaling

Joseph T. Greene (MCDB), Rajeswaran Mani, Max Yano, Frank Frissora, Kevan Zapolnik, Ronni Wasmuth (The James Comprehensive Cancer Center, The Ohio State University), Minh Tran, Bonnie Harrington, John C. Byrd (The James Comprehensive Cancer Center, The Ohio State University), Rahul Ramaswamy (Washington University), Xiaokui Mo (Center for Biostatistics, The Ohio State University), Subbarao Bondada, Vivek Rangnekar (College of Medicine, University of Kentucky)

Abstract:
Prostate apoptosis response 4 (Par-4) is a tumor suppressor protein that is commonly downregulated in cancer due to a cancer-specific apoptosis induction quality^1-3. In chronic lymphocytic leukemia (CLL), Par-4 is not downregulated, but is in fact more abundant than in healthy B cells⁴. Thus, we are exploring the therapeutic potential of targeting this naturally cancer-specific apoptosis pathway in CLL. The Eµ-TCL1 mouse is a B cell leukemia model commonly used to study CLL biology⁵. We have developed the first B cell-specific human Par-4 overexpression mouse to explore the effect of overexpression in the TCL1 model. Double transgenic Par-4xTCL1 mice were bred from single transgenic mice and tracked for disease development. TCL1 CLL-like B cells express CD5 and CD19, and become abundant in the peripheral blood and secondary lymphoid organs as the disease progresses. Accumulation of CD5+/CD19+ cells in the blood of TCL1 mice was found to occur faster than in Par-4xTCL1 litter mates. Absolute counts of CD5+/CD19+ cells in the peripheral blood of Par-4xTCL1 animals were found to be significantly lower at 10 months than in TCL1 littermates (p=.023), and a survival advantage was conferred by overexpression of human Par-4 protein (p=.005). Disease severity upon meeting euthanasia criteria was not found to differ between genotypes, with spleen sizes and degrees of malignant infiltration in the spleen and bone marrow being similar in both cohorts in the late stages of disease. It was discerned by flow cytometry-based examination of in vivo 5-ethynyl-2-deoxyuridine (EdU) incorporation that splenic leukemia cells in Par-4xTCL1 animals expand at a reduced rate relative to TCL1 counterparts (p=.01). Mechanistic interrogation has revealed that major signaling pathway activation downstream of the B cell receptor does not appear to differ between the genotypes. However, B cells from Par-4xTCL1 mice exhibit less nuclear translocation of p65 than TCL1 littermates as determined by confocal microscopy, indicating Par-4 mediated inhibition of NF-kB signaling (p=.027). Further study of the Par-4 pathway in human CLL cells will verify the possibility of translating this anti-leukemic effect to a therapeutic benefit.

References:
1. Moreno-Bueno, G et al. (2007). Inactivation of the Candidate Tumor Suppressor Par-4… Cancer Research, 67(5), 1927-1934.
2. Nagai, M et al. (2010). Down-regulation of the candidate tumor suppressor gene PAR-4.... International Journal of Oncology, 37(1).
3. El-Guendy et al. (2003). Identification of a Unique Core Domain of Par-4… Molecular and Cellular Biology, 23(16), 5516-5525.
4. Bojarska-Junak, A et al. (2011). Assessment of the pathway of apoptosis involving PAR-4…. Folia Histochemica et Cytobiologica, 49(1), 98-103.
5. Bresin, A et al. (2016). TCL1 transgenic mouse model as a tool for the study of therapeutic targets.... Cell Death and Disease, 7(1).

Keywords: Leukemia, NF-kB, Tumor Suppressor