TR3 (Nur77) is an orphan member of the retinoid/steroid family of nuclear receptors, which translocates from nucleus to mitochondria where it binds Bcl-2 and converts Bcl-2 from an anti-apoptotic to a pro-apoptotic protein (

Li, et al. Science 289: 1159, 2000
;
Lin, et al CELL 116: 527, 2004
). Because Bcl-2 is pathologically over-expressed in many ca cancers and leukemias, contributing to chemoresistance, we sought to exploit the TR3 interaction with Bcl-2 as a novel therapeutic approach. Mutagenesis studies identified a 9 amino-acid peptide from TR3 that mimics the effects of the full-length protein in terms of binding Bcl-2 and inducing conformational changes that covert Bcl-2 into a killer. A cell-permeable version of this TR3 peptide induced apoptosis of cultured leukemia cell lines (CEM; Jurkat), such that gene transfer-mediated over-expression of Bcl-2 enhanced sensitivity to the TR3 peptide. In contrast, Bcl-2 over-expression rendered these leukemia cells resistant to other inducers of apoptosis, such as the broad-spectrum kinase inhibitor Staurosporine. Mutant TR3 peptides that fail to bind Bcl-2 did not induce apoptosis. To identify chemical compounds that mimic the pro-apoptotic TR3 peptide, a Fluorescence Polarization Assay (FPA) was developed in which FITC-conjugated TR3 peptide binding to Bcl-2 or other appropriate anti-apoptotic Bcl-2-family proteins was measured in high-throughput mode. This high-throughput screening (HTS) assay performs well in 384 well format, with Z′ > 0.75. A chemical library of ~70,000 compounds was screened to identify compounds that displace the TR3 peptide, thus yielding hits that may serve as a potential starting point for drug discovery. Characterization of the properties of these compounds and their analogs will be described. (Supported by NIH grants R01-GM60554 and U54-HG003916).

Topics:
bcl2 gene, cancer, leukemia, peptides, amino acids, fluorescein-5-isothiocyanate, fluorescence polarization, kinase inhibitors, receptors, nuclear, retinoids

Disclosure: No relevant conflicts of interest to declare.

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2006, The American Society of Hematology
2006
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