A TR3/Nur77 peptide-based high-throughput fluorescence polarization screen for small molecule Bcl-B inhibitors

J Biomol Screen. 2008 Aug;13(7):665-73. doi: 10.1177/1087057108320918. Epub 2008 Jul 14.


Nuclear receptor TR3/Nur77/NR4A1 binds several antiapoptotic Bcl-2-family proteins (Bcl-B, Bcl-2, Bfl-1) in a non-BH3-dependent manner. A 9-amino-acid peptide derived from full-length TR3 with polyarginine tail (TR3-r8) recapitulates TR3's binding specificity, displaying high affinity for Bcl-B. TR3-r8 peptide was used to screen for small molecule Bcl-B inhibitors. A fluorescence polarization assay (FPA) employing fluorescein isothiocyanate (FITC)-labeled TR3-r8 peptide (FITC-TR3-r8) and Bcl-B protein was optimized, with nonfluorescent TR3-r8 serving to demonstrate reversible, competitive binding. Approximately 50,000 compounds were screened at 3.75 mg/L, yielding 145 reproducible hits with > or =50% FITC-TR3-r8 displacement (a confirmed hit rate of 0.29%). After dose-response analyses and counterscreening with an unrelated FITC-based FPA, 6 candidate compounds remained. Nuclear magnetic resonance (NMR) showed that 2 of these compounds bound Bcl-B, but not glutathione S-transferase (GST) control protein. One Bcl-B-binding compound was unable to displace FITClabeled BH3 peptides from Bcl-B, confirming a unique binding mechanism compared with traditional antagonists of antiapoptotic Bcl-2-family proteins. This compound bound Bcl-B with Kd 1.94 +/- 0.38 microM, as determined by isothermal titration calorimetry. Experiments using Bcl-B overexpressing HeLa cells demonstrated that this compound induced Bcl-B-dependent cell death. The current FPA represents a screen that can identify noncanonical inhibitors of Bcl-2-family proteins.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Calorimetry
  • DNA-Binding Proteins / chemistry*
  • Drug Evaluation, Preclinical / instrumentation
  • Drug Evaluation, Preclinical / methods*
  • Fluorescein-5-isothiocyanate / pharmacology
  • Fluorescence Polarization / methods*
  • Glutathione Transferase / metabolism
  • HeLa Cells
  • Humans
  • Kinetics
  • Magnetic Resonance Spectroscopy
  • Molecular Sequence Data
  • Nuclear Receptor Subfamily 4, Group A, Member 1
  • Peptides / chemistry*
  • Proto-Oncogene Proteins c-bcl-2 / antagonists & inhibitors*
  • Receptors, Steroid / chemistry*


  • DNA-Binding Proteins
  • NR4A1 protein, human
  • Nuclear Receptor Subfamily 4, Group A, Member 1
  • Peptides
  • Proto-Oncogene Proteins c-bcl-2
  • Receptors, Steroid
  • Glutathione Transferase
  • Fluorescein-5-isothiocyanate