Physical and Functional Interactions between Cellular Retinoic Acid Binding Protein II and the Retinoic Acid-Dependent Nuclear Complex

Abstract

Two sorts of proteins bind to, and mediate the developmental and homeostatic effects of, retinoic acid (RA): the RAR and RXR nuclear receptors, which act as ligand-dependent transcriptional regulators, and the cellular RA binding proteins (CRABPI and CRABPII). CRABPs are generally known to be implicated in the synthesis, degradation, and control of steady-state levels of RA, yet previous and recent data have indicated that they could play a role in the control of gene expression. Here we show for the first time that, both in vitro and in vivo, CRABPII is associated with RARα and RXRα in a ligand-independent manner in mammalian cells (HL-60, NB-4, and MCF-7). In the nucleus, this protein complex binds the RXR-RAR-specific response element of an RA target gene (RARE-DR5). Moreover, in the presence of retinoids that bind both the nuclear receptors and CRABPII, enhancement of transactivation by RXRα-RARα heterodimers is observed in the presence of CRABPII. Thus, CRABPII appears to be a novel transcriptional regulator involved in RA signaling.

ACKNOWLEDGMENTS

We are indebted to V. Giguère, H. de Thé, R. M. Evans, C. K. Glass, and M. P. Gaub for providing plasmids. We thank E. E. Baulieu and R. Losson for a critical analysis of the manuscript, M. P. Gaub for her participation, L. Penna for help in some experiments, G. Linares-Cruz for excellent technical advice on immunocytofluorescence, M. Schmidt and J. Vassy for assistance with confocal microscopy analysis, and the members of the Photography Laboratory of the Institute of Hematology for photography and artworks. We also thank Marie Hélène Schlageter and Philippe Lefebvre for their help in the binding studies and analysis.

This work was supported by grants from the Association pour la Recherche sur le Cancer and from the Fondation sur la Recherche contre la Leucémie. L.D. benefited from a grant from the Association pour la Recherche sur le Cancer. This work was also supported by funds from the CNRS, INSERM, the Hôpital Universitaire de Strasbourg (HUS), and the Collège de France.

L.D. and J.-N.B. contributed equally to this work.