Vinexinβ, an atypical "sensor" of retinoic acid receptor γ signaling: union and sequestration, separation, and phosphorylation

The transcriptional activity of nuclear retinoic acid receptors (RARs) relies on the association/dissociation of coregulators at the ligand-binding domain. However, we determined that the N-terminal domain (NTD) also plays a role through its phosphorylation, and we isolated vinexin beta, a cytoskeleton protein with three SH3 domains, as a new partner of the RAR gamma NTD. Here we deciphered the mechanism of the interaction and its role in RAR gamma-mediated transcription. By combining molecular and biophysical (surface plasmon resonance, NMR, and fluorescence resonance energy transfer) approaches, we demonstrated that the third SH3 domain of vinexin beta interacts with a proline-rich domain (PRD) located in RAR gamma NTD and that phosphorylation at a serine located in the PRD abrogates the interaction. The affinity of the interaction was also evaluated. In vivo, vinexin beta represses RAR gamma-mediated transcription and we dissected the underlying mechanism in chromatin immunoprecipitation experiments performed with F9 cells expressing RAR gamma wild type or mutated at the phosphorylation site. In the absence of retinoic acid (RA), vinexin beta does not occupy RAR gamma target gene promoters and sequesters non-phosphorylated RAR gamma out of promoters. In response to RA, RAR gamma becomes phosphorylated and dissociates from vinexin beta. This separation allows RAR gamma to occupy promoters. This is the first report of an RAR corepressor association/dissociation out of promoters and regulated by phosphorylation.-Lalevee, S., Bour, G., Quinternet, M., Samarut, E., Kessler, P., Vitorino, M., Bruck, N., Delsuc, M.-A., Vonesch, J.-L., Kieffer, B., Rochette-Egly, C. Vinexin beta, an atypical "sensor" of retinoic acid receptor gamma signaling: union and sequestration, separation, and phosphorylation. FASEB J. 24, 4523-4534 (2010). www.fasebj.org