Ligand binding shifts highly mobile RXR to chromatin-bound state in a coactivator-dependent manner as revealed by single cell imaging.

Brazda, P. and Krieger, J. and Dániel, Bence and Jonas, D. and Szekeres, T. and Nagy, László and Vámosi, György (2014) Ligand binding shifts highly mobile RXR to chromatin-bound state in a coactivator-dependent manner as revealed by single cell imaging. MOLECULAR AND CELLULAR BIOLOGY, 34 (7). pp. 1234-1245. ISSN 0270-7306, ESSN: 1098-5549

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Abstract

Retinoid X Receptor (RXR) is a promiscuous nuclear receptor forming heterodimers with several other receptors, which activate different sets of genes. Upon agonist treatment the occupancy of its genomic binding regions increased, but only a modest change in the number of sites was revealed by ChIP-Seq, suggesting a rather static behavior. However, such genome-wide and biochemical approaches do not take into account the dynamic behavior of a transcription factor. Therefore we characterized the nuclear dynamics of RXR during activation in single cells on the sub-second scale using live-cell imaging. By applying FRAP and fluorescence correlation spectroscopy (FCS), techniques with different temporal and spatial resolution, a highly dynamic behavior could be uncovered, which is best described by a two-state model of receptor mobility. In the unliganded state most RXRs belonged to the fast population, leaving approximately 15% for the slow, chromatin bound fraction. Upon agonist treatment, this ratio increased to approximately 43% as a result of an immediate and reversible redistribution. Coactivator binding appears to be indispensable for redistribution and has a major contribution to chromatin association. A nuclear mobility map recorded by light sheet microscopy-FCS shows that the ligand-induced transition from the fast to the slow population occurs throughout the nucleus. Our results support a model in which RXR has a distinct, highly dynamic nuclear behavior and follows hit-and-run kinetics upon activation.

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