Visualization by BIFC of different C/EBPbeta dimers and their interaction with HP1alfa reveals a differential subnuclear distribution of complexes in living cells

SEBASTIÁN SUSPERREGUY; LUCIANA P. PRENDES; MARÍA A. DESBATS; NANCY L. CHARÓ; KAREN BROWN; ORMOND A. MACDOUGALD; TOM KERPPOLA; JESSICA SCHWARTZ; GRACIELA PIWIEN-PILIPUK

EXPERIMENTAL CELL RESEARCH

ELSEVIER INC

Lugar: Amsterdam; Año: 2011 vol. 317 p. 706 - 723

0014-4827

How the co-ordinated events of gene activation and silencing that characterize cellular differentiation are influenced by the spatial organization of the cell nucleus is still poorly understood. Little is known about the molecular mechanisms controlling the subnuclear distribution of transcription factors, and their interplay with nuclear proteins that shape chromatin structure. Here we show that upon induction of adipocyte differentiation of 3T3-L1 cells C/EBPâ associates with pericentromeric heterochromatin and also interacts with the nucleoskeleton. C/EBPâ localization depends on integrity of chromatin structure since its disruption promotes C/EBPâ delocalization and interferes with adipogenesis. Different C/EBPâ dimers localize in different nuclear domains. Using BiFC in living cells, we show that LAP homodimers localize in euchromatin and heterochromatin. In contrast, LIP homodimers localize exclusively in heterochromatin. Importantly, their differential subnuclear distribution mirrors the site for interaction with HP1á. Reporter gene assays show that HP1a reduce LAP transcriptional capacity. HP1á is present in the promoters of C/EBPá and c-fos in 3T3-L1 preadipocytes, as demonstrated by ChIP. When adipogenesis is induced, HP1á binding decreases from C/EBPá but not from the c-fos promoter, allowing C/EBPá transcription. Thus, the equilibrium among different pools of C/EBPâ associated with chromatin or nucleoskeleton, as well as their dynamic changes in their interaction with HP1á plays a key role in the regulation of C/EBP target genes during adipogenesis.