Cytoplasmic localization and nucleo-cytoplasmic shuttling of BAF53, a component of chromatin-modifying complexes.

BAF53 (also known as ArpNbeta) is a nuclear arp that is a component of a number of chromatin-modifying complexes, such as the SWI/SNF and TRRAP complexes. These complexes play specific roles in chromatin remodeling and transcription. Previous studies have suggested that BAF53 is localized exclusively in the nucleus in HeLa and SW-13 cells. In this study, however, we provide evidence that it is also present in the cytoplasm of HeLa, NIH3T3, and WI-38 cells. Cytoplasmic localization was more prominent in NIH3T3 and WI-38 cells, and the cytoplasmic BAF53 staining in NIH3T3 cells appeared punctate. We also show by interspecies heterokaryon assays and in vitro export assays that BAF53 shuttles between the cytoplasm and nucleus in an energy-dependent manner. Shuttling was not blocked by leptomycin B, indicating that export of BAF53 is not mediated by CRM1. The nucleocytoplasmic shuttling and the punctate staining of the cytoplasm suggest that BAF53 can play a role distinct from its previously recognized function in transcriptional regulation.