Localization of α‐Dystrobrevin in Cajal Bodies and Nucleoli: A New Role for α‐Dystrobrevin in the Structure/Stability of the Nucleolus

ABSTRACTα‐Dystrobrevin (α‐DB) is a cytoplasmic component of the dystrophin‐associated complex involved in cell signaling; however, its recently revealed nuclear localization implies a role for this protein in the nucleus. Consistent with this, we demonstrated, in a previous work that α‐DB1 isoform associates with the nuclear lamin to maintain nuclei morphology. In this study, we show the distribution of the α‐DB2 isoform in different subnuclear compartments of N1E115 neuronal cells, including nucleoli and Cajal bodies, where it colocalizes with B23/nucleophosmin and Nopp140 and with coilin, respectively. Recovery in a pure nucleoli fraction undoubtedly confirms the presence of α‐DB2 in the nucleolus. α‐DB2 redistributes in a similar fashion to that of fibrillarin and Nopp140 upon actinomycin‐mediated disruption of nucleoli and to that of coilin after disorganization of Cajal bodies through ultraviolet‐irradiation, with relocalization of the proteins to the corresponding reassembled structures after cessation of the insults, which implies α‐DB2 in the plasticity of these nuclear bodies. That localization of α‐DB2 in the nucleolus is physiologically relevant is demonstrated by the fact that downregulation of α‐DB2 resulted in both altered nucleoli structure and decreased levels of B23/nucleophosmin, fibrillarin, and Nopp140. Since α‐DB2 interacts with B23/nucleophosmin and overexpression of the latter protein favors nucleolar accumulation of α‐DB2, it appears that targeting of α‐DB2 to the nucleolus is dependent on B23/nucleophosmin. In conclusion, we show for the first time localization of α‐DB2 in nucleoli and Cajal bodies and provide evidence that α‐DB2 is involved in the structure of nucleoli and might modulate nucleolar functions. J. Cell. Biochem. 116: 2755–2765, 2015. © 2015 Wiley Periodicals, Inc.