Lamina-associated polypeptide 2α binds intranuclear A-type lamins

ABSTRACT The nucleoskeletal protein lamina-associated polypeptide 2α (LAP2α) contains a large, unique C terminus and differs significantly from its alternatively spliced, mostly membrane-integrated isoforms, such as LAP2β. Unlike lamin B-binding LAP2β, LAP2α was found by confocal immunofluorescence microscopy to colocalize preferentially with A-type lamins in the newly formed nuclei assembled after mitosis. While only a subfraction of lamins A and C (lamin A/C) was associated with the predominantly nuclear LAP2α in telophase, the majority of lamin A/C colocalized with LAP2α in G1-phase nuclei. Furthermore, selective disruption of A-type lamin structures by overexpression of lamin mutants in HeLa cells caused a redistribution of LAP2α. Coimmunoprecipitation experiments revealed that a fraction of lamin A/C formed a stable, SDS-resistant complex with LAP2α in interphase cells and in postmetaphase cell extracts. Blot overlay binding studies revealed a direct binding of LAP2α to exclusively A-type lamins and located the interaction domains to the C-terminal 78 amino acids of LAP2α and to residues 319-566 in lamin A/C, which include the C terminus of the rod and the entire tail common to lamin A/C. These findings suggest that LAP2α and A-type lamins cooperate in the organization of internal nuclear structures.