A phosphorylation cluster in the chromatin-binding region regulates chromosome association of LAP2α

Abstract

LAP2α is a LEM family protein associated with nucleoplasmic A-type lamins and chromatin in interphase. Like lamins and other lamina proteins LAP2α is cytoplasmic in metaphase, but it associates with chromosomes prior to nuclear envelope formation in late anaphase to telophase. In vitro phosphorylation analysis and mass spectrometry identified a cluster of at least three mitotic cyclin-dependent kinase 1 phosphorylation sites in the C-terminal chromatin-binding region of LAP2α as well as four additional potential sites in the cluster, some of which were targeted alternatively in LAP2α mutated at the major sites. LAP2α mutants containing serine → alanine mutations at all seven sites revealed a clear phenotype. Mutated LAP2α remained associated with chromosomes throughout mitosis, but the dissociation of lamins into the cytoplasm and nuclear envelope disassembly were not affected. These data demonstrate the in vivo significance of mitotic phosphorylation for the dynamic behavior of LAP2α in the cell cycle and show that, unlike the interaction with lamins, the chromatin association of LAP2α is regulated by multiple mitosis-specific phosphorylation at sites clustered within a defined region in the C terminus of the protein.