Morphological and biochemical evidence for partial nuclear localization of annexin 1 in endothelial cells

Using immunofluorescence, an affinity-purified anti-annexin-1 polyclonal antibody showed both cytoplasmic and nuclear staining, whereas antibodies against annexins 2, 5 and 6 labelled almost exclusively the cytoplasm of cultured endothelial cells. This was further confirmed by immunogold labelling and electron microscopy using a monoclonal antibody, annexin 1 being detected close to the plasma membrane, in the cytoplasm, as well as inside the nucleus. Finally, using immunoblotting, purified nuclei were shown to contain annexin 1, which was not removed by EDTA treatment. These data open some new perspectives in the understanding of annexin function, including possible involvement in nucleoskeleton dynamics and regulation of proliferation through cell signalling.