Ca2+/calmodulin-dependent protein kinase II: localization in the interphase nucleus and the mitotic apparatus of mammalian cells.

Indirect immunofluorescence was used to determine the distribution of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) in rat embryo fibroblast 3Y1 cells, rat C6 glioma cells, and human epidermoid carcinoma KB cells. During interphase at growing phase, CaM kinase II was localized diffusely in the cytoplasm and in the nucleus. In the nucleus, the enzyme was localized within the whole nuclear matrix in which the enzyme was specially concentrated in nucleoli. During mitosis, CaM kinase II was found to be a dynamic component of the mitotic apparatus, particularly present at microtubule-organizing centers. In metaphase and anaphase, CaM kinase II was observed at centrosomes and between the spindle poles. During telophase, CaM kinase II was condensed as a bright fluorescent dot at the midzone of the intercellular bridge between two daughter cells, while tubulin was found at each side of the midbody. Colchicine, a microtubule inhibitor, disorganized the tubulin- and CaM kinase II specific fluorescent structure of mitotic 3Y1 cells. In cold-treated cells, CaM kinase II was localized predominantly at centrosomes. The localization of CaM kinase II in the cell nucleus and the mitotic apparatus suggests that the enzyme may play a role in the cell cycle progression of mammalian cells.